Our work developed a unique set of in vivo spectroscopic tools that have allowed us to probe the importance of 1) The effects of storage of proton motive force (pmf ) in the form of both electric field (Δψ) and pH difference (ΔpH); 2) alteration in the stoichiometry of proton pumping to electron transfer at key steps; 3) the influence of changes in the conductivity for proton efflux from the thylakoid of the ATP synthase; 4) the mechanisms of steps of the electron transfer process that pump protons; and 5) the mechanisms by which reactive O{sub 2} is generated as a side reaction to photosynthesis, and how these processes are minimized.