The effect of cold shock on the blue-green alga Anacystis nidulans

We have investigated the known susceptibility of the blue-green alga Anacystis nidulans to cold shock. After suspensions of the organism were exposed to temperatures of 0°–3° for 15 min, viability was reduced to about 2% and the photosynthetic rate to about one third. Resistance to this effect increased with age of the culture from which the cells were harvested. Polarographic measurements showed that the decline in photosynthesis was complete within a few minutes after removal from the cold, and autoradiography showed that the decline was distributed among all the cells in the suspension. The short-term 14CO2 fixation products in cold-shocked and control cells differed only in amount and the 14CO2 fixed/O2 evolved during photosynthesis was the same in control and cold-shocked cells. Cold shock also caused the loss of some of the diffusible material from the cell; the loss was rapid but did not continue beyond about one quarter of the diffusible C and P; intracellular glutamate was lost to the extent of 50–80%. It is suggested that cold shock affects the limiting membrane of the cell and that this causes cell death but it is uncertain whether it is also responsible for the decline in photosynthesis.