Water Free Space Research Articles

The Effect of Groundwater Level on Forced Convection Heat Transfer from a Buried Cylinder

The effect of groundwater level on forced convection heat transfer from a cylinder of 1 m in diameter buried at a depth of 10 m is studied numerically. The porosity and permeability of the soil are fixed at 0.5 and 1.0 × 10–11 m2, respectively, throughout the present study, while the inlet velocity U0 and the position of the phreatic surface (h), measured from the center of the cylinder, are varied in the ranges from 10–9 to 10–3 m s−1 and from − 4 to 4 m, respectively. Under these conditions, the heat fluxes on the cylinder are computed numerically. Various approximate solutions are also proposed and compared with those obtained numerically. The heat transfer results are also presented in nondimensional form for generality. The paper is divided into three parts, depending on the relative positions of the phreatic surface to the heated cylinder. First, the heat transfer rates are analyzed when the phreatic surface is above the cylinder, so that the cylinder is completely submerged in the water. In the second case, the phreatic surface is assumed to lie below the cylinder, so that the cylinder is left in the water-free space. In the third case, the phreatic surface is in contact with the cylinder surface, so that the cylinder is partially submerged in groundwater. For the above respective cases, three different approximate analyses are presented, and their validities and limitations are evaluated in comparison with the numerical calculations.

Development and Characterization of a Novel Bipedal Standing Mouse Model of Intervertebral Disc and Facet Joint Degeneration.

Intervertebral disc degeneration is a major cause of chronic low back pain, and excessive loading contributes to intervertebral disc degeneration. However, the lack of an effective bipedal in vivo animal model limits research about this condition. To evaluate the utility of a new type of bipedal standing mouse model for intervertebral disc degeneration, we asked: (1) Are there spinal degeneration changes in bipedal mice as determined by lumbar disc height, histologic features, and immunohistochemistry measures compared with control mice? (2) Are the bipedal mice comparable to aged mice for simulating the spinal degeneration caused by increased stress? Thirty-two 8-week-old male C57BL/6 mice were divided into experimental and control groups. Based on their hydrophobia, mice in the experimental group were placed in a limited water-containing space (5 mm deep) and were thereby induced to actively take a bipedal standing posture. This was conducted twice a day for a total of 6 hours a day, 7 days a week. Control mice were similarly placed in a limited but water-free space. Video surveillance was used to calculate the percentage of time spent in the bipedal stance for the two groups of mice. Compared with the control group, the percentage of time standing on both feet in the experimental group was higher (48% ± 5%, 95% confidence interval [CI], 42%-54% versus 95% ± 1%, 95% CI, 92%-97%; p < 0.001). Eight mice from both groups were then randomly euthanized at either 6 or 10 weeks and lumbar spine specimens (L3-L6) were collected. The lumbar disc height index (DHI%) of the two groups was compared using micro-CT measurements, and the extent of disc degeneration was assessed based on histologic staining (cartilage endplate height, disc degeneration score) and by immunohistochemistry (Col2a1,CollagenX, matrix metalloprotease-13 [MMP-13], osteocalcin [OCN]). In addition, the histopathologic features of spinal degeneration were compared with 12- and 18-month-old mice. A p value < 0.05 indicated a significant difference. Lumbar disc degeneration was aggravated after 10 weeks with the DHI% decreasing (5.0% ± 0.4%; 95% CI, 4.6%-5.5% versus 4.6 ± 0.3%; 95% CI, 4.3%-4.9%; p = 0.011). Histologically, the cartilage endplate height of the experimental group was decreased compared with the control group (30 ± 6 μm; 95% CI, 24-37 μm versus 70 ± 7 μm; 95% CI, 63-79 μm; p < 0.001), and the disc degeneration score was increased (5 ± 1; 95% CI, 4-6 versus 1 ± 1; 95% CI, 0-2; p < 0.001). Expression of Col2a1, vimentin, and aggrecan in the experimental group was decreased compared with the control group, whereas the expressions of collagen X (60% ± 2%; 95% CI, 55%-66% versus 19% ± 3%; 95% CI, 17%-24%; p < 0.001), MMP-13 (54% ± 8%; 95% CI, 49%-61% versus 1% ± 1%; 95% CI, 1%-2%; p < 0.001), and OCN (41% ± 3%; 95% CI, 34%-49% versus 5% ± 1%; 95% CI, 2%-7%, p < 0.001) were increased. The spine degeneration caused by this model was primarily manifested in the degeneration of the annulus fibrosus and facet joints compared with aged mice, whereas the degree of degeneration in the nucleus pulposus tissue and cartilage endplates was mild. We believe we have established a noninvasive and effective in vivo bipedal mouse model for studying disc degeneration and biologic signal transduction comparable to that seen in intervertebral disc degeneration. This in vivo mouse model of intervertebral disc degeneration can simulate the pathogenesis of spinal degeneration caused by increased stress and this can be used to study questions such as disc herniation in young adults.

