Suppression of Floral Induction by Inhibitors of Steroid Biosynthesis

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Abstract
Known inhibitors of cholesterol biosynthesis were tested for their effects on photoperiodic induction in the cocklebur (Xanthium pensyivanicum) and Pharbitis nil, strain Violet. [beta]-Diethylaminoethyldiphenylpropyl acetate hydrochloride (SK and F 525-A), 2,2-diphenyl-l-([beta]-dimethyl-aminoethoxy)-pentane hydrochloride (SK and F 3301-A), tris-(2-dimethylaminoethyl)-phosphate trihydrochloride (SK and F 7732-A3), and tris-(2-diethylaminoethyl)-phosphate trihydrochloride (SK and F 7997-A3), all obtained from Smith Kline and French Laboratories, Philadelphia, were used. In addition, triparanol (MER/29) citrate, 1-[(4-diethylaminoethoxy)-phenyl]-l-(p-tolyl)-2-(p-chlorophenyl)-ethanol, obtained from Wm. S. Merrell Co., Cincinnati, was used. The compounds SK and F 7732 and SK and F 7997, which inhibit the conversion of lanosterol to cholesterol, are powerful inhibitors of floral induction of both Xanthium and Pharbitis. Experimental results suggest that flower hormone synthesis is the process inhibited by SK and F 7997, and that the hormone may be an isoprenoid- or steroid-like compound. B-Sitosterol and stigmasterol are synthesized in both vegetative and induced Xanthium leaves, and this synthesis is inhibited by SK and F 7997. The mechanism by which SK and F 7997 suppresses flowering cannot be by blocking biosynthesis of these 2 sterols.