Effects Of Silicon Alleviating Cadmium And Manganese Toxicity In Cucumber Seedlings

Cucumber(Cucumis sativus L.) is one of the most popular vegetables in China, planted widely in greenhouse and outdoor. Many place of China,the content of Cd and Mn in soil is overstandard. Excess Cd and Mn inhibited the growth and the yield of plants.including cucumber. So it is important to look for an effective way to alleviate the toxic hazard that Cd and Mn to cucumber. In this experiment, we studied the effection and the mechanism of that Si alleviate the toxic hazard that Cd and Mn to cucumber.1 A solution culture experiment was conducted to study the effects of Cd on plant growth, photosynthesis, antioxidant enzyme activity and nitrogen metabolism in cucumber seedlings. The results indicated that cucumber plant growth, chlorophyll and carotenoid contents, net photosynthetic rate (Pn) and stomatal conductance(Gs) decreased with increasing concentration of Cd, while intracellular CO2(Ci) significantly increased. The primary maximum photochemical efficiency of PSII(Fv/Fm) was significantly inhibited by high concentrations of Cd. Low concentration of Cd increased activities of catalas(CAT),guaiacol peroxidase (G-POD),superoxide dismutase(SOD),ascorbate peroxidase(APX), while high concentration of Cd dramatically inhibited their activities. With the increasing concentration of Cd,The activities of nitrate reductase(NR),glutanine synthetase (GS),glutamate synthase(GOGAT) significantly decreased.2. Application of Si significantly alleviated the inhibition of the plant growth under Cd toxicity, one aspect, which might attribute to its inhibition to Cd accumulation in cucumber plants. On the other hand, application of Si significantly increased the content of chlorophyll, the operating quantum efficiency of electron transport, the activities of photoreactive center and the activities of catalase(CAT), guaiacol peroxidase (G-POD), superoxide dismutase(SOD), ascorbate peroxidase(APX), DR and GR,application of Si also reduced the membrane lipid peroxdation, and protected structure of mitochondria and chloroplast from damage.Application of Si significantly increased the enzymes of nitrogen metabolism inculding NR, GS, GOGAT and GDH.3. Application of Si significantly increased the activities of antioxidant enzymes inculding SOD,CAT,POD,APX,DHAR and GR in cucumber chloroplast under excess Mn, decreased the accumulation of H2O2 in chloroplast . Application of Si also significantly alleviated the chlorosis symptom of cucumber seedlings under excess Mn, increased the content of chlorophyll, thus, significantly alleviated the inhibition of the maximum yield of the photosystem II photochemical reactions (Fv/Fm) and the quantum yield of photosysytem II electron transport (Ñ„PSII) under excess Mn and resulted in keeping higher photosynthesis.