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.