Pectic polysaccharides in carrot cells growing in suspension culture

Pectic polysaccharides in the cell wall of suspension-cultured carrot cells (Daucus carota L.) were fractionated into high- and low-molecular-weight components by molecular-sieve chromatography with a Sepharose 4B column. During the phase of cell-wall expansion, the relative content of low-molecular-weight polymers rapidly increased. Electrophoretic analyses of these fractions showed that the high-molecular-weight components were largely composed of neutral and weakly acidic polymers while the low-molecular-weight fraction contained, in addition to neutral polymers, strongly acidic polyuronides in which the content of neutral sugars was very small. The accumulation of a large amount of the strongly acidic polyuronides occurred in a late stage of cell-wall growth, concomitant with a marked decrease in the high-molecular-weight components.Abbreviation MW molecular weight     

Pectic polysaccharides of rice endosperm cell walls

Two pectic polysaccharide fractions were purified from rice endosperm cell walls. Methylation analysis including carboxyl-reduction and also selective     

Pectic polysaccharides elicit chitinase accumulation in tobacco

Upon infection of leaves of tobacco ( Nicotiana tabacum L. ev. Havana) with Erwinia carotovora (Jones) Holl, strain 3912, a phytopathogenic bacterium that secretes pectinolytic enzymes, chitinase (EC 3.2.1.14) levels increased 12-fold within 48 h. Heat-killed E. carotovara cells did not induce this response. In young excised tobacco plants supplied with pectic polysaccharides, chitinase activity increased to about the same level as in leaves infected with E. carotovora . The amount of pectic polysaccharides required for half-maximal induction was about 160 μg (g fresh weight)⁻¹. Using in vivo labeling of plants with [³⁵S]-cysteine, it could be demonstrated that elicitormediated chitinase induction is due to enhanced de novo synthesis of the enzyme.     

Pectic polysaccharides of cabbage (Brassica oleracea)

Pectic substances extracted from cabbage cell walls with water, at 80°, and (NH₄)₂C₂O₄, at 80°, accounted for 45%(w/w) of the purified cell wall material. Only a small amount of neutral arabinan was isolated. Partial acid hydrolysis and methylation analysis revealed that the major pectic polysaccharide had a rhamnogalacturonan backbone to which a highly branched arabinan was linked, at C-4 of the rhamnose units, mainly through short chains of (1→4)-linked galactopyranose residues. The bulk of the soluble pectic substances had only small amounts of proteins associated with them. After further extraction of the depectinated material with 1M and 4M KOH, to remove the hemicelluloses, the cellulose residue was found to contain a pectic polysaccharide which was solubilized by treatment with cellulase. The general structural features of the pectic polymers are discussed in the light of these results.     

Pectic polysaccharides from Chinese herbs: structure and biological activity

Bioactive pectic polysaccharides have been isolated from Chinese herbs, and their structure, activity and modes of action have been studied. Complement-activating pectin from Angelica acutiloba contained a variety of neutral galactosyl chains which attached to the rhamnogalacturonan core (ramified region), and these neutral galactosyl chains were essential for the expression of complement activating activity, but the polygalacturonan moiety modulated the mode of activation by the ramified region. Another pectin-like polysaccharide, bupleuran 2IIb from Bupleurum falcatum showed a potent immune complex clearance-enhancing activity. Bupleuran 2IIb may enhance Fc receptor expression on the macrophage surface via the ramified region as an active site. An anti-ulcer pectin, bupleuran 2IIc from B. falcatum consists mainly of partially branched polygalacturonan in addition to the ramified region and the rhamnogalacturonan II-like region, and the polygalacturonan region may contribute somewhat to the expression of activity. Collectively considered results have indicated that the pharmacological activity of each of the pectic polysaccharides may depend on their fine chemical structure.     

Enzymatic modification of plant polysaccharides

Enzymes find widespread industrial use in the modification of the functional properties of plant polysaccharides both in vivo and in vitro. Reactions catalysed include depolymerization, debranching and de-esterification, depending on the specific enzyme or enzyme mixture employed and on the particular industrial requirement. Depolymerization of pentosans and/or barley β-glucans to destroy their viscosity-building properties is essential in starch and gluten manufacture, in the mashign of barley malt and in the production of maltosaccharide syrups. Depolymerization of pectin is required in juice clarification and to allow concentration. However, in other instances the aim may be to maintain or, at most, only slightly alter the molecular size of functional polysaccharides, i.e. in the conversion of guar galactomannan to a locust-bean type galactomannan and in the enzymic treatment of wheat-flour doughs. Enzymes may also be used to produce specific oligosaccharide fragments from polysaccharides and as diagnostic tools in the measurement of a particular polysaccharide in a mixture.     

Cell-wall polysaccharides in growing poplar bark tissue

In order to study changes in the cell-wall composition of growing poplar cambium during the seasonal cycle, cell walls were isolated from the cambium and newly formed vascular tissues of poplar branches at three times during the year (winter, beginning of spring, end of summer). Polysaccharide material was isolated by sequential extraction of the cell walls and analysed. The principal polysaccharides identified were pectins and xylose- and glucose-containing polysaccharides, possibly xylans and (xylo)glucans. Our results indicate changes in the relative quantities of these polysaccharides during the seasonal cycle.     

