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Carol A. Peterson - One of the best experts on this subject based on the ideXlab platform.
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permeability of iris germanica s multiseriate Exodermis to water nacl and ethanol
Journal of Experimental Botany, 2011Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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spatial and temporal deposition of suberin during maturation of the onion root Exodermis
Botany, 2011Co-Authors: Carol A. Peterson, Chris J Meyer, Mark A BernardsAbstract:Suberin is a complex biopolymer composed of a poly(aliphatic) domain (SPAD) and a poly(phenolic) domain (SPPD). Suberin is typically confined to specialized cell types including root exodermal cells, but its synthesis in a maturing Exodermis is still not well understood. For the current work, Allium cepa roots were used as a model to analyze SPAD and SPPD synthesis in a maturing uniseriate Exodermis. Roots were divided into four maturation zones based on their growth rate and the deposition of suberin lamellae in maturing exodermal cells. Exodermal and epidermal cell layers were separated from the underlying layers in each maturation zone, then soluble and insoluble suberin monomers were extracted chemically, and quantified and identified by gas chromatography – mass spectrometry. Temporal patterns for the synthesis of the SPAD, but not for the SPPD, were revealed upon resolution of the metabolite profiles. The composition of the soluble fraction was essentially unchanged as the Exodermis matured. In cont...
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Permeability of Iris germanica’s multiseriate Exodermis to water, NaCl, and ethanol
Journal of Experimental Botany, 2010Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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environmental effects on the maturation of the endodermis and multiseriate Exodermis of iris germanica roots
Annals of Botany, 2009Co-Authors: Chris J Meyer, James L. Seago, Carol A. PetersonAbstract:† Background and Aims Most studies of exodermal structure and function have involved species with a uniseriate Exodermis. To extend this work, the development and apoplastic permeability of Iris germanica roots with a multiseriate Exodermis (MEX) were investigated. The effects of different growth conditions on MEX maturation were also tested. In addition, the Exodermises of eight Iris species were observed to determine if their mature anatomy correlated with habitat. † Methods Plants were grown in soil, hydroponics (with and without a humid air gap) or aeroponics. Roots were sectioned and stained with various dyes to detect MEX development from the root apical meristem, Casparian bands, suberin lamellae and tertiary wall thickenings. Apoplastic permeability was tested using dye (berberine) and ionic (ferric) tracers. † Key Results The root apical meristem was open and MEX development non-uniform. In soil-grown roots, the Exodermis started maturing (i.e. Casparian bands and suberin lamellae were deposited) 10 mm from the tip, and two layers had matured by 70 mm. In both hydro- and aeroponically grown roots, exodermal maturation was delayed. However, in areas of roots exposed to an air gap in the hydroponic system, MEX maturation was accelerated. In contrast, maturation of the endodermis was not influenced by the growth conditions. The mature MEX had an atypical Casparian band that was continuous around the root circumference. The MEX prevented the influx and efflux of berberine, but had variable resistance to ferric ions due to their toxic effects. Iris species living in well-drained soils developed a MEX, but species in water-saturated substrates had a uniseriate Exodermis and aerenchyma. † Conclusions MEX maturation was influenced by the roots’ growth medium. The MEX matures very close to the root tip in soil, but much further from the tip in hydro- and aeroponic culture. The air gap accelerated maturation of the second exodermal layer. In Iris, the type of Exodermis was correlated with natural habitat suggesting that a MEX may be advantageous for drought tolerance.
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Suberin lamella development in maize seedling roots grown in aerated and stagnant conditions
Plant Cell and Environment, 2005Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:Hypoxia can stimulate the development of a suberized Exodermis in aquatic plants; however, its influence on this aspect of terrestrial root development is sparsely documented. To determine the effects of hypoxia on maize (Zea mays cv. Seneca Horizon) roots, seedlings were grown in vermiculite (VERM), aerated hydroponics (AER), stagnant hydroponics with agar (STAG), or aerated hydroponics with agar (AERAG). The endo- and Exodermis were examined for wall modifications. Lateral root emergence and aerenchyma formation were documented qualitatively. The endodermal Casparian band formation was unaffected by treatment. Endodermal and exodermal suberin lamella formation was earliest and most extensive in VERM. Suberization, especially in the Exodermis of aerated treatments, was depressed in all hydroponic media. In comparison with AER, STAG exodermal lamellae were increased, but endodermal lamellae were decreased. Since the suberized Exodermis forms a barrier to radial oxygen loss from roots to the medium, its stimulation in STAG roots (which also developed extensive aerenchyma) would help retain oxygen in the root. The reduction of endodermal lamellae should facilitate oxygen diffusion into the stele. Clearly, the response to environmental conditions is variable within individual cortical cell layers. Additionally, the observed patterns of lamellae, aerenchyma and lateral root development indicate a tight radial co-ordination of root development.
