Tracheary Elements Research Articles

Identification of cambium stem cell factors and their positioning mechanism.

Wood constitutes the largest reservoir of terrestrial biomass. Composed of xylem, it arises from one side of the vascular cambium, a bifacial stem cell niche that also produces phloem on the opposing side. It is currently unknown which molecular factors endow cambium stem cell identity. Here we show that TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF) ligand-activated PHLOEM INTERCALATED WITH XYLEM (PXY) receptors promote the expression of CAMBIUM-EXPRESSED AINTEGUMENTA-LIKE (CAIL) transcription factors to define cambium stem cell identity in the Arabidopsis root. By sequestrating the phloem-originated TDIF, xylem-expressed PXY confines the TDIF signaling front, resulting in the activation of CAIL expression and stem cell identity in only a narrow domain. Our findings show how signals emanating from cells on opposing sides ensure robust yet dynamically adjustable positioning of a bifacial stem cell layer.

The structure and interaction of polymers affects secondary cell wall banding patterns in Arabidopsis.

Xylem tracheary elements (TEs) synthesize patterned secondary cell walls (SCWs) to reinforce against the negative pressure of water transport. VASCULAR-RELATED NAC-DOMAIN 7 (VND7) induces differentiation, accompanied by cellulose, xylan, and lignin deposition into banded domains. To investigate the effect of polymer biosynthesis mutations on SCW patterning, we developed a method to induce tracheary element transdifferentiation of isolated protoplasts, by transient transformation with VND7. Our data showed that proper xylan elongation is necessary for distinct cellulose bands, cellulose-xylan interactions are essential for coincident polymer patterns, and cellulose deposition is needed to override the intracellular organization that yields unique xylan patterns. These data indicate that a properly assembled cell wall network acts as a scaffold to direct polymer deposition into distinctly banded domains. We describe the transdifferentiation of protoplasts into TEs, providing an avenue to study patterned SCW biosynthesis in a tissue-free environment and in various mutant backgrounds.

The Vascular Cambia of Dodder and its Allies

The vascular cambia of 20 species of the dodder and its allies belonging to the CassythaceaE, Convolvulaceae and Cuscutaceae were surveyed to assess their phenetic and phylogenetic significance. In natural condition all of them contain anomalous cambia. The Cassythaceae bore transitory cambium in the normal position but atypical by asmmetric activity. (The Cambium alternatelt retards accemtuates xylem formation on several segments and there are profuse sehizongenous spaces in wood. Haustoria contains both traheids and vessels).In stems and roots of the Convolvulaceae a series of widely different anomalous cambia were found which sometimes differed in stems and roots of the same species. Stems of arborescent group had bands of interxylary phloem in concentric rings, while in the primitive twiners these are arranged in radial plates. In general, a tendency was to increase the proportion of soft tissue. In Cuscutaceae the specified anomaly was the interfascicular cambium. Ray initials were absent but fusiform initials differentiated into profuse parenchyma cells and a few vessel elements.Haustorium develops only imperforate tracheary elements. The evolutionary history vascular cambium in the Convolvulaceae was mainly one of reduction in activity and area. Thus the vesselless haustorium of Cuscutaceae. may be regarded as a reduced farm in with the vessel bearing haustorium of Cassythaceae. It 1s also concluded that the primitive condition of Cuscutaceae is possibly derived from the general condition of Convolvulaceae.

Extracellular vesicles of Norway spruce contain precursors and enzymes for lignin formation and salicylic acid.

Lignin is a phenolic polymer in plants that rigidifies the cell walls of water-conducting tracheary elements and support-providing fibers and stone cells. Different mechanisms have been suggested for the transport of lignin precursors to the site of lignification in the cell wall. Extracellular vesicle (EV)-enriched samples isolated from a lignin-forming cell suspension culture of Norway spruce (Picea abies L. Karst.) contained both phenolic metabolites and enzymes related to lignin biosynthesis. Metabolomic analysis revealed mono-, di- and oligolignols in the EV isolates, as well as carbohydrates and amino acids. In addition, salicylic acid (SA) and some proteins involved in SA signaling were detected in the EV-enriched samples. A proteomic analysis detected several laccases, peroxidases, β-glucosidases, putative dirigent proteins, and cell wall-modifying enzymes such as glycosyl hydrolases, transglucosylase/hydrolases, and expansins in EVs. Our findings suggest that EVs are involved in transporting enzymes required for lignin polymerization in Norway spruce, and that radical coupling of monolignols can occur in these vesicles.

