Tubular sclereids: A newly identified sclerenchyma cell type in tropical seeds.

Cell type distinct accumulations of mRNA and protein for NADH-dependent glutamate synthase in rice roots in response to the supply of NH 4+

The plant body plan is quite simple, encompassing four organs (leaf, stem, root, flower), three basic tissue types (epidermal, vascular and ground), and three cell types (parenchyma, collenchyma, and sclerenchyma). Parenchyma cells are living cells, bound by a primary cell wall, and many of them are capable of differentiation into any other cell type. Parenchyma is the most diverse and versatile cell type and comprises the majority of cells in most plants. Collenchyma cells are the least common plant cell type. They have a primary cell wall and provide support in herbaceous or temporary organs such as petioles and leaves. Sclerenchyma cells have a lignified and strong secondary cell wall and are usually dead at maturity. Sclerenchyma cells are found wherever a plant needs strength and support, such as fibers, stone cells, wood, and water-conducting cells.

In order to estimate whether cytosolic glutamine synthetase (GS1; EC 6.3.1.2) is partly coupled to the reaction of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5) in developing organs of rice (Oryza sativa L.), we compared the expression pattern of transcripts and proteins for GS1 and PAL in the tissue sections from leaf blades at various stages of development. In immature vascular bundles of unexpanded leaf blades, GS1 mRNA was mainly detected in xylem parenchyma cells, mestome-sheath cells, and sclerenchyma cells. PAL transcripts were also accumulated in these cell types. Vascular bundles in midribs of immature leaf blades contained mRNAs and proteins for both GS1 and PAL abundantly in sclerenchyma cells, although distribution of these two proteins was not completely overlapped. In immature vascular bundles in midribs, lignin deposition was observed in cell walls of xylem parenchyma cells, mestome-sheath cells and sclerenchyma cells. These results implied that a part of GS1 in unexpanded leaf blades is possibly involved in reassimilation of ammonia released from PAL reaction during the lignin production.

Key messageDistributional patterns of pectin and hemicellulose epitopes in the phloem of four hardwoods vary between cell types including sieve tube elements, companion cells, parenchyma and sclerenchyma and between tree species.Using immunolocalization methods combined with monoclonal antibodies, the distribution of pectin and hemicellulose epitopes was examined in the secondary phloem of two diffuse porous (birch, aspen)- and two ring porous (oak, ash) hardwoods with a focus on sieve tube elements (SEs), companion cells (CCs), axial/ray parenchyma cells, and sclerenchyma cells (sclereids and phloem fibers). In all tree species, rhamnogalacturonan-I (RG-I), homogalacturonan (HG), and xyloglucan epitopes were common in cell walls of SEs, CCs, and axial/ray parenchyma cells. However, the amount of these epitopes varied greatly between cell types and between hardwood species. Apart from aspen, heteroxylan or/and heteromannan epitopes were detected in SEs, but were not detected in CCs and parenchyma cells. With sclerenchyma cells, RG-I, HG, and xyloglucan epitopes were common in compound middle lamellae (CML) of sclereids and phloem fibers. Except for oak, heteromannan epitopes were also detected in CML of sclereids. Distributional patterns of epitopes in CML of birch and ash sclereids varied greatly depending on anatomical structure of CML. Secondary cell walls of sclereids and phloem fibers revealed abundant heteroxylan epitopes, but showed no heteromannan epitopes. Some phloem fibers also showed sparse xyloglucan epitopes in secondary cell walls. Together, results suggest that there are great variations in distributional patterns of pectin and hemicellulose epitopes in hardwood phloem between cell types and between tree species.

