Effects And Mechanism Of Exasa On The Growth Of Rapeseed Exposed To CD

Cadmium pollution results in seedling damage, causes oxidative stress, disruptes their metabolism and decreases seedlings'resistance and ultimately affects growth and yield of oilseed rape. In order to probe into the mechanisms of ExAsA mitigation effects on Cd damage in oilseed rape (Brassica napus L.), Zhongyouza 7 was used as experiment material to obtain the optimum applying concentration of ExAsA by method of water culture. Relief effects of ExAsA to the growth and yield of oilseed rape under stress of Cd were investigated by water and soil pot cultivation experiments in Qinyou 7. The results will provide theoretical basis for ExAsA applied in the the actual production of oilseed rape.1. The results showed that growth inhibition of rapeseed was increased with increasing Cd concentration, the roots and shoots biomass decreased; seedlings became short, the leaf number and leaf area of single plant were reduced; root and rootneck were shorten; roots vigor failed; chlorophyll contents in their leaves decreased, while free proline and malondialdehyde contents increased; the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) descended. The inhibition rate "50%" could be regarded as critical concentration. It was found that all values were in the range of 4-9 mg·L-1, about 5 mg·L-1. So the critical concentration of Cd in hydroponic culture was estimated to be 5 mg·L-1.2. It is showed that 25mg·L-1Cd treatment damaged the growth of seedlings, chl.a and b content decreased significantly, the significantly reduction in stomatal conductance (Gs) and increment of intracellar CO2 (Ci) indicated that this reduction in net photosynthesis was due to the non-stomatal restriction, with the remarkable decrease in transpiration. Measurement of chlorophyll fluorescence indicated that actual quantum yield of PS II (F PS II), electron transport rate (ETR) and photochemical efficiency of PS II (Fv/Fm) reduced significantly in leaves, with a markedly increace in minimum fluorescence levels of dark-adapted state(Fo). In this research, the alleviative effect of 0.25mmol·L-1 AsA under 25mg·L-1 Cd treated seedlings was studied, rape seedlings treated were used to determine the biomass, height, root architecture (root length, root area, root volume and average diameter), chlorophyll content, carotenoid,AsA and GSH content, malondialdehyde content and relative conductivity, SOD activity, POD activity, CAT activity, protein content in leaves.The results indicated that the 25mg·L-1 Cd treatment damage the growth of seedlings, chl.a and b content, carotenoid content, SOD, POD, CAT activity first increase then decrease significantly, protein content decrease significantly, there is significant increase in GSH, and MDA content and relative conductivity increase significantly. Good alleviative effects of 0.25mmol·L-1 AsA on Cd intimidation was shown, rape seedlings biomass, chlorophyll content, carotenoid GSH content, SOD activity, POD activity, CAT activity and protein content increase significantly, with the decrease in MDA content and relative conductivity. O.25mmol·L-1 AsA can expedite the transfer of electron and activate PS II resulting the promotion of photosynthesis compared to 25 mg-L-1 Cd treatment, Pn,Gs, Tr,φPSⅡ, ETR and Fv/Fm increased significantly with remarked reduction in Ci and Fo.3. The results indicated that there is no significant difference in the four treatments in physiological characters. Good alleviative effects of 0.25mmol·L-1 AsA applied both and only after winter under Cd intimidation was shown, plant biomass, chlorophyll and carotenoid content, SOD activity, POD activity, CAT activity and protein content increased significantly, with the decrease in MDA content.0.25 mmol·L-1 AsA applied both had the best agronomic traits and highest yield, and AsA applied had the worst alleviative effects before winter only.