Effect of External pH on the Cytoplasmic and Vacuolar pHs in Mung Bean Root-Tip Cells: A 31P Nuclear Magnetic Resonance Study

The effect of the external pH on the intracellular pH in mungbean (Vigna mungo (L.) Hepper) root-tip cells was investigatedwith the ³¹P nuclear magnetic resonance (NMR) method. The ³¹PNMR spectra showed three peaks caused by cytoplasmic G-6-P,cytoplasmic P_i and vacuolar P_i. The cytoplasmic and vacuolarpHs could be determined by comparing the P_i chemical shiftswith the titration curve. When the external pH was changed overa range from pH 3 to 10, the cytoplasmic pH showed smaller changesthan the vacuolar pH, suggesting that the former is regulatedmore strictly than the latter. The H⁺-ATPase inhibitor, DCCD,caused the breakdown of the mechanism that regulates the intracellularpH. H⁺-ATPase appears to have an important part in the regulationof the intracellular pH. (Received January 4, 1984; Accepted August 27, 1984)