Polygalacturonic acid

Pectin. Pectin [9000-69-5] is a generic term for a group of polysaccharides, mainly partially methoxylated polygalacturonic acids, which are located in the cell walls of all plant tissues. The main commercial sources of pectin are citms peel and apple pomace, where it represents 20—40% and 10—20% of the dry weight respectively. The pectin is extracted, the extract purified, and the pectin precipitated (50) increased extraction times lead to the production of low methoxyl pectins. 

Pectin is a collective name for heteropolysaccharides, which consist essentially of polygalacturon acid. Pectin is soluble in water only after a partial neutralization with alkali or ammonium hydroxide [18]. 

The possible involvement of polygalacturonic acid-containing molecules in the defence reactions of tomato root cells against Fusarium oxysporum was suggested about 20 years ago by their accumulation at penetration sites. Since papillae are held to serve as a resistance mechanism to fungal penetration, it was assumed that the interrelation between pectin and other polymers - such as lignin - may contribute to enhancing the hardness of these newly formed structures (Benhamou et al., 1990). 

The source materials were commercial pectins apple A30 and citrus pectin C73 kindly supplied by Unipectine (France) and Copenhagen Pectin Factory (Denmark) respectively. Polygalacturonic acid samples (named SR) were obtained by acid hydrolysis of a fully de-esterified citrus pectin as previously described [24]. Citrus pectins with different degree of esterification (DE) were obtained by controlled acid de-esterification [8]. 

Fig 4 FTIR spectra of walls of DCB-adapted and non-adapted tomato suspension cells, onion parenchyma cell walls, and polygalacturonic acid (Sigma), a = ester peak, b = free acid stretches from pectins, y axis is absorbance, X axis is wavenumber (frequency inverse). 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

BolweU, G.P., Dalessandro, G., and Northcote, D.H. (1985) Decrease of polygalacturonic acid synthase during xylem differentiation in sycamore. Phytochemistry, 24 699-702. 

ViUemez, C.L., Lin, T.-Y., and Hassid, W.Z. (1965) Biosynthesis of the polygalacturonic acid chain of pectin by a particulate enzyme preparation from phaseolus aureus seedlings. Proc.Natl.Acad.Sci.USA, 54 1626-1632. 

Immunogold localization of the pectic epitope has been performed on different types of cells cell suspensions, roots, shoots, meristems, coleoptiles, pollen grains, protoplasts from different species carrot, sugar beet, tobacco, oat... The pattern of labeling was always the same polygalacturonic acid was essentially located on the material expanded at three-way junctions between cells or lining intercellular space, but was not found in primary walls. No epitope could be located close to the plasma membrane (Fig. lO.a). Middle lamellae far from junction zones and walls of meristematic cells were never labeled. 

However the addition of exogeneous pectic substrate increased the incorporation of radioactivity up to twelve-fold. At neutral pH, the stimulation was larger in the presence of highly methylated pectin than in the presence of polygalacturonic acid. At pH 5.5, on the other... 

Fig. 5. Effect of PGl digestion on the ethylene synthesis-inducing activity of CDTA-soluble tomato pectin (a), Na2C03-soluble tomato pectin (b) and polygalacturonic acid (c). Controls were treated with solutions of heat-inactivated PGl. Treatment doses were 10 /tg of uronic acid equivalents. The line legends shown in panel a apply to all panels. Bars indicate SEs for the means of measurements of sets of 8 discs/teatment. fr wt, Fresh weight.

Endo-polygalacturonases I and II (PGI and PGII) isolated from recombinant A. niger were characterized with respect to pH optimum, activity on polygalacturonic acid (pga), mode of action and kinetics on oligogalacturonates. 

PL activity was determined by monitoring A236 for the formation of unsaturated products released from 0.1% polygalacturonic acid (P-1879, Sigma), dissolved in 0.1 M Tris/HCl buffer, pH 8,0 supplemented with 0.1 mM CaCb. One unit of PL is the enzyme activity liberating 1 pmol of unsaturated oligoglacturonides from pectate per min at 25°C. Activities are given in mU / ml extract per min. 

The oligomer separation procedure was performed according to the protocol described elsewhere [27]. Polygalacturonic acid (O.lg) was dissolved in 10 mL of citric-citrate buffer pH... 

Deiana S., Micera G., Muggiolu G., Gessa C. Pusino A. (1983) Interaction of transition-metal ions with polygalacturonic acid a potentiometric study. Colloids Surf. 6,17-25. 

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