微囊藻毒素对陆生植物的污染途径及累积研究进展

Abstract

微囊藻毒素(Microcystins,MCs)是全世界范围内普遍存在、且随着水体污染的加剧而在自然环境中大量积聚的蓝藻毒素之一,对多种生物有着严重的毒性作用。MCs在生物体内富集并通过食物链传递,对人类健康造成威胁。近些年,MCs对陆生植物的毒害作用及累积研究尤为引人关注,取得了一批重要的研究成果。MC-LR(L为亮氨酸)和MC-RR(R为精氨酸)是淡水水体中普遍存在且危害较大的两种MCs异构体。针对这两种毒素,重点介绍其对陆生植物的污染途径、毒性作用及其在作物体内的累积量,对今后的研究进行了展望。;The occurrence of toxic cyanobacterial blooms in eutrophic lakes, reservoirs and recreational waters has become a worldwide problem. In the last 20 years, the occurrence of toxic freshwater blooms of cyanobacteria has been frequently reported in many water bodies in China, such as Taihu Lake, Chaohu Lake and Dianchi Lake. Some of the cyanobacterial genera such as <em>Microcystis</em>, <em>Anabaena</em>, <em>Nostoc</em> and <em>Aphanizomenon</em> can produce a wide range of potent toxins, including a family of hepatotoxins called microcystins (MCs) that comprise the most frequently encountered MCs in freshwater. Microcystins are produced mainly by freshwater cyanobacterial blooms, which produce mass populations in water bodies commonly produce a range of toxic effects. Some reports suggest that the incidence of human primary liver cancer in the eastern region of China is related to the presence of MCs found in drinking water. The toxic effects and mechanism of MCs on animals have been well studied. Microcystins can potently inhibit protein phosphatase type-1 and 2A after the toxin was transported to cytoplasm by the bile acid transporter in the cell membrane of hepatocytes. Microcystins can also induce the oxidative stress <em>in vitro</em> cultured rat and fish cells. In recent years, the toxic effect of MCs on terrestrial plants and their bioaccumulation became an attracting area of research, which had made quite a number of important achievements. The growth inhibitory phenomenon of MCs on plant was firstly observed in <em>Sinapis alba</em>. Thereafter, many reports demonstrated that the growth, development and physiological pathway of plants could be affected by MCs. The commonly accepted toxic mechanism of MCs on plants is that MCs inhibit protein phosphatase type-1 and 2A. At present, there has some evidence suggesting that oxidative stress might be involved in the toxicity of MCs on plants. It was reported that the activity of peroxidase (POD) and superoxide dismutase (SOD), two of antioxidant enzymes, were changed in rape (<em>Brassica napus</em>) and rice (<em>Oryza sativa</em>) seedlings when exposed to MCs. Recently, some attentions also have been paid to the toxic effects of MCs irrigated with water contained cyanobacteria on plants. The effect of irrigation with contaminative lake water containing a variety of MCs on accumulation of toxins, or toxin metabolites, and growth in plants (e.g. ryegrass, clover, rape, and some vegetables) was investigated by many studies via field experiment or indoor test. Microcystins could accumulate in living organisms and transfer through the food chain, consequently threatening human health. These problems are beginning to be addressed via water quality management programs in some countries. Hazard characterization and risk assessment of cyanobacterial toxins in relation to human health requires the identification of exposure routes. Among more than 80 isomers of MCs, MC-LR (L indicated leucine) and MC-RR (R indicated arginine) are two common and dangerous ones existing in freshwater bodies. This study was aimed at MC-LR and MC-RR, including stressing their pollution ways to terrestrial plants, toxic effect and bioaccumulation amount in plants. Furthermore, the research directions in the future, such as the transfer and degradation mechanism of MCs in soils, dose-respones relationship of MCs and its ecological risk in agriculture were discussed.