Crawford Nigel M
Section of Cell and Developmental Biology, Division of Biological Sciences, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.
J Exp Bot. 2006;57(3):471-8. doi: 10.1093/jxb/erj050. Epub 2005 Dec 15.
The discovery that nitric oxide (NO) acts as a signal fundamentally shifted our understanding of free radicals from toxic by-products of oxidative metabolism to key regulators of cellular functions. This discovery has led to intense investigation into the synthesis of NO in both animals and plants. Nitric oxide synthases (NOS) are the primary sources of NO in animals and are complex, highly regulated enzymes that oxidize arginine to NO and citrulline. Plant NO synthesis, however, appears more complex and includes both nitrite and arginine-dependent mechanisms. The components of the arginine pathway have been elusive as no known orthologues of animal NOS exist in plants. An Arabidopsis gene (AtNOS1) has been identified that is needed for NO synthesis in vivo and has biochemical properties similar to animal cNOS, yet it has no sequence similarity to any known animal NOS. An Atnos1 insertion mutant has been useful for genetic studies of NO regulation and for uncovering new roles for NO signalling. The elucidation of plant NO synthesis promises to yield novel mechanisms that may be applicable to animal systems.
一氧化氮（NO）作为一种信号分子的发现，从根本上改变了我们对自由基的理解，即从氧化代谢的有毒副产物转变为细胞功能的关键调节因子。这一发现引发了对动物和植物中NO合成的深入研究。一氧化氮合酶（NOS）是动物体内NO的主要来源，是复杂的、受到高度调控的酶，可将精氨酸氧化为NO和瓜氨酸。然而，植物中的NO合成似乎更为复杂，包括亚硝酸盐和精氨酸依赖性机制。由于植物中不存在已知的动物NOS直系同源物，精氨酸途径的组成成分一直难以捉摸。已鉴定出一种拟南芥基因（AtNOS1），它是体内NO合成所必需的，并且具有与动物cNOS相似的生化特性，但与任何已知的动物NOS没有序列相似性。Atnos1插入突变体对于NO调节的遗传学研究以及揭示NO信号传导的新作用很有用。对植物NO合成的阐明有望产生可能适用于动物系统的新机制。
