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Summary: Tree stems undergo a massive secondary growth in which secondary xylem and phloem tissues arise from the vascular cambium. Vascular cambium activity is driven by endogenous developmental signalling cues and environmental stimuli. Current knowledge regarding the genetic regulation of cambium activity and secondary growth is still far from complete. The tropical Cannabaceae tree Parasponia andersonii is a non‐legume research model of nitrogen‐fixing root nodulation. Parasponia andersonii can be transformed efficiently, making it amenable for CRISPR‐Cas9‐mediated reverse genetics. We considered whether P. andersonii also could be used as a complementary research system to investigate tree‐related traits, including secondary growth. We established a developmental map of stem secondary growth in P. andersonii plantlets. Subsequently, we showed that the expression of the co‐transcriptional regulator PanNODULE ROOT1 (PanNOOT1) is essential for controlling this process. PanNOOT1 is orthologous to Arabidopsis thaliana BLADE‐ON‐PETIOLE1 (AtBOP1) and AtBOP2, which are involved in the meristem‐to‐organ‐boundary maintenance. Moreover, in species forming nitrogen‐fixing root nodules, NOOT1 is known to function as a key nodule identity gene. Parasponia andersonii CRISPR‐Cas9 loss‐of‐function Pannoot1 mutants are altered in the development of the xylem and phloem tissues without apparent disturbance of the cambium organization and size. Transcriptomic analysis showed that the expression of key secondary growth‐related genes is significantly down‐regulated in Pannoot1 mutants. This allows us to conclude that PanNOOT1 positively contributes to the regulation of stem secondary growth. Our work also demonstrates that P. andersonii can serve as a tree research system. Significance Statement: Parasponia andersonii Pannoot1 CRISPR‐Cas9 knockout mutants are altered for secondary growth development. We show a new role for NBCL genes in tree stem secondary growth and provide a proof of concept that P. andersonii is suited for the investigation of tree‐related traits. [ABSTRACT FROM AUTHOR]

Based on mathematical modelling, this review article describes the mechanism of expansion in the circumference of vascular cambium due to radial growth leading to increase in the tree-trunk diameter, and emphasizes upon the huge difference in the rate of symplastic growth of cambial initials in two different directions, viz. radial and circumferential. On the basis of anatomical evidence regarding the role of symplastic and intrusive growths, the long-standing hypothesis that the intrusive growth contributes to the increase of cambium circumference has been falsified. It has been shown with the help of mathematical calculations as well as anatomical observations that only symplastic growth of the initial cells (in circumferential direction) is responsible for the expansion of cambial circumference. [ABSTRACT FROM AUTHOR]

Summary: The tight regulation of local auxin homeostasis and signalling maxima in xylem precursor cells specifies the organising activity of the vascular cambium and consequently promotes xylem differentiation and wood formation. However, the molecular mechanisms underlying the local auxin signalling maxima in the vascular cambium are largely unknown.Here, we reveal that brassinosteroid (BR)‐activated WALLS ARE THIN1 (WAT1) facilitates wood formation by enhancing local auxin signalling in the vascular cambium in Solanum lycopersicum.Growth defects and low auxin signalling readouts in the BR‐deficient tomato cultivar, Micro‐Tom, were associated with a novel recessive allele, Slwat1‐copi, created by the insertion of a retrotransposon in the last exon of the SlWAT1 locus. Molecular and genetic studies by generating the gain‐of‐function and loss‐of‐function tomato mutants revealed that SlWAT1 is a critical regulator for fine tuning local auxin homeostasis and signalling outputs in vascular cambium to facilitate secondary growth. Finally, we discovered that BR‐regulated SlBZR1/2 directly activated downstream auxin responses by SlWAT1 upregulation in xylem precursor cells to facilitate xylem differentiation and subsequent wood formation.Our data suggest that the BR‐SlBZR1/2–WAT1 signalling network contributes to the high level of auxin signalling in the vascular cambium for secondary growth. [ABSTRACT FROM AUTHOR]

