On the Primary Nature of Fluorescence Yield Changes Associated with Photosynthesis

摘要

Absorbance changes of C-550 and cytochrome b559, and fluorescence-yield changes were measured during irradiation of chloroplasts at -196°. The photo-reduction of C-550 proceeded more rapidly than the photo-oxidation of cytochrome b559, and the fluorescence-yield change had similar kinetics to the cytochrome b559 change. The fluorescence yield of chloroplasts exposed to a 16-μsec flash at -196° did not increase during the flash, but increased in the dark after the flash. Both of these experiments indicate that the fluorescence yield follows the dark reduction of the primary electron donor of Photosystem II, not the photoreduction of the acceptor. This explanation would also account for the recent results of Mauzerall [Proc. Nat. Acad. Sci. USA (1972) >69, 1358-1362] showing that the fluorescence yield of chloroplasts at room temperature requires about 20 μsec to reach a maximum after a very brief flash.