xylem development
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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.
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
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.
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
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
Variation in xylem vessel diameter is one of the most important parameters when evaluating plant water relations. This review provides a synthesis of the ecophysiological implications of variation in lumen diameter together with a summary of our current understanding of vessel development and its endogenous regulation. We analyzed inter-specific variation of the mean hydraulic vessel diameter (Dv ) across biomes, intra-specific variation of Dv under natural and controlled conditions, and intra-plant variation. We found that the Dv measured in young branches tends to stay below 30 µm in regions experiencing winter frost, whereas it is highly variable in the tropical rainforest. Within a plant, the widest vessels are often found in the trunk and in large roots; smaller diameters have been reported for leaves and small lateral roots. Dv varies in response to environmental factors and is not only a function of plant size. Despite the wealth of data on vessel diameter variation, the regulation of diameter is poorly understood. Polar auxin transport through the vascular cambium is a key regulator linking foliar and xylem development. Limited evidence suggests that auxin transport is also a determinant of vessel diameter. The role of auxin in cell expansion and in establishing longitudinal continuity during secondary growth deserve further study.
Although the significance of apoplasmic barriers in roots with regards to the uptake of toxic elements is generally known, the contribution of apoplasmic bypasses (ABs) to cadmium (Cd) hyperaccumulation is little understood. Here, we employed a combination of stable isotopic tracer techniques, an ABs tracer, hydraulic measurements, suberin lamellae staining, metabolic inhibitors, and antitranspirants to investigate and quantify the impact of the ABs on translocation of Cd to the xylem in roots of a hyperaccumulating (H) ecotype and a non-hyperaccumulating (NH) ecotype of Sedum alfredii. In the H ecotype, the Cd content in the xylem sap was proportional to hydrostatic pressure, which was attributed to pressure-driven flow via the ABs. The contribution of the ABs to Cd transportation to the xylem was dependent on the Cd concentration applied to the H ecotype (up to 37% at the highest concentration used). Cd-treated H ecotype roots showed significantly higher hydraulic conductance compared with the NH ecotype (76 vs 52 × 10–8 m s–1MPa–1), which is in accordance with less extensive suberization due to reduced expression of suberin-related genes. The main entry sites of apoplasmically transported Cd were localized in the root apexes and lateral roots of the H ecotype, where suberin lamellae were not well developed. These findings highlight the significance of the apoplasmic bypass in Cd hyperaccumulation in hyperaccumulating ecotypes of S. alfredii.
Several electrical methods have been introduced as non-invasive techniques to overcome the limited accessibility to root systems. Among them, the earth impedance method (EIM) represents the most recent development. Applying an electrical field between a cormus and the rooted soil, the EIM measures the absorptive root surface area (ARSA) from grounding resistance patterns. Allometric relationships suggested that this method was a valuable tool. Crucial assumptions for the applicability of the EIM, however, have not been tested experimentally. Focusing on tree root systems, the present study assesses the applicability of the EIM. Six hypotheses, deduced from the EIM approach, were tested in several experiments and the results were compared with conventional methods. None of the hypotheses could be verified and the results allow two major conclusions. First, in terms of an analogue electrical circuit, a tree-root-soil continuum appears as a serial circuit with xylem and soil resistance being the dominant components. Allometric variation in contact resistance, with the latter being the proxy for root surface area, are thus overruled by the spatial and seasonal variation of soil and xylem resistances. Second, in a tree-root-soil continuum, distal roots conduct only a negligible portion of the electric charge. Most of charge carriers leave the root system in the proximal parts of the root-soil interface.
- MeSH
- algoritmy MeSH
- biometrie MeSH
- cykasy MeSH
- elektrická impedance MeSH
- kořeny rostlin anatomie a histologie fyziologie MeSH
- Magnoliopsida MeSH
- průmyslová hnojiva MeSH
- půda MeSH
- roční období MeSH
- stromy anatomie a histologie fyziologie MeSH
- xylém fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Determining the pH values of microscopic plant samples may help to explain complex processes in plants, so it is an area of interest to botanists. Fiber-optic probes with small dimensions can be used for this purpose. This paper deals with the fiber-optic detection of the pH values of droplets of plant xylem exudate based on ratiometric fluorescence intensity measurements with an internal reference. For this purpose, novel V-taper sensing probes with a minimum diameter of around 8 μm were prepared that enable the delivery of fluorescence signal from the detection site on the taper tip to the detector. The taper tips were coated with pH-sensitive transducer (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt; HPTS) and a reference [dichlorotris-(1,10-phenanthroline) ruthenium (II) hydrate (Ru-phen dichloride)] immobilized in a xerogel layer of propyltriethoxysilane and (3-glycidoxy)propyl trimethoxysilane. The prepared probes were sensitive to pH values mainly in the range from 6.0 to 9.0. In the pH range 6-9, the results were limited by measurement errors of about 0.2 pH units, and in the pH range 5-6 by measurement errors of about 0.5 pH units. Using the developed V-taper sensing probes, the pH values of in vivo and in vitro samples of small volumes (~6 μl) of exudate were measured. The results were validated by comparison with conventional electrochemical pH measurements.
