Résumé
Nonspecific acid phosphatases are a group of enzymes whose activity increases the availability of exogenous and endogenous orthophosphate either through extra- or intracellular hydrolysis of phosphate compounds. Our study demonstrates the activity of acid phosphatases in the filamentous freshwater alga Stigeoclonium tenue. These enzymes were detected following a cerium-based method in which cerium was used as an orthophosphate-capture reagent. In thalli from S. tenue from the natural environment, acid phosphatases were found in the longitudinal cell wall,plasmalemma, and vacuole. In thalli from Bold's Basal Medium culture, these enzymes were found mainly in the plasmalemma; they were scarce in the cell wall. In the thalli grown in phosphate-enriched culture medium, enzymes were found only in the plasmalemma. The low availability of orthophosphate in the medium seems to induce the transport of these enzymes to the cell wall. Its abundance, on the contrary, seems to attenuate this response without affecting the localization of acid phosphatases in the plasmalemma.