Study On Copper Tolerance Of Different Cultivar Of Brassica Chinensis And It's Mechanisms

Copper and Zn sensitivity and tolerance of 15 cultivars of Brassica Chinensis were investigated. Two cultivars of B. Chinensis (huoqingcai and siyueman) were screened to study their Cu uptake and distribution using hydroponic cultures and pot experiments. Meanwhile, the effects of Cu on their germination and uptake of other elements were examined when different Cu concentrations were treated. The mechanisms of B. Chinensis responding to Cu toxicity were exploited in this paper. Main results are shown as following:Responses of different cultivars of B. Chinensis to Cu and Zn toxicity were different. Siyueman was sensitive to both soil Cu and Zn pollution, but the cultivars to tolerate Zn and Cu toxicity were different. Huoqingcai and Hkcaixin were relatively tolerant to Cu, and qibaoqingcai and aikanglhao were relatively tolerant to Zn. Statistic analysis results indicated that shoot Cu concentrations of B, Chinensis were positively correlated with their root Cu concentrations when the 15 cultivars of B. Chinensis grew in a clean garden soil. However, a high negative correlation coefficient between shoot Cu concentrations and root Cu concentrations; of B.Chinensis were obtained when they grew in a Cu-treated soil, which also means that Cu tolerant cultivars of B. Chinensis had a weak ability to transport Cu from their root to shoot, and stored much more Cu in root than that by Cu sensitive ones. On the contrary, shoot Zn concentrations of B. Chinensis were positively correlated with their root Zn concentrations when the 15 cultivars of B. Chinensis grew in a Zn-treated soil. Zinc tolerant cultivars of B. Chinensis had a strong ability to transport Zn from their root to shoot.In comparison to seed germination, root length and hypocotyl of B. Chinensis were more sensitive to Cu toxicity. 500 mol/1 Cu2+ in the culturing solution did not affect the germination of B. Chinensis, but heavily restrained the growth of root and hypocotyl. The Cu2+ concentrations to reduce the length of hypocotyl of huoqingcai and siyueman at a significant level (P < 0.05), compared to the case with 50 mol/1, were 100 nmol/1 and 200umol/1, respectively, which showed that huoqingcai was more tolerant to Cu than siyueman.B. Chinensis had a strong ability to transport Cu from their root to shoot. The more the increasing Cu concentration in culturing solution, the more Cu was accumulated in the shoot of B. Chinensis. The Cu distribution in the tissues of B. Chinensis varied with solution Cu concentration. When solution Cu concentration was 0.32 umol/1 (ck), the Cu content in the tissues decreased in the order of root > stem > peduncle > leaf; when solution Cu concentration was above 1.0 umol/1, the order was root > stem > leaf > peduncle.When the soil was treated with Cu and Zn simultaneously, huoqingcai and siyueman showed different responses. Low soil Zn concentration did not affect the uptake of Cu by B. Chinensis; however, when soil Zn concentration was 50 mg/kg, the Cu concentration in B. Chinensis decreased distinctly. Moreover, low soil Cu concentration promoted the Zn uptake of B. Chinensis.The responses of the root activity, ch!6rophyll and shoot sugar content of B. Chinensis to different solution Cu concentrations were different. The results showed that huoqingcai was more tolerant to copper than siyuema.The presence of Cu induced the production of GSH and dissolved proteins in the root of B. Chinensis. Through a gel filtration chromatography filled with Sephadex G-50, two Cu peaks appeared in the dilution diagram, which were consistent with the two protein peaks.