Effects of Temperature on H+ Secretion and Uptake by Excised Flexor Cells during Dark-Induced Closure of Samanea Leaflets

Previous studies reveal that dark-induced closure of Samanea leaflets is accompanied by H(+) secretion from flexor motor cells. We now report that flexor tissue excised in the light, incubated in a weakly buffered bathing solution, and then darkened at different temperatures (18 degrees C-30 degrees C) acidified the medium (indicating net H(+) efflux) at all temperatures tested, but most rapidly at the highest temperature. However, pH changes reversed direction after 20 to 70 minutes; the lower the temperature, the later pH reversal occurred, and the lower the pH at reversal and after 45 minutes. These data provide a basis for the previously reported promotive effect of low temperature on dark-induced leaflet closure, assuming net H(+) and K(+) fluxes are opposite in direction. Net H(+) efflux at all temperatures tested was greater when the impermeant molecule iminodiacetate replaced small permeant anions in the bathing solution, suggesting that H(+) uptake is coupled to anion uptake, probably via a H(+)/anion symport system. When permeant anions were deficient, the amount of malate in the tissue increased, presumably by new synthesis. Malate synthesis would substitute for H(+)/anion uptake in charge balance and in providing H(+) for cytoplasmic pH regulation.