PLANT PHYSIOLOGY , Vol 112, Issue 3 1383-1389, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
3,7-Dichloroquinolinecarboxylic Acid Inhibits Cell-Wall Biosynthesis in Maize Roots
S. J. Koo, J. C. Neal and J. M. DiTomaso
LG Chemical Limited Research Park, P.O. Box 61 Yusong, Taejon, Korea 305-380 (S.J.K.)
The mode of action of the herbicide 3,7-dichloroquinolinecar-boxylic acid
(quinclorac) was examined by measuring incorporation of [14C]glucose,
[14C]acetate, [3H]thymidine, and [3H]uridine into maize (Zea mays) root
cell walls, fatty acids, DNA, and RNA, respectively. Among the precursors
examined, 10 [mu]M quinclorac inhibited [14C]glucose incorporation into the
cell wall within 3 h. Fatty acid and DNA biosynthesis were subsequently
inhibited, whereas RNA biosynthesis was unaffected. In contrast to the
cellulose synthesis inhibitor 2,6-dichlorobenzonitrile, quinclorac strongly
inhibited cellulose and a hemicellulose fraction presumed to be
glucuronoarabinoxylan. However, the synthesis of
(1->3),(1->4)-[beta]-D-glucans was only slightly inhibited. The
degree of inhibition was time- and dose-dependent. By 4 h after treatment,
the concentration that inhibited [14C]glucose incorporation into the cell
wall, cellulose, and the sensitive hemicellulose fraction by 50% was about
15, 5, and 20 [mu]M, respectively. Concomitant with an inhibition of
[14C]glucose incorporation into the cell wall, quinclorac treatment led to
a marked accumulation of radioactivity in the cytosol. The increased
radioactivity was found mostly in glucose and fructose. However, total
levels of glucose, fructose, and uridine diphosphate-glucose were not
changed greatly by quinclorac. These data suggest that quinclorac acts
primarily as a cell-wall biosynthesis inhibitor in a susceptible grass by a
mechanism that is different from that of 2,6-dichlorobenzonitrile.
