油松茎次生结构中树脂道的结构分布和发育的研究

油松茎的次生结构中树脂道存在于次生维管组织中。其中,次生木质部内具有水平的和垂直的两类树脂道,而次生韧皮部内则仅有水平的树脂道。两类树脂道都由上皮细胞和鞘细胞包围着胞间道构成,其中木质部内的树脂道具有死鞘细胞,而韧皮部中的则都系生活细胞。在心材中,垂直树脂道形成拟侵填体。在次生木质部内,垂直树脂道常分布于早材的外部区域和最初形成的晚材中,它们与水平树脂道连接,腔道贯通,从而形成二维网状结构。垂直树脂道来源于纺锤状原始细胞的衍生细胞,而水平树脂道来源于射线原始细胞,两者都以裂生方式发生。     

Comparative wood anatomy in Abietoideae (Pinaceae)

This study, which includes 51 species and six genera of subfamily Abietoideae (Pinaceae), assesses the systematic significance of the wood structure in this group. In particular, the presence of normal and traumatic resin canals, the ray structure and the axial parenchyma constitute phylogenetically informative features. Comparative wood anatomy of Abietoideae clearly supports the monophyly of the genera Abies–Cedrus–Keteleeria–Nothotsuga–Pseudolarix–Tsuga, all of which have axial parenchyma with nodular transverse end walls in the regions of growth ring boundaries, crystals in the ray parenchyma and pitted horizontal and nodular end walls of ray parenchyma cells. Axial resin canals support a subdivision of the subfamily into two groups: Abies, Cedrus, Pseudolarix and Tsuga, without axial resin canals, and Keteleeria and Nothotsuga, with axial resin canals and a specific arrangement of traumatic axial resin canals. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 184–196.     

Cellular level observation of water loss and the refilling of tracheids in the xylem of Cryptomeria japonica during heartwood formation

The mechanism of heartwood formation in Cryptomeria japonica D. Don has long been studied since heartwood formation is a fundamental physiological feature of trees. In this study, the water distribution in the xylem of C. japonica was investigated at the cellular level to reveal the role of water distribution in the xylem during heartwood formation. Samples were taken from different heights of each trunk, in which the phases of heartwood formation differed. These were designated as SIH, which consisted of sapwood, intermediate wood, and heartwood; SI, which consisted of sapwood and intermediate wood but no heartwood; and S-all, which consisted entirely of sapwood. Cryo-scanning electron microscopic observations of the heartwood-formed (SIH) and non-heartwood-formed (SI and S-all) xylem revealed different patterns of water distribution changes in tracheids between the latewood and earlywood. In the latewood, almost all tracheids were filled with water in all areas from the sapwood to the heartwood (98–100% of tracheids had water in their lumina). In the earlywood, however, the water distribution differed between the sapwood (95–99%), intermediate wood (7–12%), and heartwood (4–100%). Many of the tracheids in the xylem, where the sapwood changed to intermediate wood lost water. In the heartwood, some tracheids remained empty, while others were refilled with water. These results suggest that the water distribution changes in individual tracheids are closely related to heartwood formation. Water loss from tracheids may be an important factor inducing heartwood formation in the xylem of C. japonica.     

Wood allocation trade-offs between fiber wall,fiber lumen,and axial parenchyma drive drought resistance in neotropical trees

Functional relationships between wood density and measures of xylem hydraulic safety and efficiency are ambiguous, especially in wet tropical forests. In this meta-analysis, we move beyond wood density per se and identify relationships between xylem allocated to fibers, parenchyma, and vessels and measures of hydraulic safety and efficiency. We analyzed published data of xylem traits, hydraulic properties and measures of drought resistance from neotropical tree species retrieved from 346 sources. We found that xylem volume allocation to fiber walls increases embolism resistance, but at the expense of specific conductivity and sapwood capacitance. Xylem volume investment in fiber lumen increases capacitance, while investment in axial parenchyma is associated with higher specific conductivity. Dominant tree taxa from wet forests prioritize xylem allocation to axial parenchyma at the expense of fiber walls, resulting in a low embolism resistance for a given wood density and a high vulnerability to drought-induced mortality. We conclude that strong trade-offs between xylem allocation to fiber walls, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees. Moreover, the benefits of xylem allocation to axial parenchyma in wet tropical trees might not outweigh the consequential low embolism resistance under more frequent and severe droughts in a changing climate.     