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For more than 225 million y, all seed plants were woody trees, shrubs, or vines. Shortly after the origin of angiosperms ~140 million y ago (MYA), the Nymphaeales (water lilies) became one of the first lineages to deviate from their ancestral, woody habit by losing the vascular cambium, the meristematic population of cells that produces secondary xylem (wood) and phloem. Many of the genes and gene families that regulate differentiation of secondary tissues also regulate the differentiation of primary xylem and phloem, which are produced by apical meristems and retained in nearly all seed plants. Here, we sequenced and assembled a draft genome of the water lily Nymphaea thermarum, an emerging system for the study of early flowering plant evolution, and compared it to genomes from other cambium-bearing and cambium-less lineages (e.g., monocots and Nelumbo). This revealed lineage-specific patterns of gene loss and divergence. Nymphaea is characterized by a significant contraction of the HD-ZIP III transcription factors, specifically loss of REVOLUTA, which influences cambial activity in other angiosperms. We also found the Nymphaea and monocot copies of cambium-associated CLE signaling peptides display unique substitutions at otherwise highly conserved amino acids. Nelumbo displays no obvious divergence in cambium-associated genes. The divergent genomic signatures of convergent loss of vascular cambium reveals that even pleiotropic genes can exhibit unique divergence patterns in association with independent events of trait loss. Our results shed light on the evolution of herbaceousness--one of the key biological innovations associated with the earliest phases of angiosperm evolution. [ABSTRACT FROM AUTHOR]

During plant growth and development mineral elements are preferentially delivered to different organs and tissues to meet the differential demand. It has been shown that the preferential distribution of mineral nutrients in gramineous plants is mediated by node-based transporters, but the mechanisms of preferential distribution in dicots are poorly understood. Here, we report a distinct mechanism for the preferential distribution of phosphorus (P) in Arabidopsis plants, revealed by detailed functional analysis of AtSPDT/AtSULTR3;4 (SULTR-like P Distribution Transporter), a homolog of rice OsSPDT. Like OsSPDT, AtSPDT is localized at the plasma membrane and showed proton-dependent transport activity for P. Interestingly, we found that AtSPDT is mainly expressed in the rosette basal region and leaf petiole, and its expression is up-regulated by P deficiency. Tissue-specific analysis showed that AtSPDT is mainly located in the vascular cambium of different organs, as well as in the parenchyma tissues of both xylem and phloem regions. Knockout of AtSPDT inhibited the growth of new leaves under low P due to decreased P distribution to those organs. The seed yields of the wild-type and atspdt mutant plants are similar, but the seeds of mutant plants contain – less P. These results indicate that AtSPDT localized in the vascular cambium is involved in preferential distribution of P to the developing tissues, through xylem-to-phloem transfer mainly at the rosette basal region and leaf petiole. Phosphorus taken up by the roots needs to be preferentially delivered to developing tissues in order to meet their active growth demands. This study reveals that the preferential distribution of phosphorus is mediated by AtSPDT, a new type of phosphorus influx transporter localized in the vascular cambium of the rosette basal region and leaf petiole of Arabidopsis that facilitates the xylem-to-phloem transfer of phosphorus. The findings highlight a mechanism of mineral element distribution that is distinct from that in rice. [ABSTRACT FROM AUTHOR]

Our study investigated the effect of stem temperature increase on xylem formation in Robinia pseudoacacia tree-trunks, caused by direct exposure to solar radiation. It is important to determine factors which may improve the concentricity of deposited wood tissue and intensify xylogenesis because a strong irregularity of wood tissue deposited in the radial direction in mature trees of R. pseudoacacia reduces the commercial value of the wood. Samples of vascular cambium along with adjacent tissues were collected from the southern (illuminated) and northern (shaded) side of tree-trunks growing in the inner and peripheral (thus exposed to direct sunlight) zones of the research plot. Sampling was performed several times during the growing season. The collected material was examined by epifluorescence microscopy and the thickness of deposited tissue comprising cambial xylem derivatives was measured. Deposition of a markedly greater amount of xylem on the southern side of tree-trunks in the peripheral zone of the plot was observed before full leaf development. Instrumental climatic data confirmed that in the early stage of the growing season, temperature on the southern side of the peripheral zone tree-trunk was higher than on the northern side. No clear response in terms of directional deposition of xylem was noticed in the inner zone trees and in peripheral zone trees after full leaf development. This study highlights the importance of temperature increase, caused by solar radiation, for R. pseudoacacia xylogenesis, which may be considered as a factor that affects the course of the radial growth before full leaf development. [ABSTRACT FROM AUTHOR]

