Light-induced absorbance changes of cytochromes and other pigments in pea chloroplasts and chloroplast fragments: I. The effect of red and near far-red actinic light and of ruby laser flashes

Abstract

Light-induced spectral changes in the region 540 to 580 nm were studied by means of dual-wavelength differential spectrophotometry and by a Q-switched ruby laser flash technique in intact chloroplasts, swollen chloroplasts, and chloroplast fragments. In intact chloroplasts the major spectral components are attributed to cytochrome f (photo-oxidized), an unknown pigment with a broad band (decrease in absorbance) centered around 572 nm, and possibly a b-type cytochrome (photo-oxidized). In swollen chloroplasts and chloroplast fragments the photo-oxidation of cytochrome f is modified, cytochrome b 6 is photoreduced, and the P-572 response is diminished. The changeover from the intact to the swollen response is brought about by the addition to the suspension medium of certain cations of which sodium, with an effect beginning at about 10 m m, is the most potent. Laser flashes onto dense suspensions of high-salt chloroplasts produced fast ( t 1 2 , 300 μsec) oxidation of cytochrome f, even in the absence of ascorbate and slower ( t 1 2 , 5 msec) reduction of a b-type cytochrome. However, it is suspected that cations leaking from the chloroplasts in these dense suspensions modified the cytochrome responses.