The Effect of Temperature on Photo-induced Carotenoid Biosynthesis in Neurospora crassa.
The temperature dependence of carotenoid synthesis in Neurospora crassa was investigated. The primary light reaction is independent of temperature, but the amount of carotenoid pigment which subsequently accumulates in the dark is strongly dependent on the temperature during the dark incubation. Carotenoid synthesis shows a sensitivity to both high and low temperatures, and of the temperatures tested, 6 C is optimal. Exposure to temperatures above 6 C for various times immediately following irradiation brings about a temperature-dependent reduction in the amount of carotenoid pigment that is synthesized in a total dark incubation time of 24 hours. This sensitivity to incubations at temperatures above 6 C is reduced by either continuous irradiation during the entire time at the higher temperature or by a short irradiation at the end of this period, and the relative effectiveness of these two types of light treatments is presented. Carotenoid production is also sensitive to amino acid analogues and inhibitors of protein synthesis during a critical period after irradiation.It is proposed that the light reaction leads to the production of a compound which can be degraded in a temperature-dependent competitive reaction. This compound (or a product derived from it) can also induce the de novo synthesis of an enzyme (or enzymes) required for carotenoid production. An alternative hypothesis, that a repressor is directly inactivated in the light reaction, can be ruled out by the results presented.
Harding
R W
RW
Radiation Biology Laboratory, Smithsonian Institution, Rockville, Maryland 20852.