The cellulose-biosynthesis inhibitor (CBI) herbicides all selectively inhibit the synthesis of cellulose despite significant chemical differences. With the exception of quinclorac, they are most effective in inhibiting cellulose synthesis in dicot plants. Dichlobenil and isoxaben are the oldest and best studied of these herbicides, whereas flupoxam is a more recent introduction 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 of two relatively late stages without affecting microtubule function. The effects of dichlobenil are different from other CBI herbicides; dichlobenil inhibits cellulose synthesis but promotes callose synthesis in its place. Suspension cells of both Lycopersicon esculentum and Nicotiana tabacum can become habituated to normally inhibitory concentrations of dichlobenil or isoxaben by replacing the normal cellulose network in their walls with pectin and extensin. Natural resistance to CBI herbicides is rare and has only been found in red algae species. Arabidopsis lines produced by mutagenesis all share changes in active site rather than alterations in uptake, translocation, or metabolism of these herbicides. The lack of cross-resistance to different CBI herbicides of these mutants indicates that no fewer than three different sites in the cellulose biosynthesis pathway are affected by the different herbicides in this class.

One to 5.6 μM DCPA (dimethyl tetrachloroterephthalate) inhibited oat (Avena sativa L. ‘Victory’) root growth within 12 to 18 h. Treated roots were severely stunted and swollen. An analysis of cell division in roots treated with DCPA revealed a disruption of normal mitosis after prophase. Metaphase, anaphase, and telophase division figures were absent 8 to 10 h after treatment with 5.6 μM DCPA. In contrast, a 24-h treatment with 5.6 μM DCPA was necessary to eliminate prophase division figures. The number of aberrant division figures increased concomitantly with the reduction in normal division figures. The predominant type of aberrant division figure was a condensed prophase. When the aberrant division cycle was completed and cells entered interphase, the dispersed chromosomes coalesced to form large, polymorphic nuclei and, occasionally, micronuclei. Approximately 60% of the outer four tiers of cells in roots treated with 5.6 μM DCPA developed abnormal cell walls. These data suggest that DCPA causes root growth inhibition by disrupting several processes involving organized microtubules.