2023-10-26 11:48:30
Hundreds of voracious caterpillars crawling on the trunks of willows and alders, poor seemingly defenseless trees, to go and munch on their fresh leaves… The experience may seem cruel, and yet it is the one that has enabled, over the years 1980, to reveal a stunning phenomenon.
If the attacked trees began to produce substances making their leaves unappetizing – or even downright indigestible – for insects, the most fascinating thing, for the scientists of the time, was to realize what was happening at around thirty meters away.
Healthy trees, although without root contact with their attacked counterparts, have put in place exactly the same chemical defenses (Rhoades DF, 1983) !
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Fluorescent under the microscope
This miracle had an explanation: trees, but also other plants (tobacco, tomatoes, sage, flowers of the mustard family, etc.), are capable of exchanging chemical messages in the form of gases – the “volatile substances of leaves”, a particular class of “volatile organic compounds”, or VOCs. And thus “warn” their peers of the presence of an attacker in the area.
However, despite the abundant research on this subject, communication between plants via volatile substances still reserves many mysteries. To better understand the processes at play, Japanese researchers therefore had the idea of making these chemical messages, or more precisely their reception by the plant, visible under a microscope. They detailed their results in the journal Nature Communications (October 17, 2023).
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To do this, the authors genetically modified plants of Arabidopsis thaliana – a flower from the mustard family, very often used by botanists in the laboratory – in order to associate fluorescence with a very important signaling mode in cells. plants: the “calcium signaling” (by calcium). Note that in animals, calcium ions are the basis of nerve impulses.
Aratani, Y., Uemura, T., Hagihara, T. et al. Green leaf volatile sensory calcium transduction in Arabidopsis. Nat Commun 14, 6236 (2023).
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A “switch” that activates defense reactions
These modified plants were exposed to different leaf volatiles. Of these compounds, only two triggered fluorescence in plant cells. In addition, calcium signaling increased first in the “guard cells” forming the stomata, that is to say the pores through which the leaves carry out their gas exchange.
Questioned by our colleagues from the Washington Post, Professor Masatsugu Toyota, researcher in biochemistry at Saitama University (Japan) and in the botany department of the University of Wisconsin in Madison (United States), explains that calcium signaling is like a “switch” which activates the plant’s defense reactions.
So, “After the increase in calcium signaling, the team found that the plant increased the production of certain defense gene expressions”, summarize our colleagues. Gene expression is simply the production of proteins – especially those that make insects sick.
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Towards a “vaccine” for plants?
The authors now hope that their results will be used to develop new methods to protect plants from pests – and thus use fewer pesticides, but also to help them better resist drought. They envisage using certain volatile substances to “immunize” plants against threats and stressors before they even occur. A bit like… a vaccine!
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