GhCKX1 is an important genetic target for improving fiber strength in cotton

Cotton is a widely grown crop to produce natural textile fiber, and improving the fiber strength (FS) is one of the main targets that cotton breeders focus on. The long-term natural selection and domestication have produced abundant germplasm resources of Gossypium hirsutum, and exploring genetic underpinnings underlying these FS innovation in elite collections is crucial. PCAMP is proposed as a most optimized NGS based bulked segregant analysis (NGS-BSA) for the high-resolution identification of markers linked to specific genomic regions through pairwise comparing multiple BSA bulks. In this study, we firstly applied PCAMP to resolved the FS genetic architecture in G. hirsutum cv. CCRI127. As an extension for PCAMP approach, graded bulks were constructed using F2 segregants with the FS phenotype revalidated by F2:3 lines, and then, a major QTL was eventually narrowed to 2.47 Mb from 8.14 Mb generated by traditional BSA approaches. Subsequently, through a saturated genetic map constructed in this locus, an novel FS gene, GhCKX1, predicted to produce a cytokinin (CTK) oxidase was isolated. It can negatively modulate the CTK signaling circuit via irreversible degradation of CTKs, resulting in an additional cell wall thickness to xylem tracheary elements in transgenic lines of Arabidopsis thaliana. Thus, the GhCKX1 gene will be an potential genetic target, with which, we can genetically manipulate the secondary wall synthesis in unicellular cotton fibers.

Analyses of high spatial resolution datasets identify genes associated with multi-layered secondary cell wall thickening in Pinus bungeana.

Secondary cell wall (SCW) thickening is a major cellular developmental stage determining wood structure and properties. Although the molecular regulation of cell wall deposition during tracheary element differentiation has been well established in primary growth systems, less is known about the gene regulatory processes involved in the multi-layered SCW thickening of mature trees. Using third-generation [long-read single-molecule real-time (SMRT)] and second-generation [short-read sequencing by synthesis (SBS)] sequencing methods, we established a Pinus bungeana transcriptome resource with comprehensive functional and structural annotation for the first time. Using these approaches, we generated high spatial resolution datasets for the vascular cambium, xylem expansion regions, early SCW thickening, late SCW thickening and mature xylem tissues of 71-year-old Pinus bungeana trees. A total of 79 390 non-redundant transcripts, 31 808 long non-coding RNAs and 5147 transcription factors were annotated and quantified in different xylem tissues at all growth and differentiation stages. Furthermore, using this high spatial resolution dataset, we established a comprehensive transcriptomic profile and found that members of the NAC, WRKY, SUS, CESA and LAC gene families are major players in early SCW formation in tracheids, whereas members of the MYB and LBD transcription factor families are highly expressed during late SCW thickening. Our results provide new molecular insights into the regulation of multi-layered SCW thickening in conifers. The high spatial resolution datasets provided can serve as important gene resources for improving softwoods.

Transcription factor PagMYB31 positively regulates cambium activity and negatively regulates xylem development in poplar.

Wood formation involves consecutive developmental steps, including cell division of vascular cambium, xylem cell expansion, secondary cell wall (SCW) deposition, and programmed cell death. In this study, we identified PagMYB31 as a coordinator regulating these processes in Populus alba × Populus glandulosa and built a PagMYB31-mediated transcriptional regulatory network. PagMYB31 mutation caused fewer layers of cambial cells, larger fusiform initials, ray initials, vessels, fiber and ray cells, and enhanced xylem cell SCW thickening, showing that PagMYB31 positively regulates cambial cell proliferation and negatively regulates xylem cell expansion and SCW biosynthesis. PagMYB31 repressed xylem cell expansion and SCW thickening through directly inhibiting wall-modifying enzyme genes and the transcription factor genes that activate the whole SCW biosynthetic program, respectively. In cambium, PagMYB31 could promote cambial activity through TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR (TDIF)/PHLOEM INTERCALATED WITH XYLEM (PXY) signaling by directly regulating CLAVATA3/ESR-RELATED (CLE) genes, and it could also directly activate WUSCHEL HOMEOBOX RELATED4 (PagWOX4), forming a feedforward regulation. We also observed that PagMYB31 could either promote cell proliferation through the MYB31-MYB72-WOX4 module or inhibit cambial activity through the MYB31-MYB72-VASCULAR CAMBIUM-RELATED MADS2 (VCM2)/PIN-FORMED5 (PIN5) modules, suggesting its role in maintaining the homeostasis of vascular cambium. PagMYB31 could be a potential target to manipulate different developmental stages of wood formation.

