Tag Archives: plants

A lot of plant genes actually come from bacteria. And this may explain the success of early land plants

The evolution of land plants (simplified). Around 500 million years ago land plants started to spread from water to land. Credit: IST Austria.

When we think of gene transfer, the first thing that pops into our mind is inheritance. We tend to physically resemble our parents, be it in terms of height, skin tone, eye color, or facial traits, because we inherited genes from each parent, who in turn got their genes from their parents, and so on. Some organisms, however, find sexual reproduction counterproductive for their needs and opt for cloning, creating perfect genetic copies of themselves in perpetuity, apart from the occasional mutated offspring that refuses to be another chip off the old block. But that’s not all there is to it.

Sometimes DNA jumps between completely different species, and the results can be so unpredictable, they can dramatically alter the course of the evolution of life on Earth. Case in point, a new study makes the bold claim that genes jumping from microbes to green algae many hundreds of millions of years ago, shifted the tides and drove the evolution of land plants. Hundreds of genes found in plants thought to be essential to their development may have originally appeared in ancient bacteria, fungi, and viruses and became integrated into plants via horizontal gene transfer.

Speaking to ZME Science, Jinling Huang, a biologist at East Carolina University and corresponding author of the new study, said there could have been two major episodes of horizontal gene transfer (HGT) in the early evolution of land plants.

“Many or most of the genes acquired during these two major episodes have been retained in major land plant groups and affect numerous aspects of plant physiology and development,” the researcher said.

Sharing (genes) is caring

Genome-swapping events are rather common in bacteria. In fact, HGT is one of the main reasons why antibiotic resistance is spreading rapidly among microbes. This exchange of genetic material can turn otherwise harmless bacteria into drug-resistant ‘superbugs’.

Until not too long ago, HGT was thought to occur only among prokaryotes like bacteria, but recent evidence suggests that it can also happen in plants and even some animals. For instance, a 2021 study made the bold claim that herrings and smelts, two groups of fish that commonly roam the northernmost reaches of the Atlantic and Pacific Oceans, share a gene that couldn’t have been transferred through normal sexual channels — in effect, the researchers claim that HGT took place between two vertebrates.

“In genetics classes, we learn that genes are transmitted from parents to offspring (as such, kids look similar to their parents). This is called vertical transmission. In horizontal gene transfer, genes are transmitted from one species to another species. Although the importance of HGT has been widely accepted in bacteria now, there are a lot of debates on HGT in eukaryotes, particularly plants and animals. The findings of this study show that HGT not only occurred in plants, but also played an important role in the evolution of land plants,” Huang told ZME Science.

In order to investigate the role of HGT in early plant evolution, Huang and colleagues from China analyzed the genomes of 31 plants, including mosses, ferns, and trees, as well as green algae related to modern terrestrial plants. The researchers suspected quite a few genes transferred over from bacteria, but the results were totally surprising. They suggest that nearly 600 gene families — far more than researchers had expected — found in modern plants were transferred from totally foreign organisms like bacteria and fungi.

Many of these genes are thought to be involved in important biological functions. For instance, the late embryogenesis abundant genes, which help plants adapt to drier environments, are bacterial in origin. The same is true for the ammonium transporter gene that’s essential for a plant’s ability to soak up nitrogen from the soil to grow. And if you just despise cutting tear-jerking onions, you have HGT to blame too. The researchers found that the genes responsible for the biosynthesis of ricin toxin and sulfine (the irritating substance released when we cut onions) are also derived from bacteria.

“We were a little surprised to find those genes,” Dr. Huang told me, adding that his team was able to reconstruct the phylogenies (the history of the evolution of a species) for the genes using independent lines of evidence to determine whether a gene is derived from bacteria and the result of some inherited mutation.

“For instance, an ABC complex in plants consists of two subunits. Phylogenetic analyses show that both genes were acquired from bacteria. We also found that the two genes are positioned next to each other on the chromosomes of both bacteria and some plants, suggesting that the two genes might have been co-transferred from bacteria to plants,” the scientist added.

The establishment of plant life on land is one of the most significant evolutionary episodes in Earth history, with evidence gathered thus far indicating that land plants first appeared about 500 million years ago, during the Cambrian period, when the development of multicellular animal species took off.

This terrestrial colonization was made possible thanks to a series of major innovations in plant anatomy and biochemistry. If these findings are true, bacteria must have played a major role. Due to HGT, the earliest plants could have gained advantageous traits that make them more adapted to their novel terrestrial environment almost immediately, rather than having to wait for who knows how many thousands or even millions of years to develop similar genetic machinery.

The findings appeared today in the journal Molecular Plant.

Europe’s woodlands want to shift north — but birds are carrying them soutwards

Birds are not navigating the right way to help plant species cope with changing climates, according to a new report.

A Eurasian blackcap. Image via Pixabay.

As climate conditions get warmer all around the world, the latitudes where individual plant species would thrive are moving towards cooler latitudes — towards the north or the south, depending on which hemisphere you’re talking about. However, while their ideal location is shifting, the actual location of most species is not.

The culprit? Most likely the plants themselves for not evolving legs. But migratory birds also play an unwitting part in this story. According to the findings, the vast majority of plant species in European woodlands are dispersed by migratory birds. However, since these birds migrate towards warmer latitudes in the south, they’re carrying seeds the wrong way.

One-way ticket

“Contemporary climate change is so fast that many plants require dispersal distances far beyond those that normally take place locally,” said lead author Juan Pedro González-Varo, of the University of Cádiz.

“This is where migratory birds can play a major role, as they are capable of dispersing seeds over tens of kilometers. With this research, we wanted to know the potential of plant species to be dispersed by migratory birds towards future favorable areas.”

Plant species rely on animals for their mobility, which is mediated by animals eating their fruits and releasing their seeds later (hopefully in another place) following digestion. Birds, especially migratory birds, generally spread them over the longest distances.

In other words, how mobile a given plant species is over regional (as opposed to local) distances is highly dependent on how many bird species live in its area, their diets, and movement patterns. The authors of this study explain that this state of affairs is impairing the ability of plants to adapt to climate change.

The research focused on bird species that consume fruits and disperse the seeds — not all species do — analyzing their migratory patterns. They also incorporated data on the fruiting periods of individual plants, pooling these together to see which species can potentially spread which seeds, and where. For example, a Eurasian blackcap (Sylvia atricapilla) will eat dogwood fruits, a plant with a short fruiting period that coincide with the bird’s migration southwards. This tells the team that blackcaps can spread dogwood seeds, not locally but over long distances, i.e. to warmer latitudes.

A total of 13 European woodlands were analyzed in this way, representing 949 interactions between 46 bird and 81 plant species. The team notes that only 35% of the plants from these woodlands had their seeds carried northwards by birds that migrate come springtime.

On the other hand, 86% of plants had their seeds dispersed by birds migrating to warmer areas in autumn. These two figures add up to more than 100% because some species of plants are dispersed both northwards and southwards during spring or autumn migrations).

“Under climate change, species redistribute themselves to track suitable climate conditions,” explains co-author Dr. Benno Simmons, of the University of Exeter. “As plants cannot move themselves, they require species like birds to disperse their seeds to new areas. We wanted to know how well migratory birds might be able to do this.”

“We found that northward dispersal to cooler areas is done by only a small number of migratory bird species, some of which are under hunting pressure. Our study emphasizes the importance of these species for helping European plant communities experiencing climate change.”

