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Articles

Metabolism of Tritiated Gibberellins in d-5 Dward Maize

II. [³H]Gibberellin A₁, [³H]Gibberellin A₃, and Related Compounds ¹

^a Department of Vegetable Crops, University of California, Davis, California 95616

After 30 minutes of incubation of young leaf sections of d-5 maize (Zea mays L.) in [³H]gibberellin A₁ ([³H]GA₁), the metabolite [³H]GA₈ was present in significant amounts, with a second metabolite, [³H]GA₈-glucose ([³H]GA₈-glu), appearing soon after. A third [³H]GA₁ metabolite, the polar uncharacterized conjugate [³H]GA₁-X, took more than 1 hour to appear. The protein synthesis inhibitor cycloheximide inhibited the production of all [³H]GA₁ metabolites, indicating a possible protein synthesis requirement for [³H]GA₁ metabolism.

By preincubating leaf sections in unlabeled GA₁ before exposure to [³H]GA₁ or by reducing the specific radioactivity of the [³H]GA₁ supplied, it was possible to reduce greatly the conversion of radioactive GA₁ to [³H]GA₈-glu, without affecting conversion to [³H]GA₁-X. Increasing the molar concentration of the [³H]GA₁ fed greatly increased the molar yield of [³H]GA₁-X, whereas the molar yields of [³H]GA₈ and [³H]GA₈-glu were much less affected.

The principal metabolite of [³H]GA₃ was a very polar compound having chromatographic properties similar to those of the conjugate [³H]GA₁-X produced from [³H]GA₁. The naturally occurring GAs [³H]GA₁, [³H]GA₃, and [³H]tetrahydroGA₃ were metabolized to a much greater extent than were the artifical derivatives [³H]ketoGA₁, [³H]GA₁-methyl ester, and [³H]pseudoGA₁. Only [³H]GA₁ and [³H]GA₃, with their identical D ring structures, were converted to [³H]GA₁-X type compounds; [³H]-ketoGA₁ and [³H]tetrahydroGA₃, with modified D rings, were not converted to this type of conjugate.

¹ This investigation was supported by United States Public Health Service Grant GM 12885 and by National Science Foundation Grant GB 21241.