以分布广泛的高等浮水植物--水鳖为研究对象,在人工模拟的含不同浓度Ce的水溶液中培养7 d,研究了Ce在水鳖叶细胞中的分布及其结构和生理效应. 随着Ce浓度的增大,水鳖叶片褪绿程度逐渐加重,光合色素(叶绿素和类胡萝卜素)含量也显著下降. Ce对保护酶系统存在不同影响,分别在2.5和5 mg·L-1时诱导SOD和POD活性达峰值,其后逐渐下降,但POD活性都高于对照,SOD则受到明显抑制,而CAT活性一直呈上升趋势. Ce导致可溶性糖在水鳖叶片内显著积累. 可溶性蛋白含量在2.5 mg·L-1 Ce时最大,比对照增加了12.98%,其后则下降并与Ce浓度显著负相关. SDS-PAGE电泳表明,当Ce浓度大于2.5 mg·L-1后,分子量为141.9,54.8和15.8 kD的蛋白/多肽表达逐渐减弱,但同时诱导出了分子量为33.0和20.7 kD的新蛋白. 电镜观察发现Ce对叶绿体、线粒体和细胞核的结构造成明显损伤,主要是被膜或外膜破裂和核质消失. 定位结果显示Ce主要分布在细胞壁以及细胞壁和质膜之间,原生质体内部没有观察到. 结果表明,(1)Ce不仅损害了水鳖的生理活性,而且也破坏了细胞的超微结构,最终导致植物死亡. (2)光合色素是反应最敏感的生理指标. (3)在实验周期内,Ce对水鳖的半效应浓度(EC50)为10 mg·L-1,水体最大允许浓度为1 mg·L-1.
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