Ray Parenchyma Cells Research Articles

Hydrolysis Patterns of Xylem Tissues of Hardwood Pretreated With Acetic Acid and Hydrogen Peroxide

The structural recalcitrance of lignocellulose limits its enzymatic hydrolysis, which leads to inefficient enzyme usage and inhibition of saccharification, depending on the pretreatment method. Research on the structural properties of xylem tissues of hardwood and their effect on enzymatic saccharification is necessary to achieve cost-effective biofuel production via improved enzyme cocktail preparation. Oak wood (Quercus acutissima) was pretreated and delignified with a hydrogen peroxide-acetic acid (HPAC) solution. Cellulose was found to undergo significant swelling in the lumen of the wood fiber, and it was sorted into readily hydrolysable (72.9%), mid-hydrolysable (8.2%), and hardly hydrolysable (18.9%) cellulose forms. Oak wood has been shown to be strongly retarded among the various types of hardwoods. The recalcitrance of the xylem tissues, such as wood fibers, tracheids, vessel elements, and ray parenchyma cells, was determined through analysis of the hydrolysis rates. It was found to increase in the following order: ray parenchyma cells < tracheids < wood fibers or vessel elements < tracheids < wood fibers. The wood fibers were almost enzymatically fragmented into pieces approximately 90 μm in length at crack sites in 6 h. The wood fibers were digested faster in the S3 or S2 wall than in the primary wall. The result indicated that the primary wall may be a structural retardation factor in the hardwood as sorted to the hardly hydrolysable cellulose. In presence of 10% substrate supplemented with enzymes to reduce the structural recalcitrance (xylanase and lytic polysaccharide monoxygenase) and end-product inhibitions (beta-glucosidase), the hydrolysis rate was increased by 55.21%. Ethanol fermentation exhibited a higher efficiency when a single substrate (Q. acutissima) rather than a mixture of various hardwoods was used. Of all the xylem tissues of hardwood that were delignified by HPAC pretreatment, wood fiber was found to be a structural retardation factor owing to the recalcitrance its primary wall. Thus, enzyme preparation can enable the rapid and efficient hydrolysis for the commercialization of bioethanol from hardwood.

Nanomechanics and Raman Spectroscopy of in Situ Native Carbohydrate Storage Granules for Enhancing Starch Quality and Lignocellulosic Biomass Production.

Alternative energy strategies based on plant biomass-derived bioenergy and biofuels rely on understanding and optimization of plant structure, chemistry, and performance. Starch, a constitutive element of all green plants, is important to food, biofuels, and industrial applications. Models of carbohydrate storage granules are highly heterogeneous in representing morphology and structure, though a deeper understanding of the role of structure in functional behavior is emerging. A better understanding of the in situ nanoscale properties of native granules is needed to help improve the starch quality in food crops as well as optimize lignocellulosic biomass production in perennial nonfood crops. Here, we present a new technique called soft mechanical nano-ablation (sMNA) for accessing the interior of the granules without compromising the inner nanostructure. We then explore the nanomechanics of granules within the ray parenchyma cells of Populus xylem, a desirable woody biofuel feedstock. The employed soft outer layer nanoablation and atomic force microscopy reveal that the inner structure comprises 156 nm blocklets arranged in a semicrystalline organization. The nanomechanical properties of the inner and outer structures of a single starch granule are measured and found to exhibit large variations, changing by a factor of 3 in Young’s modulus and a factor of 2 in viscoplastic index. These findings demonstrate how the introduced approach facilitates studies of structure–function relationships among starch granules and more complex secondary cell wall features as they relate to plant performance.

Differential Gene Profiling of the Heartwood Formation Process in Taiwania cryptomerioides Hayata Xylem Tissues.

