Collenchyma Cell Walls Research Articles

Biomechanical modeling of rice seedling stalk based on multi-scale structure and heterogeneous materials

Rice seedling stalks are biologically characterized by multilayer porous structure and multiphase inhomogeneous material properties. This biological properties make it challenging to reveal the biomechanical behavior and damage mechanism of rice seedling stalks under mechanical load. In this research, the mechanical properties of the cell wall in each leaf sheath of rice seedling stalk were measured by nanoindentation, and a three-dimensional (3D) structure model of rice seedling stalk was established using micro-computed tomography (Micro-CT). According to the gray value difference in the CT images, rice seedling stalk was defined as three types of materials: protoplasts, parenchyma cell wall and collenchyma cell wall. A 3D finite element model of rice seedling stalk with heterogeneous material distribution was established based on the mapping relationship of gray value-density-elastic modulus. The accuracy of the model was verified by radial compression and axial tensile tests from three aspects: macroscopic mechanical response, microscopic mechanical behavior, and actual load effect. The results show that the modeling method is fast and reliable, and effectively improves the analytical accuracy of biomechanical properties for living plant materials with multi-layer porous structure characteristics, heterogeneous anisotropic material properties, and high moisture content. It also provides a useful tool for revealing the damage mechanism and quantitative damage evaluation of living plants under mechanical loading. This will be of great help to the optimization of the structure and working parameters of transplanting mechanism.

Transcriptome profiling of celery petiole tissues reveals peculiarities of the collenchyma cell wall formation.

Transcriptome and biochemical analyses are applied to individual plant cell types to reveal potential players involved in the molecular machinery of cell wall formation in specialized cells such as collenchyma. Plant collenchyma is a mechanical tissue characterized by an irregular, thickened cell wall and the ability to support cell elongation. The composition of the collenchyma cell wall resembles that of the primary cell wall and includes cellulose, xyloglucan, and pectin; lignin is absent. Thus, the processes associated with the formation of the primary cell wall in the collenchyma can be more pronounced compared to other tissues due to its thickening. Primary cell walls intrinsic to different tissues may differ in structure and composition, which should be reflected at the transcriptomic level. For the first time, we conducted transcriptome profiling of collenchyma strands isolated from young celery petioles and compared them with other tissues, such as parenchyma and vascular bundles. Genes encoding proteins involved in the primary cell wall formation during cell elongation, such as xyloglucan endotransglucosylase/hydrolases, expansins, and leucine-rich repeat proteins, were significantly activated in the collenchyma. As the key players in the transcriptome orchestra of collenchyma, xyloglucan endotransglucosylase/hydrolase transcripts were characterized in more detail, including phylogeny and expression patterns. The comprehensive approach that included transcriptome and biochemical analyses allowed us to reveal peculiarities of collenchyma cell wall formation and modification, matching the abundance of upregulated transcripts and their potential substrates for revealed gene products. As a result, specific isoforms of multigene families were determined for further functional investigation.

Changes in the orientations of cellulose microfibrils during the development of collenchyma cell walls of celery (Apium graveolens L.).

During development, cellulose microfibrils in collenchyma walls become increasingly longitudinal, as determined by small-angle X-ray scattering, despite the walls maintaining a fine structure indicative of a crossed-polylamellate structure. Collenchyma cells have thickened primary cell walls and provide mechanical support during plant growth. During their development, these cells elongate and their walls thicken considerably. We used microscopy and synchrotron small-angle X-ray scattering to study changes in the orientations of cellulose microfibrils that occur during development in the walls of collenchyma cells present in peripheral strands in celery (Apium graveolens) petioles. Transmission electron microscopy showed that the walls consisted of many lamellae (polylamellate), with lamellae containing longitudinally oriented cellulose microfibrils alternating with microfibrils oriented at higher angles. The lamellae containing longitudinally oriented microfibrils predominated at later stages of development. Nevertheless, transmission electron microscopy of specially stained, oblique sections provided evidence that the cellulose microfibrils were ordered throughout development as crossed-polylamellate structures. These results are consistent with our synchrotron small-angle X-ray scattering results that showed the cellulose microfibrils become oriented increasingly longitudinally during development. Some passive reorientation of cellulose microfibrils may occur during development, but extensive reorientation throughout the wall would destroy ordered structures. Atomic force microscopy and field emission scanning electron microscopy were used to determine the orientations of newly deposited cellulose microfibrils. These were found to vary widely among different cells, which could be consistent with the formation of crossed-polylamellate structures. These newly deposited cellulose microfibrils are deposited in a layer of pectic polysaccharides that lies immediately outside the plasma membrane. Overall, our results show that during development of collenchyma walls, the cellulose microfibrils become increasingly longitudinal in orientation, yet organized, crossed-polylamellate structures are maintained.

