Biology

Plants emit sounds, especially when stressed

By ScientifiCult 30 March 2023

Plants emit sounds, especially when they are stressed

For the first time in the world, Tel Aviv University researchers recorded and analyzed sounds distinctly emitted by plants.

Left to right: Prof. Yossi Yovel & Prof. Lilach Hadany. Credits: Tel Aviv University, CC BY

Do you talk to your plants? While you may not be able to hear them, your plants could very well be chatting away as well (perhaps they are not such great listeners after all), and that’s especially true if they are having a bad day (did you forget to water them again?). For the first time in the world, TAU researchers recorded and analyzed sounds distinctly emitted by plants. The click-like sounds, resembling the popping of popcorn, are emitted at a volume similar to human speech, but at high frequencies, beyond the hearing range of the human ear. The researchers:

“We found that plants usually emit sounds when they are under stress, and that each plant and each type of stress is associated with a specific identifiable sound. While imperceptible to the human ear, the sounds emitted by plants can probably be heard by various animals, such as bats, mice, and insects.”

plants sounds — Cactus plant with Microphones. Credits: Tel Aviv University, CC BY

Resolving Old Scientific Controversy

The study was led by Prof. Lilach Hadany from the School of Plant Sciences and Food Security at The George S. Wise Faculty of Life Sciences, together with Prof. Yossi Yovel, Head of the Sagol School of Neuroscience and faculty member at the School of Zoology and the Steinhardt Museum of Natural History, and research students Itzhak Khait and Ohad Lewin-Epstein, in collaboration with researchers from the Raymond and Beverly Sackler School of Mathematical Sciences, the Institute for Cereal Crops Research, and the Sagol School of Neuroscience – all at Tel Aviv University. The paper was published in the prestigious scientific journal Cell.

“From previous studies we know that vibrometers attached to plants record vibrations,” says Prof. Hadany. “But do these vibrations also become airborne soundwaves – sounds that can be recorded from a distance? Our study addressed this question, which researchers have been debating for many years.”

At the first stage of the study the researchers placed plants in an acoustic box in a quiet, isolated basement with no background noise. Ultrasonic microphones recording sounds at frequencies of 20-250 kilohertz (the maximum frequency detected by a human adult is about 16 kilohertz) were set up at a distance of about 10cm from each plant. The study focused mainly on tomato and tobacco plants, but wheat, corn, cactus and henbit were also recorded.

Mapping Plants’ Complaints with AI

Before placing the plants in the acoustic box, the researchers subjected them to various treatments: some plants had not been watered for five days, in some the stem had been cut, and some were untouched. Prof. Hadany explains that their intention was to test whether the plants emit sounds, and whether these sounds are affected in any way by the plant’s condition:

“Our recordings indicated that the plants in our experiment emitted sounds at frequencies of 40-80 kilohertz. Unstressed plants emitted less than one sound per hour, on average, while the stressed plants – both dehydrated and injured – emitted dozens of sounds every hour.”

The recordings collected in this way were analyzed by specially developed machine learning (AI) algorithms. The algorithms learned how to distinguish between different plants and different types of sounds, and were ultimately able to identify the plant and determine the type and level of stress from the recordings. Moreover, the algorithms identified and classified plant sounds even when the plants were placed in a greenhouse with a great deal of background noise.

In the greenhouse, the researchers monitored plants subjected to a process of dehydration over time and found that the quantity of sounds they emitted increased up to a certain peak, and then diminished.

“In this study we resolved a very old scientific controversy: we proved that plants do emit sounds!” says Prof. Hadany. “Our findings suggest that the world around us is full of plant sounds, and that these sounds contain information – for example about water scarcity or injury. We assume that in nature the sounds emitted by plants are detected by creatures nearby, such as bats, rodents, various insects, and possibly also other plants – that can hear the high frequencies and derive relevant information. We believe that humans can also utilize this information, given the right tools – such as sensors that tell growers when plants need watering. Apparently, an idyllic field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds.”

In future studies the researchers will continue to explore a range of intriguing questions, such as: What is the mechanism behind plant sounds? How do moths detect and react to sounds emitted by plants? Do other plants also hear these sounds? Stay tuned.

The research team. Credits: Tel Aviv University, CC BY

Press release from Tel Aviv University.

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Biology

New flower from 100 million years ago brings fresh holiday beauty to 2020

By ScientifiCult 27 December 2020

Valviloculus pleristaminis: a new flower from 100 million years ago brings fresh holiday beauty to 2020

flower Cretaceous Valviloculus pleristaminis — Valviloculus pleristaminis. Credits: George Poinar Jr., OSU

CORVALLIS, Ore. – Oregon State University researchers have identified a spectacular new genus and species of flower from the mid-Cretaceous period, a male specimen whose sunburst-like reach for the heavens was frozen in time by Burmese amber.

