Abstract
Highly purified plasma membranes were isolated by aqueous two-phase partitioning from rice (Oryza sativa) seedling roots. The effects of lanthanum chloride (LaCl3) on the activities of lipid peroxidation, the redox system and H+-ATPase, Ca2+-ATPase of plasma membranes were studied. The lipid peroxidation of plasma membranes could be depressed by certain low concentrations of LaCl3 and enhanced by high concentrations of LaCl3, while the lipid peroxidation was also dependent on the plasma membrane protein and incubation time. The relative activity of O2 uptake of plasma membranes was inhibited by all tested LaCl3 concentrations. In contrast, the reduction rate of Fe(CN)6(3-) by plasma membranes was stimulated below 40 microM of LaCl3, but was reduced above 60 microM of LaCl3. The relative activities of both H+-ATPase and Ca2+-ATPase increased constantly from control to LaCl3 of concentration 60 microM where the activities of both enzymes were the maximum. but decreased remarkably at 80 microM LaCl3 concentrations various LaCl3 were added to culture solutions. In the other measurement case in which various LaCl3 concentrations were added directly to reaction medium and the plasma membrane vesicles only came from the control cultured rice seedling roots, the response of H+-ATPase activity to La3+ was similar to the response in culture solution. However, the La3+ concentration was only 20 microM when the activity of H+-ATPase was the maximum. In contrast to the case of LaCl3 addition to culture solution, Ca2+-ATPase activity was inhibited by all concentrations of La3+ which were added directly to the reaction medium. The above results revealed that REEs inhibited electron transfer from NADH to oxygen in plant plasma membranes, depressed the production of active oxygen radicals, and reduced the formation of lipid peroxides through plasma membrane lipid peroxidation. REEs ions also enhanced the H+ extrusion by both standard redox system and H+-ATPase in plasma membranes at certain concentrations. A possible role for the plant cell wall in REEs effects on plasma membranes was also suggested.