Plants were most likely to be dispersed northwards if they had long fruiting periods, or would bear fruit close to springtime, between February and April, when some species migrate north. Juniper and ivy are good examples of plants that are taking advantage of these spring movements of birds.

Although pretty much all migratory birds in Europe move the same direction, north in spring and south in autumn, the study reports that not all are equal in regards to seed dispersal. Palearctic species, those that winter in central and southern Europe or North Africa — had the greatest potential to spread seeds towards colder latitudes. This group includes robins, blackcaps, blackbirds, and several species of thrush, all generally abundant and widespread species on the European continent.

Although they are common, many of these species are also facing a lot of pressure from hunting or habitat destruction, both legal and illegal. The team hopes that their findings will give “added value to these species”, as they’re key players in helping Europe’s woodlands adapt to climate change.

The paper “Limited potential for bird migration to disperse plants to cooler latitudes” has been published in the journal Nature.

Scientists discover new organ in the world’s most studied plant

There’s always something new to discover, even if you’ve looked at it thousands of times. After decades of research, scientists have just found a previously unknown structure called the “cantil” in the Thale cress (Arabidopsis thaliana), which is considered one of the most widely studied organisms in biology across time.

Image credit: Flickr / Dean Morley

A model planst

It doesn’t take a biologist to know what the Thale cress looks like. The sturdy plant is a non-commercial member of the mustard family native to Africa, Asia, and Europe, where it sprouts in sandy soils or even in gaps in concrete. It’s been used in countless experiments over time, becoming a staple in science because it’s inexpensive and produces many seeds. It has even been grown on the International Space Station (ISS) a few years back. 

The plant was first scientifically described as early as the 16th century, and continues to be studied as a model organism to explore plant genetics and development since the 1940s. By 2015, scientists had written more than 54,000 papers about Arabidopsis, and since then, about 4,000 more have been published each year. We know a lot about it, or at least we thought so. 

“I first observed the cantils in 2008,” plant biologist Timothy Gooking, lead author of the new study, said in a statement. “I initially didn’t trust any of the results. I thought it must be an artifact of genetic contamination, perhaps combined with environmental contamination of the water, soil, fertilizer or even the building air supply.”

The newly discovered structure, named cantil, isn’t hidden or anything like that. While the flower-bearing stalk grows out of the main stem of the plant, the cantil grows horizontally from the stem – holding the flower stalk farther out. It’s hard to miss if it forms, but it’s rare and only forms only under a set of specific conditions. 

A new organ

As it turns out, the cantil only appears in some plants when after a delay in flowering during spring, and only if daylight is limited. Cantils make the plants look like they have bent elbows whereas those without this organ look straight. It took the researchers twelve years of investigation and looking at thousands of plants to make this discovery. 

“This study required the growth of 3,782 plants to full maturity and the manual inspection of over 20,000 flower-bearing stalks in 34 unique plant lines,” said Gookin. “I finally deemed the cantils a natural phenomenon after identifying them in wild-type plants from different sources, which were growing in independent locations and diverse conditions.”

Gookin believes the discovery of cantils provides important clues for understanding the conditional growth of plant structures in response to their environment. The cantils could represent a highly repressed ancestral linkage between different types of flowering plant architectures. Further research will likely follow to further understand what’s going on. 

University of Toronto biologist Nicholas Provart, who wasn’t involved with the study, told National Geographic that the cantils likely don’t confer a clear benefit to the plant since the organ appears only in special conditions. Still, he highlighted how far Gookin went to further understand the structure of what’s probably the world’s best-studied plant.

The study was published in the journal Development. 

Photosynthesis could be as old as life itself

Photosynthesis has been supporting life for longer than previously assumed, according to a new paper. The finding suggests that the earliest bacteria that wiggled their way around the planet were able to perform key processes involved in photosynthesis.

Image via Pixabay.

Exactly how the earliest organisms on our planet lived and evolved is an area of active interest and research — but not answers are few and scarce. However, a new paper could fundamentally change how we think about this process.

The advent of photosynthesis on a large scale is one of the most significant events that shaped life on Earth. Not only did this process feed bacteria and plants that would then support for entire ecosystems, but it also led to a massive increase in atmospheric oxygen levels, basically making our planet livable in the first place. Oxygen that we and other complex life still breathe to this day.

To the best of our understanding , it took life several billion years to evolve the ability to perform photosynthesis. However, if the findings of this new study are confirmed, it means complex life could have appeared much earlier.

A light diet

“We had previously shown that the biological system for performing oxygen-production, known as Photosystem II, was extremely old, but until now we hadn’t been able to place it on the timeline of life’s history. Now, we know that Photosystem II show patterns of evolution that are usually only attributed to the oldest known enzymes, which were crucial for life itself to evolve.”

The team led by researchers from Imperial College London studied the evolutionary process of certain proteins that are crucial for photosynthesis. Their findings show that these could possibly have first appeared in the very early days of life on Earth.

They traced the ‘molecular clock’ of key proteins involved in the splitting of water molecules. This approach looks at the time between ‘evolutionary moments’, events such as the emergence of different groups of cyanobacteria or land plants that carry a version of these proteins. They then used this to calculate the rate at which the proteins evolved over time — by backtracking this rate, researchers can estimate when a protein first appeared.

A comparison with other known proteins, including some used in genetic data manipulation that should (in theory) be older than life itself, as well as comparison with more recent events, suggests that these photosynthesizing enzymes are very old. According to the team, they have nearly identical patterns of evolution to the oldest enzymes — suggesting they evolved at a similar rate for a similar time.

Based on what we know so far, type II photosynthesis (which produces oxygen) likely appeared around 2.5 billion years ago in cyanobacteria (blue-green algae), with type I likely evolving some time before that. But there’s something that doesn’t really mesh with that timeframe: we know that there were pockets of atmospheric oxygen before this time. This means that biological communities were around to produce said oxygen even before the 2.5 billion years ago mark, since oxygen is extremely reactive and doesn’t last long in nature without binding to something. Researchers have been trying to reconcyle this for a while.

The current findings could help make everything fit. According to the team, key enzymes that underpin photosynthesis were likely present in the earliest bacteria on Earth. There’s still some uncertainty about this, as life on our planet is at least 3.4 billion years old, but it could be older than 4 billion years.

The first versions of the process were probably simplified, very inefficient versions of the one seen in plants and algae today. It took biology around one billion years to tweak and refine the process, which eventually led to the appearance of cyanobacteria. From there, it took two more billion years for plants and animals to colonize dry land, with the latter breathing oxygen produced by the former.

One interesting implication of these findings is that it could mean life would evolve much quicker and easier on other planets than previously assumed. We tend to estimate this based on how quickly and easily life appeared and then developed on Earth.

The paper “Time-resolved comparative molecular evolution of oxygenic photosynthesis” has been published in the journal Biochimica et Biophysica Acta (BBA) – Bioenergetics.

Timelapse reveals the hidden dance of roots — and how mutant plants do it differently

A group of Stanford researchers has an unusual pastime: they watch plants grow. Not in real-time, mind you: they speed it up, compressing 100 hours of growth in less than a minute. With this approach and a special robot, they’ve uncovered some surprising things about how roots grow.

Wiggling roots find their way through rough soils.

Compared to the other parts of plants, we know surprisingly little about roots. The reason is simple, but hard to overcome: they grow underground, as opposed to above it. To overcome this obstacle, several research groups have grown plants in clear gel that allows plant observations.

