Herbicides that inhibit cellulose biosynthesis

The cellulose-biosynthesis inhibitor (CBI) herbicides all selectively inhib it the synthesis of cellulose despite significant chemical differences. Wit h the exception of quinclorac they are most effective in inhibiting cellulo se synthesis in dicot plants. Dichlobenil and isoxaben are the oldest and b est studied of these herbicides, whereas flupoxam is a more recent introduc tion and acts in many ways similarly to isoxaben. Quinclorac is unusual in that it seems to act as a cellulose inhibitor in grasses but as an auxinic herbicide in dicots. These herbicides inhibit cell plate formation at one o f two relatively late stages without affecting microtubule function. The ef fects of dichlobenil are different from other CBI herbicides; dichlobenil i nhibits cellulose synthesis but promotes callose synthesis in its place. Su spension cells of both Lycopersicon esculentum and Nicotiana tabacum can be come habituated to normally inhibitory concentrations of dichlobenil or iso xaben by replacing the normal cellulose network in their walls with pectin and extensin. Natural resistance to CBI herbicides is rare and has only bee n found in red algae species. Arabidopsis lines produced by mutagenesis all share changes in active site rather than alterations in uptake, translocat ion, or metabolism of these herbicides. The lack of cross-resistance to dif ferent CBI herbicides of these mutants indicates that no fewer than three d ifferent sites in the cellulose biosynthesis pathway are affected by the di fferent herbicides in this class.