Converts the inactive gibberellin precursors GA9 and GA20 in the bioactives gibberellins GA4 and GA1. Accepts also GA15, GA44, the 2,3-unsaturated GA5 and 2,3-dihydroGA9 as substrate. No activity with GA12, GA53, GA24, GA19 and GA25. Possesses also 2-beta-hydroxylase, 2,3-desaturase, 2,3-epoxidase and 13-hydroxylase activities. 2-oxoglutarate + gibberellin A20 + O2 = CO2 + gibberellin A1 + succinate Expressed in internodes, nodes and the ear of the elongating stem. Highly expressed in the embryo and the surrounding maternal tissues, the pericarp and the integuments. Also found in the germinating grain. Belongs to the iron/ascorbate-dependent oxidoreductase family. GA3OX subfamily.