THE COLD SHOCK RESPONSE OF NEUROSPORA CRASSA: INFLUENCE OF LIGHT VS. TEMPERATURE

The filamentous fungus Neurospora crassa (Oak Ridge wild-type) exhibits a characteristic, temporary change in morphology when shifted from warmer incubation temperatures into the cold. This change was termed the "cold shock response." Other workers have suggested that the temporary morphology changes were due to the changing light conditions resulting from shifting the growing colonies from incubator to glass-fronted refrigerator. A series of experiments were conducted in order to distinguish between these two competing hypotheses. Samples of N. crassa were grown at 33[degrees]C. Half were subject to constant light, and the other half were subject to constant dark. These cultures were then shifted to 4[degrees]C while maintaining their respective light/dark exposure. The cold shock response of both the "light" and "dark" samples were similar to both conventional cold shock and each other, supporting the hypothesis that the cold shock morphological response is due to temperature rather than light changes. These competing hypotheses were further tested by subjecting Neurospora crassa growth to a gradient of temperature shifts. Identical stains of N. crassa were grown first at temperatures ranging from 37[degrees]C to 25[degrees]C and shifted to 4[degrees]C incubation. The spacing and appearance of the apical branching characteristic of the cold shock response correlated with the temperature shift despite the lighting conditions being constant. Finally, cultures were subjected to changes in the lighting conditions while maintaining constant temperature with no change in morphology. Together, these results support the conclusion that the previously described cold shock response of N. crassa is indeed the result of the temperature shift and not the changing light conditions.