| Seedlingds of oilseed rape (Brasssica napus L.) "Youyan No.8" and "Suyou No.l" were exposed to Cd at 0, 10, 20, 30 and 40umol/L in nutrient solution for 7d. The effects of Cd on oxidants and antioxidative enzymes in roots and leaves were investigated. Treatments with Cd induced a decrease in plant biomass, which was accompanied by an enhanced level of lipid peroxidation and an increased tissue concentration of hydrogen peroxide (H2O2) in both roots and leaves, indicating that Cd could cause oxidative stress in oilseed rape, "Suyou No.1" was more sensitive to Cd than "Youyan No.8". Catalase (CAT) activities in leaves and roots of "Youyan No.8" were higher than those in "Suyou No.1", indicating that the tolerance of oilseed rape to Cd in part resulted from the increase in antioxidant enzyme activities and thus led to the scavenging of active oxygen species.Seedlings of oilseed rape "Youyan No.8" were exposed to Cd at 0, 10, 20, 30 and 40μmol/L in nutrient solution supplied with and without sulphate for 7d. Treatments with Cd at 10-30μmol/L induced a general increase in activities of POD in both leaves and roots and CAT in leaves. Cd also induced increases in H2O2 and lipid peroxidation, but no significant differences in H2O2 and TBA-rm levels between the +Cd+S and +Cd-S treated tissues were found. Compared with +Cd+S, +Cd-S treatment resulted in the severe injury in leaves. Roots treated with +Cd+S showed a greater stimulation of non-protein thiols and acid-labile sulfide production than those treated with +Cd-S. This observation suggested that under Cd stress oilseed rape depended on more thiol production to bind the heavy metal, while the increases in POD and CAT activities seemed to be of the least importance for the defense againstCd-induced oxidation stress. Cd accumulation decreased in shoots and increased in roots due to the sulfate deficiency in nutrient solutions. The amount of Cd combined with proteins was increased after a 7-d period of sulfate deficiency.In oilseed rape roots and leaves, Cd (30μmol/L) exposure induced a massive formation of NPT, which consisted of major phytochelatins (PCs) in oilseed rape. PCs production is involved in de novo synthesis of GSH and Y -glutamylcysteine synthetase (r-ECS) is the key enzyme regulating GSH production. The transcript amounts for low-affinity sulfate transporter (LAST) and high-affinity sulfate transporter (HAST) were analyzed. RT-PCR analysis revealed that in roots of Cd-exposed oilseed rape, transcript amounts for r-ECS, LAST and HAST were increased, whereas LAST mRNA amounts appeared not to be affected in leaves. HAST is expressed specifically in roots which indicated that HAST have a specific function for the uptake of sulfate from soil. The LAST was expressed both in leaves and roots, suggesting that the putative LAST could be involved in sulfate transfer from roots to shoot as well as sulfate uptake from soils. These results indicated that changes in expression of the sulfate transporters might be involved in the demand for sulfate during the Cd stress.
|
PDF Full Text Request