Metabolism and translocation of gibberellins in the seedlings of Pharbitis nil .2. Photoperiodic effects on metabolism and translocation of gibberellins applied to cotyledons

We investigated the metabolism and translocation of two gibberellins (GAs), [H-3]GA(20) and [H-3]GA(1), which were applied at low concentration to the cotyledons of Pharbitis nil (Cv. Violet). Seedlings were grown under three different photoperiodic conditions: continuous light (CL-CL), continuous light followed by short day conditions (CL-DT) and long day conditions followed by short day conditions (DT-DT). Translocation of the applied [H-3]GAs from cotyledons to hypocotyls was promoted by DT for all GAs examined, While the conversion of the translocated [H-3]GA(1) to [H-3]GA(8) and its conjugates was rapid in hypocotyl, the conversion of translocated [H-3]GA(20) to [H-3]GA(29) was slow. Radioactivity in epicotyls was detected much more rapidly on application of [H-3]GA(20) than of [H-3]GA(1) under all photoperiodic conditions. The [H-3]GA(20) was translocated from cotyledons to epicotyls either un-metabolized or partly converted to [H-3]GA(1), [H-3]GA(8) and [H-3]GA(29) and their conjugates. The conversion of [H-3]GA(20) to [H-3]GA(1) in the epicotyl was more rapid under CL-CL conditions. This result is consistent with the higher level of endogenous GA(1) existing in epicotyls under CL-DT than DT-DT conditions. However, when [H-3]GA(1) was applied to the cotyledon, only small amounts of [H-3]GA(8) and its conjugates were detected in the epicotyl regardless of the photoperiodic conditions. This result may suggest that the translocation and metabolism of [H-3]GA(20) from cotyledons to epicotyl was faster under CL-CL than DT-DT conditions and may correlate with the increased epicotyl elongation of GA(20) treated plants under CL-DT than DT-DT conditions.