Simultaneous Measurement of CHL α Fluorescence and Photosynthetic O2 Evolution in Systems of Decreasing Complexity (from the Leaf to the Reconstituted Chloroplast System)

Abstract

Short term variations in the rate of photosynthesis by leaves have been frequently described. These observations, over many years, ranged from simple irregularities to dampening oscillations and were mostly observed when steady-state photosynthesis was perturbed by introducing a dark interval, a change in the gas phase surrounding the leaf, or both. In spinach and barley leaves, chlorophyll a (Chl a) fluorescence and O2 evolution have been measured simultaneously in an apparatus designed by Delieu and Walker which incorporates polarographic measurements of oxygen in the gas-phase. Irregularities in both Chl a fluorescence and oxygen signals (following re-illumination after a dark interval or when steady-state photosynthesis was perturbed by changes in the gasphase) were characterised. In high [CO2], both O2 and fluorescence can display marked dampening oscillations that are anti-parallel but slightly out of phase (a rise or fall in fluorescence anticipating a corresponding fall or rise in O2 by about 10–15 seconds), (Walker et al 1983). IRGA measurements showed that carbon dioxide uptake behaved like oxygen evolution both in the period of oscillation (about 1 minute) and in its relation to fluorescence (Fig.1).