Cadmium Accumulation And Toxicity, And The Effects Of Exogenous Proline And Abscisic Acid On Cadmium Accumulation Of Brassica Chinensis L.

Hydroponic experiments were used to study the effects of cadmium(Cd) on the growth, photosynthetic system,antioxidant system of Brassica chinensis L.seedlings.The roles of exogenous proline and abscisic acid on cadmium accumulation in plants were also studied.The results showed that Cd at 5-100μM significantly reduced the dry weight and water content of Brassica chinensis L.seedlings.B.chinensis had a high ability of Cd uptake and accumulation,and the Cd concentrations in shoots and roots of B.chinensis increased with the increasing of Cd concentrations in the growth medium.Most of Cd absorbed by plants were accumulated in the roots.Cd treatment decreased the concentrations of iron(Fe), copper(Cu) and zinc(Zn) in shoots,and increased the levels of those elements in roots of B. chinensis seedlings.While manganese(Mn) concentrations were significantly reduced both in shoots and roots.The chlorophyll and carotenoid contents in leaves of B.chinensis were significantly reduced in 10-100μM Cd stress,Cd treatments also decreased net photosynthetic rate, stomatal conductance,intracellular CO₂ concentration and transpiration rate of leaves.In addition,with the increasing Cd concentrations,the values of Fv/Fm,φPSâ…¡,ETR and qP in leaves reduced,while the values of qN increased.These results indicated that the ability of photosynthesis of B.chinensis was decreased under Cd stress.The contents of MDA and H₂O₂,and the activities of CAT,APX,GR,POD and SOD in leaves of B.chinensis,were not significantly affected at 10μM Cd treatment,but those significantly increased under 100μM Cd stress.The contents of AsA and GSH,and the ratio of AsA/DHA and GSH/GSSG in leaves of B.chinensis,were also significantly reduced in the presence of 100μM Cd.With prolonging of the Cd treatment,the activities of CAT,APX,GR,POD and SOD appeared to increase initially and tend to decline afterwards,while the contents of AsA and GSH,and the ratios of AsA/DHA and GSH/GSSG decreased in the first and then increased. The contents of proline in leaves of B.chinensis were significantly increased under 100μM Cd treatment,and accumulated more as the stress prolonged.The activities of PDH were significantly decreased under 100μM Cd treatment,while PSCS increased.Exposure with 1-5 mM proline significantly decreased the Cd concentrations in the shoots of B. chinensis seedlings,and had no effect on the Cd concentration in roots.However, exogenous proline had no alleviation effect on biomass of B.chinensis seedlings treated with Cd.A negative correlation between the contents of proline in leaves of B.chinensis and the dry weight of shoots was found under exogenous proline stress.Treatment with 5μM ABA had no effect on dry weight of shoots and net photosynthetic rate of leaves,but reduced dry weight of roots,the leaf transpiration rate and the stomatal conductance.In the presence of 100μM Cd,exogenous ABA treatments increased the concentrations of Cd in the roots,reduced the transport of Cd from roots to the shoots,and reduced Cd concentrations in shoots.The percentage of shoot/total Cd content showed a significant positive correlation with the transpiration rate.