Metabolism Of Cell Wall Polysaccharides Research Articles

Functional analysis of the pyrimidine de novo synthesis pathway in solanaceous species.

Pyrimidines are particularly important in dividing tissues as building blocks for nucleic acids, but they are equally important for many biochemical processes, including sucrose and cell wall polysaccharide metabolism. In recent years, the molecular organization of nucleotide biosynthesis in plants has been analyzed. Here, we present a functional analysis of the pyrimidine de novo synthesis pathway. Each step in the pathway was investigated using transgenic plants with reduced expression of the corresponding gene to identify controlling steps and gain insights into the phenotypic and metabolic consequences. Inhibition of expression of 80% based on steady-state mRNA level did not lead to visible phenotypes. Stepwise reduction of protein abundance of Asp transcarbamoylase or dihydro orotase resulted in a corresponding inhibition of growth. This was not accompanied by pleiotropic effects or by changes in the developmental program. A more detailed metabolite analysis revealed slightly different responses in roots and shoots of plants with decreased abundance of proteins involved in pyrimidine de novo synthesis. Whereas in leaves the nucleotide and amino acid levels were changed only in the very strong inhibited plants, the roots show a transient increase of these metabolites in intermediate plants followed by a decrease in the strong inhibited plants. Growth analysis revealed that elongation rates and number of organs per plant were reduced, without large changes in the average cell size. It is concluded that reduced pyrimidine de novo synthesis is compensated for by reduction in growth rates, and the remaining nucleotide pools are sufficient for running basic metabolic processes.

Molecular Cloning and Characterization of a beta-Galactosidase Gene Expressed Preferentially in Cotton Fibers

: β-galactosidases (EC 3.2.1.23) constitute a widespread family of enzymes in plants that is thought to be involved in metabolism of cell wall polysaccharides. We reported herein the isolation of a full-length cDNA encoding a typical β-galactosidase protein, designated GhGal1 (Gossypium hirsutum L. galactosidase), of 843 amino acids with a predicted molecular mass of nearly 94.8 kDa. In addition to a glycosyl hydrolase family 35 domain and a putative signal peptide, an unusual characteristic of GhGal1 is that, at the C-terminus of the enzyme, a domain was found that is structurally related to a sea urchin egg lectin (SUEL-lectin) with D-galactose- and L-rhamnose-binding domains. Based on results from Southern blot, we estimated that there would be two copies of the GhGal1 gene per haploid genome of G. hirsutum. The transcripts of GhGal1 were regulated spatially and temporally and were present in very high abundance at the elongation stage of the cotton fiber. The expression pattern suggests that the GhGal1 gene could be involved in metabolism of the primary cell wall. (Managing editor: Li-Hui ZHAO)

Reactive oxygen species and nitric oxide affect cell wall metabolism in tobacco BY-2 cells

The effects of hydrogen peroxide (H2O2), nitric oxide (NO), and a combination of both on the metabolism of cell wall polysaccharides were studied in tobacco (Nicotiana tabacum L.) cv Bright Yellow 2 (BY-2) suspension cultured cells in the presence of d-[U-14C]glucose or d-[U-14C]galactose as radioactive tracers. We found that the radiolabelling of newly synthesised total cell wall polysaccharides (pectins, hemicelluloses and α-cellulose), buffer-soluble polysaccharides, and membrane-associated polysaccharides decreased under the influence of exogenous systems generating H2O2 and NO. However, when the total amount of newly synthesised cell wall polysaccharides was calculated as a percentage of the total cellular radioactivity (ethanol-soluble pool plus the homogenate of ethanol-insoluble material), all treatments showed negligible effects in the presence of d-[U-14C]glucose or d-[U-14C]galactose as tracers. This occurred because the treatments generating H2O2, NO and H2O2 plus NO caused a marked decrease in the concentration of the ethanol-soluble pool as well as in the total radioactivity found in the homogenate of the ethanol-insoluble material. Most of the radioactivity taken up by the cells was evolved as 14CO2 during the respiratory processes. A qualitative and quantitative characterisation of the ethanol-soluble pool showed that radioactive UDP-sugars in BY-2 suspension cultured cells were differentially reduced by all treatments. Therefore, the decrease of the newly synthesised cell wall polysaccharides seems to be strictly dependent on the reduction of the UDP-sugars pool.

Cell wall metabolism during the development of chilling injury in cold-stored peach fruit: association of mealiness with arrested disassembly of cell wall pectins.

