Identification of a Plant Nitric Oxide Synthase Gene Involved in Hormonal Signaling

Nitric oxide (NO) serves as a signal in plants. An Arabidopsis mutant ( Atnos1 ) was identified that had impaired NO production, organ growth, and abscisic acid–induced stomatal movements. Expression of AtNOS1 with a viral promoter in Atnos1 mutant plants resulted in overproduction of NO. Purified AtNOS1 protein used the substrates arginine and nicotinamide adenine dinucleotide phosphate and was activated by Ca 2+ and calmodulin-like mammalian endothelial nitric oxide synthase and neuronal nitric oxide synthase, yet it is a distinct enzyme with no sequence similarities to any mammalian isoform. Thus, AtNOS1 encodes a distinct nitric oxide synthase that regulates growth and hormonal signaling in plants.