Ernst Steudle - One of the best experts on this subject based on the ideXlab platform.
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permeability of iris germanica s multiseriate Exodermis to water nacl and ethanol
Journal of Experimental Botany, 2011Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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Permeability of Iris germanica’s multiseriate Exodermis to water, NaCl, and ethanol
Journal of Experimental Botany, 2010Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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Blockage of apoplastic bypass‐flow of water in rice roots by insoluble salt precipitates analogous to a Pfeffer cell
Plant Cell and Environment, 2005Co-Authors: Kosala Ranathunge, Ernst Steudle, Renee LafitteAbstract:Precipitates of insoluble inorganic salts were used to clog apoplastic pores in cell walls of the outer part of rice roots (OPR) in two rice cultivars (lowland cv. IR64 and upland cv. Azucena). Aerenchyma of two different root zones (20‐ 50 and 50‐100 mm from the apex) was perfused with 1 m M potassium ferrocyanide (K 4 [Fe(CN) 6 ]) while the whole root segments were bathed in 0.5 m M copper sulphate (CuSO 4 ) medium. In another experiment, salts were applied on opposite sides of the OPR. The copper-ferrocyanide precipitation technique resembles the famous osmotic experiments of the German botanist Wilhelm Pfeffer, in which he used them with clay diaphragms. Precipitates were observed on the side where ferrocyanide was applied, suggesting that Cu 2 + and SO 4 2‐ were passing the barrier including the Casparian bands of the Exodermis much faster than ferrocyanide. There was a patchiness in the formation of precipitates, correlated with the maturation of the Exodermis. The intensity of copper ferrocyanide staining decreased along developing rice roots. No precipitates were observed in mature parts beyond 70‐80 mm from the root apex, except for sites around the emergence of secondary roots, which were fairly leaky to both water and ions. Blockage of the apoplastic pores with precipitates caused a three- to four-fold reduction of hydraulic conductivity of the OPR ( Lp OPR ). The reflection coefficient of the OPR ( s sOPR ) increased in response to the blockage with precipitates. The osmotic versus diffusive water permeability ratios of the OPR ( P fOPR / P dOPR ) were around 600 for immature and 1200 for mature root segments. Treatment significantly affected the bulk rather than the diffusive water flow and caused a three- to five-fold reduction of the P fOPR / P dOPR ratios. Results indicated that despite the existence of an Exodermis with Casparian bands, most of the water moved around cells rather than using the cell-to-cell passage.
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water permeability and reflection coefficient of the outer part of young rice roots are differently affected by closure of water channels aquaporins or blockage of apoplastic pores
Journal of Experimental Botany, 2004Co-Authors: Kosala Ranathunge, Ernst Steudle, Lukasz Kotula, Renee LafitteAbstract:The relative contribution of the apoplastic and cellto-cell paths to the overall hydraulic conductivity of the outer part of rice roots (LpOPR) was estimated using a pressure perfusion technique for 30-d-old rice plants (lowland cultivar, IR64, and upland cultivar, Azucena). The technique was based on the perfusion of aerenchyma of root segments from two different zones (20‐50 mm and 50‐100 mm from the root apex) with aerated nutrient solution using precise pump rates. The outer part of roots (OPR) comprised an outermost rhizodermis, an Exodermis, sclerenchyma fibre cells, and the innermost unmodified cortical cell layer. No root anatomical differences were observed for the two cultivars used. Development of apoplastic barriers such as Casparian bands and suberin lamellae in the Exodermis were highly variable. On average, matured apoplastic barriers were observed at around 50‐70 mm from the root apex. Lignification of the Exodermis was completed earlier than that of sclerenchyma cells. Radial water flow across the OPR was impeded either by partially blocking off the porous apoplast with China ink particles (diameter 50 nm) or by closing water channels (aquaporins) in cell membranes with 50 mM HgCl2. The reduction of LpOPR was relatively larger in the presence of an apoplastic blockage with ink (»30%) than in the presence of the water channel blocker (»10%) suggesting a relatively larger apoplastic water flow. The reflection coefficient of the OPR (ssOPR) for mannitol significantly increased during both treatments. It was larger when pores of the apoplast were closed, but absolute values were low (overall range of ssOPR=0.1‐0.4), which also suggested a large contribution of the non-selective, apoplastic path to overall water flow. The strongest evidence in favour of