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Vascular cambium in a transverse section of stem. A Schematic of a cross-section of stem axis, showing correlation between diameter and circumference of cambial cylinder. Slanted walls, indicating transformation of periclinal walls into radial ones, pointed with a white arrowhead, are typical for the area of intrusive growth and elimination of initial. The little rectangle marks the position of the enlarged fragment underneath. One initial has been enlarged to exhibit its typical dimensions. Dashed lines indicate the cambium zone; initial cells are marked with grey. The initial marked with a black circle has increased its circumferential dimension due to intrusive growth, but the change has been compensated with an equal partial elimination of the neighbouring initial. IL-initial layer, Ph-phloem, Xy-xylem, PMC-phloem mother cells, XMC-xylem mother cells. As the diameter of cambial cylinder (D) is 31,847 µm, its radius r = D/2 = 15,923.5 µm and circumference C = 2πr = 100,000 µm. Similarly, if the average circumferential dimension (Ci) of a single cambial initial cell is 20 µm, the total number of cambial initials forming the circumference N = C/Ci = 100,000 µm/20 µm = 5000. Also, if the average radial dimension of an initial is 10 µm, increase in radius of cambial cylinder due to deposition of one cell layer on xylem side Δr = 10 µm, an increase in cambial circumference after addition of one cell layer to the xylem core is ΔC = 2πΔr = 6.28 × 10 µm = 62.8 µm. Moreover, increase in circumferential direction of each cambial initial ΔC i = ΔC/N = 62.8/5000 = 0.0126 µm, and the ratio of radial growth to circumferential growth of wood (Δr/ΔC i ) = 793.65. B Cross-section of Tilia cordata. PMC-phloem mother cells; XMCxylem mother cells. Ph-phloem, Xy-xylem, R-ray, ST-sieve tube element. Black arrow indicates an intrusively growing wood fibre, whereas white arrow points to companion cell. Asterisks indicate the location of the most probable initial cells. C Cross-section of Pinus sylvestris. T-tracheid. SC-sieve cell. PMC-phloem mother cells; XMC-xylem mother cells; Ph-phloem, Xy-xylem, R-ray. Asterisks indicate the location of the most probable initial cells. Scale bars-50 μm
Source publication
Radial growth has long been a subject of interest in tree biology research. Recent studies have brought a significant change in the understanding of some basic processes characteristic to the vascular cambium, a meristem that produces secondary vascular tissues (phloem and xylem) in woody plants. A new hypothesis regarding the mechanism of intrusiv...
Contexts in source publication
Context 1
... The cambium exists in a form of cylinder of multi-layered meristematic cells between xylem and phloem tissues (Fig. 1a-c). It surrounds the central wood core and is itself surrounded by an outer cylinder of bark in the long axis (root and shoot) of woody plants. In transverse sections of the plant axis, it appears as a multi-layered circle around the xylem, comprising of a division zone in the middle, where cell divisions occur, and the differentiation ...
Context 2
... peripheral layers, where derivative cells pass through a variety of processes on way to attaining their final form and position in derivative tissues. The division zone generally consists of a layer of cambial initials sandwiched by the layers of xylem mother cells (XMCs) on the inner side and those of phloem mother cells (PMCs) on the outer side (Fig. ...
Context 3
... only a few cells normally act as initials in apical meristems, cambial initials are extremely numerous and form a sort of layer between the layers of tissue mother cells (PMCs and XMCs) around the wood core of the trunk, branches and roots of woody plants (Fig. 1). They are responsible for the production of wood cells on the inner side ( Ajmal and Iqbal 1987;Aref et al. 2014;Włoch et al. 2013) and secondary phloem cells on the outer side ( Iqbal and Ghouse 1987;Iqbal and Zahur 1995). The layer of initials is not in fact a perfect layer due to the non-parallelism of its component cells (Włoch ...
