An arabinogalactan containing 3-O-methyl-D-galactose residues isolated from the aerial parts of Salvia officinalis L

An arabinogalactan with a high content of 3-O-methyl-D-galactose residues has been isolated from the aerial parts of sage (Salvia officinalis L.). Structural studies of the polymer indicated a beta-1,6-D-galactopyranose backbone in which at least one-third of D-galactopyranosyl residues carries methoxyl groups and another one-third L-arabinosyl side chains at C-3.     

Tracing cellulose microfibril orientation in inner primary cell walls

Summary By quantitative analysis of cellulose microfibril orientation at different levels in the primary cell wall of a number of cell types, the development of wall texture was studied. Meristematic, isodiametric and cylindrical parenchyma cells and cells of a suspension culture were used. Within the newly deposited microfibril population, various orientations were recognized on the micrographs. Within subpopulations the orientation of undercrossing and overcrossing microfibrils were measured. These measurements showed a gradual shift in cellulose microfibril orientation in the different levels. Microfibrils showed predominant orientations at particular levels but microfibrils of intermediate orientation also occurred, although at a much lower density. As cellulose microfibrils of intermediate orientation were not closely packed, lamellae were not formed. Interwoven microfibrils were occasionally present, indicating that differently orientated microfibrils are occasionally deposited simultaneously. Also gradual changes in orientation over the entire inner cell wall surface were observed. From these observations it was inferred that microfibril deposition occurs with a small but regular and progressive change in orientation, the rotational motion, related to that of a helicoidal system.Dedicated to Professor Dr. M. M. A. Sassen on the occasion of his 65th birthday     

Molecular weight distribution of cellulose in primary cell walls

The distribution pattern of the degree of polymerization (DP) of cellulose present in the cell walls of mesophyll- and suspension-cultured cells of tobacco was compared to that of newly synthesized ¹⁴C-labeled cellulose from regenerating tobacco protoplasts and suspension-cultured cells. The cellulose was nitrated, and, after fractionation according to differences in solubility in acetone/water, the DP pattern of labeled or unlabeled cellulose nitrate was determined by viscosity measurements. A low (DP<500) and high DP-fraction (DP>2500) of cellulose were predominant in the cell walls of protoplasts, suspension — cultured cells, and mesophyll cells. The average DP of the high molecular weight fraction of cellulose in the cell walls of mesophyll was higher (DP4,000) than in protoplasts or suspension — cultured cells (DP 2,500-3,000). In all cell walls tested, minor amounts of cellulose molecules with a broad spectrum of a medium DP were present. Pulse — chase experiments with either protoplasts or suspension —cultured cells showed that a large proportion of the low and medium DP-cellulose are a separate class of structural components of the cellulose network. The results are discussed in relation to the organization of cellulose in the primary cell wall.Abbreviations DP degree of polymerisation - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid     

Atomic force microscopy of microfibrils in primary cell walls

Examination of angiosperm primary cell walls by transmission electron microscopy shows that they contain microfibrils that probably consist of cellulose microfibrils surrounded by associated non-cellulosic polysaccharides. Previous studies using solid-state (13)C NMR spectroscopy have shown that the cellulose is all crystalline with crystallites of cross-sectional dimensions of 2-3 nm. However, it is not known if each microfibril contains only one, or more than one crystallite because there is no agreement about the dimensions of the microfibrils. Partially hydrated primary cell walls isolated from onion ( Allium cepa L.) and Arabidopsis thaliana (L.) Heynh. were examined by atomic force microscopy and the microfibril diameters determined. The cell walls of both species contained tightly interwoven microfibrils of uniform diameter: 4.4+/-0.13 nm in the onion and 5.8+/-0.17 nm in A. thaliana. The effect was also examined of extracting the A. thaliana cell walls to remove pectic polysaccharides. The microfibrils in the extracted cell walls of A. thaliana were significantly narrower (3.2+/-0.13 nm) than those in untreated walls. The results are consistent with the microfibrils containing only one cellulose crystallite.     

