
TY  - JOUR
A1  - Chow, WS 
A1  - Hope, AB 
T1  - Light-Induced pH Gradients in Isolated Spinach Chloroplasts
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1976
VL  - 3
IS  - 2
SP  - 141
EP  - 152
KW  - 
UR  - https://doi.org/10.1071/PP9760141 
N2  - The fluorescence quenching of certain fluorescent, weakly ionizing amines has been used to estimate the pH difference (&#916;pH) between the intrathylakoid spaces of chloroplasts and the external medium under various conditions. The amines N-(1-naphthyl)ethylenediamine and 9-aminoacridine gave consistent and similar estimates of &#916;pH provided the concentration ranges 0.25 - 2 &#956;M and 0.05 - 0.5 &#956;M, respectively, were not exceeded. Values for &#916;pH of up to 4 units were estimated for control chloroplasts. Only a small decrease in &#916;pH was caused by FCCP and DCMU concentrations that decreased photophosphorylation rates to 10-20% of control.    The kinetics of the onset and decay of &#916;pH, and of the uptake and release of protons by the chloroplasts, were followed after the sudden application or withdrawal of actinic light. These kinetics suggest a model for the ionic relations of stripped chloroplasts with internal buffering capacity, [&#945;], and dissociation constant, Ka, as parameters. At pH8, [&#945;] is about 80 mol m-3 and Ka is 0.07 mol m-3 (pKa = 4.15).   The model is successful in predicting the relation between [H+]I (the internal proton concentration) and &#916;H+o (the light-driven uptake of protons from the external medium), as well as the size of &#916;H+o , but needs extending to deal with published experiments on the light-driven translocation of chloride ions. 
ER  -