Partially tree-ripened ripe fruit of peach (Prunus persica L.) were stored for 1-4 weeks at 5 degrees C and then ripened at 20 degrees C for 3 d to induce chilling injury. With increasing cold storage the incidence and severity of mealiness symptoms increased progressively, manifested as reduced quantities of free juice and internal flesh browning. Relative to juicy fruit, tissue of mealy fruit showed altered intercellular adhesion when examined by microscopy and, upon crushing, a higher proportion of cells remained intact and did not release cellular contents. Substantial alterations in the metabolism of cell wall polysaccharides were observed. Chelator-soluble polyuronides from mealy fruit were partially depolymerized during cold storage in a manner dissimilar to that in unripe or ripe juicy fruit, and were not depolymerized further during the ripening period. The solubility of these high molecular weight pectins remained low, and did not show the increase characteristic of juicy fruit. Furthermore, in mealy fruit the dramatic decline in the polymeric Ara content of base-soluble, matrix glycan-enriched fractions occurring during normal ripening was absent, indicating diminished disassembly of an arabinan-rich polysaccharide firmly attached to cellulose. A corresponding rise in the polymeric Ara content of the most soluble pectin fraction was also absent, as was a decline in the Gal content of this extract. The depolymerization of matrix glycans showed only minor differences between juicy and mealy fruit. After cold storage and ripening, the activities of endo-1,4-beta-glucanase (EC 3.2.1.4), endo-1,4-beta-mannanase (EC 3.2.1.78), beta-galactosidase (EC 3.2.1.23), alpha-arabinosidase (EC 3.2.1.55), and particularly endo-polygalacturonase (EC 3.2.1.15) were lower in mealy fruit than in juicy fruit, whereas pectin methylesterase activity (EC 3.1.1.11) was lower in slightly mealy and higher in very mealy fruit. The data suggest that cold storage affects the activities of numerous cell wall-modifying enzymes, with important consequences for pectin metabolism. These changes alter the properties of the primary wall and middle lamella, resulting in tissue breakage along enlarged air spaces, rather than across cells, which reduces the amount and availability of free juice upon tissue fragmentation.

Cell Wall Polysaccharide Metabolism during Fruit Development in Sweet Cherry 'Satohnishiki' as Affected by Gibberellic Acid.

Cell wall polysaccharide metabolism during fruit development in 'Satohnishiki' sweet cherries (Prunus avium L.) and the effect of gibberellic acid (GA) treatment on the fruit were investigated. Fruit firmness decreased dramatically, and sugar concentration increased rapidly from 30 to 36 days after full bloom (DAFB), accompanied by increases in abscisic acid (ABA) and water-soluble pectic substances (WSP) fraction and decreases in sodium hexametaphosphate-soluble pectic substances (HMP) fraction, HCl-soluble pectic substances (HP) fraction, and cell wall bound neutral sugars. Therefore, the period from 30 to 36 DAFB is considered the onset of fruit ripening. Pectinesterase (PE) activity decreased from 30 to 42 DAFB ; endo-polygalacturonase (PG) activity was not detectable. Contrarily, cell wall bound neutral sugars decreased greatly as fruit ripened which demonstrates that the softening of sweet cherries may cause, not a dissolution of homogalacturonan, but a decrease of cell wall bound neutral sugars, leading to lower molecular weight by the cleavage of the neutral sugar region. An application of 0.289 mM (100 ppm) GA3 solution to whole branches at 23 DAFB inhibited the solubilization of polysaccharides until 56 DAFB and the accumulation of anthocyanins in the skin. The effect of GA3 treatment on endogenous ABA concentration which plays an important role in the cherry fruit ripening was also examined. Although ABA concentration in GA3-treated fruit was lower than that in untreated control fruit 36 DAFB, its concentration was, contrarily, higher at 56 DAFB. These results suggest that GA3 treatment delayed fruit ripening by blocking ABA activity.

Metabolism of cell wall polysaccharides in cell suspension cultures of Populus alba in relation to cell growth

Metabolism of cell wall polysaccharides in cell suspension cultures of Populus alba in relation to cell growth

Metabolism of cell wall polysaccharides in cell suspension cultures of Populus alba in relation to cell growth

Changes in the composition of cell walls and extracellular polysaccharides (ECP) were studied during the growth of suspension-cultured Populus alba cells. Three growth phases, namely the cell division phase, cell elongation phase and stationary phase, were distinguished. The active deposition of polysaccharides in cell wall fractions (50 mM Na 2 CO 3 -, 1 M KOH-, 4 M KOH-soluble and 4 M KOH-insoluble) was observed during the elongation phase. A 50 mM Na 2 CO 3 -soluble pectic fraction mainly composed of 1,4-linked galactan and arabinan except acidic sugars. The 1,4-linked galactan decreased markedly during elongation. In I and 4 M KOH-soluble hemicellulosic fractions, non-cellulosic 1,4-glucan and xyloglucan were observed as major components, respectively. These polysaccharides also decreased during elongation. A large amount of polysaccharides was secreted into the medium as ECP. Neutral sugars were detected predominantly by sugar composition analysis. Acidic sugars, such as galacturonic acid, were less than 12% of total. In this study, active metabolism of pectic polysaccharides in addition to hemicellulosic polysaccharides, especially neutral side chains of pectin, during cell growth, was clarified.