Taiwania (Taiwania cryptomerioides) is an important tree species in Taiwan because of the excellent properties of its wood and fascinating color qualities of its heartwood (HW), as well as the bioactive compounds therein. However, limited information is available as to the HW formation of this species. The objective of this research is to analyze the differentially expressed genes (DEGs) during the HW formation process from specific Taiwania xylem tissues, and to obtain genes that might be closely associated with this process. The results indicated that our analyses have captured DEGs representative to the HW formation process of Taiwania. DEGs related to the terpenoid biosynthesis pathway were all up-regulated in the transition zone (TZ) to support the biosynthesis and accumulation of terpenoids. Many DEGs related to lignin biosynthesis, and two DEGs related to pinoresinol reductase (PrR)/pinoresinol lariciresinol reductase (PLR), were up-regulated in TZ. These DEGs together are likely involved in providing the precursors for the subsequent lignan biosynthesis. Several transcription factor-, nuclease-, and protease-encoding DEGs were also highly expressed in TZ, and these DEGs might be involved in the regulation of secondary metabolite biosynthesis and the autolysis of the cellular components of ray parenchyma cells in TZ. These results provide further insights into the process of HW formation in Taiwania.

How Long Do Wood Parenchyma Cells Live in the Stem of a Scots Pine (Pinus sylvestris L.)? Studies on Cell Nuclei Status along the Radial and Longitudinal Stem Axes

This paper deals with the spatial distribution of heartwood in Scots pine stems (Pinus sylvestris L.), determined on the basis of the absence of nuclei in parenchyma cells. Samples were collected at several heights from two Scots pine stems growing in fresh coniferous stand as codominant trees. Transverse and radial sections were cut from the samples and stained with acetocarmine to detect the nuclei and with I2KI to show starch grains. Unstained sections were also observed under ultraviolet (UV) light to reveal cell wall lignification. The shapes of the nuclei in ray and axial parenchyma cells differed: the axial parenchyma cells had rounded nuclei, while the nuclei of the ray parenchyma cells were elongated. The lifespan of the parenchyma cells was found to be 16–42 years; the longest-lived were cells from the base of the stem, and the shortest-lived were from the base of the crown. The largest number of growth rings comprising heartwood was observed at a height of 1.3–3.3 m, which signifies that the distribution of heartwood within the stem is uneven. Moreover, the distance of the cells from the apical meristem and the cambium was seen to have an effect on the presence of living parenchyma cells, i.e., those with stained nuclei.

Populus NST/SND orthologs are key regulators of secondary cell wall formation in wood fibers, phloem fibers and xylem ray parenchyma cells.

Wood fibers form thick secondary cell wall (SCW) in xylem tissues to give mechanical support to trees. NAC SECONDARY WALL THICKENING PROMOTING FACTOR3/SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN 1 (NST3/SND1) and NST1 were identified as master regulators of SCW formation in xylem fiber cells in the model plant Arabidopsis thaliana. In Populus species, four NST/SND orthologs have been conserved and coordinately control SCW formation in wood fibers and phloem fibers. However, it remains to be elucidated whether SCW formation in other xylem cells, such as ray parenchyma cells and vessel elements, is regulated by NST/SND orthologs in poplar. We knocked out all NST/SND genes in hybrid aspen using the clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 nuclease (Cas9) system and investigated the detailed histological appearance of stem tissues in the knockout mutants. Observation by light microscopy and transmission electron microscopy showed that SCW was severely suppressed in wood fibers, phloem fibers and xylem ray parenchyma cells in the knockout mutants. Although almost all wood fibers lacked SCW, some fiber cells formed thick cell walls. The irregularly cell wall-forming fibers retained primary wall and SCW, and were mainly located in the vicinity of vessel elements. Field emission-scanning electron microscope observation showed that there were no apparent differences in the structural features of pits such as the shape and size between irregularly SCW-forming wood fibers in the knockout mutants and normal wood fibers in wild-type. Cell wall components such as cellulose, hemicellulose and lignin were deposited in the cell wall of irregularly SCW-forming wood fibers in quadruple mutants. Our results indicate that four NST/SND orthologs are master switches for SCW formation in wood fibers, xylem ray parenchyma cells and phloem fibers in poplar, while SCW is still formed in limited wood fibers, which are located at the region adjacent to vessel elements in the knockout mutants.

