Biosynthesis of Gibberellins in Gibberella fujikuroi. The Sequence after Gibberellin A₄

Gibberellins A 1 , A 3 , A 4 , and A 7 biosynthetically labeled with 14 C were added to gibberellin-producing cultures of Gibberella fujikuroi. In cultures transferred to 10% glucose solution most of the gibberellin A 4 was first dehydrogenated to gibberellin A 7 before being 7-hydroxylated to gibberellin A 3 . A small amount of gibberellin A 4 was 7-hydroxylated directly to form gibberellin A 1 , but none of the gibberellin A 1 was subsequently metabolized to gibberellin A 3 . In cultures growing in a medium which supported higher yields of gibberellin A 1 , more of the 14 C-labeled gibberellin A 4 supplement was directly 7-hydroxylated to this product. Gibberellin A 3 was again formed mainly via gibberellin A 7 , but a small amount was derived by dehydrogenation of gibberellin A 1 . In these cultures gibberellin A 4 was also metabolized to an unidentified gibberellin-like substance, probably an isomer of gibberellin A 1 .