Chlorophyll a fluorescence and light-scattering kinetics displayed by leaves during induction of photosynthesis.

Light-scattering, which can be taken as an indicator of the transthylakoid proton-gradient, and chlorophyll a fluorescence, have been followed simultaneously during re-illumination of spinach leaves at different energy fluence rates and carbon dioxide concentrations. The slow fluorescence transient ("M peak"), which has been associated with photosynthetic induction, was observed in air only at the lower fluence rates used. Data are presented that indicate that M peaks in chlorophyll fluorescence kinetics can only be observed if there is also a simultaneous transient in light-scattering and that these transients are observed when the dark period is relatively long, fluence rate relatively low, and CO2 concentration relatively high.The results are discussed in relation to the varying demands on ATP by carbon assimilation during induction of photosynthesis at different carbon dioxide concentrations and the manner in which these variations influence the quenching of chlorophyll a fluorescence.