Posts Tagged ‘plant’

Goldenrods that evolved in the presence of herbivores release volatile chemicals that trigger defenses in neighboring plants of their species, even those that are genetically unrelated.

by Ashley Yeager

When a beetle larva bites into the leaf of a goldenrod plant, a perennial herb known for its bright yellow flowers, it gets a mouthful of food to fuel its growth. But the plant’s perspective is rather different. The bite damages the goldenrod (genus: Solidago), causing it to launch molecular defenses against the insect and to emit a concoction of chemicals that change the physiology of goldenrod plants nearby. It’s as if the plants are communicating about the invader.

For researchers studying plants’ responses to herbivory, the reasons for this communication are something of a mystery. “We don’t have a good understanding of why these plants are emitting these cues,” Rick Karban, an entomologist who studies plant communication at the University of California, Davis, tells The Scientist. “We don’t even know if the cues that plants are emitting—that other plants can perceive and respond to—are somewhat intentional,” or just a byproduct of leaf damage.

The notion that plants communicate was controversial until the end of the 20th century. Biologists first argued that trees and plants could “talk” to one another in the 1980s, but data supporting the idea were dismissed by many researchers as statistically sketchy. Over the past few decades, however, the scientific community has revised its opinion. A series of papers have shown that when a plant such as goldenrod is damaged, it releases volatile organic compounds (VOCs) that prompt neighboring plants to mount their own chemical defenses against an impending herbivore attack. Karban says researchers are now focused on why the emitting plant puts out this signal, and whether it derives a benefit from telling those around it that it’s being eaten.

It’s possible that surrounding plants are merely eavesdropping on the signal emitter, which derives no benefit from the situation. Researchers have also proposed two alternative hypotheses that involve a benefit to the emitter. The first—the kin selection hypothesis—states that the plant emitting the signal indirectly benefits thanks to the increased survival of genetically related individuals in its vicinity, even if the plant itself is damaged by herbivory. The second—the mutual benefit hypothesis—posits that the plant emitting the signal directly benefits from communication because the preemptive chemical defenses launched by all its neighbors result in a hostile environment that encourages the herbivorous insect to move away from the area.

Finding evidence to distinguish between these scenarios hasn’t been easy, especially because plant communication is a small field. But a long-running project offers new clues. In 1996, a team at Cornell University started an elaborate experiment on one goldenrod species, S. altissima, regularly spraying rows and rows of the plant with the insecticide fenvalerate, while leaving other rows untreated. After 12 years, the researchers collected plants from each of the rows, brought them to the lab, snipped the stems, and grew clones. Then, the team set up collections of the clones in pots at a nearby farm, let goldenrod beetle larvae munch on some of the plants, and measured the emission of VOCs.

“This research was really mostly curiosity driven,” says Aino Kalske, a postdoctoral researcher in ecology and evolution biology at the University of Turku in Finland and a former graduate student at Cornell who helped with the experiment. She and her colleagues were particularly interested to see if the goldenrod’s chemical messages would evolve differently depending on whether the plants had been treated with insecticide and were protected from insect attacks or had been left untreated and experienced higher levels of herbivory. Differences in signaling between the treated and untreated plants’ descendants might be a small step toward determining which hypothesis about plant communication was correct.

The team found that VOCs emitted by goldenrod plants whose predecessors had been sprayed with the insecticide only induced genetically identical plants to mount preemptive chemical defenses to insect invasion—consistent with the kin selection hypothesis. But VOCs emitted by goldenrod whose predecessors hadn’t been sprayed with the insecticide induced the preemptive defense from all the other goldenrod plants around them, even plants that weren’t their kin—consistent with the mutual benefit hypothesis.

Additionally, the plants exposed to herbivory converged on a shared VOC signal over the course of the study—with all of the goldenrod plants eventually emitting the same chemical signals whether they were genetically identical to the emitter plant or not. Plants treated with insecticide showed no such signal convergence, the researchers reported in Current Biology last September. This sort of convergence on a single chemical signal is thought to benefit plants exposed to herbivory by providing a stronger deterrent against invading insects or a stronger attraction for the herbivores’ natural enemies. Kalske says the study provides the first concrete evidence that plants aren’t merely eavesdropping on one another, and that the emitter derives a benefit from releasing its chemical messages.

“The main value of the paper is the extremely long-lasting experiment needed to assess an evolutionary change in an organism,” Emilio Guerrieri, a researcher at the National Research Council of Italy’s Institute for Sustainable Plant Protection who was not involved in the study, writes in an email to The Scientist. The experiment, he says, “represents a sound demonstration that herbivores shape the VOC emission of a plant.”

