Lack of influence of photoperiod on the metabolism of gibberellin A20 in Salix pentandra

Abstract

The influence of photoperiod on the metabolism of GA20 in Salix pentandra was studied by feeding [3H]‐GA20 to seedlings which had been grown previously under long day (LD) or short day (SD) conditions. After 48 h in LD or SD, metabolites were separated on sequential, silica gel partition columns and reversed‐phase C18 HPLC. The principal metabolite co‐chromatographed with [3H]‐GA1 and this conversion was confirmed by feeding [2H]‐GA20, which was converted to [2H]‐GA1 as identified by gas chromatography‐selected ion monitoring. Chromatographic evidence also indicated the minor conversion of [3H]‐GA20 to [3H]‐GA8 (via [3H]‐GA1) and trace conversion to [3H]‐GA29 (GAs A1.8,20.29 are native in Salix). Ethyl acetate‐insoluble [3H] metabolites were formed and could be cleaved by cellulase to release putative [3H]‐GA20 and [3H]‐GA1 suggesting the conversion to glucosyl conjugates of these GAs. Metabolism of [3H]‐GA20 was slightly more rapid in plants previously grown under LD than SD, an effect which reflected the generally increased shoot growth under LD. However, altering the photoperiod after [3H]‐GA20 addition had only a slight effect on the metabolism of [3H]‐GA20 in Salix seedlings. This indicates that the conversion of GA20 to GA1 is not a controlling step in the photoperiodic regulation of growth cessation in Salix.