For several years, at the Department of Plant Physiology, Institute of Biology, SGGW some intensive research on the influence of non-protein amino acids on the metabolism of plant cells have been carried out.
As part of the Preludium project “Mechanism of the toxic effect of canavanine on root growth: disruption of the organization of the root apex, ultrastructure of cells, the cell cycle and auxin transport”, the scientists are trying to answer the question, to what extent the tomato root growth disturbance observed in the presence of canavanin are caused by a disturbance in the course of the cell cycle.
The data obtained may be some day the basis for explaining the validity of canavanine-assisted anti-cancer therapy.
Proteins are biomolecules responsible for the structure and function of individual cells and entire organisms. They have a complicated system of long, twisted polymer chains, where amino acids are the basic building blocks. There are 20 amino acids which are used to build proteins of all animal and plant organisms. However, beyond the “big twenty”, some numerous amino acids have been identified that they are produced by plants and are not part of protein chains at all. Some of them are intermediate products of basic biological transformations, thus most of them have other functions, and are often highly toxic substances. The group of non-protein amino acids includes L-canavanine (Kan), which is a structural equivalent of arginine – a protein amino acid. Kan is produced by the Fabaceae family (bean family) plants and stored mainly in seeds. Mostly Kan is concentrated in tropical plants such as Canavalia ensiformis (jack bean), but the significant amounts of this non-protein amino acid are also found in alfalfa seeds and “sprouts”, as a popular addition to salads. Kan is toxic to a wide range of organisms, ranging from bacteria to plants, insects, and mammals, including humans. Kan can be incorporated into the structure of proteins in place of arginine – such proteins lose their biological activity, then. Plants containing significant amounts of Kan are used in traditional medicine, what is more, maybe Kan will be used in oncological therapy in the future. Kan inhibits the division of cancer cells, and the combined application of Kan with chemo- and radiotherapy increases the effectiveness of the treatments by sensitizing cancer cells. Nitric oxide (NO) is a gaseous molecule responsible for signal transduction – it regulates growth and development, and is also involved in the response to stress factors. Nitric oxide (NO) may be produced by the oxidation of arginine. Kan is effective in reducing NO biosynthesis in cells. A far as plants are concerned, NO together with an auxin (phytohormone) is responsible for the development and regulation of root growth, therefore the amount of auxin is a key factor influencing the proper development of the root system. The concentration of auxin in root cells is highly dependent on its transport from the above-ground part. The PIN proteins are the family of auxin transporters. The research carried out at the SGGW laboratory proved that Kan, even at very low concentrations, inhibits the root growth of tomato seedlings without affecting the cell viability. Moreover, in the roots treated with Kan, a reduction in NO emission and accumulation of auxin were found. The aim of the “Mechanism of the toxic effect of canavanine on root growth: disruption of the organization of the root apex, ultrastructure of cells, the cell cycle and auxin transport” project carried out at SGGW is to link a negative impact of Kan on the growth of the roots of young tomato seedlings with changes in cell ultrastructure, cell division and cell cycle.
Scientists are also interested in changing the expression and location of the PIN proteins responsible for polar auxin transport. Scientists from the Department of Plant Physiology, Institute of Biology, SGGW believe that thanks to those research they will be able to propose a model describing the mechanism of Kan activities in plants taking into account the influence of this non-protein amino acid on the ultrastructure of cells and the cell cycle, and the transport of auxin – a cardinal hormone for cell growth processes. The results obtained during the research will also be helpful in determining the assumed functions of Kan in oncological therapy.
More information about the project can be found at: https://projekty.ncn.gov.pl/index.php?projekt_id=410518