Context 4
... the axially aligned derivatives such as vessel elements, tracheids, fibres and sieve-tube elements of the secondary vascular tissues; whereas ray initials give rise normally to the radially aligned ray parenchyma. In transverse view, ray parenchyma appear to form radially running rays across the secondary vascular tissues, i.e. xylem and phloem (Fig. 1b, c) (Larson 1994;Iqbal 1995;Lev-Yadun and Aloni 1995). Cambial initials (stem cells) never undergo differentiation but continue to remain initials and produce tissue mother cells (Iqbal 1994(Iqbal , 1995Lachaud et al. ...
Context 5
... main activity of cambial cells is their expansion in the radial direction followed by their periclinal division, which reduces the radial thickness of the cell to almost half, but the tangential width remains unaffected (Fig. 1a). The resultant daughter cells, having a radial thickness about half of the thickness of the mother cell, expand radially to regain the original thickness of the mother cell before undergoing the next periclinal division, thus forming a radial file of cells (Bailey 1923;Philipson et al. 1971). After the periclinal division of an initial ...
Context 6
... fusiform cambial initials are axially elongated and radially flattened cells (see Figs. 1, 2), such cells should divide by transverse division as per the Errera's rule ( Kwiatkowska and Nakielski 2011). However, cambial cells divide predominantly by periclinal divisions. Transverse divisions with a minimal cell-plate surface are rare in vascular cambium and occur mainly during ray formation (Cumbie 1967;Evert ...
Context 7
... grow over 8000 times more in the radial direction than in the circumferential direction ). In fact, the circumferential increment of an individual initial due to the expansion of tangential walls is less than 0.002 μm, which is even less than the thickness of the cell wall ( Karczewska et al. 2009;Miodek et al. 2021). In the example presented in Fig. 1a, after adding only one layer of cambial cells, hence increasing the cambial radius by 10 μm, the change of circumference per one initial would be equal to ΔCi = ΔC/N = 62.8 µm/5000 = 0.0126 µm, so less than the thickness of their radial walls. The relationship between the rates of growth in the radial and circumferential directions of ...
Context 8
... a single radial row of cambial cells, which is a very small segment of the cambial circumference, it is not possible to observe the curvature of the periclinal walls (Figs. 1, 4) and usually a term 'tangential plane' is used to describe a position of dividing wall in periclinal division. Plant anatomists use this term conventionally while measuring the width of cambial cells on anatomical preparations normally referred to as the tangential, radial and transverse sections. ...
Context 9
... transverse sections of the active cambial tissue, with its cells dividing periclinally and growing symplastically as well as intrusively, one often comes across some slanted walls of the initials that have undergone intrusive growth or elimination, indicating a gradual transformation of their tangential walls into radial walls (Figs. 1, 4h, i, 5). Such a transformation (of tangential walls into radial ones) has been observed in areas with vigorous intrusive growth in the cambia of both the gymnospermous and dicotyledonous species ( Jura et al. 2006;Włoch et al. 2009;Wilczek et al. 2011a). ...
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Background
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Citations
... The vascular cambium is a lateral meristem responsible for the production of secondary vascular tissues of woody plants, i.e., secondary xylem (wood) and secondary phloem. Information on the development, structure and growth of this meristem has been reviewed by many authors (e.g., Esau, 1965;Bannan, 1968;Murmanis, 1970;Zimmermann & Brown, 1971;Catesson, 1974;Fahn, 1990;Larson, 1994;Iqbal, 1990Iqbal, , 1994Iqbal, , 1995Lachaud, 1999;Spicer & Groover, 2010;Tomescu & Groover, 2019;Shi et al., 2019;Miodek et al., 2021;Wilczek-Ponce et al., 2021). Within a stem, the vascular cambium has the shape of a cylinder composed of cambial initials that do not form a continuous layer but are rather arranged as an irregular network of cells forming "the initial surface" (Włoch & Połap, 1994;Włoch et al., 2013). ...
