Information

How does the sensitive plant detect vibrations?


The sensitive plant (Mimosa pudica) is a remarkable little plant whose characteristic feature is its ability to droop its leaves when disturbed:

Apparently, this ability to droop rests on the cells in the leaves of the sensitive plant being able to draw water out of themselves through changes in intracellular ion concentrations, which makes the leaves less turgid.

What I'm hazy about is how the plant "senses" vibrations. Plants don't really have a nervous system to speak of; how then does the sensitive plant "know" to droop when disturbed?


In fact, the idea of a plant nervous system is quite serious and constantly developing; of course those are rather local, simple signal pathways rather than an "animalian" centralized global network, but they use similar mechanisms -- depolarisation waves, neurotransmitter-like compounds, specialized cells… Here is a review paper by Brenner et al.

In the case of Mimosa, there is a good paper summing up Takao Sibaoka's long research of the topic.

In short, it seems that its petioles' phloem has cells which have polarized membranes and can trigger depolarization due to a mechanical stimulation. The signal then propagates to the corresponding pulvinus by a mixture of electrical and Cl- depolarization waves.

In the pulvinus, this signal triggers a second depolarization which coordinates the pulvinus' cells to trigger water pumping responsible for the leaf drop.

The transmission to the adjacent leaves is most likely mechanical, i.e. the movement of one dropping leaf excites another.

References:

  • Brenner ED, Stahlberg R, Mancuso S, Vivanco J, Baluska F, Van Volkenburgh E. 2006. Plant neurobiology: an integrated view of plant signaling. Trends in plant science 11: 413-9.

  • Sibaoka T. 1991. Rapid plant movements triggered by action potentials. The Botanical Magazine Tokyo 104: 73-95.


Haswell, Peyronnet, et al (2008) have shown that plants have some of the same mechanosensitive ion channels that E. coli does. The work was on the roots of Arabidopsis and not the plant you are investigating, but the mechanism could be similar.

It would not seem that vibration plays a role, as it the plant seems responsive to the touch of the human rather than his/her approach to the leaf. This could rule out air currents as a mechanism (but J.M. has noted in the comments that they do fold up when you blow on them).


Some additional notes- I have grown TickleMe Plants (sensitive plants) for years and I have seen the plants close their leaves as a reaction to the vibrations caused by my foot steps as well as blowing on the plant and placing the plant in cold, very hot and dark environments. In addition I have found the plant's ablity to detect vibrations I have observed to be dependent on temperature and the time of day. Some of this information can be found in The TickleMe Plant Book found at http://www.ticklemeplant.com I am unable to specifically say what the mechanism is that detects the vibrations and causes the TickleMe Plants turgor pressure to change. I look forward to more answers.


Mechanoreceptors (in plants)

A mechanoreceptor is a sensory organ or cell that responds to mechanical stimulation such as touch, pressure, vibration, and sound from both the internal and external environment. [1] Mechanoreceptors are well-documented in animals and are integrated into the nervous system as sensory neurons. While plants do not have nerves or a nervous system like animals, they also contain mechanoreceptors that perform a similar function. Mechanoreceptors detect mechanical stimulus originating from within the plant (intrinsic) and from the surrounding environment (extrinsic). [2] The ability to sense vibrations, touch, or other disturbance is an adaptive response to herbivory and attack so that the plant can appropriately defend itself against harm. [3] Mechanoreceptors can be organized into three levels: molecular, cellular, and organ-level. [2]


Contents

Light Edit

Many plant organs contain photoreceptors (phototropins, cryptochromes, and phytochromes), each of which reacts very specifically to certain wavelengths of light. [6] These light sensors tell the plant if it is day or night, how long the day is, how much light is available, and where the light is coming from. Shoots generally grow towards light, while roots grow away from it, responses known as phototropism and skototropism, respectively. They are brought about by light-sensitive pigments like phototropins and phytochromes and the plant hormone auxin. [7]

Many plants exhibit certain behaviors at specific times of the day for example, flowers that open only in the mornings. Plants keep track of the time of day with a circadian clock. [6] This internal clock is synchronized with solar time every day using sunlight, temperature, and other cues, similar to the biological clocks present in other organisms. The internal clock coupled with the ability to perceive light also allows plants to measure the time of the day and so determine the season of the year. This is how many plants know when to flower (see photoperiodism). [6] The seeds of many plants sprout only after they are exposed to light. This response is carried out by phytochrome signalling. Plants are also able to sense the quality of light and respond appropriately. For example, in low light conditions, plants produce more photosynthetic pigments. If the light is very bright or if the levels of harmful ultraviolet radiation increase, plants produce more of their protective pigments that act as sunscreens. [8]

Gravity Edit

To orient themselves correctly, plants must be able to sense the direction of gravity. The subsequent response is known as gravitropism.

In roots, gravity is sensed and translated in the root tip, which then grows by elongating in the direction of gravity. In shoots, growth occurs in the opposite direction, a phenomenon known as negative gravitropism. [9] Poplar stems can detect reorientation and inclination (equilibrioception) through gravitropism. [10]

At the root tip, amyloplasts containing starch granules fall in the direction of gravity. This weight activates secondary receptors, which signal to the plant the direction of the gravitational pull. After this occurs, auxin is redistributed through polar auxin transport and differential growth towards gravity begins. In the shoots, auxin redistribution occurs in a way to produce differential growth away from gravity.

For perception to occur, the plant often must be able to sense, perceive, and translate the direction of gravity. Without gravity, proper orientation will not occur and the plant will not effectively grow. The root will not be able to uptake nutrients or water, and the shoot will not grow towards the sky to maximize photosynthesis. [11]

Touch Edit

Thigmotropism is directional movement that occurs in plants responding to physical touch. [12] Climbing plants, such as tomatoes, exhibit thigmotropism, allowing them to curl around objects. These responses are generally slow (on the order of multiple hours), and can best be observed with time-lapse cinematography, but rapid movements can occur as well. For example, the so-called "sensitive plant" (Mimosa pudica) responds to even the slightest physical touch by quickly folding its thin pinnate leaves such that they point downwards, [13] and carnivorous plants such as the Venus flytrap (Dionaea muscipula) produce specialized leaf structures that snap shut when touched or landed upon by insects. In the Venus flytrap, touch is detected by cilia lining the inside of the specialized leaves, which generate an action potential that stimulates motor cells and causes movement to occur. [14]

Smell Edit

Wounded or infected plants produce distinctive volatile odors, (e.g. methyl jasmonate, methyl salicylate, green leaf volatiles), which can in turn be perceived by neighboring plants. [15] [16] Plants detecting these sorts of volatile signals often respond by increasing their chemical defenses or and prepare for attack by producing chemicals which defend against insects or attract insect predators. [15]

Plant hormones and chemical signals Edit

Plants systematically use hormonal signalling pathways to coordinate their development and morphology.

