Effects of Various Concentrations of Carbon Dioxide on Respiration and Potassium Uptake in Barley Roots

Barley roots contain a CO₂ sensitive respiratory fraction which is inhibited in 50 per cent CO₂ and is partially restored upon subsequent exposure to air. The residual O₂ consumption occurring at CO₂ concentrations between 50 per cent and 95 per cent amounts to about 40 per cent of the O₂ uptake in air and can support K⁺ uptake for a limited time at a rate equal to or higher than occurs in air. Above 95 per cent CO₂ both O₂ and K⁺ uptakes decrease rapidly. 2,4-dinitrophenol (DNP), in the range of 10^?6 to 10^?5M, stimulates O₂ uptake by the roots in air. The stimulation is absent when roots are treated with DNP in 80 per cent CO₂, presumably because of the reduced demand for inorganic phosphate and phosphate acceptor at the lower respiratory level in high CO₂. In either air or CO₂, K⁺ uptake is strongly inhibited by DNP. A comparison of the respiratory and K⁺ uptake data indicates that O₂ consumption is a necessary requirement for the uptake process in high CO₂. Protoplasmic streaming in the root cells is rapidly stopped by high CO₂ although K⁺ uptake and O₂ consumption continue. The cation uptake mechanism in high CO₂ appears to be limited to the stationary cytoplasm. It is also possible that a similar mechanism may be involved in cation uptake in air.     

Dependency of the ATPase and 32 P--ATP exchange reaction of mitochondria on K + and electron transport

The 2,4-dinitrophenol-stimulated ATPase activity and the ³²P-ATP exchange reaction has been studied in rat liver mitochondria having less than 15 nmoles of K⁺ per milligram of protein. With 200 mm sucrose in the incubation media, the permeation of K⁺ and an oxidizable substrate is required for maximal stimulation of ATPase activity by 2,4-dinitrophenol. In these conditions, the 2,4-dinitrophenol-stimulated ATPase is inhibited by antimycin, acetate and mersalyl and depends to a certain extent on the rate of electron transport. The ³²P-ATP exchange reaction of mitochondria with a low content of K⁺ also requires K⁺ permeation and is inhibited by antimycin, cyanide, 2,4-dinitrophenol, and acetate. The results suggest that the entrance of ATP into the mitochondria is compulsory linked to K⁺ uptake in a process that depends on a negative internal potential.     

Effects of temperature and dinitrophenol on the uptake of potassium and sodium ions in Ricinus communis roots

Summary Detopped root systems of Ricinus communis plants were used for the study of the effects of temperature and DNP on the uptake of K and Na ions supplied as KNO₃ and NaNO₃.When K and Na ions were offered together in equivalent concentrations, the steady state uptake rates for K⁺ and Na⁺ at 23 to 25° gave a K⁺/Na⁺ ratio of 3. Increasing the Na⁺ concentration relative to K⁺ 3-fold did not alter the preferential uptake of K⁺. The uptake of K⁺ was more sensitive to temperature in the range 10 to 40° and to the application of DNP at 1.5x10^-4 M than was the uptake of Na⁺. When NaNO₃ was the only salt supplied Na⁺ uptake became more sensitive to DNP than when both K⁺ and Na⁺ nitrates were supplied. Prolonged application of DNP led to net K⁺ efflux from the roots, even when no K⁺ was being supplied to the roots. Net Na⁺ efflux under the influence of DNP occurred only in roots previously grown on Na-containing nutrient medium.The different responses of the K⁺ and Na⁺ uptake processes to temperature and DNP suggest the operation of different uptake mechanisms for K⁺ and Na⁺ These results have been considered in relation to the recent concept of dual mechanisms for the absorption of alkali cations by plant tissues.     