• Henleophytum is a monospecific, cuban endemic genus of woody lianas largely understudied. • This is the first anatomical work for Henleophytum and unveils a new record of interxylary phloem for Malpighiaceae. • Interxylary phloem had only been recorded in the distantly related south american genus Dicella. • This new record contributes to the knowledge of how the vascular system is impacted by the evolution of lianas in the family. Lianas and vascular variants have long been correlated since it is in lianas where they are most commonly found. Structurally, these vascular variants mix soft and stiff tissues allowing lianas to twist without breaking when climbing up to the forest canopies. The study of vascular variants in Malpighiaceae lianas has a long history focusing on species-diverse taxa; however, interest in understanding them in understudied, smaller taxa has unraveled vascular variants previously unknown to the family, such as the interxylary phloem of Henleophytum , a Cuban endemic, monospecific genus. Interxylary phloem in Malpighiaceae had been previously recorded in the distantly related genera Dicella, Niedenzuella , and Tristellateia. Interxylary phloem in Henleophytum derives from a cambium that in certain periods and sites produces phloem both inward and outward, similar to the pattern described for Dicella. The phloem produced outward is not equal to that produced inward. Indeed, sieve tube elements of the inner phloem are always much wider and more abundant, something likely indicative of a division of labor between both phloem types, one specializing in conduction and the other in carbohydrate storage. This constitutes a new report of a vascular variant outside the large Tetrapteroid clade, where almost all the vascular variants have been reported for the family so far, and supports the idea of the independent, multiple origins of vascular variants in Malpighiaceae. [ABSTRACT FROM AUTHOR]

Citrus is one of the most important group of plants in agriculture because of impact on human health, industry, and environment. Commercially, citrus plants are propagated by grafting to perpetuate plant characteristics and guarantee uniformity at harvest. Mini grafting is a variation of the conventional grafting to increase efficacy during plant citrus plant propagation. To analyze the effect of mini grafting type, as well as the kind of recipient, mini grafted plants, using T-inverted and cleft methods transplanted in tubes or plastic bags, were planted in the field with three replicates per treatment and distributed with a complete randomized design. For four months, the data for plant heigh, number of branches, canopy diameter, canopy perimeter, diameter of stem above the grafting and diameter of the stem below the grafting were recorded and analyzed with an analysis of variance (α = 0.05) and means separated with a Tukey test (α = 0.05). The results evidenced that grafting type statistically affected canopy diameter, canopy perimeter and diameter of the stem below the grafting, while the kind of recipient additionally affected plant heigh, number of branches, and diameter below the grafting. [ABSTRACT FROM AUTHOR]

Mechanical stress in tree roots induces the production of reaction wood (RW) and the formation of new branch roots, both functioning to avoid anchorage failure and limb damage. The vascular cambium (VC) is the factor responsible for the onset of these responses as shown by their occurrence when all primary tissues and the root tips are removed. The data presented confirm that the VC is able to evaluate both the direction and magnitude of the mechanical forces experienced before coordinating the most fitting responses along the root axis whenever and wherever these are necessary. The coordination of these responses requires intense crosstalk between meristematic cells of the VC which may be very distant from the place where the mechanical stress is first detected. Signaling could be facilitated through plasmodesmata between meristematic cells. The mechanism of RW production also seems to be well conserved in the stem and this fact suggests that the VC could behave as a single structure spread along the plant body axis as a means to control the relationship between the plant and its environment. The observation that there are numerous morphological and functional similarities between different meristems and that some important regulatory mechanisms of meristem activity, such as homeostasis, are common to several meristems, supports the hypothesis that not only the VC but all apical, primary and secondary meristems present in the plant body behave as a single interconnected structure. We propose to name this structure “meristematic connectome” given the possibility that the sequence of meristems from root apex to shoot apex could represent a pluricellular network that facilitates long-distance signaling in the plant body. The possibility that the “meristematic connectome” could act as a single structure active in adjusting the plant body to its surrounding environment throughout the life of a plant is now proposed.

Walnuts (Juglans, Juglandaceae) are known throughout the world as economically important trees that provide fat, protein, vitamins, and minerals as a food source, and produce high-quality timber. We have amended the purpose section to say “However,” the omics resources are limited, which hampered the elucidation of molecular mechanisms resulting in their economically important traits (such as yield, fertility alternation, oil synthesis, and wood formation). To enrich the omics database of walnut, there is great need for analyses of its genomic and transcriptomic characteristics. In this study, we reported for the first time of the transcriptome landscape of six important organs or tissues in walnut interspecies hybrid using next-generation sequencing technology. Over 338 million clean reads were obtained. This yielded 74,072 unigenes with an average length of 782.71 bp. To develop an understanding of gene functions and regulatory pathways, 66,355 of the unigenes were identified as homologs of annotated genes and classified into three general categories with 61 functional subcategories. 2,288 out of 2,549 unmapped unigenes had at least one BLAST hit against the public databases. A total of 1,237 transcription factor-encoding genes (TFs) and 2,297 tissue-specific unigenes were identified. Interestingly, in the new shoot between an adult seedling and a grafted tree, the expression of 9,494 unigenes were significantly different, among which 4,388 were up-regulated and 5,106 were down-regulated. Of these, 195, 177, 232, 75, 114, and 68 unigenes were related to transcription factors, cell wall, defense response, transport, plant hormone biosynthesis, and other cambial activity-related functions, respectively. The obtained sequences and putative functional data constitute a resource for future functional analyses in walnut and other woody plants. These findings will be useful in further studies addressing the molecular mechanisms underlying grafting-related cambial activity.