Pectic polysaccharides from Biophytum petersianum Klotzsch, and their activation of macrophages and dendritic cells

The Malian medicinal plant Biophytum petersianum Klotzsch (Oxalidaceae) is used as a treatment against various types of illnesses related to the immune system, such as joint pains, inflammations, fever, malaria, and wounds. A pectic polysaccharide obtained from a hot water extract of the aerial parts of B. petersianum has previously been reported to consist of arabinogalactans types I and II (AG-I and AG-II), probably linked to a rhamnogalacturonan backbone. We describe here further structural characteristics of the main polysaccharide fraction (BP1002) and fractions obtained by enzymatic degradations using endo-alpha-d-(1-->4)-polygalacturonase (BP1002-I to IV). The results indicate that in addition to previously reported structures, rhamnogalacturan type II and xylogalacturonan areas appear to be present in the pectic polymer isolated from the plant. Atomic force microscopy confirmed the presence of branched structures, as well as a polydisperse nature. We further tested whether the BP1002 main fraction or the enzymatically degraded products could induce immunomodulating activity through stimulation of subsets of leukocytes. We found that macrophages and dendritic cells were activated by BP1002 fractions, while there was little response of T cells, B cells, and NK cells. The enzymatic treatment of the BP1002 main fraction gave important information on the structure-activity relations. It seems that the presence of rhamnogalacturonan type I is important for the bioactivity, as the bioactivity decreases with the decreased amounts of rhamnose, galactose, and arabinose. The demonstration of bioactivity by the plant extracts might indicate the mechanisms behind the traditional medical use of the plant.     

Polyribosome metabolism, growth and water status in the growing tissues of osmotically stressed plant seedlings

Relationships between growth of osmotically stressed intact seedlings and polyribosome levels and water status of growing tissues were examined. Sudden exposure of barley (Hordeum vulgare L. cv. Arivat) roots to a solution of ?0.8 MPa polyethylene glycol caused leaf growth to stop almost immedately, but growth resumed at a much lower rate after 0.5–1 h. In the growing region of leaves, the polyribosome: total ribosome ratio of free (non-membrane-bound) ribosomes was significantly reduced after 15 min stress, but a decrease in the large polyribosome:total polyribosome ratio occurred only after 1–2 h. Membrane-bound and free polyribosome levels both decreased to 70% of unstressed control values after 4 h stress. Recovery of total polyribosomes occurred within 1 h after relief of 4 h stress, but required 3 h after relief of 24 h stress. Stress detectably reduced the water potential and osmotic potential of growing tissue within 0.5–1.0 h, and osmotic adjustment continued for up to 10 h. Recovery of water status was incomplete after 1 h relief of a 4 h stress. In contrast, expanded blade tissues of stressed plants underwent minor changes in water status and slow decreases in polyribosomes levels. These results confirm that growing tissues of barley leaves are selectively responsive to stress, and suggest that changes in growth, water status and polyribosome levels may be initiated by the same signal. Measurements of seedling growth, polyribosome levels and water status of growing tissues of barley and wheat (Triticum aestivum L. cv. Zaragoza) leaves, etiolated pea (Pisum sativum L. cv. Alaska) epicotyl and etiolated squash (Cucurbita pepo L. cv. Elite) hypocotyl stressed with polyethylene glycol solutions of ?0.3 to ?0.8 MPa for 12 h or more showed that polyribosome levels were highly correlated with seedling growth rate as well as with tissue water and osmotic potentials, while turgor remained unchanged. These results suggest that long-term growth of osmotically stressed plants may be limited by a reduced capacity for protein synthesis in growing tissues and is not dictated by turgor loss.     

Pectic homogalacturonan masks abundant sets of xyloglucan epitopes in plant cell walls

Background  

Molecular probes are required to detect cell wall polymers in-situ to aid understanding of their cell biology and several studies have shown that cell wall epitopes have restricted occurrences across sections of plant organs indicating that cell wall structure is highly developmentally regulated. Xyloglucan is the major hemicellulose or cross-linking glycan of the primary cell walls of dicotyledons although little is known of its occurrence or functions in relation to cell development and cell wall microstructure.     

Microbial carbohydrate esterases deacetylating plant polysaccharides

Several plant polysaccharides are partially esterified with acetic acid. One of the roles of this modification is protection of plant cell walls against invading microorganisms. Acetylation of glycosyl residues of polysaccharides prevents hydrolysis of their glycosidic linkages by the corresponding glycoside hydrolases. In this way the acetylation also represents an obstacle of enzymatic saccharification of plant hemicelluloses to fermentable sugars which appears to be a hot topic of current research. We can eliminate this obstacle by alkaline extraction or pretreatment leading to saponification of ester linkages. However, this task has been accomplished in a different way in the nature. The acetyl groups became targets of microbial carbohydrate esterases that evolved to overcome the complexity of the plant cell walls and that cooperate with glycoside hydrolases in plant polysaccharide degradation. This article concentrates on enzymes deacetylating plant hemicelluloses excluding pectin. They are currently grouped in at least 8 families, specifically in CE families 1–7 and 16, originally assigned as acetylxylan esterases, the enzymes acting on hardwood acetyl glucuronoxylan and its fragments generated by endo-β-1,4-xylanases. There are esterases deacetylating softwood galactoglucomannan, but they have not been classified yet. The enzymes present in CE families 1–7 differ in structure and substrate and positional specificity. There are families behaving as endo-type and exo-type deacetylates, i.e. esterases deacetylating internal sugar residues of partially acetylated polysaccharides and also esterases deacetylating non-reducing end sugar residues in oligosaccharides. With one exception, the enzymes of all mentioned CE families belong to serine type esterases. CE family 4 harbors enzymes that are metal-dependent aspartic esterases. Three-dimensional structures have been solved for members of the first seven CE families, however, there is still insufficient knowledge about their substrate specificity and real physiological role. Current knowledge on catalytic properties of the selected families of CEs is summarized in this review. Some of the families are emerging also as new biocatalysts for regioselective acylation and deacylation of carbohydrates.