| The conversion of light energy into chemical energy that takes place during photosynthesis involves some of the most oxidizing and reducing, e.g. potentially damaging, chemical species known in biology. In addition, photosynthesis must respond to continuously fluctuating biochemical demands, all the while limiting the damaging consequences associated with delitarious side reactions that can occur as a result of various reactive intermediates intrinsic to the system. Such a feat requires a high degree of inherent flexibility. Modulation of qE sensitivity, the predominant process responsible for achieving variability in the harmless dissipation of excessively captured light energy over short term changes in energetic imbalance, is shown to be attributable to changes in the proton conductivity of the ATP synthase and variable storage of the proton motive force as a proton diffusion potential versus an electric field. Neither of these mechanisms modulates the ATP/NADPH output ratio of the light reactions, for which there is a fluctuating need, a feat that is suggested rather to be attributable to changes in the fractional turnover of cyclic electron flow around photosystem I. These results are discussed in the context of a novel model for regulation of the light reactions. |
