The fungicide a-(2,4dlhloropheyl)-a-phenyl5-pyrne methyl alcohol (triarimol) and four other structural analos of this substance, in which one or more of the substituents were varied, were tested for their comparative effects on growth and gibbereilin biosynthesis in the fimgus GibbereJluiuwro Each of the five analogs tested was capable of inhibiting growth as measured by dry weight In 5-day-old cultures. Three of them la-(2-chlorophenyl)-a44-chlor nyl)-5-pyre methyl alcohol, fenarimol; a-(2-chlorophenyl)-a-(4-fluorophenyl)-5-pyrmine methyl alcohol, nuarimol and triarimoll were effective at appreciably lower concent:stions than the other two la-(4-chlorophenyl)-a-(l-methylethyl)-5-pyridine methyl alcohol, experimental compound EL 509; and a-cyclopropyl-a-(4-methoxyphenyl)-5-pyrimldine methyl alcohol, ancymidoll.All five substances also inhibited gibberellin production as measured by gibbereflin content of fungus fitrates. The relative effectiveness of the compounds as inhibitors of growth and gibberellin production were similar.These analogs were also shown to inhibit eat-kaurene oxidation by microsomal preparations from fungal mycelia. Thus, the site of inhibition of gibberellin biosynthesis may be the same for the fungus as the one affected by this group of substances in hgher plant tissues.The structure-activity relatshs between the analogs are opposite to those observed in higher plant tissues. The fungicides fenarimol, nuarmol, and triarimol, which were most effective in inhibiting growth and gibberellin biosynthesis in the fungus, were much less effective than EL 509 and ancymidol in inhibiting growth and gibberellin biosynthesis in higher plants.These results indicate that the ent-kaurene oxidase systems from the two sources have somewhat different molecular characterstics, and thus, interact differently with this group of substances.Ancymidol3 is a potent inhibitor of growth and GA4 biosyn-' Supported by Grant PCM from the National Science Foundation and by Grant GM 07065 from the National Institutes of Health.'To whom reprint requests should be addressed. 'Abbreviation: GA, gibberellin. thesis in higher plants (9-11, 17, 22, 24). It has been shown previously to be ineffective at similar concentrations on the fungus, Gibberellafujikuroi (10, 17). Shive and Sisler (22) compared the effects of ancymidol and triarimol on growth and GA contents of beans and G. fujikuroi. They reported that these compounds do inhibit GA biosynthesis in the fungus, although triarimol, an experimental fungicide, is more effective than ancymidol. Ali et al. (1) also reported on the fungitoxic activity of ancymidol. In the accompanying paper (11), we have compared the effects of a number of ancymidol analogs, including triarimol, on the growth of pea seedlings and the rate of kaurene oxidation in cell-free enzyme extracts of Marah macrocarpus liquid endosperm. The results indicate that the analogs with fungicidal activity do inhibit ent-kaurene oxidation, but only at relatively high concentrations. Because of the seeming ...
