Abstract
The basic electrical plasma membrane characteristics of leaf cells from the seagrass Zostera marina L. have been investigated with respect to its primary transport system and its Na + /K + selectivity. In natural seawater Z. marina exhibits a membrane potential of -156 ± 10 mV. The phytotoxin fusicoccin stimulates H + extrusion and hyperpolarizes the plasma membrane. Ouabain, an inhibitor of the mammalian Na + /K + -ATPase did not depolarize the plasma membrane of Z. marina. Both flushing the leaves with CO 2 and 'light off' acidified the cytoplasm and hyperpolarized the cells. It is suggested that a H + -ATPase rather than a Na + -ATPase is the primary pump in Z. marina. In the presence of cyanide plus salicylhydroxamic acid the membrane potential changed to -64 ± 11 mV. This so-called diffusion potential was sensitive to external [K + ] from 0.05 to 0.5 mM in the presence of 0.5 M Na + and revealed a relative permeability P K+ /P Na+ of 303. We suggest that this high ratio is the basic adaptation which permits Z. marina to grow in high [Na + ] conditions and to exhibit a rather negative resting potential. Since amiloride, an inhibitor of the nH + /Na + antiporter, hyperpolarized the plasma membrane, it is suggested that this transporter could be present in the plasma membrane of Z. marina acting as an overflow valve for Na + which leaks into the cell.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have