A recent study in Frontiers in Sustainable Food Systems shows that the fruits of a type of tomato plant send electrical signals to the rest of the plant when they are infested by caterpillars. Plants have a multitude of chemical and hormonal signaling pathways, which are generally transmitted through the sap (the nutrient-rich water that moves through the plant). In the case of fruits, nutrients flow exclusively to the fruit and there has been little research into whether there is any communication in the opposite direction–i.e. from fruit to plant.
“We usually forget that a plant’s fruits are living and semiautonomous parts of their mother-plants, far more complex than we currently think. Since fruits are part of the plant, made of the same tissues of the leaves and stems, why couldn’t they communicate with the plant, informing it about what they are experiencing, just like regular leaves do?” says first author Dr Gabriela Niemeyer Reissig, of the Federal University of Pelotas, Brazil. “What we found is that fruits can share important information such as caterpillar attacks–which is a serious issue for a plant–with the rest of the plant, and that can probably prepare other parts of the plant for the same attack.”
A tomato’s defense
To test the hypothesis that fruits communicate by electrical signals, Niemeyer Reissig and her collaborators placed tomato plants in a Faraday’s cage with electrodes at the ends of the branches connecting the fruits to the plant. They then measured the electrical responses before, during and after the fruits had been attacked by Helicoverpa armigera caterpillars for 24 hours. The team also used machine learning to identify patterns in the signals.
The results showed a clear difference between the signals before and after attack. In addition, the authors measured the biochemical responses, such as defensive chemicals like hydrogen peroxide, across other parts of the plant. This showed that these defenses were triggered even in parts of the plant that were far away from the damage caused by the caterpillars.
The authors emphasize that these are still early results. Their measurements provide a “big picture” view of all of the electrical signals, rather than distinguishing individual signals more precisely. It will also be interesting to see whether this phenomenon holds true for other plant species, as well as different types of threats.
That said, this novel use of machine learning appears to have very high potential for answering these and other future questions. The technique may also provide new–and possibly more environmentally friendly–approaches for insect control in agriculture.
“If studies like ours continue to advance and the techniques for measuring electrical signals in open environments continue to improve, it will be possible to detect infestation of agricultural pests quite early, allowing for less aggressive control measures and more accurate insect management,” explains Niemeyer Reissig. “Understanding how the plant interacts with its fruits, and the fruits among themselves, may bring insights about how to ‘manipulate’ this communication for enhancing fruit quality, resistance to pests and shelf life after harvest.”
Reference: Gabriela Niemeyer Reissig et al., “Fruit Herbivory Alters Plant Electrome: Evidence for Fruit-Shoot Long-Distance Electrical Signaling in Tomato Plants”, Front. Sustain. Food Syst., 20 July 2021 | https://doi.org/10.3389/fsufs.2021.657401
Venom from spitting cobras has evolved to cause predators extreme pain as a form of self-defence, rather than for capturing prey, according to new research.
An international team including scientists from The University of Queensland, made the discovery by studying the composition of spitting cobra venoms from three groups of snakes — Asian spitting cobras, African spitting cobras and rinkhals.
“The fangs of these snakes are adapted to spray venom as far as 2.5 metres — the venom is aimed directly at the face, specifically the eyes, causing intense pain and can lead to the loss of eyesight,” Dr Robinson said.
Professor Vetter said the snakes had independently evolved the ability to spit their venoms at enemies.
“We tested how venom components affected pain-sensing nerves and showed that spitting cobra venoms are more effective at causing pain than their non-spitting counterparts,” she said.
The three different groups of venom-spitting snakes had increased production of an enzyme toxin, phospholipase-A2, which works cooperatively with other venom toxins to maximise pain.
Lead author Professor Nick Casewell from the Liverpool School of Tropical Medicine said venom spitting was ideally suited to deterring attacks from humans.
“It is intriguing to think that our ancestors may have influenced the origin of this defensive chemical weapon in snakes,” he said.
Professor Vetter and Dr Robinson are pain researchers, studying the molecular mechanisms of pain with the goal of developing new and more effective painkilling drugs.
“Pain-causing toxins from animal venoms can be useful tools to help us understand pain signalling at a molecular level, and are helping us to identify new targets for future painkillers,” Dr Robinson said.
This research was published in Science(DOI: 10.1126/science.abb9303).
