Xylem Maturation Research Articles

Changes in phenolic acids during maturation and lignification of scots pine xylem

The content and fractional composition of alcohol soluble phenolic acids (PhA) in cells with different degree maturation and lignification in the course of early and late timber formation in the pine (Pinus sylvestris) during vegetation were studied. Phenolic compounds (PhC), extracted by 80% ethanol, were divided into free and bound fractions of PhA. In turn, the esters and ethers were isolated from bound PhA. The contents of all substances were calculated per dry weight and per cell. Considerable differences have been found to exist in both the contents and the composition of the fractions PhA on successive stages oftracheid maturation of early and late xylem. Early timber tracheids at all secondary wall thickening steps contained PhC less and free PhA more than late timber tracheids. Throughout early timber tracheid maturation, the pool of free PhA per cell declined at the beginning oflignification and then increased gradually while that of bound PhA decreased. The maturation of late timber trecheids were accompanied by the rise of free PhA pool and the diminution of bound PhA pool. In the composition of bound PhA, the ethers were always dominant, and the amount of that in early timber cells was less than in late timber cells. The cells of early xylem at all steps of maturation contained more of ester. The sum total of free hydroxycinnamic acids, precursors of monolignols, gradually decreased during early xylem lignification as the result of the reduction of the pools of p-coumaric, caffeic, ferulic and synapic acids, while that of their ester rised. In the course of late xylem lignification, the pools of free p-coumaric, ferulic and, especially, synapic acids increased. Simultaneously, the amount of ferulic acid ester and synapic acid ether increased too. According to the data, lignin biosynthesis in early xylem and late xylem occurs with different dynamics and the structure of lignins of two xylem types might be different too.

How do galactoglucomannan oligosaccharides regulate cell growth in epidermal and cortical tissues of mung bean seedlings?

Biologically active galactoglucomannan oligosaccharides (GGMOs) alone or in combination with IBA stimulate primary root elongation and inhibit hypocotyl elongation in mung bean (Vigna radiata (L.) Wilczek) seedlings. For a more detailed view of GGMOs effect in these processes, the present work is focused on cell growth in selected tissues (epidermis and primary cortex) and on xylem formation. The GGMOs effect on tissue level has not been studied so far. The results show that GGMOs-induced stimulation of primary root growth is mainly caused by enhancing cell elongation (and in less extent by cell production rate) in all tissues observed. Xylem elements were formed at longer distance from the root tip than in the control. In hypocotyl GGMOs reduced cell elongation. IBA in roots caused decrease of cell elongation and cell production rate and acceleration of xylem maturation; in hypocotyls IBA strongly stimulated cell elongation. Application of GGMOs with IBA resulted in increase of cell elongation, cell production rate and delay of xylem maturation in roots. In GGMOs+IBA treated hypocotyls, cell length was decreased to 50% compared to IBA. Based on our results it can be concluded that GGMOs induced elongation growth in mung bean seedlings was caused by increased cell production rate and cell elongation and was accompanied with delay of xylem maturation.

Role of the Sucrose Synthase Encoding PrSus1 Gene in the Development of the Parasitic Plant Phelipanche ramosa L. (Pomel)

Phelipanche ramosa L. (Pomel) is a major root-parasitic weed attacking many important crops. Success in controlling this parasite is rare and a better understanding of its unique biology is needed to develop new specific control strategies. In the present study, quantitative polymerase chain reaction experiments showed that sucrose synthase encoding PrSus1 transcripts accumulate at their highest level once the parasite is connected to the host (tomato) vascular system, mainly in the parasite tubercles, which bear numerous adventitious roots. In situ hybridization experiments revealed strong PrSus1 expression in both shoot and root apices, especially in shoot apical meristems and in the vascular tissues of scale leaves and stems, and in the apical meristems and developing xylem in roots. In addition, immunolocalization experiments showed that a sucrose synthase protein co-localized with cell-wall thickening in xylem elements. These findings highlight the role of PrSus1 in the utilization of host-derived sucrose in meristematic areas and in cellulose biosynthesis in differentiating vascular elements. We also demonstrate that PrSus1 is downregulated in response to 2,3,5-triiodobenzoic acid-induced inhibition of polar auxin transport in the host stem, suggesting that PrSus1 activity in xylem maturation is controlled by host-derived auxin.

