Comparative toxicity of bentazon and molinate on growth, photosynthetic pigments, photosynthesis, and respiration of the Portuguese ricefield cyanobacterium Nostoc muscorum.
The effects of the carbamate herbicide molinate on growth and chlorophyll a, biliprotein, and protein content of the nitrogen-fixing cyanobacterium Anabaena sphaerica grown mixotrophically under 3000- and 300-lux light intensity were studied. Under two light intensities, the three concentrations of molinate tested (5, 25, and 50 microg ml-1) can significantly inhibit algal growth in a dose-dependent manner. The high concentration of molinate (50 microg ml-1) stimulated the synthesis of chlorophyll a and protein, but inhibited the formation of biliprotein, and these effects appear to be greater at 3000 lux than at 300 lux. The effects of the other two concentrations of molinate (5 and 25 microg ml-1) on chlorophyll a and biliprotein varied with time, but 5 microg ml-1 molinate had an inhibitory effect on the synthesis of protein. It was demonstrated that different concentrations of molinate had different effects on chlorophyll a, biliprotein, and protein content, which varied with light intensity. The results support the suggestion that the physiological mode of molinate toxicity to A. sphaerica is related to its interference with the metabolism of protein, particularly the formation and functional effectiveness of some special protein.