A new cupressaceous wood from the Lower Cretaceous of central Patagonia reveals possible clonal growth habit

A new genus and species, Austrocupressinoxylon barcinense, based on remains of cupressaceous wood is described for the Lower Cretaceous of central Patagonia, Argentina. The studied specimens are silicified fragments of picnoxylic and homoxylic wood that exhibit a combination of characters not previously reported, therefore a new genus is erected. The characters are: 1- growth ring boundaries distinct, 2- transition from earlywood to latewood gradual, 3- axial parenchyma diffuse,4- radial tracheid pitting predominantly abietinean,5- cross-field pitting cupressoid, arranged in both cupressoid and araucarioid patterns, 6- rays uniseriate heterocellular, 7- end and horizontal walls of ray parenchyma cells smooth or slightly nodular, and 8- ray tracheids with smooth walls. The cross-field pitting patterns and the presence of ray tracheids are two traits of particular interest in the context of systematic affinities. The fragments were collected from two stumps found in life position attached to each other by a main root, consequently, the disposition of the stumps suggests a case of clonal growth by root suckering. This is the second report of such mechanisms in the fossil records worldwide and the first one for South America.

Biosynthetic investigation of \u03b3-lactones in Sextonia rubra wood using in situ TOF-SIMS MS/MS imaging to localize and characterize biosynthetic intermediates

Molecular analysis by parallel tandem mass spectrometry (MS/MS) imaging contributes to the in situ characterization of biosynthetic intermediates which is crucial for deciphering the metabolic pathways in living organisms. We report the first use of TOF-SIMS MS/MS imaging for the cellular localization and characterization of biosynthetic intermediates of bioactive γ-lactones rubrynolide and rubrenolide in the Amazonian tree Sextonia rubra (Lauraceae). Five γ-lactones, including previously reported rubrynolide and rubrenolide, were isolated using a conventional approach and their structural characterization and localization at a lateral resolution of ~400 nm was later achieved using TOF-SIMS MS/MS imaging analysis. 2D/3D MS imaging at subcellular level reveals that putative biosynthetic γ-lactones intermediates are localized in the same cell types (ray parenchyma cells and oil cells) as rubrynolide and rubrenolide. Consequently, a revised metabolic pathway of rubrynolide was proposed, which involves the reaction between 2-hydroxysuccinic acid and 3-oxotetradecanoic acid, contrary to previous studies suggesting a single polyketide precursor. Our results provide insights into plant metabolite production in wood tissues and, overall, demonstrate that combining high spatial resolution TOF-SIMS imaging and MS/MS structural characterization offers new opportunities for studying molecular and cellular biochemistry in plants.

Dyeing of Eucalyptus globulus Veneers with Reactive Dye Using Sequential Vacuum and Varied Pressures

To investigate the potential application of vacuum-pressure methods for dyeing low-quality hardwood veneers produced from young, small-diameter logs, Eucalyptus globulus veneers were dyed with a 2% solution of the reactive dye Procion Brown PX-2R at a vacuum of -100 kPa for 15 min prior to pressure being applied. The effects of various pressures and pressure times on dye uptake, dye penetration, and colour change were evaluated. Veneers with varying moisture content (MC) were used and were labeled as green veneer (80% ± 5% MC) or dried veneer (12% MC). The dyeing method was based on the results of the preliminary experiments. The vacuum-pressure method had remarkable influence on the dye uptake, dye penetration, and colour change, particularly when the samples were dyed at a pressure of 1000 kPa and pressure time of 120 min. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy results indicated that the reactive dye was able to react with the wood compounds, and scanning electron microscopy (SEM) analysis showed that the ray parenchyma cells provided an effective radial path for dye penetration.

