Role of nitric oxide in heavy metal stress

Nitric oxide (NO) is a diffusible gaseous molecule first identified in mammalian systems as the endothelium-derived relaxing factor, a potent endogenous vasodilatator. No is also synthesized and released by plants, where it is involved in several physiological processes and in adaptative response against different stresses; hence, NO is considered to be a general signal molecule in plant and animal cells. In recent years, heavy metals (HMs), naturally present or added to the soil through diverse anthropogenic activities, have become a problem of agricultural and environmental significance. Although the mechanism by which HMs affect plants integrity is not fully understood, there is increasing evidence suggesting that an important component of the responses against HM stress is NO. This chapter presents an overview on the effects of HMs on endogenous NO content. In addition, the role of exogenous-applied NO in alleviating HM toxicity is summarized and discussed.