The cell biology of primary cell walls during salt stress

Salt stress simultaneously causes ionic toxicity, osmotic stress, and oxidative stress, which directly impact plant growth and development. Plants have developed numerous strategies to adapt to saline environments. Whereas some of these strategies have been investigated and exploited for crop improvement, much remains to be understood, including how salt stress is perceived by plants and how plants coordinate effective responses to the stress. It is, however, clear that the plant cell wall is the first contact point between external salt and the plant. In this context, significant advances in our understanding of halotropism, cell wall synthesis, and integrity surveillance, as well as salt-related cytoskeletal rearrangements, have been achieved. Indeed, molecular mechanisms underpinning some of these processes have recently been elucidated. In this review, we aim to provide insights into how plants respond and adapt to salt stress, with a special focus on primary cell wall biology in the model plant Arabidopsis thaliana.

This review examines the relationship between the plant cell wall and salt stress.     

The galactose residues of xyloglucan are essential to maintain mechanical strength of the primary cell walls in Arabidopsis during growth

In land plants, xyloglucans (XyGs) tether cellulose microfibrils into a strong but extensible cell wall. The MUR2 and MUR3 genes of Arabidopsis encode XyG-specific fucosyl and galactosyl transferases, respectively. Mutations of these genes give precisely altered XyG structures missing one or both of these subtending sugar residues. Tensile strength measurements of etiolated hypocotyls revealed that galactosylation rather than fucosylation of the side chains is essential for maintenance of wall strength. Symptomatic of this loss of tensile strength is an abnormal swelling of the cells at the base of fully grown hypocotyls as well as bulging and marked increase in the diameter of the epidermal and underlying cortical cells. The presence of subtending galactosyl residues markedly enhance the activities of XyG endotransglucosylases and the accessibility of XyG to their action, indicating a role for this enzyme activity in XyG cleavage and religation in the wall during growth for maintenance of tensile strength. Although a shortening of XyGs that normally accompanies cell elongation appears to be slightly reduced, galactosylation of the XyGs is not strictly required for cell elongation, for lengthening the polymers that occurs in the wall upon secretion, or for binding of the XyGs to cellulose.     

Ectopic lignification in primary cellulose-deficient cell walls of maize cell suspension cultures

Maize(Zea mays L.) suspension-cultured cells with up to 70% less cellulose were obtained by stepwise habituation to dichlobenil(DCB), a cellulose biosynthesis inhibitor. Cellulose de ficiency was accompanied by marked changes in cell wall matrix polysaccharides and phenolics as revealed by Fourier transform infrared(FTIR) spectroscopy.Cell wall compositional analysis indicated that the cellulosede ficient cell walls showed an enhancement of highly branched and cross-linked arabinoxylans, as well as an increased content in ferulic acid, diferulates and p-coumaric acid, and the presence of a polymer that stained positive for phloroglucinol. In accordance with this, cellulose-de ficient cell walls showed a fivefold increase in Klason-type lignin.Thioacidolysis/GC-MS analysis of cellulose-de ficient cell walls indicated the presence of a lignin-like polymer with a Syringyl/Guaiacyl ratio of 1.45, which differed from the sensu stricto stress-related lignin that arose in response to shortterm DCB-treatments. Gene expression analysis of these cells indicated an overexpression of genes specific for the biosynthesis of monolignol units of lignin. A study of stress signaling pathways revealed an overexpression of some of the jasmonate signaling pathway genes, which might trigger ectopic lignification in response to cell wall integrity disruptions. In summary, the structural plasticity of primary cell walls is proven, since a lignification process is possible in response to cellulose impoverishment.     

