Effects of external pH, fusicoccin and butyrate on the cytoplasmic pH in barley root tips measured by (31)P-nuclear magnetic resonance spectroscopy.

(31)P-Nuclear magnetic resonance spectroscopy was used to measure the cytoplasmic pH (pHc) in barley (Hordeum vulgare L.) root tips. As the external pH was raised from 4-10, pHc was found to increase from 7.44 to 7.75. The sensitivity of pHc to changes in external pH decreased with increasing external pH. Metabolic inhibition by sodium azide caused pHc to fall by 0.3 units. Addition of 10 mM butyrate resulted in a gradual decline in pHc, by approx. 0.3 units over 90 min. At a concentration of 1 mM, butyrate had no effect on pHc even after 2 h. Fusicoccin caused pHc to rise by 0.1-0.2 units. In maize (Zea mays L.) root tips, pHc was shown to have a similar sensitivity to fusicoccin. The results are discussed in relation to the regulation of pHc and the possible role of pHc in determining transmembrane electrical potential differences.