Reference: T. D. Kazandjian, D. Petras, S. D. Robinson, J. van Thiel, H. W. Greene, K. Arbuckle, A. Barlow, D. A. Carter, R. M. Wouters, G. Whiteley, S. C. Wagstaff, A. S. Arias, L.-O. Albulescu, A. Plettenberg Laing, C. Hall, A. Heap, S. Penrhyn-Lowe, C. V. McCabe, S. Ainsworth, R. R. da Silva, P. C. Dorrestein, M. K. Richardson, J. M. Gutiérrez, J. J. Calvete, R. A. Harrison, I. Vetter, E. A. B. Undheim, W. Wüster, N. R. Case well, “Convergent evolution of pain-inducing defensive venom components in spitting cobras”, Science 22 Jan 2021: Vol. 371, Issue 6527, pp. 386-390 DOI: 10.1126/science.abb9303
Defense and autotoxicity: Researchers elucidate the biosynthesis and mode of action of diterpene glycosides in wild tobacco.
Plants produce toxic substances to defend themselves against herbivores. In a new study, scientists from the Max Planck Institute for Chemical Ecology in Jena and the University of Münster, Germany, were able to describe in detail the biosynthesis and exact mode of action of an important group of defensive substances, the diterpene glycosides, in wild tobacco plants. Diterpene glycosides allow plants to fend off herbivores. The study shows that these plant chemicals attack certain parts of the cell membrane. To protect themselves from their own toxins and to prevent their cell membranes from being damaged, tobacco plants store these substances in a non-toxic form which is synthesized in a very particular way. Autotoxicity and the protection against it seem to play a greater role in the evolution of plant defenses than previously thought (Science, doi 10.1126/science.abe4713:, January 2021).
Many plants produce chemical defenses to protect themselves against being eaten. Still little is known about what makes these substances toxic to their consumers. Researchers at the Max Planck Institute for Chemical Ecology and the University of Münster have now investigated how plants produce toxins and store them in their tissues without harming themselves. In particular, they wanted to know whether the mechanisms of autotoxicity and its prevention share similar mechanisms as the toxic characteristics that provide defense against herbivores.
Autotoxicity and defense
For their experiments, they chose diterpene glycosides from Nicotiana attenuata plants, a wild tobacco species. “These substances occur at very high concentrations in the leaves of tobacco plants. But we had no idea why they were such effective defenses or why they could be so toxic to produce. So the situation was completely different from the other very abundant toxin that this plant produces, namely, nicotine. Nicotine is a specific neurotoxin. Since plants lack nerves and muscles, they offer no target for the toxin. So producing and storing nicotine does not harm plants,” says Ian Baldwin from the Department of Molecular Ecology at the Jena Max Planck Institute, where the study was carried out.
To their surprise, the researchers found that tobacco plants which had been transformed so they could no longer produced two proteins involved in the biosynthesis of the diterpene glycosides and thus also not form the defensive substances otherwise stored in the leaves in large amounts, showed conspicuous symptoms of self-poisoning: they were sick, unable to grow normally, and could no longer reproduce. Further experiments revealed that certain components of the cell membrane, so-called sphingolipids, had been attacked.
Targeting the cell membrane
Sphingolipids are substances found in all animals and plants, including the enemies of wild tobacco, the larvae of the tobacco hawkmoth Manduca sexta. The researchers therefore asked whether the sphingolipid metabolism could be the target of the diterpene glycosides. In fact, Manduca sexta caterpillars, which had fed on plants without diterpene glycosides, grew significantly better than larvae, which had fed on controls that contained the defensive chemicals. Analyses of the frass of Manduca sexta larvae, which had ingested diterpene glycosides with their food, provided further insights, as the degradation of the plant toxins during larval digestion is more or less in reverse order to the synthesis of the substances in the plant. Plants prevent self-harm by storing the defensive substances in a non-toxic form. However, when insects feed on the plant, a part of the non-toxic molecule is cleaved off and the chemical becomes activated or “armed”. “Interestingly, in both cases, in plants with incomplete diterpene glycoside biosynthesis and in feeding caterpillars, the target of the toxins is the sphingolipid metabolism,” says first author Jiancai Li.
Sphingolipids are mediators in many physiological processes. This makes the effect of diterpene glycosides on sphingolipid metabolism so intriguing. “Diterpene glycosides and their derivatives can have broad defensive functions against many agricultural pests and pathogenic fungi. At the same time, many human diseases, such as diabetes, cancers and some neurodegenerative diseases are also associated with elevated sphingolipid metabolisms,” says Shuqing Xu from the Institute for Evolution and Biodiversity at the University of Münster, who is one of the senior authors of the study. Physicians have been searching for effective substances to treat these diseases by inhibiting the sphingolipid metabolism. The diterpene glycosides studied here could be potential candidates for further investigations.
