3,7-DICHLOROQUINOLINECARBOXYLIC ACID INHIBITS CELL-WALL BIOSYNTHESIS IN MAIZE ROOTS

The mode of action of the herbicide 3,7-dichloroquinolinecarboxylic ac id (quinclorac) was examined by measuring incorporation of [C-14]gluco se, [C-14]acetate, [H-3]thymidine, and [H-3]uridine into maize (Zea ma ys) root cell walls, fatty acids, DNA, and RNA, respectively. Among th e precursors examined, 10 mu M quinclorac inhibited [C-14]glucose inco rporation into the cell wall within 3 h. Fatty acid and DNA biosynthes is were subsequently inhibited, whereas RNA biosynthesis was unaffecte d. In contrast to the cellulose synthesis inhibitor 2,6-dichlorobenzon itrile, quinclorac strongly inhibited cellulose and a hemicellulose fr action presumed to be glucuronoarabinoxylan. However, the synthesis of (1 --> 3),(1 --> 4)-beta-D-glucans was only slightly inhibited. The d egree of inhibition was time- and dose-dependent. By 4 h after treatme nt, the concentration that inhibited [C-14]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 in hibition of [C-14]glucose incorporation into the cell wall, quinclorac treatment led to a marked accumulation of radioactivity in the cytoso l. The increased radioactivity was found mostly in glucose and fructos e. However, total levels of glucose, fructose, and uridine diphosphate -glucose were not changed greatly by quinclorac. These data suggest th at 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.