Stem anatomy at various developmental stages of secondary growth in Turbina corymbosa (Convolvulaceae)

Background – Population growth of lianas in the tropical forest is credited to their ability of CO2 sequestration and efficiency of the narrow stems to supply water required for the amount of foliage it bears. Turbina corymbosa (L.) Raf. (Convolvulaceae Juss.) is one of the fast-growing invasive species of scrambling woody lianas. It covers trees entirely within a short period to compete with above-ground resources (particularly sunlight). However, no information is available on how it manages to cope up with an increasing demand of water supply and mineral nutrients. What are the structural and developmental patterns adapted by this species to expand the stem diameter for efficient supply of below-ground resources? Therefore, our aim was to investigate the secondary growth patterns and structure of secondary xylem and phloem in T. corymbosa.Methods – Several samples of the stem with various diameters were studied using a histological method. Morphological and anatomical analyses were carried out using light microscopy.Key results – With the initiation of secondary growth, stems lose their circular outline rapidly due to unequal deposition of secondary xylem and formation of successive cambia. New successive cambia initiate from parenchymatous cells as small crescent-shaped fragments on asymmetric/opposite sides and result in a different stem conformation. Though several segments of successive cambia are formed, very few stem samples form complete cambium rings. The secondary xylem formed by successive cambia is diffuse porous with indistinct growth rings and is composed of both wide and narrow (fibriform) vessels, tracheids, fibres, axial and ray parenchyma cells. The secondary phloem consists of sieve tube elements, companion cells, axial and ray parenchyma cells. In fully grown plants, cambial action (internal cambium) occurrs between the intraxylary phloem and protoxylem and produces secondary xylem and phloem near the pith region.Conclusion – Structural alterations and unequal deposition of conducting elements, occurrence of intraxylary phloem and flattening of the stem are suggested to facilitate rapid growth of the plants by providing required minerals and nutrients. Internal cambium formed at the periphery of the pith is bidirectional and produces secondary xylem externally and intraxylary phloem internally. Continued development of intraxylary phloem from the internal cambium provides an additional path for rapid and safe translocation of photosynthates.

Cellular level in planta analysis of radial movement of artificially injected caesium in Cryptomeria japonica xylem

Ray parenchyma cells represent the main pathway for mineral radial movement from sapwood towards intermediate wood, based on direct cryo-scanning electron microscopy/energy dispersive X-ray spectroscopy analysis. Ray parenchyma cells are considered to be associated with the radial movement of some elements from sapwood to heartwood in tree trunks. However, this function has not yet been experimentally confirmed. In this study, we analysed the radial movement of caesium (Cs), as a tracer of minerals, through the xylem at the cellular level in standing trees. A solution containing a stable Cs isotope diluted in aqueous acid fuchsin was injected into the outer sapwood of Japanese cedar trees for 3 h, 1, or 4 days. After the injection, the trunk (including the injection points) was freeze-fixed with liquid nitrogen. Subsequently, the trees were felled. The red colour from acid fuchsin was detected in the outer sapwood and did not move passively in the radial direction with free water. For detailed analysis of the Cs distribution in the radial direction (from the red-coloured sapwood towards the pith), we performed cryo-scanning electron microscopy/energy-dispersive X-ray spectroscopy point analysis of the frozen-hydrated samples to analyse the Cs distribution by detecting the characteristic Cs-Lα X-ray peak. In the outer sapwood, Cs was detected in all cell structures at all injection periods. In the inner xylem tissue, Cs was detected in the cell wall and lumen of ray parenchyma cells at 4-day injection, but not at 3-h and 1-day injection. These results suggest that ray parenchyma cells represent the main pathway whereby Cs can move radially from sapwood towards intermediate wood in standing Japanese cedar trees.