The Stanford group in biologist Philip Benfey’s lab set up a system where they took a picture every 15 minutes for several days after the plant had germinated, obtaining a time-lapse video of roots growing.

A lot of the time, roots grew in winding, corkscrew-ike movements. This phenomenon reportedly “fascinated Charles Darwin”, says Benfey, and it’s not really clear why it happens.

In the case of shoots, it’s clear why: twining and circling make it easier to latch onto things. But for roots, it’s not clear why it happens. Maybe it makes it easier to burrow into the ground or figure out where “down” is, but there’s still a lot of mystery surrounding this phenomenon. The new study helps shed a bit more light on it.

For starters, researchers found that some plants don’t do the corkscrew movements. When they investigated the cause, they found it in a mutation of a gene called HK1. Plants with a mutant HK1 grow straight down instead of meandering. They also grow down twice as deep, which raises even more questions about roots’ normal winding growth — what do they have to gain in such an inefficient pattern?

New time-lapse videos capture something that’s too slow for our eyes to see: the growing tips of rice roots make corkscrew-like motions, waggling and winding in a helical path as they burrow into the soil. Footage courtesy of Benfey/Goldman labs. Produced by Veronique Koch.

The answer could come from Daniel Goldman’s lab at Georgia Tech. Goldman and colleagues carried observations of mutant rice roots that grew over a perforated plastic plate, finding that spiraling roots were three times more likely to find a hole and grow through the other side. So if plant roots encounter an obstacle in their natural environment, straight-line growth would make it much harder to grow through.

The idea was further explored through a soft-pliable robot. The robot unfurls from its tip like a root and served as a root model. Researchers set it loose in an obstacle course with unevenly spaced pegs, without any sensors or any way to sense the pegs.

All the robot had were two inflatable plastic tubes nested inside each other. The inside tube would grow and push from the inside out, making the root elongate from the top, while a pair of contracting “muscles” also made the robot bend from side to side as it grew. With this alone, the robot was able to make its way around the pegs as it grew. But when the bending movement was stopped, it would quickly get stuck in the pegs.

The idea was further tested in a dirt mix used for baseball fields, to mimic obstacles the root would encounter in soil. It confirmed their idea: mutant seeds struggled growing adequately, while the normal seeds had no real trouble. While questions still remain about this process, the theory seems to add up: roots grow in a corkscrew movement because it helps them establish a foothold in unpleasant soils.

Journal References: Isaiah Taylor et al, Mechanism and function of root circumnutation, Proceedings of the National Academy of Sciences (2021). DOI: 10.1073/pnas.2018940118

The Earth’s “lungs” could start irremediably deteriorating in just two decades, study shows

We depend on plants much more than we care to admit, as they absorb a quarter or even more of our fossil fuel emissions. But, if we don’t stop or at least slow down global warming, up to half of the world’s forests and grassland could exceed their peak carbon dioxide (CO2) uptake in the next two or three decades, according to a new study — a tipping point that would set our climate on a crash course for centuries to come.

Image credit: Flickr / Megan Gardner

It’s like Earth has a fever that’s affecting plants’ ability to function normally, says lead author Katharyn Duffy in a statement, describing the effect of global warming. If temperatures keep rising as they do now, many of the plants on which we rely to lessen the impact of greenhouse emissions could move from being carbon sinks to carbon sources.

The Earth has about three trillion trees and other plants that act as the planet’s lungs. They take in carbon dioxide and combine it with light and water to make carbohydrates to build their bodies, a process known as photosynthesis. Oceans, algae, and plants combined stop about half the CO2 people emit from reaching the atmosphere.

Lucky for us, as CO2 rises in the atmosphere, plants boost their rate of photosynthesis, a process known as the carbon dioxide fertilization effect. That has protected us from feeling the full effect of the climate crisis. But now scientists believe that this trend would stop after a certain temperature, which is very bad news.

“We wanted to ask, how much can plants withstand?” said lead-author Duffy in a statement. Alongside a team of Northern Arizona University researchers, they used two decades of records of carbon flux from measurement towers positioned above all major ecosystems in different parts of the globe to reply to that question.

They found photosynthesis peaked at about 18ºC in most of the world’s leafy areas, then went into decline. However, respiration kept increasing, so plants were breathing out greenhouse gas faster, while taking progressively less in. With enough heat, they would move from being carbon sinks to carbon sources, the study showed.

The researchers noticed significant declines in photosynthesis above a temperature threshold in nearly every kind of ecosystem across the globe, even after removing other effects such as water and sunlight. About 10% of the ecosystems are already operating above their maximum, but only temporarily, during hot seasons.

Nevertheless, at the current rate of emissions, up to half the terrestrial biosphere could experience temperatures beyond that productivity threshold by mid-century, the study showed. Some of the most carbon-rich biomes in the world such as the Amazon in South America will be among the first to hit that tipping point.

“Any temperature increase above 18ºC is potentially detrimental to the terrestrial carbon sink. Without curbing warming to remain at or below the levels established in the Paris Climate Accord, the land carbon sink will not continue to offset our emissions and buy us time,” co-author of the study Vic Arcus said in a statement.

Under the Paris Agreement, countries agreed to limit global warming to below 2ºC above pre-industrial levels and to pursue efforts to limit it to 1.5ºC. Still, for this to happen, emissions have to drop significantly. With the current climate pledges by countries, the world is heading to a temperature increase between 3º C and 4ºC.

The study was published in the journal Science Advances.

Scientists compile the world’s largest inventory of known plant species

It can be difficult for conservationists and ecologists to keep track of the many plant species out there. That’s why they rely on taxonomic lists as their main tool.

Now, a group of researchers has just compiled the world’s most comprehensive list of plant species, which will soon become a valuable tool for all researchers out there.

Martin Freiberg constantly searches for new plant species, not only through modern genome sequencing but also in nature. Image credit: Wolfgang Teschner

The list has 1,315,562 names of vascular plants, extending the number of recognized plant species in previous lists, as well as clarifying 181,000 previously unclear species names. It took more than ten years of painstaking work to make all this happen.

The curator of the Botanical Garden of Leipzig University, Dr. Martin Freiberg, carried out the work alongside colleagues from the German Centre for Integrative Biodiversity Research (iDiv). They believe the recently published list could help to make Leipzig a leading international center of plant biodiversity research.

Known as the Leipzig Catalogue of Vascular Plants (LCVP), this outstanding research could end up replacing The Plant List (TPL) – a plant catalog created by the Royal Botanic Gardens, Kew in London. Until now, TPL has been the most important reference source for plant researchers around the world

“In my daily work I regularly come across species names that are not clear, where existing reference lists have gaps,” Freiberg said in a statement. “This always means additional research, which keeps you from doing your actual work. I wanted to eliminate this obstacle as well as possible.”

The creation of the LCVP involved a thorough search of available and relevant plant taxonomic databases and over 4,500 publications to collate a raw data table of existing plant names. Freiberg compiled the information, harmonized it, and standardized all the names listed according to the best possible criteria.

He also investigated further discrepancies such as different spellings and synonyms and added thousands of new species to the existing lists. The LCVP now has an impressive amount of 351,180 vascular plant species and 6160 natural hybrids across 13,460 genera, 564 families, and 84 orders

This means that it contains over 70,000 more species and subspecies than The Plant List, which used to be the go-to guide for conservationists. But the latter hasn’t been updated since 2013, which has turned it into a somewhat outdated tool for research, Freiberg said, hoping for the LCVP to replace it with its more updated information.