Introduction: Hybrid poplars are industrial trees in China. An understanding of the molecular mechanism underlying wood formation in hybrid poplars is necessary for molecular breeding. Although the division and differentiation of vascular cambial cells is important for secondary growth and wood formation, the regulation of this process is largely unclear., Methods: In this study, mPagGRF15 OE and PagGRF15-SRDX transgenic poplars were generated to investigate the function of PagGRF15 . RNA-seq and qRT-PCR were conducted to analyze genome-wide gene expression, while ChIP‒seq and ChIP-PCR were used to identified the downstream genes regulated by PagGRF15 ., Results and Discussion: We report that PagGRF15 from hybrid poplar ( Populus alba × P. glandulosa ), a growth-regulating factor, plays a critical role in the regulation of vascular cambium activity. PagGRF15 was expressed predominantly in the cambial zone of vascular tissue. Overexpression of mPagGRF15 (the mutated version of GRF15 in the miR396 target sequence) in Populus led to decreased plant height and internode number. Further stem cross sections showed that the mPagGRF15 OE plants exhibited significant changes in vascular pattern with an increase in xylem and a reduction in phloem. In addition, cambium cell files were decreased in the mPagGRF15 OE plants. However, dominant suppression of the downstream genes of PagGRF15 using PagGRF15-SRDX showed an opposite phenotype. Based on the RNA-seq and ChIP-seq results, combining qRT-PCR and ChIP-PCR analysis, candidate genes, such as WOX4b , PXY and GID1.3 , were obtained and found to be mainly involved in cambial activity and xylem differentiation. Accordingly, we speculated that PagGRF15 functions as a positive regulator mediating xylem differentiation by repressing the expression of the WOX4a and PXY genes to set the pace of cambial activity. In contrast, PagGRF15 mediated the GA signaling pathway by upregulating GID1.3 expression to stimulate xylem differentiation. This study provides valuable information for further studies on vascular cambium differentiation mechanisms and genetic improvement of the specific gravity of wood in hybrid poplars., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Zhou, Song and Lu.)

The aims of this study were to evaluate the cambial activity and phenology of three species with different life forms (Alchemilla procumbens, Acaena elongata and Ribes ciliatum) along an altitudinal gradient and to establish which environmental variables (light, soil humidity and temperature) had the greatest influence on cambial activity and phenological stages. Over two years, data on phenology, growth and cambium were gathered every four weeks in three to six sites per species in Sierra Nevada, Mexico. The results showed that Ribes is the only species that terminates cambial activity with leaves senescence and is influenced by the minimum soil temperature. The light environment influenced the vegetative stages in Alchemilla (cryptophyte), while in Acaena (hemicryptophyte), the mean soil temperature explained the findings related to leaf area during the dry season and growth along the gradient. In the three species, the reproductive phase dominated for a longer period at higher elevations, especially in Alchemilla. Only Ribes, the phanerophyte, showed a similar cambial activity to other trees and shrubs. Although cambium reactivates during the dry season, no xylogenesis occurs. The three species varied during the time in which vascular cambium was active, and this was dependent on the altitude. Specifically, the variation was more rhythmic in Ribes and switched on and off in Alchemilla. It is likely that, depending on the life form, vascular cambium may be more or less susceptible to one or more climate factors.

