How localized bacterial infestation puts the whole plant on alert

When plants are attacked by pathogenic bacteria, they use chemical and electrical signals to transmit the information from the point of origin on the leaf surface to the inside and go into defence mode. In order to find out how and where the perception of bacterial contact is converted into electrical signals, a research team led by PD Dr Alexandra Furch from the University of Jena investigated how the external stimulus is transmitted. The researchers discovered two different types of electrical waves that trigger both the local and the systemic defence reaction of plants. The team reports this in a recently published study in the journal Science Advances. Another new finding is that so-called barrier proteins in the pathways play a role in the defence response of the plant species studied. These findings could be used to equip plants with greater resistance of their own and thus reduce the use of pesticides.

For their investigations, the researchers stimulated leaves of thale cress (Arabidopsis thaliana) and broad bean (Vicia faba) with a bacterial molecule that triggers the immune response in plants. The plant cells then released calcium ions, which in turn set off a chain reaction. The external stimulus was transmitted from the epidermal cells to the inside of the leaf in the form of different electrical potentials. For the first time, the team was able to identify two different potentials in both plants: fast and far-reaching action potentials and slow and localized variation potentials, both of which propagated in waves and triggered different reactions.

Two types of potential

After the epidermal cells are stimulated, the slow variation potentials spread first. They cause so-called barrier proteins to temporarily close the pathways in the plant leaves. "Until now, it was only known that these barrier proteins block the pathways after injury and stress, such as heat or cold," says Alexandra Furch. In its study, the team has now shown for the first time "that this reaction also occurs in response to a biological stimulus, after contact with harmful bacteria," continues the expert, who has been intensively researching such barrier proteins for a long time. "Until now, it was assumed that these barrier proteins were solely responsible for regulating the distribution of nutrients in the sieve tubes of the plant pathways."