METABOLISM OF [14C]GA19 AND [14C]GA53 BY ECOTYPES OF BETULA PENDULA: THE ROLE OF PHOTOPERIOD

Abstract

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 GA19 and GA53. [14C]GA19 and [14C]GA53 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 A20,
A29, A1, and A8 were recovered as metabolites of [14C]GA19 both in apical stems and leaves. In 1SD and
4SD-treated plants, there was less metabolism of [14C]GA19 compared to LD-treated plants. The difference
was due to reduced metabolism of [14C]GA19 by SD-treated plants during the night period. On the other
hand, metabolism of [14C]GA53 was very limited in all day-length treatments and during both, day and
night periods. The most abundant metabolite was [14C]GA19 (10% of the activity in the samples).