Plants produce several signal molecules usually associated with animal nervous systems, such as glutamate, GABA, acetylcholine, melatonin, and serotonin. [17] They may also use ATP, NO, and ROS for signaling in similar ways as animals do. [18]

Electrophysiology Edit

Plants have a variety of methods of delivering electrical signals. The four commonly recognized propagation methods include action potentials (APs), variation potentials (VPs), local electric potentials (LEPs), and systemic potentials (SPs) [19] [20] [21]

Although plant cells are not neurons, they can be electrically excitable and can display rapid electrical responses in the form of APs to environmental stimuli. APs allow for the movement of signaling ions and molecules from the pre-potential cell to the post-potential cell(s). These electrophysiological signals are constituted by gradient fluxes of ions such as H + , K + , Cl − , Na + , and Ca 2+ but it is also thought that other electrically charge ions such as Fe 3+ , Al 3+ , Mg 2+ , Zn 2+ , Mn 2+ , and Hg 2+ may also play a role in downstream outputs. [22] The maintenance of each ions electrochemical gradient is vital in the health of the cell in that if the cell would ever reach equilibrium with its environment, it is dead. [23] [24] This dead state can be due to a variety of reasons such as ion channel blocking or membrane puncturing.

These electrophysiological ions bind to receptors on the receiving cell causing downstream effects result from one or a combination of molecules present. This means of transferring information and activating physiological responses via a signaling molecule system has been found to be faster and more frequent in the presence of APs. [22]

These action potentials can influence processes such as actin-based cytoplasmic streaming, plant organ movements, wound responses, respiration, photosynthesis, and flowering. [25] [26] [27] [28] These electrical responses can cause the synthesis of numerous organic molecules, including ones that act as neuroactive substances in other organisms such as calcium ions. [29]

The ion flux across cells also influence the movement of other molecules and solutes. This changes the osmotic gradient of the cell, resulting in changes to turgor pressure in plant cells by water and solute flux across cell membranes. These variations are vital for nutrient uptake, growth, many types of movements (tropisms and nastic movements) among other basic plant physiology and behavior. [30] [31] (Higinbotham 1973 Scott 2008 Segal 2016).

Thus, plants achieve behavioural responses in environmental, communicative, and ecological contexts.

Signal perception Edit

Plant behavior is mediated by phytochromes, kinins, hormones, antibiotic or other chemical release, changes of water and chemical transport, and other means.

Plants have many strategies to fight off pests. For example, they can produce a slew of different chemical toxins against predators and parasites or they can induce rapid cell death to prevent the spread of infectious agents. Plants can also respond to volatile signals produced by other plants. [32] [33] Jasmonate levels also increase rapidly in response to mechanical perturbations such as tendril coiling. [34]

In plants, the mechanism responsible for adaptation is signal transduction. [35] [36] [37] [38] Adaptive responses include:

  • Active foraging for light and nutrients. They do this by changing their architecture, e.g. branch growth and direction, physiology, and phenotype. [39][40][41]
  • Leaves and branches being positioned and oriented in response to a light source. [39][42]
  • Detecting soil volume and adapting growth accordingly, independently of nutrient availability. [43][44][45] .

Plants do not have brains or neuronal networks like animals do however, reactions within signalling pathways may provide a biochemical basis for learning and memory in addition to computation and basic problem solving. [46] [47] Controversially, the brain is used as a metaphor in plant intelligence to provide an integrated view of signalling. [48]

Plants respond to environmental stimuli by movement and changes in morphology. They communicate while actively competing for resources. In addition, plants accurately compute their circumstances, use sophisticated cost–benefit analysis, and take tightly controlled actions to mitigate and control diverse environmental stressors. Plants are also capable of discriminating between positive and negative experiences and of learning by registering memories from their past experiences. [49] [50] [51] [52] [53] Plants use this information to adapt their behaviour in order to survive present and future challenges of their environments.

Plant physiology studies the role of signalling to integrate data obtained at the genetic, biochemical, cellular, and physiological levels, in order to understand plant development and behaviour. The neurobiological view sees plants as information-processing organisms with rather complex processes of communication occurring throughout the individual plant. It studies how environmental information is gathered, processed, integrated, and shared (sensory plant biology) to enable these adaptive and coordinated responses (plant behaviour) and how sensory perceptions and behavioural events are 'remembered' in order to allow predictions of future activities upon the basis of past experiences. Plants, it is claimed by some [ who? ] plant physiologists, are as sophisticated in behaviour as animals, but this sophistication has been masked by the time scales of plants' responses to stimuli, which are typically many orders of magnitude slower than those of animals. [ citation needed ]

It has been argued that although plants are capable of adaptation, it should not be called intelligence per se, as plant neurobiologists rely primarily on metaphors and analogies to argue that complex responses in plants can only be produced by intelligence. [54] "A bacterium can monitor its environment and instigate developmental processes appropriate to the prevailing circumstances, but is that intelligence? Such simple adaptation behaviour might be bacterial intelligence but is clearly not animal intelligence." [55] However, plant intelligence fits a definition of intelligence proposed by David Stenhouse in a book about evolution and animal intelligence, in which he describes it as "adaptively variable behaviour during the lifetime of the individual". [56] Critics of the concept have also argued that a plant cannot have goals once it is past the developmental stage of seedling because, as a modular organism, each module seeks its own survival goals and the resulting organism-level behavior is not centrally controlled. [55] This view, however, necessarily accommodates the possibility that a tree is a collection of individually intelligent modules cooperating, competing, and influencing each other to determine behavior in a bottom-up fashion. The development into a larger organism whose modules must deal with different environmental conditions and challenges is not universal across plant species, however, as smaller organisms might be subject to the same conditions across their bodies, at least, when the below and aboveground parts are considered separately. Moreover, the claim that central control of development is completely absent from plants is readily falsified by apical dominance. [ citation needed ]

The Italian botanist Federico Delpino wrote on the idea of plant intelligence in 1867. [57] Charles Darwin studied movement in plants and in 1880 published a book, The Power of Movement in Plants. Darwin concludes:

It is hardly an exaggeration to say that the tip of the radicle thus endowed [..] acts like the brain of one of the lower animals the brain being situated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.

