SEPARATE COMPARTMENTS FOR THE PRODUCTION OF STEROLS, CAROTENOIDS AND GIBBERELLINS IN GIBBERELLA-FUJIKUROI

Substrate flow in the sterol, carotenoid and gibberellin pathways of G ibberella fujikuroi were examined by isotope-dilution experiments. The wild type and two carotenoid mutants of this fun were grown in minima l medium with abundant glucose. limiting ammonium nitrate and a radioa ctively labelled precursor (either acetate, mevalonate or leucine). Th e precursors did not affect growth or terpenoid production, with two e xceptions; leucine allowed additional growth, as expected from the nit rogen limitation In the medium, and mevalonate inhibited the accumulat ion of gibberellins, but only if added before the onset of gibberellin production. The relative contributions of glucose, mevalonate, leucin e and acetate as terpenoid precursors, calculated from tire specific r adioactivities of ergosterol, neurosporaxanthin and phytoene, were dif ferent products and different precursors. We conclude that the biosynt heses of sterols, gibberellins and carotenoids in Gibberella are physi cally separated in different subcellular compartments with independent substrate pools. The same results were obtained with the three strain s, except for carotenoid production, indicating that this pathway is r egulated independently from other terpenoid pathways.