Metabolism of [ 14 C]GA 19 and [ 14 C]GA 53 by ecotypes of Betula pendula : the role of photoperiod

In many temperate woody species, short days (SDs) induced growth cessation has been shown to be prevented by the application of gibberellins (GAs). Evidence has also been forwarded for the influence of photoperiod on the metabolism of applied GAs. Continuing with this line of research, we studied the metabolism of 14C-labelled GA 19 and GA 53 . [ 14 C]GA 19 and [ 14 C] A 53 were applied to the apices of the northern ecotype (67o N) and to the leaves of the southern ecotype (64o N) of Betula pendula Roth. under different photoperiods and at different times in order to compare metabolism during day and night periods. Assay of metabolites was made 10 h after application. Less than half of each applied GA was taken in by the plants and most of the activity was recovered from the application points. There was no clear effect of photoperiod on uptake of the GAs. After the HPLC analysis, most of the absorbed radiolabelled GAs were eluted as unmetabolised forms. However, significant levels of gibberellins A 20 , A 29 , A 1 , and A 8 were recovered as metabolites of [ 14 C]GA 19 both in apical stems and leaves. In 1SD and 4SD-treated plants, there was less metabolism of [ 14 C]GA 19 compared to LD-treated plants. The difference was due to reduced metabolism of 14 C]GA 19 by SD-treated plants during the night period. On the other hand, metabolism of [ 14 C]GA53 was very limited in all day-length treatments and during both, day and night periods. The most abundant metabolite was [ 14 C]GA 19 (10% of the activity in the samples). Key words/phrases : Conjugation, ecotype, gibberellins, metabolism, radioactivity SINET: Ethiopian Journal of Science Vol. 28 (1) 2005: 33–40