a predominantly apoplastic water transport came from the comparison between diffusional (PdOPR, measured with heavy water, HDO) and osmotic water permeability (PfOPR) or hydraulic conductivity (LpOPR). PfOPR was larger by a factor of 600‐1400 compared with PdOPR. The development of OPR along roots resulted in a decrease of PdOPR by a factor of three (segments taken at 20‐50 and 50‐100 mm from root apex, respectively). Heat-killing of living cells resulted in an increase of PdOPR for both immature (20‐50 mm) and mature (50‐100 mm) root segments by a factor of two. Even though both pathways (apoplast and cell-to-cell) contributed to the overall water flow, the findings indicate predominantly apoplastic water flow across the OPR, even in the presence of apoplastic barriers. Low diffusional water permeabilities may suggest a low rate of oxygen diffusion across the OPR from aerenchyma to the outer anaerobic soil medium (low PO2OPR). To date, there are no data on PO2OPR. Provisional data of radial oxygen losses (ROL) across the OPR suggest that, unlike water, rice roots efficiently retain oxygen within the aerenchyma. This ability strongly increases as roots/OPR develop.
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the Exodermis a variable apoplastic barrier
Journal of Experimental Botany, 2001Co-Authors: Eleonore Hose, Ernst Steudle, Lukas Schreiber, David T Clarkson, Wolfram HartungAbstract:The Exodermis (hypodermis with Casparian bands) of plant roots represents a barrier of variable resistance to the radial flow of both water and solutes and may contribute substantially to the overall resistance. The variability is a result largely of changes in structure and anatomy of developing roots. The extent and rate at which apoplastic exodermal barriers (Casparian bands and suberin lamellae) are laid down in radial transverse and tangential walls depends on the response to conditions in a given habitat such as drought, anoxia, salinity, heavy metal or nutrient stresses. As Casparian bands and suberin lamellae form in the Exodermis, the permeability to water and solutes is differentially reduced. Apoplastic barriers do not function in an all-or-none fashion. Rather, they exhibit a selectivity pattern which is useful for the plant and provides an adaptive mechanism under given circumstances. This is demonstrated for the apoplastic passage of water which appears to have an unusually high mobility, ions, the apoplastic tracer PTS, and the stress hormone ABA. Results of permeation properties of apoplastic barriers are related to their chemical composition. Depending on the growth regime (e.g. stresses applied) barriers contain aliphatic and aromatic suberin and lignin in different amounts and proportion. It is concluded that, by regulating the extent of apoplastic barriers and their chemical composition, plants can effectively regulate the uptake or loss of water and solutes. Compared with the uptake by root membranes (symplastic and transcellular pathways), which is under metabolic control, this appears to be an additional or compensatory strategy of plants to acquire water and solutes.
Daryl E Enstone - One of the best experts on this subject based on the ideXlab platform.
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Suberin lamella development in maize seedling roots grown in aerated and stagnant conditions
Plant Cell and Environment, 2005Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:Hypoxia can stimulate the development of a suberized Exodermis in aquatic plants; however, its influence on this aspect of terrestrial root development is sparsely documented. To determine the effects of hypoxia on maize (Zea mays cv. Seneca Horizon) roots, seedlings were grown in vermiculite (VERM), aerated hydroponics (AER), stagnant hydroponics with agar (STAG), or aerated hydroponics with agar (AERAG). The endo- and Exodermis were examined for wall modifications. Lateral root emergence and aerenchyma formation were documented qualitatively. The endodermal Casparian band formation was unaffected by treatment. Endodermal and exodermal suberin lamella formation was earliest and most extensive in VERM. Suberization, especially in the Exodermis of aerated treatments, was depressed in all hydroponic media. In comparison with AER, STAG exodermal lamellae were increased, but endodermal lamellae were decreased. Since the suberized Exodermis forms a barrier to radial oxygen loss from roots to the medium, its stimulation in STAG roots (which also developed extensive aerenchyma) would help retain oxygen in the root. The reduction of endodermal lamellae should facilitate oxygen diffusion into the stele. Clearly, the response to environmental conditions is variable within individual cortical cell layers. Additionally, the observed patterns of lamellae, aerenchyma and lateral root development indicate a tight radial co-ordination of root development.