Characteristics of III-nitride based laser diode employed for short range underwater wireless optical communications

An off-the-shelf green laser diode (LD) was measured to investigate its temperature dependent characteristics. Performance of the device was severely restricted by rising temperature in terms of increasing threshold current and decreasing modulation bandwidth. The observation reveals that dynamic characteristics of the LD is sensitive to temperature. Influence of light attenuation on the modulation bandwidth of the green LD was also studied. The impact of light attenuation on the modulation bandwidth of the LD in short and low turbid water channel was not obvious while slight difference in modulation bandwidth under same injection level was observed between water channel and free space even at short range.

1H NMR studies of molecular interaction of D-glucosamine and N-acetyl-D-glucosamine with capsaicin in aqueous and non-aqueous media

Complex formation of D-glucosamine (Gl) and N-acetyl-D-glucosamine (AGl) with capsaicin (Cp) were studied by 1H NMR titrations in H2O-d2 and DMSO-d6; capsaicin is the major bioactive component of chili peppers. Every titration curve has been interpreted by formulating a suitable model for the reaction equilibrium, to elucidate intermolecular interactions. In DMSO, glucosamine cations associate with each other to yield linear aggregates, and undergo pseudo-1:1-complexation with capsaicin, the formation constant being ca. 30 M−1. N-Acetylglucosamine, without self-association, forms a 2:1-complex AGl2Cp with the stability of ca. 70 M−2. These complexations are achieved by intermolecular hydrogen bonds. In D2O, glucosamine undergoes reversible protonation equilibrium between Gl0 and GlH+ with the logarithmic protonation constants log KD = 8.63 for α-glucosamine and 8.20 for β-isomer. Both anomeric isomers of deprotonated glucosamine form Gl0Cp-type complexes of capsaicin, in a competitive manner, with a formation constant of 1040 M−1 for the α-glucosamine complex and 830 M−1 for the β-complex; the anomeric carbons result in the difference in thermodynamic stability. The reactant molecules are closed up by the solvent-exclusion effect and/or the van der Waals interaction; the resulting pair is stabilized by intermolecular hydrogen bonding within a local water-free space between the component molecules. By contrast, neither protonated glucosamine (GlH+) nor N-acetylglucosamine yields a capsaicin complex with the definite stoichiometry. The monosaccharides recognize capsaicin under only a controlled condition; the same phenomena are predicted for biological systems and nanocarriers based on polysaccharides such as chitosan.

Calculation Procedure for Dynamic Condition of Ion Composition in Cell Walls Altered by Proton Fluxes

The calculation procedure has been developed to determine the dynamic condition of the ion composition in cell walls during proton extrusion, known as the Weak Acid Donnan Manning (WADM) model for fluxes. In this model, the walls of plant cells are considered as a system containing weak acid polymers where the interaction of ions obeys the Manning condensation theory and the Donnan theory. When protons are transported across the walls during proton fluxes, the transported proton will interact with the wall ions and alter the ion composition. This depends on the wall parameters such as the concentration of ionisable sites, the pK of the wall weak acid, and the wall linear charge density parameter. When the linear charge density parameter is still higher than the reciprocal of the highest valence of the involve cations, the transported protons during proton fluxes will decrease the wall pH, alter the ion composition in the wall Donnan free space and water free space, and release the condensed cations. Therefore some of the proton fluxes are represented by the flux of the condensed cations outside the walls. However when the linear charge density parameter is less than the reciprocal of the highest valence of the involve cations, there is no condensed cations in the walls so that the transported protons only alter the ion composition in the wall Donnan free space and water free space.

