Tomatoes sound the alarm

Tomato fruits inform their mother plant of a pest infestation. (Image: Denisfilm / iStock; detail: Owl butterfly caterpillar, image: Hhelene / iStock)

Fruits are connected to a kind of “plant nervous system”, report biologists: When tomatoes are eaten by caterpillars, they send electrical warning signals to their mother plants, according to analyzes of the reactions using artificial intelligence. The signal transmission can then apparently trigger biochemical alarm reactions in the entire plant, so that it can arm itself against further attacks by means of defensive measures. More detailed insights into this system could lead to the development of innovative crop protection strategies, say the scientists.

What is pinching me there? It is well known that touch stimuli or pain can warn us of dangers and trigger defense reactions. Sometimes we notice, for example, that a mosquito is trying to tap into us and then we strike. This is made possible by our nervous system, which conveys skin irritation to our brain through electrical impulses. Plants do not have nerves, but studies in recent years have shown that they too use electrical signals to convey information. The function of the nerves is taken over by the vessels that transport and redistribute water and nutrients in the plant. By releasing charged molecules, these long-distance lines, like nerves, can transmit electrical signals between parts of the plant that are far apart from one another.

The plant “nervous system” in sight

Previous studies have already shown that when leaves are damaged, they send out electrical impulses that lead to systemic reactions in the plant. The exact meaning and function of these signal transmissions are still little researched. So far it was also unknown to what extent fruits are connected to this communication network. The peculiarity here is that, in contrast to the photosynthetically active leaves, these organs only receive nutrients – they seem to be one-way streets of the pipe system. “Nevertheless, fruits are also living parts of a plant and may be functionally more complex than we previously thought,” says Gabriela Niemeyer Reissig from the Federal University of Pelotas in Brazil.

In order to sound out the extent to which these organs also communicate with the mother plant via electrical signals, she and her colleagues carried out studies on tomato plants. Their red structures are considered a vegetable, but from a botanical point of view it is a fruit – a berry. In order to record changes in the electrical potential, the researchers attached electrodes to the ends of the branches that connect the fruit to the plant. Then they continued
Pests targeted the tomatoes that were allowed to eat on them for 24 hours. These were owl butterfly caterpillars, which are notorious for their appetite for tomatoes, strawberries and the like.

AI clarifies electrical signal patterns

To compare the electrical reactions before, during and after the infestation, the researchers used machine learning methods. This form of artificial intelligence can reveal patterns in signals. As the researchers report, the analyzes showed a clear difference between the signals before and after the attack. “We were able to document that fruits can communicate threats such as a caterpillar attack to the rest of the plant, which can probably prepare other parts for the same attack,” says Niemeyer Reissig. This emerged from further research results: the scientists recorded typical biochemical alarm reactions in the test plants such as the release of hydrogen peroxide. It was found that these reactions were also triggered in parts of the plants that were far away from the damage caused by the caterpillars.

The scientists emphasize that the results provide a fundamental insight into the system: their measurements so far only provide an overall impression of the electrical signal transduction. In the future, however, they want to use machine learning to decipher the plant information system even more precisely. They also want to investigate the extent to which the reactions of tomatoes also occur in other plant species and whether there are differences in different types of threats.

Investigating electrical signal transmissions in plants may even be useful for diagnostics in agriculture, say the researchers: “If studies like ours move forward and the techniques for measuring electrical signals in open environments can be further improved, it may be possible to Detecting pest infestation early on, which enables less aggressive control measures and more precise insect management, ”says Niemeyer Reissig. “Understanding how plants interact with their fruits could also reveal ways in which the system can be favorably influenced in order to improve the quality of fruits, their resistance to pests or their shelf life after harvesting,” says the scientist.

Source: Frontiers, technical article: Frontiers in Sustainable Food Systems, doi: 10.3389 / fsufs.2021.657401

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