Conserved autophagy and diverse cell wall composition: unifying features of vascular tissues in evolutionarily distinct plants.

The formation of multifunctional vascular tissues represents a significant advancement in plant evolution. Differentiation of conductive cells is specific, involving two main pathways, namely protoplast clearance and cell wall modification. In xylogenesis, autophagy is a crucial process for complete protoplast elimination in tracheary elements, whose cell wall also undergoes strong changes. Knowledge pertaining to living sieve elements, which lose most of their protoplast during phloemogenesis, remains limited. We hypothesized that autophagy plays a crucial role, not only in complete cytoplasmic clearance in xylem but also in partial degradation in phloem. Cell wall elaborations of mature sieve elements are not so extensive. These analyses performed on evolutionarily diverse model species potentially make it possible to understand phloemogenesis to an equal extent to xylogenesis. We investigated the distribution of ATG8 protein, which is an autophagy marker, and cell wall components in the roots of ferns, gymnosperms and angiosperms (monocots, dicot herbaceous plants and trees). Furthermore, we conducted a bioinformatic analysis of complete data on ATG8 isoforms for Ceratopteris richardii. The presence of ATG8 protein was confirmed in both tracheary elements and sieve elements; however, the composition of cell wall components varied considerably among vascular tissues in the selected plants. Arabinogalactan proteins and β-1,4-galactan were detected in the roots of all studied species, suggesting their potential importance in phloem formation or function. In contrast, no evolutionary pattern was observed for xyloglucan, arabinan or homogalacturonan. Our findings indicate that the involvement of autophagy in plants is universal during the development of tracheary elements that are dead at maturity and sieve elements that remain alive. Given the conserved nature of autophagy and its function in protoplast degradation for uninterrupted flow, autophagy might have played a vital role in the development of increasingly complex biological organizations, including the formation of vascular tissues. However, different cell wall compositions of xylem and phloem in different species might indicate diverse functionality and potential for substance transport, which is crucial in plant evolution.

Responses of isolated balsam-fir stem segments to exogenous ACC, IAA, and IBA.

In this investigation, the effects of exogenous indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and 1-aminocyclopropane-1-carboxylic acid (ACC) on anatomical development within cultured segments of Abies balsamea (L.) Mill. were compared, using debudded and defoliated leaders produced in the preceding year as bioassay material. In stem apical regions, IAA promoted radial enlargement of pre-existing cortical resin ducts and attending parenchyma enlargement, whereas IBA promoted cell division and expansion of parenchyma on the outer edge of phloem without altering cortical duct shape. Cortical woody ducts, each partially surrounded by cambium, were observed as a novel but infrequent feature. A single cortical woody duct was spatially associated with each mature leaf as its vascular trace, and they were not encountered elsewhere in the cortex, nor were they induced to form in response to any hormone application. An unknown leaf factor induces the development of cortical woody ducts. Both IAA and IBA promoted cell division in the vascular cambium. The common cellular response at the interface between the latewood boundary and cambial zone was the radial expansion of primary-walled fusiform cambial cell derivatives with little if any ensuing tracheary element (TE) differentiation. Enhanced TE production at basal stem positions occurred when ACC was provided with IAA and/or IBA, and an IAA + IBA + ACC combination produced a basal stem response similar to that in untreated segments having intact leaves. The data support the conclusion that IAA, IBA, and ACC have distinct but complementary roles in the overall regulation of the types of cellular differentiation that contribute to cortex histogenesis and diameter growth of balsam-fir leaders.

