Abstract
In freshly prepared inside-out thylakoids, the periodicity of four of the oscillation patterns of fluorescence yield differs fundamentally from that of the oxygen yield (Delrieu, M.J. and Rosengard, F. (1987) Biochim. Biophys. Acta 892, 163–171). In this paper, further investigation of the oxygen and fluorescence patterns provides information on the origin of this discrepancy, i.e., the heterogeneity of the oxygen-evolving centers. The following results are reported. (1) The oscillation pattern of fluorescence yield was characteristic of an S 2 state, having maxima after one and five flashes, showing that the decay of the flash-induced fluorescence yield matches the deactivation of S 2 (half-time, 40 s), after a stability time of 2 s. (2) Under the conditions to be described, large changes in the oscillation pattern of the oxygen yield were observed when the fluorescence pattern remained the same. In freshly prepared inside-out thylakoids, a large miss (17.5%) was detected in the oxygen-yield pattern, even after addition of ferricyanide which could relieve the acceptor side of a large number of centers. In contrast, when the sample was stored with 30% ethylene glycol in liquid nitrogen and then thawed, the oscillation pattern of the oxygen yield was characterized by a progressive decrease in the mean value of the oxygen yield as a function of flash number, even in the presence of ferricyanide, but the true miss value did not exceed 7%. In this stored sample the oscillation patterns of the oxygen and fluorescence yield look very similar. Consequently, a functionally homogeneous population of oxygen-evolving centers was isolated, i.e., those which induce period-4 fluorescence oscillations. These centers, related to the plastoquinone pool, could be identified with the α centers. During flash illumination the reducing equivalents accumulated in the plastoquinone pool, through the secondary acceptor Q B 2−, prevent the centers from being reactivated between the flashes, and thus are responsible for the disappearance of a small number of centers after each flash of a series. The other types of center observed in freshly prepared samples, characterized by large misses, are not related to the plastoquinone pool and could thus be the β centers.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call