“Frassomics“ – a new powerful tool to study interactions between organisms
The analysis of larval frass proved to be the key to success in this study. The scientists call this new approach “frassomics”: a combination of frass (larval droppings) and metabolomics – the analysis of all metabolites in an organism. “From this work, we realized that frassomics can be a very powerful research tool. The analysis of larval frass can provide metabolic clues about how what one organism produces is metabolized by consumer organisms,” says Ian Baldwin.
The scientists plan to gain more insights into the “digestive duets” that occur between plants and insects, in order to better understand ecological interactions between plants, insects and microorganisms.
Li, J., Halitschke, R., Li, D., Paetz, C., Su, H., Heiling, S., Xu, S., Baldwin, I. T. (2021). Controlled hydroxylations of diterpenoids allow for plant chemical defense without autotoxicity, Science, DOI: 10.1126/science.abe4713 https://doi.org/10.1126/science.abe4713
Eagleman and colleagues hypothesized that the circuitry underlying dreaming serves to amplify the visual system’s activity periodically throughout the night, allowing it to defend its territory against takeover from other senses.
One of neuroscience’s unsolved mysteries is why brains dream. Do our bizarre nighttime hallucinations carry meaning, or are they simply random neural activity in search of a coherent narrative? And why are dreams so richly visual, activating the occipital cortex so strongly? Eagleman and colleagues in their recent paper, leverage recent findings on neural plasticity to propose a novel hypothesis.
Just as sharp teeth and fast legs are useful for survival, so is neural plasticity: the brain’s ability to adjust its parameters (e.g., the strength of synaptic connections) enables learning, memory, and behavioral flexibility.
On the scale of brain regions, neuroplasticity allows areas associated with different sensory modalities to gain or lose neural territory when inputs slow, stop, or shift. For example, in the congenitally blind, the occipital cortex is taken over by other senses such as audition and somatosensation. Similarly, when human adults who recently lost their sight listen to sounds while undergoing functional magnetic resonance imaging (fMRI), the auditory stimulation causes activity not only in the auditory cortex, but also in the occipital cortex. Such findings illustrate that the brain undergoes changes rapidly when visual input stops.
Rapid neural reorganization happens not only in the newly blind, but also among sighted participants with temporary blindness. In one study, sighted participants were blindfolded for five days and put through an intensive Braille-training paradigm. At the end of five days, the participants could distinguish subtle differences between Braille characters much better than a control group of sighted participants who received the same training without a blindfold. The difference in neural activity was especially striking: in response to touch and sound, blindfolded participants showed activation in the occipital cortex as well as in the somatosensory cortex and auditory cortex, respectively. When the new occipital lobe activity was intentionally disrupted by magnetic pulses, the Braille-reading advantage of the blindfolded subjects went away. This finding indicates that the recruitment of this brain area was not an accidental side effect—it was critical for the improved performance. After the blindfold was removed, the response of the occipital cortex to touch and sound disappeared within a day.
Of particular interest here is the unprecedented speed of the changes. When sighted participants were asked to perform a touching task that required fine discrimination, investigators detected touch-related activity emerging in the primary visual cortex after only 40 to 60 minutes of blindfolding. The rapidity of the change may be explained not by the growth of new axons, but by the unmasking of pre-existing non-visual connections in the occipital cortex.
It is advantageous to redistribute neural territory when a sense is permanently lost, but the rapid conquest of territory may be disadvantageous when input to a sense is diminished only temporarily, as in the blindfold experiment. This consideration leads Eagleman and colleagues to propose a new hypothesis for the brain’s activity at night. In the ceaseless competition for brain territory, the visual system in particular has a unique problem: due to the planet’s rotation, we are cast into darkness for an average of 12 hours every cycle. (This of course refers to the vast majority of evolutionary time, not to our present electrified world). Given that sensory deprivation triggers takeover by neighboring territories, how does the visual system compensate for its cyclical loss of input?
Eagleman and colleagues suggested that the brain combats neuroplastic incursions into the visual system by keeping the occipital cortex active at night. They term this the Defensive Activation theory. In this view, dream sleep exists to keep the visual cortex from being taken over by neighboring cortical areas. After all, the rotation of the planet does not diminish touch, hearing, taste, or smell. Only visual input is occluded by darkness.
