Pectin is a major component of primary cell walls of all land plants and encompasses a range of galacturonic acid-rich polysaccharides Three major pectic polysaccharides (homogalacturonan, rhamnogalacturonan-I and rhamnogalacturonan-II) are thought to occur in all primary cell walls This review surveys what is known about the structure and function of these pectin domains The high degree of structural complexity and heterogeneity of the pectic matrix is produced both during biosynthesis in the endomembrane system and as a result of the action of an array of wall-based pectin-modifying enzymes Recent developments in analytical techniques and in the generation of anti-pectin probes have begun to place the structural complexity of pectin in cell biological and developmental contexts The in muro de-methyl-esterification of homogalacturonan by pectin methyl esterases is emerging as a key process for the local modulation of matrix properties Rhamnogalacturonan-I comprises a highly diverse population of spatially and developmentally regulated polymers, whereas rhamnogalacturonan-II appears to be a highly conserved and stable pectic domain Current knowledge of biosynthetic enzymes, plant and microbial pectinases and the interactions of pectin with other cell wall components and the impact of molecular genetic approaches are reviewed in terms of the functional analysis of pectic polysaccharides in plant growth and development

https://link.springer.com/content/pdf/10.1023/A:1010662911148.pdf

Pectin: cell biology and prospects for functional analysis

Pectin or pectic substances are collective names for a group of closely associated polysaccharides present in plant cell walls where they contribute to complex physiological processes like cell growth and cell differentiation and so determine the integrity and rigidity of plant tissue. They also play an important role in the defence mechanisms against plant pathogens and wounding. As constituents of plant cell walls and due to their anionic nature, pectic polysaccharides are considered to be involved in the regulation of ion transport, the porosity of the walls and in this way in the control of the permeability of the walls for enzymes. They also determine the water holding capacity. The amount and composition of pectic molecules in fruits and vegetables and other plant produce strongly determine quality parameters of fresh and processed food products. Pectin is also extracted from suitable agro-by-products like citrus peel and apple pomace and used in the food industry as natural ingredients for their gelling, thickening, and stabilizing properties. Some pectins gain more and more interest for their health modulating activities. Endogenous as well as exogenous enzymes play an important role in determining the pectic structures present in plant tissue, food products, or ingredients at a given time. In this paper functional and structural characteristics of pectin are described with special emphasis on the structural elements making up the pectin molecule, their interconnections and present models which envisage the accommodation of all structural elements in a macromolecule. Attention is also given to analytical methods to study the pectin structure including the use of enzymes as analytical tools.

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Pectin, a versatile polysaccharide present in plant cell walls

8 – Structure and Function of Plant Cell Walls

The plant cell wall is composed of polysaccharides and proteins. In addition, some cells have walls impregnated with lignin. In all cases, the polysaccharides constitute the major part of the wall. The wall polysaccharides are often classified into cellulose, hemicelluloses, and pectin, and these

https://www.jstor.org/stable/pdfplus/25680860.pdf

Biosynthesis of pectin

A Perspective on the Complexity of Dietary Fiber Structures and Their Potential Effect on the Gut Microbiota

Galactomannans and other cell wall storage polysaccharides in seeds

The main polysaccharide component of the thickened cell walls in the storage parenchyma of Lupinus angustifolius L. cotyledons is a linear (1 → 4)-β-linked d-galactan, which is mobilised after germination (L.A. Crawshaw and J.S.G Reid, 1984, Planta 160, 449–454). The isolation from the germinated cotyledons of a β-d-galactosidase or exo-(1 → 4)-β-d-galactanase with a high specificity for the lupin galactan is described. The enzyme, purified using diethylaminoethyl-cellulose, carboxymethyl-cellulose and affinity chromatography on lactose-agarose, gave two bands (major 60 kDa, minor 45 kDa) on sodium dodecyl sulphate-gel electrophoresis, and two similar bands on isoelectric focusing (major, pI 7.0, minor pI 6.7, both apparently possessing enzyme activity). The minor component cross-reacted with an antiserum raised against, and affinity-purified on, the major band. Both components had a common N-terminal sequence. The minor component was probably a degradation product of the major one. The enzyme had limited β-galactosidase action, catalysing the hydrolysis of p-nitrophenyl-β-d-galactopyranoside and (1→ 4)- and (1 → 6)-β-linked galactobioses. Lactose [β-d-galactopyranosyl-(1 → 4)-d-glucose] was hydrolysed only very slowly and methyl-β-d-galactopyranoside not at all. Lupin galactan was hydrolysed rapidly and extensively to galactose, whereas other cell-wall polysaccharides (xyloglucan and arabinogalactan) with terminal non-reducing β-d-galactopyranosyl residues were not substrates. A linear (1 → 4)-β-linked galactopentaose was hydrolysed efficiently to the tetraose plus galactose, but further sequential removals of galactose to give the tetraose and lower homologues occurred more slowly. Galactose, γ-galactonolactone and Cu+2 were inhibitory. No endo-β-d-galactanase activity was detected in lupin cotyledonary extracts, whereas exo-galactanase activity varied pari passu with galactan mobilisation. Exo-galactanase protein was detected, by Western immunoblotting of cotyledon extracts, just before the activity could be assayed and then increased and decreased in step with the enzyme activity. The exo-galactanase is clearly a key enzyme in galactan mobilisation and may be the sole activity involved in depolymerising the dominant (1 → 4)-β-galactan component of the cell wall.

