Cell wall strength is decreased by both auxin treatment and low pH. In a recently proposed model of the plant cell wall, xyloglucan polymers are hydrogen-bonded to cellulose fibrils, forming the only noncovalent link in the network of polymers which cross-link the cellulose fibers. The decreased strength of the cell wall seen upon lowering the pH might be due to an effect of hydrogen ions on the rate of xyloglucan creep along cellulose fibers. This paper investigates binding of xyloglucan fragments to cellulose. At equilibrium, the per cent of nine- and seven-sugar xyloglucan fragments which are bound to cellulose is sensitive to both temperature and the concentration of nonaqueous solvents. However, neither the per cent of xyloglucan fragments bound to cellulose at equilibrium, nor the rate at which the xyloglucan fragments bind to cellulose, is sensitive to changes in hydrogen ion concentration. These results support the hypothesis that, within the cell wall, xyloglucan chains are connected to cellulose fibers by hydrogen bonds, but these results suggest that this interconnection between xyloglucan and cellulose is unlikely to be the point within the wall which regulates the rate of cell elongation.

The Structure of Plant Cell Walls: I. The Macromolecular Components of the Walls of Suspension-cultured Sycamore Cells with a Detailed Analysis of the Pectic Polysaccharides.

8 – Structure and Function of Plant Cell Walls

Publisher Summary This chapter focuses on the hemicelluloses of the Gramineae (grasses and cereals). The term “hemicelluloses” is also often extended to include certain carbohydrates in cereal endosperms—namely, non-starch polysaccharides. Hemicellulose refers to all of the types of polysaccharide in the Gramineae, other than celluloses, starches, and fructans. Hemicellulose chemistry has a vocabulary lacking invariant definitions, and insight into the nature of hemicelluloses has been gained by the work not only of chemists and biochemists but of applied scientists having research interests in animal nutrition, brewing, cereals, paper manufacture, and starch production. The chapter also discusses species and various tribes of Gramineae, isolation of hemicellulosimca materials and of pure hemicelluloses, and structural feature in hemicelluloses. The importance of knowledge about the hemicelluloses may be gauged by looking at the abundance of photosynthetically renewable grasses and bearing in mind that, apart from the materials in the seed, one third of their composition is hemicellulose.

The Hemicelluloses of Grasses and Cereals

Cell walls have been isolated from barley endosperm and found to contain a microfibrillar phase which is embedded in an amorphous matrix. The microfibrillar phase probably consists of cellulose, together with tightly bound arabinoxylan and polysaccharides rich in mannose. The matrix material is arabinoxylan (approx. 25%) and β-glucan (approx. 75%). Pectic polysaccharides are absent from the isolated cell walls. After successive removal of the matrix polysaccharides with water and 1-M NaOH, only 6% of the wall remains. The intra-cellular surfaces of the wall fragments are extensively pitted, probably as a result of adpression of starch granules into the cell wall material during endosperm development. Although polysaccharides are the major components of the cell walls, some nitrogen (less than 1%) is present. Phenolic compounds may also be wall constituents, but hydroxyproline could not be detected.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1975.tb03672.x

Margaret Meryl Smith

Papers

Chemical composition of the cell walls of Lolium multiflorum endosperm