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root endodermis and Exodermis structure function and responses to the environment
Journal of Plant Growth Regulation, 2002Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:Roots of virtually all vascular plants have an endodermis with a Casparian band, and the majority of angiosperm roots tested also have an Exodermis with a Casparian band. Both the endodermis and Exodermis may develop suberin lamellae and thick, tertiary walls. Each of these wall modifications has its own function(s). The endodermal Casparian band prevents the unimpeded movement of apoplastic substances into the stele and also prevents the backflow of ions that have moved into the stele symplastically and then were released into its apoplast. In roots with a mature Exodermis, the barrier to apoplastic inflow of ions occurs near the root surface, but prevention of backflow of ions from the stele remains a function of the endodermis. The suberin lamellae protect against pathogen invasion and possibly root drying during times of stress. Tertiary walls of the endodermis and Exodermis are believed to function in mechanical support of the root, but this idea remains to be tested. During stress, root growth rates decline, and the endodermis and Exodermis develop closer to the root tip. In two cases, stress is known to induce the formation of an Exodermis, and in several other cases to accelerate the development of both the Exodermis and endodermis. The responses of the endodermis and Exodermis to drought, exposure to moist air, flooding, salinity, ion deficiency, acidity, and mechanical impedance are discussed.
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Effects of exposure to humid air on epidermal viability and suberin deposition in maize (Zea mays L.) roots
Plant Cell and Environment, 1998Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:When the basal zones of 4-d-old hydroponically grown maize (Zea mays L. cv. Seneca Horizon) roots were exposed to moist air for 2 d, the development of both endodermis and Exodermis was affected. In the endodermis, Casparian bands enlarged and more cells developed suberin lamellae. The most striking effect was seen in the Exodermis. In submerged controls, only 4% of the cells had Casparian bands, whereas in root regions exposed to air, 93% developed these structures. Similarly, in submerged roots 11% of the exodermal cells had either developing or mature suberin lamellae compared with 92% in the air-treated region. The majority of epidermal cells remained alive in the zone exposed to air. Some cell death had occurred earlier in the experiment when the seedlings were transferred from vermiculite to hydroponic culture. The precise stimulus(i) associated with the air treatment which led to accelerated development in both endodermis and Exodermis is as yet unknown.
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suberin deposition and band plasmolysis in the corn zea mays l root Exodermis
Botany, 1997Co-Authors: Daryl E Enstone, Carol A. PetersonAbstract:The exodermal Casparian band in corn (Zea mays L.) was first seen 10 mm distal to the kernel 4 days after planting. From its inception, the band usually occupied most of the radial wall (as seen in a cross section of the root). Subsequent maturation of the band around the root was asynchronous into the region of emerging lateral roots. Thus, a continuous apoplastic barrier would have been absent over much of the young root surface. Suberin lamellae development was also asynchronous, as these structures formed in those cells which had Casparian bands. Frequently, a lamella was initially deposited in patches, progressing centripetally until a continuous lipid layer was formed around the cell protoplast. Many instances of band plasmolysis (typical of the endodermis) were observed in the developing uniform Exodermis. It could occur in cells with no detectable Casparian bands, suggesting that the tight connection between the plasmalemma and the wall that causes this phenomenon is not due to hydrophobic attract...
