The role of membrane lipids in the resistance of clapsing-leaved pondweed (Potamogeton perfoliatus L.) to excess of cadmium in water

Abstract

INTRODUCTIONThe ingress of cadmium into the environment with industrial discharges and soil washing results in severe pollution of the environment. Cadmium concentration in water may exceed the maximum permissible concentration in dozens of times. This metal gets into bodies of animals and humans along food chains, through plants, and may cause chronic and epizootic diseases (Levina, 1972;Il'in, 1991). The physiological effect of excess cadmium on plants has been studied sufficiently well. It affects water exchange and biogenesis and suppresses the growth and development of plants (Mel'nuchyk, 1990;Breckle, 1991; Drazkiewicz et al ., 2003). As cadmium ions exhibit a high affinity for thiolcontaining groups in organic molecules, they may form strong metal-thiol complexes and substitute ions of other metals linked to these groups, which results in various disturbances in cell metabolism. In response to the toxic effect of cadmium, several programs aimed at survival and adaptation are realized in plants. They include limitation of cadmium entry, activation of the systems that ensure its excretion, as well as insulation of this cation in compartments with low metabolic activity and changes of metabolism that allow the toxic effect of cadmium to be decreased or the consequences of cadmium exposure to be eliminated (Seregin and Ivanov, 2001). Realization of one or another mechanism determines the ability of plants to accumulate cadmium and resistance to its excess. Aquatic plants, macrophytes, exhibit an increased ability to accumulate heavy metals (Gavrilenko and Zolotukhina, 1989;Guilizzoni, 1991). However, the mechanisms of detoxication in them remain poorly understood compared to those of terrestrial plants. A study of changes occurring in the biochemical composition of cells under exposure to different concentrations of cadmium allows the role of cell components in the origination of resistance of aquatic plants to heavy metals to be assessed and provides for a possibility of early diagnostics of aquatic environment pollution.The goal of this work was to study the effect of cadmium nitrate within a concentration range of 1-1000 µ M on the aquatic plant clasping-leaved pondweed ( Potamogeton perfoliatus ) growing in natural environment. The level of Cd 2+ accumulation and the content of total proteins, lipids, and chlorophylls in exposed plants were measured, and the ratio between individual lipid components that determine the structure and function of biological membranes was determined. MATERIALS AND METHODSThe study was performed with Potamogeton perfoliatus L.-attached flowering aquatic plants that are widespread in freshwater bodies. These plants, growing under various conditions, are of economic importance (serve as food for fish and birds) and are involved in self-purification of water (Kokin, 1982). Reservoirs isolating 10-12 plants with roots down to the bottom were placed in a shallow area of the Saratov Reservoir overgrown with thickets of P. perfoliatus. The reservoirs with plants contained 135-140 l o...