Ameliorative effects of exogenous melatonin to heavy metal and other abiotic stress tolerance in plants

Abstract

Heavy Metal (HM) toxicity is defended by plants using mechanisms such as metal chelation and vacuolar sequestration. HM-induced oxidative stress is also limited in plants by routine scavenging of free radicals including reactive oxygen/ nitrogen species (ROS/RNS) generation. In this review, we focus on exogenous melatonin treatment to regulate its biosynthetic pathway, the metal accumulation, and redox system. Furthermore, the photosynthetic components are significantly modulated in melatonin-treated plants under metal and other abiotic stressed conditions. Melatonin is also involved in nitric oxide (NO) signaling. Evidence suggests that the improvement in stress tolerance is due to the application of melatonin in a dose-dependent manner. Reports have suggested that phytohormones such as abscisic acid and jasmonic acid are mediated by melatonin. The genes related to secondary metabolites including flavonoid, phenolic, and saponin biosynthesis are mainly over-expressed in presence of melatonin.