xylem
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The release of water from storage compartments to the transpiration stream is an important functional mechanism that provides the buffering of sudden fluctuations in water potential. The ability of tissues to release water per change in water potential, referred to as hydraulic capacitance, is assumed to be associated with the anatomy of storage tissues. However, information about how specific anatomical parameters determine capacitance is limited. In this study, we measured sapwood capacitance (C) in terminal branches and roots of five temperate tree species (Fagus sylvatica L., Picea abies L., Quercus robur L., Robinia pseudoacacia L., Tilia cordata Mill.). Capacitance was calculated separately for water released mainly from capillary (CI; open vessels, tracheids, fibres, intercellular spaces and cracks) and elastic storage compartments (CII; living parenchyma cells), corresponding to two distinct phases of the moisture release curve. We found that C was generally higher in roots than branches, with CI being 3-11 times higher than CII Sapwood density and the ratio of dead to living xylem cells were most closely correlated with C In addition, the magnitude of CI was strongly correlated with fibre/tracheid lumen area, whereas CII was highly dependent on the thickness of axial parenchyma cell walls. Our results indicate that water released from capillary compartments predominates over water released from elastic storage in both branches and roots, suggesting the limited importance of parenchyma cells for water storage in juvenile xylem of temperate tree species. Contrary to intact organs, water released from open conduits in our small wood samples significantly increased CI at relatively high water potentials. Linking anatomical parameters with the hydraulic capacitance of a tissue contributes to a better understanding of water release mechanisms and their implications for plant hydraulics.
- MeSH
- dřevo anatomie a histologie MeSH
- stromy anatomie a histologie MeSH
- voda metabolismus MeSH
- xylém metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
BACKGROUND AND AIMS: The increasing frequency of disturbances in temperate forests is responsible for the greater numbers of trees with mechanically damaged cambial zones. Adjustment of wood anatomical structure to balance between safe and efficient water conductivity is one mechanism trees employ to cope with mechanical damage. The relative role of disturbances, tree age and climate in shaping xylem conduits and affecting xylem hydraulic conductivity remains unknown. METHODS: We performed an experiment with five different mechanical treatments simulating natural disturbances of juvenile Betula pendula trees (stem scarring, tilting, decapitation, root exposure and stem-base burial). After 3 years, trees were cut down, conduit size and density were measured, and specific hydraulic conductivity of each tree ring was calculated. Between-tree and between-year variability in xylem conductivity was decomposed into effects of tree age, climate and disturbances using linear mixed-effects models. KEY RESULTS: Xylem-specific hydraulic conductivity decreased significantly after treatment in decapitated, tilted and scarred trees. In the last treatment, wood anatomical adjustment was restricted to the area next to the callus tissue zone; in contrast, specific hydraulic conductivity declined over the entire stem circumference after tilting or decapitation. The response of trees with buried stems and exposed roots was generally weak. The overall effect of disturbances on inter-annual variability of wood anatomical structure was greater than the contribution of tree age and climate. CONCLUSIONS: The results indicate that disturbances are important drivers of xylem hydraulic conductivity. Expected increases in the frequency and intensity of disturbances may alter the theoretical capacity of forest stands for water conductance with a feedback to climate.
Plant vascular tissue is essential for the exchange of water, nutrients, metabolic products, and signals among distant organs in cormophytes. The compositions of phloem and xylem saps are highly dependent on many internal and external factors, and thus their analysis provides a valuable insight into plant physiology, growth, and development as well as nutrition status or presence of biotic or abiotic stresses. Capillary electrophoresis characterized by highly efficient separations and minuscule sample requirements represents a suitable analytical technique for this purpose because the sap constitutes a complex mixture with generally minimal availability. This review aims at providing a comprehensive overview of published capillary electrophoretic methods for the analysis of primary components present in the phloem and xylem saps of higher plants.
Bending and torsional properties of young roots and stems were measured in nine woody angiosperms. The variation in mechanical parameters was correlated to wood anatomical traits and analysed with respect to the other two competing functions of xylem (namely storage and hydraulics). Compared with stems, roots exhibited five times greater flexibility in bending and two times greater flexibility in torsion. Lower values of structural bending and structural torsional moduli (Estr and Gstr, respectively) of roots compared with stems were associated with the presence of thicker bark and a greater size of xylem cells. Across species, Estr and Gstr were correlated with wood density, which was mainly driven by the wall thickness to lumen area ratio of fibres. Higher fractions of parenchyma did not translate directly into a lower wood density and reduced mechanical stiffness in spite of parenchyma cells having thinner, and in some cases less lignified, cell walls than fibres. The presence of wide, partially non-lignified rays contributed to low values of Estr and Gstr in Clematis vitalba. Overall, our results demonstrate that higher demands for mechanical stability in self-supporting stems put a major constraint on xylem structure, whereas root xylem can be designed with a greater emphasis on both storage and hydraulic functions.
