J Basic Microbiol 1986 Jan 01;261:49-53. doi: 10.1002/jobm.3620260117.

Effect of tryptophan on 2,4-dichlorophenoxyacetic acid toxicity in the nitrogen-fixing-cyanobacterium Nostoc linckia.

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The combined effect of a hormone weed killer 2,4-dichlorophenoxyacetic acid (2,4-D) and an amino acid (tryptophan) has been studied on growth and heterocyst differentiation in the cyanobacterium Nostoc linckia. 2.4-D at 100 micrograms/ml stimulated growth and heterocyst frequency in combined nitrogen-free medium while its higher concentrations inhibited both. Tryptophan under similar conditions promoted much growth yield with 3-4 fold enhanced heterocyst frequency than the control. Such heterocysts were immature and showed germination under in situ condition. The concentrations of 2,4-D (100 micrograms/ml) and tryptophan (50 micrograms/ml), stimulatory to growth and heterocyst formation, caused additive effect while herbicide inhibition of nitrogen-fixing growth at higher doses was partially relieved by tryptophan but tryptophan-induced heterocyst frequency was completely suppressed under this condition. The possible role of interaction of these two chemicals on growth and heterocyst formation has been discussed.

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