PHYSIOLOGICAL-CHARACTERISTICS AND REGULATION MECHANISMS OF THE H+ PUMPS IN THE PLASMA-MEMBRANE AND TONOPLAST OF CHARACEAN CELLS

The relationship between the physiological characteristics and changes in the activities of H+ pumps of the plasma membrane and tonoplast of characean cells is discussed. The large size of the characean internodal cells allows us to perform various experimental operations. The intracellular perfusion technique developed by Tazawa at al. (1976) is a powerful tool for analyzing the characteristics and control mechanisms of the H+ pumps (Tazawa and Shimmen 1987, Tazawa al al. 1987, Shimmen ef al. 1994). Respiration-dependent changes in the activity of the plasma membrane H+ pump are explained by changes in the supply of energy substrate. Photosynthesis-dependent changes in activities of both the plasma membrane and the tonoplast H+ pumps are explained in terms of changes in the level of inorganic phosphate in the cytoplasm. Cytoplasmic and vacuolar pHs are suggested to be controlling factors for in vivo activities of the H+ pumps. Furthermore, the membrane potential and various ions are considered to be in vivo factors that regulate the activities of the H+ pumps.