Nitric oxide decreases superoxide anion generation by microsomes from soybean embryonic axes

Experiments were carried out to evaluate the effects of exposure to nitric oxide on the ability by NADPH-dependent microsomal electron transfer to gen erate oxygen radicals. Such interactions could play a role in the potential antioxidant action of nitric oxide (NO). Isolated microsomes from soybean (Glycine max [L.] Merr. cv. Hood) embryonic axes were exposed to an exogeno usly added source of nitric oxide (NO) (S-nitrosoglutathione + dithiothreit ol). The O-2(-) generation rate by microsomes exposed to NO decreased signi ficantly as compared to the rate measured in microsomes incubated in the ab sence of NO. The exposure of the microsomes to the NO donor did not alter t he microsomal rate of hydroxyl radical generation. Preincubation of the mic rosomes with the NO donor affected neither iron reduction rate nor activity of cylochrome c reductase. However, cytochrome P-450 activity was signific antly inhibited after exposure to NO. This inhibition was completely preven ted by hemoglobin. The data are consistent with the hypothesis that NO exhi bits a potential antioxidant role in the plant cell by decreasing the rate of generation of superoxide anion. Since endogenous NO was detected in homo genates of soybean embryonic axes by EPR studies, this interaction between NO and cytochrome P-450 in soybean embryonic axes could be a factor of rele vance for the control of oxidative stress in vivo.