CHANGES IN THE ULTRASTRUCTURE OF PRASIOLA-CRISPA SSP ANTARCTICA UNDER SALINITY STRESS

The supralittoral green alga Prasiola crispa, collected in Antarctica, was grown at salinities ranging from 0.35 parts per thousand to 175 parts per thousand. Its ultrastructure was examined by electron microscopy and compared with the ultrastructure of plants grown under standard conditions (35 parts per thousand). The thalli had very thick cell walls, making up approximately 50% of the thallus volume. Most of the protoplast was occupied by a single chloroplast. Numerous starch granules in the chloroplast were enlarged under hypo-osmotic conditions and reduced in volume when subjected to hyperosmotic stress indicating a metabolic shift towards low molecular weight organic osmolytes under the latter conditions. Whilst vacuoles were lacking in plants cultured at salinities between 0.35 parts per thousand and 35 parts per thousand, they developed under hyperosmotic conditions and possibly may serve as compartments accumulating inorganic ions. Growth, photosynthesis and dark respiration were strongly inhibited under higher salinities, whilst they remained almost unaffected under lower salinities (Jacob et al., 1991).