Roles of nitric oxide in alleviating heavy metal toxicity in plants

Nitric oxide (NO) is involved in the regulation of multiple plant responses to a variety of abiotic and biotic stresses. Recently, an increasing number of articles have reported the effects of exogenous NO on alleviating heavy metal toxicity in plants. However, compared with the current understanding of the relationships between NO and other abiotic stresses, knowledge of the molecular and physiological mechanisms of NO in alleviating heavy metal toxicity is quite limited, and some results contradict one another. Therefore, to help clarify the roles of NO in heavy metal tolerance, it is valuable to review and discuss the recent advances on this research topic. In this mini-review, the latest advances in understanding the effects of heavy metals on endogenous NO content and the mechanisms and signaling pathways of exogenous NO in alleviating heavy metal toxicity in plants are summarized and discussed. A basic scheme for the roles of NO in alleviating heavy metal toxicity is also proposed.