Light-driven reversible transformation of chlorophyllide Psub(696,682) into chlorophyllide Psub(688,678) in illuminated etiolated bean leaves

Etiolated leaves were first illuminated by one flash provided by a Helium-Neon laser in order to reduce all protochlorophyllide into chlorophyllide. They were then kept in darkness for 2 min; during that interval the shift from chlorophyllide Psub(688,678) to chlorophyllide Psub(696,682) occurred. When such leaves were exposed for a few minutes to an intense continuous red laser-light at room temperature, a large fluorescence transient was observed, as well as a reversible shift in the room temperature fluorescence spectrum. By freezing the leaves after various times of exposure to light, absorption and fluorescence spectra at 77 K were recorded. They show that light causes a dark-reversible transformation of Psub(696,682) back to Psub(688,678). The room temperature fluorescence transient can be explained by the different fluorescence yield of the two chlorophyllide species. An approximate action spectrum has been established which indicates that the photoreceptor in that photoreaction is Psub(696,682) itself. The reaction is markedly slowed down when the temperature is lowered to +30C. (Auth.)