Benzothiadiazole and l-2-oxothiazolidine-4-carboxylic acid reduce the severity of Sharka symptoms in pea leaves: effect on antioxidative metabolism at the subcellular level

The effect of treatment with benzothiadiazole (BTH) or l-2-oxothiazolidine-4-carboxylic acid (OTC), and their interaction with Plum pox virus (PPV) infection, on antioxidative metabolism of pea plants was studied at the subcellular level. PPV infection produced a 20% reduction in plant growth. Pre-treatment of pea plants with OTC or BTH afforded partial protection against PPV infection, measured as the percentage of leaves showing symptoms, but neither BTH nor OTC significantly reduced the virus content. PPV infection caused oxidative stress, as monitored by increases in lipid peroxidation and protein oxidation in soluble and chloroplastic fractions. In leaves of non-infected plants, OTC increased the content of reduced glutathione (GSH) and total glutathione; accordingly, an increase in the redox state of glutathione was observed. An increase in oxidized glutathione (GSSG) was found in symptomatic leaves from infected plants. A similar increase in GSSG was also observed in asymptomatic leaves from infected, untreated plants. However, no changes in GSSG occurred in asymptomatic leaves from infected plants treated with BTH and OTC and, accordingly, a higher redox state of GSH was recorded in those leaves, which could have had a role in the reduction of symptoms, as observed in asymptomatic leaves from infected plants treated with BTH or OTC. Treatment with BTH or OTC had some effect on antioxidant enzymes in soluble and chloroplastic fractions from infected pea leaves. An increase in antioxidative mechanisms, such as GSH-related enzymes (DHAR, GR and G6PDH), as well as APX and POX, at the subcellular level was observed, which could play a role in reducing the severity of cellular damage induced by Sharka in pea leaves.