“We suggest that the brain preserves the territory of the visual cortex by keeping it active at night. In our “defensive activation theory,” dream sleep exists to keep neurons in the visual cortex active, thereby combating a takeover by the neighboring senses. In this view, dreams are primarily visual precisely because this is the only sense that is disadvantaged by darkness. Thus, only the visual cortex is vulnerable in a way that warrants internally-generated activity to preserve its territory.”, said Eagleman.
In humans, sleep is punctuated by REM (rapid eye movement) sleep about every 90 minutes. This is when most dreaming occurs. Although some forms of dreaming can occur during non-REM sleep, such dreams are quite different from REM dreams; non-REM dreams usually are related to plans or thoughts, and they lack the visual vividness and hallucinatory and delusory components of REM dreams.
REM sleep is triggered by a specialized set of neurons in the pons, Increased activity in this neuronal population has two consequences. First, elaborate neural circuitry keeps the body immobile during REM sleep by paralyzing major muscle groups. The muscle shut-down allows the brain to simulate a visual experience without moving the body at the same time. Second, they experience vision when waves of activity travel from the pons to the lateral geniculate nucleus and then to the occipital cortex (these are known as ponto-geniculo-occipital waves or PGO waves). When the spikes of activity arrive at the occipital pole, they felt as though they were seeing even though our eyes are closed. They found that the visual cortical activity is presumably why dreams are pictorial and filmic instead of conceptual or abstract.
These nighttime volleys of activity are anatomically precise. The pontine circuitry connects specifically to the lateral geniculate nucleus, which passes the activity on to the occipital cortex, only. The high specificity of this circuitry supports the biological importance of dream sleep: putatively, this circuitry would be unlikely to evolve without an important function behind it.
“As predicted, we found that species with more flexible brains spend more time in REM sleep each night. Although these two measures—brain flexibility and REM sleep—would seem at first to be unrelated, they are in fact linked.”, said Eagleman.
Their Defensive Activation theory makes a strong prediction: the higher an organism’s neural plasticity, the higher its ratio of REM to non-REM sleep. This relationship should be observable across species as well as within a given species across the lifespan. They thus set out to test their hypothesis by comparing 25 species of primates on behavioral measures of plasticity and the fraction of sleep time they spend in REM and found that measures of plasticity across 25 species of primates correlate positively with the proportion of rapid eye movement (REM) sleep.
They further found that plasticity and REM sleep increase in lockstep with evolutionary recency to humans. Finally, they concluded that their hypothesis is consistent with the decrease in REM sleep and parallel decrease in neuroplasticity with aging.
Many species adjust their acoustic signals in response to human-made noise.
According to the World Health Organization, noise caused by human activities is one of the most hazardous forms of pollution. Now, a new study shows that human-made noise could hamper the communication of a variety of different animal species, from insects to frogs to birds. The meta-analysis found that animals exposed to human-made noise adjusted parameters of their acoustic signals, with potential consequences for mate attraction, territory defense, and parent-offspring communication.
Noise from human activities—such as transportation, shipping, and industry—differs from the naturally occurring soundscapes within which animals have evolved.
“It is typically loud and low-frequency,” says Hansjoerg Kunc, a biologist at Queen’s University Belfast who led the new study. “Many acoustic signals are in the same frequency range as anthropogenic (human-made) noise, whereas in nature, often noise is distributed more equally across a wider range of frequencies.”
Kunc, with colleague Rouven Schmidt, conducted a meta-analysis to investigate how species differ in their sensitivities to human-made noise. The researchers analyzed data from 31 different animal species, collected from 23 experimental studies in which animals were exposed to human-made noise. They studied the effects of noise on different components of acoustic signals, including the amplitude (loudness), frequency (pitch), complexity, duration, and rate. For each of these components, the researchers quantified both the magnitude and direction of adjustments in response to human-made noise.
Kunc and Schmidt found that animals adjust the components of their acoustic signals when exposed to noise, but the direction of adjustments differed among species. For instance, animals changed the duration of their signals in response to noise, but some species shortened them while others increased signal duration.
Given the importance of acoustic communication to many animals, Kunc and others are concerned that these adjustments could have repercussions for individual animals and, potentially, populations and ecosystems. Females of many species decide on mates based on acoustic qualities, such as signal duration, rate, and complexity. Noise-induced adjustments to male songs could make it more difficult for females to choose the highest quality mate.
The analysis shows that noise affects acoustic signals, but whether that change is positive or negative may depend on the species or context. For instance, calling louder may make it more likely that potential mates will hear you in a noisy environment, but may also attract more predators.