Vascular tissue in plants provides a resource distribution network for water and nutrients that exhibits remarkable diversity in patterning among different species. In many succulent plants, the vascular network includes longitudinally-oriented supplemental vascular bundles (SVBs) in the central core of the succulent stems and roots in addition to the more typical zone of vascular tissue development (vascular cambium) in a cylinder at the periphery of the succulent organ. Plant SVBs evolved in over 38 plant families often in tandem with evolutionary increases in stem and root parenchyma storage tissue, so it is of interest to understand the evolutionary-developmental processes responsible for their recurrent evolution and patterning. Previous mathematical models have successfully recreated the two-dimensional vascular patterns in stem and root cross sections, but such models have yet to recreate three-dimensional vascular patterning. Here, a stochastic reaction-diffusion model of plant vascular bundle patterning is developed in an effort to highlight a potential mechanism of three dimensional patterning–Turing pattern formation coupled with longitudinal efflux of a regulatory molecule. A relatively simple model of four or five molecules recreated empirical SVB patterns and many other common vascular arrangements. SVBs failed to develop below a threshold width of parenchymatous tissues, suggesting a mechanism of evolutionary character loss due to changes in the spatial context in which development takes place. Altered diffusion rates of the modeled activator and substrate molecules affected the number and size of the simulated SVBs. This work provides a first mathematical model employing a stochastic Turing-type mechanism that recreates three dimensional vascular patterns seen in plant stems. The model offers predictions that can be tested using molecular-genetic approaches. Evolutionary-developmental ramifications concerning evolution of diffusion rates, organ size and geometry are discussed. [ABSTRACT FROM AUTHOR]

Woodiness (secondary xylem derived from vascular cambium) has been gained and lost multiple times in the angiosperms, but has been lost ancestrally in all monocots. Here, we investigate the conservation of genes involved in xylogenesis in fully sequenced angiosperm genomes, hypothesizing that monocots have lost some essential orthologs involved in this process. We analyzed the conservation of genes preferentially expressed in the developing secondary xylem of two eudicot trees in the sequenced genomes of 26 eudicot and seven monocot species, and the early diverging angiosperm Amborella trichopoda. We also reconstructed a regulatory model of early vascular cambial cell identity and differentiation and investigated the conservation of orthologs across the angiosperms. Additionally, we analyzed the genome of the aquatic seagrass Zostera marina for additional losses of genes otherwise essential to, especially, secondary cell wall formation. Despite almost complete conservation of orthology within the early cambial differentiation gene network, we show a clear pattern of loss of genes preferentially expressed in secondary xylem in the monocots that are highly conserved across eudicot species. Our study provides candidate genes that may have led to the loss of vascular cambium in the monocots, and, by comparing terrestrial angiosperms to an aquatic monocot, highlights genes essential to vasculature on land. [ABSTRACT FROM AUTHOR]

Walnuts (Juglans , Juglandaceae) are known throughout the world as economically important trees that provide fat, protein, vitamins, and minerals as a food source, and produce high-quality timber. We have amended the purpose section to say "However," the omics resources are limited, which hampered the elucidation of molecular mechanisms resulting in their economically important traits (such as yield, fertility alternation, oil synthesis, and wood formation). To enrich the omics database of walnut, there is great need for analyses of its genomic and transcriptomic characteristics. In this study, we reported for the first time of the transcriptome landscape of six important organs or tissues in walnut interspecies hybrid using next-generation sequencing technology. Over 338 million clean reads were obtained. This yielded 74,072 unigenes with an average length of 782.71 bp. To develop an understanding of gene functions and regulatory pathways, 66,355 of the unigenes were identified as homologs of annotated genes and classified into three general categories with 61 functional subcategories. 2,288 out of 2,549 unmapped unigenes had at least one BLAST hit against the public databases. A total of 1,237 transcription factor-encoding genes (TFs) and 2,297 tissue-specific unigenes were identified. Interestingly, in the new shoot between an adult seedling and a grafted tree, the expression of 9,494 unigenes were significantly different, among which 4,388 were up-regulated and 5,106 were down-regulated. Of these, 195, 177, 232, 75, 114, and 68 unigenes were related to transcription factors, cell wall, defense response, transport, plant hormone biosynthesis, and other cambial activity-related functions, respectively. The obtained sequences and putative functional data constitute a resource for future functional analyses in walnut and other woody plants. These findings will be useful in further studies addressing the molecular mechanisms underlying grafting-related cambial activity. [ABSTRACT FROM AUTHOR]