Developmental changes in collenchyma cell-wall polysaccharides in celery (Apium graveolens L.) petioles

BackgroundCollenchyma cells occur widely in eudicotyledons and provide mechanical support for growing organs. At maturity, the cells are elongated and have thick, non-lignified walls, which in celery contain cellulose and pectic polysaccharides, together with xyloglucans and heteroxylans and heteromannans. A previous study suggested that at least some of the collenchyma cell wall in celery is laid down after expansion has stopped and is thus secondary. In the present study, we re-examined this. We used chemical analysis and immunomicroscopy to determine changes in the polysaccharide compositions of these walls during development. Additionally, solid-state NMR spectroscopy was used to examine changes in polysaccharide mobilities during development.ResultsWe showed the collenchyma walls are deposited only during cell expansion, i.e. they are primary walls. During cell-wall development, analytical and immunomicroscopy studies showed that within the pectic polysaccharides there were no overall changes in the proportions of homogalacturonans, but there was a decrease in their methyl esterification. There was also a decrease in the proportions of the (1 → 5)-α-l-arabinan and (1 → 4)-β-d-galactan side chains of rhamnogalacturonan I. The proportions of cellulose increased, and to a lesser extent those of xyloglucans and heteroxylans. Immunomicroscopy showed the homogalacturonans occurred throughout the walls and were most abundant in the middle lamellae and middle lamella junctions. Although the (1 → 4)-β-d-galactans occurred only in the rest of the walls, some of the (1 → 5)-α-l-arabinans also occurred in the middle lamellae and middle lamella junctions. During development, the location of the xyloglucans changed, being confined to the middle lamellae and middle lamella junctions early on, but later occurred throughout the walls. The location of the heteroxylans also changed, occurring mostly in the outer walls in young cells, but were more widely distributed in mature cells. Solid-state NMR spectroscopy showed that particularly cellulose, but also homogalacturonans, decreased in mobility during development.ConclusionsOur studies showed that celery collenchyma cell walls are primary and that during their development the polysaccharides undergo dynamic changes. Changes in the mobilities of cellulose and homogalacturonans were consistent with the cell walls becoming stiffer as expansion ceases.

Morphoanatomical characteristics, chemical profiles, and antioxidant activity of three species of Justicia L. (Acanthaceae) under different growth conditions

Morphoanatomical and chemical changes can occur because of biotic and abiotic factors, naturally present in the environment. These changes can result in modifications in the concentrations of secondary metabolites of medicinal species, an essential aspect to produce herbal medicines. Justicia species are used for analgesic and anti-inflammatory purposes and widely used in social programs in the Northeast of Brazil. Therefore, this study aimed to evaluate how different growth conditions (greenhouse and field) affect morphoanatomical features, chemical composition and AA of the aerial organs of three economically important species of Justicia (J. brandegeeana, J. gendarussa, and J. pectoralis). The results of morphological evaluations indicate that plants grown in the field developed better than those grown in the greenhouse, which underwent etiolation. Plants grown in the greenhouse had a greater leaf area and reduced mesophyll thickness. In contrast, plants that were grown in the field had greater cuticle and mesophyll thickness, as well as increased collenchyma cell wall thickness of stems and petioles. Plants grown in the field also had a higher stomatal density than plants grown in the greenhouse. Mass spectrometric data revealed a higher overall concentration of phenols and flavonoids, as well as higher AA, in the extracts of the plants grown in the field. Thus, the different growth conditions resulted in anatomical alterations, and changes in the concentrations of some chemical components. The results help to improve the cultivation of these species, as these changes imply in the quality of the final product and the treatment.

