Limitations to photosynthesis by proton motive force-induced photosystem II photodamage.

The thylakoid proton motive force () generated during photosynthesis is the essential driving force for ATP production; it is also a central regulator of light capture and electron transfer. We investigated the effects of elevated on photosynthesis in a library of mutants with altered rates of thylakoid lumen proton efflux, leading to a range of steady-state extents. We observed the expected dependent alterations in photosynthetic regulation, but also strong effects on the rate of photosystem II (PSII) photodamage. Detailed analyses indicate this effect is related to an elevated electric field (Δ) component of the , rather than lumen acidification, which increased PSII charge recombination rates, producing singlet oxygen and subsequent photodamage. The effects are seen even in wild type plants, especially under fluctuating illumination, suggesting that Δ-induced photodamage represents a previously unrecognized limiting factor for plant productivity under dynamic environmental conditions seen in the field.