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Research: Project 3

The multiple roles of the thylakoid proton motive force.

Energy conversion by the chloroplast involves capture of light energy and its funneling through a series of pigment-excited states, electron and proton transfer reactions, ultimately into the NADP+/NADPH and ATP/ADP + Pi couples. In this way, photosynthesis drives essentially all biochemistry in our ecosystem. Many of the intermediates in energy conversion are also quite reactive, and at sufficiently high concentrations they can destroy the photosynthetic apparatus (photoinhibition or photodamage) or even kill the plant. To prevent photoinhibition, the efficiency of the light harvesting complexes is down-regulated via the dumping of excitation energy harmlessly as heat. This, of course, lowers the efficiency of photosynthesis, but prevents photodamage. There are strong indications that the balancing of photoprotection and photochemical efficiency is important for acclimation to environmental challenges. We are focusing on the dual role of the transthylakoid proton gradient, or proton motive force (pmf), which serves a pivotal role in this balancing act, both as a key intermediate in energy conversion, driving the synthesis of ATP, as well as the trigger for initiation of NPQ. New research on the structure and function of the ATP synthase and the cytochrome b6f complex, as well as on the nature of the proton motive force, has begun to reveal how pmf balances these two key roles.