Action of 2,4-dichlorophenoxyacetic acid and rifampicin on heterocyst differentiation in the blue-green alga, Nostoc linckia.

2,4-Dichlorophenoxyacetic acid, a commonly used herbicide, increased the growth of the filamentous blue-green alga, Nostoc linckia at doses upto 100 μg /ml. The herbicidetreated N2-cultures showed enhanced heterocyst frequency and N2-growth. Thus, the herbicide stimulated algal growth at the expense of molecular nitrogen under aerobic growth conditions. Rifampicin caused chain formation of heterocysts. This was effectively counteracted by 2,4-dichlorophenoxyacetic acid, suggesting a biological interaction between them at the level of the heterocyst spacing control mechanism.