Influence of Antimycin A and Uncouplers on Anaerobic Photosynthesis in Isolated Chloroplasts

Publisher Website
Google Scholar
Abstract
Anaerobiosis depresses the light- and bicarbonate-saturated rates of O2 evolution in intact spinach (Spinacia oleracea) chloroplasts by as much as 3-fold from those observed under aerobic conditions. These lower rates are accelerated 2-fold or more by the addition of 1 .mu.M antimycin A or by low concentrations of the uncouplers 0.3 mM NH4Cl or 0.25 .mu.M carbonyl cyanide m-chlorophenylhydrazone. Oxaloacetate and glycerate 3-phosphate reduction rates are also increased by antimycin A or an uncoupler under anaerobic conditions. At intermediate light intensities, the rate accelerations by either antimycin A or uncoupler are inversely proportional to the ATP demand of the reduction process for the acceptors HCO3-, glycerate 3-phosphate and oxaloacetate. The acceleration of bicarbonate-supported O2 evolution may also be produced by adding an ATP sink (ribose 5-phosphate) to anaerobic chloroplasts. Apparently a proton gradient back pressure resulting from antimycin A-sensitive cyclic electron flow is responsible for the depression of light-saturated photosynthesis under anaerobiosis.