In 2020, Paco Calvo studied the dynamic of plant movements and investigated whether French beans deliberately aim for supporting structures. [58] Calvo said: “We see these signatures of complex behaviour, the one and only difference being is that it’s not neural-based, as it is in humans. This isn’t just adaptive behaviour, it’s anticipatory, goal-directed, flexible behaviour.” [59]

In philosophy, there are few studies of the implications of plant perception. Michael Marder put forth a phenomenology of plant life based on the physiology of plant perception. [60] Paco Calvo Garzon offers a philosophical take on plant perception based on the cognitive sciences and the computational modeling of consciousness. [61]

Comparison with neurobiology Edit

Plant sensory and response systems have been compared to the neurobiological processes of animals. Plant neurobiology concerns mostly the sensory adaptive behaviour of plants and plant electrophysiology. Indian scientist J. C. Bose is credited as the first person to research and talk about the neurobiology of plants. Many plant scientists and neuroscientists, however, view the term "plant neurobiology" as a misnomer, because plants do not have neurons. [54]

The ideas behind plant neurobiology were criticised in a 2007 article [54] published in Trends in Plant Science by Amedeo Alpi and 35 other scientists, including such eminent plant biologists as Gerd Jürgens, Ben Scheres, and Chris Sommerville. The breadth of fields of plant science represented by these researchers reflects the fact that the vast majority of the plant science research community rejects plant neurobiology as a legitimate notion. Their main arguments are that: [54]

  • "Plant neurobiology does not add to our understanding of plant physiology, plant cell biology or signaling".
  • "There is no evidence for structures such as neurons, synapses or a brain in plants".
  • The common occurrence of plasmodesmata in plants "poses a problem for signaling from an electrophysiological point of view", since extensive electrical coupling would preclude the need for any cell-to-cell transport of ‘neurotransmitter-like' compounds.

The authors call for an end to "superficial analogies and questionable extrapolations" if the concept of "plant neurobiology" is to benefit the research community. [54] Several responses to this criticism have attempted to clarify that the term "plant neurobiology" is a metaphor and that metaphors have proved useful on previous occasions. [62] [63] Plant ecophysiology describes this phenomenon.

Parallels in other taxa Edit

The concepts of plant perception, communication, and intelligence have parallels in other biological organisms for which such phenomena appear foreign to or incompatible with traditional understandings of biology, or have otherwise proven difficult to study or interpret. Similar mechanisms exist in bacterial cells, choanoflagellates, fungal hyphae, and sponges, among many other examples. All of these organisms, despite being devoid of a brain or nervous system, are capable of sensing their immediate and momentary environment and responding accordingly. In the case of unicellular life, the sensory pathways are even more primitive in the sense that they take place on the surface of a single cell, as opposed to within a network of many related cells.


The secret life of plants: how they memorise, communicate, problem solve and socialise

I had hoped to interview the plant neurobiologist Stefano Mancuso at his laboratory at the University of Florence. I picture it as a botanical utopia: a place where flora is respected for its awareness and intelligence where sensitive mimosa plants can demonstrate their long memories and where humans are invited to learn how to be a better species by observing the behaviour of our verdant fellow organisms.

But because we are both on lockdown, we Skype from our homes. Instead of meeting his clever plants, I make do with admiring a pile of cannonball-like pods from an aquatic species, on the bookshelves behind him. “They’re used for propagation,” he says. “I am always collecting seeds.”

Before Mancuso’s lab started work in 2005, plant neurobiology was largely seen as a laughable concept. “We were interested in problems that were, until that moment, just related to animals, like intelligence and even behaviour,” he says. At the time, it was “almost forbidden” to talk about behaviour in plants. But “we study how plants are able to solve problems, how they memorise, how they communicate, how they have their social life and things like that”.

Flower power . Mancuso’s team has shown that Mimosa pudica can retain learned information for weeks. Photograph: Alamy

Mancuso and his colleagues have become experts in training plants, just like neuroscientists train lab rats. If you let a drop of water fall on a Mimosa pudica, its kneejerk response is to recoil its leaves, but, if you continue doing so, the plant will quickly cotton on that the water is harmless and stop reacting. The plants can hold on to this knowledge for weeks, even when their living conditions, such as lighting, are changed. “That was unexpected because we were thinking about very short memories, in the range of one or two days – the average memory of insects,” says Mancuso. “To find that plants were able to memorise for two months was a surprise.” Not least because they don’t have brains.

In a plant, a single brain would be a fatal flaw because they have evolved to be lunch. “Plants use a very different strategy,” says Mancuso. “They are very good at diffusing the same function all over the body.” You can remove 90% of a plant without killing it. “You need to imagine a plant as a huge brain. Maybe not as efficient as in the case of animals, but diffused everywhere.”

One of the most controversial aspects of Mancuso’s work is the idea of plant consciousness. As we learn more about animal and plant intelligence, not to mention human intelligence, the always-contentious term consciousness has become the subject of ever more heated scientific and philosophical debate. “Let’s use another term,” Mancuso suggests. “Consciousness is a little bit tricky in both our languages. Let’s talk about awareness. Plants are perfectly aware of themselves.” A simple example is when one plant overshadows another – the shaded plant will grow faster to reach the light. But when you look into the crown of a tree, all the shoots are heavily shaded. They do not grow fast because they know that they are shaded by part of themselves. “So they have a perfect image of themselves and of the outside,” says Mancuso.

Science struggles to view plants as active and motivated because its outlook is so humancentric, he argues. One test for self-awareness in animals is whether they can look in a mirror and understand that they are looking at themselves. “Very few animals are able to do this,” says Mancuso. “Humans, dolphins, a few apes and probably elephants. This has been taken in recent years as a kind of evidence that just these few groups of animals have self-awareness.” Mancuso believes this is wrong. “My personal opinion is that there is no life that is not aware of itself. For me, it’s impossible to imagine any form of life that is not able to be intelligent, to solve problems.”

Another misconception is that plants are the definition of a vegetative state – incommunicative and insensitive to what is around them. But Mancuso says plants are far more sensitive than animals. “And this is not an opinion. This is based on thousands of pieces of evidence. We know that a single root apex is able to detect at least 20 different chemical and physical parameters, many of which we are blind to.” There could be a tonne of cobalt or nickel under our feet, and we would have no idea, whereas “plants can sense a few milligrams in a huge amount of soil”, he says.

Far from being silent and passive, plants are social and communicative, above ground and beneath, through their roots and fungal networks. They are adept at detecting subtle electromagnetic fields generated by other life forms. They use chemicals and scents to warn each other of danger, deter predators and attract pollinating insects. When corn is nibbled by caterpillars, for example, the plant emits a chemical distress signal that lures parasitic wasps to exterminate the caterpillars.

A slower pace of life . Old Tjikko in Sweden is almost 10,000 years old. Photograph: Lars Johansson/Getty Images/iStockphoto

Plants respond to sound, too, “feeling” vibrations all over. “Plants are extremely good at detecting specific kinds of sounds, for example at 200hz or 300hz … because they are seeking the sound of running water.” If you put a source of 200hz sound close to the roots of a plant, he says, they will follow it. There is no evidence that the human voice benefits plants, although talking to plants may soothe the humans doing it.

