title: Water-polysaccharide interactions in the primary cell wall of Arabidopsis thaliana from polarization transfer solid-state NMR.
abstract: Polysaccharide-rich plant cell walls are hydrated under functional conditions, but the molecular interactions between water and polysaccharides in the wall have not been investigated. In this work, we employ polarization transfer solid-state NMR techniques to study the hydration of primary-wall polysaccharides of the model plant, Arabidopsis thaliana. By transferring water (1)H polarization to polysaccharides through distance- and mobility-dependent (1)H-(1)H dipolar couplings and detecting it through polysaccharide (13)C signals, we obtain information about water proximity to cellulose, hemicellulose, and pectins as well as water mobility. Both intact and partially extracted cell wall samples are studied. Our results show that water-pectin polarization transfer is much faster than water-cellulose polarization transfer in all samples, but the extent of extraction has a profound impact on the water-polysaccharide spin diffusion. Removal of calcium ions and the consequent extraction of homogalacturonan (HG) significantly slowed down spin diffusion, while further extraction of matrix polysaccharides restored the spin diffusion rate. These trends are observed in cell walls with similar water content, thus they reflect inherent differences in the mobility and spatial distribution of water. Combined with quantitative analysis of the polysaccharide contents, our results indicate that calcium ions and HG gelation increase the amount of bound water, which facilitates spin diffusion, while calcium removal disrupts the gel and gives rise to highly dynamic water, which slows down spin diffusion. The recovery of spin diffusion rates after more extensive extraction is attributed to increased water-exposed surface areas of the polysaccharides. Water-pectin spin diffusion precedes water-cellulose spin diffusion, lending support to the single-network model of plant primary walls in which a substantial fraction of the cellulose surface is surrounded by pectins.
authors.affiliation: Department of Chemistry and Ames Laboratory, Iowa State University , Ames, Iowa 50011, United States.
authors.forename: Paul B
authors.initials: PB
authors.lastname: White
authors.forename: Tuo
authors.initials: T
authors.lastname: Wang
authors.forename: Yong Bum
authors.initials: YB
authors.lastname: Park
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Cosgrove
authors.forename: Mei
authors.initials: M
authors.lastname: Hong
mesh_terms: D017360:Arabidopsis / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D002247:Carbon Isotopes; D002473:Cell Wall / Q000737:chemistry* / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010368:Pectins / Q000737:chemistry / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D011134:Polysaccharides; D014867:Water; D010368:Pectins; D002482:Cellulose