Molecular, genetic and biochemical studies have identified key players in the signaling pathways regulating growth and development, as well as defense responses in plants. Recently, nitric oxide (NO) - the versatile and powerful effector of animal redox-regulated signaling and immune responses - was shown to mediate plant defense responses against pathogens. Interestingly, several key components involved in NO-mediated signaling in animals also appear to be operative in plants.