Abstract
Freezing tolerance of cyanobacteria, Nostoc commune and Synechocystis sp. PCC6803, and the effects of alcohol were studied by measuring their photosynthetic activities. Because freezing stress usually causes water stress simultaneously, the effects of freezing stress were compared with those of drying stress. N. commune is terrestrial and is highly tolerant to drying stress, while Synechocystis is not. The following results were obtained. 1) N. Commune can survive freezing stress even at temperatures as low as -78oC, while Synechocystis could not when it was frozen at -20oC. 2) Decreases in fluorescence emission from photosystem (PS) II and photochemical activities of PSI and PSII showed that water loss from the N. commune cells was not so large as in the case of air drying. 3) Addition of 5% methanol to the Synechocystis solution protected the cyanobacterium from freezing damage. The effects of alcohol will be discussed.
