Growth Substances and Dormancy of Spores of Phycomyces

Abstract

Spores of Phycomyces germinate poorly at 26⚬ C. on a mineral-dextrose agar medium containing thiamine. The percentage of germination increases somewhat with age of the spores, reaching a maximum of about 12 per cent after 2 1/2 months. It is affected slightly by the temperature at which the spores are grown and by their exposure to light during development. The addition to the medium of extracts of potato tubers or other natural products, of hypoxanthine and a DR fraction (Z factors), or of acetate and some other organic acids increases germination to nearly 100 per cent. Treatment of spores with aqueous pyridine, 2 hours' exposure to temperatures of 11⚬ or 15⚬, or treatment for 30 minutes to 1 hour at 50⚬, has the same favorable effect. Failure of the spores to germinate on the basal medium is interpreted as a dormancy phenomenon. The dormant spores are considered to lack sufficient available Z factors for germination. The extracts of natural products or the Z factors furnished in the medium supply the deficiency, which may also be met by treatment with heat, cold, acetate, or pyridine. These treatments are thought to change the Z factors in the spores from an unavailable to an available form.