Sclerenchyma is a specialised tissue, adapted to withstand both compressive and tensile stresses in plants. Sclerenchyma cell types may be divided into fibres, associated with phloem, xylem and other tissues; and sclereids or varied kinds. Sclereids originate from parenchyma and expand by intrusive growth. Phloem and xylem fibres in trees originate from the vascular cambium through delicately controlled, parallel cell divisions. Sclerenchyma cells have secondary wall layers that are constructed from cellulose microfibrils in a matrix of hemicelluloses and lignin. The cell geometry and the orientation of the cellulose are tailored to provide diverse combinations of strength, flexibility and stiffness in plant organs subjected to different loads by gravity, wind and weather. These properties are utilised in wood textiles and other natural materials of commercial importance. Key Concepts: Sclerenchyma is a plant tissue providing mechanical stiffness and strength. Fibres and sclereids are the main types of sclerenchyma cells. Most sclerenchyma cells show intrusive growth. The cell walls of sclerenchyma have thickened secondary layers made from cellulose, hemicelluloses and lignin. The stiffness of sclerenchyma depends on the orientation of cellulose and varies widely under developmental control. Formation of sclerenchyma is controlled by a range of transcription factors.

Confocal Raman microscopy and confocal fluorescence microscopy were used to understand the mechanism of ionic liquid (IL) pretreatment of corn stover stem using 1-ethyl-3-methylimidazolium acetate. Three different cell types including tracheids, sclerenchyma cells and parenchyma cells were analyzed during IL pretreatment. We have established a direct correlation between changes in both the morphology and chemical composition of these plant cell walls during IL pretreatment as well as specific cell type information. It was observed that cell wall swelling occurs primarily in the secondary plant cell walls and the IL had little effect on compound middle lamella in terms of swelling. Accordingly, more significant cell wall swelling and distortion was observed in sclerenchyma cells and tracheids than in parenchyma cells, which contain primary plant cell walls. Lignin dissolution was faster in the secondary cell walls, while there was no preferential cellulose dissolution. Surprisingly, with a much thicker cell wall and a much higher original lignin content than parenchyma cells, tracheids showed much faster lignin and cellulose dissolution and cell wall swelling. Sclerenchyma cells showed an intermediate rate of lignin dissolution, while the cellulose dissolution rate and degree of cell wall swelling was comparable to that observed for tracheids. These results suggest that there is a synergistic mechanism of lignocellulose dissolution regarding cellulose and lignin dissolution and cell wall swelling that occurs during IL pretreatment. This study provides valuable new insights towards the mechanism of ionic liquid pretreatment and can potentially assist researchers in cell wall engineering for efficient cell wall deconstruction using ILs, and the methods established can be easily extended to other systems.

Internodes of maize (Zea mays L, Co125), harvested 5 days after anthesis, were sectioned into five equal parts and samples of sclerenchyma and parenchyma cells mechanically isolated from each section. Phenolic acids and syringyl and guaiacyl degradation products of lignin were released from the walls of the two cell types by microwave digestion with 4 M NaOH. Aryl ether bonded units were selectively released by thioacidolysis. Total phenolic content of cell walls from the youngest (basal) sections were approximately two-thirds of those of the oldest, topmost sections (parenchyma 70·8–99·0 and sclerenchyma 72·5–114·1 mg g-1) indicating that the process of lignification was already well advanced amongst most of the cell walls of the youngest section. The total phenolic content was marginally, but significantly, greater (P<0·05) in sclerenchyma walls than in parenchyma walls at all stages of maturity. There was no significant difference in phenolic acid concentrations between cell types from the same section but p-coumaric acid concentration increased with maturity (P<0·001) in walls from both cell types. The increase in p-coumarate with age was matched by an increased recovery of syringyl units resulting in a constant coumaroyl: syringyl molar ratio. Recovery of acetosyringone was significantly greater (P<0·001) from sclerenchyma than parenchyma walls and, in sclerenchyma, acetosyringone as a proportion of total syringyl recovery, increased significantly with age (P=0·015). Digestion with NaOH and thioacidolysis released comparable amounts of guaiacyl residues but NaOH digestion released approximately twice the amount of syringyl residues. This difference may be explained by the retention of the ester-bond between p-coumaric acid and syringyl units during thioacidolysis but not during digestion with 4 M alkali. The similarity in phenolic composition suggested that both cell types, despite their considerable anatomical differences, were exposed to a common flux of lignin precursors during the later stages of lignification as illustrated by the internode sections. Differences between cell walls arose because of differences in the regiochemistry of precursor incorporation. © 1997 SCI.

