Immunohistochemical localization of hemicelluloses and pectins varies during tissue development in the bamboo culm

The distribution of hemicelluloses and pectins in bamboo internodes was studied immunocytochemistrically at various stages of development. The ultra-structures of bamboo cell walls have been reported previously at various stages. The internodes were identically classified into three developmental phases: primary wall stage (phase I), unlignified secondary wall stage (phase II) and lignified wall stage (phase III), using the same bamboo culm. (1-->3, 1-->4)-Beta-glucans were distributed in nearly all tissues in an actively elongating stage. Limited amounts of beta-glucans were deposited in primary walls and the middle lamellae, but were limited to the phloem in secondary walls. This suggests that the function of beta-glucans might be different in phloem vis-à-vis other tissues. Highly-substituted xylans were located in nearly all tissues of early phase I, but had disappeared in all tissues immediately prior to lignification. In contrast, low-branched xylan epitopes were present only in the protoxylem in phase I, but were present in all tissues immediately prior to lignification in phase II. In phase III, the epitopes were densely localized in lignified walls, suggesting that the substitution of xylans is closely related to maturation. Methyl-esterified (but not unesterified) pectins were present in all tissues of early phase I. Just before and after lignification, both types of pectins were concentrated in the phloem and protoxylem. Xyloglucans were largely distributed in the phloem and in lignified tissues, suggesting that they might be closely correlated with maturation. This represents the first account of the distribution of hemicelluloses and pectins at the tissue and ultrastructural level in bamboo internodes at various stages of development.     

Highly substituted glucuronoarabinoxylans (hsGAXs) and low-branched xylans show a distinct localization pattern in the tissues of Zea mays L

Polyclonal antibodies which recognized highly substituted glucuronoarabinoxylans (hsGAXs) and low-branched xylans and did not cross-react with each other, were raised in order to examine localization of these epitopes in internodes of maize. Immunofluorescent labeling revealed different pattern between two succeeding developmental stages. The hsGAX epitope was localized evenly in primary walls in all tissue types, and strongly in unlignified secondary walls in phloem. However, lignified secondary walls in protoxylem, parenchyma and a part of fibers were faintly labeled with this epitope. Moreover, the epitope showed limited binding in lignified parenchyma and fiber walls at ultrastructural level. Low-branched xylan epitope was localized evenly throughout lignified walls in all tissue types. This epitope was also localized only in lignified walls of other organs such as leaf, root apex and dark-grown mesocotyl. Low-branched xylans are significantly related to lignification. Localization of hsGAX epitope in their organs was similar to that in internodes. The hsGAX epitope was distributed both in unlignified walls of all tissues and in lignified walls of parenchyma and annular thickening of protoxylem. We propose that hsGAX has separate functions in lignified and unlignified tissues. In conclusion, at tissue level, hsGAX is localized mainly in unlignified walls, and low-branched xylans in lignified walls.     

毛竹茎细胞壁半纤维素多糖的免疫细胞化学定位研究

本文以毛竹(Phyllostachys pubescens)为材料,采用免疫细胞化学标记方法对两种细胞壁半纤维素多糖成分,即木聚糖(Xylan)和(1-3)(1-4)-β-葡聚糖［(1-3)(1-4)-β-glucan］在毛竹茎中的分布进行了观察。结果表明,应用免疫细胞化学方法可以准确、有效地观察这两种半纤维素多糖成分在细胞壁中的分布;木聚糖分布在已木质化的组织细胞的细胞壁中,与细胞壁木质化有密切关系;(1-3)(1-4)-β-葡聚糖在幼竹茎基本组织中分布于短薄壁细胞细胞壁中及长薄壁细胞胞间层,而在老龄竹茎基本组织中,仅分布于短薄壁细胞细胞壁中,而长薄壁细胞细胞壁却无此成分,反映出长、短薄壁细胞细胞壁组成上的差异。     