Another reason we overlook plants’ intelligence is their vastly slower pace of life. In Mancuso’s new book, The Incredible Journey of Plants, we meet the world’s oldest plant – Old Tjikko – a red fir tree whose roots have writhed in the Swedish earth for about 9,560 years. We are also introduced to the ingenious seeds of crimson fountain grass, which choose not to germinate until the conditions are perfect – and can survive for six years while waiting.

The main thrust of the book is that plants were the original pioneers and have been forever exploring the planet. Mancuso eschews the notion of “native species” and prizes so-called invasive species above all else. “The more invasive they are, the more I like them, because they are the most brilliant example of the ability to solve problems,” he says. “Invasive species are the most beautiful plants that I can imagine.” For Mancuso, “migration is one of the most important forces of nature. All living organisms migrate. We are the only species that is not allowed to, and this is completely unnatural.”

Although new generations of botanists are increasingly embracing plant neurobiology, Mancuso still has his detractors. Last summer, a group of eight plant scientists wrote in the journal Trends in Plant Science that Mancuso and his colleagues “have consistently glossed over the unique and remarkable degree of structural, organisational and functional complexity that the animal brain had to evolve before consciousness could emerge”. Mancuso says that almost all of these botanists are retired. “It’s an older generation of plant scientists that is completely against any notion of a plant as intelligent or behaving. For them, plants are kind of a semi-living organic machine.”

The notion that humans are the apex of life on Earth is one of the most dangerous ideas around, says Mancuso: “When you feel yourself better than all the other humans or other living organisms, you start to use them. This is exactly what we’ve been doing. We felt ourselves as outside nature.” The average lifespan of a species on Earth is between 2m and 5m years. “Homo sapiens have lived just 300,000 years,” he says – and already “we have been able to almost destroy our environment. From this point of view, how can we say that we are better organisms?”

Perhaps we should try – ahem – taking a leaf out of the plant kingdom’s book. Human societies and organisations are structured like our bodies – with a brain, or a top-level control centre, and various different organs governing specific functions. “We use this in our universities, our companies, even our class divisions,” says Mancuso. This structure enables us to move fast, physically and organisationally, but it also leaves us vulnerable. If a major organ fails, it could scupper everything, and top-down leadership rarely serves the whole.

Plants, by contrast, “are kind of horizontal, diffusive, decentralised organisations that are much more in line with modernity”. Take the internet, the ultimate decentralised root system. “Look at the ability of Wikipedia to produce a wonderful amount of good-quality information by using a decentralised, diffused organisation. I’m claiming that, by studying plant networks, we can find wonderful solutions for us,” Or take the ethos of cooperation. Plants, say Mancuso, “are masters of starting symbiotic relationships with other organisms: bacteria, mushrooms, insects, even us. Just look at the way they use us to be transported all around the world.” We may think we have the upper hand, but plants may beg to differ.

The Incredible Journey of Plants by Stefano Mancuso is published by Other Press


Sound Garden: Can Plants Actually Talk and Hear?

Though often too low or too high for human ears to detect, insects and animals signal each other with vibrations. Even trees and plants fizz with the sound of tiny air bubbles bursting in their plumbing.

And there is evidence that insects and plants "hear" each other's sounds. Bees buzz at just the right frequency to release pollen from tomatoes and other flowering plants. And bark beetles may pick up the air bubble pops inside a plant, a hint that trees are experiencing drought stress.

Sound is so fundamental to life that some scientists now think there's a kernel of truth to folklore that holds humans can commune with plants. And plants may use sound to communicate with one another.

If even bacteria can signal one another with vibrations, why not plants, said Monica Gagliano, a plant physiologist at the University of Western Australia in Crawley.

"Sound is overwhelming, it's everywhere. Surely life would have used it to its advantage in all forms," she told OurAmazingPlanet.

Gagliano and her colleagues recently showed corn seedling's roots lean toward a 220-Hertz purr, and the roots emit clicks of a similar tune. Chili seedlings quicken their growth when a nasty sweet fennel plant is nearby, sealed off from the chilies in a box that only transmits sound, not scent, another study from the group revealed. The fennel releases chemicals that slow other plants' growth, so the researchers think the chili plants grow faster in anticipation of the chemicals &mdash but only because they hear the plant, not because they smell it. Both the fennel and chilies were also in a sound-isolated box.

"We have identified that plants respond to sound and they make their own sounds," Gagliano said. "The obvious purpose of sound might be for communicating with others."

Gagliano imagines that root-to-root alerts could transform a forest into an organic switchboard. "Considering that entire forests are all interconnected by networks of fungi, maybe plants are using fungi the way we use the Internet and sending acoustic signals through this Web. From here, who knows," she said.

As with other life, if plants do send messages with sound, it is one of many communication tools. More work is needed to bear out Gagliano's claims, but there are many ways that listening to plants already bears fruit.

When the bubble bursts

Scientists first recognized in the 1960s that listening to leaves revealed the health of plants.

When leaves open their pores to capture carbon dioxide, they lose huge amounts of water. To replace this moisture, roots suck water from the ground, sending it skyward through a series of tubes called the xylem. Pit membranes, essentially two-way valves, connect each of the thousands of tiny tubes. The drier the soil, the more tension builds up in the xylem, until pop, an air bubble is pulled in through the membrane.

For some plants, these embolisms are deadly &mdash as with human blood vessels &mdash because the gas bubbles block the flow of water. The more air in the tubes, the harder it is for plants to pull in water, explains Katherine McCulloh, a plant ecophysiologist at Oregon State University.

But researchers who eavesdrop on plant hydraulics are discovering that certain species, like pine trees and Douglas firs, can repair the damage on a daily or even an hourly basis.

"These cycles of embolism formation and refilling are just something that happens every single day. The plant is happy, it's just day-to-day living," McCulloh said. "In my mind, this is revolutionary in terms of plant biology. When I learned about how plants moved water, it was a passive process driven by evaporation from the leaves. What we're beginning to realize is that's just not true at all. It's a completely dynamic process."

How to listen to plants

The technology to hear plant bubbles explode is actually quite simple. Acoustic sensors designed to detect cracks in bridges and buildings catch the ultrasonic pops. A piezoelectric pickup, the same as an electric guitar pickup, goes through an amplifier to an oscilloscope that measures the waveform of each pop. The acoustic sensor is pricey, but Duke University botanist Dan Johnson has funding from the National Science Foundation and the U.S. Department of Agriculture to build a low-cost version this summer. He'll give the embolism detector to high school students at the North Carolina School of Science and Mathematics in Durham.

