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Metabolic and Non-Metabolic Uptake of Sodium in Roots of Zea Mays

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... Peoria) were use(l. The plants were grown in 0.00025 N Cat(NO)2 andl the primary roots were cut into segmiienits 0 to 1.8 mm, 1.8 to 3.8 mmtn, 3.8 to 7.8 mmin, and 7.8 to 11.8 mm measure(l froimi the tip as described previously (2). The techniqlue of periodic measuremiieint of uptake over 24 hours by a single batch of 40 root segments was again used. ...
... The analytical procedlure for Na has already been described (2). Because Cl36 and Ca45 are beta enmitters the procedure for analysis of Ca an(l Cl had to be nmodlified to eliminate errors due to self-absorption. ...
Article
The uptake of Cl- by the non-vacuolated tissue of the zone of cell division of the root tip of maize from Cl-resin and CaCl2 and from their equilibrium filtrates has been studied. The results show a greater Cl-uptake from the resin NaCl2 system than from the NaCl filtrate and little or no difference between the resin CaCl2 system and the CaCl2 filtrate. These results are explained on the basis of an interaction between the negative root surfaces and the positively charged resin particles. This interaction causes a reduction in the negative charge of the root and thus reduces electrostatic opposition to the entry of Cl. The difference in Cl-uptake from NaCl and CaCl2 filtrates reflects the effect of the valence of the associated cation on the negative charge on root surfaces and membranes. The higher the valence of the cation, the lower the negative charge of the surface and the higher the Cl-uptake. Pretreating the root segments with Na2CDTA prior to immersion in the absorption solutions caused a reduction in Cl-uptake relative to that of untreated material. The reduction was more pronounced when absorption took place from NaCl rather than CaCl2. The results support previous ones obtained with excised barley roots.
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The absorption characteristics of vacuolated and nonvacuolated sections ; of the primary root of Zea may L. with respect to the uptake of Sr were ; determined. Like Na, Ca, and Cl, uptake of Sr is a non-metabolic process in the ; meristematic portion of the root tip, but dependent upon metabolism in the ; vacuolated tissue. The data presented suggest the existence of a barrier ; probably lying close to the cell surface which normally limits the non-metabolic ; uptake of Sr. This barrier is apparently metabolically maintained and is readily ; destroyed by anaerobiosis, permitting larger arnounts of Sr to enter the tissue. ; SrClâ was found to stimulate the respiration of both vacuolated and non-; vacuolated tissue. (auth);
Article
Absorption isotherms for chloride and rubidium ions have been determined through a wide concentration range for nonvacuolate root tips, and for vacuolate subapical sections of corn root. In the range 0 to 0.5 mm, chloride absorption is hyperbolic with concentration in both tips and proximal sections. At high concentrations, 1 to 50 mm, a second multiple-hyperbolic isotherm for chloride is noted in vacuolate tissue, while the isotherm for nonvacuolate tips rises exponentially. A linear to exponentially rising isotherm is taken to signify diffusive permeation.The same distinction between tip and subapical tissue characterizes Rb absorption. Rb uptake is indifferent to the nature of the counterion at all concentrations in the tip, while the counterion exerts a predictable influence on Rb absorption in proximal tissue. The effect of a poorly absorbable anion on Rb uptake is greater in the high concentration range. Evidence is presented for the metabolic nature of ion transport into nonvacuolate root tips. Verification is offered that ion uptake is mediated by dual mechanisms, and the thesis is developed that the high-affinity (low K(s)) system mediates ion passage through the plasma membrane while the low-affinity (high K(s)) system implements transport through the tonoplast.
Article
The effects of sodium chloride and calcium chloride at concentrations of 0.005N and 0.010N upon the respiration of vacuolated and nonvacuolated portions of the root tip of maize have been investigated. In both sections CaCl2 produced marked stimulation, while NaCl had no effect. In this tissue stimulation of respiration does not appear to be directly related to metabolic ion accumulation.
Article
At salt concentrations of 0.1 mM as well as of 5.0 mM, the 22Na+ absorption capacity of bean (Phaseolus vulgaris L. cv. ‘Brittle Wax’) leaf tissue increased during the period of leaf expansion and decreased rapidly after leaf maturation. The absorption capacity for 86Rb+ and 42K+ was highest in very young leaves and decreased continuously in expanding and in mature leaves. The 86Rb+ absorption capacity of mature leaves was not increased by detopping the plants; this senescence-retarding treatment more than doubled 2Na+ absorption. The absorption of 22Na+ by bean-leaf slices was not enhanced by light, whereas 86Rb+ and 42K+ absorption was much affected. Previously absorbed 86Rb+ and 42K+ were more available for exchange than 22Na+.
Article
The loss of potassium and sodium from preloaded excised barley and bean roots was compared under identical experimental conditions. In barley roots, metabolic inhibitors stimulated the potassium loss but inhibited that of sodium, indicating an active mechanism for sodium extrusion. In excised bean roots, such a mechanism could not be demonstrated and the losses of potassium and sodium were both stimulated by DNP and cold-treatment.
