Regulation Mechanism And Endophytic Flora Of Selenium Nanoparticles Alleviating Cadmium Stress In Brassica Napus

Cadmium(Cd)has become a widespread and toxic agricultural soil contaminant deriving from various anthropogenic activities.It poses a serious threat to the ecosystem and human health.Cd could disrupt the redox homeostasis of cells and produce high levels of reactive oxygen species(ROS),which resulting in serious damage to important cell pathways and eventually cell death.It is easily absorbed by the roots of plants and transported to the stems,where it can enter the food chain and seriously affect the human body.Therefore,it is of great significance to study the biological effects of Cd in soil and plants and Cd pollution abatements for plants and humans.Selenium(Se)is recognized as one of the essential trace minerals in the animal and human.Its beneficial effects in relieving the Cd stress has been confirmed,but its mechanism is unclear.On the other hand,previous research almost focused on selenate and selenite,while they are toxic in high concentrations.Selenium nanoparticles(SeNPs)made by biological method are environmental-friendly and have excellent biological properties.However,the effects of SeNPs on plant growth under Cd stress have rarely been reportedIn this study,the effects of SeNPs and selenite on Cd stress in Brassica napus L.were studied.The main contents and results of this paper are as follows:(1)Effects of selenite and SeNPs on Cd stress of B.napus were analyzed by measuring the plant growth,Cd concentration,oxidative damage and antioxidant capacity.Exogenous Se supplementation,especially SeNPs significantly increased the biomass,root activity and chlorophyll content of B.napus,decreased the root-shoot ratio and restored the wax layer on leaf surface to a certain extent.In addition,it has been reduced the accumulation of Cd,superoxide anion and hydrogen peroxide in shoots of B.napus,increased the activity of antioxidant enzymes and inhibited lipid peroxidation in plant cells.(2)The key genes of selenite and SeNPs alleviating Se stress in B.napus were screened out by RNA-Seq and RT-qPCR combined with GO functional annotation,KEGG metabolic pathway enrichment analysis and MapMan pathway annotation.The mechanism of selenite and SeNPs alleviating Cd stress in B.napus was analyzed:Application of Se,especially in the form of SeNPs,decreased Cd-induced ROS production by inhibiting expression of NADPH oxidases(BnaRBOHC,BnaRBOHD1,and BnaRBOHF1)and glycolate oxidase(BnaGLO),thereby decreasing oxidative protein and membrane lipid damage.In addition,SeNPs improved resistance to Cd stress by decreasing Cd accumulation,maintaining intracellular calcium homeostasis,promoting disulfide bond formation,and restoring the waxy outer layer of the leaf surface(3)The synergistic regulation of SeNPs on endophytic community and B.napus under Cd stress was analyzed by endophytic sequencing:Exogenous Se supplementation significantly changed the specific composition and diversity of endophytic communities,and Cd-tolerant bacteria replaced intolerant bacteria.Compared with the control group,the addition of Cd significantly reduced the relative abundance of the endophytic community except Proteobacteria,and seriously affected the diversity of the endophytic community.Exogenous Se supplementation to some extent restored the relative abundance of Bacteroidetes and Actinobacteria and increased the relative abundance of plant growth-promoting bacteria.SeNPs inoculation can effectively reduce the negative effects of Cd growth by improving the internal microecological environment of B.napus without causing ecological damage.