Differences between Effects of Undissociated and Anionic 2,4-Dinitrophenol on Permeability of Barley Roots

Effects of 2,4-dinitrophenol (DNP) and several other substituted phenols on permeability of barley roots (Hordeum vulgare var. Trebi) to ions were assayed as a function of pH and phenol concentration. Solutions containing 0.1 micromolar undissociated DNP increase the permeability of barley root cells to small ions such as K⁺, Na⁺, Ca²⁺, and Cl⁻ with no inhibition of respiration. Undissociated forms of the other phenols increase permeability also, but they are less effective than DNP. Only the undissociated DNP is effective. Anionic DNP does not increase permeability or inhibit ion uptake, although it is the major species accumulated by the roots, both at pH 5 and pH 7. At pH 7, in contrast to pH 5, 10 micromolar DNP has no effect on ion permeability of barley roots yet it uncouples oxidative phosphorylation of barley root mitochondria. This indicates that the all too common use of DNP as a test for active transport or involvement of ATP synthesis can be misleading.     

TRANSPORT OF TYROSINE, PHENYLALANINE, TRYPTOPHAN AND GLYCINE IN NEUROBLASTOMA CLONES

Amino acid transport was studied in three neuroblastoma clones, N-TD6, which synthesizes norepinephrine, N-T16, which synthesizes small amounts of serotonin, and N-S20Y, which synthesizes acetylcholine. All three clones exhibited high-affinity saturable transport systems for tyrosine, phenylalanine, tryptophan and glycine as well as systems unsaturated at amino acid concentrations of 1 mM in the external medium. Tyrosine, phenylalanine and tryptophan enter all three clones by rapidly exchanging transport systems which appear to be relatively insensitive to lowered external [Na⁺] or to the presence of 2,4-dinitrophenol (DNP). Glycine uptake was slower and was much more sensitive to lowered external [Na⁺] and to the presence of DNP in the medium. Glycine transport in N-T16 cells was decreased more markedly at low temperature than was transport of the three aromatic amino acids. K_m and V_max values found for saturable transport of tyrosine, phenylalanine and tryptophan were sufficiently low to suggest that, if similar amino acid transport systems exist in neuronal membranes, and if amino acid levels in brain extracellular fluid are similar to levels in plasma, such systems may serve, in conjunction with transport systems in cerebral capillaries, to limit the entry of amino acids into brain cells when blood amino levels are near the normal physiological range.     

An oligomycin-resistant Mg2+-dependent ATPase in rabbit bone marrow mitochondria

Summary Rabbit bone marrow mitochondria isolated by differential centrifugation showed typical oxypolarographic tracings with glutamate oxidation with ADP:O ratio of 2.9. Similar results were obtained with liver mitochondria of the same animal. When marrow mitochondria were oxydizing a substrate such as glutamate, added MgCl₂ markedly stimulated state-4 respiration giving a respiratory rate identical to that of state-3. In contrast, no Mg²⁺-stimulation was observed with liver mitochondria. Oligomycin completely blocked the stimulation by Mg²⁺ but further addition of 2,4-dinitrophenol reactivated the oxygen consumption by uncoupling. Further purification of marrow mitochondria by density gradient centrifugation in Percoll provided identical oxypolarographic results. Moreover, when marrow mitochondria were incubated without Mg²⁺, they showed a low ATPase activity that was stimulated by 2,4-dinitrophenol and blocked by oligomycin. The presence of Mg²⁺ in the incubation medium uncovered an additional ATPase activity which was resistant to oligomycin and apparently unaffected by 2,4-dinitrophenol. It is concluded that bone marrow mitochondria possess two types of ATPase activity distinguished on the basis of their reactivity with oligomycin, 2,4-dinitrophenol and Mg²⁺.Abbreviations EDTA ethylenediamine tetraacetate - DNP 2,4-dinitrophenol - BSA bovine serum albumin - BMM bone marrow mitochondria - LM liver mitochondria - Oligo. oligomycin - Anti A antimycin A Howard Hughes Investigator.     

