Metabolism of [3H] Gibberellin A5 in Cell Suspension Cultures of Pharbitis nil

Gibberellin A₅ (GA₅), a native GA of immature seeds of Pharbitis nil, was fed to Pharbitis nil cell suspension cultures as C-l, ³H] GA₅ (3.1 Ci/mmol), and its metabolism over a 48 hr period was investigated. Radioactivity in free GA metabolites was 13.1%, with 79.9% in GA glucosyl conjugate-like metabolites. Only 7.0% of the radioactivity remained as ³H] GA₅. Tentative identifications were based on comparison with retention times of authentic free GAs and/or glucosyl conjugates after sequential chromatography on Si gel partition column → gradient-eluted C18 HPLC-radiocounting (RC) → isocratic-eluted C18 HPLC-RC, and showed that ³H] GA₅ was converted to ³H] GA₁ (2%), ³H] GA₃ (4%), ³H] GA₆ (2%), ³H] GA₂₂ (1%) and their glucosyl conjugates, and also to ³H] GA₈ glucoside, and ³H] GA₅ glucosyl conjugates. The major conjugate-like substances were ³H] GA₁ and ³H] GA₃ glucosyl esters, at 15% and 34%, respectively, of the total extractable radioactivity.