Investigations on the phototactic orientation of Anabaena variabilis

Phototaxis of the blue-green alga Anabaena variabilis was studied using both population method and observation of single trichomes by microscope. The trichomes react positively at low and negatively at high illuminance. The inversion point lies at about 1000 1x. The action spectrum of positive phototaxis indicates that the photosynthetic pigments chlorophyll a, C-phycocyanin and allo-phycocyanin are involved in the absorption of the active light. The same range of wavelengths is active in negative phototaxis, but in addition, wavelengths between 500 and 560 nm and between 700 and 750 nm are also effective. Obviously pigments of unknown chemical nature are sharing in light absorption. Two alternatives are discussed. Since inhibitors of photosynthesis such as DCMU and DBMIB do not affect phototactic orientation, a direct coupling of phototaxis with photosynthesis can be excluded.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone)Presented in part at the International Symposium on Photosynthetic Prokaryotes: August 22–28, 1976, Dundee, Scotland