“This isn’t quite a Christmas flower but it is a beauty, especially considering it was part of a forest that existed 100 million years ago,” said George Poinar Jr., professor emeritus in the OSU College of Science.

Findings were published in the Journal of the Botanical Research Institute of Texas.

“The male flower is tiny, about 2 millimeters across, but it has some 50 stamens arranged like a spiral, with anthers pointing toward the sky,” said Poinar, an international expert in using plant and animal life forms preserved in amber to learn more about the biology and ecology of the distant past.

A stamen consists of an anther – the pollen-producing head – and a filament, the stalk that connects the anther to the flower.

“Despite being so small, the detail still remaining is amazing,” Poinar said. “Our specimen was probably part of a cluster on the plant that contained many similar flowers, some possibly female.”

The new discovery has an egg-shaped, hollow floral cup – the part of the flower from which the stamens emanate; an outer layer consisting of six petal-like components known as tepals; and two-chamber anthers, with pollen sacs that split open via laterally hinged valves.

Poinar and collaborators at OSU and the U.S. Department of Agriculture named the new flower Valviloculus pleristaminis. Valva is the Latin term for the leaf on a folding door, loculus means compartment, plerus refers to many, and staminis reflects the flower’s dozens of male sex organs.

The flower became encased in amber on the ancient supercontinent of Gondwana and rafted on a continental plate some 4,000 miles across the ocean from Australia to Southeast Asia, Poinar said.

Geologists have been debating just when this chunk of land – known as the West Burma Block – broke away from Gondwana. Some believe it was 200 million years ago; others claim it was more like 500 million years ago.

Numerous angiosperm flowers have been discovered in Burmese amber, the majority of which have been described by Poinar and a colleague at Oregon State, Kenton Chambers, who also collaborated on this research.

Angiosperms are vascular plants with stems, roots and leaves, with eggs that are fertilized and develop inside the flower.

Since angiosperms only evolved and diversified about 100 million years ago, the West Burma Block could not have broken off from Gondwana before then, Poinar said, which is much later than dates that have been suggested by geologists.

Joining Poinar and Chambers, a botany and plant pathology researcher in the OSU College of Agricultural Sciences, on the paper were Oregon State’s Urszula Iwaniec and the USDA’s Fernando Vega. Iwaniec is a researcher in the Skeletal Biology Laboratory in the College of Public Health and Human Sciences and Vega works in the Sustainable Perennial Crops Laboratory in Beltsville, Maryland.

About the OSU College of Science: As one of the largest academic units at OSU, the College of Science has seven departments and 12 pre-professional programs. It provides the basic science courses essential to the education of every OSU student, builds future leaders in science, and its faculty are international leaders in scientific research.

Press release from the Oregon State University.

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Biology

Why are plants green?

By ScientifiCult 1 July 2020

Why are plants green?

UC Riverside-led research team’s model to explain photosynthesis lays out the next challenging phase of research on how green plants transform light energy into chemical energy

When sunlight shining on a leaf changes rapidly, plants must protect themselves from the ensuing sudden surges of solar energy. To cope with these changes, photosynthetic organisms — from plants to bacteria — have developed numerous tactics. Scientists have been unable, however, to identify the underlying design principle.

An international team of scientists, led by physicist Nathaniel M. Gabor at the University of California, Riverside, has now constructed a model that reproduces a general feature of photosynthetic light harvesting, observed across many photosynthetic organisms.

Nathaniel Gabor is an associate professor of physics at UC Riverside. Credits: CIFAR

Light harvesting is the collection of solar energy by protein-bound chlorophyll molecules. In photosynthesis — the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water — light energy harvesting begins with sunlight absorption.

The researchers’ model borrows ideas from the science of complex networks, a field of study that explores efficient operation in cellphone networks, brains, and the power grid. The model describes a simple network that is able to input light of two different colors, yet output a steady rate of solar power. This unusual choice of only two inputs has remarkable consequences.

“Our model shows that by absorbing only very specific colors of light, photosynthetic organisms may automatically protect themselves against sudden changes — or ‘noise’ — in solar energy, resulting in remarkably efficient power conversion,” said Gabor, an associate professor of physics and astronomy, who led the study appearing today in the journal Science. “Green plants appear green and purple bacteria appear purple because only specific regions of the spectrum from which they absorb are suited for protection against rapidly changing solar energy.”

Gabor first began thinking about photosynthesis research more than a decade ago, when he was a doctoral student at Cornell University. He wondered why plants rejected green light, the most intense solar light. Over the years, he worked with physicists and biologists worldwide to learn more about statistical methods and the quantum biology of photosynthesis.

