Effect of Photoperiod on Metabolism of [H] Gibberellins A(1), 3-epi-A(1), and A(20) in Agrostemma githago L

To determine whether daylength influences the rate of metabolism of gibberellins (GAs) in the long-day (LD) rosette plant Agrostemma githago L., ³H]GA₂₀ and ³H]GA₁ were applied under short day (SD) and LD. Both were metabolized faster under LD than under SD. ³H]GA₂₀ was metabolized to a compound chromatographically identical to 3-epi-GA₁. ³H]GA₁ was metabolized to two acidic compounds, the major metabolite having chromatographic properties similar to, but not identical with GA₈. ³H]3-epi-GA₁ applied to plants under LD was metabolized much more slowly than was ³H]GA₁, and formed a very polar metabolite which did not partition into ethyl acetate at pH 2.5. Very polar metabolites were also formed after the feeds of ³H]GA₂₀ and ³H]GA₁. It was not possible to characterize these very polar compounds further because of their apparent instability. The results obtained suggest that in Agrostemma GA₂₀ is the precursor of 3-epi-GA₁, but there is at present no evidence indicating the precursor of GA₁.