Lack of effect of photoperiod on metabolism of exogenous GA₁₉ and GA₁ in <i>Salix pentandra</i> seedlings

Abstract

The effect of photoperiod on metabolism of 16,17‐[ 3 H 2 ]GA 19 , and 1.2‐[ 3 H 2 ]GA 1 applied to intact seedlings of Salix pentandra , was investigated. No difference was found in conversion of 16,17‐[ 3 H 2 ]GA 19 to 16,17‐[ 3 H 2 ]GA 20 , and 16,17‐[ 3 H 2 ]GA 1 , or in metabolism of 1,2‐[ 3 H 2 ]GA 1 to [ 3 H]GA 8 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‐[ 3 H 2 ]GA 19 both in light and darkness. These data on metabolism of 16,17‐[ 3 H 2 ]GA 19 , contrast with previous results, which have indicated a photoperiodic control of the metabolism of GA 19 to GA 20 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‐[ 3 H 2 ]GA 19 was applied through the roots of intact plants, the relative amounts of 16,17‐[ 3 H 2 ]GA 1 present in leaves and shoot apices were higher than in roots and stems. In corresponding experiments with 1,2‐[ 3 H 2 ]GA 1 , relatively higher amounts of [ 3 H 2 ]GA 8 were found in roots and stems than in leaves and shoot apices. Twenty‐four hours after application of 16,17‐[ 3 H 2 ]GA 19 to isolated plant parts, 16,17‐[ 3 H 2 ]GA 20 and 16,17‐[ 3 H 2 ]GA 1 were found in leaves and roots, but not in internodes. Incubation of isolated plant parts with 1,2‐[ 3 H 2 ]GA 1 for 24 h resulted in presence of [ 3 H]GA 8 in all parts. The results mentioned above were obtained by monitoring metabolites by HPLC with on‐line radio counting. The conversions of 17‐[ 2 H 2 ]GA 19 to 17‐[ 2 H 2 ]GA 20 and 17‐[ 2 H 2 ]GA 1 in shoot apices and whole seedlings, and of 17‐[ 2 H 2 ]GA 8 in whole seedlings, were confirmed by GC‐MS.