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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Novel Rhamnogalacturonan I and Arabinoxylan Polysaccharides of Flax Seed Mucilage^1,[C],[OA]

Department of Botany and Plant Pathology (R.N., N.C.C.) and Department of Agricultural and Biological Engineering (G.C.), Purdue University, West Lafayette, Indiana 47907–2054

The viscous seed mucilage of flax (Linum usitatissimum) is a mixture of rhamnogalacturonan I and arabinoxylan with novel side group substitutions. The rhamnogalacturonan I has numerous single nonreducing terminal residues of the rare sugar L-galactose attached at the O-3 position of the rhamnosyl residues instead of the typical O-4 position. The arabinoxylan is highly branched, primarily with double branches of nonreducing terminal L-arabinosyl units at the O-2 and O-3 positions along the xylan backbone. While a portion of each polysaccharide can be purified by anion-exchange chromatography, the side group structures of both polysaccharides are modified further in about one-third of the mucilage to form composites with enhanced viscosity. Our finding of the unusual side group structures for two well-known cell wall polysaccharides supports a hypothesis that plants make a selected few ubiquitous backbone polymers onto which a broad spectrum of side group substitutions are added to engender many possible functions. To this end, modification of one polymer may be accompanied by complementary modifications of others to impart functions to heterocomposites not present in either polymer alone.

² Present address: Complex Carbohydrate Research Center, 315 Riverbend Road, University of Georgia, Athens, GA 30602–4712.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Nicholas C. Carpita (carpita{at}purdue.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.123513

^* Corresponding author; e-mail carpita{at}purdue.edu.

Received May 25, 2008; accepted July 22, 2008; published July 30, 2008.

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