Involved in the conversion of naringenin to apigenin. Acts via a direct 2,3-desaturation of flavanones instead of a sequential hydroxylation/dehydratation mechanism. 2-oxoglutarate + a flavanone + O2 = a flavone + CO2 + H2O + succinate Secondary metabolite biosynthesis; flavonoid biosynthesis. In contrast to the microsmal flavone synthase II, FNSI is a soluble enzyme. Belongs to the iron/ascorbate-dependent oxidoreductase family.