Summary: Secondary growth from a vascular cambium, present today only in seed plants and isoetalean lycophytes, has a 400‐million‐yr evolutionary history that involves considerably broader taxonomic diversity, most of it hidden in the fossil record. Approaching vascular cambial growth as a complex developmental process, we review data from living plants and fossils that reveal diverse modes of secondary growth. These are consistent with a modular nature of secondary growth, when considered as a tracheophyte‐wide structural feature. This modular perspective identifies putative constituent developmental modules of cambial growth, for which we review developmental anatomy and regulation. Based on these data, we propose a hypothesis that explains the sources of diversity of secondary growth, considered across the entire tracheophyte clade, and opens up new avenues for exploring the origin of secondary growth. In this hypothesis, various modes of secondary growth reflect a mosaic pattern of expression of different developmental–regulatory modules among different lineages. We outline an approach that queries three information systems (living seed plants, living seed‐free plants, and fossils) and integrates data on developmental regulation, anatomy, gene evolution and phylogeny to test the mosaic modularity hypothesis and its implications, and to inform efforts aimed at understanding the evolution of secondary growth. [ABSTRACT FROM AUTHOR]

Xylem vessel structure changes as trees grow and mature. Age‐ and development‐related changes in xylem structure are likely related to changes in hydraulic function. We examined whether hydraulic function, including hydraulic conductivity and vulnerability to water‐stress‐induced xylem embolism, changed over the course of cambial development in the stems of 17 tree species. We compared current‐year growth of young (1–4 years), intermediate (2–7 years), and older (3–10 years) stems occurring in series along branches. Diffuse and ring porous species were examined, but nearly all species produced only diffuse porous xylem in the distal branches that were examined irrespective of their mature xylem porosity type. Vessel diameter and length increased with cambial age. Xylem became both more conductive and more cavitation resistant with cambial age. Ring porous species had longer and wider vessels and xylem that had higher conductivity and was more vulnerable to cavitation; however, these differences between porosity types were not present in young stem samples. Understanding plant hydraulic function and architecture requires the sampling of multiple‐aged tissues because plants may vary considerably in their xylem structural and functional traits throughout the plant body, even over relatively short distances and closely aged tissues. Vessel structure and stem hydraulic function varied with cambial age, with older stems producing tissue with larger vessels and greater hydraulic conductivity and cavitation resistance relative to younger stems. Xylem traits measured in younger distal stems are likely not indicative of mature wood traits for many species. [ABSTRACT FROM AUTHOR]

Key message: This paper provides an overview of radial growth and tree-ring formation of two tropical tree species used in ecological restoration. It shows that trees growing in natural forests and in plantations have the same diametric growth patterns and climate responses. Understanding the outcomes of ecological restoration projects represents an important step in the conservation of endangered biomes such as the Atlantic forest in Brazil. Tree-ring analysis provides long-term information about the growth dynamics of tree species that can be used to evaluate the potential of different species for restoration projects. To evaluate the potential of using Pseudobombax grandiflorum (Cav.) A. Robyns and Citharexylum myrianthum Cham. in restoration projects in the endangered Atlantic Rain Forest (Reserva Biológica de Poço das Antas—RBPA, Rio de Janeiro, Brazil), we verified the seasonality of tree-ring formation to analyze radial growth dynamics and climate–growth relationships of these species. Cambium wounding experiments and direct anatomical analysis of the cambial zone were conducted to assess tree-ring formation periodicity. Tree-ring widths were measured to build tree-ring chronologies and to estimate radial growth rates in natural and planted areas. Both species produced annual tree rings that are produced during the wet season. Tree-ring chronologies of both species have a positive association with rainfall, but each species also responded to rainfall of a specific season. Tree-ring widths of P. grandiflorum were correlated with rainfall at the end of the previous growth season while tree-ring widths of C. myrianthum were correlated with precipitation in the beginning of the growth season. Both species have fast radial growth, but different long-term growth trends. The growth trend for Pseudobombax grandiflorum produces a positive correlation between diameter and age for the trees, while trees of Citharexylum myrianthum have an age-related growth trend and grow faster in the early years. In the present study, we confirm the success of the ecological restoration performed in RBPA as the plantation does not affect the potential growth of the studied species. [ABSTRACT FROM AUTHOR]

Stem cell populations in meristematic tissues at distinct locations in the plant body provide the potency of continuous plant growth. Primary meristems, at the apices of the plant body, contribute mainly to the elongation of the main plant axes, whereas secondary meristems in lateral positions are responsible for the thickening of these axes. The stem cells of the vascular cambium—a secondary lateral meristem—produce the secondary phloem (bast) and secondary xylem (wood). The sites of primary and secondary growth are spatially separated, and mobile signals are expected to coordinate growth rates between apical and lateral stem cell populations. Although the underlying mechanisms have not yet been uncovered, it seems likely that hormones, peptides, and mechanical cues orchestrate primary and secondary growth. In this review, we highlight the current knowledge and recent discoveries of how cambial stem cell activity is regulated, with a focus on mobile signals and the response of cambial activity to environmental and stress factors. [ABSTRACT FROM AUTHOR]

