302 Guo Fang-Qing et al. 2003 Oct. Science 302(5642):100-3. 100-3 5642 2003 Oct Identification of a plant nitric oxide synthase gene involved in hormonal signaling. 14526079 Guo Fang-Qing 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 Ca2+ 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. Crawford Nigel M Okamoto Mamoru