PLANT PHYSIOLOGY , Vol 109, Issue 4 1483-1490, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Differential Induction of Cytochrome P450-Mediated Triasulfuron Metabolism by Naphthalic Anhydride and Triasulfuron
M. W. Persans and M. A. Schuler
Department of Plant Biology, 190 Plant and Animal Biotechnology Laboratory, University of Illinois, Urbana, Illinois 61801
Cytochrome P450 monooxygenases play paramount roles in the detoxification
of herbicides as well as in the synthesis of lignins, flavonoids, and
phenolic acids. Biochemical analysis of triasulfuron metabolism in maize
(Zea mays) seedlings has demonstrated that the P450(s) responsible for
detoxification of this herbicide is induced by naphthalic anhydride (NA), a
plant safener, and by triasulfuron, the herbicide itself. Induction studies
conducted with seedlings of different ages suggest that two separate
response pathways modulate this P-450 activity. Induction by NA is
independent of the developmental age of the seedlings up to 6.5 d;
induction by triasulfuron is tightly modulated with respect to
developmental age in that triasulfuron metabolism can be induced by
triasulfuron in young (2.5 d) but not older (6.5 d) seedlings. Induction by
NA administered in combination with triasulfuron synergistically enhances
triasulfuron metabolism in younger seedlings to levels substantially above
that obtained with either herbicide or safener treatment alone. In older
seedlings, NA plus triasulfuron treatment induces triasulfuron metabolism
to only the level of NA treatment alone, indicating again that the
induction cascade responding to triasulfuron is nonfunctional in later
development. MnCl2 studies indicate that the triasulfuron insensitivity of
older seedlings does not result from a general limitation in the
inducibility of this P-450 detoxification system but rather from specific
limitations in the triasulfuron-response pathway.