Auxin resistant 1 gene (AUX1) mediates auxin effect on Arabidopsis thaliana callus growth by regulating its content and distribution pattern

Callus sustained growth relies heavily on auxin, which is supplied to the culture medium. Surprisingly, there is a noticeable absence of information regarding the involvement of carrier-mediated auxin polar transport gene in callus growth regulation. Here, we delve into the role of the AUXIN RESISTANT 1 (AUX1) influx transporter in the regulation of callus growth, comparing the effects under conditions of light versus darkness. It was observed that callus growth was significantly enhanced under light illumination. This growth-stimulatory effect was accompanied by a decrease in the levels of free auxin within the callus cells when compared to conditions of darkness. In the aux1–22 mutant callus, which lacks functional AUX1, there was a substantial reduction in IAA levels. Nonetheless, the mutant callus exhibited markedly higher growth rates compared to the wild type. This suggests that the reduction in exogenous auxin uptake through the AUX1-dependent pathway may prevent the overaccumulation of growth-restricting hormone concentrations. The growth-stimulatory effect of AUX1 deficiency was counteracted by nonspecific auxin influx transport inhibitors. This finding shows that other auxin influx carriers likely play a role in facilitating the diffusion of auxin from the culture medium to sustain high growth rates. AUX1 was primarily localized in the plasma membranes of the two outermost cell layers of the callus clump and the parenchyma cells adjacent to tracheary elements. Significantly, these locations coincided with the regions of maximal auxin concentration. Consequently, it can be inferred that AUX1 mediates the auxin distribution within the callus.

Inducible Pluripotent Suspension Cell Cultures (iPSCs) to Study Plant Cell Differentiation.

Inducing the differentiation of specific cell type(s) synchronously and on-demand is a great experimental system to understand the sequential progression of the cellular processes, their timing and their resulting properties for distinct isolated plant cells independently of their tissue context. The inducible differentiation in cell suspension cultures, moreover, enables to obtain large quantities of distinct cell types at specific development stage, which is not possible when using whole plants. The differentiation of tracheary elements (TEs) - the cell type responsible for the hydro-mineral sap conduction and skeletal support of plants in xylem tissues - has been the most studied using inducible cell suspension cultures. We herein describe how to establish and use inducible pluripotent suspension cell cultures (iPSCs) in Arabidopsis thaliana to trigger on-demand different cell types, such as TEs or mesophyll cells. We, moreover, describe the methods to establish, monitor, and modify the sequence, duration, and properties of differentiated cells using iPSCs.

Quantification of Tracheary Elements Types in Mature Hypocotyl of Arabidopsis thaliana.

Secondary growth is a highly relevant process for dicot and gymnosperm species development. The process relies on vascular tissue proliferation and culminates with the thickening of stems, roots, and hypocotyls. The formation of tracheary elements is a critical step during this process. Among such tracheary elements, four different cell types are distinguished depending on their secondary cell wall pattern, which is exclusive for each tracheary cell type. Here we describe a method to isolate, dye, and recognize each of these tracheary cell types. The method is optimized to be performed in the Arabidopsis thaliana hypocotyl. This is because, in this species, the hypocotyl is the organ undergoing the largest proportion of secondary growth. Results allow for determining the relative amounts of each of the tracheary cell types.

Evaluating Carlquist’s Law from a physiological perspective

Summary “Carlquist’s Law” is a striking pattern of association between anatomical features in the wood of vessel-bearing plants. It derives from Sherwin Carlquist’s observation that xylem vessels tend to be solitary when embedded in a matrix of imperforate tracheary elements that appear to be conductive, whereas xylem vessels tend to be grouped when surrounded by seemingly non-conductive cells. Vessel-vessel contacts (vessel grouping) allow water to travel between conduits, but also provide pathways for air to propagate from embolized (air-filled) vessels into functional vessels. If the background matrix is conductive, it is conceivable that water could bypass embolized vessels, providing an alternative transport route in species with conductive backgrounds and solitary vessels. Much remains to be tested in this hypothesis, including the topology of the vessel networks in species with solitary versus grouped vessels and how conductive the different imperforate tracheary element types are. Exploring Carlquist’s Law promises to provide key insight into the causes of embolism in plant conduits, the modes of embolism passage between conduits, and how vessels and the cells in which they are imbedded may interact to govern the pathways of water flow through plants.

