Form and function of arabinogalactans and arabinogalactan-proteins

Cross-reactive antigens of clover roots and Rhizobium trifolii were detected on their cell surfaces by tube agglutination, immunofluorescent, and radioimmunoassay techniques. Anti-clover root antiserum had a higher agglutinating titer with infective strains of R. trifolii than with noninfective strains. The root antiserum previously adsorbed with noninfective R. trifolii cells remained reactive only with infective cells, including infective revertants. When adsorbed with infective cells, the root antiserum was reactive with neither infective nor noninfective cells. Other Rhizobium species incapable of infecting clover did not demonstrate surface antigens cross-reactive with clover. Radioimmunoassay indicated twice as much antigenic cross-reactivity of clover roots and R. trifolii 403 (infective) than R. trifolii Bart A (noninfective). Immunofluorescence with anti-R. trifolii (infective) antiserum was detected on the exposed surface of the root epidermal cells and diminished at the root meristem. The immunofluorescent crossreaction on clover roots was totally removed by adsorption of anti-R. trifolii (infective) antiserum with encapsulated infective cells but not with noninfective cells. The cross-reactive capsular antigens from R. trifolii strains were extracted and purified. The ability of these antigens to induce clover root hair deformation was much greater when they were obtained from the infective than noninfective strains. The cross-reactive capsular antigen of R. trifolii 403 was characterized as a high-molecular-weight (greater than 4.6 times 10(6) daltons), beta-linked, acidic heteropolysaccharide containing 2-deoxyglucose, galactose, glucose, and glucuronic acid. A soluble, nondialyzable, substance (clover lectin) capable of binding to the cross-reactive antigen and agglutinating only infective cells of R. trifolii was extracted from white clover seeds. This lectin was sensitive to heat, Pronase, and trypsin. inhibition studies indicated that 2-deoxyglucose was the most probable haptenic determinant of the cross-reactive capsular antigen capable of binding to the root antiserum and the clover lectin. A model is proposed suggesting the preferential adsorption of infective versus noninfective cells of R. trifolii on the surface of clover roots by a cross-bridging of their common surface antigens with a multivalent clover lectin. Images

Cross-reactive antigens and lectin as determinants of symbiotic specificity in the Rhizobium-clover association.

Publisher Summary This chapter discusses important sources of polysaccharides and their molecular constitutions. Two associated plant polysaccharides are the D-fructo-furanans and β-D-glucans containing mixed linkages. The association of lignin with polysaccharides through chemical linkages as well as in the form of physical incrustation is of profound economic importance in relation to the digestion of feedstuffs by ruminants and the exploitation of carbohydrate resources through enzymatic breakdown. Pectic substances or pectins have long been considered to include diverse types of polysaccharide structure based on appropriately linked units of D-galacturonic acid, D-galactose, and L-arabinose and are, like the hemicelluloses, of great economic importance. The capacity of a plant to assemble numerous sugar residues in an orderly matter must in some measure reflect certain genetic characteristics of the species concerned. The relationships of the hemicelluloses and pectic substances in primary cell walls to the polysaccharides available in abundance from tissues in developed, mature plant stuffs are interesting because the same economy of use of relatively few sugars linked in a limited number of ways is observed throughout. The presence or absence of minor structural features in a purified, homogeneous (or at least not demonstrably heterogeneous) polysaccharide preparation is of limited significance in the cases in which the isolation of the polysaccharide requires lengthy and involves physical and chemical extraction procedures.

Other Plant Polysaccharides

Greg P. Belue

Papers

High-pressure liquid chromatography of carbohydrates

High-pressure liquid chromatography of polyhydric alcohols on silica gel columns

Degradation of hemicelluloses by piperidine