In contact with rain, plants activate a "panic" reaction

Although, as for animals, water is the basic element of life for plants, it does not mean that they appreciate the contact with water. This is revealed in a recent study that examined the behavior of plants subjected to water sprays. In contact with the droplets, a "panic" reaction is activated, initiating multiple physiological and genetic modifications so that the plant protects itself (and its neighbors) from the spread of pathogens carried by the drops of water.

Moisture is the main means of spreading disease among vegetation, even more than temperature. The longer a leaf is wet, the more likely it is that a pathogen will move into it.

" When a drop of rain splashes a leaf, tiny droplets of water ricochet in all directions, " says plant biochemist Harvey Millar of the University of Western Australia. " These droplets may contain bacteria, viruses or fungal spores. A single droplet can transmit them up to 10 meters away, to the surrounding plants .

A rapid modification of gene expression in contact with water

By mimicking the rain with a vaporizer, an international team of researchers observed a rapid domino effect of microscopic plant changes, initiated by a powerful protein called Myc2. During the first 10 minutes of contact with water, more than 700 genes from the plants reacted, and most of these genes continued to increase their expression for about 15 minutes, thus modifying proteins, transcription and the hormonal balance of the plant, before returning to normal.

After simple contact with water, the authors report that these plants immediately accumulated signaling compounds such as calcium, activating membrane responses to touch and causing transcriptional changes at the genome level. However, even if these changes were only momentary, repeated contact eventually led to stunting and delayed flowering. The results were published in the journal PNAS.

In contact with water, the expression of several genes (green arrows) is modified under the action of Myc2 to protect the plant. Credits: Alex Van Moerkercke et al. 2019

" When Myc2 is activated, thousands of genes come into action to prepare the plant's defenses. These warning signals propagate from sheet to sheet and induce a range of protective effects, "explains Millar. In total, no less than 20 protein-related genes were found to be directly targeted and regulated by Myc2 after water spraying. In addition, the same signals that these plants used to spread information among their leaves were also used to communicate with the surrounding vegetation.

A communication of the danger to the surrounding plants

According to the authors, one of the many chemicals generated in response to water droplets is jasmonic acid, which regulates many physiological processes involved in plant growth and stress management. In addition, when jasmonate chemicals are suspended in the air, they can also inform other plants of what is happening.

Jasmonic acid is a chemical compound synthesized by plants in response to stress and different stimuli. It generates a number of physiological changes. These graphs show the increase in the level of jasmonic acid synthesized by the plant during the attack of an insect (red). Credits: Ying-Bo Mao et al. 2017

If the defense mechanisms of a plant's neighbors are activated, they are less likely to spread disease, so it is in their interest that plants pass on the warning to nearby plants, " says Millar. Earlier this month, another article revealed that when plants are attacked, they develop a universal language to warn others of dangerous imminent threats.


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