Mobility-resolved 13C-NMR spectroscopy of primary plant cell walls

Primary plant cell walls contain highly hydrated biopolymer networks, whose major chemistry is known but whose relationship to architectural and mechanical properties is poorly understood. Nuclear magnetic resonance spectroscopy has been used to characterize segmental mobilities via relaxation and anisotropy effects in order to add a dynamic element to emerging models for cell wall architecture. For hydrated onion cell wall material, single pulse excitation revealed galactan (pectin side chains), provided that dipolar decoupling was used, and some of the pectin backbone in the additional presence of magic angle spinning. Cross-polarization excitation revealed the remaining pectin backbones, which exhibited greater mobility (contact time dependence, dipolar dephasing) than the cellulose component, whose noncrystalline and crystalline fractions showed no mobility discrimination. ¹HT₂ behavior could be quantitatively interpreted in terms of high resolution observabilities. Mobility-resolved spectroscopy of cell walls from tomato fruit, pea stem, and tobacco leaf showed similar general effects. Nuclear magnetic resonance study of the sequential chemical extraction of onion cell wall material suggests that galactans fill many of the network pores, that extractability of pectins is not dependent on segmental mobility, and that some pectic backbone (and not side chain) is strongly associated with cellulose. Analysis of the state of cellulose in four hydrated cell walls suggests a noncrystalline content of 60–80% and comparable amounts of Iα and Iβ polymorphs in the crystalline fraction. Comparison with micrographs for onion cell walls shows that noncrystalline cellulose does not equate to chains on fibril surfaces, and chemical shifts show that fully solvated cellulose is not a significant component in cell walls. © 1996 John Wiley & Sons, Inc.     

The modern concepts on the primary cell walls of angiosperm plants

The modern view on polysaccharide composition of the primary cell wall of angiosperm plants was considered, and five classes of structural proteins were characterized. The model which shows location of enzyme complex synthesizing cellulose, as well as structural model of primary cell walls of the most flowering plants were presented. Besides, there were shown cell wall reactions to environmental factors which have contradictory character and have to be deeply and thoroughly analyzed.     

The organization and growth of primary cell walls of lupin hypocotyl

Models of the primary cell wall are discussed in relation to results obtained by the present authors from studies of the primary cell wall of lupin and mung bean hypocotyls. A structure of the primary cell wall is suggested that differs in several respects from structures already proposed. It has a non-covalent interaction of much of the pectin, hemicellulose and glycoprotein, and a more direct interaction of the glycoprotein and cellulose microfibrils. An idea of scale is introduced through a consideration of degree of polymerization and monomer size of polymers, and of the volume of the cellulose microfibrils. Wall structure is discussed in relation to polymer orientation and elongation of the primary cell wall.     

Streptomyces species with madurose (3-O-methyl-D-galactose) as a whole-cell sugar

Madurose, an actinomycete whole-cell sugar, was found in the strains of the genus Streptomyces: three strains of S. platensis, one strain each of S. platensis subsp. malvinus, and S. albus subsp. albus. The sugar was isolated from the hydrolysate of S. platensis IFO 14008 cells, and was identified as madurose (3-O-methyl-D-galactose) by chromatographic analyses, ¹H-NMR spectrometry, mass spectrometry as its alditol acetate, and demethylation with boron trichloride. Cell walls of the strain contained peptidoglycan and teichoic acids. ll-Diaminopimelic acid, glycine, glutamic acid, and alanine were present in the peptidoglycan fraction in molar ratios of 1.0:1.3:1.2:2.3. Madurose was detected in the teichoic acid fraction, which was composed of phosphorus, glycerol, galactose, and madurose in molar ratios of 9.3:8.5:2.9:1.0. Thus, madurose was found in the glycerol teichoic acid moiety of the cell walls of this strain.Abbreviations PC paper chromatography - TLC thin-layer chromatography - HPLC high performance liquid chromatography - GLC gas-liquid chromatography - TCA trichloroacetic acid     

Structural analysis of xyloglucans in the primary cell walls of plants in the subclass Asteridae

