Multiphasic Uptake of Sulfate by Barley Roots I. Effects of Analogues, Phosphate, and pH

For sulfate uptake by barley roots, competition studies reveal that uptake and phase transitions are caused by interaction of ions with separate sites on or in the plasmalemma. Uptake is competitively, and unequally, inhibited by sulfate analogues but not by other divalent anions. In contrast, divalent phosphate and di- and trivalent pyrophosphate are equally effective in causing transitions. Phosphate is taken up mainly or entirely as H₂PO₄^? by a similar but separate multiphasic mechanism. At pH 8, sulfate uptake is mediated by fewer phases than at low and intermediate pH.     

Multiphasic Uptake of Sulfate by Barley Roots

Uptake of sulfate by excised barley roots increases upon their washing in aerated water or dilute CaCl₂ solutions. Washing increases the values for V_max and the sulfate concentrations required for transition between the lower phases, but the K_M-values remain essentially constant. At low sulfate concentrations, phase transitions do not occur in the absence of calcium or other divalent cations. These ions are about equally effective in enhancing short-term sulfate uptake. Phase transitions were not principally altered by sulfhydryl or protein reagents. These concentration-dependent transitions appear unrelated to temperature-dependent phase transitions as evidenced by similar multiphasic patterns at low and high temperature.     

Multiphasic Uptake in Plants II. Mineral Cations, Chloride, and Boric Acid

Uptake of alkali cations, metal ions, chloride, and boric acid is shown by reanalysis of available data to be mediated by single, multiphasic mechanisms which may be fundamentally similar in a variety of plants and tissues.     

Anaerobic Phosphate Uptake by Barley Plants

Considerable uptake of phosphate by both the shoot and roothas been demonstrated for young barley plants with their rootsin anoxic culture solution at concentrations of 1 to 10 µMorthophosphate. Consideration of the free space and passivetranspirational uptake indicates an accumulatory process, andthe immediate efflux caused by respiratory inhibitors supportsthis. Shoot uptake is much less at higher external concentrationsof phosphate and at o.I mM was only 14 per cent of the control.The root accumulation process was unimpaired at an externalconcentration of 1 µM phosphate when the whole plant wassubjected to anaerobic conditions (shoot illuminated) but undersimilar conditions at a concentration of 100 µM a considerableefflux of phosphate occurred. Analysis of the fate of phosphatetaken up from anoxic solution of phosphate (10 µM) indicatedthat there was a reduction in the level of inorganic phosphateafter 4.5 h and steady rise in sugar phosphates up to 6 h witha marked increase in the levels of glucose-6-phosphate, fructose-6-phosphate,and the phosphoglycerate fraction.     

Active and Passive Components of Sulfate Uptake in Sunflower Plants

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.     

Multiphasic Hexose Uptake in Chlorella

The model proposed by E. Komor and W. Tanner for hexose proton cotransport in Chlorella (Planta 123: 195–198. 1975) is shown to be incorrect. Their data cannot represent hexose uptake via a protonated and a deprotonated form of the carrier, but may be precisely represented by a single bi- or triphasic mechanism.     

Energy-linked Sulfate Uptake by Corn Mitochondria via the Phosphate Transporter

Corn shoot mitochondria possess an energy-linked transport system for sulfate uptake as demonstrated by osmotic swelling and [³⁵S]SO₄²⁻ accumulation. Maximum uptake is secured in the presence of Mg²⁺ and oligomycin with sucrose for osmotic support. Neither phosphate nor dicarboxylate anions are required. When added simultaneously, millimolar concentrations of phosphate block [³⁵S]SO₄²⁻ uptake after the initial minute. Mersalyl, N-ethylmaleimide, and 2,4-dinitrophenol are strong inhibitors of sulfate uptake; n-butylmalonate is a weak inhibitor. These inhibitors act in the same fashion on phosphate uptake. It is concluded that sulfate uptake in the absence of phosphate is by the phosphate transporter.     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: I. CONTROL OF PHOSPHATE CONCENTRATION IN SOLUTION

An existing system of flowing solution culture in which pH andthe concentration of several nutrient ions in solution are automaticallymonitored and controlled has been extended to include the monitoringand control of orthophosphate in the range 0.0013 to 0.3 mgP l^–1 (4.2 ? 10^–8–10^–5 M). Continuous-flowcolorimetry is used for the analysis of phosphate and a computeris employed to hold concentrations constant by the operationof nutrient pumps. A brief account is given of the performanceof the system with perennial ryegrass (Lolium perenne L.) asthe experimental plant.     

Uptake of Sulfate by Roots and Leaf Slices of Barley: Mediated by Single, Multiphasic Mechanisms

The uptake of 10^?1M–2.5 × 10^?1M sulfate by roots and leaf slices of barley can be described by a single isotherm having, respectively, 8 and 5 phases with regularly increasing kinetic constants. Each phase covers a limited concentration range and obeys Michaelis-Menten kinetics. The uptake of sulfate is proposed to be rate-limited by a single mechanism or structure which is located in the plasmalemma (or cytoplasm) and which changes characteristics at certain discrete external concentrations (inflection points). Examination of published data indicates that the uptake of other inorganic ions by higher plant cells is also mediated by single, multi-phasic mechanisms.     

Phosphate Uptake and its Incorporation in Some Crop Plants and their Associated Weeds

Phosphate uptake rate and its incorporation into the foliarorgan of four crop plants, viz. pearl millet, pigeon pea, wheat,and gram, and six weeds Cyperus rotundus, Chenopodium album,Asphodelus tenuifolius, Anagallis arvensis, Vicia hirsuta, andEuphorbia dracunculoides were studied with the help of P32.It is concluded that phosphate uptake and its incorporationinto the leaves depend on age and species of plant. Rate ofphosphate uptake increases in all species as they proceed towardsmaturity but the incorporation of phosphate is maximum duringearly stages of growth.     

