中文摘要：

以＂甘农三号＂紫花苜蓿幼苗为材料,在水培条件下,研究了不同浓度镉（Cd）胁迫下紫花苜蓿根、茎和叶内源一氧化氮（NO）和活性氧（ROS）的生成机制以及根系活力的变化。结果表明：在0-2.0 mmol·L^-1范围内,随着Cd浓度的增加,幼苗内NO含量呈现先升高后降低的趋势,最后可维持在略高或持平于对照的水平。幼苗内一氧化氮合成酶（NOS）活性、硝酸还原酶（NR）活性、亚硝酸根离子（NO2^-）含量和类胡萝卜素（Car）含量的变化与NO含量变化规律相似却又不全相同。NOS和NR是影响幼苗茎中NO含量的主要因素,NOS、NO2^-和NR则是影响叶中NO含量的主要因素,而根中NO含量主要与NOS活性和NO2^-含量有较大相关性。随着Cd浓度的增加,幼苗内过氧化氢（H2O2）含量、丙二醛（MDA）含量、超氧阴离子（O-2·）含量和相对电导率（REC）呈现显著升高趋势,说明高浓度的Cd处理会使ROS大量积累,细胞膜遭破坏,细胞质外流,进而引发膜脂过氧化。随着Cd浓度的增加,紫花苜蓿根系活力的变化为先升高后降低,指示了低浓度Cd处理会促进植物代谢,增强其生命力;而高浓度Cd会致使植株代谢受抑制,细胞受损害。NO和ROS的相关性不大,说明二者虽同为自由基,但它们产生和变化方式大有差别。

英文摘要：

Seedlings of alfalfa variety Medicago sativa cv. Gannong No. 3 were grown in nutrient solution with the Cd concentration between 0 to 2.0 mmol·L^-1. The generation patterns of endogenous nitric oxide（ NO） and reactive oxygen species（ ROS） in roots,stems and leaves were studied,and the changes of root activity was determined. The results showed that NO content in seedlings presented a tendency of increasing first and decreasing afterwards,finally recovering normal with increasing concentration of Cd from 0 to 2.0 mmol·L^-1. The NO content was influenced significantly by nitric oxide synthase（ NOS） and nitrate reductase（ NR） in stems,while NOS,nitrite ions（ NO2^-） and NR determined the NO content in leaves. Similarly,NOS and NO2^-had great relevance with NO content in roots. The increase of Cd concentration in solution leaded to the significantly rising of content of hydrogen peroxide（ H2O2）,malondialdehyde（ MDA）,superoxide anion（ O-2·） and relative electric conductivity（ REC） in seedlings,indicating that the stress of high Cd concentration made the ROS vast accumulated,the cell membrane damaged,and cytoplasm outflowed,further caused membrane lipid peroxidation. Besides,there was no significant correlation between NO and ROS due to their different mechanisms of generation.