Oscillations of Photosynthesis in Intact Isolated PEA Chloroplasts in the Presence of DCMU and Antimycin A

Abstract

The study of photosynthetic induction in intact isolated chloroplasts can contribute to a better understanding of photosynthetic regulatory mechanisms. In that respect, study of induced oscillations is of prime importance because they are an indication of the presence of regulated feed-back mechanisms. Oscillations of photosynthesis in intact isolated spinach chloroplasts were observed during the induction period, in non-optimal conditions, when the transport of phosphates was limited (1,2). Oscillations in both chlorophyll fluorescence yield and the rate of O2 evolution were also induced when intact isolated pea chloroplasts were re-illuminated at 27°C (3). Under these conditions, the kinetics of fluorescence quenching and the rate of O2 evolution were dependent on the length of the dark period, concentrations of bicarbonate, orthophosphate and Calvin cycle intermediates (3). The aim of the present work is to examine the effect of a deliberate change in the ratio of noncyclic and cyclic electron transport on fluorescence kinetics during oscillations. For that purpose, addition of DCMU and antimycin A, in catalytic amounts, was used.