Secondary Xylem Research Articles

Stem anatomy and ontogeny of phloem wedges in some species of Gymnema (Apocynaceae)

The anatomy of climbing plants shows a fascinating arrangement of vascular tissues, which may vary from species to species. In the present study, stem anatomy of Gymnema cuspidatum, G. latifolium, G. montanum and G. sylvestre (Apocynaceae) and the occurrence of vascular variants are described here for the first time. They were compared histologically to understand the structural variations in the secondary xylem and ontogeny of vascular variants if any within the species. All four species increase their stem diameter by a single ring of vascular cambium like most of the eudicots. In thick stems, periderm forms distinct ridges and furrows in all the species except G. sylvestre, in which it was minimal. Differential activity of the cambium resulted in the formation of distinct and deep phloem wedges in G. latifolium and G. sylvestre while in other species they were either shallow or almost absent. The secondary xylem was diffuse-porous with distinct growth rings in G. cuspidatum and G. montanum while they were indistinct in G. latifolium and G. sylvestre. Besides regular xylem elements, the presence of perforated ray cells and radially oriented laticifers in the xylem rays was observed frequently in all the investigated samples. The formation of the intraxylary primary phloem was observed concomitant to the regular protoxylem and protophloem at the pith margin. Subsequently, an additional intraxylary phloem was developed from the adjacent pith cells and by the activity of intraxylary/medullary cambium at the pith margin. In thick stems, parenchymatous cells situated between the protoxylem and intraxylary protophloem led to the initiation of intraxylary cambium. In conclusion, three species showed distinct ridges and furrows due to the formation of periderm except G. sylvestre, phloem ray parenchyma showed the formation of sclerenchyma only in the thick stems of G. sylvestre. The formation of intraxylary phloem in all four species may serve as an additional way for the transport of organic nutrients.

Network Analysis of Metabolome and Transcriptome Revealed Regulation of Different Nitrogen Concentrations on Hybrid Poplar Cambium Development.

Secondary development is a key biological characteristic of woody plants and the basis of wood formation. Exogenous nitrogen can affect the secondary growth of poplar, and some regulatory mechanisms have been found in the secondary xylem. However, the effect of nitrogen on cambium has not been reported. Herein, we investigated the effects of different nitrogen concentrations on cambium development using combined transcriptome and metabolome analysis. The results show that, compared with 1 mM NH4NO3 (M), the layers of hybrid poplar cambium cells decreased under the 0.15 mM NH4NO3 (L) and 0.3 mM NH4NO3 (LM) treatments. However, there was no difference in the layers of hybrid poplar cambium cells under the 3 mM NH4NO3 (HM) and 5 mM NH4NO3 (H) treatments. Totals of 2365, 824, 649 and 398 DEGs were identified in the M versus (vs.) L, M vs. LM, M vs. HM and M vs. H groups, respectively. Expression profile analysis of the DEGs showed that exogenous nitrogen affected the gene expression involved in plant hormone signal transduction, phenylpropanoid biosynthesis, the starch and sucrose metabolism pathway and the ubiquitin-mediated proteolysis pathway. In M vs. L, M vs. LM, M vs. HM and M vs. H, differential metabolites were enriched in flavonoids, lignans, coumarins and saccharides. The combined analysis of the transcriptome and metabolome showed that some genes and metabolites in plant hormone signal transduction, phenylpropanoid biosynthesis and starch and sucrose metabolism pathways may be involved in nitrogen regulation in cambium development, whose functions need to be verified. In this study, from the point of view that nitrogen influences cambium development to regulate wood formation, the network analysis of the transcriptome and metabolomics of cambium under different nitrogen supply levels was studied for the first time, revealing the potential regulatory and metabolic mechanisms involved in this process and providing new insights into the effects of nitrogen on wood development.

