© 2003 Heron Publishing—Victoria, Canada
Different responses of northern and southern ecotypes of Betula pendula to exogenous ABA application
Chunyang Li (1, 2), Olavi Junttila (3, 4), Pekka Heino (1) and E. Tapio Palva (1, 5)
1. Department of Biosciences, Division of Genetics and Institute of Biotechnology, Viikki Biocenter, P.O. Box 56, FIN-00014 University
of Helsinki, Finland / 2. Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, P.R. China / 3. Department of Biology, University of Tromsø, N-9037 Tromsø, Norway / 4. Department of Applied Biology, P.O. Box 27, FIN-00014 University of Helsinki, Finland / 5. Author to whom correspondence should be addressed (tapio.palva@helsinki.fi) / Received August 8, 2002; accepted November 2, 2002; published online April 1, 2003
Summary
We investigated responses of northern and southern ecotypes of silver birch (Betula pendula Roth) to exogenous abscisic acid (ABA) under controlled environmental conditions to determine the role of ABA in cold acclimation
and dormancy development. Abscisic acid was sprayed on the leaves and changes in freezing tolerance, determined by the electrolyte
leakage test, and bud dormancy were monitored. Applied ABA induced cold acclimation but had no effect on growth cessation
in seedlings grown in long day conditions (LD, 24-h photoperiod at 18 °C). It enhanced freezing tolerance and accelerated
growth cessation in seedlings grown in short day conditions (SD, 12-h photoperiod at 18 °C), and slightly enhanced freezing
tolerance in seedlings grown at low temperature (LT, 24-h photoperiod at 4 °C) in both ecotypes. There were distinct ecotypic
differences in ABA-induced cold acclimation and dormancy development. The northern ecotype was more responsive to applied
ABA than the southern ecotype, resulting in more rapid development of freezing tolerance in all treatments, and earlier dormancy
development in SD. When plants were grown in a photoperiod just above the critical photoperiod for the ecotype (defined as
the longest photoperiod that induces growth cessation), applied ABA caused growth cessation and dormancy development. Compared
with ABA-treated seedlings grown in SD, dormancy development was delayed in ABA-treated seedlings exposed to a near-critical
photoperiod, but even in this treatment dormancy developed faster in the northern ecotype than in the southern ecotype.
Keywords:
cold acclimation, dormancy, freezing tolerance, growth cessation.