Article
A critical survey is given of the active uptake processes in order to have a basis for comparing the passage through the plasmatic membranes by non-electrolytes and by electrolytes (aminoacids and salts). According to Höfler's "Two pathways theory" the lipid path introduces lipophilic substances by diffusion through the lipids and lipoproteins of the membranes and the cytoplasm into the vacuoles. The other pathway leads non-lipophilic substances through pores in the membranes and is more susceptible to outer and inner conditions influencing the rate of permeation through the pores. Collander assumed that as a consequence of the presence of lipids in the cell membranes their permeability is so small that non-lipophilic substances enclosed in the different compartments of the cell do not show a noticeable efflux. The object of this investigationwas to establish whether in Vallisneria leaves an influx of salts (chloride ions) occurs without a simultaneous efflux. In normal healthy tissue permeability of the plasma-membranes is so low that no efflux can be shown during 22 hours' uptake. For measuring the presence or absence of efflux of chloride ions during uptake a method was developed comparing the amount of labelled chloride ions absorbed with the increase of the total amount of chloride ions estimated by chemical methods.
Article
The aim of the investigation was to identify components of active and passive ion uptake and transport in roots of plants and to assess their quantitative relations under different external and internal conditions. The uptake of radiosulfate and water by young sunflower plants from complete nutrient solutions labelled with 35S was studied. The metabolism-linked nature of the sulfate uptake in the root following the passive migration into the apparent free space (AFS) was demonstrated by the addition of sodium. selenate, 2,4-dinitrophenol, potassium cyanide, and sodium azide to the nutrient solutions. The magnitude of the AFS measured on a root volume basis varied between 14 and 57 per cent depending on the pretreatment of the plants and the sulfate concentration of the nutrient solution. The variations were supposed to be due to different capacity to bind sulfate by exchange-adsorption within the AFS. The amounts of sulfate in different fractions of the total AFS-uptake were computed under certain theoretical assumptions. A quantitative connection was proposed between the magnitude of the adsorbed sulfate fraction in the AFS and the rate of active uptake into the symplasm. The exchange-adsorption probably constitutes the initial stage of active ion uptake. The stimulating effect by water on ion uptake would be an increase of the speed of transporting ions to, from, or along the adsorption sites in the AFS. Experiments conducted at temperatures in the nutrient solution between 5 and 35 C elucidated the multistep nature of ion transport within a root.
Article
The uptake of Sr by maize-root segments representing the whole root system is strongly temperature dependent but a large non-metabolic component apparently involving adsorption within the cell membranes is indicated. About 60 per cent of the Sr taken up under conditions permitting metabolism is resistant to elution. K in the ambient solution at a concentration amounting to 20 per cent of the Sr concentration essentially abolishes metabolic uptake. Non-metabolic Sr uptake is little affected by this K concentration. The inhibitory effect of Ca on Sr uptake is less than that of K and largely exerted on the non-metabolic phase. This inhibitory effect is countered to some degree by the ability of Ca to hinder the entry of Sr into the xylem and so its loss via the cut ends of the root segments. In whole-plant experiments K depressed root concentrations of Sr more than shoot concentrations indicating that the inhibition is exerted mainly at the tonoplasts of cortical cells. Ca had a smaller effect than K which was mainly evident in greater root retention of Sr.
Article
Abscisic acid (ABA) caused a 7-8-fold increase in volume flow in excised bean root systems and this was coupled with an increase in (42)K, (36)Cl and (24)Na flux into the xylem. The transport of (42)K and (36)Cl increased by a factor larger than the stimulation of volume flow, resulting in an increase in the concentration of those ions in the xylem exudate. Carbonyclcyanide-m-chlorophenyl hydrazone, on the other hand, eliminated ABA-stimulated (42)K transport and caused a further inhibition of (42)K flux, thus providing additional support for the proposition that ABA stimulation may involve an energised process of ion transport. ABA also increased the accumulation of (24)Na and (36)Cl in bean root tissue, but not that of (42)K.
Article
A method is described by which the Na(+) and K(+) content in 0.5 mm sections of single roots of Hordeum distichon L. and Atriplex hortensis L. can be determined by use of flameless atomic absorption spectroscopy. By this method the longitudinal profiles of K(+) and Na(+) along low salt roots and roots which had been equilibrated with or grown in K(+)-free 1 mM Na(+)-solution were determined. The profiles reveal that high K(+)/Na(+) ratios in the cytoplasm are maintained also in K(+)-free solutions. In solutions containing 1 mM Na(+) a high K(+)/Na(+) selectivity was found to be dependent on sufficient aeration. From the ion profiles the cytoplasmic (110 mM) and vacuolar (20 mM) K(+) concentration in low salt barley roots-values which are unobtainable by compartmental analysis-could be estimated.
