© 1997 Heron Publishing—Victoria, Canada
Role of flavanols in yellowing beech trees of the Black Forest
W. Feucht, D. Treutter and E. Christ
Technical University of Munich, Faculty of Agriculture and Horticulture, D-85354 Freising-Weihenstephan, Germany / Received February 21, 1996
Summary
Beech leaves were sampled at the end of a prolonged hot dry period at a tree decline site in the Black Forest, Germany to
investigate the potential role of flavanols in defense mechanisms against environmental stress. Green and yellowing leaves
were harvested from the uppermost canopy of trees that were more than 200 years old and 30 m high. Yellowing leaves had a
7.4-fold higher concentration of total flavanols than green leaves. Green leaves contained flavanol inclusions, but during
yellowing the inclusions disintegrated and the cells became filled with flavanols. Abscisic acid (ABA) stimulated the release
of flavanols from intravacuolar inclusions of leaf petioles and flower pedicels. In addition, ABA caused flavanols to leach
from the trichomes of beech galls. The antioxidative potential of leaf extracts, as estimated by indoleacetic acid (IAA) oxidation,
was significantly higher in yellowing leaves than in green leaves. In vitro experiments revealed that (+)-catechin promoted
growth of beech tissue.
Keywords:
abscisic acid, catechins, histology, leaf yellowing, tree decline.
