Kinetics of photoaccumulation of β-carotene in Phycomyces blakesleeanus.

Upon carbon starvation the β-carotene content of Phycomyces mycelium grown on minimal agar medium disappears with a time lag of about 90 min and a T1/2 of 68-75 min. If continuous light is given 2 h after starvation, there is an increase in β-carotene content with respect to the dark control. This increase has a time lag of 20-25 min. The fluence rate-response curve of wt is biphasic and two mutants in the gene madA (madA7, madA35) and in the gene madB (madB101, madB104) have higher thresholds than wt; madB mutants are blinder than madA mutants. Only blue light is effective and we suggest that it has an effect solely on the catabolism of β-carotene.