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

Abstract

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 μg/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 μg/ml) and tryptophan (50 μg/ml), stimulatory to growth and heterocyst formation, caused additive effect while herbicide inhihibition 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. Copyright © 1986 Wiley‐VCH