"I think plant hydraulics will be the piece of the puzzle that tells us which species are going to live and which species are going to die with climate change," Johnson told OurAmazingPlanet. "Plant hydraulics will tell us what our future forests will look like in 50 years."

Two geologists in Arizona are also building a low-cost acoustic detector, crowd-funded at about $1,000, drawn by the age-old allure of communicating with plants.

"We became fascinated with the thought of being able to listen in to the plumbing of the saguaro cactus," said Lois Wardell, owner of Tucson-based consulting firm Arapahoe SciTech. Starting with a 3-foot-tall potted saguaro, Wardell and geophysicist Charlotte Rowe hope to distinguish between cacti drying out and those complaining about other environmental stress.

"We're working on trying to differentiate these two signals: I'm cold versus I'm really thirsty," Wardell said. "We've already managed to produce a few squawks." [Saguaros: Living Bouquets of the Sonoran Desert]

What plants say about drought

Acoustic emissions, or the sound of bursting air bubbles, could also upend assumptions about the effects of drought on plants.

In the arid Southwest, Johnson was surprised to find that the plants considered the most drought-tolerant, such as junipers, did worst at repairing embolisms. Broad-leaf plants, including rhododendrons and beaked hazels, were better at fixing the damage caused by dry pipes.

"With the incredible drought going on there right now, the species we predicted to die are exactly the opposite of what's occurring," Johnson said. "We're seeing a lot of deaths in junipers, and those are typically the most drought-resistant in that area, whereas most of the broad-leaf systems go dormant and they repair whatever embolisms occur the next spring, when there's more water."

Johnson predicts that in future severe droughts, the plants that have a harder time repairing embolisms are more likely to die. "It's the plants that can repair embolisms that are going to survive," he said. [Gallery: Plants in Danger]

Living in drought-stricken Australia, Gagliano is also excited by the possibility of decoding drought signals. "We don't know if these emissions are also providing information to neighborhoods of plants," she said. "Plants have ways of protecting themselves when they run out of water, and they are really good at sharing information about danger, even if one sharing is one that's going to die."

Sensing sound by touch instead?

Critics of Gagliano's research point out that no one has found structures resembling a mouth or ears on corn or any other plant. Nor do the group's studies prove that plants "talk" among themselves.

"This is pretty provocative and worth following, but it doesn't really provide a lot of evidence that these are acoustic communications," said Richard Karban, a University of California, Davis, expert in how plants communicate via chemical signals.

But simpler life forms manage just fine without complex sound receptors and producers. Walnut sphinx caterpillars whistle by forcing air out of holes in their sides. Flying insects perform death drops when they sense a bat's sonar clicks. Earthworms flee the vibrations of oncoming moles. [Listen to caterpillars communicate with their butts]

Of course, there may be another explanation for the apparent response to sound reported by Gagliano. One that could also account for the century of researchers and home gardeners (including Charles Darwin) who manipulated plant growth with music.

Could a sense of touch be why plants seem to respond to sound?

Even humans can perceive sound without hearing it, said Frank Telewski, a botanist at Michigan State University and an expert on how trees respond to wind.

"How many times have you sat next to someone who has their car stereo at full blast? You can really feel it pounding in your chest," he said.

Trees perceive and respond to touch, like wind or an animal passing on a trail. And like the wind, sound is a wave that travels through air.

In fact, a tree needs wind to grow, Telewski said. "If you stake down a seedling, you do it a little bit of disservice, because a tree needs to perceive motion. It's like physical therapy for the tree. If you stake it too tight, it does not allow the plant to produce stronger tissues."

But Telewski is open to the idea of plant communication by sound. He said in the last few years, researchers in China have shown they can increase plant yields by broadcasting sound waves of certain frequencies. Other groups have investigated how different frequencies and intensities of sounds change gene expression. Their studies find that acoustic vibrations modify metabolic processes in plants. Some of the beneficial vibrations also drive away pesky insects that munch on crops.

"We're not there yet," Telewski said of the effort to prove plants communicate. "Sometimes a fantastic hypothesis can turn out to be true, but there has to be fantastic evidence to support it."

Answering critics

Karban, from UC Davis, notes that the plant field is not very receptive to new ideas. The idea that plants could talk via scent, or volatile chemicals, was roundly pooh-poohed in the 1980s, but Karban and others went on to prove that plants including sagebrush warn their neighbors of impending danger by wafting chemical signals into the air. "At times in my career I've tried to push new ideas and it's been very difficult," Karban said.

Gagliano remains undeterred by the skepticism.

"I was guided to sound by the long tradition in folklore of people talking to plants and listening to plants and plants making sounds," Gagliano said. "I wanted to see if there was any scientific basis for something that stays so stubbornly in our culture."

But the corn root clicks are at the lower end of the human hearing range. "In theory, we could hear it, but realistically, these were emitted from roots in the ground, so the truth is we probably wouldn't hear it," she said. And the fizzy bubble bursts in xylem are ultrasonic, about 300 kiloHertz, detectable only by insects and some other animals.

This spring, Gagliano and her collaborators will screen more plants for communication skills. "We will see whether some groups of plants might be more chatty than others, and if some plants have specific requirements for sound," she said. They also plan to record sounds emitted from plants and play them back and see what kind of response, if any, they produce in other plants.

"Shamans say they learn from the plant's sounds. Maybe they are attuned to things we don't pay attention to," Gagliano said. "It's really fascinating. We might have lost that connection and science is ready to rediscover it."


Notes on Phytochrome | Plant Physiology

In plants, there is a photo reversible pigment which is called phytochrome (P), chromophoric protein, and exists in two forms: one which absorbs red (Pr) and the other one which absorbs far-red light (Pfr).

Bestowed with such a versatility of the molecule, several bio-chemicals, physiological and morphogenetic responses can be regulated in the plants. It was in 1920 that Gardner and Allard demonstrated photoperiodism and the importance of dark period.

Thus, short day plants failed to flower once their dark period was intercepted by a short interval of light. In 1944, Borthwick, Parker and Hendricks at the U.S. Department of Agriculture, Beltsville observed that red light (660 nm) was highly effective in inhibiting flowering of short day plants.

On the contrary, it promoted flowering in long day plants. Same effect caused by red light was seen in stem elongation in barley and leaf growth in pea seedling grown in the dark. Earlier, Flint and Moallister (1935-37) had reported that red light highly promoted lettuce seed germination and the latter was inhibited by far-red light.

That is far-red light exposure following red light, reversed its effects. These observations pointed towards the existence of a single photoreceptive compound which occurred in two inter-convertible forms.

