Chitosan associated with chelated copper applied on tomatoes: enzymatic and anatomical changes related to plant defense responses

Abstract The aim of this work was study the use of an experimental product containing chitosan and chelated cooper (Cu) as a sustainable tool for the protection of tomato plants, to understand which are the mechanisms involved in resistance promotion and what could be the anatomical changes on tomato leaves related to those defense responses. The experiment was conducted in a greenhouse with tomato plants grown in pots and subjected to weekly foliar sprays of a suspension containing chitosan associated with Cu-EDTA (ChiCu). The increase in the phenolic compound concentrations and phenylalanine ammonia-lyase (PAL) enzyme activities were detected 24 hours after. In addition, an increase was observed in the activity of chitinase and β-1,3-glucanase, enzymes related to defense responses. Also, an increase was found in the thickness of the outer periclinal wall on the adaxial epidermal surface in leaves submitted to 4 ml L-1 ChiCu. The proportion of the epiderm to the leaf blade was also higher. Although the pathogenicity-related enzymes were activated as well as phenolic compounds were increased, these changes did not affected the biometric and biochemical parameters related to the primary metabolism and essential for the maintenance of productive potential of tomato plants. The increase in the outer periclinal wall as a result of ChiCu sprays could have contributed to the resistance against diseases since it is the first barrier to the infection of a wide of pathogens.