Fire, frost, and drought constrain the structural diversity of wood within southern African Erica (Ericaceae)

Abstract Erica comprises ~860 species of evergreen shrubs and trees ranged from Europe to southern Africa and Madagascar. Wood structure of the around 20 European species is well studied, but despite its relevance to adaptation across the wider geographic range, it has not yet been explored across the much greater diversity, particularly of southern African lineages. In this study, we examine wood structure of 28 Erica species from southern Africa. In the African Erica clade, loss of scalariform perforation plates could be driven by increased aridity and seasonality in the mid-Miocene, and its re-gain can represent an adaptation to freezing in the high elevation species E. nubigena. As vessels in Erica are mostly solitary, imperforate tracheary elements probably form a subsidiary conduit network instead of vessel groups. Increase of ray frequency in habitats with a prominent dry and hot season probably facilitates refilling of vessels after embolism caused by water stress. Wider rays are ancestral for the lineage comprising African Erica and the Mediterranean E. australis. The negative correlation between ray width and expression of summer drought is consistent with Ojeda’s model explaining the diversification of seeders and resprouters among southern African Erica.

Testing Carlquistian hypotheses on the functional significance of vessel element length

Summary While total vessel length is widely recognized as being of fundamental functional significance, opinion is more divided regarding the potential functional importance of vessel element length, a variable that Sherwin Carlquist regarded as functionally significant. We show that vessel element length can, as Carlquist predicted, affect vessel resistance to deformation. Perforation plates are locally thickened annuli, so tubes with annuli resist deformation better than those without, and tubes with closely-spaced annuli resist deformation better than those with distantly spaced ones. However, there is a tradeoff between deformation resistance and conductance. With a comparative analysis across more than 1000 species of angiosperms, we show that both vessel element length and the areas of individual inter-conduit pits scale positively with vessel diameter. Such covariation is expected if plants are to maintain conductance as they grow taller. Congruent with Carlquist’s thinking, we found that species with vessel elements that are exceptionally short tend to grow in drylands, whereas those with vessel elements that are exceptionally long tend to grow in moist climates. Finally, we show evidence suggesting that selection on vessel element length is an important determinant of imperforate tracheary element length. Conversely, the evidence for selection on imperforate tracheary element length affecting vessel element length appears to be weaker. These results seem sufficient to establish that, whatever the functional importance of total vessel length, vessel element length is a variable of functional significance in its own right, congruent with Sherwin Carlquist’s long-held views.

Imperforate tracheary element classification for studies of xylem structure-function relations

Summary Discovering how xylem function emerges from xylem structure requires approaches that are distinct from those invented for wood identification. I exemplify this need for different approaches by discussing the classification of imperforate tracheary elements, the cells that go by names such as “fibers,” tracheids, fiber-tracheids, and libriform fibers. Currently, there are two classification systems, one for wood identification and one championed by Sherwin Carlquist for research on xylem function. I emphasize that neither is globally “correct” for all applications, but instead each is appropriate for the aims of its field. Wood identification uses an easily-applied classification of imperforate tracheary elements, designed to remain stable over the long term. This stability allows anatomists to build large databases of wood data that are maximally useful for wood identification. In contrast, functional xylem biologists need flexible definitions that serve as hypotheses of imperforate tracheary element function to be tested, modified, and tested again, in an open-ended process of refining knowledge of xylem structure-function relations. I highlight some of the many open questions that the functional classification points to, such as the morphological correlates of the conductive/nonconductive imperforate tracheary element distinction, how imperforate tracheary element features are associated with vessel grouping, whether the libriform fiber-fiber tracheid distinction is arbitrary or not, and other topics. Recognizing that the purpose of a functional classification is to drive research shifts focus away from debates about whether a given cell type classification is “correct” and onto the empirical priorities that need study. While there is a solid tradition within comparative wood anatomy of training in wood identification, there is a need to train functional comparative wood anatomists, who can guide and interact with xylem physiologists to build more robust explanations of xylem structure and function.

Nicotiana benthamiana XYLEM CYSTEINE PROTEASE genes facilitate tracheary element formation in interfamily grafting.

Grafting is a plant propagation technique widely used in agriculture. A recent discovery of the capability of interfamily grafting in Nicotiana has expanded the potential combinations of grafting. In this study, we showed that xylem connection is essential for the achievement of interfamily grafting and investigated the molecular basis of xylem formation at the graft junction. Transcriptome and gene network analyses revealed gene modules for tracheary element (TE) formation during grafting that include genes associated with xylem cell differentiation and immune response. The reliability of the drawn network was validated by examining the role of the Nicotiana benthamiana XYLEM CYSTEINE PROTEASE (NbXCP) genes in TE formation during interfamily grafting. Promoter activities of NbXCP1 and NbXCP2 genes were found in differentiating TE cells in the stem and callus tissues at the graft junction. Analysis of a Nbxcp1;Nbxcp2 loss-of-function mutant indicated that NbXCPs control the timing of de novo TE formation at the graft junction. Moreover, grafts of the NbXCP1 overexpressor increased the scion growth rate as well as the fruit size. Thus, we identified gene modules for TE formation at the graft boundary and demonstrated potential ways to enhance Nicotiana interfamily grafting.