Short range continuous wave radar for target detection in various mediums

ABSTRACTThis article presents simulation and hardware implementation of a low cost radar that can be used as a speed sensor or a metal detector. The overall hardware costs only U.S. $25 and has maximum free space range of 3.65 m. Its underground range is 4.3 cm under wet soil conditions with free space distance of 50 cm above ground. The proposed model provides a basis for designing a mine detector based on the amplitude of the reflected wave. As the frequency of the wave or the water content of the ground increases, the amplitude of the reflected wave decreases making the detection difficult. A comparison between different attenuations offered to the signal under different soil conditions and different Target's materials is presented. The frequency selected for the design implementation was 10.525 GHz. A speed sensor module, HB100 miniature microwave motion sensor was used to sense the reflected wave and was interfaced with a frequency meter implemented using a microcontroller. The module transmitted a continuous wave with amplitude of 15 dBm. The wave reflected from the target was received by module's receiving antenna. It was amplified using a noninverting amplifier and was converted to pulses using a comparator. These pulses were fed to the in‐house microcontroller‐based frequency meter, and the speed of the target was observed on the LCD interfaced. Complete ground modeling for different water content and free space modeling was also done. The proposed model provides a low cost stand‐alone implementation of the overall radar. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2484–2489, 2014

Oxalate exudation into the root‐tip water free space confers protection from aluminum toxicity and allows aluminum accumulation in the symplast in buckwheat (Fagopyrum esculentum)

A better understanding of aluminum (Al) uptake and transport is expected to contribute to unravel the apparent contradiction between Al exclusion and Al accumulation in buckwheat. *We studied the effect of Al supply on the root-tip Al and oxalate concentrations of the apoplastic water free space fluid (WFSF) and the symplast as affected by temperature, oxalate supply and the anion-channel blocker phenylglyoxal (PG). *Aluminum supply rapidly activated the release of oxalate to the WFSF to establish a 1 : 1 Al to oxalate ratio. In the symplast, the Al concentration was 100 times higher than in the external solution, and the Al to oxalate ratio was 1 : 2. Loading and unloading of Al, but not of oxalate, into and from the symplast were reduced at low temperature and are thus under metabolic control. Application of PG reduced the constitutive and the Al-enhanced WFSF oxalate concentrations and enhanced Al-induced root-growth inhibition. Unlike a 1 : 3 Al to oxalate ratio, a 1 : 1 ratio ameliorated only partly Al-induced root-growth inhibition without affecting root-tip Al contents or WFSF Al concentrations. *We present a hypothesis with an Al oxalate (Ox)(+) plasma-membrane transporter in the root cortex and a xylem-loading Al citrate (Cit)(n-) transporter in the xylem parenchyma cells as key elements of Al accumulation in buckwheat.

Air bells of water spiders are an extended phenotype modified in response to gas composition

The water spider Argyroneta aquatica (Clerck) is the only spider that spends its whole life under water. Water spiders keep an air bubble around their body for breathing and build under-water air bells, which they use for shelter and raising offspring, digesting and consuming prey, moulting, depositing eggs and sperm, and copulating. It is unclear whether these bells are an important oxygen reservoir for breathing under water, or whether they serve mainly to create water-free space for feeding and reproduction. In this study, we manipulated the composition of the gas inside the bell of female water spiders to test whether they monitor the quality of this gas, and replenish oxygen if required. We exchanged the entire gas in the bell either with pure O2, pure CO2, or with ambient air as control, and monitored behavioural responses. The test spiders surfaced and replenished air more often in the CO2 treatment than in the O2 treatment, and they increased bell building behaviour. In addition to active oxygen regulation, they monitored and adjusted the bells by adding silk. These results show that water spiders use the air bell as an oxygen reservoir, and that it functions as an external lung, which renders it essential for living under water permanently. A. aquatica is the only animal that collects, transports, and stores air, and monitors its property for breathing, which is an adaptive response of a terrestrial animal to the colonization of an aquatic habitat.