Update on the possible mode of action of the jasmonates: Focus on the metabolism of cell wall polysaccharides in relation to growth and development

Jasmonic acid (JA) and its related compounds (jasmonates) applied to plant tissues exert either inhibitory or promotive effects in growth and developmental processes, which in some ways are similar to abscisic acid. However, little is known about the mode of action of the jamonates at the tissue or organ levels. Here, we review partial evidence for the physiological action of the jasmonates on cell elongation and abscission.Jasmonates inhibit the IAA‐induced cell elongation of oat coleoptile segments not by affecting energy production, osmoregulation and cell wall loosening, but by inhibiting the synthesis of cell wall polysaccharides. The inhibition is partially reversed by simultaneous application of sucrose. Inhibition of IAA‐induced elongation by JA is only observed in monocotyledons, not in dicotyledons. These effects suggest that jasmonates exert their inhibitory effect on cell elongation by affecting the metabolism of the cell wall polysaccharides in monocotyledons.Jasmonates promote the abscission of bean petiole explants without enhancing ethylene production. Cells in the petiole adjacent to the abscission zone expand during abscission. In the abscission zone, jasmonates decrease the amount of cellulosic but not that of noncellulosic polysaccharides. Jasmonates increase the activities of cellulase and decrease the levels of UDP‐sugars, which are important intermediates for the synthesis of cell wall polysaccharides in the abscission zone, probably resulting in the decreased level of cellulose and the mechanical weakness of cell walls.Thus, it is suggested that jasmonates exert their multiple physiological effects by affecting the metabolic processes of cell wall polysaccharides.

Update on the possible mode of action of the jasmonates: Focus on the metabolism of cell wall polysaccharides in relation to growth and development

Update on the possible mode of action of the jasmonates: Focus on the metabolism of cell wall polysaccharides in relation to growth and development

Changes in the Autolytic Activities of Maize Coleoptile Cell Walls during Coleoptile Growth

Autolytic activities of coleoptile cell walls were measured in developing maize seedlings. The major neutral sugar components of the cell wall polysaccharides were arabinose, xylose and glucose. The quantities of all these components per coleoptile increased for 5 d after germination, suggesting that levels are augmented by biosynthetic processes during coleoptile growth. However, cell wall preparations isolated from the coleoptiles also revealed increasing rates of autolytic activity directed toward each of the sugar components. This result suggests that the constitutive hydrolytic activities expressed by cell walls also increase as a function of coleoptile age. The proportion of glucose in autolysis products relative to that present in the cell walls specifically increased with coleoptile age, while the ratios for arabinose and xylose decreased. Kinetic analyses of autolysis demonstrated that the reactions specific for pentoses at the early growth stage are transient events and that initial low rates of glucan autolysis increased sharply and persisted longer. In these experiments the products of glucan autolysis were largely monomeric while those of the pentose-specific reactions consisted of both monomeric and polymeric sugars. Based on these results, we concluded that two distinct phases of autolytic activities are expressed in the mediation of cell wall polysaccharide metabolism in situ.

Jasmonates promote abscission in bean petiole expiants: Its relationship to the metabolism of cell wall polysaccharides and cellulase activity

Jasmonic acid (JA) and its methyl ester (JA-Me) promoted the abscission of bean petiole expiants in the dark and light, and the activity of these compounds was almost same. JA and JA-Me did not enhance ethylene production in bean petiole expiants in the light, indicating that the abscission-promoting effects of these compounds are not the result of ethylene. Cells in the petiole adjacent to the abscission zone expanded during abscission but not in the pulvinus, and JA-Me promoted cell expansion in the petiole and the pulvinus. JA-Me had no effect on the total amounts of pectic and hemicellulosic polysaccharides in 2-mm segments of the abscission region, which included 1 mm of pulvinus and 1 mm of petiole from the abscission zone. On the other hand, the total amounts of cellulosic polysaccharides in this region were reduced significantly by the addition of JA-Me in the light. JA-Me had no effect on the neutral sugar composition of hemicellulosic polysaccharides during abscission. The decrease in the endogenous levels of UDP-sugars in the petiole adjacent to the abscission zone was accelerated during abscission by the addition of JA-Me in the light. Cellulase activities of pulvinus and petiole in 10-day-old seedlings were enhanced by the addition of JA. These results suggest that the promoting effect of JA or JA-Me on the abscission of bean petiole explants is due to the change of sugar metabolism in the abscission zone, in which the increase in cellulase activity involves the degradation of cell wall polysaccharides. Jasmonic acid (JA) and its methyl ester (JA-Me) are considered to be putative plant hormones for a number of reasons, including their wide occurrence in the plant kingdom, biologic, activities in multiple aspects at low concentrations, and their interaction with other plant hormones (for reviews see Parthier 1991, Hamberg and Gardner 1992, Sembdner and Parthier 1993, Ueda et al. 1994a). We have already reported that JA and JA-Me and C18-unsaturated fatty acids, which are considered to be the substrates of the biosynthesis of jasmonates, are powerful senescence-promoting substances (Ueda et al. 1982b, 1991a). Senescence symptoms induced by these compounds are identical to those of natural senescence. Recently we have also found that JA inhibited indole-3-acetic acid (IAA)-induced elongation of oat (Avena sativa L. cv. Victory) coleoptile segments by inhibiting the synthesis of cell wall polysaccharides (Ueda et al. 1994b, 1995). These facts led us to study the mode of actions of JA and JA-Me on promoting abscission, which is considered the last dramatic phenomenon of senescence. In this paper we report that JA and JA-Me promote abscission in bean (Phaseolus vulgaris L. cv. Masterpiece) petiole expiants and that the changes in the metabolism of cell wall polysaccharides in the petiole and the pulvinus adjacent to the abscission zone are involved in the promotive effects of these compounds.