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functions of passage cells in the endodermis and Exodermis of roots
Physiologia Plantarum, 1996Co-Authors: Carol A. Peterson, Daryl E EnstoneAbstract:Passage cells frequently occur in the endodermis and Exodermis but are not ubiquitous in either layer. Passage cells occur in the form of short cells in the dimorphic type of Exodermis. In both layers, Casparian bands are formed in all cells, but the subsequent development of suberin lamellae and thick, cellulosic walls are delayed or absent in the passage cells. Available evidence suggests that passage cells of the endodermis are important for the transfer of calcium and magnesium into the stele and thus into the transpiration stream. They become the only cells which present a plasmalemma surface to the soil solution (and are thus capable of ion uptake) when the epidermis and central cortex die. This occurs naturally in some herbaceous and woody species and is known to be promoted by drought. Most evidence indicates that the development of suberin lamellae in both the endodermis and Exodermis increases the resistance of the root to the radial flow of water. Passage cells thus provide areas of low resistance for the movement of water, and the position of these cells in the endodermis (i.e., in close proximity to the xylem) is explained in terms of function. Exodermal passage cells have a cytoplasmic structure suggesting an active role in ion uptake. This may be related to the tendency of the epidermis to die, leaving the passage cells as the only ones with their membranes exposed to the soil solution. Passage cells in the Exodermis attract endomycorrhizal fungi while those in the endodermis do not. It is clear that passage cells of the endodermis and Exodermis play a variety of roles in the plant root system.
Chris J Meyer - One of the best experts on this subject based on the ideXlab platform.
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permeability of iris germanica s multiseriate Exodermis to water nacl and ethanol
Journal of Experimental Botany, 2011Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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spatial and temporal deposition of suberin during maturation of the onion root Exodermis
Botany, 2011Co-Authors: Carol A. Peterson, Chris J Meyer, Mark A BernardsAbstract:Suberin is a complex biopolymer composed of a poly(aliphatic) domain (SPAD) and a poly(phenolic) domain (SPPD). Suberin is typically confined to specialized cell types including root exodermal cells, but its synthesis in a maturing Exodermis is still not well understood. For the current work, Allium cepa roots were used as a model to analyze SPAD and SPPD synthesis in a maturing uniseriate Exodermis. Roots were divided into four maturation zones based on their growth rate and the deposition of suberin lamellae in maturing exodermal cells. Exodermal and epidermal cell layers were separated from the underlying layers in each maturation zone, then soluble and insoluble suberin monomers were extracted chemically, and quantified and identified by gas chromatography – mass spectrometry. Temporal patterns for the synthesis of the SPAD, but not for the SPPD, were revealed upon resolution of the metabolite profiles. The composition of the soluble fraction was essentially unchanged as the Exodermis matured. In cont...
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Permeability of Iris germanica’s multiseriate Exodermis to water, NaCl, and ethanol
Journal of Experimental Botany, 2010Co-Authors: Chris J Meyer, Carol A. Peterson, Ernst SteudleAbstract:The Exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate Exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the Exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature Exodermis) and on air-gapexposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5310 28 to 3.9310 28 ms 21 MPa 21 . Puncturing the MEX increased Lppc to 19310 28 ms 21 MPa 21 , indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress.
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environmental effects on the maturation of the endodermis and multiseriate Exodermis of iris germanica roots
Annals of Botany, 2009Co-Authors: Chris J Meyer, James L. Seago, Carol A. PetersonAbstract:† Background and Aims Most studies of exodermal structure and function have involved species with a uniseriate Exodermis. To extend this work, the development and apoplastic permeability of Iris germanica roots with a multiseriate Exodermis (MEX) were investigated. The effects of different growth conditions on MEX maturation were also tested. In addition, the Exodermises of eight Iris species were observed to determine if their mature anatomy correlated with habitat. † Methods Plants were grown in soil, hydroponics (with and without a humid air gap) or aeroponics. Roots were sectioned and stained with various dyes to detect MEX development from the root apical meristem, Casparian bands, suberin lamellae and tertiary wall thickenings. Apoplastic permeability was tested using dye (berberine) and ionic (ferric) tracers. † Key Results The root apical meristem was open and MEX development non-uniform. In soil-grown roots, the Exodermis started maturing (i.e. Casparian bands and suberin lamellae were deposited) 10 mm from the tip, and two layers had matured by 70 mm. In both hydro- and aeroponically grown roots, exodermal maturation was delayed. However, in areas of roots exposed to an air gap in the hydroponic system, MEX maturation was accelerated. In contrast, maturation of the endodermis was not influenced by the growth conditions. The mature MEX had an atypical Casparian band that was continuous around the root circumference. The MEX prevented the influx and efflux of berberine, but had variable resistance to ferric ions due to their toxic effects. Iris species living in well-drained soils developed a MEX, but species in water-saturated substrates had a uniseriate Exodermis and aerenchyma. † Conclusions MEX maturation was influenced by the roots’ growth medium. The MEX matures very close to the root tip in soil, but much further from the tip in hydro- and aeroponic culture. The air gap accelerated maturation of the second exodermal layer. In Iris, the type of Exodermis was correlated with natural habitat suggesting that a MEX may be advantageous for drought tolerance.