Living Cells in Wood 3. Overview; Functional Anatomy of the Parenchyma Network

The very different evolutionary pathways of conifers and angiosperms are very informative precisely because their wood anatomy is so different. New information from anatomy, comparative wood physiology, and comparative ultrastructure can be combined to provide evidence for the role of axial and ray parenchyma in the two groups. Gnetales, which are essentially conifers with vessels, have evolved parallel to angiosperms and show us the value of multiseriate rays and axial parenchyma in a vessel-bearing wood. Gnetales also force us to re-examine optimum anatomical solutions to conduction in vesselless gymnosperms. Axial parenchyma in vessel-bearing woods has diversified to take prominent roles in storage of water and carbohydrates as well as maintenance of conduction in vessels. Axial parenchyma, along with other modifications, has superseded scalariform perforation plates as a safety mechanism and permitted angiosperms to succeed in more seasonal habitats. This diversification has required connection to rays, which have concomitantly become larger and more diverse, acting as pathways for photosynthate passage and storage. Modes of growth such as rapid flushing, vernal leafing-out, drought deciduousness and support of large leaf surfaces become possible, advantaging angiosperms over conifers in various ways. Prominent tracheid-ray pitting (conifers) and axial parenchyma/ray pitting to vessels (angiosperms) are evidence of release of photosynthates into conductive cells; in angiosperms, this system has permitted vessels to survive hydrologic stresses and function in more seasonal habitats. Flow in ray and axial parenchyma cells, suggested by greater length/width ratios of component cells, is confirmed by pitting on end walls of elongate cells: pits are greater in area, more densely placed, and are often bordered. Bordered pit areas and densities on living cells, like those on tracheids and vessels, represent maximal contact areas between cells while minimizing loss of wall strength. Storage cells in rays can be distinguished from flow cells by size and shape, by fewer and smaller pits and by contents. By lacking secondary walls, the entire surfaces of phloem ray and axial phloem parenchyma become conducting areas across which sugars can be translocated. The intercontinuous network of axial parenchyma and ray parenchyma in woods is confirmed; there are no “isolated” living cells in wood when three-dimensional studies are made. Water storage in living cells is reported anatomically and also in the form of percentile quantitative data which reveal degrees and kinds of succulence in angiosperm woods, and norms for “typically woody” species. The diversity in angiosperm axial and ray parenchyma is presented as a series of probable optimal solutions to diverse types of ecology, growth form, and physiology. The numerous homoplasies in these anatomical modes are seen as the informative results of natural experiments and should be considered as evidence along with experimental evidence. Elliptical shape of rays seems governed by mechanical considerations; unusually long (vertically) rays represent a tradeoff in favor of flexibility versus strength. Protracted juvenilism (paedomorphosis) features redirection of flow from horizontal to vertical by means of rays composed predominantly or wholly of upright cells, and the reasons for this anatomical strategy are sought. Protracted juvenilism, still little appreciated, occurs in a sizeable proportion of the world’s plants and is a major source of angiosperm diversification.

Tandem Mass Spectrometry Imaging and in Situ Characterization of Bioactive Wood Metabolites in Amazonian Tree Species Sextonia rubra.

Driven by a necessity for confident molecular identification at high spatial resolution, a new time-of-flight secondary ion mass spectrometry (TOF-SIMS) tandem mass spectrometry (tandem MS) imaging instrument has been recently developed. In this paper, the superior MS/MS spectrometry and imaging capability of this new tool is shown for natural product study. For the first time, via in situ analysis of the bioactive metabolites rubrynolide and rubrenolide in Amazonian tree species Sextonia rubra (Lauraceae), we were able both to analyze and to image by tandem MS the molecular products of natural biosynthesis. Despite the low abundance of the metabolites in the wood sample(s), efficient MS/MS analysis of these γ-lactone compounds was achieved, providing high confidence in the identification and localization. In addition, tandem MS imaging minimized the mass interferences and revealed specific localization of these metabolites primarily in the ray parenchyma cells but also in certain oil cells and, further, revealed the presence of previously unidentified γ-lactone, paving the way for future studies in biosynthesis.

In vivo quantification of plant starch reserves at micrometer resolution using X-ray microCT imaging and machine learning.

