Presence of nitric oxide synthase activity in roots and nodules of Lupinus albus

NO is a widespread messenger molecule in physiology. We were interested in investigating whether an NO-generating system could be present in plants. NO and l-[ 14C]citrulline were synthesized by roots and nodules of Lupinus albus in an l-arginine-dependent manner. l-[ 14C]Citrulline production was inhibited by N G - monomethyl- l-arginine , a nitric oxide synthase antagonist, in a competitive way. NADPH-diaphorase activity was localized in the vascular bundles in root and nodules, and also in the nodule infected zone. This staining was significantly reduced in the presence of N G - monomethyl- l-arginine . These results indicate the presence of a putative nitric oxide synthase in plants.