Showing papers by "Kevin C. Vaughn published in 1999"

Herbicides that inhibit cellulose biosynthesis

Abstract: 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.

Structural and immunocytochemical characterization of the walls of dichlobenil-habituated by-2 tobacco cells

Abstract: BY‐2 tobacco cells, grown in the presence of the cellulose biosynthesis inhibitor herbicide dichlobenil (DCB), change in morphology from finely dispersed clumps and filaments to large aggregates after 6 mo. In this article, we utilize structural, cytochemical, and immunocytochemical techniques to characterize the cell wall changes that accompany the habituation of the cells to DCB. Wall structure is altered radically in the habituated cells, revealing a lamellate structure with no distinct middle lamella, even at cell junctions. Plasmodesmata traverse the cell wall by more circuitous routes than in the control cells. Habituated cells also produce unusual appositions of the wall that extend into the cytoplasm. Immunogold localization of various pectin epitopes reveals a 30‐fold‐greater density of gold particles detected in the walls of habituated cells compared to the controls and less density when the labeling of the middle lamellae is included. Antiextensin labeling was also found along the strands of pe...

The primary walls of cotton fibers contain an ensheathing pectin layer

Abstract: Cotton fiber walls (1–2 days post anthesis) are distinctly bilayered compared to those of nonfiber epidermal cells, with a more electron-opaque outer layer and a less electron-opaque, more finely fibrillar inner layer. When probed with antibodies and affinity probes to various saccharides, xyloglucans and cellulose are found exclusively in the inner layer and de-esterified pectins and extensin exclusively in the outer layer. Ovular epidermal cells that do not differentiate into fibers have no pectin sheath, but are labelled throughout with antixyloglucan and cellulase-gold probes. Middle lamellae between adjacent cells were clearly labelled with the antibodies to de-esterified pectins, however. Similarly, cell walls of leaf trichomes have a bilayered wall strongly enriched in pectin, whereas other epidermal cells are not bilayered and are pectin poor. These data indicate that one of the early markers of fiber and trichome cells from other epidermal cells involves the production of a pectin layer. The de-esterified pectins present in the ensheathing layer may allow for expansion and elongation of the fiber cells that does not occur in the other epidermal cells without such a sheath or may even be a consequence of the elongation process.

Structural and Immunological Characterization of the Cuscuta pentagona L. Chloroplast

Abstract: Structural and immunochemical studies were used to determine the photosynthetic potential of the dodder (Cuscuta pentagona) chloroplast. Ultrastructural studies revealed that thylakoid membranes of pre-parasitic phase Cuscuta pentagona are almost all organized into long, overlapping grana stacks of mainly two to five thylakoids with little space between adjacent stacks. Immunoblots reveal chloroplast proteins associated with PSI and 11, as well as cytochrome f and plastocyanin. Stromal extracts contained immmunologically-detectable RuBisCO and phosphoribulokinase. Cytochemical localizations of the oxidizing side of PSI showed product localization on the lumen side of the thylakoid. Immunocytochemical localizations of RuBisCO reveal exclusive labeling in the stroma, whereas antibodies to the PSII proteins, light-harvesting Chl a/b complex and the oxygen-evolving complex of PSII, are concentrated over the thylakoids. A limited capacity for C02 fixation was found in seedlings by monitoring exchange rates in the presence and absence of atrazine. These data indicate that the chloroplast from this species of dodder contains a number of the proteins required for a successful fixation of C02 and the proteins in the thylakoids are organized much like other higher plants, with the exception of the large percentage of the thylakoids organized into grana.