3D analysis of anatomical reactions in conifers after mechanical wounding: first qualitative insights from X-ray computed tomography

The ability of trees to recover from damage beyond the last-formed periderm as well as the drivers and nature of associated wound reactions have been studied for more than two centuries using macroscopic (desiccation, aeration or discoloration of wood) and microscopic approaches (anatomical and chemical reactions). However, no studies currently exist which address large-scale macroscopic and microscopic reactions surrounding wounds in the tangential, axial, and radial directions over continuous segments of tree stems. This note explores the potential of 3D X-ray computed tomography in assessing effects of wounding under natural conditions in European conifers (Abies alba, Larix decidua, Picea abies). We present results from a pilot study and qualitatively evaluate the potential of the approach used in assessing and illustrating the formation and spread of de-differentiated xylem parenchyma cells, xylem decay compartmentalization, resin ducts, and stabilizing compression wood cells.     

Wood anatomical correlates with theoretical conductivity and wood density across China: evolutionary evidence of the functional differentiation of axial and radial parenchyma

Background and Aims

In recent years considerable effort has focused on linking wood anatomy and key ecological traits. Studies analysing large databases have described how these ecological traits vary as a function of wood anatomical traits related to conduction and support, but have not considered how these functions interact with cells involved in storage of water and carbohydrates (i.e. parenchyma cells).

Methods

We analyzed, in a phylogenetic context, the functional relationship between cell types performing each of the three xylem functions (conduction, support and storage) and wood density and theoretical conductivity using a sample of approx. 800 tree species from China.

Key Results

Axial parenchyma and rays had distinct evolutionary correlation patterns. An evolutionary link was found between high conduction capacity and larger amounts of axial parenchyma that is probably related to water storage capacity and embolism repair, while larger amounts of ray tissue have evolved with increased mechanical support and reduced hydraulic capacity. In a phylogenetic principal component analysis this association of axial parenchyma with increased conduction capacity and rays with wood density represented orthogonal axes of variation. In multivariate space, however, the proportion of rays might be positively associated with conductance and negatively with wood density, indicating flexibility in these axes in species with wide rays.

Conclusions

The findings suggest that parenchyma types may differ in function. The functional axes represented by different cell types were conserved across lineages, suggesting a significant role in the ecological strategies of the angiosperms.     

The accumulation pattern of ferruginol in the heartwood-forming Cryptomeria japonica xylem as determined by time-of-flight secondary ion mass spectrometry and quantity analysis

Background and Aims

Heartwood formation is a unique phenomenon of tree species. Although the accumulation of heartwood substances is a well-known feature of the process, the accumulation mechanism remains unclear. The aim of this study was to determine the accumulation process of ferruginol, a predominant heartwood substance of Cryptomeria japonica, in heartwood-forming xylem.

Methods

The radial accumulation pattern of ferruginol was examined from sapwood and through the intermediate wood to the heartwood by direct mapping using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The data were compared with quantitative results obtained from a novel method of gas chromatography analysis using laser microdissection sampling and with water distribution obtained from cryo-scanning electron microscopy.

Key Results

Ferruginol initially accumulated in the middle of the intermediate wood, in the earlywood near the annual ring boundary. It accumulated throughout the entire earlywood in the inner intermediate wood, and in both the earlywood and the latewood in the heartwood. The process of ferruginol accumulation continued for more than eight annual rings. Ferruginol concentration peaked at the border between the intermediate wood and heartwood, while the concentration was less in the latewood compared wiht the earlywood in each annual ring. Ferruginol tended to accumulate around the ray parenchyma cells. In addition, at the border between the intermediate wood and heartwood, the accumulation was higher in areas without water than in areas with water.

