Effect of Temperature and External pH on the Cytoplasmic pH ofChara corallina

Abstract

Cytoplasmic pH (pHc) in Chara corallina was measured (from f14C]DMO distribution) as a function of external pH (pH0) and temperature. With pHc near 7, pHc at 25 °C is 7-80; pHc increases by 0-005 pH units °C_1 temperature decrease, i.e. pHc at 5 °C is 7-90. With pH0 near 5-5, the increase in pHc with decreasing temperature is 0-015 units °C-1 between 25 and 15 °C, but 0-005 units °C_1 between 15 and 5 °C. This implies a more precise regulation of pHc with variations in pH0 at 5 or 15 °C compared with 25 °C. The observed dpHJdT is generally smaller than the -0-017 units °C-1 needed to maintain a constant H+/OH, or a constant fractional ionization of histidine in protein, with variation in temperature. It is closer to that needed to maintain the fractional ionization of phosphorylated compounds or of COj-HCOj. The value of dpHjdT has important implications for several regulatory aspects of cell metabolism. These include (all as a function of temperature) the rates of enzyme reactions, the A//H+ (at the plasmalemma (and hence the energy available for cotransport processes), and the mechanism for pHc regulation by the control of bidirectional H+ fluxes at the plasmalemma.