广东鲂幼鱼对铜、镉胁迫的氧化应激响应及其指示意义

Responses towards Oxidative Stress of Juvenile Guangdong Bream Megalobrama terminalis to Cu^(2+) and Cd^(2+) Exposure

广东鲂(Megalobrama terminalis)是具重要经济价值的珠江流域特有鱼类,已列入国家级水产种质资源保护品种。近年来,随着河流固有生境持续破坏,重金属等水体污染问题不断加剧,以广东鲂为代表的当地特有鱼类资源急剧下降。文章以铜、镉暴露对广东鲂幼鱼48 h的半致死浓度值LC50暴露浓度强度为1个毒性单位(TU)为基准,以室内静水实验法研究了铜、镉离子在低效应浓度、中效应浓度、高效应浓度(分别对应于0.01 TU、0.03 TU和0.11 TU)胁迫对广东鲂幼鱼的氧化应激效应,以期找出适宜的生物标记物,完善珠江水域污染评价与预警体系。结果显示,广东鲂幼鱼MDA、GSH、T-AOC、SOD和CAT(以Pr计)随暴露浓度及暴露时间发生变化,其范围分别在1.08~7.34 nmol·mg-1、0.42~22.82 mg·g-1、0.10~1.32U·mg-1、2.45~13.24 U·mg-1和0.01~0.09 U·mg-1之间。其中,GSH、MDA和T-AOC在铜、镉暴露后第1天迅速响应至高值,相应的各浓度处理组明显高于对照组。曲线回归结果显示,GSH与暴露浓度c(以TU量计)之间呈显著的二次曲线关系,拟合方程为GSH=-2112(c-0.084)2+18.1,r=0.847,n=10,P=0.012,暴露浓度阈值为0.084 TU。SOD和CAT则在暴露后第4天响应至高值。曲线回归结果显示,SOD与c及CAT与c之间均呈显著的二次曲线关系,拟合方程分别为SOD=-2073(c-0.059)2+14.3,r=0.840,n=10,P=0.014;CAT=-21.2(c-0.056)2+0.102,r=0.877,n=10,P=0.006,相应的暴露浓度阈值分别为0.059 TU和0.056 TU。与暴露浓度呈显著的二次曲线关系的各指标中,GSH响应最为迅速,SOD和CAT的响应最为灵敏,加之SOD与CAT相关性极强,表明GSH、SOD和CAT这3种氧化应激指标可作为珠江流域水体污染的潜在生物标记物。

Guangdong bream （Megalobrama terminalis） is an endemic fish species with great economic value in the Pearl River watershed. It has been listed in the National Aquatic Germ-plasma Resources Conservation Project in China. However, as the natural habitats of the fishes is continuously destroyed, and heavy metals and other water pollution problems are aggravated, many endemic fish resources represented by Guangdong bream is sharply declined in recent years. In this study, a series static bioassay were carried out on Guangdong bream juvenile in order to find the appropriate biomarkers to improve the evaluation and early warning system for pollution in the Pearl River watershed. The fish were exposed to the separated or combined Cu2＋ and Cd2＋ at low, medium, and high toxic concentrations responding to 0.01 TU, 0.03 TU and 0.11 TU, respectively（1 TU, toxic unit is the 48 h LC50 of Cu2＋ or Cd2＋ in Guangdong bream juvenile） for 14 days. The substances and enzymes towards to oxidative stress including malondialdehyde （MDA）, glutathione （GSH）, superoxide dismutase （SOD）, catalase （CAT）, and total antioxidant capacity （T-AOC） were determined on day 1, 4, 7, and 14 during the exposure period. The results show that MDA, GSH concentrations and T-AOC, SOD and CAT activities （all of the five substances were calculated by protein content, similarly hereinafter） in the juvenile bream were within the range of 1.08~7.34 nmol·mg-1, 0.42~22.82 mg·g-1, 0.10~1.32 U·mg-1, 2.45~13.24 U·mg-1and 0.01~0.09 U·mg-1, respectively, and varied according to exposure time and exposure concentrations.. The concentrations of GSH, MDA and the T-AOC activity in the fish were significantly increased after Cu2＋ and Cd2＋ exposure, and rapidly reached the peak on day 1. The relationship between GSH level and the exposure concentration （c, in the unit of TU） of Cu2＋ and Cd2＋ were well fitted with the conic curves GSH=-2112（c-0.084）2＋18.1, r=0.847,n=10,P=0.012 on day 1, and the toxic concentration threshold was calculated as 0.084 TU. The other two substances SOD and CAT activities were also significantly elevated after Cu2＋ and Cd2＋ exposure and reached the peak on day 4. The relationships between SOD, CAT activities and the exposure toxic units of Cu2＋ and Cd2＋ were also well fitted with the conic curves SOD=-2073（c-0.059）2＋14.3,r=0.840,n=10,P=0.014; CAT=-21.2（c-0.056）2＋0.102,r=0.877,n=10,P=0.006, respectively on day 4, and the thresholds concentrations were 0.059 TU to SOD and 0.056 TU to CAT. In summary, GSH was the most rapid response substance to the exposure, while SOD and CAT activities were more sensitive to the exposure and more correlated to each other. This study suggests that GSH, SOD and CAT in the juvenileM. terminaliscould be developed as potential biomarkers for water pollution in the Pearl River watershed.