Oscillations in levels of metabolites from the photosynthetic carbon reduction cycle in spinach leaf disks generated by the transition from air to 5% CO2

Abstract

Variations in the endogenous concentrations of leaf metabolites were measured during the transition from steady-state photosynthesis in air to that in 5% CO2, 21% O2. The transition in the CO2 supply to the leaf caused a pronounced oscillation in the overall rate of photosynthesis, as indicated by chlorophyll a fluorescence, which was accompanied by large changes in the levels of metabolites associated with carbon metabolism. A dramatic increase in the ATP concentration occurred immediately following the gas transition and was maximal at the point at which the chlorophyll a fluorescence showed a transient decrease. During the first large fluorescence increase the ATP level rapidly declined. Oscillations in the level of 3-phosphoglycerate were the most pronounced of the photosynthetic metabolites measured. These accompanied the oscillations in chlorophyll a fluorescence which showed an inverse relationship to the oscillations in ATP/ADP ratio. The ribulose 1,5-bisphosphate concentration showed a small increase following the gas transition but subsequently fell much lower, enforced by the high level of CO2 supplied. Less pronounced oscillations in the intracellular concentrations of fructose 1,6-bisphosphate, fructose 6-phosphate, glucose 6-phosphate, and triose phosphate were also observed.