Abstract
Ammonium-induced inhibition of nitrate utilization was monitored in cell suspensions of the unicellular alga Cyanidium caldarium. It was found that the inhibition followed an exponential pattern with a t 1/2 value of about 1.5 min in cells previously grown under conditions of excess nitrate, and of about 15 min in cells grown under conditions of severe nitrate limitation. In the latter cells only, a pretreatment with cycloheximide greatly increased the t 1/2 value of inhibition. Also the resumption of nitrate utilization when ammonium was depleted followed an exponential pattern with a t 1/2 value of about 4.5 min.
Our results are consistent with the hypothesis that inhibition of nitrate utilization occurs at the level of nitrate reductase activity.
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Fuggi, A., Rigano, V.D.M., Vona, V. et al. Pattern of inhibition of nitrate utilization by ammonium in the acidophilic thermophilic unicellular alga Cyanidium caldarium . Arch. Microbiol. 130, 349–352 (1981). https://doi.org/10.1007/BF00414598
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DOI: https://doi.org/10.1007/BF00414598