Expanding the diversity of conifer xyloflora from Early Cretaceous Crato Fossil Lagerstätte, Brazil

Remains of gymnosperms are the most abundant plant macro-fossils in the outcrops of a fossil lagerstätte preserved in lacustrine limestones in the likely lower Aptian Crato Formation of the Araripe Basin in NE Brazil. However, the systematics of most fossil-taxa are mainly based on foliage and reproductive structures, whereas wood anatomy has rarely been used to study fossil plant diversity, despite the abundance of wood fragments. Here we describe a new fossil gymnosperm taxon based on anatomical characters of a well-preserved specimen from this lithostratigraphic unit. The new fossil-genus and fossil-species Cratoxylon placidoi gen. nov. et sp. nov. are established using characters of the secondary xylem and the bark, features that are also crucial for their affiliation into conifers. This finding reinforces the already known remarkable preservation potential of organisms in this konservat lagerstätte, since bark tissues are rarely preserved in the fossil record of Mesozoic gymnosperms. The results reveal the great potential of fossil woods for studying diversity of the Crato Formation flora and thus contribute to expand our knowledge on fossil vegetation in equatorial Gondwana during the early diversification of angiosperms.

Exogenous applications of brassinosteroids promote secondary xylem differentiation in Eucalyptus grandis.

Brassinosteroids (BRs) play many pivotal roles in plant growth and development, especially in cell elongation and vascular development. Although its biosynthetic and signal transduction pathway have been well characterized in model plants, their biological roles in Eucalyptus grandis, a major hardwood tree providing fiber and energy worldwide, remain unclear. Here, we treated E. grandis plantlets with 24-epibrassinolide (EBL), the most active BR and/or BR biosynthesis inhibitor brassinazole. We recorded the plant growth and analyzed the cell structure of the root and stem with histochemical methods; then, we performed a secondary growth, BR synthesis, and signaling-related gene expression analysis. The results showed that the BRs dramatically increased the shoot length and diameter, and the exogenous BR increased the xylem area of the stem and root. In this process, EgrBRI1, EgrBZR1, and EgrBZR2 expression were induced by the BR treatment, and the expressions of HD-ZIPIII and cellulose synthase genes were also altered. To further verify the effect of BRs in secondary xylem development in Eucalyptus, we used six-month-old plants as the material and directly applied EBL to the xylem and cambium of the vertical stems. The xylem area, fiber cell length, and cell numbers showed considerable increases. Several key BR-signaling genes, secondary xylem development-related transcription factor genes, and cellulose and lignin biosynthetic genes were also considerably altered. Thus, BR had regulatory roles in secondary xylem development and differentiation via the BR-signaling pathway in this woody plant.

Fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China, and its geological implications

Fossil charcoal can provide important evidence for understanding the ancient forest fires and predicting changes in vegetation, paleoclimate and paleoenvironment throughout geological history. In this research, a systematic study was conducted on fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China. The charred wood is secondary xylem, pycnoxylic and homoxyleous, composed of tracheids and parenchymatous rays. Based on their anatomical features, the charcoal fossils are identified as Protophyllocladoxylon sp. The presence of well-preserved macroscopic charcoal fossils, along with carbonized leaves, suggests that these fossils were formed as a result of local surface fires. Based on the analysis of the mean random reflectance (Romean) values of charcoal from the Karamay Formation, the estimated temperature range for the production of the charcoal is between 407.49 °C and 369.17 °C. This temperature range aligns with the typical temperatures associated with surface fires, indicating that the fires in this region during the Late Triassic were of low intensity and occurred under relatively low temperatures. The presence of fossil charcoal in Junggar Basin suggests that the paleoatmospheric oxygen level in northwest China during Late Triassic was above 13% or 15%, which is the minimum required for sustained burning of natural wildfires. This finding is in accordance with the paleoatmospheric oxygen concentration models on the basis of variations in inertinite content and Phanerozoic wildfire history combined with the phosphorus cycle. The abundant presence of fossil charcoal herein suggests a humid and warm climate with intermittent droughts in the Late Triassic Junggar Basin.

Evidence for poplar PtaPLATZ18 in the regulation of plant growth and vascular tissues development.