Freiberg also compared the LCVP with a recent program by Kew called Plants of the World Online (POWO), which includes a new taxonomic reference backbone and could become the successor of TPL. He found that his own research contains significantly more species name information than POWO.

“The catalog will help considerably in ensuring that researchers all over the world refer to the same species when they use a name,” said Freiberg. “I intended the data set for internal use in Leipzig. But colleagues from other botanical gardens in Germany urged me to make the work available to everyone.”

The research that led to the new list was published in the journal Scientific Data.

New Guinea is the island with the greatest plant diversity in the world

New Guinea, an island located in the Pacific Ocean measuring around 787,000 square kilometers, is the island with the greatest plant diversity in the world. It’s home to more than 13,500 species of plants, two-thirds of which are endemic, according to a new comprehensive study.

The New Guinea Impatiens. Credit Flickr Gailhampshire (CC BY 2.0)

The island has fascinated naturalists for centuries. It is home to the best-preserved ecosystems on the planet and to several ecological gradients (transitions between different types of ecosystems), from mangroves to tropical alpine grassland. Nevertheless, there has been no attempt so far to critically catalog the entire vascular plant diversity of the island.

A group of more than 90 botanists from 56 institutions in 19 countries worked with a wide array of samples, the earliest collected by European travelers in the 1700s. They found that the island has 13,634 species from 1,742 genera and 264 families, with New Guinea surpassing plant diversity from other islands on Earth.

“New Guinea is extraordinary: it is a paradise island teeming with life,” said the paper’s lead author, Rodrigo Cámara-Leret in a statement. “As the second-largest island in the world after Greenland and the world’s largest tropical island, it supports a mosaic of ecosystems and is globally recognized as a center of biological diversity.”

Only five families represent more than a third of the plant species on the island. The most diverse are orchids, with 2,856 species or 21% of the island species. New Guinea also has 3,962 species of trees, which is four times the number found across all of North America, for example.

A diverse island

Divided into the Indonesian provinces of Papua and West Papua, and the independent state of Papua New Guinea, the island is the most mountainous and largest tropical island in the world. This allows for different habitats, such as mangroves, swamp forests, and montane forests to coexist in close proximity.

The island is located between Malaysia, Australia, and the Pacific. It has a diverse but young geological history, with a large number of species forming in the last million years. Many of the plants are exclusive to the island. For example, 95% of the ginger species and 96% of the African violets here are endemic.

The biodiversity in the island. Credit Nature

Researchers had long suspected that the island would be very diverse, but data remained very limited. New Guinea had never been systematically surveyed, with previous estimates suggesting that the island could have anything between 9,000 to 25,000 species.

“I was just pleased that we could nail a number. This is not the end, this is a first step,” said Cámara-Leret, who is now trying to encourage researchers from around the world to continue working on this dataset, which will be very important for the International Union for Conservation of Nature (IUCN) Red List assessments.

But the island might be running out of time. Since 2002, it has lost over one million hectares of primary forest and almost two million hectares of total tree cover. More than 50% of the tree cover loss was recorded in Papua New Guinea. The main threats are small-scale agriculture and logging.

The study was published in the journal Nature.

Nanoplastics can contaminate plants, making them smaller, shorter

New research reports that microplastics can and do accumulate in plants. Such findings have implications for ecology as well as food safety.

Image via Pixabay.

Micro- and nanoplastics in water and seafood is a growing concern. They are present in ocean water at very high levels, and we ingest an impressive amount of them every year.

Now, researchers are looking into how these particles behave in terrestrial environments, as well. A new study reports that they can accumulate in plants. This impairs their growth and reduces their nutritional value, the authors explain. Such findings suggest that fruits and vegetables can act as a carrier for microplastics, and point to a possible impact on crop yield as we release more and more plastics.

Plasticrops

“Our findings provide direct evidence that nanoplastics can accumulate in plants, depending on their surface charge,” says Baoshan Xing, a Professor at the University of Massachusetts Amherst and corresponding author of the paper.

“Plant accumulation of nanoplastics can have both direct ecological effects and implications for agricultural sustainability and food safety.”

For the study, the team grew Arabidopsis thaliana (thale cress, a model organism) in plots of soil with nanoplastics. These particles were “fluorescently labeled” to allow tracking. After a seven-week growing period, the team compared the plants’ weights, heights, root growth, and levels of chlorophyll.

The fresh weight of plants grown in soils with nanoplastics were between 41.7% and 51.5% lower and they had shorter roots than the controls, the team explains. Exposure to high concentration of nanoplastics also caused plants to grow “significantly shorter than the control” and those exposed to lower concentrations.

The growing zone of the roots after four days of incubation (with different types and concentrations of plastic particles mixed into their soil).
Image credits Xiao-Dong Sun et al., (2020), Nature.

Particles tended to concentrate in certain tissues, depending on their electrical charge. Negatively-charged ones “were observed frequently in the apoplast and xylem” (both involved in transporting fluids around the plant), while positively-charged ones concentrated in the tips of the roots. The latter, while only present at lower levels, have a higher impact on the plant’s health overall, the team estimates.

“Our experiments have given us evidence of nanoplastics uptake and accumulation in plants in the laboratory at the tissue and molecular level using microscopic, molecular and genetic approaches. We have demonstrated this from root to shoot,” says Xing.

With nanoparticles being present in water, they will inevitably find their way into soils as well, especially in irrigated croplands. Their size and electric charge seem to be the main determining factors of whether they’re absorbed and how much they damage the plant.

The team showed that cress can take in plastic particles of up to 200 nanometers, which is way smaller than most microplastic particles. However, we do have evidence of plastic degrading into ever-smaller bits in water. If they break down similarly on dry land, or if irrigation water is contaminated with nanoplastics, they will contaminate crops as well, leading to reduced yields and food insecurity.

The paper “Differentially charged nanoplastics demonstrate distinct accumulation in Arabidopsis thaliana” has been published in the journal Nature.

Scientists create glowing plants using mushroom DNA and they are incredible

Whether you’ve seen the movie or not, one of the things that were most surprising about Avatar is the glowing plants that could be found all over the world of Pandora. Similar plants could soon be found on Earth, thanks to a new study.

Scientists found that it’s actually possible to create plants that produce their own visible luminescence, thanks to the fact that the bioluminescence found in some mushrooms is metabolically similar to the natural processes common among plants.

This means that the DNA obtained from the mushroom could be inserted into the plants, making them glow much brighter than previously possible, according to the group of researchers from the UK, Russia, and Austria.

The discovery could be used to create glowing flowers or other ornamental plants, and change the make-up of the plants that surround us, the team argued. It can also be used by scientists to learn more about the plants they study, watching the glow to see their inner workings.

“In the future this technology can be used to visualize activities of different hormones inside the plants over the lifetime of the plant in different tissues, absolutely non-invasively. It can also be used to monitor plant responses to various stresses and changes in the environment,” Karen Sarkisyan, lead-author, told The Guardian.

The new plants can produce more than a billion photons per minute, according to the researchers who created it. That is far brighter than any previous example, and the glow they obtained is more stable. The new findings will be commercialized soon in ornamental house plants by the companies Light Bio and Planta.

Designing new biological features is more complex than merely moving genetic parts from one organism to another, which has caused past attempts to create glowing parts to fail. All the genetic parts must metabolically integrate within the host and for most organisms the parts needed for bioluminescence are not all known.