Researchers still don’t know much about how the plants actually receive and respond to the VOC cues, Kalske notes, or whether the presence of other types of herbivores, such as mammals, influences similar signal changes. These are questions that the team would still like to answer, she says, not least because of the potential agricultural applications. “Understanding the intricacies of the plant world and plant-plant communication in more detail can potentially help us in plant protection in the agricultural context, if we can learn how to use these volatiles to turn on defenses in crop plants effectively.”

by Emily Makowski

Some ants produce natural antibiotic chemicals to defend themselves against fungi and bacteria. Ecologist Joachim Offenberg of Aarhus University in Denmark wondered what effect these compounds had on the health of the plants the ants called home. “We had this thought that if ants produce antibiotics, maybe these antibiotics could have an effect . . . on the diseases of the plants they walk on,” he tells The Scientist.

In a review of studies investigating the effect of ants on plant pathogens, he and fellow Aarhus ecologist Christian Damgaard found that, out of 30 plant species that were commonly inhabited by some kind of ant, 18 showed a decrease in the effects of pathogens. These included reduced bacterial load and increased germination rates enjoyed by plants inhabited by ants compared with plants of the same species that did not host ants.

Data have long confirmed that ants provide protection to their botanical hosts by eating pests, says Andreas Schramm, a microbiologist at Aarhus University who was not involved with the study. “The chemical defense of plants is really another direction that the authors quite convincingly put out here,” he says. Overall, Offenberg and Damgaard estimated that the effects of ants’ antibiotics were comparable to the benefits plants receive from the insects’ consumption of herbivorous pests.

Six of the plant species had increased pathogen incidence with ants, however, and six either had no significant difference between groups or insufficient data. Offenberg notes that a plant that hosts ants may already have a major infection that can’t be controlled with ant-produced antimicrobial compounds. Moreover, the insects can inadvertently disperse pathogens: fungal spores, for example, can cling to their legs.

Although it has been revealed in recent years that plants are capable of seeing, hearing and smelling, they are still usually thought of as silent. But now, for the first time, they have been recorded making airborne sounds when stressed, which researchers say could open up a new field of precision agriculture where farmers listen for water-starved crops.

Itzhak Khait and his colleagues at Tel Aviv University in Israel found that tomato and tobacco plants made sounds at frequencies humans cannot hear when stressed by a lack of water or when their stem is cut.

Microphones placed 10 centimetres from the plants picked up sounds in the ultrasonic range of 20 to 100 kilohertz, which the team says insects and some mammals would be capable of hearing and responding to from as far as 5 metres away. A moth may decide against laying eggs on a plant that sounds water-stressed, the researchers suggest. Plants could even hear that other plants are short of water and react accordingly, they speculate.

“These findings can alter the way we think about the plant kingdom, which has been considered to be almost silent until now,” they write in their study, which has not yet been published in a journal.

Previously, devices have been attached to plants to record the vibrations caused by air bubbles forming and exploding – a process known as cavitation – inside xylem tubes, which are used for water transport. But this new study is the first time that sounds from plants have been measured at a distance.

On average, drought-stressed tomato plants made 35 sounds an hour, while tobacco plants made 11. When plant stems were cut, tomato plants made an average of 25 sounds in the following hour, and tobacco plants 15. Unstressed plants produced fewer than one sound per hour, on average.

It is even possible to distinguish between the sounds to know what the stress is. The researchers trained a machine-learning model to discriminate between the plants’ sounds and the wind, rain and other noises of the greenhouse, correctly identifying in most cases whether the stress was caused by dryness or a cut, based on the sound’s intensity and frequency. Water-hungry tobacco appears to make louder sounds than cut tobacco, for example.

Although Khait and his colleagues only looked at tomato and tobacco plants, they believe other plants may make sounds when stressed too. In a preliminary study, they also recorded ultrasonic sounds from a spiny pincushion cactus (Mammillaria spinosissima) and the weed henbit dead-nettle (Lamium amplexicaule). Cavitation is a possible explanation for how the plants generate the sounds, they say.

Enabling farmers to listen for water-stressed plants could “open a new direction in the field of precision agriculture”, the researchers suggest. They add that such an ability will be increasingly important as climate change exposes more areas to drought.

“The suggestion that the sounds that drought-stressed plants make could be used in precision agriculture seems feasible if it is not too costly to set up the recording in a field situation,” says Anne Visscher at the Royal Botanic Gardens, Kew, in the UK.

She warns that the results can’t yet be broadened out to other stresses, such as salt or temperature, because these may not lead to sounds. In addition, there have been no experiments to show whether moths or any other animal can hear and respond to the sounds the plants make, so that idea remains speculative for now, she says.

