We studied the response of glutathione‐ and ascorbate‐related antioxidant systems of the two tomato cultivars toPseudomonas syringaepv.tomatoinfection. In the inoculated susceptible A 100 cultivar a substantial decrease in reduced glutathione (GSH) content, oxidised glutathione accumulation and GSH redox ratio decline as well as glutathione peroxidase activity increase were found. The enhanced glutathione reductase activity was insufficient to keep the glutathione pool reduced. A transiently increased dehydroascorbic acid (DHA) content and ascorbic acid (AA) redox ratio decrease together with ascorbate peroxidase activity suppression were observed. Adversely to the progressive reduction in GSH pool size, AA content tended to increase but the changes were more modest than those of GSH. By contrast, in interaction with the resistant Ontario cultivar the glutathione pool homeostasis was maintained throughoutP. syringaeattack and no significant effect on the ascorbate pool was observed. Moreover, in the resistant interaction there was a significantly higher constitutive and pathogen‐induced glutathione‐S‐transferase (GST) activity. The relationship between GST activity and DHA content found in this study indicates that this enzyme could also act as dehydroascorbate reductase. These results reflect the differential involvement of GSH and AA in tomato‐P. syringaeinteraction and, in favour of the former, they clearly indicate the role of GSH and GSH‐utilizing enzymes in resistance toP. syringae. The maintenance of glutathione pool homeostasis and GST induction appear to contribute to tissue inaccessibility to bacterial attack.
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Kuźniak et al. (2004) studied this question.
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