Nitric oxide(NO) is an essential signaling molecule, which is involved in many aspects of plant growth and development. There is increasing evidence that NO plays a vital role in the process of flower development, which, however, has not been comprehensively reviewed for a long time. In this review, we provide an overview of the multiplicity of NO production in plants, and discuss the potential repression mechanism of NO in flower transition and the role of NO in pollen germination and pollen tube elongatio...