The researchers unveiled the parts that sustain bioluminescence in mushrooms last year. Now, with the living light of an advanced multicellular organism fully defined, they were able to make glowing plants that are at least ten-fold brighter (as judging from illumination coming from leaves, roots, stems, and flowers).

Although mushrooms are not closely related to plants, the researchers discovered that the organic molecule at the center of the light emission from mushrooms is also used by plants when building cell walls, giving the scientists their opening to graft the needed genes. By dropping the DNA from the mushroom into the plants, they were able to create specimens that glowed ten times as bright, the researchers said. They are so bright that light could be seen coming from leaves, stems, roots, and flowers and captured using a normal smartphone camera, they claimed.

The researchers said that thanks to their finding even brighter plants could be developed in the future and that new features, such as changing brightness or color in response to people and surroundings could also be mixed in. But for that to happen there’s more work to be done.

“The challenge now is to figure out how to make this engineered bioluminescence responsive to specific environmental, developmental, chemical or pathogenic stimuli,” University of Cambridge professor John Carrr told The Guardian.

The study was published in the journal Nature Biotechnology.

Ecosystems with varied plant species are lusher, more efficient

Greater plant diversity benefits everyone in the ecosystem, a new study reports.

Image credits Tien Vu.

Higher levels of plant diversity allow ecosystems to utilize more energy and more efficiently, new research found. Ecosystems with 60 or more plant species contained twice the amount of living biomass, on average, than ecosystems built on plant monocultures.

This is the first study to look at energy flow throughout an entire ecosystem; previous efforts of this type only focused on a single feeding type (or ‘trophic level’), such as herbivore or carnivore.

Trickle-up energonomics

“We have analyzed an entire feeding network — in other words, multitrophic interactions — above- and belowground. This is indispensable for understanding the effects resulting from global species extinction,” explained Dr. Sebastian T. Meyer, a researcher at the Chair for Terrestrial Ecology at the Technical University of Munich (TUM) and lead author of the study.

Aboveground food chains are those that form, you’ll be surprised to hear, above the ground. One such food chain could, for example, start with grasses, extending to grasshoppers, and finally spiders. Belowground food chains are also very important for the health of an ecosystem and include such elements as bacteria, plant roots, and other burrowing species.

What the team analyzed were energy flows inside these food chains and the wider ecosystem. They looked at how much energy flows into the system (this is handled exclusively by plants), how much remains in the system, i.e. how much biomass is present, and how much energy is leaving the system. They used data gathered through the Jena Experiment a large-scale biodiversity mapping program first started in 2002.

The team established the trophic networks that form in each of the 80 plots of the Jena Experiment, the standing biomass at each level, and how energy flows through the networks. All in all, the ecosystems with the most plant biodiversity showed more efficient use of energy.

“The study shows that higher plant diversity leads to more energy stored, greater energy flow and higher energy-use efficiency in the entire trophic network, therefore across all trophic levels,” explained Dr. Oksana Buzhdygan from Freie Universitaet Berlin, co-lead author of the study.

“Seeing positive effects on one level does not imply that there cannot be simultaneous positive effects on other feeding levels,” said Dr. Meyer.

He notes that high plant biodiversity can keep ecosystems stable even when faced with high consumption lower down the food chain. Furthermore, the team explains that higher plant diversity makes ecosystems more resilient in the face of perturbations.

The findings showcase the benefits that may be obtained from increasing plant diversity in various ecosystems, from urban parks to croplands. Planting mixed crops, for example, can help maintain healthy ecosystems with virtually no effort on our part.

The paper “Biodiversity increases multitrophic energy use efficiency, flow and storage in grasslands” has been published in the journal Nature Ecology & Evolution.

The Biodiversity Heritage Library made over 150,000 illustrations and 55 million pages of research free to download

The world’s “largest open-access digital library for biodiversity literature and archives” has made 55 million pages of literature and at least 150,000 illustrations open for the public to enjoy.

Illustration from the Transactions of the Entomological Society of London, 1911.
Image credits Biodiversity Heritage Library / Flickr.

Do you like life, science, cool art, or all three? Then the Biodiversity Heritage Library (BIH) has a treat for you. The BIH pools together diagrams, sketches, studies, and data pertaining to life on Earth from hundreds of thousands of journals and libraries, some of them from as far back as the 15th century. You can see it all, and download it all, without paying a dime.

Science for all

“To document Earth’s species and understand the complexities of swiftly-changing ecosystems in the midst of a major extinction crisis and widespread climate change, researchers need something that no single library can provide – access to the world’s collective knowledge about biodiversity,” the Library’s about page explains.

“Scientists have long considered this lack of access to biodiversity literature as a major impediment to the efficiency of scientific research.”

The sheer wealth of information that the BIH contains is staggering. However, this is a goldmine even if you’re not too keen on learning biology, even if you don’t need some citations for your degree paper — there is a lot of beauty to be found here. Illustrations of plants, animals, and the biological mechanisms that keep them going abound. They’re analyzed in hand-drawn diagrams, detailed in bright watercolors, and celebrated in dazzling lithography.

From “Report on the work of the Horn Scientific Expedition to Central Australia, pt. 2 – zoology, London: Dulau, 1896.”
Image credits Biodiversity Heritage Library / Flickr.
From “Beiträge zur Pflanzenkunde des Russischen Reiches. Lf. 10 (1857)”.
Image credits Biodiversity Heritage Library / Flickr.

Among the works in the BIH is a digitized copy of Joseph Wolf’s 19th-century The Zoological Sketches, two volumes totaling around 100 lithographs of wild animals kept in London’s Regent’s Park (which are drop-dead gorgeous). Dig around deep enough and you will find a DIY taxidermy guide, full with illustrated guides, published in 1833. Weird, but cool. One of my personal favorites is Osteographia, or the Anatomy of the Bones, a body of sketches published in London, 1733, looking at the human skeleton and its afflictions. Die Cephalopoden by one G. Fischer and Margaret Scott’s British sea-weeds could easily pass for surrealist artwork in my book. The striking yet translucent watercolors of The genus Iris make for an almost otherworldly look at the family of flowers.

From “Die Cephalopoden T.2”.
Image credits Biodiversity Heritage Library / Flickr.
From “British sea-weeds, v. 1”.
Image credits Biodiversity Heritage Library / Flickr.
From “The genus Iris”.
Image credits Biodiversity Heritage Library / Flickr.

Still, this is, when you get down to it, a resource aimed at scientists. As such, it comes with a wide range of tools to help navigation and assist research: these include features to monitor online conversations related to books and articles in the archive or to find works related to a particular species. But, if all you want to do is look at the pretty pictures (I don’t blame you), the BIH also has an Instagram and Flickr account that you can check out.

“Through Flickr, BHL provides access to over 150,000 illustrations, enabling greater discovery and expanding its audience to the worlds of art and design. BHL also supports a variety of citizen science projects that encourage volunteers to help enhance collection data,” the Library’s about page adds. “Since its launch in 2006, BHL has served over 8 million people in over 240 countries and territories around the world.”

“Through ongoing collaboration, innovation, and an unwavering commitment to open access, the Biodiversity Heritage Library will continue to transform research on a global scale and ensure that everyone, everywhere has the information and tools they need to study, explore and conserve life on Earth.”

That’s definitely a goal I can get behind.

