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Changes in the Differentiation Program of Birch Cambial Derivatives following Trunk Girdling. FORESTS 2022. [DOI: 10.3390/f13081171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
The mechanisms regulating the tree trunk radial growth can be studied in original experiments. One technique for studying cambium activity (the meristem involved in radial growth) under conditions of an increased photoassimilate level is trunk girdling. We girdled the trunks of 17- to 22-year-old silver birch plants (Betula pendula Roth var. pendula) during the active growth period and collected xylem and phloem samples at two height levels (1 cm and 35 cm) above girdle, 10, 20, and 30 days after girdling. We investigated the changes that occurred at the anatomical level, as well as the activities of sucrose-metabolizing enzymes and antioxidant-system enzymes and the expression of genes that encode proteins involved in sucrose and auxin transport and metabolism. A moderate increase in photoassimilates (35 cm above the girdle) resulted in a change in the ratio of phloem to xylem increments and an increase in the proportion of parenchyma in the conducting tissues. The increase of photoassimilates above the level at which they can be used in the processes of normal tissue growth and development (1 cm above the girdle) led to xylogenesis suppression and the stimulation of phloem formation, a significant increase in the parenchyma proportion in the conducting tissues, and formation of large sclereid complexes. The differentiation of parenchyma and sclereid cells coincided with biochemical and molecular markers of abnormal conducting tissue formation in Karelian birch, which are also characterized by high proportions of parenchyma and sclereid near the cambium. The results obtained are important in understanding the cambium responses to the photoassimilate distribution changes and estimating tree productivity and survival under changing environmental conditions.
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Sevanto S. Methods for Assessing the Role of Phloem Transport in Plant Stress Responses. Methods Mol Biol 2019; 2014:311-336. [PMID: 31197806 DOI: 10.1007/978-1-4939-9562-2_25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Delivery of carbohydrates to tissues that need them under stress is important for plant defenses and survival. Yet, little is known on how phloem function is altered under stress, and how that influences plant responses to stress. This is because phloem is a challenging tissue to study. It consists of cells of various types with soft cell walls, and the cells show strong wounding reactions to protect their integrity, making both imaging and functional studies challenging. This chapter summarizes theories on how phloem transport is affected by stress and presents methods that have been used to gain the current knowledge. These techniques range from tracer studies and imaging to carbon balance and anatomical analyses. Advances in these techniques in the recent years have considerably increased our ability to investigate phloem function, and application of the new methods on plant stress studies will help provide a more comprehensive picture of phloem function and its limitations under stress.
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Affiliation(s)
- Sanna Sevanto
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
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De Schepper V, De Swaef T, Bauweraerts I, Steppe K. Phloem transport: a review of mechanisms and controls. JOURNAL OF EXPERIMENTAL BOTANY 2013; 64:4839-50. [PMID: 24106290 DOI: 10.1093/jxb/ert302] [Citation(s) in RCA: 157] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
It is generally believed that an osmotically generated pressure gradient drives the phloem mass flow. So far, this widely accepted Münch theory has required remarkably few adaptations, but the debate on alternative and additional hypotheses is still ongoing. Recently, a possible shortcoming of the Münch theory has been pointed out, suggesting that the Münch pressure flow is more suitable for herbs than for trees. Estimation of the phloem resistance indicates that a point might be reached in long sieve tubes where the pressure required to drive the Münch flow cannot be generated. Therefore, the relay hypothesis regained belief as it implies that the sieve tubes are shorter then the plant's axial axis. In the source phloem, three different loading strategies exist which probably result from evolutionary advantages. Passive diffusion seems to be the most primitive one, whereas active loading strategies substantially increase the growth potential. Along the transport phloem, a leakage-retrieval mechanism is observed. Appreciable amounts of carbohydrates are lost from the sieve tubes to feed the lateral sinks, while a part of these lost carbohydrates is subsequently reloaded into the sieve tubes. This mechanism is probably involved to buffer short-term irregularities in phloem turgor and gradient. In the long term, the mechanism controls the replenishment and remobilization of lateral stem storage tissues. As phloem of higher plants has multiple functions in plant development, reproduction, signalling, and growth, the fundamental understanding of the mechanisms behind phloem transport should be elucidated to increase our ability to influence plant growth and development.
