Learning the language of bushes

Plants, using molecular codes, call for help, drive away insects and save each other

Entomologist Richard Karban knows how to make wormwood talk. To start a conversation, he pretends to be a grasshopper or a bug — he uses scissors to cut leaves on one of the bushes. And cutting the leaves completely bush can not be fooled. Therefore, it cuts off many pieces along the edge of the sheet - “a lot of small bites”.

A few months later, Karban, a professor at the University of California, Davis, who studies the protective messaging of plants, returns to the bush and studies its leaves, many of which are damaged by real grasshoppers or beetles. However, at a distance of 50-60 cm from the branches they cut off, the leaves did not suffer from the bites of hungry insects. This is because the Karban cuts convinced the damaged sheets that they were being attacked, so they sent chemical alarms into the air. Neighboring leaves intercepted and decoded the code messages, and began to prepare their defense against beetles.

If plants seem silent to us, it is because we do not pay attention to their conversations - we are just starting to decipher their cryptograms. Plants constantly emit codes into the air, which helps them protect themselves from insects and other threats, and in some cases serves as a warning to their neighbors. Moreover, plants can send “SOS” signals, calling for help, and summon predators that feed on insects.

Plants talk using chemical codes - carbon-containing molecules, volatile organic substances.(BOW). BOW are characterized by the ease with which they rise into the air, and are quite diverse: only plants produce more than 30,000 species. Some PWL give familiar smells of flowers or plants. Others are emitted only in response to a specific impact. Just a few seconds after the damage, the plants release volatile deciduous substances that we can also fix - for example, like the smell of a freshly cut lawn.

People do not receive specific information from the VLO. But waves of molecules produced by a plant transmit packets of encrypted messages. And, like any transmitted signals, “listgrams” can be received, decoded, overheard and even distorted.

Plants send BOV in response to physical damage or chemicals from saliva, vomiting, or liquids surrounding insect eggs. Insect bites can activate plant hormones, such as jasmonic acid , ethylene or salicylic acid , to increase the activity of plant protective genes. These hormones can also be released as BOV for the prevention of other leaves and branches of the plant, as well as neighbors in the plant community. In particular, says Karban, methyljamsonat- volatile form of jasmonic acid - it seems “quite powerful”. He also found that such communication is more effective for genetically identical plants - those that grow from the same parental bushes. And when Karban put on plastic bags on the cut leaves of wormwood, and tied them up so that the PWS could not scatter, the leaves and neighboring plants closest to them did not increase their degree of protection.

LOV-messages can target themselves or relatives, but plants of other species can sometimes intercept them. Anxiety wormwood can cause a protective reaction in tomatoes and tobacco, although it is not known how many plants can crack other types of signals.

Moreover, scientists say that plants do not always want their cries to be heard. "It is not in the interest of the plant to tell its neighbor that it is being attacked," says Amy Trowbridge, a postdoc at Indiana University in Bloomington. Neighboring plants compete with each other, and to warn a neighbor means to help him survive, while the good Samaritan himselfmay be subject to insect infestation. So why do plants still scream? Partly because it is inevitable: the “chemical weapons” that plants use to repel insects will inevitably seep into the air, as they are volatile - so other plants learned to eavesdrop as a result of evolution. Like predatory insects, they tune their receivers to the call for dinner. Apple trees that chew spider mites send messages that attract other ticks that eat insects attacking the plant. When squirrel flies lay eggs in pine needles, BWF trees are attracted to wasp parasites that kill eggs. Tobacco, which moth larvae chew, causes red-tailed wasps, parasites, laying eggs into the bodies of caterpillars, which are then eaten from the inside by the larvae.

Although plants and insects have evolved to exchange these chemical messages, people are just starting to crack their code. “We don’t know how these chemicals are perceived,” says Trowbridge. The researchers do not understand how plants collect BOW from the air and what their recognizable concentration should be. They also do not know whether the stomata absorb molecules from the surface of the leaf, or through the pores . But they know that “listening” plants should not only receive, but also decipher the message in order to trigger a protective chemical reaction. “Just the fact that a plant can take a chemical does not mean anything,” says Trowbridge. If the intercepted signal fails to decode, it will not help.

Moreover, messages can be encoded in a combination of several molecules. “The bouquet, produced by incising wormwood, contains hundreds of chemicals that can be measured,” says Karban. He collects BOV in plastic bags filled with fibers that absorb chemical substances and analyzes them in a gas chromatograph. But, he says, “it’s very difficult to determine the active ingredients.” Chris Jeffrey, a specialist in organic chemistry and environmental chemistry at the University of Nevada, believes that scientists need to decipher the chemistry of entire ecosystems to crack plant cryptography. “You find a very complex mixture of molecules,” he says, comparing this phenomenon with our sense of smell. “Not one molecule causing one reaction.”

Why do we need to hack into plant codes? For example, they will help us understand how plants react to climate change. Scientists warn that these changes can disrupt communication and destabilize ecosystems. Some signals will be amplified, while others will be muffled or not detected.

“Volatility depends on temperature,” says Trowbridge, so a BWW will warm up more easily on a warming-up planet. High temperatures can also increase the activity of enzymes producing BWO. On the other hand, plants trying to survive in drought will compress the stoma so as not to lose fluid. Closed stomata suck up less carbon dioxide required for the production of BWO. With a decrease in communication with BOW, plants may not recognize the alarms and become more vulnerable to insects, or succumb to them completely, Trowbridge argues. But with an excess of VLO, plant populations may begin to protect themselves too well, and insects will begin to look for other food sources, destroying other types of plants that will change ecosystems.

So, the next time you enjoy the silence of the garden alone, remember that this silence is illusory. There is a whole chorus of screams, if only you could hear them.