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Metabolism of Tritiated Gibberellins in d-5 Dwarf Maize

I. In Excised Tissues and Intact Dwarf and Normal Plants ¹

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

Metabolism of [³H]gibberellin A₁ ([³H]GA₁) was followed in intact seedlings and excised apices and leaf tissue of both dwarf and normal (tall) plants of d-5 maize (Zea mays L.). The three metabolites produced were tentatively identified as [³H]GA_s, [³H]GA_s-glucoside ([³H]GA_s-glu), and [³H]GA₁-X, an unknown.

In 3-hour, pulse-labeling experiments with tissues of incubated, expanding leaves, more than 70% of the [³H]GA₁ taken up was metabolized to the three products within 12 to 15 hours. [³H]GA₁ fed to the roots of 7-day-old seedlings was readily translocated to the leaves, and all three metabolites were found in both roots and leaves. [³H]GA₁-X was the major metabolite in roots, whereas in leaves the major metabolite was [³H]GA_s-glu. There were no consistent differences in [³H]GA₁ metabolism between dwarf and normal plants, indicating that dwarfism in d-5 maize is not associated with modified GA₁ metabolism.

In excised, mature leaf tissue, [³H]GA₁ metabolism was slower than in excised, young leaf tissue. Mature leaf tissues produced [³H]GA_s-glu as by far the major metabolite, with [³H]GA_s and [³H]GA₁-X as minor metabolites. In contrast, in young leaves the three metabolites appeared sequentially in significant proportions: [³H]GA₈ first, followed by [³H]GA_s-glu and, finally, [³H]GA₁-X.

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