The aim of this work was to study the influence of chitosans of different molecular weight on the dynamics of the content of phenolic compounds in tomato plants of the 'Zagadka' variety. In the experiment, tomato plants treated with chitosan with a molecular weight of 50-190 kDa and 310-375 kDa were studied. Using the method of high-performance thin-layer chromatography (HPTLC), biochemical profiling of the extracts of the studied plants was performed. Differences in the primary reactions of plants to chitosans of different molecular weights were revealed. Low molecular chitosan caused a significant increase in the content of phenols and, accordingly, increased the antioxidant potential of leaf tissues. The increase in the content of phenols in response to the action of low-molecular-weight chitosan occurs due to the activation of phenylpropanoid synthesis and an increase in the total antioxidant potential, which indicates the mobilization of the plant organism against a potential pathogen. Thus, an hour after the treatment of plants with a solution of low molecular weight chitosan, the content of rutin in the leaves was 3.36 mg/g, and after 18 hours - 5.56 mg/g. The content of chlorogenic and caffeic acids in the leaves increased in 12 hours. In 18 hours, the content of chlorogenic acid was 1.64 mg/g, and caffeic acid was 0.18 mg/g. This may be due to the gradual decomposition of chlorogenic acid into its constituent components under the influence of low molecular weight chitosan, which is accompanied by the release of caffeic acid. A positive correlation was established between the pool of chlorogenic and caffeic acid (r = 0.995; p < 0.06). Therefore, depending on the molecular weight, chitosan causes significant changes in the synthesis of phenylpropanoids and biochemical transformation of complex and simple esters of hydroxycinnamic acids in tomato plants.
The high-molecular chitosan solution caused a decrease in the number of compounds with high antioxidant potential in tomato leaves, which indicates the activation of another plant defense system. The content of rutin in leaves treated with high-molecular-weight chitosan after 18 hours was 1.32 mg/g, which is four times less compared to the treatment of plants with low-molecular-weight chitosan. At the same time, in response to treatment with high molecular weight chitosan, the content of caffeic acid in the leaves increased significantly. The decrease in the content of phenols is associated with the isolation of tissues from a potential threat, which is aimed at its neutralization. The result of such a reaction is the oxidation of phenolic compounds, additional lignification and suberinization of cell walls. The activation of various induced immunity reactions in the plant organism already in the first hours after eating low-molecular or high-molecular chitosan indicates the existence of a system of differential recognition of complex bipolymers by plants.