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Affiliation(s)
- Veerle De Schepper
- Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
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De Schepper V, Bühler J, Thorpe M, Roeb G, Huber G, van Dusschoten D, Jahnke S, Steppe K. (11)C-PET imaging reveals transport dynamics and sectorial plasticity of oak phloem after girdling. FRONTIERS IN PLANT SCIENCE 2013; 4:200. [PMID: 23785380 PMCID: PMC3684848 DOI: 10.3389/fpls.2013.00200] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 05/29/2013] [Indexed: 05/02/2023]
Abstract
Carbon transport processes in plants can be followed non-invasively by repeated application of the short-lived positron-emitting radioisotope (11)C, a technique which has rarely been used with trees. Recently, positron emission tomography (PET) allowing 3D visualization has been adapted for use with plants. To investigate the effects of stem girdling on the flow of assimilates, leaves on first order branches of two-year-old oak (Quercus robur L.) trees were labeled with (11)C by supplying (11)CO2-gas to a leaf cuvette. Magnetic resonance imaging gave an indication of the plant structure, while PET registered the tracer flow in a stem region downstream from the labeled branches. After repeated pulse labeling, phloem translocation was shown to be sectorial in the stem: leaf orthostichy determined the position of the phloem sieve tubes containing labeled (11)C. The observed pathway remained unchanged for days. Tracer time-series derived from each pulse and analysed with a mechanistic model showed for two adjacent heights in the stem a similar velocity but different loss of recent assimilates. With either complete or partial girdling of bark within the monitored region, transport immediately stopped and then resumed in a new location in the stem cross-section, demonstrating the plasticity of sectoriality. One day after partial girdling, the loss of tracer along the interrupted transport pathway increased, while the velocity was enhanced in a non-girdled sector for several days. These findings suggest that lateral sugar transport was enhanced after wounding by a change in the lateral sugar transport path and the axial transport resumed with the development of new conductive tissue.
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Affiliation(s)
- Veerle De Schepper
- Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent UniversityGhent, Belgium
| | - Jonas Bühler
- IBG-2: Plant Sciences, Forschungszentrum JülichJülich, Germany
| | - Michael Thorpe
- IBG-2: Plant Sciences, Forschungszentrum JülichJülich, Germany
- Research School of Biology, Australian National UniversityCanberra, ACT, Australia
- High Resolution Plant Phenomics Centre, CSIRO Plant IndustryCanberra, ACT, Australia
| | - Gerhard Roeb
- IBG-2: Plant Sciences, Forschungszentrum JülichJülich, Germany
| | - Gregor Huber
- IBG-2: Plant Sciences, Forschungszentrum JülichJülich, Germany
| | | | | | - Kathy Steppe
- Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent UniversityGhent, Belgium
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Goodsman DW, Lusebrink I, Landhäusser SM, Erbilgin N, Lieffers VJ. Variation in carbon availability, defense chemistry and susceptibility to fungal invasion along the stems of mature trees. THE NEW PHYTOLOGIST 2013; 197:586-594. [PMID: 23157572 DOI: 10.1111/nph.12019] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 09/28/2012] [Indexed: 06/01/2023]
Abstract
If carbon (C) sinks withdraw carbohydrates as they are transported along tree stems, carbohydrate availability may depend on local sink strength and distance from sources. Defenses, including monoterpenes--a major component of resin--limit the invasibility of pines. Since carbohydrate reserves fund monoterpene synthesis, we hypothesized that monoterpene concentrations in pine stems would decrease from the crown to the lower stem, and susceptibility to fungal infection would increase. Here, we measured carbohydrate and monoterpene concentrations along the stems of lodgepole pine trees (Pinus contorta var. latifolia) before inoculating with a blue-stain fungus at different heights. After 6 wk, we assessed tree responses to fungal infection based on lesion length and carbohydrate mobilization. Concentrations of carbohydrates and monoterpenes in the phloem before inoculation decreased with distance from the crown, whereas lesion lengths after inoculation increased. However, trees mobilized sugars in response to fungal infection such that carbohydrate reserves near lesions were similar at all heights. Despite C mobilization, the lower stem was more vulnerable than the upper stem. Consistent with predictions based on sink-source relationships, vulnerability occurred where carbohydrates were less available, and likely resulted from C withdrawal by sinks higher in the supply chain.
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Affiliation(s)
- Devin W Goodsman
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB, Canada
| | - Inka Lusebrink
- Centre for Biological Sciences, University of Southampton, Southampton, UK
| | - Simon M Landhäusser
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB, Canada
| | - Nadir Erbilgin
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB, Canada
| | - Victor J Lieffers
- Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB, Canada
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De Schepper V, Vanhaecke L, Steppe K. Localized stem chilling alters carbon processes in the adjacent stem and in source leaves. TREE PHYSIOLOGY 2011; 31:1194-1203. [PMID: 22001166 DOI: 10.1093/treephys/tpr099] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Transport phloem is no longer associated with impermeable pipes, but is instead considered as a leaky system in which loss and retrieval mechanisms occur. Local stem chilling is often used to study these phenomena. In this study, 5-cm- lengths of stems of 3-year-old oak trees (Quercus robur L.) were locally chilled for 1 week to investigate whether observations at stem and leaf level can be explained by the leakage-retrieval mechanism. The chilling experiment was repeated three times across the growing season. Measurements were made of leaf photosynthesis, carbohydrate concentrations in leaves and bark, stem growth and maximum daily stem shrinkage. Across the growing season, a feedback inhibition in leaf photosynthesis was observed, causing increased dark respiration and starch concentration. This inhibition was attributed to the total phloem resistance which locally increased due to the cold temperatures. It is hypothesized that this higher phloem resistance increased the phloem pressure above the cold block up to the source leaves, inducing feedback inhibition. In addition, an increase in radial stem growth and carbohydrate concentration was observed above the cold block, while the opposite occurred below the block. These observations indicate that net lateral leakage of carbohydrates from the phloem was enhanced above the cold block and that translocation towards regions below the block decreased. This behaviour is probably also attributable to the higher phloem resistance. The chilling effects on radial stem growth and carbohydrate concentration were significant in the middle of the growing season, while they were not at the beginning and near the end of the growing season. Furthermore, maximum daily shrinkages were larger above the cold block during all chilling experiments, indicating an increased resistance in the xylem vessels, also generated by low temperatures. In conclusion, localized stem chilling altered multiple carbon processes in the source leaves and the main stem by changing hydraulic resistances.