Polysaccharide compositions of collenchyma cell walls from celery (Apium graveolens L.) petioles

BackgroundCollenchyma serves as a mechanical support tissue for many herbaceous plants. Previous work based on solid-state NMR and immunomicroscopy suggested collenchyma cell walls (CWs) may have similar polysaccharide compositions to those commonly found in eudicotyledon parenchyma walls, but no detailed chemical analysis was available. In this study, compositions and structures of cell wall polysaccharides of peripheral collenchyma from celery petioles were investigated.ResultsThis is the first detailed investigation of the cell wall composition of collenchyma from any plant. Celery petioles were found to elongate throughout their length during early growth, but as they matured elongation was increasingly confined to the upper region, until elongation ceased. Mature, fully elongated, petioles were divided into three equal segments, upper, middle and lower, and peripheral collenchyma strands isolated from each. Cell walls (CWs) were prepared from the strands, which also yielded a HEPES buffer soluble fraction. The CWs were sequentially extracted with CDTA, Na2CO3, 1 M KOH and 4 M KOH. Monosaccharide compositions of the CWs showed that pectin was the most abundant polysaccharide [with homogalacturonan (HG) more abundant than rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II)], followed by cellulose, and other polysaccharides, mainly xyloglucans, with smaller amounts of heteroxylans and heteromannans. CWs from different segments had similar compositions, but those from the upper segments had slightly more pectin than those from the lower two segments. Further, the pectin in the CWs of the upper segment had a higher degree of methyl esterification than the other segments. In addition to the anticipated water-soluble pectins, the HEPES-soluble fractions surprisingly contained large amounts of heteroxylans. The CDTA and Na2CO3 fractions were rich in HG and RG-I, the 1 M KOH fraction had abundant heteroxylans, the 4 M KOH fraction was rich in xyloglucan and heteromannans, and cellulose was predominant in the final residue. The structures of the xyloglucans, heteroxylans and heteromannans were deduced from the linkage analysis and were similar to those present in most eudicotyledon parenchyma CWs. Cross polarization with magic angle spinning (CP/MAS) NMR spectroscopy showed no apparent difference in the rigid and semi-rigid polysaccharides in the CWs of the three segments. Single-pulse excitation with magic-angle spinning (SPE/MAS) NMR spectroscopy, which detects highly mobile polysaccharides, showed the presence of arabinan, the detailed structure of which varied among the cell walls from the three segments.ConclusionsCelery collenchyma CWs have similar polysaccharide compositions to most eudicotyledon parenchyma CWs. However, celery collenchyma CWs have much higher XG content than celery parenchyma CWs. The degree of methyl esterification of pectin and the structures of the arabinan side chains of RG-I show some variation in the collenchyma CWs from the different segments. Unexpectedly, the HEPES-soluble fraction contained a large amount of heteroxylans.

Comparison of celery (Apium graveolens L.) collenchyma and parenchyma cell wall polysaccharides enabled by solid-state 13C NMR

Collenchyma cells with their thickened walls are one of specific mechanical support tissues for plants, while parenchyma cells are thin walled and serve multiple functions. The parenchyma tissue is what you enjoy eating, while collenchyma, because of its fibrous nature, is not so attractive. Celery is a useful model for comparing the cell walls (CWs) of the two cell types such as collenchyma and parenchyma. However, to date, the structural characteristics of collenchyma and parenchyma cell walls from the same plant have not been compared. Monosaccharide composition suggested the collenchyma cell walls contained less pectin but more hemicellulose in comparison to parenchyma. High-resolution solid-state NMR spectra of highly mobile pectins revealed that the arabinan signals were more evident in the collenchyma spectrum, while galactan showed a much stronger resonance in the parenchyma spectrum. In addition, methyl esterified and non-esterified galacturonic acid signals were observed in parenchyma CWs, but only the latter one appeared in the collenchyma. The ratio of cellulose surface/interior obtained from CP/MAS spectra for collenchyma suggested the cellulose microfibrils were ~2.4 nm, while in the parenchyma, these were somewhat larger. X-ray diffraction indicated the size of the cellulose microfibrils were the same for both types of CWs.

Plasma membrane and cell wall properties of an aspen hybrid (Populus tremula × tremuloides) parenchyma cells under the influence of salt stress

The effect of salinity on cell turgor, plasma membrane permeability and cell wall elasticity has been measured in petioles of an aspen hybrid using the cell pressure probe. Control plants were grown in soil without the addition of NaCl and treated plants were grown in soil with 50 mM of NaCl for 1, 2, 3 and 4 weeks. In parenchyma cells from Populus tremula × tremuloides petioles with an increased level of NaCl in the soil: (a) turgor pressure was reduced after 1 week of treatment but afterward it was similar to untreated plants, (b) the value of elastic modulus of the cell walls increased, and (c) hydraulic conductivity of the plasma membrane of treated plants decreased in comparison to untreated ones. No histological differences and distribution of JIM5 antibody between the petioles of plants grown under salinity and the untreated were found. In cell walls of parenchyma and collenchyma from plants grown under salinity, the presence of pectic epitopes recognized by JIM7 antibodies was increased in comparison to the control plants. The obtained results indicate that under salt stress the permeability of water through plasma membrane is disturbed, cell walls became more rigid but the turgor pressure did not change.

A Multiscale Mechanical Model for Plant Tissue Stiffness

Plant petioles and stems are hierarchical cellular structures, displaying structuralfeatures defined at multiple length scales. The current work focuses on the multi-scalemodelling of plant tissue, considering two orders of structural hierarchy, cell wall and tissue.The stiffness of plant tissue is largely governed by the geometry of the tissue cells, thecomposition of the cell wall and the structural properties of its constituents. The cell wallis analogous to a fiber reinforced composite, where the cellulose microfibril (CMF) is theload bearing component. For multilayered cell wall, the microfibril angle (MFA) in themiddle layer of the secondary cell wall (S2 layer) largely affects the longitudinal stiffnessfor values up to 40o. The MFA in turn influences the overall wall stiffness. In this work,the effective stiffness of a model system based on collenchyma cell wall of a dicotyledonousplant, the Rheum rhabarbarum, is computed considering generic MFA and volume fractions.At the cellular level, a 2-D Finite Edge Centroidal Voronoi tessellation (FECVT) has beendeveloped and implemented to generate the non-periodic microstructure of the plant tissue.The effective elastic properties of the cellular tissue are obtained through finite elementanalysis (FEA) of the Voronoi model coupled with the cell wall properties. The stiffness ofthe hierarchically modeled tissue is critically important in determining the overall structuralproperties of plant petioles and stems.

Morphological and anatomical modifications in leaf, stem and roots of four plant species under boron deficiency conditions

Boron (B) is a structural component of plant cell wall and B deficiency causes disruption in development of plants. In this work, influence of low B supply on plants morphology and anatomy was studied in turnip (Brassica rapa L.), red cabbage (B. oleracea L. var. capitata f. rubra), tobacco (Nicotiana rustica L.) and celery (Apium graveolens L.). Visual B deficiency symptoms were observed in all studied species including curling of leaf margins in turnip, reduction of red coloration in red cabbage, shoot stunting in tobacco and turning dark purple colors in celery. Microscopic examination of cross-sections revealed that diameter of tracheary elements decreased and the phloem tissue became disorganized. Hypertrophy of leaf parenchyma cells in tobacco and increased thickening of collenchyma cell walls in the stem of celery were also observed. Anatomical alterations due to B deficiency were more pronouncedly observed in the leaf blades followed by the petiole, stem and roots. Our results indicated that remarkable disruptions occur in development of leaf primordia and vascular bundles upon B starvation.

Collenchyma: a versatile mechanical tissue with dynamic cell walls.

Collenchyma has remained in the shadow of commercially exploited mechanical tissues such as wood and fibres, and therefore has received little attention since it was first described. However, collenchyma is highly dynamic, especially compared with sclerenchyma. It is the main supporting tissue of growing organs with walls thickening during and after elongation. In older organs, collenchyma may become more rigid due to changes in cell wall composition or may undergo sclerification through lignification of newly deposited cell wall material. While much is known about the systematic and organographic distribution of collenchyma, there is rather less information regarding the molecular architecture and properties of its cell walls. This review summarizes several aspects that have not previously been extensively discussed including the origin of the term 'collenchyma' and the history of its typology. As the cell walls of collenchyma largely determine the dynamic characteristics of this tissue, I summarize the current state of knowledge regarding their structure and molecular composition. Unfortunately, to date, detailed studies specifically focusing on collenchyma cell walls have not been undertaken. However, generating a more detailed understanding of the structural and compositional modifications associated with the transition from plastic to elastic collenchyma cell wall properties is likely to provide significant insights into how specific configurations of cell wall polymers result in specific functional properties. This approach, focusing on architecture and functional properties, is likely to provide improved clarity on the controversial definition of collenchyma.

The Structural Adaptation of Aerial Parts of Invasive Alternanthera philoxeroides to Water Regime

Alternanthera philoxeroides has successfully invaded diverse habitats with considerably various water availability, threatening biological diversity in many parts of the world. Because its genetic variation is very low, phenotypic plasticity is believed to be the primary strategy for adapting to the diverse habitats. In the present paper, we investigated the plastic changes of anatomical traits of the aerial parts of A. philoxeroides from flooding to wet then to drought habitat; the results are as follows: A. philoxeroides could change anatomical structures sensitively to adapt to water regime. As a whole, effects of water regime on structures in stem were greater than those in leaf. Except for principal vein diameter and stoma density on leaf surfaces, all other structural traits were significantly affected by water regime. Among which, cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, and hair density on both leaf surfaces thickened significantly with decrease of water availability, whereas, pith cavity and vessel lumen in stem lessened significantly; wet habitat is vital for the spread of A. philoxeroides from flooding to drought habitat and vice versa, because in this habitat, it had the greatest structural variations; when switching from flooding to wet then to drought habitat, the variations of cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, pith cavity area ratio, diameter of vessel lumen, and hair density on both leaf surfaces, played the most important role. These responsive variables contribute most to the adaptation of A. philoxeroides to diverse habitats with considerably various water availability.

Degradation of pruning wastes by Phanerochaete sordida growing in SSF: Ultrastructural, chemical, and enzymatic studies

A solid standard fermentation (SSF) with the fungus Phanerochaete sordida in a medium with Nephrolepis cordifolia (entire pinnae separated from the rachis) and Laurus nobilis (fragmented leaves) was performed over 92 days to study the degradation of leaves with histological, chemical, and enzymatic methods. The fungus entered the leaves early, through the stomata in N. cordifolia and L. nobilis, and also through mechanical cuts that had been made in the latter. The initial attack affected the mesophyll in both plant species, and the phloem in L. nobilis. The vascular bundle of N. cordifolia was protected by a sheath of cells with thick lignified walls. The collenchyma cell walls situated near the principal vein in L. nobilis swelled during the initial stages of enzymatic action, but reduced their thickness afterwards, mainly in regions of contact with the hyphae. At the end of the experiment, no species had leaves with mesophyll. In L. nobilis, phloem was also lacking, and a partial and heterogeneous attack on the xylem became evident. The histological changes are compared with the enzymatic activities and the chemical composition of the culture media, describing the stages of fungal colonization.

Hydration effects on spacing of primary-wall cellulose microfibrils: a small angle X-ray scattering study

Celery collenchyma cell walls are typical of primary plant cell walls in their composition but contain unusually well-oriented cellulose microfibrils that are packed with more regularity than normal, permitting small-angle X-ray scattering (SAXS) experiments that would not otherwise be possible. Small-angle scattering data were obtained for the cell walls in essentially their native state and for isolated cellulose, in a fibrous form that retained the physical shape and microfibril orientation of the native cell walls. The scattering patterns showed a distinct peak attributed to the interference contribution to the convolution of form and interference functions. The position of the peak attributed to the interference function implied a mean centre-to-centre microfibril spacing of approximately 3.2 nm in dry isolated cellulose and 3.8 nm in dry cell walls. Hydration increased the mean microfibril spacing in the cell walls to 5.4 nm but had only a small effect on the mean microfibril spacing of isolated cellulose. In the scattering profile from intact, hydrated cell walls it was just possible to discern the position of the first Bessel minimum, from which a microfibril diameter in the range 3.1–3.6 nm may be estimated. This estimate is likely to include attached hemicellulose chains. Porod plots of scattering intensity indicated a relatively sharp interface between microfibrils and their immediate surroundings. The SAXS data imply that cellulose microfibrils 2.6–3.0 nm in diameter are not quite in lateral contact with one another in the isolated cellulose and are augmented by hemicelluloses and separated by readily hydrated matrix polysaccharides in the native plant cell wall.

