Radioactive Gibberellin A5 and Its Metabolism in Dwarf Peas

Radioactive gibberellin A(5) ((3)H-GA(5)) was synthesized from gibberellic acid. When it was applied to dwarf peas grown in the dark, an average of 3% was converted to another acid gibberellin within 48 hours. The biological activity of the metabolite did not account for the response to applied GA(5). GA(5) is therefore assumed to be biologically active per se.(3)H-GA(5) did not appear to form a stable complex with a macromolecule in pea shoots. When injected into dwarf pea pods, (3)H-GA(5) was readily metabolized by maturing seed to more water-soluble substances and to two other acidic compounds. This metabolism continued even throughout germination of the seed without reconversion of the metabolites to GA(5). It is concluded that "bound" GA(5) plays no part in the germination of dwarf pea seeds.