Effects of Tl<Superscript>+</Superscript> on ion permeability,membrane potential and respiration of isolated rat liver mitochondria

It is known that permeability of the inner mitochondrial membrane is low to most univalent cations (K⁺, Na⁺, H⁺) but high to Tl⁺. Swelling, state 4, state 3, and 2,4-dinitrophenol (DNP)-stimulated respiration as well as the membrane potential (ΔΨ_mito) of rat liver mitochondria were studied in media containing 0–75 mM TlNO₃ either with 250 mM sucrose or with 125 mM nitrate salts of other monovalent cations (KNO₃, or NaNO₃, or NH₄NO₃). Tl⁺ increased permeability of the inner mitochondrial membrane to K⁺, Na⁺, and H⁺, that was manifested as stimulation of the swelling of nonenergized and energized mitochondria as well as via an increase of state 4 and dissipation of ΔΨ_mito. These effects of Tl⁺ increased in the order of sucrose <K⁺ <Na⁺ ≤ NH₄⁺. They were stimulated by inorganic phosphate and decreased by ADP, Mg²⁺, and cyclosporine A. Contraction of energized mitochondria, swollen in the nitrate media, was markedly inhibited by quinine. It suggests participation of the mitochondrial K⁺/H⁺ exchanger in extruding of Tl⁺-induced excess of univalent cations from the mitochondrial matrix. It is discussed that Tl⁺ (like Cd²⁺ and other heavy metals) increases the ion permeability of the inner membrane of mitochondria regardless of their energization and stimulates the mitochondrial permeability transition pore in low conductance state. The observed decrease of state 3 and DNP-stimulated respiration in the nitrate media resulted from the mitochondrial swelling rather than from an inhibition of respiratory enzymes as is the case with the bivalent heavy metals.     

Multiphasic uptake of potassium by barley roots of low and high potassium content: Separate sites for uptake and transitions

In the range 10^?6M - 5 × 10^?2M uptake of K⁺ in excised roots of barley (Hordeum vulgare L. cv. Herta) with low and high K content could in both cases be represented by an isotherm with four phases. Uptake, especially in the range of the lower phases, was reduced in high K roots through decreases in V_max and increases in K_m. Similar data for other plants are also shown to be consistent with multiphasic kinetics. The concentrations at which transitions occurred were not affected by the K status, indicating the existence of separate uptake and transition sites. Uptake was markedly reduced in the presence of 10^?5M 2,4-dinitrophenol, especially at low K⁺ concentrations, but the isotherms remained multiphasic. This contraindicates major contributions from a non-carrier-mediated, passive flux. A tentative hypothesis for multiphasic ion uptake envisions a structure which changes conformation as a result of all-or-none changes in a separate transition site. The structure is “tight” at low external ion concentrations (low V_max. low K_m. active uptake, allosteric regulation) and “loose” at high concentrations (high V_max- high K_m- facilitated diffusion, no regulation).     

Effect of tentoxin on K+transport in winter wheat seedlings of different K+-status

Klotz, M. G. and Erdei, L. 1988. Effect of tentoxin on K⁺ transport in winter wheat seedlings of different K⁺-status. The influence of the phytoeffective mycotoxin, tentoxin, [cyclo-(L-leucyl-N-methyltrans-dehydronhenyl-alanyl-glycyl-N-methyl-L-alanyl)] (in K⁺ uptake and on translocation of K⁺ from roots to shoot was studied in 14-day-old winter wheat plants (Triticum aestivum L. cv. Martonvásári-8) grown at different levels of K⁺ supply. For comparison, the effects of 2,4-dinilrophcnol and valinomycin were also investigated. In I-h experiments I pM tentoxin reduced K⁺ influx in the routs over the external K⁺ concentration range 0.1 to 1 m^M (low-K⁺ plants), whereas stimulation was observed al lower and higher K⁺ concentrations. On the other hand, in plants grown at 0.3 m^M K⁺, tentoxin stimulated the translocation of K⁺ from roots to shoots in 5-h experiments. Valinomycin affected K⁺ transport only al high K⁺-status (slight stimulation). In low-K⁺ plants 2,4-dinitrophenol (DNP) caused drastic inhibition of K⁺ uptake, but in high-K⁺ plants uptake was only slightly inhibited and translocation slightly stimulated, It is concluded that the opposite effects of tentoxin on K⁺ uptake and translocation agree1 with the directions of the H⁺-ATPases pumping H⁺ towards the apoplast and located at the cortex plasmalemma and the xylem parenchyma plasma-membrane, respectively. These effects should probably be attributed to the interaction between tentoxin and the K⁺-carrier protein rather than to a direct influence of tentoxin on H⁺-ATPase.     

