| Three cultivars (No.31,shipai, and NO,49)of flowering Chinese cabbage (Brassica parachinens), spinach (Spinacia oleracea L.) and Chinese cabbage (Brassica camprestris ssp chinesis) were objected to study cadmium (Cd) adaptation diversity among the vegetables and corresponded mechanisms. The growth response, absorption of Cd by the plants, accumulation and distribution of Cd in plants, and membrane stabilization of plant under Cd stress were investigated in present study through hydroponic culture method to provide a support on reasonably distribution in vegetable production and the breeding of Cd-resistant vegetables. The results showed as follows:After exposure of 30-d-old vegetablesto Cd (1,3,6μg·mL-1) solution for 5 d, the content and accumulation of Cd in vegetables, the leaf electrolyte leakage and the content of MDA in the leaves increased significantly, while both the biomass of the vegetables and the chlorophyll in the leaves of spinach and Chinese cabbage decreased observably. These results demonstrated that Cd resulted in the cell membrane damage of the vegetable and the inhibition of vegetable growth.The response of vegetables to Cd stress had difference obviously. The depressing of biomass of flowering Chinese cabbage by Cd in No.31 was the most significantly, followed by shipai, and then No.49. After the treatment with Cd (6μg·mL-1), the leaf electrolyte leakage and the content of MDA in the leaves followed as the same as order in biomass. The relative biomass of spinach was higher than that of Chinese cabbage in Cd (1, 3μg·mL-1) solution. Furthermore, after 5-d treatment with Cd (3μg·mL-1), both the leaf electrolyte leakage and the MDA content in leaves of Chinese cabbage were greater than that in spinach, while leaf chlorophyll in the leaves was opposite. The results indicated that No.49 flowering Chinese cabbage was Cd-resistant cultivar, while spinach was better tolerance to Cd than Chinese cabbage.Both Cd content and Cd accumulation in vegetables increased with the Cd treatment dose. The Cd accumulation in different cultivars of flowering Chinese cabbage followed by No.49, shipai, No.31 in order, while lower content and accumulation of Cd were found in spinach than those in Chinese cabbage. These results demonstrated that the adaptability to Cd stress environment in NO.49 flowering Chinese cabbage was resulted from stronger resistance to Cd in vegetables, while Cd exclusion by plants was a mechanism for spinach to adapt Cd-stress environment.After the treatment with Cd, the order of Cd content in the organs of three cultivars of flowering Chinese cabbage, spinach and Chinese cabbage was as follow: roots>stems >leaves. The distribution of Cd in the organs and cell fractions of plants varied among vegetables. No.49, which is a high adaptive cultivar of flowering Chinese cabbage, could depress the entrance of Cd to root organelle but enhance Cd distributing in vacuole and transport tissue of stems. Further more, No 49 cultivar could avoid Cd entrance to soluble fractions and organelle of leaf cells, while those were in opposition for No.31, Cd sensitivity cultivar of flowering Chinese cabbage. In other way, the distribution rate of Cd in stems and leaf cell fractions was stable for spinach under Cd stress, but increasing in soluble fractions was found in Chinese cabbage, Cd-sensitive species of vegetable. All of these results suggested that the resistance to Cd entrancing soluble fractions of cells and organelles of leaves was another important mechanism for Cd adaptation in No.49, while stable Cd-distribution in different organs and cell fractions was Cd-resistance mechanism for spinach .Relative activity of SOD and POD in flowering Chinese cabbage leaves increased after the treatment with Cd (1, 3, 6μg·mL-1). The order of the relative activity of POD and CAT was followed in order: No.49>shipai>No.31. Relative activity of POD and CAT in spinach leaves increased gradually after Cd treatment, while relative CAT activity for Chinese cabbage decreased. Moreover, the relative POD and CAT activity of leaves in spinach was higher than that in Chinese cabbage. These indicated that under Cd stress the effective anti-oxidized system in No.49 and spinach was also a reason for plants resisting Cd toxicity.
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