Effect of methyl viologen on slow secondary fluorescence kinetics associated with photosynthetic carbon assimilation in intact isolated chloroplasts
Methyl viologen in catalytic amounts induces pronounced secondary kinetics in fluorescence in intact isolated chloroplasts performing photosynthetic carbon assimilation. These transient increases in fluorescence and oscillations were associated with the induction phase of O 2 evolution in a similar manner to the transient ‘shoulder’ detected previously (Z. G. Cerović, M. N. Sivak and D. A. Walker, Proc . R . Soc . Lond . B 220, 327–338 (1984)). Experiments with the addition of antimycin A and gramicidin D demonstrated that methyl viologen induced an increased ATP production linked to pseudocyclic electron transport. The adjustment of ATP and NADPH production to meet the requirements of the reductive pentose phosphate pathway during induction is thought to be the cause of the detected transients and oscillations in fluorescence.