... However, later Kojs et al. (2004b), Jura et al. (2006) and Wilczek et al. (2011) have suggested that intrusive growth and cell elimination are two faces of the same process, and elimination is not a separate cambial event. Also, the findings, referring to the cambia of species like Laburnum anagyroides, Lonchocarpus sericeus, Picea abies, Pinus sylvestris, Robinia pseudo-acacia, Tilia cordata and Wisteria floribunda, have produced structural and quantitative evidence to establish that the cambial initials grow intrusively between the periclinal walls of the adjacent initial and its immediate derivative, and that merely the symplastic growth of cambial cells is sufficient to attain the required increase in the circumference of the cambial cylinder, irrespective of the cambium being storied or non-storied (Włoch and Połap 1994;Włoch et al. 2002Włoch et al. , 2009Włoch et al. , 2013Kojs et al. 2004a, b;Jura et al. 2006;Karczewska et al. 2009;Wilczek et al. 2018;Miodek et al. 2021Miodek et al. , 2022Wilczek-Ponce et al. 2021). ...
... (a) the vascular cambium is a uniseriate layer of initial cells (Schmid, 1976), able to grow (symplastically and intrusively) and divide (anticlinally and periclinally); (b) ray cells and fusiform cells have similar width in transverse section (Catesson, 1974(Catesson, , 1984; (c) the average width of one initial cell is approximately 20 μm and thickness 10 μm (Esau, 1965;Evert, 2006;Miodek et al., 2021;Wilczek-Ponce et al., 2021); ...
The expansion of the vascular cambium cylinder in the stem of woody plants has been modeled many times, using different approaches and focusing on contributions of different cell events (cell divisions, intrusive cell growth and symplastic cell growth). Although there are many case studies in the literature, a universal model is still lacking. Therefore, the aim of this study is to estimate the quantitative changes in the contribution of symplastic growth of a single cambial cell (a sector of the cambial circumference) to the expansion of the vascular cambium cylinder, as the stem increases in girth. The proposed calculations, using the number π, and considering the actual dimensions of cambial cells, show (a) that the average symplastic increase per one initial cell in the circumferential direction decreases exponentially with the enlargement of cambial circumference, and (b) that the significant difference in the magnitude of symplastic increment of a single initial in the radial and circumferential directions increases proportionally to the increase in the circumference of the cambial cylinder. The proposed mathematical formula helps to understand the general rules that govern the gradual increase of the vascular cam-bium cylinder during wood production and would further facilitate the description/ modeling of stem growth and formation of wood structural patterns.
... For intrusive growth to occur, a tensile stress acting perpendicularly to the alignment of the middle lamella and separating neighbouring cells is necessary. As intrusive growth can only occur into a free space (microspace) [35,36] which can only be created by exceeding the threshold value of the tensile stress, the observation of such growth between tangential walls [34,[37][38][39] indicates that the middle lamella is being stretched in the radial direction. At this point, the following question can be asked: is it possible to correctly characterise the radial growth of the vascular cambium without taking intrusive growth into account? ...
... At this point, the following question can be asked: is it possible to correctly characterise the radial growth of the vascular cambium without taking intrusive growth into account? More recent works on the functioning of this meristem have linked enlargement of the cambial cylinder exclusively to symplastic growth [28,34], whereas the rearrangement of cambial cells has been linked specifically to intrusive growth [28,39]. This allowed a fundamental redefinition of the role of intrusive growth in the radial expansion of the stem [27,28,34,[37][38][39][40][41][42][43]. ...
... More recent works on the functioning of this meristem have linked enlargement of the cambial cylinder exclusively to symplastic growth [28,34], whereas the rearrangement of cambial cells has been linked specifically to intrusive growth [28,39]. This allowed a fundamental redefinition of the role of intrusive growth in the radial expansion of the stem [27,28,34,[37][38][39][40][41][42][43]. ...