The transepithelial potential difference in the gills of the fiddler crab,Uca tangeri: Influence of some inhibitors

Summary Euryhaline Crustacea living in dilute media, counterbalance the salt loss by active absorption of NaCl across the gill epithelium. To investigate the mechanisms involved in salt absorption, transeptithelial potential difference (PD_te) was measured in isolated, perfused gills of the fiddler crab,Uca tangeri. The influence of some specific inhibitors of epithelial ion transport on the PD_te was tested.With symmetrical conditions on both sides of the epithelium, the posterior gills ofUca tangeri showed a spontaneous PD_te of +5 to +10 mV, that is an active transport potential which was positive on the bath side as referred to the hemolymph side. This potential decreased considerably after application of KCN or 2,4-dinitrophenol (DNP) to the perfusion saline.Omission of K⁺ from the perfusion saline or addition of ouabain led to a reversible drop of the PD_te, suggesting that the absorption of Na⁺ and also of Cl^– is driven by the (Na⁺+K⁺)ATPase located in the basolateral membrane of the epithelial cells.Perfusion of the hemolymph space with saline containing diphenylamine-2-carboxylate (DPC) or the loop diuretic furosemide resulted in a decrease of the PD_te.After application of amiloride to the bath saline the PD_te increased. Half-maximum response to amiloride was reached at a concentration of about 10^–5 mol·l^–1. This suggests that one of the Na⁺ pathways across the apical membrane may consist of Na⁺ channels.Abbreviations PD _te transepithelial potential difference - DPC diphenylamine-2-carboxylate - R _ps resistance of perfusate shunt - R _te transepithelial resistance - R _in input resistance - DNP 2,4-dinitrophenol Parts of this study have been reported at the 1st Congress of Comparative Physiology and Biochemistry, Liège 1984, and at the Vth European Colloquium on Renal Physiology, Frankfurt, 1985     

Simultaneous Measurement of Dissolved Oxygen and Oxidation-Reduction Potentials in the Aerobic Culture

The most dominant factor influencing the oxidation-reduction potentials (E) in the cultured system was oxygen tension. H was an useful index to express the degree of oxygen supply in place of dissolved oxygen (P_L) under a limited oxygen supply. The conversion of microbial products caused by the change in oxygen supply was clearly analyzed by the use of E value. Bacillus subtilis excreted lactic acid at the E value ?220 mV, 2,3-butyleneglycol at ?195 mV and acetoin at ?160mV as the main product. E also gave the significant information concerning the changes in cell’s respiration. Cyanide at the concentration of 10^?5m, azide at 10^?3m and 2,4-dinitrophenol (DNP) at 10^?2m inhibited cell respiration causing the decrease in E and the increase in P_L, and DNP at 0.4×10^?3m promoted oxygen uptake of the cells causing the decrease in both E and P_L.     