If plants are making sounds when stressed, cavitation is the most likely mechanism, says Edward Farmer at the University of Lausanne, Switzerland. But he is sceptical of the findings, and would like to see more in the way of controls, such as the sounds of drying soil without plants in it.

Farmer adds that the idea moths might be listening to plants and shunning stressed ones is a “little too speculative”, and there are already plenty of explanations for why insects avoid some plants and not others.

Reference: bioRxiv, DOI: 10.1101/507590

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By Yasemin Saplakoglu

Drinking a cup of tea or eating a handful of berries a day may help protect against heart disease, a new study suggests.

The research, presented November 10 at the American Heart Association’s Scientific Sessions annual meeting, found that daily consumption of small amounts of flavonoids — compounds found in berries, tea, chocolate, wine and many other fruits and plants — was associated with a lower risk of heart disease.

This association (which is not to be confused with a cause-and-effect finding) is not new; previous research has also found a link between flavonoids and heart disease risk. But the new study — one of the largest done to date — adds stronger evidence to the idea that flavonoids may protect the heart, said co-lead study author Nicola Bondonno, a postdoctoral researcher at the School of Biomedical Science at the University of Western Australia.

In the study, Bondonno and her team analyzed data from nearly 53,000 people who had participated in the long-running Danish Diet, Cancer and Health Study, which began in the 1990s. At the beginning of that study, participants filled out a questionnaire with information about what types of foods they ate and how often they ate them. The researchers then tracked the participants’ health for more than two decades.

After a 23-year follow-up period, around 12,000 of the participants had developed some sort of heart condition.

The researchers found that people who reported eating around 500 milligrams or more of flavonoids daily had a lower risk of developing ischemic heart disease (where the heart’s major blood vessels are narrowed, reducing blood flow to the heart), stroke and peripheral artery disease (where blood vessels in the body are narrowed, reducing blood flow throughout the body). This association was the greatest for the latter, the researchers found.

Bondonno noted that 500 mg of flavonoids is “very easy to eat in one day.” You would get that amount of flavonoids from “a cup of tea, a handful of blueberries, maybe some broccoli,” she said. They also found that, on average, it didn’t make too much of a difference how much more flavonoids healthy people consumed once they passed the 500 mg/day threshold.

The reason flavonoids could have a protective role against heart disease is because of their anti-inflammatory properties, Bondonno told Live Science. Inflammation is a risk factor for heart disease, she said.

The researchers noted that the association between flavonoids and reduced heart disease risk varied for different groups of people. The link between flavonoids and reduced risk of heart disease in smokers, for example, wasn’t observed at 500 mg of flavonoids a day; rather, smokers needed to eat more flavonoids for the link to be apparent. Similar results were seen in people who drank alcohol and in men. However, it was in these three groups that the researchers found that flavonoid intake was associated with the greatest reduction in risk.

In their analysis, Bondonno and her team made sure to take people’s whole diets into consideration, because people who tend to eat lots of fruits and vegetables (and in turn, consume a lot of flavonoids), tend to have better diets in general, eating more fiber and fish and less processed food, which are all “associated with heart disease,” Bondonno said. When they adjusted for these diets in their report, they found that the association between flavonoid intake and reduced heart disease risk was still there, but a bit weaker. In other words, flavonoids may not play as big a role in heart disease risk as a healthy diet would in general.

Further, the study was conducted only in Danish people, and though these results shouldn’t be extrapolated, “these kinds of associations have been seen in other populations,” Bondonno said.

The findings have not yet been published in a peer-reviewed journal.



When somebody mentions anaesthetics, we probably think straight away of pain relief, but there’s a lot more going on in these complex chemical compounds than the simple negation of discomfort.

While there’s a range of chemicals that can induce anaesthesia in humans, just how these unrelated compounds trigger a lack of consciousness remains somewhat unclear.

And the mystery deepens when you consider it isn’t only animals that are affected by anaesthetics – plants are, too.

Humans in ancient societies were using things like herbs for various sedative purposes thousands of years ago, but the roots of modern anaesthesia began around the mid-19th century, when physicians began administering diethyl ether to patients during surgical procedures.

It was only a few decades later that scientists realised plants were similarly affected by ether, leading French physiologist Claude Bernard to conclude plants and animals shared a common biological essence that could be disrupted by anaesthetics.


A century and a half later, scientists are still investigating this strange commonality – basically by slipping plants the mickey and seeing what it does to them.

In a new study by Japanese and European researchers, the team filmed a number of plants that exhibit the phenomenon of rapid plant movement to see what kinds of anaesthetic chemicals affected them.

The sensitive plant (Mimosa pudica) usually closes its leaves in response to touch stimuli; but when exposed to diethyl ether, the dosed-up plants completely lost this response, becoming motionless, with the movement response only returning to normal after 7 hours.