Similar situation was reported in several other phenomena. Butler used the term phytochrome for this photoreversible pigment. Norris (1959) demonstrated the photo reversibility of the pigment using a dual spectrophotometer in the cotyledons of turnip seedling.

However, it was in 1962 that this pigment was extracted from shoots of dark grown maize seedlings and was shown to be a chromoprotein and the chromophore was a cyclic tetrapyrole. Soon after it came to be recognized that the active form was far-red absorbing (P730) and this gradually changed to P660 in the dark. The change in configuration during these reversals was also unravelled (Fig. 12-1, 2).

Correl (1965, 1969) using analytical centrifugation studies revealed the occurrence of phytochrome tetramers which were made up of subunits. It was shown to be of similar absorption spectra. Over the years, several aspects of phytochrome chemistry have attracted attention and these are phototransformation of the pigment at low temperature in relation to subsequent dark reaction at normal temperature changes in the optical activity during photoreversibility of the pigment.

The pigment is found to be stable between pH 6 and pH 8. The photoreversibility is gradually lost in TFA (trifloroacetic acid), DMS (dimethyl sulfamide), urea and mercapto-binders. The presence of glutaraldehyde seems to inhibit the Pr-Pfr transformation.

Such absorption in all probability is attributed to cross linkages between the peptide chains. In a nutshell, it is imperative that chromophore is surrounded by a specific configuration of the protein.

Indeed, studies relating to optical activity of the two forms have shed sufficient light on the role of protein moiety and also on the mechanism of photoreversibility. It is very interesting to note that in the Pr to Pfr transformation several intermediate photo-isomers are produced which are cold temperatures stable.

Further, Pfr to Pr transformation is very simple but dark reversion of Pfr to Pr is highly temperature dependent in vitro. When oxygen is present, there is destruction. That this destruction is inhibited by EDTA. EM and ultracentrifugation techniques have shown that photoreversible part may have a dimer structure.

Since phytochrome mediates a wide range of responses, (Table 12-2), it is difficult to propose a generalized model. By far, most efforts revolve around gene activity. Several enzyme-systems are regulated by phytochrome (nitrate reductase invertase peroxidase).

The inhibition of enzyme synthesis by Actinomycin D or Cycloheximide following phytochrome action points towards transcription and translation. Even though possible for several systems, gene activity is unable toexplain short term responses e.g. orientation of Mougeotia chloroplast, pulvinus movement in Albizzia, etc.

Through polarizing microscope, it is evident that this pigment is membrane localized and by changing its orientation it regulagtes membrane permeability. The general view is that chromophore component acts as a photo-receptor and undergoes cis-trans isomerization and causes change in the conformation of protein moiety.

Thus chain of significant events is altered. However, precise mechanism of its action has been described in an oversimplified way and many questions about the mechanism of its action await detailed answers. A photo-response can be defined as phytochrome-mediated one if it could be induced by a short irradiation of red light (nearly 5 min or so, of medium quantum flux density).

Further, the induction by red light should be reversed by far-red light. The responses may be positive or negative or may be highly complex. Then the responses may be developmental or rapid responses. The developmental responses are mediated by phytochrome but involve other physiological processes e.g., growth, differentiation and periodic phenomena. Such processes take long time for the production of a response.

Such responses include photoperiodism, seed germination, anthocyanin formation, chlorophyll synthesis, unfolding of monocot leaves, etc. On the other hand, rapid responses are manifested in a short time after irradiation with red light and do not interact with complex physiological processes.

This category includes orientation of chloroplast in Maugeotia filaments, leaflet, and movements in Mimosa pudica, increased permeability of water on the basis of permeability changes affected by red phytochrome, whereas developmental responses indicate an effect at gene, enzyme or hormonal level. In the following some of the phytochrome-mediated phenomenon are briefly discussed (See Table 12-2).

(i) Phytochrome and flowering:

The inhibition of flowering in short day plants by a red (R)- break indicates the existence of some important reactions which cause synthesis of floral stimulus. This is completed in dark. It was shown that there was involvement of a ‘light- Pfr’—’high Pfr’ reaction and a ‘low Pfr’ reaction but their sequence varies.

During the formation of floral stimulus, there is GA-like compound synthesized. Thus, distinct ratios of P660/P730 are essential to induce flower formation.

(ii) Chloroplast development:

The effect of light on chloroplast development is surely mediated by phytochrome, since red illumination promotes chloroplast development and synthesis of photosynthetic enzymes.

(iii) DNA- and Protein synthesis:

Red light is also shown to induce DNA and protein synthesis in the cells of etiolated pea stem apices.

In dwarf peas, R-light induced proteins which were complexed with GA3 and suggestively this complex prevented normal growth of the dwarf peas.

(iv) Water uptake:

Another significant effect of R-light consists of its role in regulating the uptake of different substances such as water, acetate and also exogenously applied auxins.

(v) Seed germination/dormancy:

In the air dried seeds of Cucurbitapepo, whole of the phytochrome exists as Pfr. On moistening of the seeds, phytochrome increased in steps as below:

(vi) Pollen germination:

Studies in Arachishypogaea pollen have shown that short exposure to R-light caused early tube emergence and its enhanced elongation, and that this effect was annulled by FR exposure. Obviously, the effects of R and FR were mutually reversible. Furthermore, acetylcholine and GA3 could replace the R-light effect.

In apple, anthocyanin synthesis is regulated by the phytochrome system. M.J. Jaffe has proposed how phytochrome might affect changes in membrane permeability. His group also demonstrated that acetylcholine, the animal neurohumor, could mimic the effect of far-red light.

These workers further proposed that acetylcholine possibly mediated several phytochrome responses in roots. There is a good possibility to believe that Red-light results in the synthesis of acetylcholine and the latter affects membranes and mitochondria and regulates the transport as well as oxygen uptake, etc.

It is only recently that much attention is being devoted to the distribution and functions of acetylcholine in plants. H.Mohr highlighted the role of phytochrome in chloroplast development.

From his studies a few points may be summarized below:

The rate, at which grana appear under continuous white light saturating with respect to chlorophyll formation, is controlled by red light pulse pre-treatment.

i. Chlorophyll a which is a characteristic marker-molecule of the plastid compartment, its formation is controlled by phytochrome.

ii. The level of Calvin cycle enzymes is also controlled by phytochrome.

iii. Phytochrome has also been shown to regulate photophosphorylation.

iv. Phytochrome has also been shown to control chlorophyll b appearance.

It is still debatable whether or not the multiple controls exerted by phytochrome during pattern realisation in plastogenesisis the result of a single initial action of Pfr or not. However, one fact is obvious that Pfr controls chloroplast development at different levels and through several independent initial actions.

