The cytoplasmic pH and the vacuolar pH in root-tip cells of intact mung bean seedlings under high-NaCl stress were measured by in vivo 31P-nuclear magnetic resonance (31P-NMR) spectroscopy. When roots were incubated with high levels (100 mM) of NaCl at the control external concentration (0.5 mM) of Ca2+ ions, the vacuolar pH increased rapidly from 5.6 to 6.2 within 3 h, while the cytoplasmic pH only decreased by a mere 0.1 pH unit even after a 24-h incubation under high-NaCl conditions. The increase in vacuolar pH induced by the high-NaCl stress was diminished by an increase in the external concentration of Ca2+ ions from 0.5 mM to 5 mM. The intracellular concentration of Na+ ions in the root-tip cells increased dramatically upon perfusion of the root cells with 100 mM NaCl, and high external levels of Ca2+ ions also suppressed the in flow of Na+ ions into the cells. The vacuolar alkalization observed in salt-stressed roots may be related to the inhibition of an H+-translocating pyrophosphatase in the tonoplast, caused by the increase in the cytoplasmic concentration of Na+ ions. It is suggested that, although the vacuolar pH increased markedly under salt stress, the cytoplasmic pH was tightly regulated by some unidentified mechanisms, such as stimulation of the H+-translocating ATPase of the plasmalemma, in roots of mung bean under salt stress.
|ジャーナル||Plant and Cell Physiology|
|出版ステータス||Published - 1992 10月|
ASJC Scopus subject areas