Investigation Of Physiological Mechanisms Of Cadmium Accumulation And Toxicity In Pakchoi

The present study was focused on the elucidation of the mechanisms of Cd accumulation and toxicity in pakchoi(Brassica campestris ssp. chinensis (L.) Makino), based on the investigation of Cd uptake and accumulation and subcellular distribution, and effects of Cd on the growth and physiological metabolisms in pakchoi. The main results as follows:1 Genotypic differences in effects of cadmium exposure on plant growth and contents of cadmium and elements in 14 cultivars of pakchoiFourteen cultivars of pakchoi were grown in the nutrient solutions containing 0-0.5 mg/L of cadmium(Cd)to investigate genotypic differences in the effects of Cd exposure on the plant growth and uptake and distribution of Cd in pakchoi. The Cd exposure significantly reduced the dry and fresh weights of roots and shoots and total biomass. Cd concentrations in pakchoi ranged from 13.3-74.9 ug g-1 DW in shoots and from 163.1 to 574.7 ug g-1 DW in roots under Cd exposure, respectively. The considerable genotypic differences of Cd concentrations and accumulations in both shoots and roots were observed among 14 pakchoi cultivars. Moreover, Cd mainly accumulated in the roots. Cd also caused the changes of uptake and distribution of nutrients in pakchoi, and under the influence of cadmium, the concentration of potassium(K)decreased in shoot and increased in root. However, the concentrations of magnesium(Mg), phosphorus(P), manganese(Mn), boron(B), iron(Fe)increased in shoots and decreased in roots. In addition, Cd exposure resulted in an increase in calcium(Ca), sulphur(S), zinc(Zn)concentrations in both shoots and roots but had no significant effects on the whole uptake of the examined mineral nutrients except for S.2 Effects of different cadmium levels on the growth and nutrient elements in pakchoiA hydroponic experiment was carried out to determine the effects of different Cd levels on the growth and nutrient elements in two pakchoi cultivars, cv. Huqing No.l and cv. Hangzhouyoudong. Cd inhibited the growth and reduced chlorophyll contents of two cultivars. Cd was easily taken up by the plants and its concentrations in shoots and roots increased with increasing concentrations in the growth medium in both of two cultivars. Most of Cd absorbed by plants remained in the roots. Cd affected the nutrient elements absoption and transport, and the effects of Cd on the nutrient elements were dependent on the elements, plant tissue, Cd concentrations and genotypes.3 Effects on the growth and contents of cadmium and nutrients in shoot of pakchoi in soil contaminated with cadmiumA pot experiment indicated that Cd(3 mg kg-1 and 6 mg kg-1DW)did not affect or activated the growth of pakchoi, there were differences among cultivars in the effects of Cd on the growth of shoots. The concentrations and accumulations of Cd in shoots were increased with increasing Cd concentrations in the soil, and significant differences exsisted among cultivars. Cd affected shoots nutrient elements of pakchoi, and the effects of Cd on the nutrient elements were dependent on cultivar, Cd concentration and kinds of elements.4 Cadmium uptake and subcellular distribution in shoots of pakchoi and Cd-Ca interactionCd uptake, subcellular distribution and interaction between Cd and Ca were studied. The results showed that Cd was mainly kept in the roots of two cultivars of pakchoi, and the concentration of Cd in shoot of cv. Hangzhouyoudong was higher than that of cv. Huqing No.l, but the concentration of Cd in root was the opposite. The Cd concentrations of subcellular fraction increased with increasing Cd concentration in the growth medium. Cd was accumulated in shoots mainly in cytoplasm and this accumulation was fairly independent of Cd level in nutrient solution. The lowest Cd concentration was found in organelles fraction for both Cd levels tested. There were differences between two cultivars which the distribution rate of cell wall fraction in cv. Hangzhouyoudong was higher than that of cv. Huqing No.l. Ca was mainly retained in the cytopla...