The structures of xyloglucans from several plants in the subclass Asteridae were examined to determine how their structures vary in different taxonomic orders. Xyloglucans, solubilized from plant cell walls by a sequential (enzymatic and chemical) extraction procedure, were isolated, and their structures were characterized by NMR spectroscopy and mass spectrometry. All campanulids examined, including Lactuca sativa (lettuce, order Asterales), Tenacetum ptarmiciflorum (dusty miller, order Asterales), and Daucus carota (carrot, order Apiales), produce typical xyloglucans that have an XXXG-type branching pattern and contain alpha-d-Xylp-, beta-D-Galp-(1-->2)-alpha-D-Xylp-, and alpha-L-Fucp-(1-->2)-beta-D-Galp-(1-->2)-alpha-D-Xylp- side chains. However, the lamiids produce atypical xyloglucans. For example, previous analyses showed that Capsicum annum (pepper) and Lycopersicon esculentum (tomato), two species in the order Solanales, and Olea europaea (olive, order Lamiales) produce xyloglucans that contain arabinosyl and galactosyl residues, but lack fucosyl residues. The XXGG-type xyloglucans produced by Solanaceous species are less branched than the XXXG-type xyloglucan produced by Olea europaea. This study shows that Ipomoea pupurea (morning glory, order Solanales), Ocimum basilicum (basil, order Lamiales), and Plantago major (plantain, order Lamiales) all produce xyloglucans that lack fucosyl residues and have an unusual XXGGG-type branching pattern in which the basic repeating core contains five glucose subunits in the backbone. Furthermore, Neruim oleander (order Gentianales) produces an XXXG-type xyloglucan that contains arabinosyl, galactosyl, and fucosyl residues. The appearance of this intermediate xyloglucan structure in oleander has implications regarding the evolutionary development of xyloglucan structure and its role in primary plant cell walls.     

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.Analysis of the structure of the B–RG-II complex reveals that the complex is composed of boric acid and two chains of monomeric RG-II. Boric acid does not merely bind to sugars but crosslinks two chains of pectic polysaccharide at the RG-II region through borate-diester bonding, thus forming a network of pectic polysaccharides in cell walls. The B–RG-II complex is reconstituted in vitro only by mixing monomeric RG-II and boric acid at pH 4.0. In the in vitro reconstitution, germanic acid can substitute for boric acid to some extent. The RG-II epitope, which cross reacts with the antibody toward the B-RG-II complex, is detected in walls of every cell in radish roots. The epitope is also detected in growing pollen tube cell walls, which are claimed to require B.Whilst it is now clear that boric acid links some cell wall components, it is not yet clear whether there is a structural requirement for B in cell wall function.     

Lignin isolated from primary walls of hybrid aspen cell cultures indicates significant differences in lignin structure between primary and secondary cell wall.

Hybrid aspen (Populus tremula x tremuloides) cell cultures were grown for 7, 14 and 21 days. The cell cultures formed primary cell walls but no secondary cell wall according to carbohydrate analysis and microscopic characterization. The primary walls were lignified, increasingly with age, according to Klason lignin analysis. Presence of lignin in the primary walls, with a higher content in 21-day old cells than in 7-day old cells, was further supported by phloroglucinol/HCl reagent test and confocal microscopy after both immunolocalization and staining with acriflavin. Both laccase and peroxidase activity were found in the cultures and the activity increased during lignin formation. The lignin from the cell culture material was compared to lignin from mature aspen wood, where most of the lignin originates in the secondary cell wall, and which served as our secondary cell wall control. Lignin from the cell walls was isolated and characterized by thioacidolysis followed by gas chromatography and mass spectrometry. The lignin in the cell cultures differed from lignin of mature aspen wood in that it consisted exclusively of guaiacyl units, and had a more condensed structure. Five lignin structures were identified by mass spectrometry in the cell suspension cultures. The results indicate that the hybrid aspen cell culture used in this investigation may be a convenient experimental system for studies of primary cell wall lignin.