Study On The Absorption And Accumulation Of Selenium Stress By Alfalfa And Detoxification Mechanism

Selenium(Se)is an essential trace element for human beings and animals,and plants play an important role in the transformation of selenium which is critial for human health.Appropriate amounts of selenium can promote plant growth and development,improve crop yield and quality,and enhance the antioxidant activity of crops.However,when the amount of selenium exceeds the tolerance range of plants,it will inhibit the growth of plants,even leading to the death.Therefore,it is of very well application prospects to find new plants with high biomass,fast growth,good resistance and heavy metal accumulation.Alfalfa(Medicago sativa L)is a perennial herbaceous plant with large biomass,fast growth and strong resistance to stress and has important economic and ecological value.The experiments took three alfalfa cultivars,the Medicago sativa cv.Medicago sativa ssp.and Vitoria Alfalfa as test materials to study the selenium stress in 100,900mol/L concentration on chlorophyll and carotenoid contents in different alfalfa varieties inorder to make clear that the effect of selenium stress with different concentration on alfalfa root,stem and leaf reflecting in biomass,the tolerance index,antioxidant defense system,MDA content and osmotic adjustment.Another aim is to reveal the difference mechanisms of enrichment ability of different Alfalfa cultivars with selenium to explore new ways to cultivate new alfalfa varieties resistant to selenium.The main conclusions of this study are as follows:(1)the effects of different alfalfa cultivars on photosynthetic pigments in leaves under selenium stress: With the increasing of stress treatment time and concentration of selenium,chlorophyll a,chlorophyll b,total chlorophyll,carotenoids content and Fv,Fm,Fv/Fm and Fv/Fo values in Medicago sativa ssp were significantly higher than the control on 60 d,and the difference was significant(P < 0.05).Under the stress of 900?M selenium,three alfalfa varieties were compared with each other.The restuls indicated that alfalfa leaf chlorophyll a,total chlorophyll,carotenoids content and Fv,Fm and Fv/Fm in Medicago sativa ssp were higher than the other two varieties,showing that alfalfa leaves had stronger tolerance to selenium.(2)the effects of different alfalfa cultivars on biomass and the accumulation of relativegrowth amout under selenium stress: With the extension of selenium stress treatment time,100 mol/L selenium treatment significantly improved biomass accumulation in three varieties of alfalfa at 20 and 40 d.When the selenium concentration is 900 mol/L,biomass and relative biomass in Medicago sativa ssp were significantly higher than that in other two varieties.(3)effects of Alfalfa Cultivars on antioxidant enzymes under selenium stress:Under different concentrations of selenium,the activity of SOD,CAT,APX and POD and GSH content of Medicago sativa ssp alfalfa were significantly higher than those of the other two alfalfa varieties,and the differences were significant.The antioxidant ability of Medicago sativa ssp was the strongest,and the antioxidant ability of Vitoria alfalfa was the worst.(4)the effects of different cultivars of alfalfa on osmotic adjustment substances under selenium stress: With the increasing of the degree of selenium stress,the soluble protein,proline and superoxide anion contents increased,indicating that they were suffered from stress of selenium in different degrees of oxidation.The oxidation stress is greater as the degree of selenium stress increasing.(5)alfalfa cultivars had strong absorption,accumulation and tolerance to selenium: with the increment of the concentration of selenium,the transport coefficient,tolerance index,selenium accumulation and selenium content in the root,stem and leaf of tested alfalfa were higher than that of the control.selenium treatment(100 mol/L)significantly improved the selenium content,tolerance index and selenium accumulation in the roots,stems and leaves of three varieties of alfalfa.When the selenium concentration is 900 mol/L and the organ selenium accumulation amount,enrichment coefficient,leaf transfer coefficient are greater than 0.5 in the Medicago sativa cv.and Medicago sativa ssp,the selenium accumulation amount in Medicago sativa ssp was higher than 1 and which is significantly higher than that of the other two varieties.(6)the effects of selenium stress on the absorption of other elements in alfalfa cultivars:With selenium stress time prolonged,K,P,Ca,Mg absorption increased in the root,stem andleaf of three varieties of alfalfa with 100 mol/L selenium treatment at 60 d.When the concentration of selenium was 900 mol/L,the accumulations of Zn absorption by different organs of the Medicago sativa cv.and Vitoria Alfalfa and the root and stem of Medicago sativa ssp were reduced.Compared with the other two varieties,the selenium accumulationand K,P,Mg uptake of Medicago sativa ssp were significantly higher than that of other alfalfa varieties.The comprehensive evaluation showed that the Medicago sativa ssp had good absorption and accumulation abilities.The results showed that selenium accumulation,uptaken of K,Ca,Mg and antioxidant capacity of Medicago sativa ssp were significantly higher than those of the other two alfalfa,and the differences were significant.Therefore,the preliminary judgment was able to made that the Medicago sativa ssp has the ability of detoxification and enrichment of selenium.Therefore,it is of potential application for remediation of selenium contaminated soil.