PLANT PHYSIOLOGY , Vol 101, Issue 3 745-749, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Anticyclic Timing of Leaf Senescence in the Parasitic Plant Viscum album Is Closely Correlated with the Selective Degradation of Sulfur-Rich Viscotoxins
G. Schrader-Fischer and K. Apel
Swiss Federal Institute of Technology (ETH), Institut fur Pflanzenwissenschaften, Abteiling Pflanzengenetik, Universitatsstrasse 2, 8092 Zurich, Switzerland
Leaf senescence and abscission have been studied in the semi-parasitic
plant mistletoe (Viscum album). Leaf senescence and abscission occur in the
summer, when the metabolic activity of the host has reached its maximum. In
contrast with their hosts, mistletoes selectively degrade only one major
leaf protein during leaf senescence, the sulfur-rich viscotoxin, whereas
most of the remaining leaf proteins are lost during abscission. The changes
in viscotoxin content are paralleled by changes in the concentration of the
corresponding mRNA. Shortly before the onset of leaf senescence, the mRNA
for viscotoxin has disappeared from the leaves. The anticyclic timing of
leaf senescence and the degradation of only one major leaf protein seems to
reflect an adaptation of the parasite to its habitat.