Thus far, most of the studies of the effects of noise on animals have focused on the senders of acoustic signals. To unravel the downstream ecological effects of human-made noise, more research incorporating the receivers of such signals is needed. We still have a limited understanding of the potential consequences of noise for receivers, as well as the long-term effects of noise on populations and communities.
Kunc and Schmidt argue that the difference in sensitivity among species has important conservation implications. Their analysis shows it is not enough to assess the consequences of human-made noise for only a few species. A “one size fits all” legislation cannot protect species effectively since the magnitude and direction of responses vary so much among species.
“Given what we know about the effects of noise on animals, the best conservation approach to protect different species is to preserve the natural soundscapes to which animals have adapted,” says Kunc.
“When we protect habitats, we should be including natural soundscapes, free from anthropogenic noise, as part of those habitats.”
Reference: Kunc HP, Schmidt R. Species sensitivities to a global pollutant: A meta-analysis on acoustic signals in response to anthropogenic noise. Glob Change Biol. 2020;00:1–14. Doi: 10.1111/gcb.15428.
This article is originally written by Mary Bates, who specializes in neuroscience, animal behavior, psychology, and biology. This article is republished here from psychology today under common creative licenses.
Decades of pursuit uncovers receptor, the product of an evolutionary arms race for survival, used by plants to sense herbivores.
For decades, scientists have known that plants protect themselves from the devastation of hungry caterpillars and other plant-munching animals through sophisticated response systems, the product of millions of years of evolution.
The biological mechanisms underlying this attack-counter defense paradigm have been vigorously pursued by plant biologists given that such details will help unlock a trove of new strategies for improved plant health. From countering crop pest damage to engineering more robust global food webs, such information is valuable for ensuring sustainable and reliable yields.
Now, researchers at the University of California San Diego and their colleagues have identified the first key biological switch, or receptor, that sounds an alarm in plants specifically when herbivores attack. The discovery is described in the online publication of the Proceedings of the National Academy of Sciences.
Animals such as humans, cows and insects are heterotrophs that derive their energy either directly or indirectly through the consumption of autotrophs, such as photosynthetic plants. This basic foundation shapes biological interactions across planet Earth. More than 30 years ago plant biologists came to understand that plants can sense an attack from herbivorous animals in a way that is distinct from damage caused by hail storms or falling tree branches.
Similar to how human immune defenses counter an attack from viruses, plants have been shown to respond to danger from plant-eating animals through an intricate immune system of receptors. Using a method of pinpointing genetic variants, called forward genetics, research led by Adam Steinbrenner, Alisa Huffaker and Eric Schmelz of UC San Diego’s Division of Biological Sciences enabled discovery the inceptin receptor, termed INR, in bean plants. The receptor detects conserved plant protein fragments accidently released as digestive products during caterpillar munching, thereby enabling plant recognition of attack.
“INR represents the first documented mechanism of a plant cell surface receptor responsible for perceiving animals,” said Schmelz, whose work was accomplished by deconstructing and leveraging the active evolutionary arms race between plants and herbivores. “Our work provides some of the earliest defined mechanistic insights into the question of how plants recognize different attacking herbivores and activate immunity to animals. It is a fundamental question in biology that has been pursued for 30 years.”
Beyond beans, the finding raises interest in using INR, and potentially other receptors that remain to be discovered, as a way to boost defenses in essential agricultural crops.
“A key lesson is that plant perception mechanisms for herbivores can be precisely defined and moved into crops to afford enhanced protection,” said Schmelz. “We have shown one example but it’s clear that hundreds if not thousands of opportunities exist to identify and stack key traits to enhance crop plant immunity to herbivores.”
References: Adam D. Steinbrenner, Maria Muñoz-Amatriaín, Antonio F. Chaparro, Jessica Montserrat Aguilar-Venegas, Sassoum Lo, Satohiro Okuda, Gaetan Glauser, Julien Dongiovanni, Da Shi, Marlo Hall, Daniel Crubaugh, Nicholas Holton, Cyril Zipfel, Ruben Abagyan, Ted C. J. Turlings, Timothy J. Close, Alisa Huffaker, Eric A. Schmelz, “A receptor-like protein mediates plant immune responses to herbivore-associated molecular patterns”, Proceedings of the National Academy of Sciences Nov 2020, 202018415; DOI: 10.1073/pnas.2018415117 https://www.pnas.org/content/early/2020/11/20/2018415117