Photophosphorylation in Chloroplasts With Varied Proton Motive Force (PMF): I. The PMF and Its Onset

Publisher Website
Google Scholar
Abstract
The transthylakoid [pea] pH difference (.DELTA.pH) following shuttered periods of actinic light from 10 ms to 30 s duration was estimated from fluorescence quenching of N-(1-naphthyl)ethylenediamine or 9-aminoacridine in phosphorylating conditions, .+-. valinomycin and .+-. nigericin. .DELTA.pH in controls varied from .apprx. 2 units after 10 ms to a maximum of 3.6-3.8 units in the steady state. The transthylakoid potential difference (.DELTA.V), defined as the average electric potential energy for protons moving from the intrathylakoid spaces to the outside, was estimated from the size of .DELTA.A520-500 (the electrochromic shift) during similar light periods, with a correction for diffuse-double-layer potentials on the outside and inside of the thylakoids. A relation between .DELTA.A520-500 and .DELTA.V followed from the assumption that the former signal during a single-turnover flash represented 30 mV between the insides of the thylakoid surfaces. On this basis, .DELTA.V rose rapidly to .apprx. 80 mV at .apprx. 25 ms, and declined thereafter, to reach a steady-state level of .apprx. 13 mV at 10-30 s. The total proton motive force (PMF) thus estimated rose to .apprx. 225 mV within 20 ms and remained constant (controls) or declined slowly (plus nigericin). With added valinomycin plus K+, the PMF rose from 120 mV at 10 ms to .apprx. 190 mV in the steady state, corresponding to low values of .DELTA.V throughout. The findings are discussed in relation to present concepts of electron transport, proton translocation and charge accumulation in chloroplast thylakoids, especially on the ms timescale, and compared with other estimates of .DELTA.pH and .DELTA.V.

This publication has 12 references indexed in Scilit: