Cell Walls Of Higher Plants Research Articles

Molecular cloning of a cDNA encoding a (1-->4)-beta-mannan endohydrolase from the seeds of germinated tomato (Lycopersicon esculentum).

Mannose-containing polysaccharides are widely distributed in cell walls of higher plants. During endosperm mobilization in germinated tomato seeds (1-->4)-beta-mannan endohydrolases (EC 3.2.1.78) participate in the enzymic depolymerization of these cell wall polysaccharides. A cDNA encoding a (1-->4)-beta-mannanase from the endosperm of germinated tomato (Lycopersicon esculentum Mill.) seeds has been isolated and characterized. The amino acid sequence deduced from the 5'-region of the cDNA exactly matches the sequence of the 65 NH2-terminal amino acids determined directly from the purified enzyme. The mature enzyme consists of 346 amino acid residues, it has a calculated M(r) of 38,950 and an isoelectric point of 5.3. Overall, the enzyme exhibits only 28-30% sequence identity with fungal (1-->4)-beta-mannanases, but more highly conserved regions, which may represent catalytic and substrate-binding domains, can be identified. Based on classification of the tomato (1-->4)-beta-mannanase as a member of the family 5 group of glycosyl hydrolases, Glu-148 and Glu-265 would be expected to be the catalytic acid and the catalytic nucleophile, respectively. Southern hybridization analyses indicate that the enzyme is derived from a family of about four genes. Expression of the genes, as determined by the presence of mRNA transcripts in Northern hybridization analyses, occurs in the endosperm of germinated seeds; no transcripts are detected in hypocotyls, cotyledons, roots or leaves.

Hypolipidemic effects of hydrolyzed xyloglucan

AbstractXyloglucan is found in the primary cell walls of higher plants, where it plays important biological roles. It also exists in certain seeds, for example tamarind, as a reserve polysaccharide. Some xyloglucan oligosaccharides possess plant growth promotion activity.We prepared hydrolyzed xyloglucan from the tamarind seed xyloglucan using endo‐(1 → 4)‐ β ‐glucanase and examined its effects on lipid metabolism in rats fed a high fat diet. Among the plasma lipids, total lipid, cholesterol, triglyceride and β ‐ lipoprotein were each reduced 14 ‐ 17% by hydrolyzed xyloglucan. Hydrolyzed xyloglucan significantly reduced both adipose tissue weight and plasma GOT. Among the hepatic lipids, total lipid, cholesterol, triglyceride and phospholipid were significantly reduced by hydrolyzed xyloglucan.These hypolipidemic effects may be important for the treatment and prevention of geriatric diseases, including diabetes and cardiac disorders.

Two general branching patterns of xyloglucan, XXXG and XXGG.

Recent advances in chemical and physical techniques have shed considerable light on the molecular architecture of the primary cell walls of higher plants. According to current models, the primary cell wall is composed of at least two independent polysaccharide networks. The cellulose-xyloglucan network is considered to be an important load-bearing structure of the primary cell wall. Gaps in the cellulose-xyloglucan network are filled by a network of pectic polysaccharides that may control the porosity of the cell wall.

Effects of Microgravity on the Structure and Function of Plant Cell Walls

The structural, biochemical, cytofluorimetric and electron cytochemical features of the cell walls of higher plants grown under weightlessness and simulated microgravity are described. Space flight and laboratory clinostatic experiments with plants show that the ultrastructure of the cell wall, its polysaccharide composition, and metabolic organization depend on the type of tissue and the duration of weightlessness. Horizontal clinostating that reproduced the biological effects of microgravity on cell walls showed that the structure of the external walls of the epidermis of aboveground organs is very sensitive to microgravity. Various responses occur in the primary and secondary walls under weightlessness and clinorotation: rearrangement of cell walls and organelles and changes in the content of cellulose, lignin, callose, and hemicelluloses. It is shown that plant cell wall changes under microgravity are connected with changes in cellulase, pectinase, and peroxidase activity and a change in the calcium balance in the cytoplasm and apoplast.

Boron in plant cell walls

Boron is an essential element for higher plants, yet the primary functions remain unclear. In intact tissues of higher plants, this element occurs as both water soluble and water insoluble forms. In this review, the intracellular localisation of B and possible function of B in cell walls of higher plants are discussed. The majority of the water soluble B seems to be localised in the apoplastic region as boric acid. The water insoluble B is associated with rhamnogalacturonan II (RG-II) and the complex is ubiquitous in higher plants. In the Brassicaceae, Apiaceae, Chenopodiaceae, Asteraceae, Amaryllidaceae, and Liliaceae, nearly all the cell wall B is associated with RG-II, while in the Cucurbitaceae, only half of the cell wall B is in this complex. In duckweed, a different type of B-polysaccharide complex has been identified.

Cell Wall Esterified Phenolic Dimers: Identification and Quantification by Reverse Phase High Performance Liquid Chromatography and Diode Array Detection

An optimized high performance liquid chromatography (HPLC) procedure has been developed for the analysis and quantification of all of the known ferulic acid dehydrodimers, and the principle phenolic aldehydes and acids, found in the cell walls of higher plants. The HPLC system uses an ODS2 reverse phase column (5 μm particle size) eluted with a methanol, acetonitrile and water gradient with detection at 280 nm. In addition to providing baseline resolution of most components, the method employs a spectrometric detector which enables the precise identification of eluted components through the analysis of their spectral properties. Analysis of the cell wall phenolics of wheat straw stem (Triticum vulgare) was carried out using this method which is highly versatile and, for certain components, more sensitive than the current gas chromatography–mass spectrometry methodology.

A Cell Wall-associated, Receptor-like Protein Kinase

Physical connections between higher plant cell walls and the plasma membrane have been identified visually, but the molecules involved in the contact are unknown. We describe here an Arabidopsis thaliana protein kinase, designated Wak1 for wall-associated kinase, whose predicted extracytoplasmic domain contains several epidermal growth factor repeats and identity with a viral movement protein. Wak1 fractionates with insoluble material when plant tissue is ground in a variety of buffers and detergents, suggesting a tight association with the plant extracellular matrix. Immunocytochemistry confirms that Wak1 is associated with the cell wall. Enzymatic digestion of the cell wall allows the release of Wak1 from the insoluble cell wall fraction, and protease experiments indicate that Wak1 likely has a cytoplasmic kinase domain, and the EGF containing domain is extracellular. Wak1 is found in all vegetative tissues of Arabidopsis, and has relatives in other angiosperms, but not Chlamydomonas. We suggest that Wak1 is a good candidate for a physical continuum between the cell wall and the cytoplasm, and since the kinase is cytoplasmic, it also has the potential to mediate signals to the cytoplasm from the cell wall.

Effects of hydrolyzed xyloglucan on lipid metabolism in rats

Xyloglucan is a component of the cell walls of higher plants. Hydrolyzed xyloglucan, which consists of xyloglucan heptasaccharide (Glu 4Xyl 3), octasaccharide (Glu 4Xyl 3Gal) and nona-saccharide (Glu 4Xyl 3Gal), is known to regulate plant growth. However its effects on animals are unknown. In this study we prepared hydrolyzed xyloglucan from the tamarind plant using endo-1, 4- β-glucanase and examined its effects on lipid metabolism in rats fed a high-fat diet containing corn oil (2%) and lard (15%) for 35 days. Among the plasma lipids, total lipid, cholesterol, triglyceride and β-lipoprotein were each reduced 14–17% by hydrolyzed xyloglucan. Hydrolyzed xyloglucan significantly reduced adipose tissue weight, total plasma lipid and plasma GOT. Among the hepatic lipids, total lipid, cholesterol, triglyceride and phospholipid were each significantly reduced by hydrolyzed xyloglucan. This report is the first to demonstrate the biological activity of hydrolyzed xyloglucan in animals.

An antibody Fab selected from a recombinant phage display library detects deesterified pectic polysaccharide rhamnogalacturonan II in plant cells.

Rhamnogalacturonan II (RG-II) is a structurally complex, low molecular weight pectic polysaccharide that is released from primary cell walls of higher plants by treatment with endopolygalacturonase and is chromatographically purified after alkaline deesterification. A recombinant monovalent antibody fragment (Fab) that specifically recognizes RG-II has been obtained by selection from a phage display library of mouse immunoglobulin genes. By itself, RG-II is not immunogenic. Therefore, mice were immunized with a neoglycoprotein prepared by covalent attachment of RG-II to modified BSA. A cDNA library of the mouse IgG1/kappa antibody repertoire was constructed in the phage display vector pComb3. Selection of antigen-binding phage particles resulted in the isolation of an antibody Fab, CCRC-R1, that binds alkali-treated RG-II with high specificity. CCRC-R1 binds an epitope found primarily at sites proximal to the plasma membrane of suspension-cultured sycamore maple cells. In cells deesterified by alkali, CCRC-R1 labels the entire wall, suggesting that the RG-II epitope recognized by CCRC-R1 is masked by esterification in most of the wall and tha such RG-II esterification is absent near the plasma membrane.

Two Chains of Rhamnogalacturonan II Are Cross-Linked by Borate-Diol Ester Bonds in Higher Plant Cell Walls.

Polysaccharide moiety of the boron-polysaccharide complex (T. Matoh, K. Ishigaki, K. Ohno, J. Azuma [1993] Plant Cell Physiol 34: 639-642) isolated from radish (Raphanus sativus) roots has been shown to be rhamnogalacturonan II by glycosyl-linkage analysis and the presence of diagnostic monosaccharides, including apiose, aceric acid, 2-O-methylfucose, and 3-deoxy-D-manno-2-octulosonic acid. Removal of boron from the complex reduced the molecular weight by one-half without causing a significant increase in the number of reducing end groups, indicating that boron, as boric acid, links two rhamnogalacturonan II chains together to form the boron-polysaccharide complex.

Polysaccharide-Modifying Enzymes in the Plant Cell Wall

Enzymes found in the cell walls of higher plants are surveyed briefly, especially those in the primary cell walls of growing tissue. Attention is focused on hydrolases and transglycosylases that attack the structural carbohydrates of the wall. The reactions catalyzed by these enzymes in vitro are described. Exo-O-glycosylhydrolases are divided into two categories based on specificity for the aglycone group of the substrate: Those with low specificity are in the majority over those with high specificity. Endo-O-glycosylhydrolase-catalyzed reactions are discussed, especially the ability of cellulase to hydrolyze cellulose, xyloglucan, and mixed-linkage glucan. Transglycosylation is defined, and the distinction is drawn between exo- and endo-transglycosylation. Enzymes that catalyze only exo-transglycosylation have not been found in plant cell walls, although some exo-O-glycosylhydrolases can catalyze limited exo-transglycosylation under suitable conditions. In contrast, xyloglucan endo-transglycosylase (XET) catalyzes endo-transglycosylation in the absence of hydrolysis. The evidence that these enzymes act in the walls of living cells is evaluated critically, and the natural and biotechnological regulation of wall enzyme action is discussed. Many enzymes occur in cell walls, and many biological roles have been proposed for them, but we still have far to go in investigating the reactions catalyzed by wall enzymes in vivo and in testing the proposed roles of these enzymes.

Polysaccharide-Modifying Enzymes in the Plant Cell Wall

Enzymes found in the cell walls of higher plants are surveyed briefly, especially those in the primary cell walls of growing tissue. Attention is focused on hydrolases and transglycosylases that attack the structural carbohydrates of the wall. The reactions catalyzed by these enzymes in vitro are described. Exo-O-glycosylhydrolases are divided into two categories based on specificity for the aglycone group of the substrate: Those with low specificity are in the majority over those with high specificity. Endo-O-glycosylhydrolase-catalyzed reactions are discussed, especially the ability of cellulase to hydrolyze cellulose, xyloglucan, and mixed-linkage glucan. Transglycosylation is defined, and the distinction is drawn between exo- and endo-transglycosylation. Enzymes that catalyze only exo-transglycosylation have not been found in plant cell walls, although some exo-O-glycosylhydrolases can catalyze limited exo-transglycosylation under suitable conditions. In contrast, xyloglucan endo-transglycosylase (XET) catalyzes endo-transglycosylation in the absence of hydrolysis. The evidence that these enzymes act in the walls of living cells is evaluated critically, and the natural and biotechnological regulation of wall enzyme action is discussed. Many enzymes occur in cell walls, and many biological roles have been proposed for them, but we still have far to go in investigating the reactions catalyzed by wall enzymes in vivo and in testing the proposed roles of these enzymes.

Isodityrosine cross-linking mediates insolubilization of cell walls in Chlamydomonas.

