Identification of a NaCl-induced ascorbate oxidase activity in Chaetomorpha linum suggests a novel mechanism of adaptation to increased salinity

The filamentous chlorophyte Chaetomorpha linum (Müller) Kützing can stand wide changes in salinity occurring in brackish and estuarine waters. In an attempt to characterize C. linum adaptation, a NaCl-induced ascorbate oxidase (AAO) activity was identified and partially characterized. Immunogold-transmission electron microscopy analysis showed AAO labelling in the cytosol, walls and chloroplasts of C. linum cells, whereas in angiosperms this enzyme is almost exclusively confined to the extracellular matrix. The possible function of AAO in adaptation and functional evolution of its cellular location is discussed.