铜胁迫对黄芪幼苗的生理学毒性与凹凸棒黏土的缓解作用

为探究黄芪幼苗对铜离子（Cu²⁺）胁迫的耐性机理以及凹凸棒黏土对Cu²⁺污染的缓解作用，研究了不同浓度CuSO₄（2~20mmol/L）胁迫对黄芪幼苗的生理学毒性与凹凸棒黏土的缓解作用.结果表明，2mmol/L CuSO₄胁迫使得根系Cu²⁺含量、H₂O₂（过氧化氢）含量、MDA（丙二醛）含量分别较对照显著上升1.82倍、1.04倍、2.14倍.CuSO₄胁迫浓度达8mmol/L时，根系SOD（超氧化物歧化酶）活性、根尖膜损伤程度和叶片Cu²⁺含量分别较对照显著上升1.13倍、1.12倍和2.62倍；同时，叶片PS Ⅱ（光系统II）实际光化学效率[Y（II）]、光化学淬灭系数（qP）、PSⅡ电子传递速率（ETR）和叶绿素含量较对照分别显著降低22.88%、24.44%、21.49%和28.31%，而NPQ和qN（非光化学荧光猝灭系数）则较对照分别显著上升2.35倍和1.58倍.根系POD（过氧化物酶）和CAT（过氧化氢酶）活性、可溶性糖和可溶性蛋白含量在8mmol/L CuSO₄处理下达到最高值后呈下降趋势.CuSO₄浓度为15~20mmol/L时，根系APX活性和叶片光适应下PS II潜在最大光化学效率（F_v'/F_m'），以及幼苗全株鲜重、全株干重、地下部鲜重、地下部干重较对照显著下降.在非CuSO₄胁迫条件下，基质中凹凸棒黏土的存在使得幼苗根系MDA含量较对照显著降低15.93%，但未对其它所测生理学指标产生显著影响；在20mmol/L CuSO₄胁迫条件下，基质中凹凸棒黏土的存在使得幼苗根系和叶片中Cu²⁺含量分别显著下降30.78%和23.12%；同时显著缓解了20mmol/L CuSO₄胁迫对根系活性氧水平、抗氧化酶活性、膜脂质过氧化程度、根尖膜损伤程度、可溶性蛋白和可溶性糖含量，叶片PS II光化学活性和叶绿素含量的不良影响，以及对幼苗生长的抑制作用.研究结果表明，培养基质中凹凸棒黏土的存在能够显著降低幼苗组织中Cu²⁺的生物有效性，继而缓解CuSO₄胁迫对黄芪幼苗的生理学毒性作用.

Physiological toxicity of copper stress on Astragalus membranaceus seedlings and mitigation of attapulgite clay

In order to explore the mechanism of the resistance of Astragalus membranaceus seedlings to stress of copper ion (Cu²⁺) and the mitigative effects of attapulgite clay on Cu²⁺ pollution, the physiological toxicity of CuSO₄ (2~20mmol/L) to Astragalus membranaceus seedlings and the alleviative effects of attapulgite clay on such physiological toxicity were investigated. The results showed that, after treatment with 2mmol/L CuSO₄, the Cu²⁺ content, H₂O₂ (hydrogen peroxide) content, and MDA (malondialdehyde) content of roots were significantly increased by 1.82, 1.04 and, 2.14 folds, respectively, compared to the controls. After treatment with 8mmol/L CuSO₄, the SOD (superoxide dismutase) activity in the roots, the degree of damages on root apical membrane, and leaf Cu²⁺ content were significantly increased by 1.13, 1.12, and 2.62 folds, respectively, compared to the controls. Under the stress of 8mmol/L CuSO₄, the Y(Ⅱ) (photochemical quantum yield of PS Ⅱ), qP (photochemical quenching coefficient), ETR (the rate of non-cyclic electron-transport through PS Ⅱ), and chlorophyll content of the leaves significantly decreased by 22.88%, 24.44%, 21.49%, and 8.31%. While the NPQ and qN (non-photochemical quenching) of the leaves was significantly increased by 2.35 and 1.58 fold, respectively, compared with controls. The POD (peroxidase) activity, CAT (catalase) activity, and soluble protein and sugar content of roots reached maximum at 8mmol/L CuSO₄ and decreased afterwards. CuSO₄ at the concentrations as high as 15~20mmol/L caused the significant decreases of the APX (ascorbate peroxidase) activity of roots, maximum photochemical efficiency of PS II under light adaptation (F_v'/F_m') of leaves, and fresh or dry weight of whole seedlings and below-ground parts. Under the condition without CuSO₄ stress, the presence of attapulgite clay in the growth substrate made the MDA content of roots significantly decreased by 15.93% but did not affect other physiological indicators. Under the stress of 20mmol/L CuSO₄, attapulgite clay made the Cu²⁺ content in roots and leaves significantly decreased by 30.78% and 23.12%, respectively. In addition, it alleviated the effects of CuSO₄ on the production of reactive oxygen species antioxidant enzyme activities, membrane lipid peroxidation, the degree of damage on root apical membrane, and the content of soluble protein and sugar of roots. The presence of attapulgite clay in the growth also effectively alleviated the inhibition of PS II photochemical activity, chlorophyll content, and growth of the seedlings under CuSO₄ stress. These results suggested that attapulgite clay in the growth medium could effectively alleviate the CuSO₄-induced physiological toxicity to Astragalus membranaceus seedlings through reducing the bioavailability of Cu²⁺ in seedlings.