Lack of effect of photoperiod on metabolism of exogenous GA19 and GA1 in Salix pentandra seedlings

Abstract

The effect of photoperiod on metabolism of 16,17‐[3H2]GA19, and 1.2‐[3H2]GA1 applied to intact seedlings of Salix pentandra, was investigated. No difference was found in conversion of 16,17‐[3H2]GA19 to 16,17‐[3H2]GA20, and 16,17‐[3H2]GA1, or in metabolism of 1,2‐[3H2]GA1 to [3H]GA8 between plants grown in continuous light and plants exposed for 14 days to a 12‐h photoperiod. Also, leaf discs from plants grown in long or short days, converted 16,17‐[3H2]GA19 both in light and darkness. These data on metabolism of 16,17‐[3H2]GA19, contrast with previous results, which have indicated a photoperiodic control of the metabolism of GA19 to GA20 in S. pentandra.Presence of these applied labelled GAs and their metabolites in different parts of seedlings was recorded, after application to intact seedlings as well as to isolated plant parts. When 16,17‐[3H2]GA19 was applied through the roots of intact plants, the relative amounts of 16,17‐[3H2]GA1 present in leaves and shoot apices were higher than in roots and stems. In corresponding experiments with 1,2‐[3H2]GA1, relatively higher amounts of [3H2]GA8 were found in roots and stems than in leaves and shoot apices. Twenty‐four hours after application of 16,17‐[3H2]GA19 to isolated plant parts, 16,17‐[3H2]GA20 and 16,17‐[3H2]GA1 were found in leaves and roots, but not in internodes. Incubation of isolated plant parts with 1,2‐[3H2]GA1 for 24 h resulted in presence of [3H]GA8 in all parts.The results mentioned above were obtained by monitoring metabolites by HPLC with on‐line radio counting. The conversions of 17‐[2H2]GA19 to 17‐[2H2]GA20 and 17‐[2H2]GA1 in shoot apices and whole seedlings, and of 17‐[2H2]GA8 in whole seedlings, were confirmed by GC‐MS.