Comparative functional analysis of PdeNAC2 and AtVND6 in the tracheary element formation.

Tracheary elements (i.e. vessel elements and tracheids) are highly specialized, non-living cells present in the water-conducting xylem tissue. In angiosperms, proteins in the VASCULAR-RELATED NAC-DOMAIN (VND) subgroup of the NAC (NAM, ATAF1,2, and CUC2) transcription factor family (e.g. AtVND6) are required for the differentiation of vessel elements through transcriptional regulation of genes responsible for secondary cell wall formation and programmed cell death. Gymnosperms, however, produce only tracheids, the mechanism of which remains elusive. Here, we report functional characteristics of PdeNAC2, a VND homolog in Pinus densiflora, as a key regulator of tracheid formation. Interestingly, our molecular genetic analyses show that PdeNAC2 can induce the formation of vessel element-like cells in angiosperm plants, demonstrated by transgenic overexpression of either native or NAC domain-swapped synthetic genes of PdeNAC2 and AtVND6 in both Arabidopsis and hybrid poplar. Subsequently, genome-wide identification of direct target (DT) genes of PdeNAC2 and AtVND6 revealed 138 and 174 genes as putative DTs, respectively, but only 17 genes were identified as common DTs. Further analyses have found that PdeNAC2 does not control some AtVND6-dependent vessel differentiation genes in angiosperm plants, such as AtVRLK1, LBD15/30 and pit-forming Rho-like GTPases from plant (ROP) signaling genes. Collectively, our results suggest that different target gene repertoires of PdeNAC2 and AtVND6 may contribute to the evolution of tracheary elements.

The role of imperforate tracheary elements and narrow vessels in wood capacitance of angiosperm trees

Summary There is a broad diversity of imperforate tracheary elements (ITEs) — libriform fibers, fiber-tracheids, true tracheids and vasicentric/vascular tracheids — described thoroughly by Sherwin Carlquist. However, in a quantitative sense, the functional meaning of different ITE types present in the wood of vessel-bearing angiosperms remains unclear because very few structure–function studies measure ITEs’ properties. ITEs with abundant pits and wide pit borders — vascular tracheids, vasicentric tracheids, and true tracheids sensu Carlquist — have been shown to conduct water and, thanks to this conductive ability and the multitude of pits, they could also contribute to wood capacitance. A dataset of 30 temperate angiosperm tree species was reanalysed to record the presence/absence of true, vasicentric, and vascular tracheids including data on conduits15 fraction and vessel-conduit15 contact fraction (conduits15 were defined as cells resembling vessels and with a maximum lumen diameter of 15 μm. They encompassed narrow vessels, vasicentric tracheids, and vessel tails). The presence of tracheids, conduits15 fraction, and contact fraction had no effect on wood capacitance, except, per given wood volumetric lumen water content, species with true tracheids tended to have lower capacitance. These results suggest that the presence of tracheids or conduits15 properties do not limit wood capacitance, but the results do not exclude the potential role these cells may play in internal water dynamics.

Parenchyma is not the sole site of storage: storage in living fibres

Summary Storage of nutrients and water are important functions of secondary xylem that have received much attention lately. In most of these studies, the storage role has been attributed to the fraction and arrangement of ray and axial parenchyma. However, in the current article, we show that in many species, especially those from tropical and subtropical regions (where most of the world’s plant species are found), nutrient and water storage is carried out by living imperforate tracheary elements (ITEs), colloquially termed “living fibres”. The occurrence of living fibres has been long recognized by anatomists, and especially emphasized in the work of Sherwin Carlquist. In spite of this, living fibres have remained largely unacknowledged by most plant physiologists and ecologists. To raise awareness about the existence of living fibres and to celebrate the illuminating work of Sherwin Carlquist, we summarize our current understanding of the structure, function, and occurrence of living fibres and emphasize that they should receive more attention when studying storage in wood.