Conclusions

TOF-SIMS clearly revealed ferruginol distribution at the cellular level. Ferruginol accumulation begins in the middle of intermediate wood, initially in the earlywood near the annual ring boundary, then throughout the entire earlywood, and finally across to the whole annual ring in the heartwood. The heterogeneous timing of ferruginol accumulation could be related to the distribution of ray parenchyma cells and/or water in the heartwood-forming xylem.     

Stem anatomy of Dolichos lablab Linn (Fabaceae): Origin of cambium and reverse orientation of vascular bundles

Secondary growth in the stem of Dolichos lablab is achieved by the formation of eccentric successive rings of vascular bundles. The stem is composed of parenchymatous ground tissue and xylem and phloem confined to portions of small cambial segments. However, development of new cambial segments can be observed from the obliterating ray parenchyma, the outermost phloem parenchyma and the secondary cortical parenchyma. Initially cambium develops as small segments, which latter become joined to form a complete cylinder of vascular cambium. Each cambial ring is functionally divided into two distinct regions. The one segment of cambium produces thick-walled lignified xylem derivatives in centripetal direction and phloem elements centrifugally. The other segment produces only thin-walled parenchyma on both xylem and phloem side. In mature stems, some of the axial parenchyma embedded deep inside the xylem acquires meristematic activity and leads to the formation of thick-walled xylem derivatives centrifugally and phloem elements centripetally. The secondary xylem comprises vessel elements, tracheids, fibres and axial parenchyma. Rays are uni-multiseriate in the region of cambium that produces xylem and phloem derivatives, while in some of the regions of cambium large multiseriate, compound, aggregate and polycentric rays can be noticed.     

Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity‐Ecosystem Functioning experiment at Jiangxi (BEF‐China). Information‐theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi‐layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi‐predictor models for stomatal conductance (g_s) and xylem cavitation vulnerability. In addition, maximum g_s was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum g_s increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ₅₀) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ₅₀ values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses.     

Wood anatomy and wood density in shrubs: Responses to varying aridity along transcontinental transects

Wood density plays a key role in ecological strategies and life history variation in woody plants, but little is known about its anatomical basis in shrubs. We quantified the relationships between wood density, anatomy, and climate in 61 shrub species from eight field sites along latitudinal belts between 31° and 35° in North and South America. Measurements included cell dimensions, transverse areas of each xylem cell type and percentage contact between different cell types and vessels. Wood density was more significantly correlated with precipitation and aridity than with temperature. High wood density was achieved through reductions in cell size and increases in the proportion of wall relative to lumen. Wood density was independent of vessel traits, suggesting that this trait does not impose conduction limitations in shrubs. The proportion of fibers in direct contact with vessels decreased with and was independent of wood density, indicating that the number of fiber-vessel contacts does not explain the previously observed correlation between wood density and implosion resistance. Axial and radial parenchyma each had a significant but opposite association with wood density. Fiber size and wall thickness link wood density, life history, and ecological strategies by controlling the proportion of carbon invested per unit stem volume.     

Differential anatomical response of Norway spruce stem tissues to sterile and fungus infected inoculations