毛竹细胞壁自发荧光的显微荧光分光光度分析

利用冰冻切片、荧光显微镜、显微荧光分光光度计、组织化学等方法,观察分析了毛竹（ＰｈｙｌｏｓｔａｃｈｙｓｐｕｂｅｓｃｅｎｓＭａｚｅｌ）茎不同组织在０．１ｍｏｌ／Ｌ氨水、１ｍｏｌ／ＬＮａＯＨ及过氧化氢／冰醋酸混合液处理前后细胞壁自发荧光变化。毛竹茎所有组织在紫外光激发下均产生蓝色荧光;氨水处理后,所有组织荧光强度增加,富含阿魏酸的组织,荧光颜色由蓝色转变为绿色,荧光发射光谱峰值由４７０ｎｍ移至５１０ｎｍ;ＮａＯＨ处理使所有组织荧光强度降低;过氧化氢／冰醋酸混合液处理后,木质化组织仍保持较强的蓝色荧光,而未木质化的组织荧光消失。结果表明,原生木质部导管在维管束分化早期就已木质化;阿魏酸广泛分布于竹笋各种幼嫩组织中,随着毛竹生长、细胞壁木质化的发展其含量下降。此外,过氧化氢／冰醋酸混合液处理可以有效地区分木质素与结合于半纤维素中的酚酸成分     

Lignification and lignin heterogeneity for various age classes of bamboo (Phyllostachys pubescens) stems

The lignification process and lignin heterogeneity of fibre, vessel and parenchyma cell walls for various age classes of bamboo stems of Phyllostachys pubescens Mazel were investigated. It was shown that protoxylem vessels lignified in the early stage of vascular bundle differentiation, metaxylem vessel and fibre walls initiated lignification from the middle lamella and cell corners after the completion of vascular bundle differentiation. Most of the parenchyma cell walls lignified after the stem reached its full height, while a few parenchyma cells remained non-lignified even in the mature culm. The cell walls of fibres and most parenchyma cells thickened further during the stem growth to form polylamellate structure and the lignification process of these cells may last even up to 7 years. The fibre walls were rich in guaiacyl lignin in the early stage of lignification, and lignin rich in syringyl units were deposited in the later stage. Vessel walls mainly contained guaiacyl lignin, while both guaiacyl and syringyl lignin were present in the fibre and parenchyma cell walls.     

Toward understanding the different function of two types of parenchyma cells in bamboo culms

The bamboo, woody monocot, has two types of parenchyma cells in the ground tissues of its culm, in contrast to a single type of parenchyma cell in rice, maize and other major crop species. The distribution of cell wall components, including lignin, (1-->3), (1-->4)-beta-D-glucans (MGs), the highly-substituted glucuronoarabinoxylans (hsGAXs) and low-branched xylans (lbXs) in ground parenchyma tissue of Phyllostachys heterocycla var. pubescens culms was studied at various developmental stages using light microscopy (LM), UV-microscopy, transmission electron microscopy (TEM) and immunolabeling techniques. The short parenchyma cell walls were lignified in 2-month-old bamboo culms just as the long parenchyma cell walls were. The lignified regions were confined to the portions in contact with the long parenchyma cell walls, while the walls at the cell corner region never lignified, even in 7-year-old culms. Significant differences were also found in the hemicellulose distribution between the short and long parenchyma cell walls. In bamboo parenchyma tissue, MGs were localized in short parenchyma cell walls and few were found in long parenchyma cell walls in both young and 7-year-old culms. The distribution of hsGAXs was similar to that of MGs in young culms, but they only appeared in the cell corner region of short parenchyma cells in old culms. Low-branched xylans were distributed in the lignified, but not in unlignified parenchyma cell walls. Based on this evidence, the differences of function in both short and long parenchyma cells in a bamboo culm are discussed.     

