Salt-adaptive mechanisms of K~+-channel in plasma membrane of tobacco callus

摘要

One of the detrimental effects of high salinity on plant cells is considered to be the result of an ion imbalance, particularly a high ratio of Na~+ to K~+ ions, in the cytoplasm. Such an imbalance is probably due to a great increase of entry of Na~+ions into cells and a decline in absorption of K~+ ions under high-salinity conditions. Thus, plant cells must have the ability to maintain normal ionic conditions for survival in high-salinity environment, Previous studies showed that the active ion-transport systems, such as the Na~+/K~+, Na~+/H~+ antiports and H~+ pumps, in the plasma membrane and tonoplast play an important role in the process by which plant cells maintain a high ratio of K~+ to Na~+ ions in the cytoplasm. These active transport systems could sequester Na~+ ions in the vacuole and pump them out of the plasma membrane. However, the role of passive ion-transport systems, for example ion channels, in salt-adaptive mechanisms has been studied little relatively. It was postulated that ion channels in the plasma membrane and tonoplast as well as active transport systems should play an important role in maintaining a high ratio of K~+ to Na~+ ions in cytoplasm. Recently, Murata et al. (1994) used the whole-cell patch-clamp technique to study the permeability of K~+-channels in the plasma membrane of tobacco cells in suspension after being adapted to NaCl. Adaptation of tobacco cells to salinity resulted in reduced permeability, other than selectivity of the plasma membrane to both K~+ and Na~+ ions. The results suggested that permeability of K~+-channel could play an important role in the process of salt-adaptation, Studies on the characterizations of a single channel in plasma membrane of salt-adapted cells may provide a new clue forresearching mechanisms of salt tolerance in plant.