Antioxidant Profile and Polyphenol Oxidase Activities in Apple Leaves after Erwinia amylovora Infection and Pretreatment with a Benzothiadiazole‐type Resistance Inducer (BTH)

Abstract

AbstractThis study focused on the biochemical effects of benzo‐(1,2,3)‐thiadiazole‐7‐carbothioic acid S‐methyl ester (BTH), an active compound of the commercial preparation Bion, as an elicitor of resistance to fire blight (Erwinia amylovora) in apple. We determined activities of main antioxidant enzymes: ascorbate peroxidase (APX), catalase, glutathione peroxidase (GSH‐Px) and glutathione transferase (GST), enzymes associated with phenolic metabolism: phenylalanine ammonia‐lyase and polyphenol oxidases (PPOs), levels of low molecular antioxidants [ascorbate, glutathione, tocopherol (TOC)], phenolic acids and flavonoids as well as markers of oxidative processes: superoxide anion radical (O2·−) and thiobarbituric acid reactive substances in apple leaf tissues pretreated and non‐pretreated with BTH before inoculation with E. amylovora. The results indicate that successful invasion of pathogen might be associated with a significant decrease in the ascorbate pool in an early phase of plant–pathogen interaction. Generation of O2·− and changes in some antioxidant parameters (APX, GSH‐Px, GST, TOC) were less intensive and/or occurred earlier in the BTH‐pretreated apple leaves than in non‐pretreated ones. In the BTH‐pretreated group, PPOs activities were higher than in the control throughout the experiment, whereas in the non‐pretreated group, the increase started from the 7th day after inoculation. Infection strongly enhanced chlorogenic and o‐coumaric acids accumulation, and BTH weakened this effect. The opposite was observed with respect to phloretin and phloridzin.