PLANT PHYSIOLOGY , Vol 114, Issue 4 1433-1442, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Enrichment in Specific Soluble Sugars of Two Eucalyptus Cell-Suspension Cultures by Various Treatments Enhances Their Frost Tolerance via a Noncolligative Mechanism
S. Travert, L. Valerio, I. Fouraste, A. M. Boudet and C. Teulieres
Signaux et Messages Cellulaires chez les Vegetaux, Unite Mixte de Recherche no. 5546, Centre National de la Recherche Scientifique/Universite Paul Sabatier, Centre de Biologie et Physiologie Vegetales, 118 Route de Narbonne, 31062 Toulouse cedex, France
A cell-suspension culture obtained from the hybrid Eucalyptus
gunnii/Eucalyptus globulus was hardened by exposure to lower temperatures,
whereas in the same conditions cells from a hybrid with a more
frost-sensitive genotype, Eucalyptus cypellocarpa/Eucalyptus globulus, were
not able to acclimate. During the cold exposure the resistant cells
accumulated soluble sugars, in particular fructose and sucrose, with a
limited increase in cell osmolality. In contrast, the cell suspension that
was unable to acclimate did not accumulate soluble sugars in response to
the same cold treatment. To an extent similar to that induced after a cold
acclimation, frost-hardiness of the cells increased after a 14-h incubation
with specific soluble sugars such as sucrose, raffinose, fructose, and
mannitol. Such hardening was also observed for long-term cultures in
mannitol-enriched medium. This cryoprotective effect of sugars without
exposure to lower temperatures was observed in both the resistant and the
sensitive genotypes. Mannitol was one of the most efficient carbohydrates
for the cryoprotection of eucalyptus. The best hardiness (a 2.7-fold
increase in relative freezing tolerance) was obtained for the resistant
cells by the cumulative effect of cold-induced acclimation and mannitol
treatment. This positive effect of certain sugars on eucalyptus freezing
tolerance was not colligative, since it was independent of osmolality and
total sugar content.