Key message: Mg deficiency affected only the differentiation zone in Citrus sinensis roots. Phloem impairment in Mg-deficient leaves resulted in cell wall lignifications of both vascular cambium and spongy parenchyma cells. Decrease of Mg content in the roots hampered secondary lignification of endodermal and protoxylem cell walls.Abstract: Magnesium (Mg) is a vital nutrient for plant photosynthesis and biochemical reactions. Mg deficiency is a widespread problem in citrus production, directly affecting yield and quality. With the objective of investigating the relationship among root and leaf anatomy, photosynthetic efficiency and mineral nutrient uptake and transport in Mg-deficient citrus, the effects of Mg deficiency in 'Xuegan' (Citrus sinensis) seedlings on plant biomass, leaf gas exchange and chlorophyll, nutrient contents, root and leaf anatomy and lignin biosynthesis were studied. Mg deficiency decreased root and shoot dry weight, leaf CO2 assimilation, chlorophyll and Mg, phosphorus (P), boron (B), cupper (Cu) and iron (Fe) concentration in roots, stems and leaves, and increased potassium (K) and calcium (Ca) concentration. Mg deficiency in the leaves resulted in phloem disorder that blocked phloem transport, leading to carbohydrate accumulation in chloroplasts and secondary lignifications of both vascular cambium and spongy parenchyma cell walls. In contrast, decrease of Mg content in the roots hampered lignin deposition on the protoxylem and endodermal cell walls at the root differentiation zone. Poorly lignified Casparian strip and xylem cell walls in Mg-deficient root tips might decrease xylem loading efficiency of nutrients, lowering their contents in the above ground parts, which ultimately inhibited whole plant growth. [ABSTRACT FROM AUTHOR]

Premise of the Study: New growth in the spring requires resource mobilization in the vascular system at a time when xylem and phloem function are often reduced in seasonally cold climates. As a result, the timing of leaf out and/or flowering could depend on when the vascular system resumes normal function in the spring. This study investigated whether flowering time is influenced by vascular phenology in plants that flower precociously before they have leaves. Methods: Flower, leaf, and vascular phenology were monitored in pairs of precocious and non‐precocious congeners. Differences in resource allocation were quantified by measuring bud dry mass and water content throughout the year, floral hydration was modelled, and a girdling treatment completed on branches in the field. Key Results: Precocious flowering species invested more in floral buds the year before flowering than did their non‐precocious congeners, thus mobilizing less water in the spring, which allowed flowering before new vessel maturation. Conclusions: A shift in the timing of resource allocation in precocious flowering plants allowed them to flower before the production of mature vessels and minimized the significance of seasonal changes in vascular function to their flowering phenology. The low investment required to complete floral development in the spring when the plant vascular system is often compromised could explain why flowers can emerge before leaf out. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Yang et al. (2020), 226: 59–74. [ABSTRACT FROM AUTHOR]

All cell types of the secondary xylem arise from the meristematic cells (initials) of the vascular cambium and grow under mechanical constraints emerging from the circular-symmetrical geometry that characterises many tree trunks. The course of intrusive growth of cambial initials has been elucidated, but is yet to be described in the case of xylem fibres. This study explains the geometry of intrusive growth of the secondary xylem fibres in the trunk of Robinia pseudoacacia. Long series of serial semi-thin sections of the vascular cambium and the differentiating secondary xylem were analysed. Since fibres grow in close vicinity to expanding cells of the derivatives of the vascular cambium, we assumed that they have similar growth conditions. Dealing with the cylindrical tissue of the vascular cambium in a previous study, we used a circularly symmetrical equation for describing the growth mechanism of cambial initials. Like the cambial initials, some of the cambial derivatives differentiating into the various cell types composing the secondary xylem also exhibit intrusive growth between the tangential walls of adjacent cells. As seen in cross sections of the cambium, intrusively growing initials form slanted walls by a gradual transformation of tangential (periclinal) walls into radial (anticlinal) walls. Similarly, the intrusive growth of xylem fibres manifests initially as slants, which are formed due to axial growth of the growing cell tips along the tangential walls of adjacent cells. During this process, the tangential walls of adjacent cells are partly separated and dislocated from the tangential plane. The final shape of xylem fibres, or that of vessel elements and axial parenchyma cells, depends upon the ratio of their intrusive versus symplastic growths in the axial, circumferential and radial directions. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Dimensions and spatial distribution of vessels are critically important features of woody stems, allowing for adaptation to different environments through their effects on hydraulic efficiency and vulnerability to embolism. Although our understanding of vessel development is poor, basipetal transport of auxin through the cambial zone may play an important role. METHODS: Stems of Populus tremula x alba were treated with the auxin transport inhibitor N-1- naphthylphthalamic acid (NPA) in a longitudinal strip along the length of the lower stem. Vessel lumen diameter, circularity and length; xylem growth; tension wood area and hydraulic conductivity before and after a high pressure flush were determined on both NPA-treated and control plants. KEY RESULTS: NPA-treated stems formed aberrant vessels that were short, small in diameter, highly clustered and angular in cross section, whereas xylem formed on the untreated side of the stem contained typical vessels that were similar to those of controls. NPA-treated stems had reduced specific conductivity relative to controls, but this difference was eliminated by the high-pressure flush. The control treatment (lanolin + dimethyl sulfoxide) reduced xylem growth and increased tension wood formation, but never produced the aberrant vessel patterning seen in NPA-treated stems. CONCLUSIONS: These results are consistent with a model of vessel development in which basipetal polar auxin transport through the xylem-side cambial derivatives is required for proper expansion and patterning of vessels and demonstrate that reduced auxin transport can produce stems with altered stem hydraulic properties. [ABSTRACT FROM AUTHOR]

