Metabolism and Biological Activity of Gibberellin A₄ in Vegetative Shoots of Zea mays, Oryza sativa, and Arabidopsis thaliana

[17-13C,3H]Gibberellin A4 (GA4) was injected into the shoots of tall (W23/L317), dwarf-1 (d1), and dwarf-5 (d5) Zea mays L. (maize); tall (cv Nipponbare), dwarf-x (dx), and dwarf-y (dy) Oryza sativa L. (rice); and tall (ecotype Landsberg erecta), ga4, and ga5 Arabidopsis thaliana (L.) Heynh. $[{}^{13}\text{C}]\text{GA}_{4}$ and its metabolites were identified from the shoots by full-scan gas chromatography-mass spectrometry and Kovats retention indices. GA4 was metabolized to $\text{GA}_{1}$ in all nine genotypes. GA4 was also metabolized in some of the genotypes to 3-epi-$\text{GA}_{1}$, $\text{GA}_{2}$, 2β-OH-$\text{GA}_{2}$, 3-epi-$\text{GA}_{2}$, endo-GA4, 16α, 17-H2-16,17-(OH)2-GA4, $\text{GA}_{34}$, endo-$\text{GA}_{34}$, $\text{GA}_{58}$, 15-epi-$\text{GA}_{63}$, $\text{GA}_{71}$, and 16-epi-$\text{GA}_{82}$. No evidence was found for the metabolism of GA4 to $\text{GA}_{7}$ or of GA4 to GA3. The bioactivities of GA4 and $\text{GA}_{1}$ were determined using the six dwarf mutants for assay. GA4 and $\text{GA}_{1}$ had similar activities for the maize and rice mutants. For the Arabidopsis mutants, GA4 was more active than $\text{GA}_{1}$ at low dosages; GA4 was less active than $\text{GA}_{1}$ at higher dosages.