Simultaneous Measurement of Oscillations in Oxygen Evolution and Chlorophyll a Fluorescence in Leaf Pieces

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Abstract
In spinach (Spinacia oleracea) and barley (Hordeum vulgare) leaves, chlorophyll a fluorescence and O2 evolution were measured simultaneously following re-illumination after a dark interval or when steady state photosynthesis has been perturbed by changes in the gas phase. In high CO2 concentrations, both O2 and fluorescence can display marked dampening oscillations that are antiparallel but slightly out of phase (a rise or fall in fluorescence anticipating a corresponding fall or rise in O2 by about 10-15 s). Infrared gas analysis measurements showed that CO2 uptake behaved like O2 evolution both in the period of oscillation (about 1 min) and in its relation to fluorescence. In the steady state, oscillations were initiated by increases in CO2 or by increases or decreases in O2. Oscillations in O2 or CO2 did not occur without associated oscillations in fluorescence and the latter were a sensitive indicator of the former. The relationship between such oscillations in photosynthetic C assimilation and chlorophyll a fluorescence is discussed in the context of the effect of ATP or NADPH consumption on known quenching mechanisms.