Effect of Photoperiod on Metabolism of [3H] Gibberellins A1, 3-epi-A1, and A20 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., [(3)H]GA(20) and [(3)H]GA(1) were applied under short day (SD) and LD. Both were metabolized faster under LD than under SD. [(3)H]GA(20) was metabolized to a compound chromatographically identical to 3-epi-GA(1). [(3)H]GA(1) was metabolized to two acidic compounds, the major metabolite having chromatographic properties similar to, but not identical with GA(8). [(3)H]3-epi-GA(1) applied to plants under LD was metabolized much more slowly than was [(3)H]GA(1), 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 [(3)H]GA(20) and [(3)H]GA(1). It was not possible to characterize these very polar compounds further because of their apparent instability. The results obtained suggest that in Agrostemma GA(20) is the precursor of 3-epi-GA(1), but there is at present no evidence indicating the precursor of GA(1).