中文摘要：

本文以不同浓度Zn（0、5、10、15、20mg/L）处理荇菜（Nymphoides peltatum（Gmel.）O.Kuntze）9d,分析了Zn对叶片超氧化物歧化酶（SOD）和过氧化物酶（POD）活性、渗透调节物质（脯氨酸和可溶性糖）含量的影响,并用焦锑酸钙沉淀的细胞化学方法观察了Zn胁迫条件下叶肉细胞内Ca^2＋水平和分布的动态变化,以揭示水生植物对Zn胁迫的应答机制。研究结果表明,Zn明显抑制了SOD活性和刺激POD活性上升;脯氨酸和可溶性糖积累显著。电镜观察发现,正常条件下叶细胞中的Ca^2＋主要定位在胞间隙和液泡中,细胞基质和细胞核中较少。添加Zn后,胞间隙和液泡中的Ca2＋逐渐进入细胞质,使细胞质中Ca^2＋浓度明显升高,特别是在质膜内侧和细胞核中出现大量较大的呈圆环状的钙沉淀颗粒。作者认为与保护酶活性紊乱相比,脯氨酸和可溶性糖在荇菜对Zn胁迫的适应中发挥更大的作用。同时细胞内Ca^2＋水平的增加,可能与许多生理生化过程的改变有关,其在质膜和细胞核等局部区域的大量分布,将会引发对植物的伤害,直至最终死亡。由此可见,荇菜体内多种防御系统同时对Zn胁迫做出反应,包括诱导胁迫相关酶（POD）活性,增加渗透调节物质（脯氨酸和可溶性糖）合成或含量以及改变疏松结合钙的亚细胞分布和含量等。

英文摘要：

Zinc （Zn） is an essential microelement for normal growth and development of plants at low concentration ; however, it is also an important environmental pollutant due to anthropogenic pressure as well. In the present study, Nymphoides peltatum,a rooted-floating aquatic macrophyte, was cultivated with elevated concentration of Zn （0,5,10,15 and 20mg/L） for 9d respectively. The response of activities of superoxide dismutase （SOD） and peroxidase （POD） , osmolytes （proline and soluble sugar） to Zn stress was investigated and Ca^2＋ ultrastructural distribution in leaf cells was examined with the cytochemical method of calcium antimonate precipitation. The results indicated that Zn decreased SOD activity by 11. 46%-75.22% and the inhibition action reached significant level （R = -0. 8642, p 〈 0.05） compared with that of control; while it stimulated POD activity and increased by 2.55-3.89 fold over that of control; in response to Zn pollution, N. peltatum exhibited a enhancement in proline level and increased by 49.93%-142.31% in comparison to control; the same tendency was also recorded in soluble sugar level under Zn stress, its accumulation showed progressive increase with the rise of external Zn concentration and enhanced by 13.83% to 100.64% , respectively. Electron microscope observation showed that Ca^2＋ mainly distributed within intercellular space and vacuole, some calcium deposits could be randomly found in cytoplasmic matrix and nucleus under normal conditions, when different dose of Zn was added into the culture solution, and the calcium level in these compartments lowered while that in cytoplasm increased remarkably, espe cially bigger panicles of calcium deposits appeared at the inner aspect of plasmalemma and cell nucleus, which might be attributed to the opening of the calcium channels in plasmalemma and tonoplast and the loss of activity of the Ca^2＋ pump, this, in turn further enhanced the calcium level of cell interior. The rise of Ca^2＋ level in cytoplasm and cell nuc