Pectin represents a very heterogeneous biopolymer whose functionality remains largely puzzling. The link between the pectin fine structure and functional properties with relevance to plant growth and development, as well as food processing, is continually being explored. This review describes the current knowledge of pectin structure–function relationships. Key mechanisms dictating pectin structure–function relationships are discussed, including the polymer biosynthesis, cross-linking mechanisms, enzymatic and nonenzymatic conversion reactions, solubility properties, and more. Insight into the polymer structure–function relationships is highlighted by examining traditional and advanced methodologies used in pectin research. The role of pectin in modulating the quality characteristics of plant-based foods is underlined while pin-pointing some of the main challenges and perspectives. An integrated approach using the pectin structure–function relationship in the precision engineering of mechanical properties of tissue-based systems is proposed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2009.00071.x

Pectins in Processed Fruits and Vegetables: Part II—Structure–Function Relationships

One characteristic feature of many phytopathogenic organisms is their ability to produce an array of enzymes capable of degrading the complex polysaccharides of the plant cell wall (Bateman and Millar, 1966; Wood, 1967; Albersheim et al., 1969; Wood, 1973) and membrane constituents (Porter, 1966; Tseng and Bateman, 1968). These enzymes usually are produced inductively. Generally, they are extracellular, highly stable and present in infected host tissues. In most plant diseases caused by microbial agents, cell walls are penetrated, tissues are colonized, and permeability of host cells is altered. A brief summary of our understanding of cell wall and membrane structure, coupled with knowledge of the enzymes capable of degrading the components of these structures, and an analysis of the association of these enzymes with diseased tissue, should enable us to make an appraisal of their involvement in pathogenesis and point the way to an objective consideration of this area of disease physiology.

Degradation of Plant Cell Walls and Membranes by Microbial Enzymes

Polysaccharide lyases (or eliminases) are a class of enzymes (EC 4.2.2.-) that act to cleave certain activated glycosidic linkages present in acidic polysaccharides. These enzymes act through an eliminase mechanism, rather than through hydrolysis, resulting in unsaturated oligosaccharide products. Acidic polysaccharides are ubiquitous and so are the lyases that degrade them. This review article examines lyases that act on acidic polysaccharides of plant, animal, and microbial origin. These lyases are predominantly of microbial origin and come from a wide variety of both pathogenic and nonpathogenic bacteria and fungi. The lyases discussed include alginate lyase (EC 4.2.2.3), pectin lyase (EC 4.2.2.10), pectate lyase (EC 4.2.2.2), oligogalacturonide lyase (EC 4.2.2.6), exopolygalacturonate lyase (EC 4.2.2.9), chondroitin lyases (EC 4.2.2.4 and EC 4.2.2.5), hyaluronate lyase (EC 4.2.2.1), heparin lyase (EC 4.2.2.7), heparan lyase (EC 4.2.2.8), and other unclassified lyases. This review examines the sources, regulation, purification, and properties of these polysaccharide lyases.

Polysaccharide lyases

Publisher Summary This chapter provides an overview on the main groups of plant polysaccharide other than those, such as starch and fructans. Plant polysaccharides fall into a number of well-defined structural families. The availability of modern techniques has made possible the development of a new and powerful complementary approach to the study of plant cell polysaccharides. Biologically homogeneous primary cell walls are readily obtained from undifferentiated cells grown in suspension culture. The methylation technique is then applied to the total mixture of polysaccharides present in the cell wall and to fractions derived there from by the use of purified hydrolytic enzymes. In addition to cellulose, two other β-D-glucans are of widespread although not abundant occurrence in plants, namely, those containing 1–3 linkages only and those containing both 1–3 and 1–4 linkages. In contrast to cellulose and callose, the mixed glucans are generally rather soluble in aqueous solvents. Some β -D-glucans are only isolated by extraction with alkali, and evidence shows that these glucans are cell wall components and are probably covalently linked to other macro-molecules.

Chemistry of Cell Wall Polysaccharides

Investigations were conducted to determine how a systemic plant-colonizing bacterium Enterobacter asburiae JM22 enters cotton plant tissues. Passive uptake was excluded for JM22 by experimentation with glutaraldehyde-fixed (killed) bacterial cells applied to seeds and leaves; no bacteria were found internally or externally on roots or leaves. In contrast, application of live JM22 cells led to colonization of external and internal root and leaf tissues. Active penetration of JM22 in the absence of external wounding was demonstrated for cotton seedlings germinated on water agar and inoculated with the bacterial suspension. The mean internal bacterial population density for seedlings was 3.8 x lo3 CFUIg surface-disinfected radicle tissue. Studies of in planta enzymatic activity demonstrated hydrolysis of wall-bound cellulose in the vicinity of JM22 bacterial cells. The same phenomenon was observed for a cortical root colonizing bacterium, Pseudomonas fluorescens 89B-61, a plant growth-promoting strain with biocontrol potential against various pathogens.

Bacterial endophytes in cotton: mechanisms of entering the plant

This review deals mainly with the literature which has appeared since the discovery of pectin lyases in 1960. Those papers have been selected which are reports of investigations carried out with purified enzyme preparations and rather well defined substrates. According to their action on high polymer pectic substances, the enzymes are placed in one of six different groups. Mutual relationships of some of the groups are discussed. It is emphasized that the choice of substrates and reaction conditions, as well as that of methods of analysis, to a large extent influence the values found for a number of enzyme properties. Trends for future research are outlined.

W. Pilnik

Papers

Research on pectin depolymerases in the sixties ‐ a literature review