SYNOPSISThe emulsion polymerization of large monodisperse MMA/BA copolymer particles by surfactant-free means at high solids content is described. A series of sequential seeded growth reactions were used to obtain monodisperse particles with diameters of a t least 3 microns. A combination of an oil-soluble initiator, AIBN, and a water-soluble initiator, ammonium persulfate (AP), was used. The AIBN initiated the bulk of the polymerization and the AP provided the stabilization for the polymer particles through its charged endgroups. The amount of AP initiator to be used in each growth step was calculated empirically using a criterion of a constant ratio of moles of sulfate groups to the polymer particle surface area.

Plants of Brassica napus were assessed quantitatively for their susceptibility to lateral root crack colonization by Azorhizobium caulinodans ORS571(pXLGD4) (a rhizobial strain carrying the lacZ reporter gene) and for the concentration of glucosinolates in their roots by high-pressure liquid chromatography (HPLC). High-and low-glucosinolate-seed (HGS and LGS) varieties exhibited a relatively low and high percentage of colonized lateral roots, respectively. HPLC showed that roots of HGS plants contained a higher concentration of glucosinolates than roots of LGS plants. One LGS variety showing fewer colonized lateral roots than other LGS varieties contained a higher concentration of glucosinolates than other LGS plants. Inoculated HGS plants treated with the flavonoid naringenin showed significantly more colonization than untreated HGS plants. This increase was not mediated by a naringenin-induced lowering of the glucosinolate content of HGS plant roots, nor did naringenin induce bacterial resistance to glucosinolates or increase the growth of bacteria. The erucic acid content of seed did not appear to influence colonization by azorhizobia. Frequently, leaf assays are used to study glucosinolates and plant defense; this study provides data on glucosinolates and bacterial colonization in roots and describes a bacterial reporter gene assay tailored easily to the study of ecologically important phytochemicals that influence bacterial colonization. These data also form a basis for future assessments of the benefits to oilseed rape plants of interaction with plant growth-promoting bacteria, especially diazotrophic bacteria potentially able to extend the benefits of nitrogen fixation to nonlegumes.

Following inoculation with Azorhizobium caulinodans ORS571(pXLGD4), lateral root development of rice and colonization of lateral root cracks by bacteria were shown to be stimulated by the £avonoid naringenin. Rice seedlings growing aseptically in the presence of naringenin were inoculated with ORS571(pXLGD4), carrying the lacZ reporter gene. By microscopic analysis of sections of inoculated rice roots, it has been demonstrated that the xylem of rice roots can be colonized by Azorhizobium caulinodans. We discuss whether this colonization of the xylem of rice roots by azorhizobia could provide a suitable niche for endophytic nitrogen ¢xation.

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Improved conditions were used for the aseptic growth of Arabidopsis thaliana to investigate whether xylem colonization of A. thaliana by Azorhizobium caulinodans ORS571 might occur. When seedlings were inoculated with ORS571 (pXLGD4) tagged with the lacZ reporter gene, nearly all of the plants showed blue regions of ORS571 colonization at lateral root cracks (LRC). The flavonoids naringenin and liquiritigenin significantly stimulated colonization of LRC by ORS571. Blue bands of ORS571 (pXLGD4) bacteria were observed histochemically in the xylem of intact roots of inoculated plants. Detailed microscopic analysis of sections of primary and lateral roots from inoculated A. thaliana confirmed xylem colonization. Xylem colonization also occurred with an ORS571 nodC mutant deficient in nodulation factors. There was no significant difference in the percentage of plants with xylem colonization or in the mean length of xylem colonized per plant between plants inoculated with either ORS571 (pXLGD4) or ORS571::nodC (pXLGD4), with or without naringenin.

SYNOPSISThe emulsion polymerization of large MMA/BA copolymer particles with narrow particle size distributions and core-shell structure is described. A series of sequential seeded growth emulsion polymerizations were used to obtain monodisperse particles with diameters of at least 3 Km, at 30% solids contents. Because the core and shell polymers used here were chemically similar, core-shell structures could not be verified by differential staining techniques. Core-shell structure was demonstrated by minimum film-forming temperature studies and by scanning electron microscopy in conjunction with energy dispersive x-ray analysis, using chlorine-labeled core polymers. 0 1995 John Wiley & Sons, Inc.

A novel pathway of invasion of the legume Sesbania rostrata by Azorhizobium caulinodans is described that involves colonization of the root xylem, possibly following entry into the natural ¢ssures created during emergence of lateral roots. Azorhizobia were detected microscopically, and their presence con¢rmed by the expression of a lacZ reporter gene. We have shown that rhizobial Nod factors are not required for either xylem colonization or for crack-entry of lateral roots. We discuss the extent to which this discovery of xylem colonization by azorhizobia is likely to improve our understanding of both symbiosis and of pathogenicity in plant^bacterial interactions.