GLUCOSE-6-PHOSPHATE DEHYDROGENASE IS REQUIRED FOR HPA1x00 (HARPIN PROTEIN FRAGMENT)-MEDIATED SALT STRESS TOLERANCE IN TRANSGENIC ARABIDOPSIS THALIANA

Harpin induces salicylic acid and abscisic acid signaling in plants under biotic and abiotic stress, respectively. Our previous report showed that the effective harpin fragment Hpal. enhanced H2O2 production and pathogen resistance in a transgenic Arabidopsis mutant. In this study, we examined contents of thiobarbituric acid reactive substance (TBARS), H2O2 and glutathione, and glucose-6-phosphate dehydrogenase (G6PDH), glutathione reductase (GR) and glutathione peroxidase (GPX) enzyme activity in Hpal(xoo)-expressing Arabidopsis under salt stress. The results revealed increased amounts of TBARS and H2O2 in wild-type (WT) compared to mutant plants under salt stress conditions. In contrast, increased levels were observed in the mutant under stress-free conditions. Moreover, a higher reduced glutathione (GSH) content and ratio of GSH/oxidized glutathione (GSSG) was observed in mutant compared to WT plants under bothstress-free and salt stress conditions. In addition, mutant plants exhibited significantly higher G6PDH, GR and GPX activity than WT plants under salt stress. Suppression of G6PDH activity via 6-aminonicotinamide (6-AN, a specific inhibitor of G6PDH) was partly reversed by L-buthionine-sulfoximine (BSO, a specific inhibitor of GSH regeneration) and aggravated by GSH. Combined with previous reports, these fmdings suggest that the G6PDH enzyme plays a key role in harpin fragment (Hpal(xoo))-mediated salt stress tolerance in transgenic Arabidopsis.