The vascular cambium is the main lateral meristem responsible for the secondary growth of trees. There are a number of explicit and implicit assumptions behind this statement which allow questions to be raised about the mechanism underlying the radial growth of trees. Based on the hypothesis of the diurnal strains of plant organs, it is anticipated that the process of radial growth can be understood as an adaptation to the cyclically changing mechanical stress in the radial direction generated by the phloem during the 24 h day cycle. This qualitative hypothesis treats cambium as a tissue subjected to nighttime stretching and daytime compression in the radial direction. The proposed osmo-mechanical hypothesis of the radial growth of vascular cambium links the daily change in water status and the considerable daily strains in the xylem and phloem with the radial net expansion of a tree trunk. We highlight transpiration as a major factor influencing the secondary growth of woody plants. Thus, we indirectly relate all the biotic (e.g., insect infestation, fungi infections , injuries, shadowing, intra-and interspecies competition, parasitism, symbiosis, etc.) and abi-otic (e.g., humidity, water availability, wind, injuries, shadowing, day length in a vegetative season, altitude, temperature, insolation, etc.) processes influencing transpiration with radial growth. In the proposed hypothesis, we also infer that differences in the strains in phloem and xylem are the direct source of tensile stress, tensile stress relaxation, compressive stress, and compressive stress relaxation in the vascular cambium. This sequence appears to be crucial in understanding both the process of the radial growth of trees and the formation of differential wood patterns, within the same genotype as well as in different genotypes. It also provides arguments for the discussion on the mechanisms regulating processes in the vascular cambium. It points out the important role of the variable mechanical stresses in the radial, circumferential, and axial directions and their interference in the development of this lateral meristem. Thus, this hypothesis supports the concept of the epigenetic and systemic regulation of intrinsic wood patterns and tree forms by environmental factors. The hypothesis is focused exclusively on broadleaved trees and symplastic growth. This limitation of the scope is due to a concern for clarity. In this form, the hypothesis provides an alternative explanation for a pure process of radial growth and paves the way for a better interpretation of such phenomena as earlywood and latewood formation. At the same time, this approach to the vascular cambium provides answers to many questions related to the generation of the mechanical conditions necessary for the occurrence of intrusive growth between tangential cell walls; this is of fundamental importance for fusiform initials readjustment, vessel element and fibre formation, ring-porous wood formation, etc. Citation: Kojs, P.; Miodek, A.; Miodek, A.P.; Włoch, W. Vascular Cambium-Between the Hammer and the Anvil: A Tensile Stress Hypothesis on the Mechanism of Radial Growth of Broadleaved Trees. Forests 2023, 14, 823. https://doi.
... wood fibres, is symplastic. Cells growing symplastically do so in unison (in a coordinated way), thus maintaining contacts between them ( Fig. 1; Wilczek-Ponce et al. 2021). Cells of the vascular cambium and their differentiating derivatives show anisotropic symplastic growth. ...
... Approximated location of initial surface of the vascular cambium is marked by white, dashed line tangential direction intrusive growth of vessel elements also occurs intrusively between tangential walls of axial system cells (Wilczek et al. 2011;Hejnowicz 2012;Gizińska et al. 2021). Location of intrusive growth of initial cells between tangential walls of initial cells and their closest derivatives was shown qualitatively (Włoch et al. 2001(Włoch et al. , 2002(Włoch et al. , 2013Kojs et al. 2004a,b;Jura et al. 2006;Karczewska et al. 2009;Miodek et al. 2021b;Wilczek-Ponce et al. 2021), and in the recent time also quantitatively (Miodek et al. 2022). Thus, intrusive growth between tangential cell walls appears as a common element of cambial initials, VEMCs, and FMCs functioning. ...
... Intrusive growth also takes place between radial cell walls, but in general it does not contribute to an increase in tangential dimension of the differentiating xylem (Fig. 2). Tips of wood fibres grow symplastically in radial direction with the tissue (Wilczek et al. 2018) -the main direction of symplastic growth for most cambial derivatives (Karczewska et al. 2009;Wilczek et al. 2018;Miodek et al. 2021b;Wilczek-Ponce et al. 2021). The question arises: how is it possible that a fibre tip can grow intrusively between radial walls without enlarging the circumferential dimension of differentiating secondary xylem? ...