Starch is the primary energy storage molecule used by most terrestrial plants to fuel respiration and growth during periods of limited to no photosynthesis, and its depletion can drive plant mortality. Destructive techniques at coarse spatial scales exist to quantify starch, but these techniques face methodological challenges that can lead to uncertainty about the lability of tissue-specific starch pools and their role in plant survival. Here, we demonstrate how X-ray microcomputed tomography (microCT) and a machine learning algorithm can be coupled to quantify plant starch content invivo, repeatedly and nondestructively over time in grapevine stems (Vitis spp.). Starch content estimated for xylem axial and ray parenchyma cells from microCT images was correlated strongly with enzymatically measured bulk-tissue starch concentration on the same stems. After validating our machine learning algorithm, we then characterized the spatial distribution of starch concentration in living stems at micrometer resolution, and identified starch depletion in live plants under experimental conditions designed to halt photosynthesis and starch production, initiating the drawdown of stored starch pools. Using X-ray microCT technology for invivo starch monitoring should enable novel research directed at resolving the spatial and temporal patterns of starch accumulation and depletion in woody plant species.

Distribution of Living Ray Parenchyma Cells and Major Bioactive Compounds During the Heartwood Formation of Taiwania cryptomerioides Hayata

The heartwood of Taiwania (Taiwania cryptomerioides Hayata) has the excellent decay resistance and fascinating color qualities due to the accumulation of bioactive compounds. However, limited information was addressed to the heartwood formation of this species. In this study, we established the distribution of the living ray parenchyma cells and profiled the major bioactive compounds across and along the Taiwania stem. The ray parenchyma cells would die within 1–2 annual rings of the transition zone, which occurs around 8–13 annual rings counted from the cambium. The gradual loss of the starch grains accompanied with the deposition of the colored materials into the cell lumens started from the outer transition zone. The radial distribution of the extractive contents and its signature bioactive compounds across Taiwania stems gradually increased from the transition zone toward the heartwood tissues. The aforementioned properties did not show specific trends along the vertical direction of the Taiwania stems.

Changes in the morphology and functions of vacuoles during the death of ray parenchyma cells in Cryptomeria japonica

Changes in the morphology and functions of vacuoles provide useful information about the mechanism of cell death. In the present study, we monitored the morphology and contents of vacuoles during the death of ray parenchyma cells in the conifer Cryptomeria japonica. In differentiating xylem, ray parenchyma cells had large central vacuoles. In sapwood, vacuoles in ray parenchyma cells contained proteins, an indication that one of the main functions of these vacuoles might be protein storage. A dramatic decrease in the protein content of some vacuoles was detected in the intermediate wood before the initiation of vacuole rupture. Although vacuole rupture was detected from the intermediate wood to the outermost heartwood, some vacuoles were obviously enlarged in the inner intermediate wood. Condensed nuclei were first observed after the rupture of these large vacuoles in ray parenchyma cells. It seems plausible that the autolysis of the contents of ray parenchyma cells might be caused by the rupture of the enlarged vacuoles in the inner intermediate wood.

Automated identification of Lauraceae by scale-invariant feature transform

An image dataset of the cross-sectional optical micrographs of the Lauraceae species including 39 species in 11 genera, capturing at least one full annual ring, was investigated by scale-invariant feature transform (SIFT), a computer vision-based feature extraction algorithm. We found an image of 900 × 900-pixel size at a pixel resolution of ca. 3 µm, corresponding to the actual size of 2.65 × 2.65 mm2, as the minimum requirement for the image dataset in terms of the accuracy of the recognition at both the genus and species levels. Among the several classifiers investigated, the linear discriminant analysis (LDA) presented the best performance reaching a maximum of 89.4% in the genus with a species identification of approximately 96.3%. Cluster analysis of all the SIFT descriptors for each image yielded practical information regarding the descriptors; they recognize selectively the cell lumina, cell corners, vessels, and axial and ray parenchyma cells. Therefore, the difference between the genus or species levels was determined per the variation in the quantities of these computer-based properties. Another clustering approach, the hierarchal dendrogram, was applied to visualize the numerical distances between the genus and species. Interestingly, even Machilus and Phoebe, which are difficult to distinguish by conventional visual inspection, are quite distantly classified at the genus level. In contrast, some species in Cinnamomum, Machilus and Litsea were categorized into different subgroups rather than the original genus. Microscopic wood identification is found to be possible at the genus level; however, the numerical dataset of the morphological features has various overlapping clusters, causing the genus-level identification of the Lauraceae to be more difficult than species-level identification.

