
TY  - JOUR
A1  - Hope, AB 
A1  - Ranson, D 
A1  - Dixon, PG 
T1  - Photophosphorylation in Chloroplasts With Varied Proton Motive Force (PMF): I. The PMF and Its Onset
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1982
VL  - 9
IS  - 4
SP  - 385
EP  - 397
KW  - 
UR  - https://doi.org/10.1071/PP9820385 
N2  - The transthylakoid pH difference (&#916;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. &#916;pH in controls varied from about 2 units after 10 ms to a maximum of 3.6 - 3.8 units in the steady state.    The transthylakoid potential difference (&#916;V), defined as the average electric potential energy for protons moving from the intrathylakoid spaces to the outside, was estimated from the size of &#916;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 &#916;A520-500 and &#916;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 &#916;V rose rapidly to about 80 mV at ~25 ms, and declined thereafter, to reach a steady-state level of ~13 mV at 10-30 s.    The total proton motive force (PMF) thus estimated rose to about 225 mV within 20 ms and remained constant (controls) or declined slowly (+nigericin). With added valinomycin + K+, the PMF rose from 120 mV at 10 ms to c. 190 mV in the steady state, corresponding to low values of &#916;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 millisecond timescale, and compared with other estimates of &#916;pH and &#916;V. 
ER  -

