Soluble Cell Wall Polysaccharides Released from Pea Stems by Centrifugation

Abstract

The metabolism of polysaccharides by pea stem segments treated with and without auxin was investigated using a centrifugation technique for removing solution from the free space of the cell wail. Glucose is the predominant sugar in both the ethanol-soluble and ethanol-insoluble fracdons of the cell wall solution extracted with water. In the water-soluble, ethanol-insoluble polysaccharides, arabinose, xylose, galactose, and glucose make up 9.5, 23.8, 23.9, and 39.9%, respectively, of the neutral sugars, while rhamnose, fucose, and mannose are present at concentrations between 0.5 and 2.0%.Auxin treatment enhances the levels of xylose and glucose in ethanolinsoluble polysaccharides relative to controls, and this difference can be detected within 30 minutes of auxin treatment. Cellulose-binding experiments show that the enhanced levels of xylose and glucose are in a polymer having the cellulose-binding properties of xyloglucan. 3H-glucose labeling experiments confirm the auxin-enhanced metabolism of the xyloglucan fraction; however, increased labeling of arabinose is also observed in auxintreated sections. Auxin treatment also causes a marked increase in the level of uronic acids centrifuged from pea internode sections. Thus, after 3 hours of incubation in indoleacetic acid, the level of uronic acids in the ethanol-insoluble polysaccharides which can be recovered by centrifugation is increased 2-to 3-fold over sections incubated in water. These auxinenhanced changes in xylose, glucose, and uronic acids are correlated with enhanced rates of section growth.Incubation of excised pea internode sections in acidic buffers also enhances the rate of xyloglucan and polyuronide metabolism. This acidenhanced metabolism of xyloglucan and polyuronide is inhibited by low temperature, suggesting that it is enzyme-mediated.Extraction of the ceUl wan solution with CaC2 increases the yield of an neutral sugars. Arabinose and mannose are increased 4-and 3-fold, respectively, and xylose and glucose by about 20%, while galactose levels are 40% higher in cell wan solution extracted with CaCI2 than in that extracted with water. Although calcium increases the amoumt of neutral sugars extracted, it does not affect the auxin-induced changes in neutral sugars. Extraction of the cell wanl solution with ethyleneglycol-bis-4f-aminoethyl ether)-N,N'tetraacetic acid enhances the yield of uronic acids and also increases the difference due to auxin treatment.The cell wall has become the focus of research into the mechanism whereby plant hormones stimulate cell expansion. Heyn (7)

Pea Xyloglucan and Cellulose

“…The integrity of xyloglucan could then control the ability of microfibrils to separate (loosen) and the whole cell to expand during growth. This idea is supported by observations (4,15,16,19,20,24) that treatment of young plant tissue with the auxin-type of growth hormone leads to solubilization of part of the normally insoluble xyloglucan and to decrease in the average mol wt of the polysaccharide. The question at issue concerns the mechanism ofhormone action, specifically whether auxin-induced endo-l,4-fl-glucanases could be responsible for the observed degradation and solubilization of pea xyloglucan in the wall by hydrolyzing accessible chains during cell expansion.…”

Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth

“…This hypothesis has been accepted slowly because of some peculiarities about the levels of p-o-glucan in the wall during growth. In species with type I walls, growth induced by regulators is correlated with a distinct decrease or solubilization of XG in vivo and in vitro (Hayashi eta/., 1984;Labavitch and Ray, 1974;Taiz, 1984;Terry et a/., 1981). Most of the confusion about a similar role for p-oglucan in type II walls results from lack of a clear correlation between growth and loss of polysaccharide.…”

Soluble Cell Wall Polysaccharides Released from Pea Stems by Centrifugation

“…The effects of ethylene on growth contrast with those of auxin since auxin stimulates elongation of intact or excised pea internodes (6, 7, 10). In auxin-treated tissue, cell elongation is correlated with an increase in cell wall plasticity (9) and with the enhanced metabolism of a water-soluble xyloglucan fragment (12,13,22,23) and a pectic polymer (23) in the cell wall. There have been numerous attempts to correlate changes in cell wall polymers with ethylene-induced growth; however, most studies have emphasized changes in the hydroxyproline-rich proteins of the cell wall.…”