• This is the first study to report anatomy and endogenous hormonal profiles in the early seedling stage of kohlrabi. • The de novo formation of supplementary vascular bundles and phloem ring are the key features of kohlrabi stem. • IAA, IAAsp, GA and tZ profiles were significantly varied in the stems while the ABA profile was different in the leaves. • The stunted stem and vascular activity of cambium are positively correlated with endogenous GA and cytokinin in kohlrabi stem. To unveil the mechanism of tuberous stem formation at early growth stages in kohlrabi, the comparative stem morphology, anatomy, and endogenous plant hormone profiles were studied at different days after germination (10 to 30 DAG). Stem anatomy revealed that the notable feature of the kohlrabi stem during the transition from primary to secondary growth was the formation of vascular bundle circles, with many phloems formed separately and arranged in a circular pattern along with the cambium layer, resulting in an expanded ring of primary and secondary phloem. In addition, medullary supplemental vascular bundles were differentiated in the central region of pith and successively supplied small-sized meristematic parenchymatous cells which contribute to the tuber initiation in kohlrabi. Six phytohormones were quantified in the stems and leaves of both genotypes. The absence of Gibberellin A4 (GA4) in kohlrabi stem might be the cause of the stunted stem of kohlrabi. The total endogenous cytokinin in stem of kohlrabi was more than twice of that of broccoli, where trans-zeatin was the most abundant bioactive form. This can be explained by the meristematic nature of the cambium of kohlrabi stem. Profiles for Indole-3-acetic acid, Indole-3-acetylaspartic acid, and Abscisic acid of the stems and leaves of kohlrabi and broccoli were significantly different at several time points tested. Thus, the key features of kohlrabi during the initiation of tuberous stem were the formation of the phloem ring along with the cambium and the supplemental vascular bundles. This is the first paper showing the hormonal profile in the early seedling stage of kohlrabi. These findings provide useful information to elucidate the mechanism of tuberous stem formation of kohlrabi and other tuber crops. [ABSTRACT FROM AUTHOR]

Developmental initiation of plant vascular tissue, including xylem and phloem, from the vascular cambium depends on environmental factors, such as temperature and precipitation. Proper formation of vascular tissue is critical for the transpiration stream, along with photosynthesis as a whole. While effects of individual environmental factors on the transpiration stream are well studied, interactive effects of multiple stress factors are underrepresented. As expected, climate change will result in plants experiencing multiple co-occurring environmental stress factors, which require further studies. Also, the effects of the main climate change components (carbon dioxide, temperature, and drought) on vascular cambium are not well understood. This review aims at synthesizing current knowledge regarding the effects of the main climate change components on the initiation and differentiation of vascular cambium, the transpiration stream, and photosynthesis. We predict that combined environmental factors will result in increased diameter and density of xylem vessels or tracheids in the absence of water stress. However, drought may decrease the density of xylem vessels or tracheids. All interactive combinations are expected to increase vascular cell wall thickness, and therefore increase carbon allocation to these tissues. A comprehensive study of the effects of multiple environmental factors on plant vascular tissue and water regulation should help us understand plant responses to climate change.