Hexavalent Chromium Induces Gametogenesis in the Freshwater Alga Scenedesmus acutus

The aggregates formed by Scenedesmus acutus cultivated in the presence of 1 mg/liter Cr(VI) persist even after 7 days of treatment. They were examined by fluorescence and electron microscopy and were found to be an early stage of sexual reproduction. They consist of four small cells deprived of a true cell wall and enclosed in a common envelope. When the envelope breaks up they are released in the culture medium as biflagellated mobile cells. These cells have been identified as gametes.