Enzymatic removal of the cell wall induces vegetative Chlamydomonas reinhardtii cells to transcribe wall genes and synthesize new hydroxyproline-rich glycoproteins (HRGPs) related to the extensins found in higher plant cell walls. A cDNA expression library made from such induced cells was screened with antibodies to an oligopeptide containing the (SP)x repetitive domains found in Chlamydomonas wall proteins. One of the selected cDNAs encodes an (SP)x-rich polypeptide that also displays a repeated YGG motif. Ascorbate, a peroxidase inhibitor, and tyrosine derivatives were shown to inhibit insolubilization of both the vegetative and zygotic cell walls of Chlamydomonas, suggesting that oxidative cross-linking of tyrosines is occurring. Moreover, insolubilization of both walls was concomitant with a burst in H2O2 production and in extracellular peroxidase activity. Finally, both isodityrosine and dityrosine were found in hydrolysates of the insolubilized vegetative wall layer. We propose that the formation of tyrosine cross-links is essential to Chlamydomonas HRGP insolubilization.

Hemicelluloses as structure regulators in the aggregation of native cellulose

The influence of hemicelluloses on the aggregation of cellulose in higher plant cell walls was modelled by adding hemicelluloses to cultures of the cellulose producer Acetobacter xylinum. Characterization of the celluloses by X-ray diffractometry showed them to be more like those that occur in higher plants; the coaggregation of the hemicelluloses suggests their occlusion within and between the crystalline domains of the celluloses. The authors propose that hemicelluloses may be primary moderators of the tertiary structure of cell wall celluloses, allowing the development of a wide range of properties.

Oligogalacturonides are able to induce flowers to form on tobacco explants

SummaryOligogalacturonides (α‐1,4‐D‐galactosyluronic acid oligomers) are fragments of the homogalacturonan component of the primary cell walls of higher plants. Treatment of cell walls with endopolygalacturonase (EPG) releases the polysaccharides rhamnogalacturonan‐1 (RG‐I) and rhamnogalacturonan‐II (RG‐II), and variously sized oligogalacturonide fragments of homogalacturonan. The EPG‐released sycamore cell wall components are able to regulate several morphogenetic processes of tobacco thin‐cell layer (TCL) explants. We followed one of these morphogenesis‐regulating activities, namely, the induction of flower formation on TCLs, to purify the biologically active component from EPG‐released material. Saponification of the methyl and acetyl esters of the EPG‐released material did not reduce the flower‐inducing activity. However, EPG treatment of the deesterified EPG‐released material destroyed the flower‐inducing activity, establishing that the active substance contained several, consecutive α‐1,4‐linked galactosyluronic acid residues that are required for the flower‐inducing activity. The flower‐inducing activity was purified and shown to be α‐1,4‐linked Oligogalacturonides with a degree of polymerization (DP) of 12‐14, which exhibited half‐maximum activity at approximately 0.4 μM. Smaller oligogalacturonides, RG‐I and RG‐II, did not, even at higher concentrations, induce flowers to form. The ability of oligogalacturonides to stimulate the formation of flowers on tobacco explants provides further evidence of the pleiotropic nature of this oligosaccharin.

Structure‐activity relationships of biologically active oligosaccharides

Abstract. Oligosaccharides that exert biological effects on higher plants (other than as carbon or energy sources) have been termed‘oligosaccharins'. A limited number of specific oligo‐β‐glucans derived from fungal cell walls exhibit oligosaccharin activity, at very low doses, switching on the synthesis of phytoalexins. The structural requirements for this biological activity are stringent, and there is strong evidence that the oligosaccharins of fungal origin act through a receptor in the plant cell membrane. Chemically unrelated oligosaccharins can also be produced by partial digestion of pectins and xyloglucans from higher plant cell walls. In some cases, for example, the α‐l‐fucosylated oligoxyloglucans that antagonise the growth‐promoting effect of auxin, these plant‐derived oligosaccharins have relatively strict structural requirements for activity and act at ∼10−6 mol m−3; these may act via specific receptors. In other cases, for example, the growth‐promoting action of other oligoxyloglucans, the stringency is somewhat lower and the activity is only seen at ∼10−3 mol m−3, and these oligosaccharins are proposed to influence growth through their ability to modulate the activity of an enzyme, cellulase. A third class of plant‐derived oligosaccharins, the oligo‐α‐galacturonides, appear to have much less stringent structural requirements; a number of unrelated physiological responses are evoked by the same range of oligo‐α‐galacturonides at ∼10−3 to 1 mol m−3. We suggest that these oligosaccharins may act via a mechanism not involving a specific receptor, perhaps by interacting with the plasma membrane to bring about a change in its physical properties.