Understanding the Biological Rationale for the Diversity of Cellulose-directed Carbohydrate-binding Modules in Prokaryotic Enzymes

Plant cell walls are degraded by glycoside hydrolases that often contain noncatalytic carbohydrate-binding modules (CBMs), which potentiate degradation. There are currently 11 sequence-based cellulose-directed CBM families; however, the biological significance of the structural diversity displayed by these protein modules is uncertain. Here we interrogate the capacity of eight cellulose-binding CBMs to bind to cell walls. These modules target crystalline cellulose (type A) and are located in families 1, 2a, 3a, and 10 (CBM1, CBM2a, CBM3a, and CBM10, respectively); internal regions of amorphous cellulose (type B; CBM4-1, CBM17, CBM28); and the ends of cellulose chains (type C; CBM9-2). Type A CBMs bound particularly effectively to secondary cell walls, although they also recognized primary cell walls. Type A CBM2a and CBM10, derived from the same enzyme, displayed differential binding to cell walls depending upon cell type, tissue, and taxon of origin. Type B CBMs and the type C CBM displayed much weaker binding to cell walls than type A CBMs. CBM17 bound more extensively to cell walls than CBM4-1, even though these type B modules display similar binding to amorphous cellulose in vitro. The thickened primary cell walls of celery collenchyma showed significant binding by some type B modules, indicating that in these walls the cellulose chains do not form highly ordered crystalline structures. Pectate lyase treatment of sections resulted in an increased binding of cellulose-directed CBMs, demonstrating that decloaking cellulose microfibrils of pectic polymers can increase CBM access. The differential recognition of cell walls of diverse origin provides a biological rationale for the diversity of cellulose-directed CBMs that occur in cell wall hydrolases and conversely reveals the variety of cellulose microstructures in primary and secondary cell walls.

Localization and effects of cadmium in leaves of a cadmium-tolerant willow ( Salix viminalis L.) : Part II Microlocalization and cellular effects of cadmium

Leaves largely control the phytoextraction of cadmium in terrestrial ecosystems but can be injured by cadmium toxicity. Cadmium sinks at the cell and tissue level vary between different species of plants. Cadmium has several still debated direct and indirect toxic effects on leaf physiology. In this study, the cadmium microlocalization and the associated structural changes were investigated in leaves of a tolerant clone of Salix viminalis to assess cadmium distribution, stress and tolerance. Rooted stem cuttings were exposed during 13 weeks in hydroponics to increasing concentrations of CdCl 2 (0–200 μM). Cadmium was cytochemically revealed with the method of physical development in leaves from the 0, 10 and 50 μM treatment. The resulting cellular injuries and defence reactions were analyzed with several histochemical techniques using light and fluorescence microscopy. The main cadmium sink was in the pectin-rich layers of the collenchyma cell walls of the veins. Active storage was indicated by homogeneous cell wall thickenings with cellulose and proanthocyanidins. Cadmium microlocalization and cell injury in the conducting phloem indicated metal cycling. In the leaf blade, oxidative stress and accelerated cell senescence increased in those areas of the mesophyll with a low cadmium content. Local cadmium accumulation in veinlets near the leaf edges caused tannin plugging in xylem and necroses in the surrounding mesophyll and upper epidermis. When sinks approached saturation, random accumulation of cadmium appeared at sites in the leaf blade. Higher exposure to cadmium also enhanced the intensity of stress reactions. The role of different markers in metal binding and stress mitigation is discussed.

