Nitric oxide synthase activity is required for development of functional nodules in soybean

The effects of a nitric oxide synthase inhibitor (Nω-nitro-l-arginine) on soybean growth parameters and nodule functioning were investigated, along with soybean nodule cell viability and cysteine endopeptidase activity. Nω-nitro-l-arginine reduced soybean growth parameters, inhibited nodule nitrogenase activity, and caused a decrease in nodule cell viability. The negative effects of Nω-nitro-l-arginine were reversed by the nitric oxide donor 2,2′-(hydroxynitrosohydrazono)bis-ethanimine. Cysteine endopeptidase activity was higher in plants treated with Nω-nitro-l-arginine than untreated plants (controls), but decreased to levels similar to the controls when plants were exposed to a combination of Nω-nitro-l-arginine and 2,2′-(hydroxynitrosohydrazono)bis-ethanimine. These results suggest that nitric oxide, resulting from nitric oxide synthase activity, is required for development of functional soybean nodules.