SPECTRAL CHARACTERIZATION OF PHOTOOXIDATION PRODUCTS FORMED IN CHLOROPHYLL SOLUTIONS AND UPON PHOTODAMAGE TO THE CYANOBACTERIUM ANABAENA-VARIABILIS

To detect and characterize products of chlorophyll degradation, chloro phylls were photobleached in methanol solutions and compared with thos e occurring in vivo upon photodamage to the cyanobacterium Anabaena va riabilis. In chlorophyll a solutions, visible light induced the format ion of photoproducts with an absorption peak at 410-420 nm and a broad long-wavelength absorption band extending to 750 nm. Several photopro ducts with absorption peaks at 405 nm and higher polarity than chlorop hyll were resolved by reversed-phase HPLC. In addition, some intermedi ate photoproducts that emit fluorescence at 620-630 nm were detected. Spectral changes in the visible region that appear during photooxidati on of the total pigments extracted from leaves of Urtica dioica L. wer e mainly due to products formed from chlorophyll a. pigment bleaching in isolated membranes and whole cells of A. variabilis under irradiati on with visible or UV light was associated with the formation of an ab sorption peak at 410-420 nm, which could be also attributed to the pro ducts of chlorophyll a photodegradation. It is suggested that the prod ucts of chlorophyll oxidation in vivo (presumably linear tetrapyrroles and porphyrin-like compounds) can act as endogenous photosensitizers. The changes revealed in chlorophyll absorption spectra can serve as i ndicators of(photo)oxidative damage to plants.