Effects of propanil on growth and cell constituents of Nostoc calcicola

The rice field herbicide, propanil, was toxic to the nitrogen-fixing cyanobacterium Nostoc calcicola. A decrease in growth was observed with the increasing concentrations of propanil, 30 μg/ml being lethal. Since toxicity of the herbicide could be reversed by exogeneous supplementation of assimilable organic carbon glucose, it is suggested that carbon fixation was sensitive to the herbicide. The herbicide inhibited heterocyst differentiation and nitrogen fixation. There was a rapid decrease in total protein, nucleic acids (DNA, RNA), and carbohydrate content accompanied by a loss of photosynthetic pigments. The phycocyanin: chlorophyll a ratio showed positive correlation with increased dosages of the herbicide, suggesting the inhibition of chlorophyll a.