Ion-mediated changes in hydraulic conductivity (ΔKh) represent a mechanism allowing plants to regulate the rate of xylem transport. However, the significance of ΔKh for ring-porous (RPS) and diffuse-porous tree species (DPS) remains unknown. Here, we examined ΔKh in young branches of three coexisting, temperate RPS (Fraxinus excelsior, Quercus robur, Robinia pseudoacacia) and three DPS (Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica) across the whole year, and assessed the relationships of ΔKh to branch anatomy. Ring-porous species exhibited twice as high ΔKh (10.3% vs 5.3%) within the growing season (i.e., during wood production) compared with DPS, and the production of the annual ring was identified as a crucial process affecting maximum ΔKh within the season. In addition, xylem in branches of RPS generally contained more axial parenchyma (AP; 18% vs 7%) and was characterized by a greater relative contact fraction between vessels and parenchyma (FVP; 59% vs 18%) than xylem in DPS. Simultaneously, ΔKh measured within the growing season was positively correlated with AP, FVP and bark proportions, suggesting that parenchyma in branches may be important for high ΔKh. Significant increase in ΔKh observed during the growing season may help RPS to restore conductive capacity after winter, better compensate transport loss by drought-induced embolism and thereby improve water delivery to leaves.
The interaction between xylem phenology and climate assesses forest growth and productivity and carbon storage across biomes under changing environmental conditions. We tested the hypothesis that patterns of wood formation are maintained unaltered despite the temperature changes across cold ecosystems. Wood microcores were collected weekly or biweekly throughout the growing season for periods varying between 1 and 13 years during 1998-2014 and cut in transverse sections for assessing the onset and ending of the phases of xylem differentiation. The data set represented 1321 trees belonging to 10 conifer species from 39 sites in the Northern Hemisphere and covering an interval of mean annual temperature exceeding 14 K. The phenological events and mean annual temperature of the sites were related linearly, with spring and autumnal events being separated by constant intervals across the range of temperature analysed. At increasing temperature, first enlarging, wall-thickening and mature tracheids appeared earlier, and last enlarging and wall-thickening tracheids occurred later. Overall, the period of wood formation lengthened linearly with the mean annual temperature, from 83.7 days at -2 °C to 178.1 days at 12 °C, at a rate of 6.5 days °C(-1) . April-May temperatures produced the best models predicting the dates of wood formation. Our findings demonstrated the uniformity of the process of wood formation and the importance of the environmental conditions occurring at the time of growth resumption. Under warming scenarios, the period of wood formation might lengthen synchronously in the cold biomes of the Northern Hemisphere.
- MeSH
- cévnaté rostliny * MeSH
- ekosystém MeSH
- nízká teplota * MeSH
- roční období MeSH
- stromy MeSH
- vývoj rostlin MeSH
- xylém * MeSH
- Publikační typ
- časopisecké články MeSH
The development and growth of plants, as well as their successful adaptation to a variety of environments, is highly dependent on the conduction of water, nutrients and other important molecules throughout the plant body. Xylem is a specialized vascular tissue that serves as a conduit of water and minerals and provides mechanical support for upright growth. Wood, also known as secondary xylem, constitutes the major part of mature woody stems and roots. In the past two decades, a number of key factors including hormones, signal transducers and (post)transcriptional regulators have been shown to control xylem formation. We outline the main mechanisms shown to be essential for xylem development in various plant species, with an emphasis on Arabidopsis thaliana, as well as several tree species where xylem has a long history of investigation. We also summarize the processes which have been shown to be instrumental during xylem maturation. This includes mechanisms of cell wall formation and cell death which collectively complete xylem cell fate.
