Bleaching of photosynthetic pigments in Chlorella protothecoides grown in the presence of SANDOZ 9785 (4-chloro-5-dimethylamino-2-phenyl-3 (2H) pyridazinone).

The unicellular green alga Chlorella protothecoides was grown in the presence of various concentrations (30–300 μΜ) of the herbicide SANDOZ 9785 (4-chloro-5-(dimethylamino)- 2-phenyl-3 (2H) pyridazinone). When the cells were grown autotrophically in the presence of the herbicide, there was a decrease in chlorophylls and carotenoids estimated on culture volume basis compared to the control. The absorption spectra of carotenes and colourless precursors extracted from photosynthetic particles showed that there was a higher carotenoid precursors/carotene ratio in the treated cells. Similarly the carotenoid precursors/xanthophyll ratio was increased by SANDOZ 9785 treatment. Chlorophyll a synthesis appeared to be inhibited more than chlorophyll b synthesis in SANDOZ 9785 treated cells resulting in a decrease in the chlorophyll a/b ratio.