Wood Properties of Young Acacia mangium Trees Planted in Indonesia

Abstract This study evaluated the wood properties of 5- and 7-year-old Acacia mangium trees planted in West Java, Indonesia. A plot (20 by 20 m) was selected in each stand. The stem diameter and stress-wave velocity (SWV) were measured for all trees (n = 24 and 18 for 5- and 7-y-old trees, respectively) in the plots. Core samples were taken from all trees in each plot using an increment borer to measure the basic density (BD) and compressive strength parallel to the grain (CS). The mean ± standard deviation stem diameter was 13.1 ± 3.0 and 21.9 ± 3.8 cm in 5- and 7-year-old trees, respectively. There was no significant correlation between stem diameter and SWV. The mean BD and CS for 5-year-old trees were 0.42 ± 0.02 g cm−3 and 30.0 ± 4.4 MPa, respectively, and for 7-year-old trees were 0.45 ± 0.02 g cm−3 and 32.8 ± 3.6 MPa, respectively. There was a positive correlation between BD and CS in 5- and 7-year-old trees (r = 0.790 and 0.583, respectively). The radial variation patterns for BD and CS were similar in 5- and 7-year-old trees: BD and CS gradually increased to about 6 cm from the pith, after which it was almost constant toward the bark. The results suggest that xylem maturation depends on the growth diameter in A. mangium.

Xylem cell death: emerging understanding of regulation and function

Evolutionary, as well as genetic, evidence suggests that vascular development evolved originally as a cell death programme that allowed enhanced movement of water in the extinct protracheophytes, and that secondary wall formation in the water-conducting cells evolved afterwards, providing mechanical support for effective long-distance transport of water. The extant vascular plants possess a common regulatory network to coordinate the different phases of xylem maturation, including secondary wall formation, cell death, and finally autolysis of the cell contents, by the action of recently identified NAC domain transcription factors. Consequently, xylem cell death is an inseparable part of the xylem maturation programme, making it difficult to uncouple cell death mechanistically from secondary wall formation, and thus identify the key factors specifically involved in regulation of cell death. Current knowledge suggests that the necessary components for xylem cell death are produced early during xylem differentiation, and cell death is prevented through the action of inhibitors and storage of hydrolytic enzymes in inactive forms in compartments such as the vacuole. Bursting of the central vacuole triggers autolytic hydrolysis of the cell contents, which ultimately leads to cell death. This cascade of events varies between the different xylem cell types. The water-transporting tracheary elements rely on a rapid cell death programme, with hydrolysis of cell contents taking place for the most part, if not entirely, after vacuolar bursting, while the xylem fibres disintegrate cellular contents at a slower pace, well before cell death. This review includes a detailed description of cell morphology, function of plant growth regulators, such as ethylene and thermospermine, and the action of hydrolytic nucleases and proteases during cell death of the different xylem cell types.

Cell Morphology and wood properties of Shorea Acuminatissima Planted in Indonesia

In view of the importance of long-rotation plantation forestry in SE Asia to limit soil erosion, the cell morphology and wood properties of 35-yearold plantation trees of yellow meranti, Shorea acuminatissima Sym. were studied. To understand the effects of growth rate on cell morphology and wood properties, 131 trees in a stand were classified according to their stem diameter as fast-, medium-, and slow-growing. Five trees in each category were selected for determining the cell morphology and wood properties. There were significant differences in vessel diameter, vessel frequency, and cell wall thickness of wood fibers in the three categories. The fast-growing trees had a relatively low frequency of wide vessels and thick-walled wood fibers. However, no significant differences in basic density or compressive strength parallel to grain were identified in the three categories. The radial variation in the cell morphology and wood properties showed an almost identical pattern in the three categories, suggesting that xylem maturation depends on the cambial age rather than growth rate.

Causes and correlations in cambium phenology: towards an integrated framework of xylogenesis

Although habitually considered as a whole, xylogenesis is a complex process of division and maturation of a pool of cells where the relationship between the phenological phases generating such a growth pattern remains essentially unknown. This study investigated the causal relationships in cambium phenology of black spruce [Picea mariana (Mill.) BSP] monitored for 8 years on four sites of the boreal forest of Quebec, Canada. The dependency links connecting the timing of xylem cell differentiation and cell production were defined and the resulting causal model was analysed with d-sep tests and generalized mixed models with repeated measurements, and tested with Fisher’s C statistics to determine whether and how causality propagates through the measured variables. The higher correlations were observed between the dates of emergence of the first developing cells and between the ending of the differentiation phases, while the number of cells was significantly correlated with all phenological phases. The model with eight dependency links was statistically valid for explaining the causes and correlations between the dynamics of cambium phenology. Causal modelling suggested that the phenological phases involved in xylogenesis are closely interconnected by complex relationships of cause and effect, with the onset of cell differentiation being the main factor directly or indirectly triggering all successive phases of xylem maturation.

Gymnosperm trees from the Permian of Antarctica: An anatomically preserved trunk of Kaokoxylon sp.

Anatomically preserved gymnosperm axes are relatively abundant in Permian localities of Antarctica, but their anatomy has rarely been studied in detail, which limits comparison with other Gondwanan morphotaxa. Here we describe a silicified trunk collected from the Upper Permian Buckley Formation at Coalsack Bluff, in the central Transantarctic Mountains. The trunk has a small heterogeneous pith approximately 4mm in diameter containing conspicuous sclerotic nests, endarch primary xylem maturation, paired leaf traces, and secondary xylem of the Araucarioxylon type. Comparison with contemporaneous gymnosperm axes from Antarctica indicates that the Coalsack Bluff trunk represents a new Permian morphotaxon for the region. The anatomical characters of the pith and secondary xylem suggest an affinity with the genus Kaokoxylon Kräusel, previously reported from Permian and Triassic localities of Southern Africa, South America, India, and Australia.

Xylem phenology and wood production: resolving the chicken‐or‐egg dilemma

Delays in the start of the growing season reduce the period available for growth and the amount of xylem production. However, a higher number of developing tracheids could prolong cell differentiation and, consequently, lengthen the growing season. The relationship between the amount and duration of cell production in the xylem remains an unresolved issue. The aim of this study was to resolve the chicken-or-egg causality dilemma about duration of growth and cell production through simple- and double-cause models. This was achieved by (1) analysing the intra-annual growth dynamics of the xylem in Picea mariana (Mill.) BSP during 2006-2009 in two contrasting sites of the boreal forest of Quebec, Canada, and (2) extracting the dates of onset and ending of xylem formation and the number of radial cells along the tree ring. A higher number of cells was linked to an earlier onset (r=0.74) and later ending (r=0.61) of cell differentiation. The absence of a relationship between the residuals of the onset and ending of xylogenesis (r(p)=-0.06) indicated that cell production influenced the correlation between the two phenophases of the xylem. These results demonstrated that a higher number of cells produced delay the ending of xylem maturation, so extending the duration of wood formation.

Seasonal water relations of Lyginia barbata (Southern rush) in relation to root xylem development and summer dormancy of root apices

*Periods of dormancy in shallow roots allow perennial monocotyledons to establish deep root systems, but we know little about patterns of xylem maturation, water-transport capacities and associated economies in water use of growing and dormant roots. *Xylem development, anatomy, conductance and in situ cellular [K] and [Cl] were investigated in roots of field-grown Lyginia barbata (Restionaceae) in Mediterranean southwestern Australia. Parallel studies of gas exchange, culm relative water loss and soil water content were conducted. *Stomatal conductance and photosynthesis decreased during summer drought as soil profiles dried, but rates recovered when dormant roots became active with the onset of wetter conditions. Anatomical studies identified sites of close juxtaposition of phloem and xylem in dormant and growing roots. Ion data and dye tracing showed mature late metaxylem of growing roots was located >or= 100 mm from the tip, but at only <or= 10 mm for dormant roots. Dormant roots remained hydrated in dry soils (0.001-0.005 g g(-1)). *Effective regulation of growth and water-conserving/obtaining properties permits the survival of shallow roots of L. barbata during summer drought and may represent important strategies for establishing deeper perennial root systems in other monocotyledonous plants adapted to seasonally dry habitats.