The anatomical defense responses in stems of Norway spruce (Picea abies) clones of different resistance to pathogenic fungi were characterized over time and distance from small mechanical wounds or wounds inoculated with the root rot fungus Heterobasidion annosum. Common responses for both treatments included division of ray parenchyma and other cells in the cambial zone, accumulation of phenolic inclusions in ray parenchyma cells, activation of phloem parenchyma (PP) cells, and formation of traumatic resin ducts (TDs) in the xylem. TD formation occurred synchronously from a tangential layer of cells, or symplasmic domain, within the zone of xylem mother cells. TD induction is triggered by a signal, which propagates a developmental wave in the axial direction at about 2.5 cm per day. TDs are formed at least 30 cm above single inoculations within 16–36 days after inoculation. The size and number of TDs is attenuated further away from the inoculation site, indicating a dose-dependent activity leading to TD development. Compared to sterile wounding, fungal inoculation gave rise to more and larger TDs in all clones, and multiple rows of TDs in weak clones. Fungal inoculation also induced the formation of more new PP cells, increasing the number of PP cells in the phloem in the year of inoculation up to 100%. TD and PP cell formation was greater in susceptible compared to resistant clones and after fungal versus sterile inoculation. Potential mechanisms responsible for this variable response are discussed.     

A NEW SPECIES OF PICEA BASED ON SILICIFIED SEED CONES FROM THE OLIGOCENE OF WASHINGTON

Picea eichhornii n. sp. is described from anatomically preserved seed cones. The fossils are from the Early Oligocene Jansen Creek Member of the Makah Fm. which is exposed along the northern shore of the Olympic Peninsula, Washington. The cones are at least 5.5 cm long and up to 3.5 cm in diameter. The cone axis is 4–6 mm in diameter and contains a pith made up of thick-walled parenchyma cells. Resin canals occur in a single ring in the secondary xylem in some specimens but are absent in others. The cortex is mostly parenchymatous and contains numerous large axial resin canals that branch to supply the bract and scale. Vascular traces to each scale and its subtending bract diverge separately from the vascular cylinder of the cone axis. The bract is tongue-shaped and keeled at its base. It is 5 mm wide and up to 9 mm long. The bract trace fades out before entering the bract base while two resin canals extend into the bract base. The ovuliferous scale is about 2.3 cm long and has a thin, probably papery, apex. Resin canals of the scale occur abaxial to the vascular tissue in the scale base, but some bend around the margins of the vascular strand to become adaxial outward. About 20 resin canals occur in the abaxial scale sclerenchyma, and this is the main anatomical feature that distinguishes these cones as a new species. There are less than 14 such canals in cones in a reference collection of 15 modern species and in the two fossil species known from anatomically preserved material. While the new species adds to our knowledge of the diversity of Cenozoic Picea, its affinities within the genus remain undetermined.     

WOOD FORMATION IN PROSOPIS: EFFECT OF 2,4-D, 2,4,5-T,AND TIBA

Treatment of erect stems of Prosopis with near phytotoxic levels of 2,4-D or 2,4,5-T causes the formation of an unusual wood with narrow, thick-walled vessels and axial parenchyma in which cell wall thickening is inhibited. Although reduced in diameter, the vessels formed during 2,4-D and 2,4,5-T treatment are so numerous that there is no significant difference between phenoxyacetic acid and control seedling groups with regard to total area of xylem occupied by vessels. The preferential maturation of xylem vessels over parenchyma and the transformation of fusiform initials into septate parenchyma strands in phenoxyacetic acid-treated Prosopis resemble the structural changes reported to occur after girdling in the cambial tissue of other arborescent angiosperms. Bending experiments indicate that tension-wood fibers of Prosopis differentiate in response to an auxin deficiency. However, xylogenesis in erect stems treated with TIBA is affected such that a significantly higher proportion of the cambial cell population becomes axial xylem parenchyma.     

The Secondary Xylem Anatomy of 6 Desert Plants of Caragana

The structures of secondary xylem of 6 species of Caragana, which grow in desert regions of Northwest of China, are described in details. The main quantitative characters are compared with species. And a key to the identification of wood structures of 6 species is given. The main similarities of secondary xylem of these 6 species are as follows: vessels per mm2 very numerous, percentage of multiple vessels high; vessel elements very short, perforations simple and in almost horizontal end walls; intervessel bordered pits alternate and vestured, and vessels with spiral thickenings. Libriform fibres are very short, and usually with thick end walls, and with simple pits. Rays are heigh to very low, and with multiseriate and uniseriate, and with heterogeneous type Ⅰ and Ⅱ. In addition, there are differences in other characters, e.g. vessel distribution, amount of axial parenchyma and distribution, ray frequency, crystals present or absent, and crystal distribution, if present. These differences can be used as the anatomical characters to identify the wood structures of the 6 species. In this article we also discuss the relation between the structure of xylem elements and the environmental influences.     

