Action of 2,4-Dichlorophenoxyacetic Acid onNostoc linckia: Impact of Glucose and Tryptophan

2,4-Dichlorophenoxyacetic acid (2,4-D) stimulated growth and heterocyst differen- tiation ofNostoc linckia in nitrogen-free medium at lower concentrations (100 μ.g/mL) while its higher concentrations inhibited both processes and 1500 μg/mL proved to be lethal. Dry mass and specific growth rate of the alga declined with increasing concentration of 2,4-D in the range of 100–1500 μg/mL. Glucose slightly increased the heterocyst frequency without any lag in their differentiation. Tryptophan promoted growth of the alga, and formation of heterocysts (nearly three-fold). Tryptophan (50 μg/mL) complex medium with 1 mg 2,4-D per mL did not produce mature heterocysts. The filaments were fragmented at the point of hererocyst development and detached heterocysts germinatedin situ. Glucose and tryptophan protected the alga, its growth and heterocyst differentiation even at the lethal concentration of the herbicide. We are grateful to the Head, Department of Botany,Banaras Hindu University, Varanasi, for providing the necessary facilities. The first author is also grateful to the Principal,K.D. College, Kutir-Chakkey, Jaunpur, for his interest in this study.