杜仲次生木质部分化过程中木质素与半纤维素组分在细胞壁中分布的动态变化

利用紫外光显微镜、透射电子显微镜结合免疫胶体金标记,研究了杜仲（Eucommia ulmoides Oliv.)次生木质部分化过程中木质素与半纤维素组分（木葡聚糖和木聚糖）在细胞壁分布的动态变化。在形成层及细胞伸展区域,细胞壁具有木葡聚糖的分布,而没有木聚糖和木质素沉积,随着次生壁S1层的形成,木质素出现在细胞角隅和胞间层,木聚糖开始出现在S1层中,此时木葡聚糖则分布在初生壁和胞间层;随着次生,壁S2层及S3层的形成和加厚,木质逐逐步由细胞角隅和胞间层扩展到S1、S2和S3层,其沉积呈现出不均匀的块状或片状沉积模式,在次生壁各层形成与其木质化的同时,木聚糖逐渐分布于整个次生壁中,而木糖聚糖仍局限分布于初生壁和胞间层。结果表明,随着细胞次生壁的形成与木质化,细胞壁结构发生较大变化。细胞壁的不同区域,如细胞角隅、胞间层、初生壁和次生壁各层,具有不同的半纤维素组成,其与木质等细胞壁组分结构构成不同的细胞壁分子结构。     

Dynamic Changes in Distribution of Lignin and Hemicelluloses in Cell Walls During Differentiation of Secondary Xylem in Eucommia ulmoides (in English)

The dynamic changes in the distribution of lignin and hemicelluloses (xylans and xyloglucans) in cell walls during the differentiation of secondary xylem in Eucommia ulmoides Oliv. were studied by means of ultraviolet light microscopy and transmission electron microscopy combined with immunogold labelling. In the cambial zone and cell expansion zone, xyloglucans were localized both in the tangential and radial walls, but no xylans or lignin were found in these regions. With the formation of secondary wall S1 layer, lignin occurred in the cell corners and middle lamella, while xylans appeared in S1 layer, and xyloglucans were localized in the primary walls and middle lamella. In pace with the formation of secondary wall S2 and S3 layer, lignification extended to S1, S2 and S3 layer in sequence, showing a patchy style of lignin deposition. Concurrently, xylans distributed in the whole secondary walls and xyloglucans, on the other hand, still localized in the primary walls and middle lamella. The results indicated that along with the formation and lignification of the secondary wall, great changes had taken place in the cell walls. Different parts of cell walls, such as cell corners, middle lamella, primary walls and various layers of secondary walls, had different kinds of hemicelluloses, which formed various cell wall architecture combined with lignin and other cell wall components.     

Alfalfa Stem Tissues: Cell-wall Development and Lignification

Alfalfa stems contain a variety of tissues with different patternsof cell-wall development. Development of alfalfa cell wallswas investigated after histochemical staining and with polarizedlight using light microscopy and scanning electron microscopy.Samples of the seventh internode, from the base of stems grownon cut stems, were harvested at five defined stages of developmentfrom early internode elongation through to late maturity. Internodeseven was elongating up to the third sample harvest and internodediameter increased throughout the entire sampling period. Chlorenchyma,cambium, secondary phloem, primary xylem parenchyma and pithparenchyma stem tissues all had thin primary cell walls. Pithparenchyma underwent a small amount of cell-wall thickeningand lignification during maturation. Collenchyma and primaryphloem tissues developed partially thickened primary walls.In contrast to a recent report, the formation of a ring shaped,lignified portion of the primary wall in a number of cells inthe exterior part of the primary phloem was found to precedethe deposition of a thick, non-lignified secondary wall whichwas degradable by rumen microbes. In numerous xylem fibres fromthe fourth harvest date onwards, an additional highly degradablesecondary wall layer was deposited against a previously depositedlignified and undegradable secondary wall. The pattern of lignificationobserved in alfalfa stem tissues suggests that polymerizationof monolignols by peroxidases at the luminal border of the primarycell wall creates an impermeable zone which restricts lignificationof the middle lamella region of tissues with thick primary walls.Copyright1998 Annals of Botany Company Alfalfa,Medicago sativaL., stem tissue, cell wall, development, lignification, degradation.     

