Kasapis S, Morris ER, Gross M, Rudolph K Solution properties of levan polysaccharide from Pseudomonas syringae pv. phaseolicola, and its possible primary role as a blocker of recognition during pathogenesis Carbohydrate Polymers23(1) (1994)
55-64
Taxonomic group: plant / Streptophyta (Phylum: Streptophyta) Organ / tissue:seed
Publication DOI:10.1016/0144-8617(94)90090-6 Journal NLM ID:8307156 Publisher: Elsevier Institutions: Department of Food Research and Technology, Cranfield University, Silsoe College, Silsoe, Bedford MK45 4DT, UK, Institut für Pflanzenpathologie und Pflanzenschutz der Universität Göttingen, Grisebachstr.6, D-3400 Göttingen, Germany
Bacterial levan, a highly branched, high molecular weight polymer of fructose, was purified from culture supernatants of Pseudomonas syringaepv.phaseolicola grown in a liquid high-sucrose medium, and the predominance of β-(2 → 6) linkages was confirmed by 13C NMR. The solution properties of this material resembled those of disordered linear polysaccharides in the response to low-amplitude oscillatory shear (frequency dependence of G′ and G″); the absence of any detectable conformational change with temperature (as monitored by optical rotation); close superposition of steady-shear viscosity (η) and complex dynamic viscosity (gh*) at equivalent values of shear-rate (γs-1) and frequency (ωrad s-1); a similar form of shear-thinning (giving linear plots of η versus ηγ0.76); and the onset of semi-dilute behaviour at a closely comparable degree of space-occupancy (c[η] ≈ 3·6). The intrinsic viscosity, however, was unusually low ([η] ≈ 0·17 dl g−1) and the concentration dependence of ‘zero-shear’ viscosity in the semi-dilute regime unusually high (η0 ∼ c9·3), as anticipated from the densely packed, branched molecular structure. Solutions of levan and pectin, matched to approximately the same initial viscosity, showed a substantial reduction in viscosity when mixed. Similar behaviour was observed for mixed solutions of levan with locust bean gum (LBG), chosen for its structural similarity to cellulose and hemicelluloses of the plant cell wall. Viscosity reduction was eliminated at low concentrations (indicating that it does not arise from heterologous association), but became very pronounced at high concentrations, and was then accompanied by resolution into levan-rich and LBG-rich solution phases. This evidence of strong thermodynamic incompatibility and exclusion behaviour with (1 → 4)-linked plant polysaccharides suggests that the primary role of levan during pathogenesis may be as a barrier to intimate morphological contact (recognition) between plant cell walls and those of the parasite, thus inhibiting initiation of a hypersensitive response by the host.
Structure type: polymer chemical repeating unit ; n is large
Kasapis S, Morris ER, Gross M, Rudolph K Solution properties of levan polysaccharide from Pseudomonas syringae pv. phaseolicola, and its possible primary role as a blocker of recognition during pathogenesis Carbohydrate Polymers23(1) (1994)
55-64
Publication DOI:10.1016/0144-8617(94)90090-6 Journal NLM ID:8307156 Publisher: Elsevier Institutions: Department of Food Research and Technology, Cranfield University, Silsoe College, Silsoe, Bedford MK45 4DT, UK, Institut für Pflanzenpathologie und Pflanzenschutz der Universität Göttingen, Grisebachstr.6, D-3400 Göttingen, Germany
Bacterial levan, a highly branched, high molecular weight polymer of fructose, was purified from culture supernatants of Pseudomonas syringaepv.phaseolicola grown in a liquid high-sucrose medium, and the predominance of β-(2 → 6) linkages was confirmed by 13C NMR. The solution properties of this material resembled those of disordered linear polysaccharides in the response to low-amplitude oscillatory shear (frequency dependence of G′ and G″); the absence of any detectable conformational change with temperature (as monitored by optical rotation); close superposition of steady-shear viscosity (η) and complex dynamic viscosity (gh*) at equivalent values of shear-rate (γs-1) and frequency (ωrad s-1); a similar form of shear-thinning (giving linear plots of η versus ηγ0.76); and the onset of semi-dilute behaviour at a closely comparable degree of space-occupancy (c[η] ≈ 3·6). The intrinsic viscosity, however, was unusually low ([η] ≈ 0·17 dl g−1) and the concentration dependence of ‘zero-shear’ viscosity in the semi-dilute regime unusually high (η0 ∼ c9·3), as anticipated from the densely packed, branched molecular structure. Solutions of levan and pectin, matched to approximately the same initial viscosity, showed a substantial reduction in viscosity when mixed. Similar behaviour was observed for mixed solutions of levan with locust bean gum (LBG), chosen for its structural similarity to cellulose and hemicelluloses of the plant cell wall. Viscosity reduction was eliminated at low concentrations (indicating that it does not arise from heterologous association), but became very pronounced at high concentrations, and was then accompanied by resolution into levan-rich and LBG-rich solution phases. This evidence of strong thermodynamic incompatibility and exclusion behaviour with (1 → 4)-linked plant polysaccharides suggests that the primary role of levan during pathogenesis may be as a barrier to intimate morphological contact (recognition) between plant cell walls and those of the parasite, thus inhibiting initiation of a hypersensitive response by the host.
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