Molecular Size and Separability Features of Pea Cell Wall Polysaccharides

Abstract

Relative molecular size distributions of pectic and hemicellulosic polysaccharides of pea (Pisum sativum cv Alaska) third intemode primary walls were determined by gel filtration chromatography. Pectic polyuronides have a peak molecular mass of about 1100 kilodaltons, relative to dextran standards. This peak may be partly an aggregate of smaller molecular units, because demonstrable aggregation occurred when samples were concentrated by evaporation. About 86% of the neutral sugars (mostly arabinose and galactose) in the pectin cofractionate with polyuronide in gel filtration chromatography and diethylaminoethyl-cellulose chromatography and appear to be attached covalently to polyuronide chains, probably as constituents of rhamnogalacturonans. However, at least 60% of the wall's arabinan/ galactan is not linked covalently to the bulk of its rhamnogalacturonan, either glycosidically or by ester links, but occurs in the hemicellulose fraction, accompanied by negligible uronic acid, and has a peak molecular mass of about 1000 kilodaltons. Xyloglucan, the other principal hemicellulosic polymer, has a peak molecular mass of about 30 kilodaltons (with a secondary, usually minor, peak of approximately 300 kilodaltons) and is mostly not linked glycosidically either to pectic polyuronides or to arabinogalactan. The relatively narrow molecular mass distributions of these polymers suggest mechanisms of co-or postsynthetic control of hemicellulose chain length by the cell. Although the macromolecular features of the mentioned polymers individually agree generally with those shown in the widely disseminated sycamore cell primary wall model, the matrix polymers seem to be associated mostly noncovalently rather than in the covalently interlinked meshwork postulated by that model. Xyloglucan and arabinan/galactan may form tightly and more loosely bound layers, respectively, around the cellulose microfibrils, the outer layer interacting with pectic rhamnogalacturonans that occupy interstices between the hemicellulose-coated microfibrils.The cell wall plays a critical role in plant cell enlargement. A wide range of growth-regulating agents, including both hormones and environmental factors, apparently act by modifying the ability of the primary wall to extend irreversibly.

Cell wall polysaccharides of common beans (Phaseolus vulgaris L.)

“…These results are very coherent with the legume seed sugar compositions reported in the literature [11,15,19,20,25,27,33,37]. BHATTY [4] inferred that the lentil cell wall was probably composed of arabinan and arabinogalactan polysaccharides, because such polysaccharides are commonly distributed in the primary cell wall of cotyledonous plants.…”

Temporal Sequence of Cell Wall Disassembly in Rapidly Ripening Melon Fruit1

“…Arabinogalactans or arabinans and galactans have been identified as side chains of rhamnogalacturonans or proposed to exist as free macromolecules, possibly forming a separate layer surrounding the xyloglucan/cellulose network (Talbott and Ray, 1992). A prominent peak of xylo- glucan co-eluted in the void volume and showed a similar pattern during softening to that of the arabinogalactan-rich TS peak, exhibiting apparent degradation in the last two ripening stages.…”

“…Compositional analysis indicated that at the IG and R1 stages, prior to its loss, subfraction i was particularly rich in Gal (40 mol %), with smaller amounts of Ara and Glc (Table III) and approximately 5 mol % Rha. The presence of substantial amounts of Gal and Ara in discrete, highmolecular-mass hemicellulosic polymers (Ͼ 1000 kD) has been described previously (Talbott and Ray, 1992). This was attributed to the presence of large arabinogalactan molecules, possibly comprised of glycosidically linked arabinan and galactan subunits.…”

Solid-State 13C Nuclear Magnetic Resonance Characterization of Cellulose in the Cell Walls of Arabidopsis thaliana Leaves

“…This is a surprising finding that requires further work because xyloglucans are a major component of the primary cell walls of dicotyledons, including A. thaliana (Zablackis et al, 1995), and it is well known that xyloglucans bind to cellulose in vitro (Vincken et al, 1995;Whitney et al, 1995). This binding of xyloglucans to cellulose is an important feature of models of dicotyledon primary cell walls (Talbott and Ray, 1992;Carpita and Gibeaut, 1993) in which the xyloglucans are believed to coat and cross-link the cellulose microfibrils. Furthermore, McQueen-Mason and Cosgrove (1994) tentatively suggested that expansins (proteins that catalyze the extension of isolated plant cell walls) act by inducing slippage between the cellulose microfibril and its surface coat of xyloglucans.…”