Key message
At initial stages of fibre development, radial enlargement of growing fibre tip is achieved, on average, in 37.8% intrusively and in 62.2% symplastically, whereas tip tangential enlargement is purely intrusive.
Abstract
In this study, we have investigated the mode of growth of black locust wood fibre tips at initial stages of their development using detailed measurements. Growth of fibre tips may be considered in three directions: axial, tangential, and radial. An axial elongation of a fibre tip was described as intrusive and related to the separation of walls of neighbouring cells. However, determination of the contribution of intrusive vs. symplastic component of growth in tangential and radial directions was missing. Semi-thin transverse sections of the vascular cambium and adjacent tissues were obtained by ultramicrotome and stained with PAS and toluidine blue. An anatomical analysis of contribution of intrusive and symplastic growths in fibre tip radial and tangential enlargement was performed. Our study showed that during its development an average wood fibre tip grows only intrusively in tangential direction and shows intrusive-symplastic growth in radial direction. On average, at initial stages of its development, a fibre tip radial enlargement is achieved in 37.8% by intrusive growth and in 62.2% by coordinated (symplastic) growth.
... From there, other possible variables are the proportion and density of Earlywood, Latewood and Transition wood (where applicable). These models rely heavily on being able to capture the key dynamics of cell production, expansion and wall thickening rates and durations, the important interplay between which was shown by Cuny et al. [122]. ...
Purpose of Review
Producing wood of the right quality is an important part of forest management. In the same way that forest growth models are valuable decision support tools for producing desired yields, models that predict wood quality in standing trees should assist forest managers to make quality-influenced decisions. A challenge for wood quality (WQ) models is to predict the properties of potential products from standing trees, given multiple possible growing environments and silvicultural adjustments. While much research has been undertaken to model forest growth, much less work has focussed on producing wood quality models. As a result, many opportunities exist to expand our knowledge.
Recent Findings
There has been an increase in the availability and use of non-destructive methods for wood quality assessment in standing trees. In parallel, a range of new models have been proposed in the last two decades, predicting wood property variation, and as a result wood quality, using both fully empirical (statistical) and process-based (mechanistic) approaches.
Summary
We review here models that predict wood quality in standing trees. Although other research is mentioned where applicable, the focus is on research done within the last 20 years. We propose a simple classification of WQ models, first into two broad groupings: fully empirical and process-based. Comprehensive, although not exhaustive, summaries of a wide range of published models in both categories are given. The question of scale is addressed with relevance to the range of possibilities which these different types of models present. We distinguish between empirical models which predict stand or tree-level wood quality and those which predict within-tree wood quality variability. In this latter group are branching models (variation up the stem) and models predicting pith-to-bark clear-wood wood property variability. In the case of process-based models, simulation of within-tree variability, and specifically, how that variability arose over time, is always necessary. We discuss how wood quality models are, or should increasingly be, part of decision support systems that aid forest managers and give some perspectives on ways to increase model impact for forest management for wood quality.
... In angiosperm trees, a lateral meristem-vascular cambium-is responsible for producing cells of an axial and radial system of secondary xylem and secondary phloem 1,2 . Cells deposited by cambial initials, i.e. cambial derivatives, may undergo tangential, radial, and axial growth (depending on the type of cell) and differentiation followed by the maturation process [3][4][5][6] . As a consequence, secondary vascular tissues are formed. ...
... If it was the case that intrusive growth of a cambial initial contributes to circumferential enlargement of the vascular cambium, one should be able to observe an increase in tangential dimension of rearranging cells (tangential dimension of a growing initial cell together with tangential dimension of two neighbouring radial files would be larger than tangential dimension of these two files before occurrence of intrusive growth). Such analysis is justified because the spatial arrangement of cambial derivatives constitutes a historical record of events that took place in the initial layer in the past 6,15,24,25,28,29 . Thus, the arrangement of cells in layers located farther from the initial layer (on the xylem or phloem side), is a record of cellular events that took place in the initial layer further in the past. ...