What is disjunctive xylem parenchyma? A case study of the African tropical hardwood Okoubaka aubrevillei (Santalaceae)

The morphological variation and structure-function relationships of xylem parenchyma still remain open to discussion. We analyzed the three-dimensional structure of a poorly known type of xylem parenchyma with disjunctive walls in the tropical hardwood Okoubaka aubrevillei (Santalaceae). Disjunctive cells occurred among the apotracheal parenchyma cells and at connections between axial and ray parenchyma cells. The disjunctive cells were partly detached one from another, but their tubular structures connected them into a continuous network of axial and ray parenchyma. The connecting tubules had thick secondary walls and simple pits with plasmodesmata at the points where one cell contacted a tubule of another cell. The imperforate tracheary elements of the ground tissue were seven times longer than the axial parenchyma strands, a fact that supports a hypothesis that parenchyma cells develop disjunctive walls because they are pulled apart and partly separated during the intrusive growth of fibers. We discuss unresolved details of the formation of disjunctive cell walls and the possible biomechanical advantage of the wood with disjunctive parenchyma: the proportion of tissue that improves mechanical strength is increased by the intrusive elongation of fibers (thick-walled tracheids), whereas the symplastic continuum of the parenchyma is maintained through formation of disjunctive cells.     

MORPHOGRAM: A NOVEL DIAGRAM TO ORGANIZE THE TRANSITIVE SECONDARY XYLEM ELEMENTS OF BASAL TOMATO (SOLANUM LYCOPERSICUM) INTERNODES

In the internodal secondary xylem of tomato (Solanum lycopersicum L. cv. Moneymaker) there are five main groups of secondary xylem elements which can be distinguished in wood macerates of basal internodes of the plant. Their top-frequency lengths are distinct: ray parenchyma cells (80 μm); fusiform parenchyma cells and strands (250 μm); vessel members (290 μm); tracheids (350 μm); and fibrous elements (590 μm), although there is overlap in length and morphology. The imperforate axial elements are strikingly diverse and morphologically intergrading, precluding ready classification according to traditional wood anatomical standards. In a novel, more appropriate, flexible categorization the variability in imperforate axial elements is depicted in a morphogram in which pit shape is plotted against cell length and cell morphology. This morphogram organizes the various elements without imposing an absolute classification. It is concluded that the appreciable variation in tomato wood samples results from developmental plasticity. The morphogram elucidates the extent and nature of element variation at the morphological level. Thus, it can be used to record developmental plasticity of wood tissues to assess interplant variation in wood tissue development, as well as intraplant plasticity.     

The function of intercellular spaces along the ray parenchyma in sapwood, intermediate wood, and heartwood of Cryptomeria japonica (Cupressaceae)

? Premise of the study: Intercellular spaces along ray parenchyma (ISRP) are common in many conifer xylems, but their function is uncertain because the in-situ structural network among ISRP, ray parenchyma, and tracheids has not been evaluated. Analysis of water distribution in ISRP from sapwood to heartwood is needed to elucidate the function of ISRP in sapwood, intermediate wood, and heartwood. ? Methods: We used cryo-scanning electron microscopy, x-ray photography, and water content measurement in xylem to analyze the presence of liquids in ISRP, ray parenchyma, and tracheids from sapwood to heartwood in Cryptomeria japonica (Cupressaceae). ? Key results: In sapwood, almost all ISRP were empty. "Cingulate-cavitated regions", which lose water along the tangential direction within one annual ring, formed in the earlywood tracheids, and their frequency increased toward the inner annual rings, whereas ray parenchyma cells were alive and not involved in the partial cavitation. In intermediate wood, almost all ISRP and earlywood tracheids and many of the ray cells were empty, and only some latewood tracheids retained liquid in their lumina. The ISRP were connected with tracheids via gas-filled ray parenchyma cells. ? Conclusions: The ISRP work as a pathway of gas for aspiration of ray parenchyma cells in sapwood. On the other hand, the occurrence of a gas network between ISRP, ray parenchyma, and tracheids facilitates cavitation of tracheids, resulting in the generation of low-moisture, intermediate wood.     

