PHYSIOLOGY AND ULTRASTRUCTURE OF DESICCATION IN THE GREEN-ALGA PRASIOLA-CRISPA FROM ANTARCTICA

Physiological and fine structural responses of the antarctic green alga Prasiola crispa ssp. antarctica (Kutz.) Knebel to desiccation and reimmersion in seawater are described. Experiments were conducted in the dark over a 14 day period, using a range of relative humidities (5% to 95%). Emersed thalli lost about 75% of the total cellular water during 6 hours of desiccation. Maximum water loss (86%) occurred after 1 day exposure to 50% relative humidity (r. h.), and then remained stable for 14 days. Water loss of more than 90% led to irreversible damage of the plants. After 7 or 14 days exposure to high humidity conditions the fresh weight of the thalli increased, indicating an uptake of water vapour. Growth rates after reimmersion in seawater medium depended on the water content and length of the period of desiccation. Dark respiration was not inhibited immediately after reimmersion in seawater, while photosynthetic rates were only 10-25% of the controls but recovered with time. The ultrastructural features of desiccated thalli were studied without rehydration after embedding in Nanoplast FB 101 resin. Only little changes in the fine structure became evident after desiccation times of up to 2 weeks. The very thick cell walls of P. crispa and the absence of vacuoles are regarded as essential prerequisites for the ability to survive periods of desiccation. The drought tolerance of P. crispa is discussed in relation to its habitat and its high salinity tolerance.