Richard Cogdell, a renowned botanist at the University of Glasgow in the United Kingdom and a coauthor on the research paper, encouraged Gabor to extend the model to include a wider range of photosynthetic organisms that grow in environments where the incident solar spectrum is very different.

“Excitingly, we were then able to show that the model worked in other photosynthetic organisms besides green plants, and that the model identified a general and fundamental property of photosynthetic light harvesting,” he said. “Our study shows how, by choosing where you absorb solar energy in relation to the incident solar spectrum, you can minimize the noise on the output — information that can be used to enhance the performance of solar cells.”

Coauthor Rienk van Grondelle, an influential experimental physicist at Vrije Universiteit Amsterdam in the Netherlands who works on the primary physical processes of photosynthesis, said the team found the absorption spectra of certain photosynthetic systems select certain spectral excitation regions that cancel the noise and maximize the energy stored.

“This very simple design principle could also be applied in the design of human-made solar cells,” said van Grondelle, who has vast experience with photosynthetic light harvesting.

Gabor explained that plants and other photosynthetic organisms have a wide variety of tactics to prevent damage due to overexposure to the sun, ranging from molecular mechanisms of energy release to physical movement of the leaf to track the sun. Plants have even developed effective protection against UV light, just as in sunscreen.

“In the complex process of photosynthesis, it is clear that protecting the organism from overexposure is the driving factor in successful energy production, and this is the inspiration we used to develop our model,” he said. “Our model incorporates relatively simple physics, yet it is consistent with a vast set of observations in biology. This is remarkably rare. If our model holds up to continued experiments, we may find even more agreement between theory and observations, giving rich insight into the inner workings of nature.”

To construct the model, Gabor and his colleagues applied straightforward physics of networks to the complex details of biology, and were able to make clear, quantitative, and generic statements about highly diverse photosynthetic organisms.

“Our model is the first hypothesis-driven explanation for why plants are green, and we give a roadmap to test the model through more detailed experiments,” Gabor said.

Photosynthesis may be thought of as a kitchen sink, Gabor added, where a faucet flows water in and a drain allows the water to flow out. If the flow into the sink is much bigger than the outward flow, the sink overflows and the water spills all over the floor.

“In photosynthesis, if the flow of solar power into the light harvesting network is significantly larger than the flow out, the photosynthetic network must adapt to reduce the sudden over-flow of energy,” he said. “When the network fails to manage these fluctuations, the organism attempts to expel the extra energy. In doing so, the organism undergoes oxidative stress, which damages cells.”

The researchers were surprised by how general and simple their model is.

“Nature will always surprise you,” Gabor said. “Something that seems so complicated and complex might operate based on a few basic rules. We applied the model to organisms in different photosynthetic niches and continue to reproduce accurate absorption spectra. In biology, there are exceptions to every rule, so much so that finding a rule is usually very difficult. Surprisingly, we seem to have found one of the rules of photosynthetic life.”

Gabor noted that over the last several decades, photosynthesis research has focused mainly on the structure and function of the microscopic components of the photosynthetic process.

“Biologists know well that biological systems are not generally finely tuned given the fact that organisms have little control over their external conditions,” he said. “This contradiction has so far been unaddressed because no model exists that connects microscopic processes with macroscopic properties. Our work represents the first quantitative physical model that tackles this contradiction.”

Next, supported by several recent grants, the researchers will design a novel microscopy technique to test their ideas and advance the technology of photo-biology experiments using quantum optics tools.

“There’s a lot out there to understand about nature, and it only looks more beautiful as we unravel its mysteries,” Gabor said.

Gabor, Cogdell, and van Grondelle were joined in the research by Trevor B. Arp, Jed Kistner-Morris, and Vivek Aji at UCR.

The research was supported by the Air Force Office of Scientific Research Young Investigator Program, the National Science Foundation, and through a U.S. Department of the Navy’s Historically Black Colleges and Universities/Minority Institutions award. Gabor was also supported through a Cottrell Scholar Award and a Canadian Institute for Advanced Research Azrieli Global Scholar Award. Other sources of funding were the NASA MUREP Institutional Research Opportunity program, the U.S. Department of Energy, the Biotechnological and Biological Sciences Research Council, the Royal Netherlands Academy of Arts and Sciences, and the Canadian Institute for Advanced Research.

The research paper is titled, “Quieting a noisy antenna reproduces photosynthetic light harvesting spectra.”

Press release from the University of California, Riverside

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Biology

When pollen is in short supply, Bumblebees speed up flowering

By ScientifiCult 28 May 2020

When pollen is in short supply, bumblebees damage plant leaves in a way that accelerates flower production, as an ETH research team headed up by Consuelo De Moraes and Mark Mescher has demonstrated.

