S-Nitrosylation - another biological switch like phosphorylation?

Nitric oxide (NO) has emerged as a key-signaling molecule affecting plant growth and development right from seed germination to cell death. It is now being considered as a new plant hormone. NO is predominantly produced by nitric oxide synthase (NOS) in animal systems. NOS converts L-arginine (substrate) to citrulline and NO is a byproduct of the reaction. However, a similar biosynthetic mechanism is still not fully established in plants as NOS is still to be purified. First plant NOS gene (AtNOS1) was cloned from Arabidopsis suggesting the existence of NOS in plants. It was shown to be involved in hormonal signaling, stomatal closure, flowering, pathogen defense response, oxidative stress, senescence and salt tolerance. However, recent studies have raised critical questions/concerns about its substantial role in NO biosynthesis. Despite the ever increasing number of NO responses observed, little is known about the signal transduction pathway(s) and mechanisms by which NO interacts with different components and results in altered cellular activities. A brief overview is presented here. Proteins are one of the major bio-molecule besides DNA, RNA and lipids which are modified by NO and its derivatives. S-nitrosylation is a ubiquitous NO mediated posttranslational modification that might regulate broad spectrum of proteins. In this review S-nitrosylation formation, catabolism and its biological significance is discussed to present the current scenario of this modification in plants.