Characterization of the Leaf Epidermis of Barley (Hordeum vulgareL. 'Himalaya')

Leaf forms are diverse in angiosperms, and different types of cells are differentiated depending on the species. Rice leaves are composed of a leaf blade, a leaf sheath and the junction region between them. Cells with characteristic features, such as bulliform cells and sclerenchyma cells, are differentiated in the leaf blade, together with standard epidermal and mesophyll cells. To understand the genetic mechanism underlying leaf morphogenesis in rice, we focused on a mutant, half-pipe-like leaf1 (hal1), whose leaves are adaxially curled. Histological observation revealed that the bulliform cells, which are responsible for leaf rolling under dry conditions, were small in size and abnormal in shape in a semidominant hal1-d mutant. Bulliform cell files were often ambiguous in semi-transparent hal1-d leaves cleared by the TOMEI method, suggesting that the bulliform cells were undeveloped. Therefore, a reduction in the growth of the bulliform cells seemed to be a major cause of leaf curling in the hal1-d mutant. The hal1-d mutation also affected the size of the leaf blade and the spikelet.

ABSTRACTTo arrive at a better understanding of variation in specific leaf mass (SLM, leaf weight per unit leaf area), we investigated the chemical composition and anatomical structure of the leaves of 14 grass species varying in potential relative growth rate. Expressed on a dry weight basis, the fast‐growing grass species with low SLM contained relatively more minerals and organic N‐compounds, whereas slow‐growing species with high SLM contained more (hemi)cellulose and lignin. However, when expressed per unit leaf area, organic N‐compounds, (hemi)cellulose, total structural carbohydrates and organic acids increased with increasing SLM.For the 14 grasses, no trend with SLM was found for the leaf volume per unit leaf area. Leaf density was positively correlated with SLM. Variation in density was not caused by variation in the proportion of intercellular spaces. The proportion of the total volume occupied by mesophyll and veins did not differ either. A high SLM was caused, at least partly, by a high proportion of non‐veinal sclerenchymatic cells per cross‐section. The epidermal cell area was negatively correlated with SLM.We conclude that the differences in SLM and in the relative growth rate (RGR) between fast‐ and slow‐growing grass species are based partly on variation in anatomical differentiation and partly on chemical differences within cell types.

The differentiation of the ectodermal, entodermal, and mesodermal cell lines in developing plutei of the ophiuroid Amphipholis kochii was examined using electron microscopy and the immunochemical staining technique. The ectodermal cells form the pseudostratified epithelium of the ciliary band, the flattened epithelium of the body wall, and the esophageal epithelium. The epithelium of the ciliary band consists of ciliated and mucous cells; at its base is an axonal tract formed of the processes of neurons. The serotoninergic neurons form two lateral ganglia located along the paraoral ciliary band and the posterolateral arms’ ciliary band. The prominent features of the neurons are large size, the presence of a cilium, an electron-light cytoplasm filled with microvesicles with neurotransmitters, and a large nucleus with a predominant euchromatin. The ectoderm cells (except mucous cells) are characterized by the presence of a cilium surrounded by a collar of microvilli and a thin layer of apical extracellular matrix. The entodermal cells form the digestive tract epithelium and differentiate into four cell types: type I and II cells probably function in the nutrient uptake and assimilation; type III cells perhaps secrete digestive enzymes; and myoepithelial cells that constitute the cardiac and pyloric sphincters and the anus. Sclerenchymatous cells, which are the descendants of the primary mesenchyme, form a syncytium around the developing spicules. The biomineralization process is intrasyncytial, the ophioplutei spicules retain the cytoplasmic covering throughout the period of larval development. The secondary mesenchyme gives rise to smooth muscle cells and amebocytes. Muscle cells compose the circumesophageal musculature, the cell processes of each “muscle band” seem to fuse together. At the base of the preoral band are two symmetrically located groups of muscles, viz., the anterior dilators. Amebocytes function in excretion either near the epidermis or are able to penetrate through the epidermis and excrete wastes into the external environment. The mesoderm formed by the enterocoely gives rise to three pairs of coeloms; their cells remain unspecialized during the entire period of larval development. Results of this study are compared with the micro- and neuroanatomy of the larvae of other echinoderms.

