Crosstalk between nitric oxide (NO) and abscisic acid (ABA) signalling molecules in higher plants

The key signalling molecules nitric oxide (NO) and abscisic acid (ABA) regulate plant growth and developmental processes as well as the mechanisms of response to environmental stresses. NO metabolism contains different biochemical mechanisms to regulate ABA homeostasis which is involved in important plant functions including seed dormancy, germination, stomatal movement, leaf senescence, fruit ripening and stress responses. Accordingly, NO induces post-translational modifications (PTMs) such as S-nitrosation (also called S-nitrosylation) and tyrosine nitration of proteins involved in the finely tuned regulatory mechanisms of the ABA signalling pathway. Furthermore, ABA-induced reactive oxygen species (ROS) generation is regulated by antioxidant systems such as catalase, superoxide dismutases (SODs) and the ascorbate-glutathione cycle which are also modulated by NO-induced PTMs. This review provides a comprehensive summary of current knowledge on the interaction between NO and ABA, especially for researchers who are unfamiliar with these molecules. NO and ABA are two of the most important plant cell regulators affecting almost all stages of plant development and responses to many environmental stresses. However, it is also important to consider the involvement of other compounds, such as hydrogen sulfide (H2S) and melatonin, whose synergetic and antagonistic interactions increase the complexity of regulatory mechanisms.