Climate change is causing more plants to grow higher in the Himalayans

Remote and hard to reach, the Himalayan region extends across all or part of eight countries, from Afghanistan in the west to Myanmar in the east. Its ecosystems are filled with short-stature plants, which haven’t been fully researched so far. A new study takes a look into the vast area, discovering that life is actually expanding there.

Credit Wikipedia Commons

A group of researchers from the University of Exeter used NASA satellite data from 1993 to 2018 to measure the extent of the so-called subnival vegetation in the area, plants that grow between the treeline and the snowline.

“It’s important to monitor and understand ice loss in major mountain systems, but subnival ecosystems cover a much larger area than permanent snow and ice and we know very little about them and how they moderate water supply,” said Dr Karen Anderson, author of the study.

The team discovered small but significant increases in vegetation cover across four height brackets from 4,150-6,000 meters above sea level. The results varied according to altitude and location. The interval between 4,150-6,000 meters above sea level showed the most increase in vegetation levels. Around Mount Everest, the researchers discovered a large increase in vegetation in all the height brackets analyzed. The finding is quite remarkable, considering conditions at the mountain range were considered in the past to push plants to the limit.

The study didn’t look at the reasons for the increased plant growth, but the findings agree with modeling that showed a decline across the Himalayan region of so-called “temperature-limited areas”, places where temperatures are too low for plants to grow. The decline is due to climate change, modeling showed.

Other studies in the past have looked at the ecosystems in the Himalayan region, suggesting that they are highly vulnerable to shifts in vegetation because of climate change. In 2006, research showed that the rate of ice loss in the area doubled between 2000 and 2016.

“Snow falls and melts here seasonally, and we don’t know what impact changing subnival vegetation will have on this aspect of the water cycle — which is vital because this region feeds the ten largest rivers in Asia,” said Anderson, who says now fieldwork will be needed to see how plants interact with soil and snow

More plants and trees could help the US reduce air pollution by 27% according to new research

Trees and other plants can help slash pollution near factories and other sources by an average of 27%, a new study suggests.

Image via Pixabay.

Planting trees tends to be cheaper than implementing new technology. And, according to a new paper, they can be of great help in our efforts to curtail air pollution. The study shows that plants are a cheap but effective alternative to cleaning the air around industrial sites, roadways, powerplants, or drilling sites.

Plant a tree, get fresh air free

“The fact is that traditionally, especially as engineers, we don’t think about nature; we just focus on putting technology into everything,” said Bhavik Bakshi, lead author of the study and professor of chemical and biomolecular engineering at The Ohio State University.

“And so, one key finding is that we need to start looking at nature and learning from it and respecting it. There are win-win opportunities if we do — opportunities that are potentially cheaper and better environmentally.”

For the study, the team collected public data on air pollution and vegetation, on a county-by-county basis, for the continental 48 states. They analyzed the effect trees and other plants have on air pollution levels and then calculated the costs of adding extra plants and trees. In effect, they checked to see how able current vegetation levels are at mitigating air pollution, and then estimated the effect of increased plant presence on air pollution.

The team reports that for 75% of the counties that were included in this analysis, it was cheaper to use plants to mitigate air pollution instead of technological solutions (smokestack scrubbers for powerplants, for example). In several cases, the team explains that plants may actually be the better choice when combating pollution.

There is one area where the team found technology to be superior to plants at cleaning air pollution — industrial boilers. In the manufacturing industry, both ecosystem upgrades and technological solutions can perform the task, and both offer up cost-saving opportunities. However, because this sector is so broad and varied, it’s hard to find a one-size-fits-all solution. They should be implemented on a case-by-case basis while taking account of the particularities of each situation.

They found that adding trees or other plants could lower air pollution levels in both urban and rural areas as well, though the success rates varied depending on, among other factors, how much land was available to grow new plants and the current air quality.

“[The findings] suggest that even though vegetation cannot fully negate the impact of emissions at all times, policies encouraging ecosystems as control measures in addition to technological solutions may promote large investments in ecological restoration and provide several societal benefits.”

All in all, they estimate that restoring vegetation “to county-level average canopy cover” can reduce air pollution by an average of 27% across the investigated counties. The figure varies by county and region — for example, a county in Nevada would have a lower plant cover than a same country in Ohio, because the desert can support less vegetation. The analysis didn’t include ozone pollution because data on ozone emissions is lacking, the team explains. Furthermore, they didn’t consider whether certain species are better at cleaning air pollution, although Bakshi said it’s likely that the local species will have an effect on air quality.

“The thing that we are interested in is basically making sure that engineering contributes positively to sustainable development,” Bakshi said. “And one big reason why engineering has not done that is because engineering has kept nature outside of its system boundary.”

The paper “Nature-Based Solutions Can Compete with Technology for Mitigating Air Emissions Across the United States” has been published in the journal Environmental Science & Technology.

Climate change might mean more rain, but less water for everybody

In a hotter future, plants will consume more water than they do today — which means a drier future despite the anticipated increases in precipitation.

Climate heating is estimated to increase precipitation levels in places like the United States and Europe through the generation of more water vapor and weather pattern disruptions. However, humans may find themselves in a net drier future, a new paper explains: as the climate changes, crops and wild plants will use up more water in these areas.

More supply, much more demand

“Approximately 60% of the global water flux from the land to the atmosphere goes through plants, called transpiration. Plants are like the atmosphere’s straw, dominating how water flows from the land to the atmosphere. So vegetation is a massive determinant of what water is left on land for people,” explained lead author Justin S. Mankin, an assistant professor of geography at Dartmouth.

“The question we’re asking here is, how do the combined effects of carbon dioxide and warming change the size of that straw?”

Led by scientists at Dartmouth College, the paper notes a drier future for people in areas that are already facing water stress despite anticipated increases in precipitation levels.

The prevailing theory up to this study was that the increase in CO2 gas in the atmosphere will lead to reduced water consumption in plants — which would ultimately mean more water in streams and rivers. The underlying mechanism is that higher concentrations of CO2 allow plants to perform photosynthesis with greater water efficiency, as they can close off some of their pores (stomata) on their leaves. These pores shuttle CO2 molecules inside leaves, but also bleed out water through evaporation while they are open. All the water they don’t take, the logic goes, will instead percolate through the ground and into groundwater reserves.

This assumption isn’t wrong; however, it’s only accurate to the tropics and the extremely high latitudes, where freshwater is plentiful and competition for it is low. For most areas of the mid-latitudes, the team explains, plant responses to climate change will make the land drier, not wetter.

The researchers used climate modeling to analyze how freshwater availability will shift under our current projections of climate change and the ways precipitation will be divided among plants, rivers, and soils. They used a new, self-developed method to partition future precipitation and to calculate runoff in a warmer climate with higher levels of atmospheric carbon dioxide.

All in all, the team reports that as carbon dioxide levels rise in the atmosphere, plants will indeed take in less water, which will make the land wetter. However, warmer climates will mean a longer and warmer growing season. So, after the initial wet period, plants will actually start drying out the land (as they grow for longer than before). As CO2 levels keep increasing and mean temperatures keep rising after this second phase, plants are likely to grow even more (as photosynthesis is further amplified).

In some areas of the world, the water burden of the latter two factors (longer growing seasons and stronger photosynthesis) will out-pace gains from closing stomata, meaning that vegetation will, overall, consume more water than before. Vast swathes of mid-latitude lands will have less water in the soil and less water draining into streams, despite the projected increase in precipitation and plant water-efficiency.