Developmental Changes in the Anatomy of the Sugarcane Stem in Relation to Phloem Unloading and Sucrose Storage

Transverse sections of immature and mature sugarcane internodes were investigated anatomically with white and fluorescence light microscopy. The pattern of lignification and suberization was tested histo-chemically. Lignification began in the xylem of vascular bundles and progressed through the sclerenchymatic bundle sheath into the storage parenchyma. Suberization began in parenchyma cells adjacent to vascular bundle sheaths and spread to the storage parenchyma and outer sheath cells. In mature internodes most of the storage parenchyma was lignified and suberized to a significant degree, except in portions of walls of isolated cells. The pattern of increasing lignification and suberization in maturing internodes more or less paralleled an increase of sucrose in stem tissue. In mature internodes having a high sucrose concentration, the vascular tissue was surrounded by thick-walled, lignified and suberized sclerenchyma cells. The apoplastic tracer dyes triso-dium 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS) and amido black 10 B, fed into cut ends of the stalk, wereconfined to the vascular bundles in all internodes above the one that was cut — with no dye apparently in storage parenchyma tissue. Thus both structural and experimental evidence is consistent with vascular tissue being increasingly isolated from the storage parenchyma as maturation of the tissue proceeds. We conclude that in mature internodes the pathway for sugars from the phloem to the storage parenchyma is symplastic. The data suggest that an increasingly greater role for a symplastic pathway of sugar transfer occurs as the tissue undergoes lignification/suberization.     

Structural cell-wall proteins in protoxylem development: evidence for a repair process mediated by a glycine-rich protein

Polyclonal antibodies were used to localize structural cell-wall proteins in differentiating protoxylem elements in etiolated bean and soybean hypocotyls at the light- and electron-microscopic level. A proline-rich protein was localized in the lignified secondary walls, but not in the primary walls of protoxylem elements, which remain unlignified, as shown with lignin-specific antibodies. Secretion of the proline-rich protein was observed during lignification in different cell types. A glycine-rich protein (GRP1.8) was specifically localized in the modified primary walls of mature protoxylem elements and in cell corners between xylem elements and xylem parenchyma cells. The protein was secreted by Golgi bodies both in protoxylem cells after the lignification of their secondary walls and in the surrounding xylem parenchyma cells. The modified primary walls of protoxylem elements were visualized under the light microscope as filaments or sheets staining distinctly with the protein stain Coomassie blue. Electron micrographs of these walls show that they are composed of an amorphous material of moderate electron-density and of polysaccharide microfibrils. These materials form a three-dimensional network, interconnecting the ring- or spiral-shaped secondary wall thickenings of protoxylem elements and xylem parenchyma cells. The results demonstrate that the modified primary walls of protoxylem cells are not simply breakdown products due to partial hydrolysis and passive elongation, as believed until now. Extensive repair processes produce cell walls with unique staining properties. It is concluded that these walls are unusually rich in protein and therefore have special chemical and physical properties.     

Immunogold labelling of xylans and arabinoxylans in the plant cell walls of maize stem

Summary— Polyclonal antibodies against 4-O-methyl-glucuronoxylan and α L-1-3 arabinofuranosyl poly-β-d-1-4-xylopyranosyl were raised from rabbits. An immunocytochemical technique was used to localize xylans and arabinoxylans in the plant cell walls of the apical internode of two maize lines of different digestibility. The sclerenchyma, fibres and xylem (lignified tissues) and the parenchyma (non-lignified tissue) were studied. The arabinoxylans were more heavily labelled than the xylans in the lignified tissues of the less digestible maize whereas in the more digestible line the labelling of the two polysaccharides was similar. The xylans and arabinoxylans were localized in the secondary cell wall. In both maize lines, labelling increased from the base upwards of the apical internode, reflecting the changes in growth stage.     

