Abstract: Nitric oxide (NO) is a freely diffusible, gaseous compound and an important signal molecule in living organisms. It has been widely agreed that NO is endogenously produced in plant cells, possibly via NO synthase, nitrate reducatases, and/or through nonenzymatic reactions. In plants, NO influences aspects of growth and development, and can affect plant responses to stress. Increasing evidences indicated that NO is a key signal messenger in disease resistance in plants. More and more attentions have been drawn to its mechenism of signal transduction. This review discusses the functions of NO in plants via its generation , its influence on life cycle of plant, the regulation of signal in plant metabolism and participation in programmed cell death .