Nitric Oxide Signalling in Plants: Cross-Talk With Ca2+, Protein Kinases and Reactive Oxygen Species

Nitric oxide (NO) is a gaseous free radical recognized as a ubiquitous signal transducer that contributes to various biological processes in animals. It exerts most of its effects by regulating the activities of various proteins including Ca2+ channels, protein kinases and transcription factors. In plants, studies conducted over the past ten years revealed that NO also functions as an endogenous mediator in diverse physiological processes ranging from root development to stomatal closure. Its biological role as an intracellular plant messenger molecule, however, remains poorly understood. Here, we review the molecular basis of NO signaling in animals and discuss current knowledge of NO signaling in plants, focusing on its interplay with Ca2+, protein kinases and reactive oxygen species which are well established as widespread key regulators of signal transduction.