Secondary fluorescence kinetics of spinach leaves in relation to the onset of photosynthetic carbon assimilation.

When spinach leaves are re-illuminated, after dark periods of 90 s or less, an initial fluorescence peak is observed which rapidly gives way to a much lower terminal value. After 2 min or more in the dark, however, there is a secondary rise, at about 50-70 s, which then gives way, more slowly, to approximately the same low terminal value as before. The secondary rise is eliminated or disguised by feeding D,L-glyceraldehyde (a specific inhibitor of photosynthetic carbon assimilation) and by manose, 2-deoxyglucose and glucosamine, all of which are believed to sequester cytoplasmic orthophosphate. This secondary rise in fluorescence is discussed in relation to photosynthetic induction and the manner in which these compounds may modulate fluorescence by their effect on the availability of orthophosphate and their consequent impact on the adenylate status of the stroma.