ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Primary plant cell walls contain highly hydrated biopolymer networks, whose major chemistry is known but whose relationship to architectural and mechanical properties is poorly understood. Nuclear magnetic resonance spectroscopy has been used to characterize segmental mobilities via relaxation and anisotropy effects in order to add a dynamic element to emerging models for cell wall architecture.For hydrated onion cell wall material, single pulse excitation revealed galactan (pectin side chains), provided that dipolar decoupling was used, and some of the pectin backbone in the additional presence of magic angle spinning. Cross-polarization excitation revealed the remaining pectin backbones, which exhibited greater mobility (contact time dependence, dipolar dephasing) than the cellulose component, whose noncrystalline and crystalline fractions showed no mobility discrimination. 1HT2 behavior could be quantitatively interpreted in terms of high resolution observabilities. Mobility-resolved spectroscopy of cell walls from tomato fruit, pea stem, and tobacco leaf showed similar general effects.Nuclear magnetic resonance study of the sequential chemical extraction of onion cell wall material suggests that galactans fill many of the network pores, that extractability of pectins is not dependent on segmental mobility, and that some pectic backbone (and not side chain) is strongly associated with cellulose.Analysis of the state of cellulose in four hydrated cell walls suggests a noncrystalline content of 60-80% and comparable amounts of Iα and Iβ polymorphs in the crystalline fraction. Comparison with micrographs for onion cell walls shows that noncrystalline cellulose does not equate to chains on fibril surfaces, and chemical shifts show that fully solvated cellulose is not a significant component in cell walls. © 1996 John Wiley & Sons, Inc.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
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