Two separate zones of helicoidally orientated microfibrils are present in the walls ofNitella internodes during growth

The dynamic changes in microfibril architecture in the internode cell walls of the giant unicellular algaNitella translucens were studied during cell expansion. Thin section electron microscopy in conjunction with mild matrix polysaccharide extraction techniques revealed three distinct architectural zones in the walls of fully grown cells. These zones were related to distinct phases of growth by monitoring changes in cell wall architecture of internodes during active cell expansion. The initial microfibril deposition before the onset of active cell growth is helicoidal. A helicoid is a structurally complex but ordered arrangement of microfibrils that has been detected increasingly often in higher plant cell walls. During active cell elongation microfibrils are deposited transversely to the direction of cell elongation as shown in earlier studies by birefringence measurements in the polarizing microscope. The gradual decline in cell elongation corresponds with a final helicoidal deposition which continues after cell expansion ceases entirely.

Glucuronoxylan xylanohydrolase. A unique xylanase with the requirement for appendant glucuronosyl units.

A new category of beta-(1----4)-xylan xylanohydrolases that exhibit a specific capacity to hydrolyze glucuronoxylans was characterized using heteroxylans prepared from Vigna (Vigna angularis Ohwi et Ohashi cv. Takara) and maize (Zea mays L.) cell walls together with appropriate derivatives as substrates. Glucuronopyranosyl moieties, as side chains, were prerequisite for enzyme-mediated hydrolysis of the beta-(1----4)-xylosyl linkages. The enzyme degraded glucuronoxylans derived from Vigna cell walls to yield a major oligomeric species (formula; see text) where Xyl represents xylose and GlcA represents glucuronic acid. The enzyme also degraded glucuronoarabinoxylans derived from maize cell walls to yield a major oligomeric species containing a single glucuronosyl side chain and a single unsubstituted beta 1----4Xyl pendant terminal. These results indicate that this xylanohydrolase recognizes glucuronosyl moieties inserted as monomeric side chains along the xylan backbone and mediates the hydrolysis of the beta-(1----4)-xylosyl linkage of the adjacent unsubstituted xylosyl residue in heteroxylans. This enzyme is the first xylanohydrolase identified that recognizes distinctly different sugars constituting side chains. We propose to designate this new enzyme as a glucuronoxylan xylanohydrolase to be abbreviated as glucuronoxylanase. Use of this unique enzyme demonstrated the presence of repeating units in heteroxylans in cell walls of higher plants.

The extensin signal peptide allows secretion of a heterologous protein from protoplasts

Extensins are hydroxyproline-rich glycoproteins which are amongst the most abundant proteins present in the cell wall of higher plants. Here, we describe the structural analysis of an extensin-encoding gene from Nicotiana plumbaginifolia. The encoded protein (46 kDa) has a highly repetitive structure and contains 37% proline, 18.1% tyrosine, 13.4% lysine, 8.1% serine and 7.1% histidine. The extensin-encoding sequence contains a typical signal peptide for translocation of the protein to the endoplasmic reticulum. By using chimeric genes consisting of different 5' parts of the extensin-encoding gene and the neomycin phosphotransferase II-encoding gene ( nptII) as reporter gene, we show that the N-terminal part of extensin can mediate the secretion of NPTII from electroporated N. tabacum protoplasts.

Preliminary crystallographic analysis of a plant pathogenic factor: Pectate lyase

Pectate lyase is a saccharide-binding enzyme that lyitically depolymerizes polypectate in higher plant cell walls, thus causing soft-rot diseases in food crops. A pectate lyase from Erwinia chrysanthemi, EC16 (PLe), crystallizes in the orthorhombic space group P2 12 12 1 with unit cell dimension of a = 39.0Å, b = 91.0Å and c = 103.4Å. The asymmetric unit consists of one molecule with a molecular mass of 38,118 daltons and the X-ray diffraction extends to a resolution of 1.8 Å. The crystals reproducibly grow to large dimensions and are suitable for a high-resolution X-ray diffraction analysis.