Cryo-scanning electron microscopy (CSEM) in the advancement of functional plant biology: energy dispersive X-ray microanalysis (CEDX) applications

The capacity to make measurements of elemental concentrations at the level of single cells by energy dispersive X-ray microanalysis of cryo-fixed, inherently-hydrated plant parts (CEDX) is changing or extending our understanding of many plant functions. We include in this review a wide-ranging catalogue of studies that have used CEDX which provides access to the literature on elements measured, plants and tissues studied, techniques used, level of quantitation and the significant findings. These findings include new perspectives on the following areas: salt tolerance; xylem maturation and solute content, root pressure and embolism refilling; the contents of intercellular spaces; sequestration of toxic elements; biomineralisation with silicon; movement of tracer homologues of native cations; indirect localisation of molecules with a distinctive element component; transfer of nutrients from vesicular-arbuscular (VA) mycorrhizas; the role of mucilages in protection and in generating mechanical force. In an Appendix we discuss the procedures involved in CEDX: cryo-fixation, specimen planing, etching, elemental quantitation and mapping. Limitations on sample numbers, elements measurable, spatial resolution, sensitivity and threshold concentrations quantifiable are outlined. A brief discussion of the potential of emerging technologies for cell-specific analysis of cryo-fixed, hydrated specimens is included. In the Accessory Publication we list our standard protocol for CEDX.

Effect of the lateral growth rate on wood properties in fast-growing hardwood species

We investigated the feasibility of using several fast-growing tropical or subtropical hardwood species for timber production by measuring key wood qualities in relationship to the high rates of lateral growth. The trees tested were sampled from even-aged plantations of Acacia mangium, A. auriculiformis, hybrid Acacia (A. mangium × A. auriculiformis), Eucalyptus grandis, E. globulus, and Paraserianthes falcataria (Solomon and Java origin) that had already reached commercial harvesting age. The released strain of the surface growth stress (RS), xylem density (XD), microfibril angle (MFA), and fiber length (FL) were measured at the outermost part of the xylem at breast height in each tree. Results were then compared to the lateral growth rate (radius/age) at breast height, which provides a relative indicator of the amount of tree growth per year. Our findings indicated that RS was constant, regardless of lateral growth rate in each species. Similar results were observed for XD, MFA, and FL, with a few exceptions, suggesting that high growth rates do not intrinsically affect the wood properties of fast-growing tropical or subtropical species that have reached harvesting age. However, special attention must be paid to patterns of xylem maturation when developing plantations of such species.

Determining factor of xylem maturation in Eucalyptus grandis planted in different latitudes and climatic divisions of South America: a view based on fiber length

The objective of this study was to determine the factor of xylem maturation in Eucalyptus grandis W. Hill ex Maid. planted in four different latitudes and climatic divisions of South America, based on the pattern of the radial distribution of fiber length. In the plantation closest to the equator, the extent of juvenile wood is determined by distance from the pith and is consistent from tree to tree, regardless of growth rate. In contrast, in the plantation farthest from the equator, xylem maturation is controlled by cambial age and varies from tree to tree, depending on growth rate. To produce as much mature wood as early as possible in E. grandis planted closer to the equator, lateral growth should be accelerated from the early growing stage, because the formation of mature wood starts after a certain trunk diameter is reached. Conversely, in plantations far from the equator, it is necessary to first arrest lateral growth at an early growth stage and then accelerate lateral growth after a certain cambium age is reached.

LeFRK2 is required for phloem and xylem differentiation and the transport of both sugar and water

