STATE I‐STATE II TRANSITIONS IN THE GREEN ALGA Scenedesmus obliquus*

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Abstract
Illumination of dark adaptedScenedesmuscells with system II light induced a typical fluorescence transient known as the Kautsky effect. Fluorescence spectra at 77 K showed no change in transfer of light energy from system II to I during this system II illumination. By contrast, illumination of the dark adapted cells with system I light induced an increase of one of system II fluorescence bands (at – 700 nm) at 77 K and a shift of system I fluorescence to a shorter wavelength. This change was accompanied by an increase of system II activity and by a decrease of system I activity and hence can be considered to be a state II‐I transition. A mutant which lacks light‐harvesting chlorophyllalbproteins (LHCP) also showed similar changes.These results show (1) that the dark adapted state is state II. (2) that the Kautsky effect is not related to state I–II transitions, (3) that the state I–II transition preferentially affected only one of the system II fluorescence bands at 77 K. and (4) that the presence of the LHCP chromophore is not necessary for the state changes.

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