The Role of Calcium in Implementation of the Effect of Brassinosteroids during the Induction of Oxidative Stress in Tobacco

Brassinosteroids are plant hormones that play an important role in the regulation of the growth, development, and stress responses in plants, particularly, in the induction of tolerance to oxidative stress. It is known that the oxidative stress in plants, which consists in a sharp accumulation of reactive oxygen species (ROS), is induced by a methyl viologen herbicide. Since calcium plays an important role in the transduction of brassinosteroid signals in plant cells and closely interacts with a ROS network in the cells, the role of calcium in the modulation of ROS balance by brassinosteroids was studied using 35S::AtCAX1 transgenic tobacco plants. It was established that 35S::AtCAX1 tobacco plants with an artificial calcium deficiency in the cytosol are more sensitive to the oxidative damage induced by the effect of methyl viologen. The level of lipid peroxidation and oxidized glutathione was higher; however, the activation of superoxide dismutase and glutathione reductase was lower in mutated plants. In 35S::AtCAX1 plants, the effect of brassinosteroids on the induction of the oxidative state changes. A partial restoration of the chlorophyll level, weakening of lipid peroxidation, and a decrease in the level of oxidized glutathione, as well as the activation of superoxide dismutase and glutathione reductase, induced by brassinosteroids were less pronounced in the transgenic plants. The results of the analysis of gene coexpression, protein–protein interactions, and posttranslational modifications in silico confirm that brassinosteroids regulate the mechanisms of tobacco plant response to the effect of methyl viologen using calcium-dependent signaling processes, contributing to the formation of a balance of reactive oxygen species.