Reducing power generated in the second photoact of photosynthesis.

Photosyntlhesis is presently conceived as a cooperation between 2 photoacts, photosystem I generating a strong reductant and a weak oxidant, photosystem II generating a srong oxidant (yielding O2) and a weak reductant. Coupling between the 2 photosteps presumably occurs between the weak reductant and the weak oxidant, a step possibly generating high energy phosphate. A number of means are available to observe photosystem I separated from photosystem II. The latter system can be inhibited by poisons like DCMU3 or not sensitized by usinlg long wave radiation. Unfortunately, no such means have been available to observe photosystem II isolated from photosystem I. Of great importance, therefore, seems the isolation by Dr. NT. Bishop of a Sccnedesnuts mutant (no. 8) which appears to be devoid of photosystem I (1). Dr. Bishop kindly has put this mutant at our disposition. Following some spectroscopic observations reported earlier (8), we have investigated in more detail the photosynthetic electron transport in this mutant. This paper is mainly concerned with the reducing power generated by the light in photosysteni II.