| Arsenic(As)is a widespread environmental contaminant.As-contaminated soils,sediments and water columns are major sources for As contamination in food chains.A recent risk assessment suggested that the arsenic pollution of food had become a major public concern in many countries in recent years.Decontamination of As polluted soils has also become one of the globally environmental concern,particularly in Southeast Asia.Rice is a typical siliciphilous plant.There is sufficient evidence suggestting that Si is an essential nutrient for achieving and maintaining high yields of rice.In this research,the effect of silicon(Si)on arsenic(As)uptake and toxicity for two 2rice plants(Oochikara sativa L.and lis1 sativa L.)was investigated. Key results can be summarized as follows:(1)Interaction between As and Si on the activities of antioxidant enzyme and MDA concentration in rice seedlings under soil culture.The results indicated that the membrane lipid peroxide level increased after As addition and decreased when spiking As-contaminated soil with Si. Compared with controls,spiking with Si and As lead to an increase of SOD, CAT,while APX activity decreased,POD activity increased first and then decreased of Oochikara sativa L.,However,in lis1 sativa L.,activities of CAT,APX decreased,and POD activity decreased first and then increased.(2)To investigation the effect of exogenous Si on the uptake kinetics of As(Ш)and As(v).Results demonstrated that both of the two rice species uptake more As(Ш)than As(v)when sufficient Si presented.Exogenous Si significantly inhibited the transportation of As into the plant roots,compared with-Si,+Si lead to a reduction of As(Ш),by 94.1%,for As(v),by 64.5% in Oochikara sativa L.,74.4%(As(Ш))and 90.2%(As(v))in lis1 sativa L. under 20μM As treatments respectively.For 100μM As treatments,the As concentrations were reduced by 92.2%of As(Ш),91.2%of As(v)in Oochikara sativa L.,and 76.1%of As(Ш)90.6%of As(v)in lis1 sativa L., respectively.(3)To investigate the influence of Si on the distribution fo As in rice plant.As could significantly decreased the above-ground biomass and grain yield for two rice species.Addition of 200mg.kg-1of Si,increased the biomass by 29.9～50.9%in Oochikara sativa L.and 47.4～50%in lis1 sativa L..After the Addition of 400mg.kg-1of Si,the biomass was increased by 83.5～145%and 97.6～204.7%at the As pollution level. As-accumulation within mature rice plants was at different degree reduced, being 8～44%in grain,21.9～44.0%in glume,5.6～58.2%in shoot,8.2～22.5%in root,As concentration ranked grain＜glume＜shoot＜root. (4)The Ultrastructure of rice leaves was investigated.We found that exposure to As,siliceous cells larger than control in two rice species. Exposure to As together with Si,in lis1 sativa L,siliceous cells larger than control,however,less than control in Oochikara sativa L.,and,the structure of stomatal apparatus was changed,the number of papicles on stomata was reduced. |
