Some properties of a fluoride-resistant mutant of the marine dinoflagellate Amphidinium carterae

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Abstract
A fluoride-resistant mutant, with abnormal ultrastructural features, was developed in culture from prolonged exposure of A. carterae to 10.5 mM NaF in nutrient-enriched seawater under continuous illumination. This phenotype mutant showed little change in external morphology, but some important alterations in internal organelles (pyrenoid, nucleolus, microbodies) of the original dinoflagellate (hereafter referred to as wild-type). These structural abnormalities were persistently retained by the mutant when repeatedly subcultured in medium with or without added fluoride. The mutant showed growth rates, chlorophyll a and c content, and net photosynthesis similar in magnitude to those of the wild-type. However, the endogenous respiration of the mutant measured considerably greater, and the evidence suggested that a major proportion of this respiration could be due to enhancement of photorespiration. A cytochemical test showed the mutant microbodies to be catalase-negative, suggesting that they may be functioning as glyoxysomes rather than peroxisomes; their suspected role in the mutant photorespiration remains unsolved. Survival of A. carterae in the face of inhibitory fluoride concentration was ensured by the mutation restoring cell division and photosynthesis to nearly normal levels, despite some loss in efficiency due to enhanced respiration.