Plant A/T-rich protein and zinc-binding protein (PLATZ) are plant-specific transcription factors playing a role in plant development and stress response. To assess the role of PLATZs in vascular system development and wood formation in poplar, a functional study for PtaPLATZ18, whose expression was associated with the xylem, was carried out. Poplar dominant repressor lines for PtaPLATZ18 were produced by overexpressing a PtaPLATZ18-SRDX fusion. The phenotype of three independent transgenic lines was evaluated at morphological, biochemical, and molecular levels and compared to the wild type. The PtaPLATZ18-SRDX lines showed increased plant height resulting from higher internode length. Besides, a higher secondary xylem thickness was also evidenced in these dominant repression lines as compared to the wild type suggesting an activation of cambial activity. A higher amount of lignin was evidenced within wood tissue as compared to the wild type, indicating an alteration in cell wall composition within xylem cell types. This latter phenotype was linked to an increased expression of genes involved in lignin biosynthesis and polymerization. The phenotype observed in the PtaPLATZ18-SRDX lines argues that this transcription factor targets key regulators of plant growth and vascular tissues development.

The microRNA7833-AUX6 module plays a critical role in wood development by modulating cellular auxin influx in Populus tomentosa.

The critical role of auxin on secondary vascular development in woody plants has been demonstrated. The concentration gradient of endogenous indole-3-acetic acid and the cellular and molecular pathways contributing to the auxin-directed vascular organization and wood growth have been uncovered in recent decades. However, our understanding of the roles and regulations of auxin influx in wood formation in trees remains limited. Here, we reported that a microRNA, miR7833, participates in the negative regulation of stem cambial cell division and secondary xylem development in Populus tomentosa. The miR7833 is mainly expressed in the vascular cambium during stem radical growth and specifically targets and represses two AUX/LAX family auxin influx carriers, AUX5 and AUX6, in poplar. We further revealed that poplar AUX6, the most abundant miR7833 target in the stem, is preferentially enriched in the developing xylem and is a positive regulator for cell division and differentiation events during wood formation. Moreover, inhibition of auxin influx carriers by 1-naphthoxyacetic acids abolished the regulatory effects of miR7833 and AUX6 on secondary xylem formation in poplar. Our results revealed the essential roles of the miR7833-AUX6 module in regulating cellular events in secondary xylem development and demonstrated an auxin influx-dependent mechanism for wood formation in poplar.

Genome-wide identification and expression analysis of GDP-D-mannose pyrophosphorylase and KATANIN in Corymbia citriodora.

The GDP-D-mannose pyrophosphorylase (GMP) and microtubule severing enzyme KATANIN (KTN) are crucial for wood formation. Although functional identification has been performed in Arabidopsis, few comprehensive studies have been conducted in forest trees. In this study, we discovered 8 CcGMP and 4 CcKTN genes by analyzing the whole genome sequence of Corymbia citriodora. The chromosomal location, genome synteny, phylogenetic relationship, protein domain, motif identification, gene structure, cis-acting regulatory elements, and protein-interaction of CcGMP and CcKTN were all investigated. KTN has just one pair of segmentally duplicated genes, while GMP has no duplication events. According to gene structure, two 5' UTRs were identified in CcGMP4. Furthermore, there is no protein-interaction between KTN and GMP. Based on real-time PCR, the expression of most genes showed a positive connection with DBH diameters. In addition, the expression of CcGMP4 and CcKTN4 genes were greater in different size tree, indicating that these genes are important in secondary xylem production. Overall, this findings will enhance our comprehension of the intricacy of CcGMP&CcKTN across diverse DBHs and furnish valuable insights for future functional characterization of specific genes in C. citriodora.

The effect of heavy metal-containing wastewater sediment on the microanatomical characteristics of the leaves and stem of Salix viminalis L.

A comparative microanatomical study of Salix viminalis L. shoots was performed in order to get an idea of the effect of toxic elements stress on the microanatomical parameters of the shoot (leaves, stem). The examined Salix viminalis L. shoots originated from the Lovász-zug suburban area of Debrecen city, where a sewage settling pond was formerly operated as a secondary biological purification unit. The control Salix triandra x viminalis L. 'Inger' samples originated from the Nyíregyháza experiment with uncontaminated soil. As a result of our research, we can state the following in the case of the leaf samples grown on contaminated soil: the leaf lamina thickness decreased; the extent of the palisade parenchyma decreased; the extent of the intercellular spaced increased inside the spongy parenchyma; the width and the height of the main veins increased; the extent of the collenchyma bordering the main vein increased; the stomatal density increased both in the case of the adaxial and abaxial epidermis; the size of the stomas decreased. In the case of the stem samples, we observed the following: in the case of the samples grown on contaminated soil the extent of the primer cortex increased; the cell wall of the cells building the sclerenchimatic fibers thickened; the number of Ca-oxalate crystal rosettes and sclereids increased; the extent of secondary phloem increased; the lumen of the tracheas in the secondary xylem increased; the average width of the annual rings decreased; the extent of the central stele of the stem increased.