Broad Anatomical Variation within a Narrow Wood Density Range—A Study of Twig Wood across 69 Australian Angiosperms

ObjectivesJust as people with the same weight can have different body builds, woods with the same wood density can have different anatomies. Here, our aim was to assess the magnitude of anatomical variation within a restricted range of wood density and explore its potential ecological implications.MethodsTwig wood of 69 angiosperm tree and shrub species was analyzed. Species were selected so that wood density varied within a relatively narrow range (0.38–0.62 g cm^-3). Anatomical traits quantified included wood tissue fractions (fibres, axial parenchyma, ray parenchyma, vessels, and conduits with maximum lumen diameter below 15 μm), vessel properties, and pith area. To search for potential ecological correlates of anatomical variation the species were sampled across rainfall and temperature contrasts, and several other ecologically-relevant traits were measured (plant height, leaf area to sapwood area ratio, and modulus of elasticity).ResultsDespite the limited range in wood density, substantial anatomical variation was observed. Total parenchyma fraction varied from 0.12 to 0.66 and fibre fraction from 0.20 to 0.74, and these two traits were strongly inversely correlated (r = -0.86, P < 0.001). Parenchyma was weakly (0.24 ≤|r|≤ 0.35, P < 0.05) or not associated with vessel properties nor with height, leaf area to sapwood area ratio, and modulus of elasticity (0.24 ≤|r|≤ 0.41, P < 0.05). However, vessel traits were fairly well correlated with height and leaf area to sapwood area ratio (0.47 ≤|r|≤ 0.65, all P < 0.001). Modulus of elasticity was mainly driven by fibre wall plus vessel wall fraction rather than by the parenchyma component.ConclusionsOverall, there seem to be at least three axes of variation in xylem, substantially independent of each other: a wood density spectrum, a fibre-parenchyma spectrum, and a vessel area spectrum. The fibre-parenchyma spectrum does not yet have any clear or convincing ecological interpretation.     

Wood diameter indicates diurnal and long-term patterns of xylem water potential in Norway spruce

The stem diameter of adult Norway spruce trees was measured to see whether changes in xylem water potential lead to detectable radial deformation of the wood. The dendrometers used in these experiments measured only the dimensional changes of the woody cylinder (sap- and heartwood). Wood diameter was measured close to the ground and just below the living crown. After correction for thermal expansion of dendrometers and wood, diurnal variation of wood diameter ranged between 50 and 180 µm. Psychrometric measurements showed that xylem water potential varied in parallel to wood diameter. Diameter changes were always more pronounced at the higher stem position and exhibited a clear diurnal pattern. During the day, wood diameter decreased with increasing vapor pressure deficit and transpiration rate and with decreasing twig water potential. At night, the wood re-expanded but did not always reach the dimension of the previous day. Pre-dawn wood diameter decreased during periods of soil drought, a process which rapidly stopped and reversed after rain events. On several days, oscillation in wood diameter was observed during the mid-day hours. The oscillation had a period of approximately 50 min and showed a phase shift between different stem heights. All observed patterns of wood shrinkage and expansion were consistent with the hypothesis that xylem water tension leads to an elastic contraction of xylem conduits. The results demonstrate that xylem diameter is more suitable than whole-stem diameter for monitoring changes in xylem water potential.