Silicon nutrition of tomato and bitter gourd with special emphasis on silicon distribution in root fractions

AbstractTwo plant species, tomato (Lycopersicon esculentum Mill.) and bitter gourd (Momordica charantia), were used for in‐depth studies on the dynamics of silicon (Si) uptake and translocation to the shoots and compartmentation of Si in the roots. The experiments were conducted under controlled environmental conditions in nutrient solutions, which were partly amended with 1 mM Si in the form of silicic acid. At harvest, xylem exudates were collected, and Si concentrations and biomass of roots and shoots were determined. Mass flow of Si was calculated based on the Si concentration of the nutrient solution and transpiration determined in a parallel experiment. Plant roots were subjected to a fractionated Si analysis, allowing attributing Si to different root compartments. Silicon concentrations in the roots compared to the shoots were higher in tomato but lower in bitter gourd. A more ready translocation from the roots to the shoots in bitter gourd was in agreement with Si concentrations in the xylem exudates which were higher than in the external solution. In tomato, the xylem‐sap Si concentration was lower than in the nutrient solution. Calculated Si mass flow to the root exceeded Si uptake in tomato, which was consistent with the measured accumulation of Si in the root water‐free space (WFS). In contrast, Si concentration in the root WFS was lower than in the nutrient solution in bitter gourd, reflecting the calculated Si depletion at the root surface based on the comparison of Si mass flow and Si uptake. Within the roots, more than 80% of the total Si was located in the cell wall and less than 10% in the cytoplasmic fractions in tomato. In bitter gourd, between 60% and 70% of the total root Si was attributed to the cell‐wall fraction whereas the proportion of the cytoplasmic fraction reached more than 30%. Our results clearly confirm that tomato belongs to the Si excluders and bitter gourd to the Si‐accumulator plant species for which high Si concentrations in the cytoplasmic root fraction appear to be characteristic.

Effect of Postharvest Calcium Chloride Treatments on Tissue Water Relations, Cell Wall Calcium Levels and Postharvest Life of `Golden Delicious' Apples

Changes in tissue water relations, cell wall calcium (Ca) levels and physical properties of Ca-treated and untreated `Golden Delicious' apples (Malus×domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to 0.34 mol·L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreated fruit. Fruit that were pressure infiltrated with CaCl2 solutions between 0.14 and 0.20 mol·L-1 and then waxed to reduce water loss during storage showed no peel injury. Calcium efflux patterns from apple tissue disks indicated two distinct Ca compartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrations up to 0.20 mol·L-1, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The osmotic potential of apples harvested over three seasons ranged between-1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions up to 0.34 mol·L-1, turgor potential was ≥0.6 MPa in tissue incubated in 0.14 or 0.17 mol·L-1 solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (≤0.03 mol·L-1) or high (≥0.27 mol·L-1) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40% higher in Ca-than in sorbitol-treated tissue. The results suggest that postharvest treatment with 0.14 to 0.20 mol·L-1 solutions of CaCl2 are best for maintaining fruit water relations and storage life of `Golden Delicious' apples while minimizing the risk of salt-related injuries to the fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the risk of fruit injury.

Changes of the Apoplastic pH and K+Concentration in thePhaseolusPulvinusin situin Relation to Rhythmic Leaf Movements

The apoplastic pH and K+ concentration of the extensor of the Phaseolus primary-leaf pulvinus in relation to rhythmic leaf movements have been investigated with double-barrelled ion-sensitive micro-electrodes. Simultaneous measurements of leaf movement and ion activities in a fine hole of the extensor in situ showed co-existence of ultradian and circadian leaf movements as well as of ultradian and circadian pH changes in the Water Free Space (WFS) of the extensor apoplast in situ. During circadian leaf movement the H+ and K+ activities in the WFS of the extensor change in an antagonistic manner. When extensor cells swell (upward movement of the lamina) the H+ activity increases from approximately pH 6.7 to 5.9 and the K+ concentration decreases from approximately 50 to 10 mol m−3 and vice versa when extensor cells shrink. These changes in the ionic activities in the WFS must be correlated with large changes in the ion content of the DFS and thus support the hypothesis that the cell walls of pulvinar cells serve as reservoirs for K+ and H+.

