Metabolism of [3H]gibberellin A4 in somatic suspension cultures of anise

The native gibberellin A₄ (GA₄) was fed as [1, 2-³H]GA₄ (1.3 Ci/mmol) to anise somatic cultures maintained either at a proembryo-like stage with 2,4-dichlorophenoxyacetic acid (2,4-D), or allowed to undergo embryogenic development on a - 2,4-D medium. Proembryos, although only 20% of the dry wt of embryos, absorbed 1.4-times more [³H]GA₄/g dry wt than embryos. The [³H]GA₄ was metabolized to GA₁ and GA₈, and at least six conjugates [GA₄-glucoside (GA₄-G), GA₄ glucosyl ester (GA₄-GE), GA₁-0(3)-G, GA₁-0(13)-G, GA₁-GE and a GA₈-glucosyl conjugate]. The major metabolite was GA₄-G at each of two, 204 and 348 hr harvests (56–71 %), with GA₈-G increasing from < 1 % to 13 % with harvest time. The percentage and amount of GA₄-GE was highest at 204 hr (2% and 8 %, for embryos and proembryos, respectively), dropping to < 1 % at 348 hr, thereby indicating hydrolysis (e.g. reversible conjugation). Embryos had reduced amounts and percentages of biologically active GA₄ and GA₁, and most of their conjugates, but increased amounts and percentages of GA₈ and its conjugate(s). This finding is consistent with the hypothesis (based on present and past work) that high levels of biologically active GAs, especially GA₁, inhibit somatic embryogenesis in anise and carrot. The auxin, 2,4-D, may thus derive, at least in part, its ability to maintain the proembryo-like stage by inhibiting oxidative metabolism and conjugation of biologically active GAs.