There is evidence that many of the blue-green algae (Nostocales) contain photochromic (photoreversible) pigments regulating morphogenesis, mobility and pigment synthesis. These photochromic pigments resemble the phytochrome of higher plants but have their absorption peaks at shorter wavelengths.

In blue-green algae there is green vs. red antagonism instead of red vs far-red. As analogues of phytochrome they are referred to as cynophyceanphycochromes. Recently phycochromes a, b and c have been described. A pigment system sensing blue light (400-450 nm) and not reversible has been located in several higher and lower plants (e.g., Neurosporacrassa. Dictyostelium sp.).

This photoreceptor may be a flavoprotein, which absorbs blue light. The reduced cytochrome gets reoxidized in dark. In Arabidopsis there are five phytochrome genes encoding five species of phytochrome (PHYA- E). Of these PhytochromeA (PHYA) accumulates in darkgrown seedlings as PrA which is stable. PfrA is unstable and is destroyed with a half-life of 1 to 1.5 hours. PHYB is expressed at low levels in both light and dark.

PfrB is stable, with a half-life of 8-hours or more. A mixture of red and FR light will establish a photoequilibrium mixture of Pr and Pfr. Phytochrome-mediated effects are conveniently grouped into three categories on the basis of their energy requirements: very low fluence responses (VLFR), low fluence responses (LFR), and high irradiance reactions (HIR).

LFR includes seed germination and deetiolation. VLFR are not photoreversible, is HIR requires prolonged exposure to high irradiance, are time dependent, and are not photoreversible. It seems that PHYB is the sensor that detects changes in R/FR fleucne ratio.


New insights into how phytochromes help plants sense and react to light, temperature

Credit: Shutterstock

Plants contain several types of specialized light-sensitive proteins that measure light by changing shape upon light absorption. Chief among these are the phytochromes.

Phytochromes help plants detect light direction, intensity and duration the time of day whether it is the beginning, middle or end of a season and even the color of light, which is important for avoiding shade from other plants. Remarkably, phytochromes also help plants detect temperature.

New research from Washington University in St. Louis helps explain how the handful of phytochromes found in every plant respond differently to light intensity and temperature, thus enabling land plants to colonize the planet many millions of years ago and allowing them to acclimate to a wide array of terrestrial environments.

The new work from the laboratory of Richard D. Vierstra, the George and Charmaine Mallinckrodt Professor of Biology in Arts & Sciences, is published this week in the Proceedings of the National Academy of Sciences (PNAS).

For the first time, these biologists fully characterized the phytochrome family from the common model plant Arabidopsis thaliana on a biochemical level.

The scientists also extended that characterization into the phytochromes of two important food crops: corn and potatoes. Instead of finding that all phytochrome isoforms are identical, they found surprising differences.

"A major hurdle toward understanding how phytochromes direct most aspects of plant growth and development has been defining how the related isoforms work collectively and uniquely to regulate specific cellular activities," Vierstra said.

Plants typically express three or more phytochromes. It was well-known that plants can respond to wide ranges of light intensities but other factors such as expression levels and signaling potential were considered as the likely culprits.

"Now we know that the differing biophysical properties of the isoforms also underpin the unique signaling potentials within the plant phytochrome photoreceptor families," Vierstra said. "These properties are evident in Phy families in plants ranging from Arabidopsis to maize and potatoes, indicating that they likely emerged very early in phytochrome evolution."

A deeper understanding of these proteins will allow scientists to use phytochromes as tools both in agriculture and for research in the field of optogenetics, which has exploited phytochromes to precisely control cellular events simply by shining light.

"It is striking how differently the two major Arabidopsis phytochromes respond to varying light levels, where low levels of light akin to heavy shade can nearly fully activate the PhyA isoform, while the PhyB isoform requires near full sun to become fully active," said Zachary Gannam, postdoctoral fellow in biology in Arts & Sciences and co-first author of the new paper.

The results also show why PhyB may have the greatest role in how plants sense temperature—something that will become even more important in a warming world.

"A plant's struggle for survival is foreign to us. They are rooted in place and must adapt to their immediate environment or perish," said E. Sethe Burgie, research scientist in biology and co-first author of the new paper.

"Graded responses to light are important to keep plant growth under appropriate control as the plant adapts to its environment," he continued. "They're likely integral for detecting waxing or waning daylight hours to allow flowering and setting seed in the proper season."

In coming months, the researchers plan to modify and grow plants that manifest different variations and combinations of the phytochromes included in this laboratory study, with the goal of modifying light and temperature sensation of crops for agricultural benefit.


Secret Lives

Karban started off as a cicada researcher, studying how trees cope with the plague of sap-sucking bugs that descends upon them every 17 years. Back then, the assumption was that plants survived by being tenacious, adapting their physiology to hunker down and suffer through droughts, infestations and other abuse. But in the early 1980s, the University of Washington zoologist David Rhoades was finding evidence that plants actively defend themselves against insects. Masters of synthetic biochemistry, they manufacture and deploy chemical and other weapons that make their foliage less palatable or nutritious, so that hungry bugs go elsewhere. For Karban, this idea was a thrilling surprise — a clue that plants were capable of much more than passive endurance.

Electric Signals
How does one leaf know it’s being eaten, and how does it tell other parts of the plant to start manufacturing defensive chemicals? To prove that electrical signals are at work, Ted Farmer’s team placed microelectrodes on the leaves and leaf stalks of Arabidopsis thaliana (a model organism, the plant physiologist’s equivalent of a lab rat) and allowed Egyptian cotton leafworms to feast away. Within seconds, voltage changes in the tissue radiated out from the site of damage toward the stem and beyond. As the waves surged outward, the defensive compound jasmonic acid accumulated, even far from the site of damage. The genes involved in transmitting the electrical signal produce channels in a membrane just inside the plant’s cell walls the channels maintain electrical potential by regulating the passage of charged ions. These genes are evolutionary analogues to the ion-regulating receptors that animals use to relay sensory signals through the body. “They obviously come from a common ancestor, and are deeply rooted,” Farmer said. “There are lots of interesting parallels. There are far more parallels than differences.”


How Chemical Sensing Devices Work

Breathing in and out is something our bodies do without our having to think about it. In fact, we rarely even give a second thought to the air surrounding us until the quality is low somehow – maybe from the smoke of a nearby fire or smog enveloping our crowded cities.

But there can be dangerous gases that are not always visible. Carbon monoxide and radon are two examples of deadly air contaminants that are completely invisible. We don't realize we're being poisoned from the air we breathe until it is too late. Luckily, these gases aren't that prevalent, and with the help of a little chemical sensing technology, we can let carbon monoxide and radon detectors do the worrying for us.