In a separate experiment with the sensitive plants, a lidocaine solution also immobilised the leaves.

Similarly, the Venus flytrap (Dionaea muscipula) lost its ability to close its trap when exposed to diethyl ether – despite repeated prongings by the researchers – but the mechanism recovered in just 15 minutes.

Another carnivorous plant, Cape sundew (Drosera capensis), captures prey via sticky tentacles on its leaves, but experiments showed they lost the ability to bend their leaves and tentacles when exposed to the ether.

As for why plants are incapacitated by these chemicals, the researchers hypothesise it is to do with the inhibition of action potentials, preventing electrical impulses that help plants’ biological systems function.

“[B]ioelectricity and action potentials animate not only humans and animals but also plants,” the researchers explain.

“That animals/humans and also plants are animated via action potentials is of great importance for our ultimate understanding of the elusive nature of plant movements and plant-specific cognition/intelligence based plant behaviour.”

Ultimately, the team thinks these similarities between plant and animal reactions to anaesthetic compounds could lead to future research where plants might function as a substitute model or test system to explore human anaesthesia – something scientists are still pretty uncertain about.

It’s not easy being green, perhaps, but at least they shouldn’t feel any pain.

The findings are reported in Annals of Botany.


When humans are attacked, sensory cells transmit signals through our nervous system, spitting out the neurotransmitter–glutamate. Glutamate stimulates our brain’s amygdala and hypothalamus. This triggers the stress hormone–adrenaline–that jolts us into fight or flight mode. Plants don’t have neurotransmitters. They don’t have nervous systems. The don’t have brains. But now, for the first time, scientists are able to observe how a plant responds to an attack with vivid real-time imagery that illuminates the remarkable differences and similarities between plants and humans. Same substance, same results, different anatomy. In the video below, a plant gets chomped on by a caterpillar. At the site of the wound, the plant spills out glutamate–the same chemical as our glutamate neurotransmitter, but not a neurotransmitter. This triggers a calcium wave throughout the plant body, stimulating a plant stress hormone that prepares it for the vegetal version of fight or flight.

To observe what’s happening, scientists sampled a gene from jellyfish that makes them glow green. Then they genetically modified plants to produce a protein that fluoresces around calcium. The results are a blazing calcium wave that undulates through the plant vascular system when it gets bit.

“[For] the first time, it’s been shown that glutamate leakage at a wound site triggers a system-wide wound response, and the first time we’ve been able to visualize this process happening ,” says Simon Gilroy, professor of botany at the Gilroy Lab at the University of Wisconsin-Madison, and senior author on the paper out today in the journal Science.

An incidental breakthrough

The discovery came about via “the classic opportunistic randomness of science,” says Gilroy. The lab wasn’t investigating plant wounds. It was looking at how plants take in and assimilate information. One day, postdoctoral researcher and first author on the paper, Masatsugu Toyota, approached the team: “‘You have to see this. This is amazing,” he said.’ It just played out in front of us,” says Gilroy.


Rip Van Winkle, the titular ne’er-do-well of Washington Irving’s 1819 short story, famously spent 20 years napping in a forest. This lengthy slumber, apparently triggered by ghost liquor, caused Van Winkle to sleep through the American Revolutionary War.

Nearly two centuries later, scientists are shedding light on plants that do something similar in real life. A surprisingly diverse mix of plants around the world can live dormant underground for up to 20 years, researchers report in the journal Ecology Letters, a strategy that allows the plants to survive hard times by simply napping until things get better.

At least 114 species from 24 plant families are capable of this trick, in which a plant abandons photosynthesis to focus on survival in the soil. It’s a way for plants to hedge their bets, the study’s authors explain, by accepting certain short-term hardships — like missed opportunities to grow and reproduce — for the longer-term benefits of avoiding mortal dangers on the surface.

“It would seem to be paradoxical that plants would evolve this behavior, because being underground means they cannot photosynthesize, flower or reproduce,” says co-author Michael Hutchings, an ecology professor at the University of Sussex, in a statement. “And yet this study has shown that many plants in a large number of species frequently exhibit prolonged dormancy.”

So how do these Rip Van Winkle plants survive for up to 20 years without sunlight? Many species have found other ways to endure dormancy, Hutchings says, especially “by evolving mechanisms enabling them to obtain carbohydrates and nutrients from soil-based fungal associates.” Befriending soil fungi, he adds, “allows them to survive and even thrive during dormant periods.”

This strategy is used by many orchid species (including the lady’s slipper orchids pictured above), along with a wide variety of other plant types. It typically occurs in only part of a population or species during any given year, the researchers note, so the broader population can keep growing and reproducing while the designated survivors wait underground as backup.