Temperature-jump-induced release of hydrogen ions from chloroplasts and its relaxation characteristics in the presence of ionophores

Abstract

Temperature-jump-induced absorption changes of a bromocresol purple in chloroplast suspensions in the dark were studied. After a rapid rise in temperature (less than 10 mus), a slow absorbance decrease of bromocresol purple (t1/2 approximately 0.2 s) following a fast absorbance decrease of chloroplasts and bromocresol purple (t1/2 less than 1 ms) was observed. The slow absorbance decrease corresponds to acidification of the suspending medium, indicating H+ efflux from chloroplasts after the temperature jump. Nigericin and gramicidin D suppressed the slow absorbance change completely in the presence of 10 mM KC1, while valinomycin did not affect it. The fast absorbance change was not affected by the above ionophores. 3-(3,4-dichlorophenyl)-1,1-dimethylurea also diminished the slow absorbance change.