Chemical sensors are helpful far beyond just detecting deadly gases. These devices can be found in our homes, hospitals and in the military. There are many different types of sensors that detect different target molecules (also known as analytes). Although the sensors work in various ways, the gist is that a chemical interaction happens between the analyte and something in the sensor, and the device produces a measurable signal – a beeping or a color change to alert us to the presence of the target molecule.

Despite the differences in the construction of sensors, there are a few guiding principles that make any sensor good. The ideal one is inexpensive, foolproof and portable. Most importantly, any chemical sensor has two vital features: selectivity and sensitivity. There are more than 10 billion molecular substances in the world, so selectively detecting a single substance is no small feat [source: National Research Council]. Sensitivity is also incredibly important for detecting chemicals from a considerable distance or for trying to find very low concentrations of a target molecule. Other important sensor features are response time, packaging size and limit of detection — the lowest quantity of a substance that can be detected.

So Sensitive! How Sensors Detect Target Molecules

Scientists and engineers have developed a variety of sensors for different purposes, and as you can imagine, they all have their own ways of working. After all, a pregnancy test kit is not likely to have the same detection mechanism as a radon detector, right?

All chemical sensors target some sort of analyte, but what happens once the analyte is in the sensor is where the differences emerge. For example, the sensor can bind the analyte (think a lock-and-key type mechanism, but on the molecular level). Or, the sensor may be set up so that the analyte selectively passes through a thin film. Imagine the film being a chemical gatekeeper that only lets the target molecule through and stops everything else from going in. This type of sensor has the positive feature of being continually reusable. A third form of sensor uses up the analyte in a chemical reaction that generates a product that creates the readable signal [source: National Research Council]. These three very broad mechanisms cover the workings of most sensors, but there are still other types.

For example, there are direct-read electrochemical sensors that use the diffusion of charged molecules to look for changes in current, conductivity or potential to see if a target analyte is present. Surface acoustic wave sensors employ acoustic waves sent from one electrode to another across a surface. The sensor is designed so that if the speed of the wave changes or if it loses intensity, it signals the presence of a target molecule bound to the surface. By taking measurements of these changes, the sensor may even be able to detect quantities of the material present [source: National Research Council].

Another cool innovation in chemical sensing technology moves toward detecting inherent properties of different chemical targets instead of using a molecular interaction to drive the detection. Different bonds in molecules each have signature vibration patterns that can be detected in the infrared region of the electromagnetic spectrum. By combining light sources, filters and detectors onto a single chip, scientists at Massachusetts Institute of Technology have been able to detect these molecular fingerprints in order to sense a whole host of molecules, from contaminants in water to electrolytes in the blood of newborn babies [source: Bender].

How Chemical Sensors Help

No matter how they operate, chemical sensing devices are, without a doubt, working for you. Your home probably has at least a one detector for radon gas, smoke or carbon monoxide, depending on the laws in your state or country. Many radon sensors work by absorbing the radon itself or detecting the radioactive decay products of the lethal gas. Carbon monoxide, on the other hand, is not a radioactive material, so the detectors for this gas operate differently. One of the most common mechanisms for this chemical sensor is a riff on biology. These detectors mimic how carbon monoxide interacts with hemoglobin in blood in order to determine the presence of the gas. Another common detector in the home is a smoke detector. While some use radioactive materials to help sniff out smoke, most of the sensing in smoke detectors comes from the physical, not chemical, phenomenon of the smoke particles causing interference that is sensed by the detector.

Chemical sensing devices also have widespread use outside the home. One of the main places you'll see these devices in action is in search of biomolecules in medical settings. Biomolecule sensors are essentially specialized chemical sensors. Although they detect substances like hormones, these bodily substances are all molecules. After all, these sensors are made with many of the same guiding principles as other chemical sensors – selectivity, sensitivity and portability.

Some of the most portable biomolecule sensors you may be aware of are associated with fertility measurements: pregnancy tests and ovulation tests. Both these chemical sensors detect the presence of certain hormones in urine. In the case of pregnancy tests, the sensor looks for the hormone human chorionic gonadotropin (hCG) in urine. The stick on which the woman urinates has antibodies that are coated with a chemical that bonds to hCG. If the biomolecule is present, the test reads positive [source: Parents Magazine]. Usually these chemical sensors have a colorimetric component so that when the analyte – in this case hCG – binds, it triggers a color change in the sensor, making the readout of the results pretty foolproof.

In the clinical setting, two of the most common methods for chemical-based biomolecule detection are ELISA (enzyme-linked immunoabsorbent assay) and the Western blot. Depending on the size and type of the biomolecule in question and the information they want about the molecule, scientists and clinicians will often turn to one of these chemical sensing techniques to identify different analytes in mixtures of biomolecules [sources: ThermoFisher Scientific, Mahmood and Yang].


Conclusions and future perspective

The perception and processing of vibrations in the form of sound waves are very advantageous from an ecological perspective, and thus it is unjustified to exclude plants from this exciting field of study. From the recent discoveries that have been made it is amply clear that plants perceive the SV stimulus, which is appreciably different from other mechanical stimuli. Our attempt to critically assess SV-mediated cellular adjustments in this paper has resulted in a model defining the sound-signaling pathway ( Fig. 1 ). There appear many similarities in the sound- and touch-signaling pathways, and thus, the field of plant acoustics can benefit from the information available in signaling of thigmoresponses. However, the molecular components involved in the signaling of the SV stimulus in plants are still debated. Deciphering the precise role(s) of phytohormones in SV-mediated regulation of plant development and growth will be a matter of extensive research. ROS and sugars are versatile molecules also implicated in signaling and thus their probable role(s) in the SV-mediated response need to be thoroughly investigated. With the advancement of molecular biology technologies, there is certainly a need to make available the whole genome transcriptomic maps to identify all the genes specifically affected by the SV stimulus. This will highlight the similarities and/or dissimilarities among the acoustic and mechano-perceptions and help to decipher acoustic signaling in plants. Several specific knowledge gaps have been highlighted in the text and Fig. 1 of this paper. Most importantly, we urge for more studies on the response of plants exposed to natural SVs that may provide a beneficial stimulus, recorded at the correct and appropriate intensities.

Finally, more focused attention is needed to unravel the hidden facets in this under-studied field of plant biology. The time has come to move on from the debate about whether plants can sense and communicate SVs, which has constrained us so far in our understanding of plant communication: scientists should now set themselves the task of revealing the fascinating details that are currently hidden in the field of plant acoustics. We should be enthusiastic about this new emerging field of plant research that holds the promise to provide us with a new dimension to look at plant as a perceiving organism: much smarter and more sensitive to various environmental stimuli than we might think.