Localization of hydrogen peroxide production in Zinnia elegans L. stems

Abstract Hydrogen peroxide is required for a variety of physiological processes associated with plant cell wall biosynthesis. Several recent studies have suggested that starch-KI could be used as an effective histochemical stain for studying the spatial and temporal regulation of H2O2 production during plant development. In this study, we found that detection of H2O2 in Zinnia elegans stems using starch-KI staining was highly dependent upon plant age, developmental status, and the manner in which the tissue was handled prior to staining. An alternative staining technique based on cerium perhydroxide deposition clearly showed that most of the H2O2 detected by starch-KI resulted from wounding at the cut surfaces of stem sections. However, with cerium staining, substantial H2O2 production was apparent well below the cut surface in collenchyma cell walls where previous work had demonstrated localization of peroxidase activity. Co-localization of H2O2 and peroxidase in collenchyma tissues may suggest an involvement in crosslinking of the pectins and hemicelluloses that predominate the walls of these cells. Cerium deposition also suggested that H2O2 production in xylem vessel walls may lag slightly behind secondary cell wall thickening.

Control of thickness of collenchyma cell walls by pectins

Near-isotropic stresses were generated within collenchyma cell walls of celery (Apium graveolens L.) by exchanging K(+) for Ca(2+) ions, varying the ionic strength and de-esterifying the pectic carboxyl groups, treatments that changed the free-charge density of the pectic polysaccharides. The collenchyma strands swelled radially with increasing free-charge density but there was very little longitudinal swelling. Depolymerising the pectins by β-elimination also induced much more radial than longitudinal swelling. Supported by earlier work on Nitella, these results indicate that pectins control the interlamellar spacing in cell walls and hold them together across their thickness, particularly against turgor stresses tending to delaminate the walls at the cell corners.

Direct Observation of Cell Wall Structure in Living Plant Tissues by Solid-State 13C NMR Spectroscopy

Solid-state (13)C nuclear magnetic resonance (NMR) spectra of the following intact plant tissues were recorded by the crosspolarization magic-angle spinning technique: celery (Apium graveolens L.) collenchyma; carob bean (Ceratonia siliqua L.), fenugreek (Trigonella foenum-graecum L.), and nasturtium (Tropaeolum majus L.) endosperm; and lupin (Lupinus polyphyllus Lindl.) seed cotyledons. All these tissues had thickened cell walls which allowed them to withstand the centrifugal forces of magic angle spinning and which, except in the case of lupin seeds, dominated the NMR spectra. The celery collenchyma cell walls gave spectra typical of dicot primary cell walls. The carob bean and fenugreek seed spectra were dominated by resonances from galactomannans, which showed little sign of crystalline order. Resonances from beta(1,4')-d galactan were visible in the lupin seed spectrum, but there was much interference from protein. The nasturtium seed spectrum was largely derived from a xyloglucan, in which the conformation of the glucan core chain appeared to be intermediate between the solution form and solid forms of cellulose.

Unequal Distribution of Fixed Negative Charges in Isolated Cell Walls of Various Tissues in Primary Leaves of Phaseolus

Summary Microelectrode technique was used to determine the activity of fixed charges of cell walls of various tissues of primary leaves of Phaseolus coccineus L. by measuring the electric potential differences generated by the fixed negative charges of the isolated but morphologically intact walls. An unequal distribution of the activity of fixed charges was found in the walls of parenchyma and collenchyma cells of the petiole: at the layer facing the cell lumen the activity was low (approx. 220 meq 1 −1 in 100 mM KCl at pH 7) compared to that of the wall layer facing the intercellularies in parenchyma cells (approx. 550 meq 1 −1 in 100 mM KCI, pH 7) or of the thickened corners of the collenchyma cell walls (approx. 610 meq 1 -1 in 100 mM KCI, pH 7). In contrast, the activity of fixed charges determined in pulvinar motor cells at the wall layers facing the cell lumen was high. In both the primary and secondary pulvinus the walls of motor cells located above the stele exhibited a higher activity of fixed charges (approx. 640–680 meq 1 −1 in 100 mM KCI, pH 7) than the motor cells located below the stele (approx. 550–600 meq 1 −1 in 100 mM KCI, pH 7). The results indicate that wall layers rich in pectic substances exhibit high fixed charge activities. Consequently, the walls of most tissues should be characterized by a layering of fixed charge activities corresponding to the layering in the biochemical composition. The functional importance of the negative fixed charges of the cell wall and of their heterogenous distribution is discussed with respect to the activity of wall-bound enzymes, membrane transport processes and the role of walls as cation reservoirs.