Archangelskyoxylon carlquistii gen. et sp. nov. Taxonomy and phylogeny of an unequivocal gnetoid Jurassic fossil wood from Argentina

Archangelskyoxylon carlquistii gen. et sp. nov. is based on anatomical secondary xylem from the Lower Jurassic (Sinemurian–Toarcian) in the Roca Blanca Formation of Santa Cruz Province, Patagonia, Argentina. The woods are preserved as siliceous permineralization and examined by light and scanning electron microscopy. The new fossil wood shows a set of anatomical features of the secondary xylem (e.g., vessels with simple, scalariform, foraminate, and modified foraminate perforation plates; vessel with bordered pits with outer aperture vestured or non-vestured, and inner aperture vestured; tracheids with bordered pits; septate fiber-tracheids, and uni to biseriate parenchyma rays), that are related to the Gnetidae and closely resembles those of Gnetum. The new taxon was compared with existing Gnetidae species and included in a phylogenetic analysis to test its relationships with fossil and extant genera of Gnetidae. In the resulting phylogenetic hypothesis, Archangelskyoxylon is placed into a clade that is closely related to Weltwitschia and Gnetum. This finding supports the existence of this lineage in the south of Gondwana during the Jurassic and reinforces the hypothesis that lineages related to the Gnetaceae diverged earlier in South America.

Chemical Composition in Juvenile and Mature Wood of Branch and Main Trunk of Leucaena leucocephala (Lam.) de Wit

Secondary growth is the most dynamic developmental aspect during the terrestrialization of plants. The development of secondary xylem tissue composed of thick-walled cells with characteristic changes in its structure and chemistry facilitates the growth and development of woody plants. In the present study, the chemical composition of the secondary xylem of juvenile and mature wood from the branch and main trunk of Leucaena leucocephala, has been investigated and the differences established. The biochemical analysis of different cell wall components in the mature wood of the main trunk revealed high holocellulose and α-cellulose and less lignin content in the juvenile wood while its syringyl/guaiacyl (S/G) ratio was less than for the mature wood. As compared to the branch xylem, concentration of cell wall polysaccharides and lignin content was higher in both juvenile and mature wood collected from the main trunk. Thioacidolysis and GC-MS analysis of wood lignin from juvenile and mature wood showed that an increased concentration in lignin content in mature wood is associated with a corresponding increase in S/G ratio. The structural information of the acetylated lignin was investigated by 1H NMR spectroscopy. Our results indicate that the mature wood from the main trunk is superior in pulp yielding and lignin degradability as compared to the juvenile wood of the branch and trunk.

Transcriptome and miRNAs Profiles Reveal Regulatory Network and Key Regulators of Secondary Xylem Formation in "84K" Poplar.

Secondary xylem produced by stem secondary growth is the main source of tree biomass and possesses great economic and ecological value in papermaking, construction, biofuels, and the global carbon cycle. The secondary xylem formation is a complex developmental process, and the underlying regulatory networks and potential mechanisms are still under exploration. In this study, using hybrid poplar (Populus alba × Populus glandulosa clone 84K) as a model system, we first ascertained three representative stages of stem secondary growth and then investigated the regulatory network of secondary xylem formation by joint analysis of transcriptome and miRNAs. Notably, 7507 differentially expressed genes (DEGs) and 55 differentially expressed miRNAs (DEMs) were identified from stage 1 without initiating secondary growth to stage 2 with just initiating secondary growth, which was much more than those identified from stage 2 to stage 3 with obvious secondary growth. DEGs encoding transcription factors and lignin biosynthetic enzymes and those associated with plant hormones were found to participate in the secondary xylem formation. MiRNA-target analysis revealed that a total of 85 DEMs were predicted to have 2948 putative targets. Among them, PagmiR396d-PagGRFs, PagmiR395c-PagGA2ox1/PagLHW/PagSULTR2/PagPolyubiquitin 1, PagmiR482d-PagLAC4, PagmiR167e-PagbHLH62, and PagmiR167f/g/h-PagbHLH110 modules were involved in the regulating cambial activity and its differentiation into secondary xylem, cell expansion, secondary cell wall deposition, and programmed cell death. Our results give new insights into the regulatory network and mechanism of secondary xylem formation.

Regulation of secondary growth by poplar BLADE-ON-PETIOLE genes in Arabidopsis.

BLADE-ON-PETIOLE (BOP) genes are essential regulators of vegetative and reproductive development in land plants. First characterized in Arabidopsis thaliana (Arabidopsis), members of this clade function as transcriptional co-activators by recruiting TGACG-motif binding (TGA) basic leucine zipper (bZIP) transcription factors. Highly expressed at organ boundaries, these genes are also expressed in vascular tissue and contribute to lignin biosynthesis during secondary growth. How these genes function in trees, which undergo extensive secondary growth to produce wood, remains unclear. Here, we investigate the functional conservation of BOP orthologs in Populus trichocarpa (poplar), a widely-used model for tree development. Within the poplar genome, we identified two BOP-like genes, PtrBPL1 and PtrBPL2, with abundant transcripts in stems. To assess their functions, we used heterologous assays in Arabidopsis plants. The promoters of PtrBPL1 and PtrBPL2, fused with a β-glucuronidase (GUS) reporter gene showed activity at organ boundaries and in secondary xylem and phloem. When introduced into Arabidopsis plants, PtrBPL1 and PtrBPL2 complemented leaf and flower patterning defects in bop1 bop2 mutants. Notably, Arabidopsis plants overexpressing PtrBPL1 and PtrBPL2 showed defects in stem elongation and the lignification of secondary tissues in the hypocotyl and stem. Finally, PtrBPL1 and PtrBPL2 formed complexes with TGA bZIP proteins in yeast. Collectively, our findings suggest that PtrBPL1 and PtrBPL2 are orthologs of Arabidopsis BOP1 and BOP2, potentially contributing to secondary growth regulation in poplar trees. This work provides a foundation for functional studies in trees.

A unique Late Cretaceous fossil wood assemblage from Chilean Patagonia provides clues to a high‐latitude continental environment

AbstractFossil plants, including large trunks, stems, some branches, and twigs, were collected from the Maastrichtian (68.9 Ma), upper Dorotea Formation in the Magallanes–Austral Basin, 16 km north of the Cerro Guido–Las Chinas complex in the southern Chilean Magallanes region. These fossil trunks range from 0.2 to 2.2 m in length. Petrographic slides were made in three sections (transverse, radial and tangential) and analysed under a light microscope to study the permineralized fossils. The woods and stems belong to Austroginkgoxylon gen. et sp. nov., Agathoxylon antarcticum, Podocarpoxylon paradoxi sp. nov., Podocarpoxylon mazzonii, Palmoxylon subantarcticae and Notomalvaceoxylon magallanense gen. et sp. nov. The growth rings of gymnosperms and anatomical characters of angiosperms were analysed to obtain palaeoecological data. Interactions between gymnosperm roots growing into the secondary xylem of an angiosperm (nurse logs) are recorded. The data obtained from the fossil woods suggest warm and humid conditions in this southern South American locality during the Late Cretaceous, providing a unique opportunity to study continental environments at high southern latitudes, which are poorly represented on a global scale.

Ontogeny of multiple variants in the stems of Phaseolus lunatus L. (Fabaceae)

