Novel hybrid modulators of plant immune responses based on chitosan and bioactive anti-oxidants and pro-oxidants

During the infection of plants with pathogens, the equilibrium between oxidative processes and antioxidant activity shifts toward an increase in the formation of ROS, which affects the course of the development of the disease and manifests itself differently in phytopathosystems of various types of parasitism. So, to protect plants from biotrophic pathogens, ROS generation is necessary, but the resulting high level of ROS does not protect, but, on the contrary, favors the pathological process caused by necrotrophs. Substances that can control not only ROS generation, but also their utilization, can become effective immunomodulators to protect plants when infected with pathogens of different lifestyles. For the first time, chitosan-based hybrid immunomodulators (Chit-Van+SA) were created, in the structure of which there are fragments of biologically active substances that have antioxidant and prooxidant effects. The basis of such systems is chitosan (Chit), containing covalently attached vanillin (Chit-Van), which reduces the ROS level by stimulating cellular antioxidant activity (antioxidant effect), and salicylic acid (Chit+SA), which is associated with a labile ionic bond, generating ROS (prooxidant act). It was shown that (Chit+SA) increases the wheat resistance to Puccinia recondita Roberge ex Desmaz f. sp. tritici biotroph and Cochliobolus sativus Drechs hemibiotroph, while (Chit-Van) effectively induces resistance only to C. sativus hemibiotroph. The effectiveness (Chit+CA) as an inducer of stability is 1.2-2.0 times higher than the inducing effect of chitosan itself (Chit). It was found that hybrid immunomodulators (Chit-Van+SA) with respect to both the biotroph (brown rust) and the hemibiotroph (dark brown spotting) with a molar ratio of vanillin and salicylic acid in them in the range 1:1-1:2 show a high immunomodulating activity, regardless of the molecular weight of chitosan, which is expressed in a decrease in the area of leaf damage to 5-10 % of the control. The results obtained indicate that the biological effectiveness of the hybrid polymer system (Chit-Van+SA) as an immunomodulator correlates with the content of SA in them, which confirms the participation of the signal salicylate system in the induction of resistance. It is established that specific enzymatic antioxidants superoxide dismutase, catalase and peroxidase, which regulate the relationship between oxidative processes and antioxidant activity, play an important role in the development of induced resistance when using the created immunoinductors. In general, the results of studying the effect of the hybrid immunomodulators (Chit-Van+SA) on the activity of antioxidant enzymes in the model system wheat- C. sativus suggest that the increase in plant resistance to pathogens is realized through the control of the intensity of redox processes in plants, which is caused by the presence in the structure of hybrid immunomodulators of a certain pro- and antioxidant balance.