Cell walls as reservoirs of potassium ions for reversible volume changes of pulvinar motor cells during rhythmic leaf movements

The laminar pulvinus of primary leaves of Phaseolus coccineus L. was investigated with respect to the total K(+) content, the apoplastic K(+) content, and the water potential of extensor and flexor sections in relation to the leaf positions in a circadian leaf-movement cycle, as well as the cation-exchange properties of isolated extensor- and flexor-cell walls. Turgid tissue showed a high total but low apoplastic K(+) content, shrunken tissue a low total but high apoplastic K(+) content. Thus, part of the K(+) transported into and out of the swelling or shrinking protoplasts is shuttled between the protoplasts and the surrounding walls, another part between different regions of the pulvinus. The K(+) fraction shuttled between protoplasts and walls was found to be 30-40% of the total transported K(+) fraction. Furthermore, 15-20% of the total K(+) content of the tissue is located in the apoplast when the apoplastic reservoir is filled, 5-10% when the apoplastic reservoir is depleted. The ion-exchange properties of walls of extensor and flexor cells appear identical in situ and in isolated preparations. The walls behave as cation exchangers of hhe weak-acid type with a strong dependence of the activity of fixed negative charges as well as of the K(+)-storing capacity on pH and [K(+)] of the equilibration solution. The high apoplastic K(+) contents of freshly cut tissues reflect the cation-storing capacity of the isolated walls. We suggest that K(+) ions of the Donnan free space are used for the reversible volume changes (mediating the leaf movement) mainly by an electrogenic proton pump which changes the pH and-or the [K(+)] in the water free space of the apoplast.

Relationships between Adsorption, Chemical State and Fluxes of Cadmium Applied as Cd(NO3)2in Isolated Xylem Cell Walls of Tomato

Wolterbeek, H. Th. 1987. Relationships between adsorption, chemical state and fluxes of cadmium applied as Cd(N03)2 in isolated xylem cell walls of tomato.—J. exp. Bot. 38: 419-432. Isolated xylem cell wall pieces were applied as membranes in ion diffusion experiments. The cell walls were isolated from tomato internodes (Lycopersicon esculentum Mill, cv. Tiny Tim) and sealed in a two-compartment diffusion system. In flux and adsorption calculations, the cell wall was regarded as a leaky membrane with parallel fluxes through Donnan Free Space (DFS) and Water Free Space (WFS). During the experiments absorption into and diffusion across the walls was determined of Cd2+, applied as 115Cd(N03)2. Flux experiments with 82Br indicated that excluded volume effects and path tortuosity resulted in apparent WFS diffusion coefficients in the walls which were 0 012 times as high as in water. The free proton concentration in the DFS was shown to be related to a complex formation between fixed charges and Cd2 + . The cell wall permeability for Cd2+ and NO, varied with applied and absorbed concentrations, and the Cd2+ flux curve showed an inflexion point coinciding with a buffered degree of dissociation of fixed charges in the DFS. The necessary coupling of fluxes of opposite charges resulted in relatively high N03 and small Cd2+ permeability of the DFS for strongly diluted solutions (P = 104 m s' and I CP11 m s-1 for NOf and Cd2+ respectively). The results demonstrate the possible regulatory effects of the cell wall in processes of ion transfer from xylem vessels, or ion uptake in plant tissues. Key words—Cadmium, chemical state, DFS, WFS, ion flux, permeability, xylem cell walls, tomato, bromium, nitrate. Correspondence to: Interuniversitair Reactor Institute, Mekelweg 15,2629 JB Delft, The Netherlands.