Wolfram Hartung - One of the best experts on this subject based on the ideXlab platform.
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Lateral ABA transport in maize roots (Zea mays): visualization by immunolocalization.
Journal of Experimental Botany, 2004Co-Authors: Daniela Schraut, Cornelia I. Ullrich, Wolfram HartungAbstract:: The intensity of an ABA (abscisic acid) signal as a root-to-shoot signal, as well as its action on root hydraulic conductivity, strongly depends on the distribution of ABA during its radial transport across roots. Therefore ABA was visualized by immunolocalization with monoclonal ABA antibodies under conditions of lateral water flow induced by the application of a pressure gradient to the cut surface of the mesocotyl of maize seedlings. From the labelling of rhizodermis, hypodermis, cortical cells, and endodermis of roots of hydroponically (no Exodermis) and aeroponically (with Exodermis) grown seedlings it is concluded that the Exodermis acts as a barrier to apoplastic transport that controls ABA uptake and efflux, but that the endodermis can easily be overcome via an apoplastic bypass. In longitudinal sections the strongest ABA signals originated from the root cap and the meristematic root tip, which is in agreement with the non-vacuolated cells of these tissues being an effective anion trap for ABA.
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the Exodermis a variable apoplastic barrier
Journal of Experimental Botany, 2001Co-Authors: Eleonore Hose, Ernst Steudle, Lukas Schreiber, David T Clarkson, Wolfram HartungAbstract:The Exodermis (hypodermis with Casparian bands) of plant roots represents a barrier of variable resistance to the radial flow of both water and solutes and may contribute substantially to the overall resistance. The variability is a result largely of changes in structure and anatomy of developing roots. The extent and rate at which apoplastic exodermal barriers (Casparian bands and suberin lamellae) are laid down in radial transverse and tangential walls depends on the response to conditions in a given habitat such as drought, anoxia, salinity, heavy metal or nutrient stresses. As Casparian bands and suberin lamellae form in the Exodermis, the permeability to water and solutes is differentially reduced. Apoplastic barriers do not function in an all-or-none fashion. Rather, they exhibit a selectivity pattern which is useful for the plant and provides an adaptive mechanism under given circumstances. This is demonstrated for the apoplastic passage of water which appears to have an unusually high mobility, ions, the apoplastic tracer PTS, and the stress hormone ABA. Results of permeation properties of apoplastic barriers are related to their chemical composition. Depending on the growth regime (e.g. stresses applied) barriers contain aliphatic and aromatic suberin and lignin in different amounts and proportion. It is concluded that, by regulating the extent of apoplastic barriers and their chemical composition, plants can effectively regulate the uptake or loss of water and solutes. Compared with the uptake by root membranes (symplastic and transcellular pathways), which is under metabolic control, this appears to be an additional or compensatory strategy of plants to acquire water and solutes.
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apoplastic transport of abscisic acid through roots of maize effect of the Exodermis
Planta, 2000Co-Authors: Elenor Freundl, Ernst Steudle, Wolfram HartungAbstract:The exodermal layers that are formed in maize roots during aeroponic culture were investigated with respect to the radial transport of cis-abscisic acid (ABA). The decrease in root hydraulic conductivity (Lpr) of aeroponically grown roots was stimulated 1.5-fold by ABA (500 nM), reaching Lpr values of roots lacking an Exodermis. Similar to water, the radial flow of ABA through roots (JABA) and ABA uptake into root tissue were reduced by a factor of about three as a result of the existence of an Exodermis. Thus, due to the cooperation between water and solute transport the development of the ABA signal in the xylem was not affected. This resulted in unchanged reflection coeffcients for roots grown hydroponically and aeroponically. Despite the well-accepted barrier properties of exodermal layers, it is concluded that the endodermis was the more effective filter for ABA. Owing to concentration polarisation effects, ABA may accumulate in front of the endodermal layer, a process which, for both roots possessing and lacking an Exodermis, would tend to increase solvent drag and hence ABA movement into the xylem sap at increased water flow (JVr). This may account for the higher ABA concentrations found in the xylem at greater pressure difference.