Sodium nitroprusside pretreatment alters responses of Chinese cabbage seedlings to subsequent challenging stresses

Nitric oxide (NO) is a self-regulating gaseous molecule as well as an interacting partner with different reactive oxygen species (ROS). Endogenous NO increased, but hydrogen peroxide (H2O2) and superoxide radical anion (O-2(center dot-)) decreased in Chinese cabbage leaves treated with sodium nitroprusside (SNP) (0.5 mM). Antioxidant enzyme genes BrCat1, BrCat2, BrAPX, BrGR1, and BrGST1 expressions were transiently induced by the SNP (0.5 mM). Pretreated SNP (0.5 mM) enhanced tolerance to subsequent challenges by phytotoxic SNP (5 mM) and methyl viologen (MV) (50 mu M), but accelerated cellular damage by H2O2 (4 M) shown by electrolyte leakage and lipid peroxidation. The SNP (0.5 mM) differentially modulated endogenous NO and ROS levels as well as antioxidant enzyme gene expressions by excess SNP, MV, and H2O2 stresses. These results suggest that NO as a signal molecule differentially interacts with challenging stresses in Chinese cabbage leaves, followed by differential cellular damage and antioxidant responses.