Relations between electron transport and carbon assimilation; simultaneous measurement of chlorophyll fluorescence, transthylakoid pH gradient and O 2 evolution in isolated chloroplasts

Abstract

An apparatus is described that allows simultaneous measurement of photosynthetic O 2 evolution, chlorophyll fluorescence and the trans­thylakoid pH gradient (∆pH) in isolated chloroplasts irradiated with light sufficient to saturate photosynthesis. In intact chloroplasts, quenching of chlorophyll fluorescence due to both oxidation of the primary electron acceptor of photosystem II (Q) and formation of ∆pH was seen. The relative proportions of the two kinds of quenching varied in response to ( a ) the light intensity, ( b ) the presence of phosphoglycerate and ( c ) whether or not the chloroplasts were in the induction period or in a period of linear photosynthetic O 2 evolution. In broken chloroplasts reconstituted for CO 2 fixation, transient changes in the rates of O 2 evolution, ∆pH, the redox state of Q and chlorophyll fluorescence were observed as a result of changes in ( a ) the availability of electron acceptor as determined by the additions of NADP and phosphoglycerate and ( b ) the ratio of ATP to ADP, as manipulated by addition of ribose 5-phosphate. The changes in chlorophyll fluorescence in this system could be manipulated to show a pattern very similar to that observed in leaves.