Structure and Ontogeny of Intraxylary Secondary Xylem and Phloem Development by the Internal Vascular Cambium in Campsis radicans (L.) Seem. (Bignoniaceae)

Bignoniaceae is known for the presence of different growth forms like trees, shrubs, lianas and herbs that show a wide range of variations in their wood structure. Trees, shrubs and lianas are characterised by the presence of normal secondary growth except the lianoid forms of the tribe Bignonieae that have a unique type of the cambial variant (that is, wedged/furrowed xylem) whereas other lineages lack it. Campsis radicans belongs to tribe Tecomeae and thus is expected to lack the cambial variant but it develops a quantifiable amount of intraxylary secondary xylem and phloem in the pith. Therefore, the main aim of the present investigation is to elucidate the ontogeny of intraxylary phloem and the secondary xylem formed by internal vascular cambium. Development of intraxylary phloem is delayed significantly as compared to other families of eudicots that show the presence of intraxylary phloem. Subsequently, a functionally bidirectional complete ring of internal vascular cambium initiates along the pith margin that produces secondary xylem centrifugally and secondary phloem centripetally. In thick stems, an internal vascular cambium forms quantifiable amounts of inversely oriented secondary xylem and phloem that completely replace the pith. Structurally, this secondary xylem remains similar to the xylem formed by the regular (external) cambium. It is composed of vessels, fibres, axial and ray parenchyma cells while the secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. The development of internal vascular cambium completely replaced the parenchyma of the pith by producing intraxylary secondary xylem and phloem. The reason for the occurence of intraxylary phloem in C. radicans remains unknown. However, to the lesser extent it may be playing a secondary role in conductive safety of the conduit.

Development of successive cambia and formation of flat stems in Rhynchosia pyramidalis (Lam.) Urb. (Fabaceae)

Stem flattening in Rhynchosia pyramidalis (Fabaceae) is achieved by the development of crescent-shaped successive cambia on two opposite sides of the stem (referred hereafter as distal side). Other lateral sides of the stem (adjacent to supporting host and its opposite side, referred as proximal sides) usually possess single cambium. In the young stems, parenchymatous cells located outside to protophloem of distal side dedifferentiate and develop small segments of cambium. Concomitant to bidirectional differentiation of the secondary xylem and phloem, these newly developed cambial segments also extend in tangential directions. Differential activity of newly developed crescent-shaped cambial segments deposits more secondary xylem at median position as compared to their terminal ends of the stem on distal side; consequently, it pushes the cambial segment outside, thus resulting in crescent-shaped arcs of the cambia only on two opposite sides. After the production of 1–2 mm of secondary xylem, they cease to divide and new segments of cambial arc develop on the same side in a similar fashion. Such repeated behaviour of successive cambia development consequently leads to the formation of tangentially flat stems. The secondary xylem is diffusely porous with indistinct growth rings and is composed of vessels (wide and narrow), fibres, axial ray parenchyma cells, while phloem consisted of sieve elements, companion cells, axial and ray parenchyma. Rays in both xylem and phloem are uni- to multiseriate and heterocellular. The structure of secondary xylem and development of successive cambia is correlated with climbing habit.

6. 低温馴化によるシラカンバ木部放射柔細胞の細胞壁の変化(平成11年度第45回低温生物工学会研究報告)

6. 低温馴化によるシラカンバ木部放射柔細胞の細胞壁の変化(平成11年度第45回低温生物工学会研究報告)

3. 樹木木部放射柔細胞の凍結適応機構の変遷(平成9年度第43回低温生物工学会研究報告)

3. 樹木木部放射柔細胞の凍結適応機構の変遷(平成9年度第43回低温生物工学会研究報告)