So why is this a problem? Well, fresh water is essential for life, be it humans, animals, plants, or everything smaller. Our industries also depend on it. However, it is a limited resource, both in quantity and supply. Many areas of the world receive most precipitation during the cold part of the year (around winter) but consume most during the warm period (summer).

“Throughout the world, we engineer solutions to move water from point A to point B to overcome this spatiotemporal disconnect between water supply and its demand. Allocating water is politically contentious, capital-intensive and requires really long-term planning, all of which affects some of the most vulnerable populations,” Mankin adds.

“Our research shows that we can’t expect plants to be a universal panacea for future water availability. So, being able to assess clearly where and why we should anticipate water availability changes to occur in the future is crucial to ensuring that we can be prepared,”

The paper “Mid-latitude freshwater availability reduced by projected vegetation responses to climate change” has been published in the journal Nature Geoscience.

People used marijuana in rituals 2,500 years ago

East Asians grew cannabis over 6,000 years ago, but it’s not entirely clear what they did with it. Most evidence shows that they were consuming its oily seeds and making clothes and rope from the plant’s fibers, but evidence for inhalation and smoking remains limited. A cemetery from 2,500 years ago might help us better understand how ancient people used cannabis for its mind-altering properties.

The grave from above. Image credits: Xinhua Wu.

Jirzankal Cemetery lies some 3,000 meters above sea level, in the Pamir Mountains. It’s a rocky environment, riddled with circular mounts of earth covering tombs. The tombs themselves are outlined by one or two rings of stones, while black and white stone strips run across the site’s entire surface. It’s an important site that has remained remarkably intact over the centuries.

A team led by archaeologist Yimin Yang of the University of Chinese Academy of Sciences in Beijing found and analyzed chemical residues on 10 wooden burners (braziers) found in eight tombs at the site. When they analyzed these burners, they found an unusually high level of THC (the psychoactive substance inside cannabis) inside nine of them, as well as two stones that had been heated to burn plants — a clear indication that ancient people were using marijuana for burial rituals.

Ancient cannabis plants have much lower THC content than today’s plants, which have been carefully selected for this purpose. For the plants meant to be used for clothes and rope, the THC quantity was virtually negligible, and even for the ancient plants such as those found at the Jirzankal Cemetery, the effects wouldn’t have been quite as strong. Nevertheless, it seems that high up in the mountains, ancient Chinese were using the plants to also get (ritually) high.

It’s not known whether these people grew the plants themselves or if they harvested them from the wild. But, what is known is that this marijuana smoking might also tell us a thing or two about trade at the time.

It’s a remarkable indication of how early humans were interacting with the surrounding environment.

“I think this is a wonderful example of how closely intertwined humans are and have been with the world around them,” said archaeobotanist Robert Spengler of the Max Planck Institute for the Science of Human History, who was also a co-author of the study.

“They impose evolutionary pressures on the plants around them, and in some cases this actually leads to domestication. Humans have always sought out plants with secondary metabolites that have an effect on the human body. Premodern humans had an intimate understanding of the plants around them.”

This is hardly the first ancient indication of cannabis usage. The Greek historian Herodotus wrote of cannabis smoking some 2,500 years ago in the steppes of central Asia. High-elevation mountain passes such as the area around Jirzankal were part of important trade routes along the early Silk Road, which linked China to Europe and the rest of Western Asia. Spengler, who works at the Max Planck Institute for the Science of Human History in Jena, Germany, says that cannabis may have been a significant trade commodity.

“Our study implies that knowledge of cannabis smoking and specific high-THC varieties of the cannabis plant were among the cultural traditions that spread along Silk Road exchange routes,” Spengler said at a recent conference.

In support of this theory, previous chemical analyses from bones and teeth found in the Jirzankal Cemetery indicated that people were eating plants grown outside of China, presumably brought along the Silk Road. Some items (including silk and a harp brought from West Asia) also supports this theory.

The research has been published in Science Advances.

Eat more plant protein for a longer and healthier life, new study concludes

In recent times, the human diet has changed substantially. We have access to an unprecedented variety of foods, yet meat consumption has increased dramatically: from 20 kilograms a year in 1961, to around 43 kilograms in 2014. However, recent studies have increasingly found that meat consumption can have negative health effects, and substitute meat for plant protein can provide important benefits.

The latest study followed almost 71,000 middle-aged Japanese adults for an average of almost two decades. They split the people into five groups based on how much plant protein they ate. People who ate the most plants were 13% less likely to die during the study and 16% less likely to die of cardiovascular causes than people who ate the least amount of plants.

Furthermore, when people replaced just 4% of processed meat in their diet with plant protein, they were 46% less likely to die of any cause and 50% less likely to die of cancer.

This is hardly the first study to come up with these conclusions. Numerous previous studies have found that higher consumption of animal protein is associated with chronic diseases and mortality and higher consumption of plant protein reduces this risk. However, most of these studies were conducted on people in the Western World, where consumption of animal protein is much higher. This study, carried on people with a high plant protein consumption, showcases that more plant protein is always helpful.

Leaner meat, such as fish, is also a decent alternative, researchers say.

“Our study suggests that plant protein may provide beneficial health effects and that replacement of red and processed meat protein with plant or fish protein may increase longevity,” the researchers write.

Contrary to popular belief, many plants are protein-rich — up to the point where they rival and even surpass meat. Lean beef contains around 26 grams of protein per 100 grams, comparable to lean pork (although fatter meats have way less protein). Meanwhile, kidney beans and chickpeas have around 24 grams of protein per 100 grams — and plenty of other plants can serve as excellent alternatives.

Furthermore, it’s not just the proteins — these plants are also rich in fiber and other important nutrients which meat is lacking. Fiber, in particular, has been shown to provide important health benefits and is often lacking from meat-rich diets.

There’s also a shortcoming to this study: the participants’ diets were only assessed once, at the start of the study. It’s possible that along the road, some of their dietary patterns changed. However, this adds to the growing body of evidence regarding the negative effects of a meat-rich diet. The science is in: if you want to live a healthy life, eat less meat and more plants.

The study has been published in JAMA Internal Medicine.

A 36-hour timelapse of slow gravitropism (left; a fern) and fast gravitropism (flowering plant). Credit: IST Austria, Yuzhou Zhang.

How plants evolved to follow gravity

It’s common sense that plants have root systems that grow downward, following gravity. However, it hasn’t always been like this. Plant-life first evolved in water and only began spreading to land around 500 million years ago. Although the evolutionary origin of the mechanism of gravity-induced root growth — called gravitropism — remains a mystery, scientists have now uncovered new insights that offer a broader view of how and when gravitropism evolved.

A 36-hour timelapse of slow gravitropism (left; a fern) and fast gravitropism (flowering plant). Credit: IST Austria, Yuzhou Zhang.

A 36-hour timelapse of slow gravitropism (left; a fern) and fast gravitropism (flowering plant). Credit: IST Austria, Yuzhou Zhang.

The researchers at the Institute of Science and Technology of Austria analyzed various plant species, representing various lineages from the more primitive mosses, ferns, lycophytes, to the more modern seed plants (gymnosperms and flowering plants). The roots of each type of plant were forced to grow horizontally so that the researchers could observe if and when the roots would bend downwards to follow gravity.

Mosses and other rudimentary types of plants turned out to have a very slow gravity response. However, gymnosperms and flowering plants, which first appeared around 350 million years ago bent downward much faster, thereby exhibiting a more efficient form of gravitropism.

Simplified schematic of plant evolution. Credit: IST Austria.