Selenite uptake and incorporation by Selenomonas ruminatium

Selenite uptake and incorporation in Selenomonas ruminantium was constitutive with an inducible component. It was distinct from sulphate or selenate transport, since sulphate and selenate did not inhbit uptake, nor could sulphate or selenate uptake be demonstrated. Selenite uptake had an apparent K _m of 1.28 mM and a V _max of 148 ng Se min^-1 mg^-1 protein. Uptake was sensitive to inhibition by 2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), azide, iodoacetic acid (IAA) and N-ethylmaleimide (NEM), but not chloropromazine (CPZ), N,N-dicyclohexyl-carbodiimide (DCCD), quinine, arsenate, or fluoride. Treatment of cells accumulating ⁷⁵[Se]-Selenite with 2,4,DNP inhibited uptake, but did not cause efflux. Transport of selenite was inhibited by sulphite and nitrite, but not by nitrate, phosphate, sulphate of selenate. ⁷⁵[Se]-Selenite was incorporated into selenocystine, selenoethionine, selenohomocysteine, and selenomethionine and was also reduced to red elemental selenium.     

Interactions of bacteria and microflagellates in sequencing batch reactors exhibiting enhanced mineralization of toxic organic chemicals

Community level interactions were studied in non-axenic sequencing batch reactors (SBRs) being used to treat 2,4-dinitrophenol (DNP). Increasing the influent DNP concentrations from 1 to 10 μg ml⁻¹ eliminated large predatory organisms such as rotifers and ciliated protozoa from the SBRs. Under steady-state conditions at a DNP concentration of 10 μg ml⁻¹, supplemental additions of glucose enhanced DNP degradation and led to the establishment of a microbial community consisting of five species of bacteria and a variety of microflagellates. The bacteria and flagellates exhibited oscillating population dynamics in this system, possibly indicating predator-prey interactions between these two groups. Only two of the five bacteria isolated from this system could utilize glucose as a growth substrate, and one of these two species was the only organism that could mineralize DNP in the system. The other three bacteria could grow using metabolic by-products of one of the glucose-utilizing strains (Bacillus cereus) found in the reactors. Supplemental glucose additions increased the average size of bacterial floc particles to 172 μm, compared with 41 μm in SBRs not receiving glucose. It is theorized that the enhanced mineralization of DNP in this non-axenic system was attributable to increased community interactions resulting in increased bacterial flocculation in SBRs receiving supplemental glucose additions. Offprint requests to: S. K. Schmidt.     

Membranes as targets of ultraviolet radiation

In non-photosynthetic cells, evidence for UV (ultraviolet radiation) damage to membranes comes from electron microscopy, chemical analysis and observations of transport processes. Specific perturbations in transport across membranes occur quickly after a relatively low fluence of UV. As an example, irradiation of suspension-cultured rose cells with 500-2000 J m^?2 (at 254 nm) causes an appearance of K⁺ in the extracellular medium at the rate of 5 × 10^?10μmol cell^?1 min^?1 for 30 to 60 min and more slowly thereafter. The early, rapid phase of appearance of K⁺ reflects both an increase in efflux and a decrease in influx. The appearance of K⁺ is matched by an appearance of HCO^?₃ in the medium. The HCO^?₃ comes from respiratory CO₂, which hydrates and dissociates in the cytoplasm, leading to a decrease in cytoplasmic pH. Overall, these results not only demonstrate UV damage to membrane function, but also suggest several ways by which UV may alter the general metabolic state of the cell. A demonstration of direct effects of UV on membrane components requires a purified system. At lower fluence, < 1800 J m^?2 (254 nm), the ATPase of membrane vesicle preparations is inactivated in a two-phase process that suggests the presence of enzymes with different UV sensitivities. The existence of two non-mitochondrial enzymes in rose cell vesicles has been confirmed by solubilizing the vesicle proteins with 1% cholic acid and separating the components on G-150 Sephadex. One component of relatively high molecular weight is especially sensitive. The fact that it is still sensitive when it is dissolved in cholic acid strongly suggests that its sensitivity is intrinsic and does not depend on sensitization by other membrane components. The action spectrum for the inactivation of the ATPase has a major peak at 290 nm and extends into the UV-C and UV-A regions. The physiological effects of UV-stimulated membrane changes are uncertain. There is little evidence that the UV damage to membranes is responsible for cell death. A UV-induced loss of K⁺ from guard cells may result in lower stomatal conductance. UV-stimulated membrane changes may play a role in the UV-induced synthesis of anthocyanins.     

