Effects Of Fulvic Acid On Physiological Characteristics And Resistance Gene Expression Of Salix Matsudana Koidz Under Cadmium And Drought Stress

With the rapid development of modern industry and the increasingly scarce global water resources,even sewage irrigation and other factors,the problem of heavy metal pollution in arid and semi-arid areas has become increasingly serious.The interaction of cadmium(Cd)and other stresses makes the effects of compound stress more complex than that of single cadmium pollution,and the effects of compound stress on Cd migration in shoot are also different.Fulvic acid(FA)has unique structural basis of biological and chemical activities.As a metabolic antitranspirant,it can effectively alleviate drought.Recently,FA has been widely used to remove heavy metals in water media.FA has the potential to bind with heavy metals,but the study on detoxification of metals by FA in plants is not extensive.It has a good application prospect in promoting plant growth and resisting abiotic stress.Salix matsudana Koidz is resistant to various stresses,including drought stress and heavy metal stress,and plays an important role in ecological restoration.In order to reveal the effect mechanism of FA on heavy metal stress and drought stress in plants,the effects of FA on Cd and PEG treatments were studied by using PEG6000 to simulate drought conditions.Eight treatments of CK,PEG(10%),Cd(50?M),Cd+PEG,FA(0.5 g L^-1),FA+Cd,FA+PEG and FA+Cd+PEG were set up in the experiment.Samples were taken on the 7th and 14th days for testing.The results are as follows:(1)Compound stress of Cd and PEG increased the accumulation of Cd in Salix matriculata.Compared with single stress,leaf area increment,root length increment and stem length increment of Salix matriculata were also significantly inhibited on the 7th and 14th days.Spraying FA significantly improved the growth parameters and biomass of Salix matriculata.Spraying FA could significantly reduce the accumulation of Cd in Salix matriculata,reduce the bioconcentration coefficient of shoot,and alleviate the damage caused by single and compound stress.(2)The active oxygen species(ROS)in the leaves of Salix matsudana Koidz.were accumulated with the increase of stress species and the prolongation of stress time,Compared with CK,the contents of hydrogen peroxide(H₂O₂)and superoxide radical(O₂.^-)increased,the contents of malondialdehyde(MDA),glutathione(GSH)and proline(Pro)and the activities of superoxide dismutase(SOD),catalase(CAT),glutathione reductase(GR)and ascorbate peroxidase(APX)increased,while the contents of ascorbate(As A),relative water content(RWC)and relative chlorophyll content(SPAD)decreased.Spraying FA under Cd and PEG treatments increased the activity of antioxidant enzymes and the content of non-enzymatic antioxidants,decreased the level of ROS,and increased the RWC and SPAD values,which was beneficial to improve the tolerance of Salix matsudana Koidz.under single and compound stresses.(3)Spraying FA could up-regulate SOD,CAT,APX and GR antioxidant enzyme genes at different time,improve the antioxidant level and alleviate the damage caused by Cd and PEG stress.Spraying FA increased the expression of NCED1 and NCED2,decreased the expression of protein phosphatase 2C(PP2C)and up-regulated the expression of SNF1-related protein kinase(Sn RK2.6)under single and combined stress on the 14th day.In conclusion,under the combined stress,Salix matriculata absorbed more Cd,the growth began to be more seriously inhibited,and more ROS was produced,which made Salix matriculata suffer more serious oxidative damage.Excessive production of ROS deepens the degree of membrane lipid peroxidation,which leads to the decrease of RWC and SPAD,and the defense system and protective mechanism are rapidly activated during stress to resist injury.However,foliar spraying FA under single and combined stress reduced Cd content in plants,enhanced reactive oxygen scavenging system,increased antioxidant content,significantly increased the expression of antioxidant enzyme related genes and ABA biosynthesis and signal transduction related genes,alleviated oxidative damage,reduced leaf evapotranspiration loss,and improved the tolerance of Salix matriculata to Cd and PEG.