Oscillatory Transpiration and Water Uptake of Avena Plants I. Preliminary Observations

Oscillations in transpiration and water uptake of individual, young oat plants have been studied. The free-running period of these oscillations was about 30 minutes. Conditions were reached under which the oscillations were sustained for about two days. Short perturbations were given to the transpiration oscillations, the perturbations consisting of a short time increase or decrease in the illumination. The phase shifts of the oscillations as well as the amplitude effects caused by these perturbations were investigated. Simultaneous recordings of transpiration and water uptake of a single plant showed that these functions were oscillating in phase. Both oscillations disappeared if the leaf was excised.     

Multiphasic Uptake of Ammonium by Soybean Roots

Uptake of ammonium by intact soybean (Glycine max Merr. cv. Amsoy) plants can be represented by 3 phases of a single, multiphasic mechanism in the range 1.78 × 10^-5-3.57 × 10^-3M. Each phase covers a limited concentration range and obeys Michaelis-Menten kinetics. The multiphasic pattern of NH₄⁺ uptake is remarkably consistent at all stages of soybean growth (20, 40, 60 and 80 days).     

Multiphasic Uptake of Amino Acids by Barley Roots

Concentration-dependence and other characteristics of uptake of ³H-labeled l -lysine, l -methionine and l -proline by excised roots of barley (Hordeum vulgare L.) were studied. Use of relatively short uptake and wash periods and low solute concentrations ensured good estimates of influx across the plasmalemma. Uptake in the range of 10^?7M– 6.3 × 10^?3M can be precisely represented by four or five phases of single, multiphasic mechanisms. The mechanisms appear to be relatively specific as judged from the competition by unlabeled analogues. Structural requirements for interaction of a compound with the uptake site for methionine are given, as are the effects of analogues on the phase pattern for this amino acid. There is no indication of separate uptake and transition sites for methionine or lysine. i.e. phase transitions seem in this case to be caused by binding of molecule(s) to the uptake site. Uptake, but not phase patterns, was highly pH-dependent. The optima were pH 5 for lysine, pH 3–5 (a broad peak) for methionine and about pH 5.5 for proline. Uptake of the three amino acids was strongly inhibited by 2,4-dinitrophenol. sulfhydryl reagents and deoxycholate.     

Uptake of Phosphate by White Clover: I. EVIDENCE FOR AN ELECTROGENIC PHOSPHATE PUMP

Uptake of phosphate from flowing solution and cell membraneelectrical potential differences (PD) have been followed simultaneouslyin the roots of Trifolium repens L. Intact plants were usedand it was found that uptake and PD were strongly influencedby the shoot. They were reduced by excision of the root, defoliationof the plant, and lowering the light intensity at the leaf surface.2, 4-Dinitrophenol caused the PD to decline by approximately40 mV. A close correlation between phosphate uptake and PD wasobtained over a wide range of conditions and removal of phosphatefrom the solution resulted in a decline in PD of about 35 mV.It was concluded that there is an electrogenic phosphate pumpin T. repens roots which is closely dependent on the carbohydratesupply from the shoot.     

Sulfate Uptake and Its Regulation in Lemna paucicostata Hegelm. 6746

The steady state concentrations of S-containing compounds formed in Lemna paucicostata Hegelm. 6746 in response to variations in source and concentrations of sulfur were measured. Neither growth rates nor protein accumulation were markedly affected by the various growth conditions. Ignoring complications due to possible compartmentation, the results are consistent with internal pools of both SO(4) (2-) and cyst(e)ine (or products of their metabolism), but not methionine, being effectors of regulation of high affinity SO(4) (2-) uptake. As SO(4) (2-) in the growth medium was increased to 10 mm, down-regulation of high affinity SO(4) (2-) uptake was more than compensated for by unregulated uptake via the "non-saturating" uptake system. Tissue inorganic SO(4) (2-) accumulated but formation of reduced sulfur remained constant. Some conversion of l-cystine sulfur to SO(4) (2-) occurred. Presence of l-cystine in the medium (a) down-regulated high affinity SO(4) (2-) uptake and (b) decreased the rate of SO(4) (2-) organification. The net results were decreased (7 mum l-cystine) or normal (14 mum l-cystine) total tissue SO(4) (2-) and dose-dependent accumulation of soluble cyst(e)ine and glutathione, but not of soluble methionine. l-Methionine was not metabolized to cyst(e)ine or its products. Presence of l-methionine in the medium led to increased total tissue sulfur, accounted for almost wholly by manyfold increases in soluble methionine, AdoMet, and S-methylmethionine sulfonium. Soluble cyst(e)ine increased slightly.     

The Influence of Phosphate Uptake on Cation Uptake in Fusarium oxysporum f. sp. vasinfectum

Fusarium oxysporum grown in a low phosphate medium was found to take up several times as much K from KH₂PO₄ as from KCI solutions. Large amounts of phosphate also were taken up from KH₂PO₄. Similar large uptakes of Na and phosphate took place from solutions of NaH₂PO₄. Substantial quanties of phosphate were taken up from solutions of Ca(H₂PO₄)₂ in the absence of any appreciable Ca uptake. When the fungus was grown in a medium containing high phosphate, little or no uptake of phosphate from KH₂PO₄ solutions occured and the K Uptake was at the same level as from KCI solutions. During large phosphate uptake sizable reductions in the organic acid content of the fungal cells were observed. Much, but not all, of the data could be explained on the basis of maintenance of charge balance within the cells. – The respiratory rate of fungus, grown in a low P medium, was markedly increased in KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄ solution. Fungus, grown in a medium with high phosphate, had a higher respiratory rate which showed only a slight response to KH₂PO₄.