Do plants whisper to each other? Uncovering their communication signals

Without plants, we wouldn't be here today. Just think about how amazing they are: they provide oxygen, provide organic matter, provide greenery, help maintain ecological balance, and they never chatter on and on, like that group of people you hate running into most when you're trying to watch a movie......

Did you come here to watch a movie or to chat?! Image: clickme.net

Huh?Wait a minute, do plants really not talk?Or is it just that they do it in a way we can't hear?

If you asked scientists to place a bet, they would most likely say that plants have their own unique way of "talking." A short review published in the Journal of Integrative Plant Biology summarized the findings of researchers around the world who have peeked into "plant language."

Syllables, phrases and sentences? Plants can have them too

Don't assume that plant language is just the rustle of leaves in the wind or the pitter-patter of rain on banana leaves. In fact, for plants, "speaking" is accomplished by releasing chemical substances. This way of communicating is fundamentally different from the way humans speak with sound,and is more like a kind of secretive "whispering"。

What they say makes no sound, but it may have a scent - like the pine scent, mothball scent, lemon scent and black pepper pungency we are all familiar with, which are actuallyall chemical substances released by plants, known in technical terms as "biogenic volatile organic compounds" (BVOCs). These volatile organic compounds are both the plant'smain secondary metabolitesand the medium for transmitting signals between plants, and between plants and other organisms.

"Let them guess~ guess all they want~ it~ doesn't~ mat~ter~ connecting to each other's~ signals~ is all we~ need~ to~ hold on~~" Image: ransomnaturals.com

Many types of BVOC substances are formed fromterpenoidsThe isoprene monomer containing 5 C atoms (C5) is the basic unit that makes up terpenoids, so some scientists compare it to theindividual "syllables"in plant "language." These monomers are arranged and combined in different orders to form an extremely large number of monoterpenes (C10) and sesquiterpenes (C15), which becomeindividual "phrases"Finally, BVOCs mixed from a variety of different terpenoids are released by the plant, just like the individual sentences they "speak," sustaining plant communication.

Even more amazing is that plants even have "dialects." Among the BVOC substances released by different plant species, the quantity and quality of terpenoids differ. Individuals of the same plant species communicate more efficiently using their own set of BVOCs with the same chemical properties, and suffer fewer pest attacks.

Defense code: Careful, danger is coming!

How do plants "hear" their companions' "words"? Research has found that plants can take in gaseous compounds through their stomata, such as CO2 and BVOCs, and the BVOCs taken in can enter the plant's metabolic pathways.

Dalmatian chrysanthemum(Chrysanthemum cinerariaefolium) releases BVOCs when damaged that caninduce neighboring plants to synthesize pyrethrinsand in the released BVOCs, the proportion and concentration of each compound play a decisive role in pyrethrin synthesis.

Forthale cressgene expression profiling also confirms that the BVOCs released by one plant canactivate the defense genes of neighboring plants。

These results suggest that during communication between plants, the release of specific BVOC components provides neighboring plants with an important signal that "danger is coming."

A patch of Dalmatian chrysanthemum. When damaged, they can watch out for each other through communication. Image: John Logan

Indeed, one important role of communication between plants is active defense against possible threats from pests and diseases. When a plant suffers a pest or disease attack, it willrelease BVOCs to notify its nearby companionsafter the companions receive the signal, they will activate the expression of their own disease-resistance-related genes, thereby arming themselves fully to resist the enemy's invasion.

This makes me think of scenes from Plants vs. Zombies. Every plant about to face danger, like the Peashooters, gets its own trump card ready, preparing to bravely drive away the "lingering" invaders and never waiting passively to be defeated.

Eavesdropping diners and "off-flavor" food

Conversely,herbivorous insects also "eavesdrop" on what plants sayAs the saying goes, "radishes and cabbages, everyone has their own preference." Specific herbivorous insects like to eat a specific few plants. And because the proportions of compounds in the BVOCs released by different plants differ greatly,herbivorous insects are able to locate their own delicious food among a sea of flowers by sensing these BVOCsAlthough the air is filled everywhere with BVOC signals released by different plants, they can, based on the proportions of specific compounds, accurately separate the signal they need from a pile of "noise," find their target, and attempt to enjoy a big meal.

"Hehe, were you careless?" Image: pansci.asia

Faced with such a "precise" threat,plants have also established ingenious defensive pathways：When suffering insect damage, they immediately change the proportions of compounds in the BVOCs they releaseand once the insect senses that the "taste" of the food has changed, it may no longer be interested in that plant. Researchers found that when European white birch (Betula pendula) was used to feed inchworm moth larvae, within 2-3 minutes of the larvae beginning to chew the plant, some C6 aldehyde compounds in European white birch were rapidly released and reached a peak.

Compared with the more direct insect-resistance pathway,plants also have an indirect defense methodWhen a plant's leaves are damaged, the plant body will synthesize and release another BVOC substance within a very short time, and secrete a special nectar to attract the natural enemies of the insect attacking it. You eat me, so I'll call in something that eats you. That way, those herbivorous insects won't dare act so cocky. Plants are smart enough to understand the principle of "repaying others in their own way."

"You eat me, and if you do eat me, I'll call it over to eat you. Let's see who was careless?" Image: Robert Krulwich/NPR

Standing too far away, you can't hear it

In the air, different types of BVOCs have different "lifespans." This is because they can react with ozone (O3), hydroxyl (-OH) and nitrate radicals (-NO3), and the number of double bonds in BVOCs affects their reactivity. Generally speaking,communication between plants needs to take place within a relatively short distance of no more than 1 mAffected by oxidants in the air, the effective signal communication distance may be even shorter, or may require a higher component concentration.

By comparison, herbivorous insects are quite impressive: studies show that in air rich in ozone,a decrease in BVOC concentration or even its complete disappearance does not eliminate the signal transmitted to insectsindicating that the reaction products after the original BVOCs are oxidized in the air still have signal value for insects, though this point still needs more experiments to verify.

Although plant "language" cannot be directly heard by people, this communication plays a vital role in the plants' own survival, and deciphering it will also help us better understand nature. When walking in a garden or a tree-lined path,you may be able to view those plants that do not run, jump or make sounds from a more dynamic perspective - who knows, maybe they are happily chatting right now!

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