Development of the cambial variant is characteristic to most of the climbing members of the Fabaceae and is considered as an alternative path to increase their stem diameter for efficient supply of minerals and photosynthate within limited stem diameter. These alternative forms of secondary growths are ascribed as an adaptive character to increase stem flexibility and most often they are found to be taxon-specific. In the present study, histological investigation on the main stems of Phaseolus lunatus L. (Fabaceae) showed multiple combinations of variant secondary growth like the formation of vascular cylinders external to the secondary phloem and proliferation of parenchyma (axial and ray) followed by the development of interxylary phloem, interxylary cambia (functionally regular and inverse) and ray cambia. The secondary xylem produced by regular cambium was diffuse-porous with indistinct growth rings and composed of an abundance of thin-walled unlignified parenchyma. With the increase in age, phloem rays underwent dilatation, subsequently became meristematic and formed oval to circular vascular cylinders/units with irregular orientation. Concomitantly, dedifferentiation xylem parenchyma not only formed small islands of interxylary phloem but also led to the origin of interxylary cambial segments that differentiated bidirectionally and deposited xylem and phloem having inverse, diagonal, tangential or radial orientations. Similar cell division activity was also observed in marginal xylem ray cells (ray cambium) that produced both the xylem and phloem on either side. All these cambial variants are described in detail and their possible significance in the climbing habit is discussed.

Effect of the HCT gene on lignin synthesis and fiber development in Gossypium barbadense

As one of the key enzymes in the metabolic pathway of phenylpropane, shikimate hydroxycinnamoyl transferase (HCT) is mainly involved in the biosynthesis of the plant secondary cell wall, which is closely related to cotton fiber quality. In this study, whole-genome identification and bioinformatics analysis of the HCT gene family were performed in G. barbadense. In the whole genome, we identified 136 GbHCT genes encoding 309–504 amino acids. Phylogenetic analysis divided the genome into 5 subfamilies, which were located on 25 chromosomes. Collinear analysis of polyploidization and tandem duplication events were the main driving forces for the rapid expansion and evolution of this family, and the genes underwent loose purifying selection constraints after duplication. Gene promoters identified a variety of cis-acting elements related to plant hormones and the stress response. Several members of the GbHCT family were highly expressed during the development of cotton fiber, and different members had different expression patterns in cotton fiber. After GbHCT114 gene silencing in cotton, the amount of stem surface trichomes and lignin content decreased, and the cell morphology and arrangement changed. After the GbHCT114 gene was overexpressed in Arabidopsis thaliana (L.) Heynh., the number of stem and leaf surface trichomes and the cross-sectional area of the secondary xylem duct cell wall increased. In addition, utilizing transcriptomic analysis, differentially expressed genes associated with lignin synthesis and fiber development were identified. Taken together, the results obtained in this study confirm that the GbHCT114 gene regulates plant trichome development, which lays a theoretical foundation for future studies on the function of GbHCT114 in cotton.

Histochemical Detection of Peroxidase and Laccase Activities in Populus Secondary Xylem.

Peroxidases (PRXs) and laccases (LACs) are enzymes involved in catalyzing the oxidation of the lignin monomers to facilitate lignin polymerization. However, due to the large number of genes composing these two families of enzymes, many details regarding their specific localization are only partially understood. Here, we present a fast and easy histochemical method that makes use of the artificial substrate 3,3',5,5'-tetramethylbenzidine (TMB) to visualize PRX and LAC activities in the hybrid aspen (Populus tremula x P. tremuloides) xylem tissue. In addition, we describe a protocol that allows the detection of the PRX substrate, H2O2, using the nonfluorescent dye 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) in woody tissues.

Genes expression profiles in vascular cambium of Eucalyptus urophylla × Eucalyptus grandis at different ages

BackgroundWood is a secondary xylem generated by vascular cambium. Vascular cambium activities mainly include cambium proliferation and vascular tissue formation through secondary growth, thereby producing new secondary phloem inward and secondary xylem outward and leading to continuous tree thickening and wood formation. Wood formation is a complex biological process, which is strictly regulated by multiple genes. Therefore, molecular level research on the vascular cambium of different tree ages can lead to the identification of both key and related genes involved in wood formation and further explain the molecular regulation mechanism of wood formation.ResultsIn the present study, RNA-Seq and Pac-Bio Iso-Seq were used for profiling gene expression changes in Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) vascular cambium at four different ages. A total of 59,770 non-redundant transcripts and 1892 differentially expressed genes (DEGs) were identified. The expression trends of the DEGs related to cell division and differentiation, cell wall biosynthesis, phytohormone, and transcription factors were analyzed. The DEGs encoding expansin, kinesin, cycline, PAL, GRP9, KNOX, C2C2-dof, REV, etc., were highly expressed in E. urograndis at three years old, leading to positive effects on growth and development. Moreover, some gene family members, such as NAC, MYB, HD-ZIP III, RPK, and RAP, play different regulatory roles in wood formation because of their sophisticated transcriptional network and function redundantly.ConclusionsThese candidate genes are a potential resource to further study wood formation, especially in fast-growing and adaptable eucalyptus. The results may also serve as a basis for further research to unravel the molecular mechanism underlying wood formation.

