Studies of cyclic electron transport in bundle sheath chloroplasts and isolation of the NDH complex from chloroplasts of Zea mays

Abstract

Methods have been available for some time to probe photosynthetic electron transfer reactions in intact plants. However, the proton fluxes that accompany these electron transfer reactions have not been studied. It can be argued that, because the DpH component of the proton motive force is the key intermediate in the down regulation of photosynthesis, the proton fluxes are even more important for understanding the responses of plants to the environment. We have developed a series of instruments and techniques with which to estimate in intact plants, the fluxes of protons through the photosynthetic apparatus, the extent of pmf and its partitioning into DpH and Dy components. This talk is an overview of results obtained with these tools and will briefly summarize our findings about the following questions. 1) Is the Q-cycle catalyzed by the cytochrome b6f complex always engaged in vivo? 2) How acidic is the lumen? 3) Does Dy contribute to pmf? 4) Does ATP synthesis limit photosynthesis? 5) How does the photosynthetic machinery balance the output of ATP and NADPH? and 6) How does feed-back regulation via lumen acidification work when photosynthesis is limited by the availability of PS I electron acceptors? 7) How large is pmf in the dark? A model for regulation of photosynthesis based on these findings will be presented. This work was supported by US Department of Energy Grant DE-FG03-98ER20299.