GIBBERELLINS AND CAROTENOIDS IN THE WILD-TYPE AND MUTANTS OF GIBBERELLA-FUJIKUROI

A new screening procedure was used to isolate 14 gib mutants of Gibberella fujikuroi with modifications in the production of gibberellins. The production of carotenoids and gibberellins was investigated in the gib mutants and in representative car mutants with various modifications of carotenoid biosynthesis. The determinations of gibberellins were carried out with a simplified fluorescence method. One of the mutants lacked both gibberellins and carotenoids. In many mutants the two pathways compensated each other: an increase in the production of one group of compounds was accompanied by a decrease in the production of the other. Under certain conditions the compensation was quantitative when the output of the two pathways was measured in moles of the common precursor, geranylgeranyl pyrophosphate. alpha-Picoline, an inhibitor of lycopene cyclase in G. fujikuroi, inhibits gibberellin biosynthesis. Other agents that affect the accumulation of carotenoids have no noticeable effect on the accumulation of gibberellins; such is the case with diphenylamine and beta-ionone, two inhibitors of phytoene dehydrogenation, and visible light, which stimulates carotenogenesis.