Comprehensive Time-Course Transcriptome Reveals the Crucial Biological Pathways Involved in the Seasonal Branch Growth in Siberian Elm (Ulmus pumila).

Timber, the most prevalent organic material on this planet, is the result of a secondary xylem emerging from vascular cambium. Yet, the intricate processes governing its seasonal generation are largely a mystery. To better understand the cyclic growth of vascular tissues in elm, we undertook an extensive study examining the anatomy, physiology, and genetic expressions in Ulmus pumila. We chose three robust 15-year-old elm trees for our study. The cultivars used in this study were collected from the Inner Mongolia Autonomous Region in China and nurtured in the tree farm of Shandong Normal University. Monthly samples of 2-year-old elm branches were taken from the tree from February to September. Marked seasonal shifts in elm branch vascular tissues were observed by phenotypic observation: In February, the cambium of the branch emerged from dormancy, spurring growth. By May, elms began generating secondary xylem, or latewood, recognized by its tiny pores and dense cell structure. From June to August, there was a marked increase in the thickness of the secondary xylem. Transcriptome sequencing provides a potential molecular mechanism for the thickening of elm branches and their response to stress. In February, the tree enhanced its genetic responses to cold and drought stress. The amplified expression of CDKB, CYCB, WOX4, and ARF5 in the months of February and March reinforced their essential role in the development of the vascular cambium in elm. Starting in May, the elm deployed carbohydrates as a carbon resource to synthesize the abundant cellulose and lignin necessary for the formation of the secondary wall. Major genes participating in cellulose (SUC and CESA homologs), xylan (UGD, UXS, IRX9, IRX10, and IRX14), and lignin (PAL, C4H, 4CL, HCT, C3H, COMT, and CAD) biosynthetic pathways for secondary wall formation were up-regulated by May or/and June. In conclusion, our findings provided a foundation for an in-depth exploration of the molecular processes dictating the seasonal growth of elm timber.

A new conifer stem, Yiwupitys elegans, from the Yiwu Jurassic Forest, Hami, Xinjiang, Northwest China

Fossil wood not only provides a comprehensive understanding of the ancient floral composition and the evolution history of wood through time, but also sheds light on the paleoclimate, paleoenvironment, and paleoecology. Permineralized conifer wood commonly occurs in the Jurassic of China; however, the detailed anatomical study has been sparsely conducted on the Jurassic wood from Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China. Here, we describe a unique permineralized stem, Yiwupitys elegans Gou et Feng gen. nov. et sp. nov. from the Middle Jurassic Xishanyao Formation in Naomaohu Town of Yiwu County, Hami City, Xinjiang, Northwest China. The fossil stem is preserved with pith, primary xylem, and secondary xylem. The solid pith is heterocellular and characterized mainly by clustered or isolated secretory cells and pitted parenchymatous cells at the pith periphery. The primary xylem is mesarch showing annular, helical, and scalariform thickenings on the tracheid walls from the protoxylem to the metaxylem. The secondary xylem is pycnoxylic and exclusively composed of tracheids and parenchymatous rays. Growth rings are distinct. The secondary xylem tracheids are featured commonly by bent ends overlapping each other. They have mostly uniseriate or biseriate, or partially triseriate alternately or oppositely arranged bordered pits on the radial walls and uniseriate or biseriate bordered pits on the tangential walls. The rays are uniseriate and up to sixteen cells high. There are four to eight cupressoid pits in each cross-field, arranged in the araucarioid type. Leaf traces initiate from the pith margin and possess a single vascular strand in each trace. The anatomical structures indicate that Yiwupitys elegans has a closer affinity with conifers, although it shows few characteristics of ginkgophytes. Our study shed new light on the plant diversity of the Yiwu Jurassic Forest.