... independently of periclinal divisions of the mother cells, would be universal for both types of cambia and result in a gradual rearrangement of the initial surface 22,[24][25][26] . A current arrangement of the cambial initials is constantly recorded in the newly formed layers of cambial derivatives deposited on the xylem or phloem side 6,29 . ...
This study aimed to test the hypothesis whether intrusive growth of initial cells is related to the increase in circumference of Robinia pseudoacacia vascular cambium—both qualitatively and quantitatively. The mode of intrusive growth of cambial initial cells was also studied. Samples collected from tree trunks were examined using series of semi-thin transverse sections. Anatomical reconstructions of radial and tangential planes of analysed fragments of cambial tissue were made. Observations and measurements have shown that the intrusive growth of R. pseudoacacia initial cells does not contribute to an increase in tangential dimension of observed tissue fragments where cell rearrangement occurs. Moreover, initially separated tangential walls of cells (between which cambial initial cell elongates intrusively) are transformed into obliquely oriented walls. These results stand in accordance with a statement that only symplastic growth of initials, not intrusive growth, is responsible for the increase in circumference in all woody plants with the continuous cambial cylinder. Moreover, we managed to capture the moment of transition of initial status from one cell to another for the first time. This phenomenon may be explained on the basis of the system of mechanical stresses operating not only in the secondary meristematic tissue but also in a whole plant organism.
Premise
The recognition of the Miocene Climate Optimum (MCO) in terrestrial palaeoenvironments of the Eastern Mediterranean is restricted to Lesbos and Lemnos Islands, Greece. This area is significant for its wood microfossils. A recently-discovered fossil wood assemblage from Gökçeada (Imbros) Island, Turkey, including tree species similar to the Greek findings, is thought to have an early Miocene age. Here, we revise the age of the latter plant fossiliferous locality, re-evaluate the area for the study of MCO for the terrestrial palaeoecosystems of the Eastern Mediterranean and the nomenclature errors referring to the occurrence of fossil wood. We present the plant–insect–environment interactions using detailed anatomical descriptions, of an extinct conifer and its extinct cambium miner feeding traces observed in its secondary xylem.
Methods
Three thin sections were prepared with standard palaeoxylotomical techniques from a small section of the silicified wood; the sections were observed under a light microscope. The anatomy of the conifer and its damage patterns were compared with those of extant and fossil Cupressaceae and Agromyzidae, respectively.
Pivotal results
The common anatomical features of the studied wood specimen and Hesperocyparis macrocarpa (Hartw.) Bartel and a shared characteristic (the number of the cross-field pits – a feature we consider of diagnostic value) with Xanthocyparis vietnamensis Farjon & T.H. Nguyên led to its assignment to the Hesperocyparis–Xanthocyparis–Callitropsis clade. The detailed study of the wound scars and anatomical abnormalities, the anatomical–environmental associations, and structural–functional reactions follow the identification of the wood’s anatomy sensu Carlquist providing decisive results.
Conclusions
Based on the distinctive characteristics presented, we identify our macrofossil as Cupressinoxylon matromnense Grambast, a stem or an extinct lineage of the Hesperocyparis – Xanthocyparis vietnamensis–Callitropsis nootkatensis clade with feeding traces of the fossil cambium miner of the genus Protophytobia Süss (Diptera: Agromyzidae), and anatomical damage and reaction tissue on adventitious shoots. The use of Protopinaceae and Pinoxylon F. H. Knowlton from the eastern Mediterranean are re–evaluated and corrections are provided. The age of the studied plant fossiliferous locality in Gökçeada is revised as middle Miocene, allowing the proposal of an eastern Mediterranean MCO hotspot, including Lesbos, Lemnos, and Gökçeada (Imbros) Islands.
