S-nitrosylation of SlAPX Is Involved in Alleviating Oxidative Damage in Transgenic Tobacco under Nitrate Stress

Nitric oxide (NO) modulates plant response by post-translationally modifying proteins, mainly through S-nitrosylation. Ascorbate peroxidase (APX) in the ascorbate-glutathione (AsA-GSH) cycle participates in the removal of hydrogen peroxide (H2O2). However, the relationship between S-nitrosylation and the role of tomato APX (SlAPX) under nitrate stress is still unclear. In this study, the enzyme activity, mRNA expression, and S-nitrosylation level of SlAPX were significantly increased in tomato roots after nitrate treatment. SlAPX protein could be S-nitrosylated by S-nitrosoglutathione in vitro, and APX activity was significantly increased after S-nitrosylation. The SlAPX overexpressed tobacco plants grew better than the wild type (WT) plants under nitrate stress. Meanwhile, the transgenic plants showed lower reactive oxygen species and malondialdehyde content, higher APX, monodehydroascorbate reductase, glutathione reductase activities, ascorbic acid/dehydroascorbic acid, and reduced glutathione/oxidized glutathione ratio, proline, and soluble sugar contents than those in the WT plants under nitrate treatment. Moreover, overexpressed transgenic seeds showed higher tolerance to methyl viologen induced oxidative stress compared with the WT. The NO accumulation and S-nitrosylation APX level were higher in transgenic plants than in WT plants after nitrate stress treatment. Our results provide novel insights into the mechanism of SlAPX modulation excess nitrate stress tolerance involving the S-nitrosylation modification.