广东省自然科学基金项目 (No. 031510)，香港裘槎基金资助。
Natural Science Foundation of Guangdong Province (No. 031510), Hong Kong Croucher Foundation.
为了探讨外源钙对重金属镉 (Cd) 缓解南美蟛蜞菊Wedelia trilobata毛状根毒害的生理机理，采用溶液培养法研究了重金属Cd单独及其与Ca组合对南美蟛蜞菊毛状根生长、抗氧化酶超氧化物岐化酶 (SOD) 和过氧化物酶 (POD) 活性及对Cd2+吸收的影响。结果表明，Cd≤50 μmol/L时促进毛状根生长；高于100 μmol/L Cd则抑制其生长，使其侧根短小，根尖变褐或变黑。与对照相比，不同浓度Cd培养的毛状根POD活性、SOD活性和MDA含量都比对照明显提高，但高于100 μmol/L Cd培养的毛状根可溶性蛋白含量均比对照降低。与仅添加200 μmol/L或300 μmol/L Cd的毛状根相比，Cd和10~30 mmol/L Ca组合培养可促进毛状根生长，使其主、侧根变粗；提高其可溶性蛋白含量；降低其MDA含量、POD活性及SOD活性。原子吸收分光光度法测定结果表明，南美蟛蜞菊毛状根能吸收和吸附重金属Cd2+，当Cd2+浓度为100 μmol/L时毛状根对Cd2+的吸收量最大，而Cd2+浓度为300 μmol/L时毛状根对Cd2+的吸附量最大。外源加入10~30 mmol/L Ca2+可显著减少毛状根对Cd2+的吸收和吸附，并可调节其抗氧化酶活性，降低其膜脂过氧化水平而解除重金属镉对毛状根生长的抑制或毒害。
In order to study the physiological mechanism of exogenous calcium on the toxicity of heavy metal cadmium (Cd) to Wedelia trilobata hairy roots, the effects of Cd alone, and in combination with different concentrations of Ca on growth, contents of soluble protein and malondialdehyde (MDA), activities of superoxide dismutase (SOD) and peroxidase (POD), Cd2+ absorption in W. trilobata hairy roots were investigated. Cd concentrations lower than 50 μmol/L enhanced the growth of hairy roots, while concentrations higher than 100 μmol/L inhibited growth, making the branched roots short and small, and also turning the root tips brown, even black. In comparison with the control (0 μmol/L Cd), the soluble protein content in hairy roots was found to increase when cultured with 10~50 μmol/L Cd, and decrease when exposed to a cadmium concentration higher than 100 μmol/L Cd. In addition, the activities of POD and SOD activity and MDA content were significantly higher than the control. Compared to the control (hairy roots cultured without 10~30 mmol/L Ca), 100 μmol/L Cd or 300 μmol/L Cd in combination with 10~30 mmol/L Ca resulted in increased growth, causing the main root and secondary roots thicker and also an increase in soluble protein content. On the contrary, MDA content and POD and SOD activities decreased. Quantitative analysis by Atomic Absorption Spectrophotometry showed that W. trilobata hairy roots can absorb and adsorb heavy metal Cd in the ionic form of Cd2+. The maximum content of Cd2+ absorbed by the hairy roots was obtained with a concentration 100 μmol/L Cd2+ while that of Cd2+ adsorbed by hairy roots was achieved with a concentration of 300 μmol/L Cd2+. The exogenous addition of 10~30 mmol/L Ca2+ was found to reduce the absorption, adsorption of Cd2+ and the toxicity of Cd significantly. This reduction in toxicity was caused by the reduction in the absorption of Cd and decreasing the lipid peroxidation through regulating the activities of antioxidant enzymes SOD and POD in the hairy roots.