The impact of low (negative) temperature and long dark period (conditions of the polar night) on the morphophysiology of unicell algae are discussed on the basis of original and literature data.

It has been shown that most microalgae grown under the darkness conditions during a long time suffer from development of lysis processes, intensity of which depends on whether they are cultured in organic or inorganic media.

In the organic media in dark conditions many species switch their metabolism to heterotrophic nutrition, while cell division goes on and chloroplasts are rapidly transformed to proplastids.

Under the conditions of inorganic media and darkness the cell division ceases, the autophagy and step-by-step degradation of membrane structures of cells are observed. Mitochondria first suffer from the lysis process followed by nuclei and chloroplasts. Reversibility of all these processes (survival under the conditions of complete darkness) depends on taxonomic status of an alga and its cell structure.

Under low temperature in the darkness conditions a dormant stage may develop in microalgae which is accompanied with abrupt lowering of the intensity of all metabolic processes.

The above experiments have demonstrated a possibility for microalgae to survive when being kept in superlow temperature and complete darkness conditions for up to half a year. The degree of survival depends on both morphophysiological features of algae and freezing techniques applied.

Dr. Grigorii Voskoboinikov 
Murmansk marine biol. institute
Vladimirskaja, 17
183010, Russia
Phone: (8152) 562029
Fax: (4778) 910288
Email: vladimd@fivo.hsf.no