Characterization of a lignified secondary phloem fibre-deficient mutant of jute (Corchorus capsularis)

BACKGROUND AND AIMS: High lignin content of lignocellulose jute fibre does not favour its utilization in making finer fabrics and other value-added products. To aid the development of low-lignin jute fibre, this study aimed to identify a phloem fibre mutant with reduced lignin. METHODS: An x-ray-induced mutant line (CMU) of jute (Corchorus capsularis) was morphologically evaluated and the accession (CMU 013) with the most undulated phenotype was compared with its normal parent (JRC 212) for its growth, secondary fibre development and lignification of the fibre cell wall. KEY RESULTS: The normal and mutant plants showed similar leaf photosynthetic rates. The mutant grew more slowly, had shorter internodes and yielded much less fibre after retting. The fibre of the mutant contained 50 % less lignin but comparatively more cellulose than that of the normal type. Differentiation of primary and secondary vascular tissues throughout the CMU 013 stem was regular but it did not have secondary phloem fibre bundles as in JRC 212. Instead, a few thin-walled, less lignified fibre cells formed uni- or biseriate radial rows within the phloem wedges of the middle stem. The lower and earliest developed part of the mutant stem had no lignified fibre cells. This developmental deficiency in lignification of fibre cells was correlated to a similar deficiency in phenylalanine ammonia lyase activity, but not peroxidase activity, in the bark tissue along the stem axis. In spite of severe reduction in lignin synthesis in the phloem cells this mutant functioned normally and bred true. CONCLUSIONS: In view of the observations made, the mutant is designated as deficient lignified phloem fibre (dlpf). This mutant may be utilized to engineer low-lignin jute fibre strains and may also serve as a model to study the positional information that coordinates secondary wall thickening of fibre cells.     

Ultrastructural Localization of a Bean Glycine-Rich Protein in Unlignified Primary Walls of Protoxylem Cells

A polyclonal antibody was used to localize a glycine-rich cell wall protein (GRP 1.8) in French bean hypocotyls with the indirect immunogold method. GRP 1.8 could be localized mainly in the unlignified primary cell walls of the oldest protoxylem elements and also in cell corners of both proto- and metaxylem elements. In addition, GRP 1.8 was detected in phloem using tissue printing. The labeled primary walls of dead protoxylem cells showed a characteristically dispersed ultrastructure, resulting from the action of hydrolases during the final steps of cell maturation and from mechanical stress due to hypocotyl growth. Primary walls of living protoxylem and adjacent parenchyma cells were only weakly labeled. This was true also for the secondary walls of proto- and metaxylem cells, which in addition showed high background labeling. Inhibition of lignification with a specific and potent inhibitor of phenylalanine ammonia-lyase did not lead to enhanced labeling of secondary walls, showing that lignin does not mask the presence of GRP 1.8 in these walls. Dictyosomes of living proto- and metaxylem cells were not labeled, but dictyosomes of xylem parenchyma cells without secondary walls, adjacent to strongly labeled protoxylem elements, were clearly labeled. These observations suggest that GRP 1.8 is not produced by xylem vessels but by xylem parenchyma cells that export the protein to the wall of protoxylem vessels.     

Immunocytochemical localization of pectins in the maturing anther of Allium cepa L.

Distribution of pectins in cell walls of maturing anther of Allium cepa L. was investigated. The monoclonal antibodies against defined epitopes of pectin were used: JIM5 recognizing unesterified pectin and JIM7 recognizing esterified pectin. It has been found that the cell walls of all anther tissues mainly contain esterified pectins. In the somatic tissues only small amounts of unesterified pectins are present in the cell wall junctions and adjacent middle lamellae and in the cell walls of the connective tissue. Thickening of the epiderm cell walls and growth of trabeculae in endothecium are completed through deposition of esterified pectins. In the cell walls of the middle layer and tapetum, unesterified pectins have been found only prior to their disintegration. The primary wall of microsporocytes is made up mainly of esterified pectins. Unesterified pectins occur outside microsporocytes only prior to the callose isolation stage. The presence of esterified pectins has also been detected on the surface of the callose wall surrounding dividing microsporocytes. Lysis of those pectins takes place after microsporogenesis, simultaneously with the lysis of the callosic walls. Before these processes pectins are unesterified. In the sporoderm of pollen grains mainly esterified pectins occur. They have been localized in the intine and aperture. The level of unesterified pectins in the intine is markedly lower.     