Simplified schematic of plant evolution. Credit: IST Austria.

By analyzing the distinct phases of gravitropism, the researchers led by Yuzhou Zhang, a postdoc at IST Austria, identified two crucial components. One is represented by amyloplasts — plant organelles filled with starch granules — which function as a sort of gravity sensor. This particular component was particularly evident in gymnosperms and flowering plants which have amyloplasts concentrated in the very bottom of the root tips. In contrast, amyloplasts in ferns, clubmosses, and firmosses are randomly distributed within and above the root tip.

Amyloplast perception is then signaled from cell to cell by the second gravitropism component: the growth hormone auxin. Genetic experiments on Arabidopsis thaliana, a small flowering plant native to Eurasia and Africa and a common model plant used in research, revealed that a transporter molecule called PIN2 directs auxin flow.

Almost all green plants produce PIN proteins, but it’s only in seed plants that PIN 2 molecules gather at the shoot-ward side of the root system. This unique configuration to seed plant plants enables them to transport auxin towards the shoot, allowing the growth hormone to travel from the place of gravity perception to that of growth regulation.

Amyloplasts are filled with strach granules (black dots). The organelles are seen her in the root of a fern (left) and that of a seed and flowering plant (right). In the latter, the amyloplasts gather at the very bottom of the root tip, enabling more efficient gravitropism. Credit: IST Austria.

Amyloplasts are filled with starch granules (black dots). The organelles are seen her in the root of a fern (left) and that of a seed and flowering plant (right). In the latter, the amyloplasts gather at the very bottom of the root tip, enabling more efficient gravitropism. Credit: IST Austria.

Beyond gaining a better understanding of how plants sense and follow gravity for optimal growth, the researchers believe that their findings could also be of practical significance.

“Now that we have started to understand what plants need to grow stable anchorage in order to reach nutrients and water in deep layers of the soil, we may eventually be able to figure out ways to improve the growth of crop and other plants in very arid areas,” Zhang said in a statement, adding that: “Nature is much smarter than we are; there is so much we can learn from plants that can eventually be of benefit to us.”

The findings were reported in the journal Nature Communications

Cigarette butts are damaging plants, new study shows

Cigarette butts, one of the most common forms of pollution, significantly hamper plant growth. Both regular and menthol cigarette filters reduce plant growth and germination success, researchers write.

Plant growth around a wooden stick versus plant growth around a cigarette butt. Image credits: Danielle Green.

Cigarette butts have become nigh ubiquitous — they’re so widespread that one recent study found them to be the most abundant form of garbage in the oceans. More than 5.5 trillion cigarettes are manufactured globally every year with a plastic-based filter, made of cellulose acetate. It is estimated that around 4.5 trillion cigarette butts are littered every year, and this type of plastic takes decades to disintegrate.

But what happens after they’re littered?

Cigarette butts are not inert. They contain a myriad of chemicals from the tobacco which they can release into the environment. A previous study found that birds purposely bring cigarette butts into their nests because these chemicals can help keep ticks at bay — but the substances also have a negative effect.

In the new study, the team used a greenhouse experiment to assess the impact of discarded filters on two common and representative plants: Lolium perenne (perennial ryegrass) and Trifolium repens (white clover). They used a number of different scenarios (smoked and unsmoked cigarettes, regular or menthol), assessing their impact on the plants’ health.

After 21 days, the results were in, and the damage was visible. Shoot length and germination success were significantly reduced by exposure to any type of cigarette filter, and the damage was more substantial when the plants were exposed to filters from smoked regular cigarettes, as opposed to those which still had some leftover tobacco.

Image credits: Danielle Green.

Although this is hardly surprising, this is the first study to assess the impact of cigarette butts on plants, says lead author Dannielle Green from Anglia Ruskin University (ARU), said:

“Ryegrass and white clover, the two species we tested, are important forage crops for livestock as well as being commonly found in urban green spaces. These plants support a wealth of biodiversity, even in city parks, and white clover is ecologically important for pollinators and nitrogen fixation.”

“We found they had a detrimental effect on the germination success and shoot length of both grass and clover, and reduced the root weight of clover by over half.”

The main takeaway of this study, researchers say, is to convince people that cigarette butts are indeed litter and they have a negative impact

“Dropping cigarette butts seems to be a socially acceptable form of littering and we need to raise awareness that the filters do not disappear and instead can cause serious damage to the environment.”

“Many smokers think cigarette butts quickly biodegrade and therefore don’t really consider them as litter. In reality, the filter is made out of a type of bioplastic that can take years, if not decades, to break down.”

The study was published in the journal Ecotoxicology and Environmental Safety.

Scientists modify plant mitochondrial DNA for the first time

Japanese researchers at the University of Tokyo have recently achieved a major milestone in biotech. For the first time, a plant’s mitochondrial DNA has been edited. This offers important implications for securing the world’s food supply.

Infertile rice (right) stands straight, but fertile rice (left) bends under the weight of heavy seeds. Credit: Tomohiko Kazama.

This was the culmination of decades of research in the field. Nuclear DNA was first edited in the early 1970s, then came chloroplast DNA in 1988, and animal mitochondrial DNA in 2008.

Nuclear DNA is the most famous type of DNA — what most people recognize as the familiar double-helix molecule that contains the instructions for life. Nuclear DNA is inherited from both parents. However, mitochondria — the organelles that provide energy to cells — have their own DNA, known as the mitochondrial DNA (mtDNA). Mitochondrial DNA is generally solely passed on by the mother’s side, although there is recent evidence that, at least in some family lines, it can also be passed on from father’s side.

In animals, the mitochondrial genome is encased in a relatively small molecule, whose shape is comprised of a single circular structure. It’s also remarkably similar among many species.

“Even a fish’s mitochondrial genome is similar to a human’s,” said Shin-ichi Arimura, an Associate Professor at the University of Tokyo and lead author of the new study.

On the other hand, a plant’s mtDNA is a whole different story.

“The plant mitochondrial genome is huge in comparison, the structure is much more complicated, the genes are sometimes duplicated, the gene expression mechanisms are not well-understood, and some mitochondria have no genomes at all – in our previous studies, we observed that they fuse with other mitochondria to exchange protein products and then separate again,” Arimura said in a statement.

For a long time, the food and biotech industry has been seeking for a way to access and edit plant genomes in order to increase crop resilience and yield. One prime example that illustrates the potentials of mtDNA editing is the 1970 fungal infection of Texas corn farms. Virtually all corn that had the same gene in their mtDNA genome were killed by the fungus, so corn with that specific gene has not been planted since.

“We still have a big risk now because there are so few plant mitochondrial genomes used in the world. I would like to use our ability to manipulate plant mitochondrial DNA to add diversity,” said Arimura.

In order to edit the plant genome, Arimura and colleagues adapted a technique designed for editing the mtDNA genomes of animal cells growing in a dish. The method, known as mitoTALENs, involves using a single protein to locate the mtDNA genome, cut the DNA at the desired gene, and delete it.

In an experiment that demonstrated the new method, Arimura’s team removed an mtDNA gene in three germlines of rice and three lines of rapeseed. This particular gene is known to cause cytoplasmic male sterility (CMS).

“While deleting most genes creates problems, deleting a CMS gene solves a problem for plants. Without the CMS gene, plants are fertile again,” said Arimura.

“This is an important first step for plant mitochondrial research,” he added.

The findings appeared in the journal Nature Plants.