Response Of Astragalus Membranaceus Seedlings To Treatments Of Selenium And Cadmium And Mechanism Of Selenium Relieving Cadmium Stress

The seedlings of Astragalus Membranaceus(Fisch.)Bunge(hereinafter referred to as A.membranaceus)were used as materials to study different concentrations of Cadmium(Cd)and Selenium(Se)under hydroponic conditions.The effects of treatment on growth and develop-ment indicators,mineral element absorption and transport,and the synthesis of marker secon-dary metabolites were discussed.The response of A.membranaceus seedlings to Cd and Se treatment was discussed.On this basis,we studied the alleviation effect of exogenous Se on Cd stress of A.membranaceu seedlings,and further analyzed the changes of mineral element absorption and distribution,antioxidant system and secondary metabolites in seedlings during Cd stress alleviation.The physiological mechanism of Se to alleviate the Cd stress of A.mem-branaceu seedlings was analyzed,in order to provide a theoretical basis for using exogenous Se to reduce the Cd toxicity of medicinal plants.The main results and conclusions of this paper are as follows:Treatment with 25-200 ?mol L-1 Cd for 7 d significantly inhibited the growth of roots and shoots of A.membranaceus seedlings and caused a significant increase in MDA content and a decrease in photo synthetic pigment content in new leaves.The Cd absorbed by the plant mainly accumulates in the roots of A.membranaceus seedlings,and the accumulation of Cd in the upper part of the plant is the upper<middle<basal.Cd treatment reduces the absorption and transport of various mineral nutrients by plants.In addition,the content of four isoflavones in the roots was significantly increased under Cd treatment,and the content of Astragaloside ?-? was decreased by Cd treatment.Similar to the response to Cd treatment,10-320 fimol L-1 Se treatment for 7 d also signi-ficantly inhibited the biomass growth of A.membranacezus seedlings,increased the content of MDA and decreased the chlorophyll content of leaves.Different from Cd treatment,high concentration Se treatment not only reduced the chlorophyll content in new leaves,but also reduced the chlorophyll content in old leaves.Selenite is also mainly transported into the roots and shoots of the A.membranaceus by passive transport,and the proportion of transport to the shoots is low.Se treatment also caused changes in the contents of various mineral nutrients in the roots and shoots of A.mermbranaceus seedlings,resulting in an imbalance of nutrient dis-tribution.Se treatment induced an increase in the accululation of isoflavones in the roots of A.membranaceus.In addition,low concentration of Se inhibited the accumulation of Astraga-loside ?-?,while high concentration of Se promoted the accumulation of Astragaloside ? and?.The addition of low concentration of Se significantly increased the biomass gro.wth of A.memhranaceus seedlings under 50 ?mol L-1 Cd stress,decreased the MDA content of the plants,and increased the chlorophyll content and the activity of root tip cells.It was found that the absorption of Se and Cd in A.membranaceus seedlings had obvious antagonistic effect.The addition of Se significantly reduced the content of Cd in the shoots and roots of plants,and to some extent eliminated the Cd stress on the mineral nutrients of A.membranaceus seedlings.The effects of absorption and distribution.In addition,the addition of Se failed to reduce the oxidative stress caused by Cd treatment by increasing the activity of antioxidant enzymes in the roots and shoots of A.membranaceus.The decrease of H2O2 and O2-content after Se add-ition may be mainly caused by the decrease of Cd absorption.The addition of Se significantly promoted the increase of isoflavones in the roots of A,membranaceus under Cd stress,but it seemed to indicate that isoflavones also played an active role in the alleviation of Cd stress in Se.In summary,the treatment of Cd and Se alone eaused similar stress responses of A.mem-branaceu seedlings,such as inhibition of biomass growth,increased degree of membrane lipid peroxidation,decreased chlorophyll content,and disturbance of mineral nutrient absorption and transport.In the face of Cd or Se stress,A.membranaceu seedlings actively face stress by regulating the regionalization of element distribution and increasing the synthesis of isofla-vones,and improve tolerance to stress.Low concentration of Se can effectively alleviate Cd stress in A.membranaceu seedlings.The main physiological mechanisms include reducing Cd uptake and transport,improving mineral nutrient absorption and transport,and promoting isoflavone synthesis.