It has been suggested that LeFRK2, the major fructose-phosphorylating enzyme in tomato plants, may be required for stem xylem development. Yet, we do not know if this enzyme affects the development of individual vessels, whether it affects water conductance, or whether it affects phloem development and sugar transport. Here, we show that suppression of LeFRK2 results in a significant reduction in the size of vascular cells and slows fiber maturation. The vessels in stems of LeFRK2-antisense plants are narrower than in WT plants and have thinner secondary cell walls. Although the cambium produces rounded secondary vessels, these vessels become deformed during the early stages of xylem maturation. Water conductance is then reduced in stems, roots, and leaves, suggesting that LeFRK2 influences xylem development throughout the entire vascular system. Interestingly, the build-up of positive xylem pressure under static (no-flow) conditions was also decreased. Suppression of LeFRK2 reduced the length and width of the sieve elements, as well as callose deposition. To examine the effect of LeFRK2 suppression on phloem transport, we created triple-grafted plants in which a portion of the wild-type stem was replaced with an antisense interstcok, and compared the contents of the transported sugar, sucrose, in the different portions of these stems. Sucrose contents above and within the LeFRK2-antisense interstock were significantly higher than those below the graft. These results show that the antisense interstock restricted the downward movement of sucrose, suggesting that LeFRK2 is required for both phloem and xylem development.

Anatomically Preserved Pteridosperm Stems and Rachises from Permian Floras of China

Pteridosperms are common in the Permian floras of China and are known from both vegetative and fertile organs in adpression assemblages and as dispersed ovules and seeds in permineralized assemblages. In contrast, reports of vegetative organs from permineralized assemblages are limited, and in all cases, accounts have not been verified by detailed descriptions nor illustration. Here we report four taxa of pteridosperm stem or rachis from the Permian permineralized floras of China. Coal balls from the Asselian‐Sakmarian (Cisuralian) Taiyuan Formation are shown to contain specimens of a medullosan and a lyginopterid pteridosperm. The medullosan rachis has a distinctive collateral organization of vascular bundles interspersed within a crushed parenchymatous ground tissue that also has scattered resin ducts, and it is identified as Myeloxylon Brongniart. The lyginopterid has a vitalized protostelic stem with manoxylic secondary xylem and mesarch xylem maturation and is confirmed as Heterangium sp. 1. From vol...

Hamatophyton from the Late Devonian of Anhui Province, South China and Evolution of Sphenophyllales

Abstract:Well‐preserved specimens of Hamatophyton verticillatum collected from the Upper Devonian (Famennian) Wutong Formation of Chaohu district, Anhui Province, South China, display more complete fertile axes in three orders and multiple divisions. Comparisons indicate that Hamatophyton possibly does not have palmate planate sterile leaves but hook‐like linear ones with rare divisions. We propose seven definitive characters of Sphenophyllales: (1) completely whorled lateral organs; (2) sterile leaves; (3) strobili; (4) “sporangiophores” or stalks with reflexed tips bearing sporangia; (5) three‐ or four‐ribbed primary xylem; (6) exarch maturation of primary xylem; and (7) secondary xylem. The Sphenophyllales probably originated from the Iridopteridales based on similarities in whorled lateral organs, ribbed primary xylem and peripheral protoxylem strands. In transition from Iridopteridales to Sphenophyllales, morphological changes involve partially whorled to completely whorled lateral organs, sterile ultimate appendages to leaves, and fertile ultimate appendages to “sporangiophores”/stalks with bracts; anatomical modifications include configuration and maturation of primary xylem, and presence of secondary xylem.

Cordaitalean Seed Plants from the Early Permian of North China. II. Reconstruction of Cordaixylon tianii

From a single Early Permian locality in the Taiyuan Formation of northern China, a new whole‐plant cordaitalean is reconstructed and named Cordaixylon tianii (B. Tian and S.‐J. Wang) S.‐J. Wang and J. Hilton sp. nov. The reconstruction is based on pairs of plant organs found in organic attachment, supplemented with cases where two or more co‐occurring morphospecies share distinctive anatomical features. Stems have sympodial primary vascular architecture with endarch primary xylem maturation of the cauline bundles, which surround a septate pith. Leaf traces are endarch, most diverging from the pith margin as double bundles (less frequently singly) and bearing leaves in 3/8 and 5/13 phyllotaxis. Leaves are long and straplike, resembling those of the previously reconstructed Cordaixylon dumusum Rothwell and S. Warner, but with a geniculate posture that justifies their segregation as Cordaites tianii S.‐J. Wang and J. Hilton sp. nov. Both male and female cones are compound, borne irregularly as epicormic branches, and when isolated conform to the morphogenus Cordaitanthus. Pollen cones with numerous pollen organs borne on apically concentrated fertile scales are largely consistent with the morphospecies Cordaitanthus concinnus Delevoryas, but subtle distinctions permit their description as C. tianii S.‐J. Wang and J. Hilton sp. nov. Ovulate cones are described as Cordaitanthus shanxiensis S.‐J. Wang and J. Hilton sp. nov.; each cone contains several cardiocarpalean ovules that have a distinctive tuberculate integumentary structure and are assignable to the morphospecies Cardiocarpus tuberculatus S.‐J. Wang, J. Hilton, and B. Tian. The reconstructed plant most closely resembles C. dumusum from the Late Pennsylvanian of North America, but (often subtle) diagnostic characters are well distributed across the organs of the two conceptual whole plants, permitting confident distinction at species level. The plant is reconstructed as a large, suberect or fully erect shrub.

