Influence of the Structure of the Sterol Molecule on Sterol-induced Reproduction in Phytophthora cactorum

Publisher Website
Google Scholar
Abstract
Production of oospores by P. cactorum in media supplemented with 10 .DELTA.5-sterols, differing in the structure of their side chains, was measured. Spore production increased with increasing size of the substituent at C-24: H < CH3 < C2H5. A 24.alpha.-methyl group conferred greater activity than a 24.beta.-methyl, but there was less difference between .DELTA.5-sterols with 24.alpha.- and 24.beta.-ethyl groups. There was a greater difference between .DELTA.7-sterols with 24.alpha.- and 24.beta.-ethyl substituents. A double bond at C-22 had no effect on spore production when trans, but reduced activity when cis. Four .DELTA.7-sterols were compared with their corresponding .DELTA.5-sterols. Fewer oospores were produced at low concentrations (0.2-1 mg 1-1) of each .DELTA.7-sterol than with the .DELTA.5-sterol, but a higher concentrations (10-30 mg 1-1), the numbers with the .DELTA.7-sterol bore no consistent relation to the numbers with the .DELTA.5-sterol. The difference between 2 sterols in promoting sexual reproduction in P. cactorum is not apparently related to differences in uptake into the mycelium or to known effects on properties of membranes, but is believed to be due to differences in metabolism of the sterols, and to differences in the hormone activity of compounds derived from them.