Increased abscisic acid levels in transgenic tobacco over-expressing 9 cis-epoxycarotenoid dioxygenase influence H2O2 and NO production and antioxidant defences.

Abscisic acid (ABA) regulates the plant's adaptive responses to abiotic stresses. Over-expression of the 9-cis-epoxycarotenoid dioxygenase gene (SgNCED1) in the transgenic tobaccos increased ABA content and tolerance to drought and salt stresses. H2O2 and nitric oxide (NO) contents were enhanced in guard cells and mesophyll cells of the transgenic plants, accompanied with increased transcripts and activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). The enhancements of H2O2 and NO and transcripts and activities of antioxidant enzymes in the transgenic plants were blocked by pre-treatments with inhibitor of ABA biosynthesis, scavengers of H2O2 and NO, and inhibitors of NADPH oxidase and NO synthase-like (NOS-like). The elevated production of NO in the transgenic plants was blocked by scavenger of H2O2 and inhibitors of NADPH oxidase, whereas H2O2 level was not affected by scavenger of NO and inhibitor of NOS-like, indicating that H2O2 is essential for the elevated production of NO. The results demonstrate that the increased drought and salt tolerance in the transgenic plants is associated with ABA-induced production of H2O2 via NADPH oxidase and NO via NOS-like, which sequentially induce transcripts and activities of SOD, CAT, APX and GR.