外源钙对黑藻抗镉胁迫能力的影响

以分布广泛的沉水植物——黑藻为实验材料,对比研究了Cd胁迫和施加适宜浓度的外源Ca后,黑藻体内Cd积累、矿质营养、光合色素、可溶性蛋白、渗透调节物质、抗氧化能力以及非蛋白巯基(NP-SH)和植物络合素(PCs)的变化,以探讨Ca缓解水生植物Cd毒害的生理生化机制。结果表明:(1)Cd胁迫使黑藻体内Cd含量极显著增加,并造成明显的矿质营养失衡,主要表现为显著降低了P、K、Fe、Cu、Mn的含量,而外源Ca则削弱了黑藻对Cd的蓄积,并在一定程度上减轻了Cd胁迫所造成的矿质元素失衡;(2)Cd处理使黑藻体内叶绿素含量、叶绿素a/b值和可溶性蛋白含量大幅度下降并显著降低了黑藻的总抗氧化能力(T-AOC)和小分子保护物质[谷胱甘肽(GSH)、抗坏血酸(AsA)]的含量,而外源Ca延缓了黑藻的失绿症状,促进了可溶性蛋白的合成并提高了黑藻的抗氧化能力;(3)Cd胁迫使黑藻体内脯氨酸积累显著,而外施Ca减缓了其积累;可溶性糖变化趋势与之相反;(4)Cd胁迫诱导了NP-SH和PCs在黑藻体内的大量累积,外源Ca处理后,其增加幅度减小。以上结果说明外源Ca能通过抑制Cd的吸收,促进光合色素、可溶性蛋白和可溶性糖的合成,维持高的总抗氧化能力和抗氧化物质含量以及矿质营养平衡等途径来增强黑藻对Cd胁迫的抗性。

Effects of exogenous calcium on resistance of Hydrilla verticillata (L. f.) Royle to cadmium stress

Heavy metal contamination is an ever-increasing worldwide issue due to its toxic effects on plant metabolism and public health. Cadmium (Cd), an environmental stressor considering its toxicity, persistence and accumulation in biota, is widespread in the aquatic environment. As an essential macroelement, calcium (Ca) plays a crucial role in regulating the growth and development in plants, and also has been shown to alleviate heavy metal toxicity in many plants. Hydrilla verticillata (L. f.) Royle, a common submerged macrophyte as a potential accumulator of heavy metals, distributes universally and grows at a rapid rate. In the present study, it was chosen as the experimental material to investigate whether application of exogenous Ca enhanced the resistance of H.verticillata to cadmium stress. To address this issue, the effects of exogenous Ca application (20 mM Ca) on the Cd accumulation, mineral nutrition, photosynthetic pigments, soluble protein, osmolytes (proline and soluble sugar), antioxidant capacity, non-protein thiols (NP-SH) and phytochelatins (PCs) of H.verticillata under 0.01 mM Cd stress were analyzed. The results demonstrated that, (1) Cd stress induced a substantial accumulation of Cd and resulted in serious imbalance of nutrient elements, such as inhibiting the absorption of P, K, Fe, Cu and Mn significantly, whereas exogenous addition of Ca significantly reduced the accumulation of Cd by 50.24% and effectively reversed the Cd-induced imbalance of nutrient elements in H.verticillata. (2) Cd treatment severely reduced chlorophyll concentration, chlorophyll a/b ratio and soluble protein content, as well as the levels of total antioxidant capacity (T-AOC) and micromolecule antioxidants such as reduced glutathione (GSH) and ascorbic acid (AsA). Exogenous application of Ca markedly retarded the degradation of photosynthetic pigments and promoted the synthesis of soluble protein in Cd-treated H.verticillata. It also significantly increased the levels of antioxidant capacity of the tested plants. (3) In comparison with the control, Cd treatment induced a massive accumulation of proline significantly in H.verticillata, which was 108.29% higher than that of control. When applied with exogenous Ca, the content of proline displayed 29.39% decline compared with 0.01 mM Cd treatment. However, the effect of Cd on soluble sugar was contrary to that on proline in H.verticillata, which showed a significant reduction under Cd stress. Exogenous Ca alleviated the decline in soluble sugar level efficiently. (4) Cd exposure dramatically induced the production of NP-SH and PCs in H.verticillata compared with the control. By contrast, the addition of Ca drastically decreased the levels of NP-SH and PCs by 12.52% and 26.01% compared to the treatment with 0.01 mM Cd, respectively. In conclusion, our results have shown that the supplement of exogenous Ca in a optimal concentration effectively relieved the phytotoxicity of Cd to H.verticillata by decreasing the excessive accumulation of Cd, retarding the degradation of photosynthetic pigments, promoting the synthesis of soluble protein and soluble sugar, keeping high levels of T-AOC/antioxidants and maintaining the balance of nutrient elements, etc.