藻类对重金属的耐性与解毒机理

Mechanisms for Heavy Metal Detoxification and Tolerance in Algae

重金属是一类具有潜在危害的重要污染物,越来越多的重金属被排入水体,对水生生态环境构成严重威胁.藻类在长期响应重金属胁迫过程中,建立起一系列的适应机制.藻类通过控制重金属的吸收、富集、转运与解毒,使不同细胞组分中的重金属维持在正常浓度范围内.这些保护机制主要包括藻细胞的某些胞外组分与重金属结合,从而减少重金属进入胞内;在重金属诱导下藻细胞可合成金属结合蛋白或多肽;重金属诱导藻细胞合成一些代谢物使其免受伤害或修复由重金属胁迫造成的损伤;藻细胞通过液泡区室化作用使重金属远离代谢;藻细胞对重金属具有排斥与排出作用.

With the development of industry and agriculture, more and more heavy metals are released into water bodies. Today, many heavy metals constitute a global environmental hazard. Heavy metals such as copper, zinc, and nickel are essential for many physiological processes yet can be toxic at higher levels. Other metals such as cadmium, mercury and lead are nonessential and potentially highly toxic. Algae possess a range of potential cellular mechanisms that may be involved in the detoxification of heavy metals and thus tolerance to metal stress. These include roles for the following: for sequesteration of metals on extracellular components that reduce metal bioavailability; for chelation of metals in the cytosol by peptides and proteins; for sequestration of metals in polyphosphate bodies; for the compartmentation of metals away from metabolic process by transporting them into the vacuole; for increasing the efflux or exclusion of metals; for producing stress proteins such as heat shock proteins that repair the stress damaged proteins; in addition, some heavy metals cause oxidative stress in algae, with the result that metal toxicity can be altered by synthesis of appropriate enzymes or metabolites counteracting metal induced oxidative stress.In recent years, some attempts to engineer the production of metallothioneins (MTs) and phytochelatins (PCs) in algae to increase metal tolerance and/or accumulation have been reported. To date, however, it is mainly the model plant species that have been genetically engineered. Phytoremediation strategies have been proposed as an attractive alternative owing to their low cost and high efficiency. The concept of phytoremediation of heavy metal contaminated water has been increasingly supported by research. And, algae have been widely used as pollution indicators in water quality determination. Thus, studies on tolerance and detoxification mechanism of heavy metal in algae have numerous ecological and public health implications.