Purification and properties of a novel beta-galactosidase or exo-(1-->4)-beta-D-galactanase from the cotyledons of germinated Lupinus angustifolius L. seeds.

Galactomannan deposition was investigated in developing endosperms of three leguminous species representative of taxonomic groups which have galactomannans with high, medium and low galactose content. These were fenugreek (Trigonella foenum-graecum L.; mannose/galactose (Man/Gal) = 1.1), guar (Cyamopsis tetragonoloba (L.) Taub.; Man/Gal = 1.6) and Senna occidentalis (L.) Link. (Man/Gal = 3.3), respectively. Endosperms were analysed at different stages of seed development for galactomannan content and the levels, in cell-free extracts, of a mannosyltransferase and a galactosyltransferase which have been shown to catalyse galactomannan biosynthesis in vitro (M. Edwards et al., 1989, Planta 178, 41-51). There was a close correlation in each case between the levels of the biosynthetic mannosyl- and galactosyltransferases and the deposition of galactomannan. The relative in vitro activities of the mannosyl- and galactosyltransferases in fenugreek and guar were similar, and almost constant throughout the period of galactomannan deposition. In Senna the ratio mannosyltransferase/galactosyltransferase was always higher than in the other two species, and it increased substantially throughout the period of galactomannan deposition. In fenugreek and guar the galactomannans present in the endosperms of seeds at different stages of development had the Man/Gal ratios characteristic of the mature seeds. By contrast the galactomannan present in Senna endosperms at the earliest stages of deposition had a Man/Gal ratio of about 2.3. During late deposition this ratio increased rapidly, stabilising at about 3.3, the ratio characteristic of the mature seed. The levels of α-galactosidase in the developing endosperms of fenugreek and guar were low and remained fairly constant throughout the deposition of the galactomannan. In Senna, α-galactosidase activity in the endosperm was low during early galactomannan deposition, but increased subsequently, peaking during late galactomannan deposition. The developmental patterns of the α-galactosidase activity and of the increase in Man/Gal ratio of the Senna galactomannan were closely similar, indicating a cause-and-effect relationship. The endosperm α-galactosidase activity in Senna was capable, in vitro, of removing galactose from guar galactomannan without prior depolymerisation of the molecule. In fenugreek and in guar the genetic control of the Man/Gal ratio in galactomannan is not the result of a post-depositional modification, and must reside in the biosynthetic process. In Senna, the Man/Gal ratio of the primary biosynthetic galactomannan product is controlled by the biosynthetic process. Yet the final Man/Gal ratio of the galactomannan in the mature seed is, to an appreciable extent, the result of galactose removal from the primary biosynthetic product by an α-galactosidase activity which is present in the endosperm during late galactomannan deposition.

J. S. G. Reid

Papers

Galactomannans and other cell wall storage polysaccharides in seeds

Purification and properties of a novel beta-galactosidase or exo-(1-->4)-beta-D-galactanase from the cotyledons of germinated Lupinus angustifolius L. seeds.

Control of mannose/galactose ratio during galactomannan formation in developing legume seeds.

A new family of oligosaccharides from the xyloglucan of Hymenaea courbaril L. (Leguminosae) cotyledons

Tamarind seed polysaccharide: preparation, characterisation and solution properties of carboxylated, sulphated and alkylaminated derivatives