We investigated feasibility of the Full-length complementary DNA OvereXpression (FOX) system as a mutagenesis approach in poplar, using developing xylem tissue. The main goal was to assess the overall mutation rate and if the system will increase instances of mutants affected in traits linked to the xylem tissue. Indeed, we found a high mutation rate of 17.7%, whereas 80% of all mutants were significantly affected in cellulose, lignin and/or hemicellulose. Cell wall biosynthesis is a major process occurring during xylem development. Enrichment of mutants affected in cell wall composition suggests that the tissue source for the FOX library influenced the occurrence of mutants affected in a trait linked to this tissue. Additionally, we found that FLcDNAs from mutants affected in cell wall composition were homologous to genes known to be involved in cell wall biosynthesis and most recovered FLcDNAs corresponded to genes whose native expression was highest in xylem. We characterized in detail a mutant line with increased diameter. The phenotype was caused by a poplar homolog of LONELY GUY 1 (LOG1), which encodes an enzyme in cytokinin biosynthesis and significantly increased xylem proliferation. The causative role of LOG1 in the observed phenotype was further reaffirmed by elevated cytokinin concentration in the mutant and recapitulation overexpression experiment wherein multiple independent lines phenocopied the original FOX mutant. Our experiments show that the FOX approach can be efficiently used for gene discovery and molecular interrogation of traits specific to woody perennial growth and development.
- MeSH
- buněčná stěna genetika metabolismus MeSH
- dřevo * genetika metabolismus MeSH
- genová knihovna MeSH
- lignin metabolismus MeSH
- mutační rychlost MeSH
- Populus * genetika metabolismus MeSH
- regulace genové exprese u rostlin genetika MeSH
- rostlinné proteiny genetika metabolismus MeSH
- xylém genetika metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Xylem vulnerability to embolism represents an essential trait for the evaluation of the impact of hydraulics in plant function and ecology. The standard centrifuge technique is widely used for the construction of vulnerability curves, although its accuracy when applied to species with long vessels remains under debate. We developed a simple diagnostic test to determine whether the open-vessel artefact influences centrifuge estimates of embolism resistance. Xylem samples from three species with differing vessel lengths were exposed to less negative xylem pressures via centrifugation than the minimum pressure the sample had previously experienced. Additional calibration was obtained from non-invasive measurement of embolism on intact olive plants by X-ray microtomography. Results showed artefactual decreases in hydraulic conductance (k) for samples with open vessels when exposed to a less negative xylem pressure than the minimum pressure they had previously experienced. X-Ray microtomography indicated that most of the embolism formation in olive occurs at xylem pressures below -4.0 MPa, reaching 50% loss of hydraulic conductivity at -5.3 MPa. The artefactual reductions in k induced by centrifugation underestimate embolism resistance data of species with long vessels. A simple test is suggested to avoid this open vessel artefact and to ensure the reliability of this technique in future studies.
- MeSH
- nemoci rostlin * MeSH
- Olea fyziologie MeSH
- voda metabolismus MeSH
- xylém metabolismus fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
Cortical microtubules (MTs) play a major role in the patterning of secondary cell wall (SCW) thickenings in tracheary elements (TEs) by determining the sites of SCW deposition. The EXO70A1 subunit of the exocyst secretory vesicle tethering complex was implicated to be important for TE development via the MT interaction. We investigated the subcellular localization of several exocyst subunits in the xylem of Arabidopsis thaliana and analyzed the functional significance of exocyst-mediated trafficking in TE development. Live cell imaging of fluorescently tagged exocyst subunits in TE using confocal microscopy and protein-protein interaction assays were performed to describe the role of the exocyst and its partners in TE development. In TEs, exocyst subunits were localized to the sites of SCW deposition in an MT-dependent manner. We propose that the mechanism of exocyst targeting to MTs involves the direct interaction of exocyst subunits with the COG2 protein. We demonstrated the importance of a functional exocyst subunit EXO84b for normal TE development and showed that the deposition of SCW constituents is partially compromised, possibly as a result of the mislocalization of secondary cellulose synthase in exocyst mutants. We conclude that the exocyst complex is an important factor bridging the pattern defined by cortical MTs with localized secretion of the SCW in developing TEs.
- MeSH
- Arabidopsis růst a vývoj metabolismus ultrastruktura MeSH
- biologické modely MeSH
- buněčná diferenciace MeSH
- buněčná membrána metabolismus MeSH
- buněčná stěna metabolismus MeSH
- cévní svazky rostlin metabolismus MeSH
- glukosyltransferasy metabolismus MeSH
- konzervovaná sekvence MeSH
- mikrotubuly metabolismus ultrastruktura MeSH
- mutace genetika MeSH
- podjednotky proteinů metabolismus MeSH
- proteiny huseníčku metabolismus MeSH
- xylém cytologie růst a vývoj metabolismus ultrastruktura MeSH
- Publikační typ
- časopisecké články MeSH
