Metabolism of gibberellins in a cell-free system from immature seeds of Phaseolus vulgaris L.

The biosynthetic steps from gibberellin A12-aldehyde (GA12-aldehyde) to C19-GAs were studied by means of a cell-free system from the embryos of immature Phaseolus vulgaris seeds. Stable-isotope-labeled GAs were used as substrates and the products were identified by gas chromatography-mass spectrometry. Gibberellin A12-aldehyde was converted to GA4 via non-hydroxylated intermediates and to GA1 via 13-hydroxylated intermediates. 13-Hydroxylation took place at the beginning of the pathway by the conversion of GA12-aldehyde to GA53-aldehyde. The conversion of GA20 to GA5 and GA6 was also shown but no 2β-hydroxylating activity was found. Endogenous GAs from embryos and testas of 17-dold seeds were re-examined by gas chromatography-selected ion monitoring using stable-isotopelabeled GAs as internal standards. Gibberellins A9, A12, A15, A19, A23, A24, and A53 were identified for the first time in P. vulgaris, in addition to GA1, GA4, GA5, GA6, GA8, GA17, GA20, GA29, GA37, GA38 and GA44, which were previously known to occur in this species. The levels of all GAs, except the 2β-hydroxylated ones, were greater in the embryos than in the testas. Conversely, the contents of GA8 and GA29, both 2β-hydroxylated, were much higher in the testas than in the embryos.