Metabolism of cell wall polysaccharides from persimmon fruit. Pectin solubilization during fruit ripening occurs in apparent absence of polygalacturonase activity

Metabolism of cell wall polysaccharides from persimmon fruit. Pectin solubilization during fruit ripening occurs in apparent absence of polygalacturonase activity

Metabolism of cell wall polysaccharides from persimmon fruit. Pectin solubilization during fruit ripening occurs in apparent absence of polygalacturonase activity

Pectins from persimmon (Diospyros kaki L.) fruit pericarp were sequentially extracted with 0. 05 M trans‐1,2‐diaminocyclohexane‐N,N, N′, N′‐tetraacetic acid (CDTA), 0. 05 M Na2CO3 (1°C) and Na2CO3 (20°C) and the carbohydrate composition and metabolism during development determined. Young persimmon fruits contained a large proportion of pectins, 46% by dry weight, that decreased to 20% with ripening. This decrease occurred in the CDTA and Na2CO3 (1°C) fractions, mainly composed of uronic acids, and represents a net loss of uronic acids, arabinose and galactose. The amount of non‐cellulosic neutral sugars was especially high in the Na2CO3 (20°C) fraction. The loss of pectins was also accompanied by a depolymerisation of the polysaccharides extracted in the three pectic fractions. However, none of these changes can be attributed to the action of polygalacturonase activity. Proteins were extracted from the pericarp tissue, but endopolygalacturonase (EC 3. 2. 1. 15) activity, determined as a decrease in viscosity of polygalacturonic acid, was not observed in the extract. Determination of exopolygalacturonase (EC 3. 2. 1. 67) activity by measuring the release of reducing groups from polygalacturonic acid was also negative. The results presented indicate that polygalacturonase is not responsible for the metabolism of pectins during persimmon fruit ripening.

Effect of IAA on Growth and Soluble Cell Wall Polysaccharides Centrifuged from Pine Hypocotyl Sections

Auxin-induced elongation and cell wall polysaccharide metabolism were studied in excised hypocotyl sections of ponderosa pine (Pinus ponderosa) seedlings. Sections excised from hypocotyls of ponderosa pine elongate in response to the addition of auxin. The neutral sugar composition of the extracellular solution removed from hypocotyl sections by centrifugation was examined. In cell wall solution from freshly excised sections, glucose, galactose, xylose, and arabinose make up more than 90% of the neutral sugars, while rhamnose, fucose, and mannose are relatively minor components. The neutral sugar composition of the polysaccharides of the pine cell wall solution is both qualitatively and quantitatively similar to that of pea. Following auxin treatment of pine hypocotyls, the neutral sugar composition of the cell wall changes; glucose, xylose, rhamnose, and fucose increase by nearly 2-fold relative to controls in buffer without auxin. These changes in neutral sugars in response to auxin treatment are similar to those found in pea, with the exception that in pea, rhamnose levels decline in response to auxin treatment.

Effect of coumarin on growth and metabolism of Pythium.

Coumarin concentrations that inhibited growth of Pythium sp. rapidly decreased the rate of incorporation of [14C]glucose into the mycelium. Coumarin also reduced drastically the carbohydrate and protein content of the cytoplasm and, to a lesser extent, the amino acid content and cell wall fraction. Enzymes related to the metabolism of cell wall polysaccharides were not affected during early exposure to the inhibitor. The possible mechanism of coumarin action via inhibition of glucose uptake is discussed in the light of the present findings.