Spring has sprung earlier than ever before this year, accompanied by temperatures more typical of early summertime. Many plants were already in full bloom by mid-April, about three to four weeks earlier than normal. These types of seasonal anomalies are becoming increasingly frequent due to climate change, and the resulting uncertainty threatens to disrupt the timing of mutualistic relationships between plants and their insect pollinators.

A research team led by ETH Professors Consuelo De Moraes and Mark Mescher has now discovered that one peculiar bumblebee behaviour may help to overcome such challenges by facilitating coordination between the bees and the plants they pollinate. The group has found that bumblebee workers use their mouth parts to pinch into the leaves of plants that haven’t flowered yet, and that the resulting damage stimulates the production of new flowers that bloom earlier than those on plants that haven’t been given this “nudge”.

Their study has just been published in the journal Science. “Previous work has shown that various kinds of stress can induce plants to flower, but the role of bee-inflicted damage in accelerating flower production was unexpected,” Mescher says.

bumblebees pollen — If bumblebees find too little pollen, they pierce the leaves of non-flowering plants in order to force them to produce flowers more quickly. Credits: Photograph: Hannier Pulido / ETH Zurich

Surprising behaviour from bumblebees

The researchers first noticed the behaviour during other experiments being undertaken by one of the authors, Foteini Pashalidou: pollinators were biting the leaves of test plants in the greenhouse. “On further investigation, we found that others had also observed such behaviours, but no one had explored what the bees were doing to the plants or reported an effect on flower production,” Mescher explains.

Following up on their observations, the ETH researchers devised several new laboratory experiments, and also conducted outdoor studies using commercially available bumblebee colonies – typically sold for the pollination of agricultural crops – and a variety of plant species.

Based on their lab studies, the researchers were able to show that the bumblebees’ propensity to damage leaves has a strong correlation with the amount of pollen they can obtain: Bees damage leaves much more frequently when there is little or no pollen available to them. They also found that damage inflicted on plant leaves had dramatic effects on flowering time in two different plant species. Tomato plants subjected to bumblebee biting flowered up to 30 days earlier than those that hadn’t been targeted, while mustard plants flowered about 14 days earlier when damaged by the bees.

“The bee damage had a dramatic influence on the flowering of the plants – one that has never been described before,” De Moraes says. She also suggests that the developmental stage of the plant when it is bitten by bumblebees may influence the degree to which flowering is accelerated, a factor the investigators plan to explore in future work.

The researchers tried to manually replicate the damage patterns caused by bees to see if they could reproduce the effect on flowering time. But, while this manipulation did lead to somewhat earlier flowering in both plant species, the effect was not nearly as strong as that caused by the bees themselves. This leads De Moraes to suggest that some chemical or other cue may also be involved. “Either that or our manual imitation of the damage wasn’t accurate enough,” she says. Her team is currently trying to identify the precise cues responsible for inducing flowering and characterising the molecular mechanisms involved in the plant response to bee damage.

Phenomenon also observed in the field

The ETH research team was also able to observe the bees’ damaging behaviour under more natural conditions, with doctoral student Harriet Lambert leading follow-up studies on the rooftops of two ETH buildings in central Zurich. In these experiments, the researchers again observed that hungry bumblebees with insufficient pollen supplies frequently damaged the leaves of non-blooming plants. But the damaging behaviour was consistently reduced when the researchers made more flowers available to the bees.

Furthermore, it was not only captive-bred bumblebees from the researchers’ experimental colonies that damaged plant leaves. The investigators also observed wild bees from at least two additional bumblebee species biting the leaves of plants in their experimental plots. Other pollinating insects, such as honeybees, did not exhibit such behaviour, however: they seemed to ignore the non-flowering plants entirely, despite being frequent visitors to nearby patches of flowering plants.

Delicate balance starting to tip

“Bumblebees may have found an effective method of mitigating local shortages of pollen,” De Moraes says. “Our open fields are abuzz with other pollinators, too, which may also benefit from the bumblebees’ efforts.” But it remains to be seen whether this mechanism is sufficient to overcome the challenges of changing climate. Insects and flowering plants have evolved together, sharing a long history that strikes a delicate balance between efflorescence and pollinator development. However, global warming and other anthropogenic environmental changes have the potential to disrupt the timing of these and other ecologically important interactions among species. Such rapid environmental change could result in insects and plants becoming increasingly out of sync in their development, for example. “And that’s something from which both sides stand to lose,” Mescher says.

Reference paper on bumblebees when pollen is in short supply

Paschalidou FG, Lambert H, Peybernes T, Mescher MC, De Moraes CM. Bumble bees damage plant leaves and accelerate flower production when pollen is scarce. Science, published online May 21st 2020. DOI: 10.1126/science.aay0496

Press release from ETH Zürich

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