The electrical and chemical components of the protonmotive force in chloroplasts as measured with capillary and pH-sensitive microelectrodesстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:After impaling an isolated giant chloroplast of Peperomia metallica with a glass-insulated antimony pH-microelectrode, the potential difference between this microprobe and the external reference electrode was monitored during light activation and compared with the light-induced change of the membrane potential. The signal recorded with the pH-sensitive microelectrode during illumination was composed of a change of the membrane potential and an additional component, consisting of a slow (20–30 s) voltage increase up to +80–+120 mV with respect to the initial dark level. The superposition of two components was interpreted as being due to the location of the tip of the pH-sensitive microelectrode inside the thylakoid. The slow component in the pH-microelectrode signal reflects presumably an acidification of the internal thylakoid by 1.8 pH units at saturating light intensity. An addition of 5 mM NH4Cl to the medium resulted in a suppression of the slow component, but it also produced a significant increase in the stationary level of the membrane potential. The results are consistent with the suggestion that a decrease of a pH gradient in the presence of NH4Cl is compensated by an increase in the membrane potential. It appears that the photo-induced voltage recorded with pH-sensitive antimony electrode inside the chloroplast reflects the time-course of the protonomotive force, provided that the change of pH in the chloroplast stroma is relatively small.