PLANT PHYSIOLOGY , Vol 103, Issue 2 329-334, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Biochemical Basis of Resistance of Tobacco Callus Tissue Cultures to Hydroxyphenylethylamines
J. Negrel, F. Javelle and M. Paynot
Laboratoire de Phytoparasitologie, Station de Genetique et d'Amelioration des Plantes,Institut National de la Recherche Agronomique BV 1540 21034, Dijon Cedex France
It has been reported that hydroxyphenylethylamines, such as tyramine and
octopamine, are toxic to tobacco (Nicotiana tabacum L.) callus cultures
grown in the presence of auxins, whereas calli grown in the presence of
cytokinins and crown gall cultures are resistant to these amines (P.
Christou and K.A. Barton [1989] Plant Physiol 89: 564-568). In an attempt
to understand the underlying mechanism of this resistance, we compared the
fates of tyramine in tyramine-sensitive and tyramine-resistant tobacco
tissue cultures (cv Xanthi nc). The very rapid formation of black-colored
oxidation products from tyramine in sensitive tissues suggested that the
toxicity might be caused by the oxidation of tyramine by phenol oxidases
present in the tissues or released into the medium after subculture. This
was confirmed through many indirect procedures (effect of exogenously added
tyrosinase, induction of polyphenol oxidase [PPO] activity by auxin, etc.).
The study of tyramine structure-activity relationships further suggested
that the toxicity of tyramine might be due to the formation of
indolequinones after oxidation by PPO. Subculture of calli grown on
2,4-dichlorophenoxyacetic acid in a medium containing benzyladenine
triggered a slow decrease in PPO activity and dramatic increases in
peroxidase and tyramine hydroxycinnamoyl transferase (THT) activities. THT
was undetectable in calli grown on 2,4-dichlorophenoxyacetic acid but very
active in tyramine-resistant crown gall cultures. Moreover, when
[3H]tyramine was fed in vivo to tyramine-resistant tissues, it was rapidly
integrated into cell walls in the wound periderm formed at the periphery of
the calli. Both the conjugation of tyramine and its integration into cell
walls could compete with the formation of toxic quinones and therefore play
a part in the resistance. Thus, it seems likely that the control of the
toxicity of hydroxyphenylethylamines by cytokinins results primarily from
changes in the metabolism and the compartmentation of these amines.
