镉致背角无齿蚌消化腺组织损伤及调节消化腺和斧足的抗氧化酶活性

采用酶学和组织学方法,研究了镉(Cd)对背角无齿蚌(Anodonta woodiana)消化腺和斧足组织中超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性和组织形态结构的影响.Cd浓度设置为4.22、8.43、16.86、33.72和67.45 mg·L-1,处理时间为24 h、48 h、72 h和96 h.结果显示,与对照组相比,同一时间随着Cd浓度的增加,消化腺中SOD和CAT活性,在24 h呈现升高的趋势;96 h消化腺中SOD活性逐渐升高,差异极显著(p0.01);48 h和72 h呈现先升后降的趋势.斧足中SOD和CAT在72 h和96 h时活性升高明显,差异显著或极显著(p0.01,p0.05).Cd浓度67.45 mg·L-1处理24 h,消化腺组织细胞结构变化不明显;在48 h以后,消化管间结缔组织松散,腺体结构损伤严重,上皮细胞形态结构异常,细胞界限模糊,甚至消失;细胞膜肿胀、变形;有的细胞核碎裂、明显肿胀甚至消失,上皮细胞部分与基膜分离、脱落;斧足组织未出现显著变化和损伤.研究表明,消化腺在酶活性和组织结构上对镉的反应较快且更具规律性,而且具有明显的时间和剂量效应关系.但是,斧足对镉的胁迫反应与消化腺相比较为迟缓,说明组织之间对重金属的敏感性具有差异性.

Tissue damage and regulation of antioxidant enzyme activity by cadmium in the digestive gland and foot of freshwater mussel Anodonta woodiana

The study examined the effects of cadmium on the activities of antioxidant enzymes and tissue integrity of the digestive gland as well as foot of the freshwater mussel Anodonta woodiana. The freshwater mussels were exposed to different concentrations of cadmium (Cd) (4.22, 8.43, 16.86, 33.72 and 67.45 mg·L^-1) for 24, 48, 72 and 96 hours, respectively. Activities of superoxide dismutase (SOD) and catalase (CAT) were measured. In the digestive gland, Cd increased the activities of SOD and CAT in 24 h in a dose-dependent manner, after which the enzymatic activities in the high dose Cd group returned to the levels of that in the control group. In the foot, activities of SOD and CAT increased significantly after the mussels exposed to Cd for 72 h and 96 h. Moreover, after Cd treatment for 48 h, serious tissue damages in the digestive gland cells were observed. The damages were shown by the following features:1 the outer layer connective tissue cells was arranged loosely; 2 epithelial cells lost their normal morphology; 3 the cell boundaries were fuzzy or disappeared; 4 the cells were swollen and deformed in shape; 5 the nucleus became fragmented, obviously swollen or was not detectable at all; and 6 large spaces without cytoplasm were observed beneath the basilemma, which separated epithelial cells from the basement membrane. In contrast, there was no notably damage to the foot. Our results showed that Cd caused tissue damages to the digestive gland but not to the foot. It also increased the activities of the antioxidant enzymes, which may be a self-protection mechanism against oxidative stress. In conclusion, our results indicate that Cd can cause significant damages to the digestive gland of the animal.