Activity of Fixed Negative Charges of Isolated Extensor Cell Walls of the Laminar Pulvinus of Primary Leaves of Phaseolus

Summary The activity of fixed charges of isolated, morphologically intact extensor cell walls of the laminar pulvinus of the primary leaves of Phaseolus coccineus L. was determined by measuring the electric potential generated by the fixed negative charges. The activity of fixed charges depends strongly on the pH and KCl concentration of the bathing solution. The maximum activity measured was approx. 570 meq 1 -1 at pH 5 in 100 mM KCl and 400 meq 1 -1 at pH 6 in 10 mM KCl, respectively. The apparent maximum activity of fixed charges in the walls of living extensor cells (250 meq 1 -1 in 10 mM KCl) is lower than in isolated cell walls. The apparent pKa value of 3.1 calculated from the titration curves of isolated extensor cell walls in both 100 mM and 10 mM KCl indicates that the carboxyl-groups of pectins are the source of the fixed charges. In isolated cell walls the mean concentration of fixed anions as calculated from the K + concentration in the walls is lower than that calculated from the wall potential. This indicates that a large fraction of the cell wall solution is unaffected by the fixed anions, i.e. may be divided into a water free space and Donnan free space. The volume of the Donnan free space is estimated to be 55 % of the total wall water or 2.9 ml g -1 dry weight. We suggest that, due to the high activity of fixed negative charges, the Donnan free space of the extensor cell wall serves as a K + reservoir which is used to change the cell volume via the pH of the apoplastic solution.

Compartmentation of PO4 - Uptake and 32P Efflux in the Rhizoid Cells of Chara hispida L.

The uptake of 32 P-orthophosphate by the rhizoid of Chara hispida has been measured by disappearance from the medium. The time course of the loss of 32 P associated radioactivity of previously “loaded” rhizoid cells was also studied. The time courses in the two experimental series are similar, and yield in both cases. three different components which have corresponding half-times for the exchange of the isotope 31 P with 32 P. In the uptake study these are 1–3 min, 28 ± 3 min and 378 ± 52 min (n = 3); for the efflux they are 2.2 ± 0.35 min 8.1 ± 0.4 min and 374 ± 77 min (n = 5). The results are consistent with a three-compartment system representing the water free space, the cytoplasm and the vacuole.

Water exchange in plant tissue studied by proton NMR in the presence of paramagnetic centers

The proton NMR relaxation of water in maize roots in the presence of paramagnetic centers, Mn2+, Mn- EDTA2 -, and dextran-magnetite was measured. It was shown that the NMR method of Conlon and Outhred (1972, Biochem. Biophys. Acta. 288:354-361) can be applied to a heterogenous multicellular system, and the water exchange time between cortical cells and the extracellular space can be calculated. The water exchange is presumably controlled by the intracellular unstirred layers. The Mn- EDTA2 - complex is a suitable paramagnetic compound for complex tissue, while the application of dextran-magnetite is probably restricted to studies of water exchange in cell suspensions. The water free space of the root and viscosity of the cells cytoplasm was estimated with the use of Mn- EDTA2 -. The convenience of proton NMR for studying the multiphase uptake of paramagnetic ions by plant root as well as their transport to leaves is demonstrated. A simple and rapid NMR technique (spin-echo recovery) for continuous measurement of the uptake process is presented.

Uptake of 14C-α-aminoisobutyric acid by Phaseolus vulgaris

Specific uptake (S.U.) of α-aminoisobutyric acid ([1- 14C]AIB), a non-metabolizable neutral amino acid analog, by dwarf bush bean plants ( Phaseolus vulgaris cv Top Crop) demonstrated wide differences in active transport between various plant organs. The kinetic and timed uptake data reported were expressed as S.U. because this corrects for the diffusion of AIB which is part of the total AIB uptake process. Roots accumulated AIB to concentrations up to 18 times and leaf disks to twice those of the incubation medium. Stem tissue showed very little uptake, if any, that could not be accounted for by simple diffusion or water free space. Although initial rate kinetic studies demonstrated the presence of a normal transport system, timed uptake studies revealed greatly decreased transport by etiolated plants, suggesting a relationship between active transport and the lack of photosynthate. The reproducibility of the AIB uptake pattern by mature roots strongly supports the concept that the transport of neutral amino acids is biphasic and suggested one or more carrier systems are inducible by either low intracellular concentrations or repressed by high intracellular concentrations of the amino acid.