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Affiliation(s)
- Veerle De Schepper
- Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
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Mencuccini M, Hölttä T. The significance of phloem transport for the speed with which canopy photosynthesis and belowground respiration are linked. THE NEW PHYTOLOGIST 2010; 185:189-203. [PMID: 19825019 DOI: 10.1111/j.1469-8137.2009.03050.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Ecosystem respiration is known to vary following changes in canopy photosynthesis. However, the timing of this coupling is not well understood. Here, we summarize the literature on soil and ecosystem respiration where the speed of transfer of photosynthetic sugars from the plant canopy via the phloem to the roots was determined. Estimates of the transfer speed can be grouped according to whether the study employed isotopic or canopy/soil flux-based techniques. These two groups should provide different estimates of transfer times because transport of sucrose molecules, and pressure-concentration waves, in phloem differ. A steady-state and a dynamic photosynthesis/phloem-transport/soil gas diffusion model were employed to interpret our results. Starch storage and partly soil gas diffusion affected transfer times, but phloem path-length strongly controlled molecule transfer times. Successful modelling required substantially different phloem properties (higher specific conductivity and turgor pressure difference) in tall compared with small plants, which is significant for our understanding of tall trees' physiology. Finally, we compared isotopic and flux-based approaches for the determination of the link between canopy photosynthesis and ecosystem respiration. We conclude that isotopic approaches are not well suited to document whether changes in photosynthesis of tall trees can rapidly affect soil respiration.
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Affiliation(s)
- Maurizio Mencuccini
- University of Edinburgh, School of GeoSciences, Crew Building, West Mains Road, EH9 3JN Edinburgh, UK.
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Hölttä T, Mencuccini M, Nikinmaa E. Linking phloem function to structure: analysis with a coupled xylem-phloem transport model. J Theor Biol 2009; 259:325-37. [PMID: 19361530 DOI: 10.1016/j.jtbi.2009.03.039] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 02/26/2009] [Accepted: 03/30/2009] [Indexed: 11/30/2022]
Abstract
We carried out a theoretical analysis of phloem transport based on Münch hypothesis by developing a coupled xylem-phloem transport model. Results showed that the maximum sugar transport rate of the phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the phloem. Because xylem water potential affected both xylem and phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the phloem and vice versa.
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Affiliation(s)
- T Hölttä
- School of GeoSciences, University of Edinburgh, Crew Building, West Mains Road, EH9 3JN Edinburgh, UK.
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Hölttä T, Vesala T, Perämäki M, Nikinmaa E. Refilling of embolised conduits as a consequence of 'Münch water' circulation. FUNCTIONAL PLANT BIOLOGY : FPB 2006; 33:949-959. [PMID: 32689305 DOI: 10.1071/fp06108] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2006] [Accepted: 07/27/2006] [Indexed: 06/11/2023]
Abstract
'Münch water' is pushed from the phloem to the xylem at locations of phloem sugar unloading. Consequently, an internal radial water potential imbalance is developed in the plant at these sugar-unloading sites. The phloem is at a higher water potential than the xylem. The magnitude of this radial water potential imbalance is determined by the magnitude of the radial water flux and the hydraulic resistance along the phloem-to-xylem pathway. If, as a result, the water potential in the ray parenchyma cells adjacent to xylem conduits is higher than that in the embolised xylem conduits, then a proportion of the water flow from the phloem would be directed towards embolised xylem conduits, in addition to conduits under tension. In this theoretical paper we demonstrate how recycled 'Münch water' passing from the phloem to the xylem can induce xylem embolism refilling. We also calculate the conditions and the structural composition of the phloem-to-xylem pathway that are required for embolism refilling by 'Münch water' circulation, and the time that is required for the complete refilling of embolised conduits in varying conditions.
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Affiliation(s)
- Teemu Hölttä
- School of GeoSciences, University of Edinburgh, Crew Building, West Mains Road, EH9 3JN Edinburgh, UK
| | - Timo Vesala
- Department of Physical Sciences, University of Helsinki, PO Box 64, FIN-00014 Helsinki, Finland
| | - Martti Perämäki
- Department of Forest Ecology, University of Helsinki, PO Box 24, FIN-00014 Helsinki, Finland
| | - Eero Nikinmaa
- Department of Forest Ecology, University of Helsinki, PO Box 24, FIN-00014 Helsinki, Finland
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