GIBBERELLIN BIOSYNTHESIS IN GIB MUTANTS OF GIBBERELLA-FUJIKUROI

The Ascomycete Gibberella fujikuroi synthesizes gibberellins, fujenal, carotenoids, and other terpenoids. Twelve gib mutants, isolated throu gh the modified gibberellin fluorescence of their culture media, were subjected to chemical and biochemical analyses. Two mutants were speci fically defective in the hydroxylation of carbon 13; their total gibbe rellin production was normal, but their main gibberellin was GA(7) ins tead of GA(3). Four mutants were blocked in the early reactions betwee n geranylgeranyl pyrophosphate and 7-hydroxy-kaurenoic acid; two of th em could not synthesize kaurene and another one was blocked in several oxidative steps. Six mutants had partial defects in early reactions, leading to the production of one-fifth to one-third of the wild type a mounts of gibberellins and fujenal. Two of these produced considerable amounts of kaurenolides due to a defect in the conversion of kaurenoi c acid to 7-hydroxykaurenoic acid. Another one produced no carotenoids , but attempts to isolate mutants of reactions shared by the carotenoi d and gibberellin pathways failed. The gib mutations did not modify th e ability of the fungus to live as a saprophyte.