Key oxidase enzyme in the biosynthesis of gibberellin that catalyzes the conversion of GA12 and GA53 to GA9 and GA20 respectively, via a three-step oxidation at C-20 of the GA skeleton. 2 2-oxoglutarate + gibberellin A12 + H(+) + 3 O2 = 3 CO2 + gibberellin A9 + 2 H2O + 2 succinate 2 2-oxoglutarate + gibberellin A53 + H(+) + 3 O2 = 3 CO2 + gibberellin A20 + 2 H2O + 2 succinate Not detected in nodes and the ear of the elongating stem. Expressed in the embryo and the surrounding maternal tissues, the pericarp and the integuments. Also found in the germinating grain. The expression of this protein encoded by the B genome of the hexaploid wheat is much lower than the one of the two homologous proteins encoded by the A and D genomes. Belongs to the iron/ascorbate-dependent oxidoreductase family. GA20OX subfamily.