Distribution of Chlorophyll between the Two Photoreactions in Photosynthesis of the Blue-Green Alga Anacystis nidulans Grown at Two Different Light Intensities

Anacystis nidulans was grown in white light of two different intensities, 7 and 50 W ·m^?2. The in vivo pigmentations of the two cultures were compared. The ratio phycocyanin/chlorophyll a was 0.96 for cells grown at 7 W · m^?2 and 0.37 for cells grown at 50 W · m^?2. Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared, using French press treatment and fractionated centrifugation. Algae grown in the irradiance of 50 W · m^?2 showed a chlorophyll a/P700 ratio of 260, while algae grown at 7 W · m^?2 had a value of 140. Corresponding PSI-particles showed values of 122 and 109 respectively. Light-induced absorption difference spectra measured between 400–450nm indicated different ratios between cytochrome f and P700 in the two algal cultures. Enhancement studies of photosynthetic oxygen evolution were carried out. When a background beam of 691 nm was superimposed upon a signal beam of 625 nm, good enhancement was observed for both cultures. With the wavelengths 675 and 691 nm together a pronounced enhancement could be detected only in algae grown at the higher light level. Absorption spectra recorded on whole cells at 77°K revealed a small shift of the main red chlorophyll a absorption peak caused by light intensity. It is proposed that the reduction of the phycocyanin/chlorophyll a ratio in high light-grown cells is accompanied by an increased energy distribution by chlorophyll a into PSII.