生菜对镉胁迫的生理响应及体内镉的累积分布

为了揭示生菜对镉毒害的响应,采用种子发芽和营养液基质栽培试验,从种子萌发、生理特性及镉的累积、分布等方面研究镉胁迫对生菜的影响。结果表明,镉胁迫显著降低种子发芽势,1 mg·L~(-1)镉胁迫显著提高发芽率,而其他浓度显著降低发芽率。基质栽培试验中,50、100 mg·L~(-1)镉对生菜生物量有显著促进作用,不同浓度镉对根冠比无显著影响;低浓度(5 mg·L~(-1))镉显著促进叶绿素总量和叶绿色a含量;高浓度镉(10~200 mg·L~(-1))胁迫显著降低叶绿素总量、叶绿素a、叶绿素b含量。镉浓度为5 mg·L~(-1)时,丙二醛(MDA)含量显著增加,随着镉浓度进一步提高,除20 mg·L~(-1)时MDA出现显著下降外,其他处理与对照无显著差异;随着镉浓度增加,超氧化物歧化酶(SOD)活性显著降低,过氧化氢酶(CAT)活性先升高后下降,过氧化物酶(POD)活性逐渐升高。生菜地下部分和地上部分镉含量均随镉浓度的升高而显著增加;且在同一镉浓度下,地下部分镉含量显著高于地上部分;随镉浓度的升高,地上部分的生物富集系数逐渐下降,而地下部分呈现先升高后下降的趋势,转运系数则显著下降。随着添加镉浓度的增加,地下部分亚细胞中各部分镉含量呈现指数累积趋势,而地上部分亚细胞中镉含量呈直线累积趋势;同一镉浓度下,地上部分亚细胞中的镉含量远低于地下部分;地下部分镉在亚细胞中的分布特征为细胞壁可溶组分细胞器,地上部分为细胞壁、可溶组分细胞器。因此,地下部分(根系)的滞留作用和细胞壁的固持是生菜应对镉胁迫的重要机制。

Physiological adaptations to cadmium stresses and cadmium accumulation in lettuce

Cadmium(Cd)pollution is a major environmental factor limiting crop growth. Lettuce is an important vegetable for human consumption and the physiological responses of lettuce to Cd stress are not well understood. In the present research, the effects of Cd stresses on lettuce growth were tested using seed germination and substrate culture experiments. The results showed that Cd stress significantly reduced the germination potential of lettuce seeds; the seed germination rate of lettuce was significantly inhibited by Cd stress, except in the 1 mg·L^-1 Cd treatment. Lettuce biomass(fresh and dry weight)was significantly increased in the 50 mg·L^-1 and 100 mg·L^-1 Cd treatments, while Cd stress had no significant effect on the root/shoot ratio. In contrast to 10~200 mg·L^-1 Cd, with 5 mg·L^-1 Cd the concentrations of total chlorophyll, chlorophyll-a and chlorophyll-b were significantly higher than that of the control. Malondialdehyde(MDA)concentration was markedly increased with 5 mg·L^-1 Cd and was unchanged with further increases of Cd stress, except for a significant decrease with 20 mg·L^-1 Cd. Superoxide dismutase(SOD)activity decreased significantly and catalase(CAD)activity increased after inhibition with the increase of Cd stress, while peroxidase(POD)activity increased gradually. Cd concentrations in the underground and upper parts of lettuce increased with Cd concentration in the substrate, and the former was always higher than the latter for the same Cd concentration in the substrate. With increasing Cd concentration in the substrate, Cd enrichment coefficients decreased gradually in the upper parts of lettuce and decreased after an initial increase in the underground parts of lettuce, while Cd transport coefficients always decreased. Subcellular Cd concentrations in the underground parts of lettuce increased exponentially with increasing Cd concentration in substrate and increased linearly in the upper parts, while the former was always higher than the latter. Subcellular Cd distributions occurred in the following sequence:cell wall > soluble part > organelle in the underground parts, and cell wall and soluble part > organelle in the upper parts. Therefore, retention in the underground part(root system)and immobilization of the cell wall are important for adaptation to Cd stresses in lettuce.