Changes in Ion Transport in Spring Wheat during Ontogenesis

AbstractThe influence of plant age on free space uptake to the root, rate of continuous uptake and translocation of potassium and sulphate was investigated during about 100 days in intact, high‐salt plants of spring wheat (Triticum aestivum L. cv. Svenno). The plants were grown in a green‐house in complete nutrient solution. For the short term uptake experiments, the test solutions were labelled with 36Rb+ and 35S‐sulphate.Free space uptake to the roots increased during the entire growth period. The SO2‐4 free space uptake was divided into a Water Free Space (WFS) fraction and a labile‐bound fraction. The labile‐bound SO2‐4 was considered to be constant during development, and the WFS fraction of SO−24 could then be computed. WFS increased from 2% of total cell volume in 1‐day‐old plants to 30% in 100‐day old plants, apparently due to an increasing proportion of freely permeable root cells. As the WFS fraction of the free space uptake was known, the binding capacity (BC) of K+(86Rb−) of the cell walls and at the cytoplasmic surfaces could be computed. It is suggested that the increasing BC for cations with age was due to an increasing proportion of soluble pectate in the cell walls.Except for the initial 20 days, the continuous ion uptake rate decreased during development. It is suggested that the low uptake rate in young plants is limited by the energy supply to the roots and that the decreased uptake in older plants is due to the increasing proportion of metabolically inactive and collapsed roots. At the end of the cultivation period the ion uptake rate increased at the same time as there was a shift from active to passive ion uptake. This was shown by uptake experiments with 2,4‐dinitrophenol (2,4‐DNP).By changing the air humidity around the shoots and using 2,4 DNP, it was shown that ion and water uptake were closely linked to root activity in young plants but that transpiration pull became gradually more important for water uptake with age.

Boron Uptake by Excised Barley Roots

At 2 C, all boron accumulated by excised barley roots (Hordeum vulgare L. cv. Herta) remains in the free space; i.e. active uptake is nil at this temperature. Three component fractions of free space B were apparent: (a) a surface contaminant film of B on blotted roots, (b) water free space B, and (c) B reversibly bound in the cell walls. A stoichiometric release of H(+) from the roots in the presence of B indicated that B was bound by borate complexes with polysaccharides in the cell walls. Polysaccharide-borate complexes are much less stable than those of monosaccharides, and the bound B fraction could be readily removed by rinsing the roots in the presence of a monomeric polyol possessing the necessary cis-diol configuration. Cell wall material separated from excised barley roots had a B binding capacity 66% greater than that of intact roots.A 30-minute rinse in distilled H(2)O or 0.5 mm CaSO(4) was required to remove all cell wall-bound B from the roots after a 30-minute uptake period. Thus, although B in the contaminant surface film and the water free space is rinsed from the roots within 10 minutes, a 30-minute rinse is essential if all reversibly accumulated B is to be removed from the free space.

Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L.

From compartmental analysis of radioisotope elution measurements, concentrations and fluxes of Mg(2+) were estimated for cortical cells in root segments of onion, Allium cepa L., relative to a complete nutrient solution containing 0.25 mM Mg(2+). Five compartments for Mg(2+) in the cortex were found and, in order of increasing rates of exchange, identified with the vacuoles and the cytoplasm of the cortical parenchyma, the Donnan free space, the water free space, and the superficial film of solution on the segments. With the Ussing-Teorell flux ratio equation as the criterion, it was concluded that Mg(2+) entered the cytoplasm passively and was actively pumped back across the plasmalemma. Mg(2+) concentration in the vacuole could be estimated only as lying between wide limits (1.3 to 14.3 μeq ml(-1)), but whatever the concentration within this range, it was concluded that Mg(2+) was passively distributed across the tonoplast. Net flux was zero and the vacuolar concentration commensurate with this was found to be 6.6 μeq ml(-1). The transported fraction of total efflux, appearing at the segment cut ends, was estimated separately. Magnesium was found to be transported almost exclusively in the basipetal direction.