Localization of cell wall polysaccharides in normal and compression wood of radiata pine: relationships with lignification and microfibril orientation

The distribution of noncellulosic polysaccharides in cell walls of tracheids and xylem parenchyma cells in normal and compression wood of Pinus radiata, was examined to determine the relationships with lignification and cellulose microfibril orientation. Using fluorescence microscopy combined with immunocytochemistry, monoclonal antibodies were used to detect xyloglucan (LM15), β(1,4)-galactan (LM5), heteroxylan (LM10 and LM11), and galactoglucomannan (LM21 and LM22). Lignin and crystalline cellulose were localized on the same sections used for immunocytochemistry by autofluorescence and polarized light microscopy, respectively. Changes in the distribution of noncellulosic polysaccharides between normal and compression wood were associated with changes in lignin distribution. Increased lignification of compression wood secondary walls was associated with novel deposition of β(1,4)-galactan and with reduced amounts of xylan and mannan in the outer S2 (S2L) region of tracheids. Xylan and mannan were detected in all lignified xylem cell types (tracheids, ray tracheids, and thick-walled ray parenchyma) but were not detected in unlignified cell types (thin-walled ray parenchyma and resin canal parenchyma). Mannan was absent from the highly lignified compound middle lamella, but xylan occurred throughout the cell walls of tracheids. Using colocalization measurements, we confirmed that polysaccharides containing galactose, mannose, and xylose have consistent correlations with lignification. Low or unsubstituted xylans were localized in cell wall layers characterized by transverse cellulose microfibril orientation in both normal and compression wood tracheids. Our results support the theory that the assembly of wood cell walls, including lignification and microfibril orientation, may be mediated by changes in the amount and distribution of noncellulosic polysaccharides.     

Ultrastructure of fibre and parenchyma cell walls during early stages of culm development in Dendrocalamus asper

BACKGROUND AND AIMS: The anatomy of bamboo culms and the multilayered structure of fibre cell walls are known to be the main determinant factors for its physical and mechanical properties. Studies on the bamboo cell wall have focussed mainly on fully elongated and mature fibres. The main aim of this study was to describe the ultrastructure of primary and secondary cell walls in culm tissues of Dendrocalamus asper at different stages of development. METHODS: The development of fibre and parenchyma tissues was classified into four stages based on light microscopy observations made in tissues from juvenile plants. The stages were used as a basis for transmission electron microscopy study on the ultrastructure of the cell wall during the process of primary and early secondary cell wall formation. Macerations and phloroglucinol-HCl staining were employed to investigate fibre cell elongation and fibre cell wall lignification, respectively. KEY RESULTS: The observations indicated that the primary wall is formed by the deposition of two distinct layers during the elongation of the internode and that secondary wall synthesis may begin before the complete cessation of internode and fibre elongation. Elongation was followed by a maturation phase characterized by the deposition of multiple secondary wall layers, which varied in number according to the cell type, location in the culm tissue and stage of shoot development. Lignification of fibre cell walls started at the period prior to the cessation of internode elongation. CONCLUSIONS: The structure of the primary cell wall was comprised of two layers. The fibre secondary cell wall began to be laid down while the cells were still undergoing some elongation, suggesting that it may act to cause the slow-down and eventual cessation of cell elongation.     

