Mobility-resolved 13C-NMR spectroscopy of primary plant cell walls

Abstract

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.

Celery ( Apium graveolens L.) parenchyma cell walls examined by atomic force microscopy: effect of dehydration on cellulose microfibrils

“…Moreover, the common practice of partially removing water from cell wall samples to improve the resolution of the signals in solid-state 13 C NMR spectra (Newman et al 1994(Newman et al , 1996Foster et al 1996;Jarvis et al 1996), will result in varying degrees of aggregation of the cellulose micro®brils.…”

Galactose loss and fruit ripening: high-molecular-weight arabinogalactans in the pectic polysaccharides of fruit cell walls

“…Therefore, it seems that these regions were not retained in the CWM-residue by entanglement of the arabinogalactan structure but by interactions which involved either the homogalacturonan or less-rami®ed regions (0.5 M fractions, Table 5) of the pectin molecule. This conclusion is supported by results of a mobility-resolved 13 C-nuclear magnetic resonance study of onion cell walls (Foster et al 1996). The authors inferred that pectic material which resisted extraction with 4 M KOH was associated with cellulose via the backbone rather than the side-chain regions of the pectic polysaccharide.…”

Biophysical consequences of remodeling the neutral side chains of rhamnogalacturonan�I in tubers of transgenic potatoes

“…the specimen is not under tension. Both galactans and arabinans have been found to be very mobile polymers in isolated walls (Foster et al 1996;Renard and Jarvis 1999). Tang et al (1999) measured the effects of hydration of potato cell walls and observed that the pectic polysaccharides responded to increased hydration very differently and showed a broad distribution of mobilities.…”