PLANT PHYSIOLOGY , Vol 106, Issue 2 437-445, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Utilization of Amygdalin during Seedling Development of Prunus serotina
E. Swain and J. E. Poulton
Department of Biological Sciences, The University of Iowa, Iowa City, Iowa 52242
Cotyledons of mature black cherry (Prunus serotina Ehrh.) seeds contain the
cyanogenic diglucoside (R)-amygdalin. The levels of amygdalin, its
corresponding monoglucoside (R)-prunasin, and the enzymes that metabolize
these cyanoglycosides were measured during the course of seedling
development. During the first 3 weeks following imbibition, cotyledonary
amygdalin levels declined by more than 80%, but free hydrogen cyanide was
not released to the atmosphere. Concomitantly, prunasin, which was not
present in mature, ungerminated seeds, accumulated in the seedling
epicotyls, hypocotyls, and cotyledons to levels approaching 4 [mu]mol per
seedling. Whether this prunasin resulted from amygdalin hydrolysis remains
unclear, however, because these organs also possess UDPG:mandelonitrile
glucosyltransferase, which catalyzes de novo prunasin biosynthesis. The
reduction in amygdalin levels was paralleled by declines in the levels of
amygdalin hydrolase (AH), prunasin hydrolase (PH), mandelonitrile lyase
(MDL), and [beta]-cyanoalanine synthase. At all stages of seedling
development, AH and PH were localized by immunocytochemistry within the
vascular tissues. In contrast, MDL occurred mostly in the cotyledonary
parenchyma cells but was also present in the vascular tissues. Soon after
imbibition, AH, PH, and MDL were found within protein bodies but were later
detected in vacuoles derived from these organelles.