Article
From compartmental analysis of radioisotope elution measurements, concentrations and fluxes of K(+), Na(+) and Cl(-) were estimated for cortical cells in root segments of onion, Allium cepa L., relative to a complete nutrient solution. The transported fraction of the total efflux was estimated separately. With the Ussing-Teorell flux ratio equation as the criterion, it was concluded that all three ions were actively accumulated from the outside medium into the cytoplasm and that only Na(+) was actively accumulated into the vacuole. K(+) and Cl(-) moved passively, in both directions across the tonoplast. Failure to account for leakage from the stele via the segment cut ends resulted in an over-estimate of exchange across the tonoplast but did not alter the conclusions qualitatively. The consequences of changing the assumed value of the tonoplast electrical potential (from 0 to+10- mV), and the effects of different experimental procedures, were also assessed, and found not to affect the main conclusions significantly. Separate measurement of ions leaking from the segment ends revealed that Na(+) was transported almost exclusively in an acropetal direction in the stele. Cl(-) appeared at both ends of the segments in similar amounts and K(+) was transported mainly in the basipetal direction. The implications of these findings for the mechanism and site of ion selectivity are discussed.
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Transport of calcium-45 in 20-mm root segments is basipetal and requires metabolic maintenance. Such transport reaches a maximum rate after immersion of the roots in tracer solution for approximately 12 hours and is still pronounced after 50 hours. Acropetal movement is slight, probably non-metabolic, and essentially constant. Amounts transported are linearly dependent on the absorbing area exposed to tracer solution.
Article
• Data are presented which show the change in volume, dry weight, respiration, and protein content of the cell during development from the meristematic to the mature fully extended state. • The data have been obtained by making serial sections of known thickness along the root, making the relevant observations on the sections, and relating the values obtained to the total number of cells in the sections. An apparatus is described for obtaining serial sections from a group of roots. • It is shown that the weight of the wall, the protein content, and respiration all increase during extension, and the increases during active growth with respect to respiration and protein content occur in two phases. In the first the increases are large per unit increment in volume; in the second they are relatively smaller. When extension ceases a third phase in the development of the cell sets in in which respiration and protein content decrease slightly. • The data show that the protein content and the respiration in the meristematic cell are considerably lower than they are in fully vacuolated cell.
Article
The purpose of this investigation is the study of the properties of the cell with regard to potassium absorption as the cell expands. Serial sections each 1·5 mm. in length have been cut along the course of maize roots over the first 9·0 mm. from the tip. The sections have been immersed in 0·01 N. solution of potassium chloride in water and in 2 per cent. fructose. Absorption from these solutions has been measured over a period of 48–72 hours. It is shown that absorption by the first section which consists almost entirely of meristematic cells is abnormally low, and this is attributed to the absence of a tonoplast surrounding a central vacuole in the cells of this section. The different initial rates with the different sections indicate that after vacuolation in the root has occurred the rate per unit area of surface decreases as the cell expands. When the data are reduced to a unit cell basis, however, they show that, per cell, absorption increases as expansion occurs in the root. This is attributed to an increasing protein content, and the decrease in rate per unit area to a corresponding decrease in protein per unit area. At the same time it is shown that during cell growth in the root the cytoplasm differentiates in such a way that absorption per unit protein increases. After excision, whether growth occurs or not, the protein content does not increase. The final internal concentrations in the different sections vary according to the growth that occurs. When vacuolation has occurred and growth is limited the final internal concentration is greater than it is at the beginning of the experiment. When growth occurs, on the other hand, the final internal concentration may be lower. This is taken to indicate that absorption depends on an inward secretion into the vacuole which is independent of surface area and an outward diffusion into the medium which increases with increase in surface area. It is suggested that the results obtained with sugar support this interpretation. When sugar is provided the rate of absorption is always stimulated and when growth does not occur the final internal concentration is enhanced. When growth occurs, however, sugar not only stimulates absorption but also the expansion of the cell, and the latter effect leads to a final concentration which may be lower than that given in the absence of sugar.
Article
The proportion of a given length of bean root tissue which appears to reach the external concentration when placed in KCI solutions (the apparent free space, == A.F.S.) increases as the external concentration is increased.
The apical meristem of the root affords an excellent material with which to study changes in cellular components accompanying growth and differentiation. The ontogeny of cytoplasmic particles can be followed, since the younger cells are constantly dividing and reforming new cytoplasm. Electron microscope pictures of these newly formed cells reveal a dense background of microsomal granules and small, thin walled vesicles of the endoplasmic reticulum. Two types of mitochondria are noted and, as the cells enlarge, mitochondria regarded as immature can no longer be seen, but only mitochondria with well developed cristae. The development of these cristae was found to be associated with an increase in respiration of the tissue as well as with increased rates of oxidation and phosphorylation of isolated mitochondria. As the cells grow and mature, the mitochondria make up an increasing percentage of the total cytoplasmic protein, and this increase probably accounts to a great extent for the increase in tissue respiration. Concomitantly, there is a decrease in microsomal granules. All these changes have been verified by electron microscope pictures of cells in situ, chemical analysis of isolated particulates, and metabolic studies of tissue and isolated fractions.
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