Diversity of Mississippian Arborescent Lignophytes: A New Species of Eristophyton from the Middle Tournaisian of France

Decorticated woody stems from the Tournaisian (early Mississippian) of Montagne Noire, Southern France, are characterized by a wide eustele with a parenchymatous pith and numerous primary xylem strands in contact with the secondary xylem. Primary xylem maturation is endarch to mesarch. Small leaf traces are emitted according to a spiral phyllotaxis. Secondary xylem is dense, composed of tracheids with araucarian pitting, and uni‐ to triseriate rays that do not exceed 40 cells in height. Anatomy of the primary and secondary vascular system of the Montagne Noire specimens allows their assignment to Eristophyton, an arborescent genus of putative seed plant affinities. However, they display a combination of characters unknown in previously reported species and are assigned to Eristophyton feistii sp. nov. This new species extends both the stratigraphical and geographical range of the genus. Eristophyton feistii contributes to enlarge the taxonomic diversity and anatomical disparity of putative arborescent see...

Maturation property of fast-growing hardwood plantation species: A view of fiber length

The development of human civilization has caused many problems, among them increases in atmospheric CO 2 and shortage of fossil fuel resources. Fast-growing tree species can help solve these problems. Short rotations cause concern that fast-growing species contain a high proportion of juvenile wood, thus limiting their use. To use fast-growing species for timber, this concern must be addressed. We consider whether xylem maturation depends on cambium age or diameter growth in the tree, and when and where this maturation occurs. To evaluate these options for typical fast-growing species, Acacia mangium, A. auricuriformis, Eucalyptus globulus, E. grandis, Paraserianthes falcataria (Java origin), and P. falcataria (Solomon origin), we have developed a new parameter, the “ b-value”, on the basis of radial distribution of fiber length. From our evaluation using “ b-value”, we reached the following conclusions. For Acacia spp. and Paraserianthes spp., xylem maturation depends on diameter growth. Formation of mature wood in these species starts after a certain diameter is reached, suggesting that accelerating lateral growth from an early growing stage will produce mature wood as soon as possible. In Eucalyptus spp., xylem maturation is controlled by cambium age. In those species, formation of mature wood starts once a certain cambium age is attained. This suggests that it is important to arrest lateral growth at an early growth stage, and then accelerate lateral growth after a certain cambium age is reached. Depending on the tree species concerned, those results will be helpful in the development of plantation management programs.

Reconsidering Differences between Cladoxylopsida and Iridopteridales: Evidence from Polyxylon australe (Upper Devonian, New South Wales, Australia)

A new permineralized specimen of Polyxylon australe collected from the type locality at Barraba in New South Wales, Australia, represents a portion of stem showing a node in its proximal part. Analysis of its primary vascular system and pattern of branch trace emission indicates that the plant had a hierarchized architecture. The stem, ca. 2.5 cm wide, is radially symmetrical and bears a whorl of nine or 10 branches followed by a long internode. The bilateral symmetry of first‐order branches, assessed from trace arrangement in individual branch bases, is a trait previously reported in three other nonpseudosporochnalean cladoxylopsid genera, Pietzschia, Cladoxylon, and Panxia. Xylem maturation in the stele of the new stem is exarch, but at node level, one mesarch strand of protoxylem differentiates around a cavity filled with thin‐walled cells. The diagnosis of P. australe is emended, and the significance of architectural characters for distinguishing the Cladoxylopsida from the Iridopteridales is discusse...