Plants engaged in chemical warfare

Plants engage in a molecular dialogue with each other, producing and secreting various metabolites. These are often toxic substances, and their purpose is to eliminate a neighbour from the environment. Such chemical warfare is allelopathy. Its targets may also be bacteria, insects and even birds and mammals.

One of the effects of stress in plants are reactive oxygen forms. It turns out that they have the ability to modify proteins. Paweł Staszek from the Warsaw University of Life Sciences investigates their influence on plants. He focuses on toxic L-canavanine, a non-proteinic amino acid, which is particularly toxic to insects. The poison is in the seeds of plants from the bean family, for example in medick. Its presence can protect seeds from being eaten by pests, and when released into the environment it may be toxic to neighbouring plants. It can threaten people who are tempted by medick sprouts. However, for the parent plant it is beneficial as a good way to store nitrogen.

Reactive forms of oxygen and nitrogen indicate that the organism is under oxidative stress. It is necessary for the plant to defend itself, for example, from drought - explained Paweł Staszek, PhD student at the Department of Plant Physiology at the Faculty of Agriculture and Biology of WULS-SGGW.

"Not fully reduced oxygen is produced in aerobic respiration or photosynthesis reactions in the plant organism. These molecules are reactive and have a dual function. Firstly, they are signalling molecules that cause appropriate reactions in plants. For example, in response to drought stress, the plant closes the stomata so that it does not lose any water. Otherwise, there may be an oxygen explosion, that is, overproduction of reactive oxygen forms, for example in plant-pathogen contact. The objective here is to stop or kill a biological enemy" - said Paweł Staszek.

However, stress can cause overproduction of reactive oxygen forms in the organism. There are too many of them and damage to cells and biomolecules occurs. Reactive oxygen forms can interact with lipids, which can lead to cell membrane damage. Even more serious problems arise when they react with nucleic acids. DNA damage occurs, which can lead to reproductive problems.

The fact of particular interest to researchers is that these reactive oxygen forms are capable of modifying proteins. "They are oxidized proteins, they most often lose their function and cease to be biologically active. In the case of plants, it is not possible to repair these proteins, they degrade. Such oxidization is beneficial in maturation of seeds" - said Paweł Staszek

He added that the reactive forms of oxygen are very unstable, so it is difficult to measure whether their levels have increased and oxidative stress has occurred. A good marker, or indicator of change, is carbonylation of proteins.

In his lab, the researcher studies L-canavanine produced by plants. This amino acid is toxic to many organisms, from bacteria to mammals, especially to insects (plant/pest interaction). Scientists do not yet know how it affects plant organisms. It can be assumed that this amino acid is incorporated into proteins instead of a similar protein amino acid. In the future, better understanding of toxicity mechanisms will allow to develop natural plant protection products.

Phytotoxins can be used in the future as natural herbicides for weed control. According to Paweł Staszek, applications are still far away because these substances are unstable and easily degraded by soil microflora. The investigator argues, however, that it is now worth investigating what biological mechanisms are responsible for the toxic properties of plants, because before introducing anything into the ecosystem, the mechanism of action of chemicals must be thoroughly understood.

PAP - Science and Scholarship in Poland, Karolina Duszczyk

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