Adhesion of Bacteroides succinogenes in pure culture and in the presence of Ruminococcus flavefaciens to cell walls in leaves of perennial ryegrass (Lolium perenne)

Bacteroides succinogenes and Ruminococcus flavefaciens are two of the most important cellulolytic bacteria in the rumen. Adhesion of B. succinogenes in pure culture, and in mixed culture with R. flavefaciens, to the various types of cell walls in sections of perennial ryegrass (Lolium perenne L. cultivar S24) leaves was examined by transmission and scanning electron microscopy. B. succinogenes adhered to the cut edges of most plant cell walls except those of the meta- and protoxylem. It also adhered, though in much smaller numbers, to the uncut surfaces of mesophyll, epidermal, and phloem cell walls. In mixed culture, both species adhered in significant numbers to the cut edges of most types of plant cell wall, but R. flavefaciens predominated on the epidermis, phloem, and sclerenchyma cell walls. B. succinogenes predominated on the cut edges and on the uncut surfaces of the mesophyll cell walls, and its ability to adhere to uncut surfaces of other cell walls was not affected by the presence of the ruminococcus. Both organisms rapidly digested the epidermal, mesophyll, and phloem cell walls. Zones of digestion were observed around bacteria of both species when attached to the lignified cell walls of the sclerenchyma, but not when attached to the lignified xylem vessels.     

Adhesion of Bacteroides succinogenes in pure culture and in the presence of Ruminococcus flavefaciens to cell walls in leaves of perennial ryegrass (Lolium perenne).

Bacteroides succinogenes and Ruminococcus flavefaciens are two of the most important cellulolytic bacteria in the rumen. Adhesion of B. succinogenes in pure culture, and in mixed culture with R. flavefaciens, to the various types of cell walls in sections of perennial ryegrass (Lolium perenne L. cultivar S24) leaves was examined by transmission and scanning electron microscopy. B. succinogenes adhered to the cut edges of most plant cell walls except those of the meta- and protoxylem. It also adhered, though in much smaller numbers, to the uncut surfaces of mesophyll, epidermal, and phloem cell walls. In mixed culture, both species adhered in significant numbers to the cut edges of most types of plant cell wall, but R. flavefaciens predominated on the epidermis, phloem, and sclerenchyma cell walls. B. succinogenes predominated on the cut edges and on the uncut surfaces of the mesophyll cell walls, and its ability to adhere to uncut surfaces of other cell walls was not affected by the presence of the ruminococcus. Both organisms rapidly digested the epidermal, mesophyll, and phloem cell walls. Zones of digestion were observed around bacteria of both species when attached to the lignified cell walls of the sclerenchyma, but not when attached to the lignified xylem vessels.     

Comparative characterization of degraded and non-degradative hemicelluloses from barley straw and maize stems: Composition, structure, and thermal properties

Three organic solvents and one aqueous alkaline solution for fully fractional dissolving hemicelluloses from mild ball-milled cell wall of lignified barley straw and maize stems are described: 90% neutral dioxane, 80% dioxane containing 0.05 M HCl, dimethyl sulfoxide (DMSO), and 8% aqueous KOH. The four successive extractions resulted in dissolution of 94.6% and 96.4% of the original hemicelluloses and 93.7% and 95.3% of the original lignin from barley straw and maize stems, respectively. The structures of the hemicellulosic fractions released during the treatment with the neutral solvents of 90% dioxane and DMSO was found to remain intact, while the extractions with 80% acidic dioxane and 8% KOH under the conditions used resulted in a partial depolymerization of dissolved polysaccharides by cleavage of the glycosidic bonds and saponification of the ester groups in the polymers. The 90% neutral dioxane-soluble hemicellulosic fractions consisted mainly of the more branched arabinoxylans and mixed-linkage glucans such as β-glucans, whereas the hemicellulosic fractions solubilized during the sequential treatments with 80% acidic dioxane, DMSO, and 8% KOH are composed of arabino-(4-O-methyl-d-glucurono) xylans as the major hemicellulosic materials. In addition, the hemicellulosic polymers contained small amounts of ferulic and p-coumaric acids and lignins, revealing that the hemicelluloses removed are mostly unbound to the lignins in the cell walls of cereal straws. This non-degradative cell wall dissolution offers the potential to analyze polysaccharide components for the first time, and improve current hemicellulosic isolation method by using high concentration of aqueous alkali from the delignified cell walls.