一氧化氮对植物重金属胁迫抗性影响的研究进展

Abstract

Heavy metal pollution has become an increasingly serious environmental problem because heavy metal can be easily taken up by plants,leading to inhibition of plant growth and development. Hence,it is necessary to investigate resistances of plants to heavy metal stress. As an important signaling molecule,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 NO on resistances of plants to heavy metal stress. However,studies which systematically summarize the molecular mechanisms of NO on resistances of plants to heavy metal stress are quite limited. This research mainly reviews the pathways of NO production,changes of endogenous NO contents under heavy metal stress and influences of exogenous and endogenous NO on resistances to heavy metal stress. The sources of NO production in plants involve not only enzymatic reaction pathways which include nitric oxide synthase( NOS),nitrate reductase( NR),nitrite reductase( Ni-NOR) pathways and etc. but also non- enzymatic reaction pathways. Many authors have noted discrepant reports on the effects of heavy metal stress on endogenous NO content in plants and the observed differences in endogenous NO accumulation are frequently ascribed to the use of different duration of treatment,heavy metal concentrations,species and genotypes of plants and varieties of plant tissues. Interestingly,all plant cell suspensions show a visible increase in endogenous NO accumulation under heavy metal stress,which is attributed to the fact that they are lacking of network regulation between cells and cells. Meanwhile,it has been demonstrated that exogenous NO could enhance antioxidant defence system of plant cells,act as an antioxidant promoting direct scavenging of reactive oxygen species,induce metallothioneins( MTs) gene expression by displacing heavy metal bound to MTs,and affect the uptake of heavy metal intoplants and the distribution of heavy metal in plant cells though regulating the metabolism of cell wall composition,consequently relieve heavy metal toxicity and enhance resistances of plants to heavy metal stress. However,the functional roles of endogenous NO in regulating resistances of plants to heavy metal stress are controversial. Some research show that endogenous NO is helpful for alleviating heavy metal-induced toxicity. On the contrary,some evidences indicate that endogenous NO is harmful,and participates in heavy metal-induced cell toxicity and programmed cell death through accelerating the absorption of heavy metal and S-nitrosylation of phytochelatins. These conflicting data suggest that NO may have a dual effect on resistances to heavy metal stress,but great efforts are required in order to clarify this speculation.Finally,interrelated perspectives are also discussed to further study the relationship between NO and resistances to heavy metal stress.