STEROIDS AND THE STIMULATION OF SEXUAL REPRODUCTION OF A SPECIES OF PYTHIUM

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Abstract
The fatty acid compositions of the mycelia of a parasitic species of Pythium and of various hosts are reported. The Pythium spp. contained high concentrations of myristic acid and low concentrations of linoleic and linolenic acids in comparison with concentrations in other fungi tested. Appreciable amounts of unsaturated C20 acids, uncommon in fungi, were found in the Phycomycetes tested. Vegetable oils and other fats of widely varying fatty acid compositions were all effective in stimulating sexual reproduction of the Pythium sp. It was concluded that substance(s) other than fatty acids present in the vegetable oils were responsible for the stimulation observed. The most active fraction in sunflower seed oil was isolated and identified as a phytosterol, probably β-sitosterol. The results of testing for stimulatory activity a series of structurally related compounds indicated that the sexual reproduction of the Pythium sp. studied required the presence of a substance such as β-sitosterol or cholesterol or one with similar structure and which similarly satisfied certain specific structural requirements regarding length of the C17 side chain, stereochemistry, and position of the oxygenated function. β-Sitosterol and cholesterol were effective at 0.2 γ/ml in potato dextrose agar.

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