LIGHT-INDUCED CHANGES IN ABSORBANCY AND FLUORESCENCE OF CHLOROPHYLLOUS PIGMENTS ASSOCIATED WITH THE PIGMENT SYSTEMS 1 AND 2 IN BLUE-GREEN ALGAE.

Abstract

1. 1. The kinetics and the difference spectra of light-induced changes in absorbancy and of changes in the near infrared fluorescence were measured in the blue-green algae Schizothrix calcicola and Anacystis nidulans . 2. 2. The action spectrum of the photooxidation of P 700 in Schizothrix was measured in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea at 2°. 3. 3. The following quantum requirements q ( λ ), for actinic wavelength λ, were estimated for P 700 and cytochrome oxidation and for P 700 reduction. Schizothrix: P 700 oxidation, q (680 m μ ) varies between 2.0 and 2.6, and q (430 m μ ) between 5.6 and 6.4; cytochrome oxidation, q (680 m μ ) = 3.0−3.5; P 700 reduction, q (680 m μ ) = 3.0. Anacystis: cytochrome oxidation, q (680 m μ ) = 2.8. The requirements per quantum absorbed by the photochemical system responsible for the reaction will be lower. The results are not inconsistent with the assumption that the true quantum requirement for the photochemical transport of 1 electron is 1 for each of the two pigment systems. 4. 4. A new “differential” flow attachment for a fluorescence apparatus was constructed by means of which small changes in fluorescence could be measured with increased precision, because the noise due to actinic light was eliminated. 5. 5. In addition to the earlier observed light-induced changes in the fluorescence of chlorophyll a 2 , a relatively small light-induced increase in red fluorescence, excited by blue light, was observed in Schizothrix calcicola, Porphyridium cruentum and Porphyra sp. It was activated by Pigment System 1, was not reversed by light of System 2, and was not associated with redox changes of P 700. The difference spectrum of this fluorescence was different from that of chlorophyll a 2 , in having a higher hump at 720 mμ.