July 28, 2021

An aromatic warning sign unites female plants | Science

An aromatic warning sign unites female plants | Science

The plants communicate by the aroma. Volatile organic compounds are for them like words for humans. And as it happens among people, there are more plants loquacious than others and congeners that connect better or worse among them. Almost all this dictionary of the vegetal world is at the moment an unknown. But little by little they reveal secrets like the one that has just been published in two different articles. Xoaquín Moreira, researcher of the Biological Mission of Galicia (CSIC). Among other things, the scholar has found that in a situation of danger such as a plague of herbivorous insects, the male plants of the bush Baccharis salicifolia they communicate with their peers of both sexes and issue warning signals in the form of volatile organic compounds. But the females only warn the females, and somehow they do it loudly.

"The first works aimed at demonstrating the existence of communication between plants through the emission of volatile organic compounds" in response to the attack of insects "generated a lot of controversy in the scientific community, especially due to methodological problems", explains the Council Superior of Scientific Investigations in Galicia. But in recent years, throughout the world, studies have been conducted on this mysterious language "in 30 vegetables belonging to 16 different families," says Moreira. They are, for now, specific works for each species, usually very focused on those of greater agricultural and forestry interest. It is tested with tomato, corn or beans to find in this language of plants a possible alternative to pesticides, and the Galician team plan to do it with the potato if you get from here to June a public subsidy to which you have presented your project.

For now Moreira, researcher Ramón y Cajal hired from the group of Genetics and Forest Ecology of the Biological Mission of Galicia, has spent more than three years focused on the chemical communication of azumiate or yellow jara (Baccharis salicifolia), a highly fragrant medicinal species that extends from southern California to Argentina and is especially abundant in Mexico. The azumiate is dioic, that is to say, that it presents separated sexual structures in different plants, and the investigation has demonstrated that, before the attack of the insects, the males transmit alert signals that can be detected as much by the masculine as feminine bushes. However, the females show a marked solidarity with those of their own sex because they only notify the other females and do not communicate with the males.

With this kind of ninguneo to masculinity, only the female Baccharis silicifolia will understand that it is necessary to prepare the defense against the herbivorous species that already attacks the station. In addition, before the danger looms, one could almost say that the female plants that suffer the plague shout to the others what is to come: they emit "up to five times more than the male" a compound called pinocarvone, says Moreira. Healthy plants that receive this signal from their attacked peers prepare their defense system (but do not activate it) by the time the plague arrives.

Moreira Tomé has led in these years two studies in which researchers from the universities of California (USA) and Neuchâtel (Switzerland) have collaborated. The results have been published in magazines Ecology Y New Phytologist. When an undamaged plant recognizes the warning signal dispersed by its attacked neighbor, it responds by activating a state of "pre-alert or priming to respond defensively more quickly and effectively to the damage once it occurs ", explains the scientist. It has been observed that the communication by volatile organic compounds is more effective when the emitting and receiving plants are genetically related and when they are attacked by the same species of herbivore.

"There are several ecological theories that explain why plants could help those species with which they are genetically related. [el sexo es un carácter determinado genéticamente]. And the most accepted thesis is that communication between non-related plants is a very high cost for broadcasters, as they would be providing altruistically a benefit to other plants with which they compete for the same resources, "says Moreira. Communication is stronger between Baccharis salicifolia of the same sex, but in the case of females is exclusive, male plants are left in the margin.

The second research channel, published in New Phytologist, confirms that the plants communicate with each other but that the language with which they do so through the emission of volatile compounds is very specific to the herbivores that attack them. "Plants are able to identify herbivores that are attacking neighbors through the volatile compounds they emit," the specialist sums up. Thus, they can prepare a "more effective response".

"Communication between plants constitutes a very incipient line of research at an international level," says Moreira. "Its relevance is such that in North America the use of chemical communication between plants has already been proposed, through the exogenous application of volatile compounds, such as a pest control tool that replaces insecticides in crops such as corn or beans. "In any case," this chemical communication between plants is not a generalizable phenomenon and depends largely on environmental conditions. "

The team of the Biological Mission of Galicia plans to start working in June with the potato and some of its predators, like the Guatemalan moth that has quarantined several Spanish regions. Nobody in the world, so far, has studied chemical communication in this tubercle of mass consumption. The CSIC wants to evaluate if in addition to the genetic identity of the host plant and the different herbivorous insects that attack it, "the abiotic context" (availability of resources such as nutrients, water and light) in which the interactions are developed "determines the presence intensity of the effects of communication ".


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