Hyperspectral Raman imaging was used to study the tissue/cell type specific distribution of lignin and cellulose polymers within the plant cell walls. Distinct differences in cell wall compositions were identified between two potential bioenergy feedstocks: corn stover and Eucalyptus globulus. Characteristic bands of 627, 1,175, 1,206, and 1,428 cm⁻¹ were only observed for corn stover and 1,381 cm⁻¹ was only present in E. globulus. One-dimensional and two-dimensional chemical maps of lignin and cellulose were generated for the stem of corn stover, ranging from the epidermis to the pith area and revealed that lignin and cellulose abundance varies significantly among different cell types in the following order: sclerenchyma cells and tracheids (∼5 times) > epidermal cells (∼3 times) > bundle sheath cells > parenchyma cells. The Raman mapping methods developed on corn stover were also validated on E. globulus and clearly highlighted their difference in lignin composition.

ABSTRACTModerate leaf rolling, which probably results from changes of various cells that constitute leaf blades, is an important trait for rice (Oryza sativa L.) breeding. To elucidate the cytological mechanism of leaf rolling, 46 stable mutants with inward (adaxial) or outward (abaxial) rolling phenotypes were obtained from more than 100,000 transfer DNA insertion lines in rice. Histological analyses of those mutants show that changes of number, size, and pattern of bulliform cells, sclerenchyma cells, parenchyma cells, and mesophyll cells as well as vascular bundles could lead to leaf rolling. Here, eight groups have been categorized according to their cytological characteristics in these mutants: increased bulliform cell number and area, decreased bulliform cell number and area, disordered bulliform cell number and area, partial sclerenchyma cell absence, phloem expansion, increased number of parenchyma cells, changes in multiple cell types, and parenchyma‐like cells from partial mesophyll cells. Our study demonstrates that changes in each individual cell type can result in rolled‐leaf formation.

Legume and grass stems decrease substantially in digestibility as they mature. This review evaluates how anatomical and chemical factors restrict digestion of cell walls in legume and grass stems. Cells that make up legume stems fall into 2 groups: cells with high (? 100%) digestibility (e.g. cortex and pith) and cells that appear indigestible (e.g. xylem). The digestibility of xylem cells is restricted by the highly lignified secondary walls (SW). Although cortex and pith cells may develop SW or thickened primary walls, digestibility is high because these cell types do not undergo lignification. In contrast, as grass stems mature, SW thickening and lignification occur in all main cell types. However, lignified SW in grass is readily digested when accessible to rumen microorganisms. Analysis of tissue and cell architecture in grasses strongly supports the hypothesis that observed poor digestion of lignified SW in vivo is due to limits imposed by anatomical structure. Compositional limitation to wall digestion lies in the lignified, indigestible middle lamella–primary wall. This structure confines SW digestion to inner (lumen) surfaces of cells with an open end. Low sclerenchyma SW degradation in vivo can be explained by limited movement of bacteria into sclerenchyma cells and low surface area on interior walls. For example, the ratio of surface area to total cell wall volume for sclerenchyma cells is 100-fold lower than for mesophyll cells. Apparent relationships of some wall constituents–chemical structures to wall digestibility may be the result of the increasing SW and, therefore, may simply reflect limitations imposed by anatomical structure.

Polystyrene nanoplastics induce cell type-dependent secondary wall reinforcement in rice (Oryza sativa) roots and reduce root hydraulic conductivity