Manipulation of cellular energy reveals the relationship between ultraweak luminescence and cellular energy during senescence of strawberry (<Emphasis Type="Italic">Fragaria</Emphasis> × <Emphasis Type="Italic">ananassa</Emphasis>) fruits

The goal of this study was to investigate the ultraweak luminescence (UWL) of strawberry fruits in relation to mitochondrial functions and energy production during strawberry senescence. Fully ripe strawberry fruits and mitochondria isolated from those fruits were treated with either adenosine triphosphate (ATP) or the respiratory chain uncoupler 2,4-dinitrophenol (DNP). The activities of H⁺-ATPase and Ca²⁺-ATPase, the content of ATP, the free radical O₂^? as well as the UWL intensity were measured. Our results showed that activities of H⁺-ATPase and Ca²⁺-ATPase as well as the ATP content gradually decreased during fruit senescence in all three groups. Compared with the control, DNP treatment exacerbated, while ATP treatment reduced the decrease of H⁺-ATPase and Ca²⁺-ATPase activity, the energy charge and UWL intensity. UWL intensity was positively correlated with mitochondrial function and ATP content. Our results strongly suggest that mitochondria are a major source of UWL of strawberry fruits, and that the cellular energy ATP plays important roles in senescence of strawberry fruits, and in UWL formation. Our study provides convincing evidence of the interrelationship between cellular energy and UWL, which helps researchers to better understand the process of senescence in strawberry fruits.     

Aluminium interactions with K+(86Rb+) and 45Ca2+ fluxes in three cultivars of sugar beet (Beta vulgaris)

Three cultivars of sugar beet (Beta vulgaris L.), which are sensitive to aluminium (Al) in the order Primahill > Monohill > Regina, were grown in water culture for 2 weeks. Nutrients were supplied at 15% increase of amounts daily, corresponding to the nutrient demand for maximal growth. The 2.4-dinitrophenol (DNP)-sensitive (metabolic) and DNP-insensitive (non-metabolic) uptake of aluminium, phosphate. ⁴⁵Ca²⁺ and K⁺(⁸⁶Rb⁺) in roots were measured as well as transport to shoots of intact plants. All 3 cultivars absorbed more aluminium if DNP was present during the aluminium treatment than in its absence. It is suggested that sugar beets are able to extrude aluminium activity or that they possess an active mechanism to keep Al outside the cell. The presence of Al in the medium during the 1-h experiment affected the metabolic and non-metabolic fluxes of ⁴⁵Ca²⁺ and K⁺(⁸⁶Rb⁺) in different ways. In the presence of DNP, the influx of both ⁴⁵Ca²⁺ and K⁺(⁸⁶Rb⁺) and the efflux of ⁴⁵Ca²⁺ were inhibited by Al in a competitive way. At inhibition of ⁴⁵Ca²⁺ influx, 2 Al ions are probably bound per Ca²⁺ uptake site in cv. Regina (Al-tolerant), but in cvs Primahill and Monohill only one Al ion is bound (more Al sensitive). Aluminium competitively inhibited the active efflux of ⁴⁵Ca²⁺ (absence of DNP) in almost the same way in the 3 cultivars. In contrast, aluminium stimulated the influx of K⁺(⁸⁶Rb⁺) in cvs Primahill, Monohill and Regina in the absence of DNP. Thus, the Al effects on active and passive K⁺(⁸⁶Rb⁺) influx are different. The total influx of K⁺(⁸⁶Rb⁺) increased in the presence of Al and might be connected to an active exclusion of Al. Regina is the least Al-sensitive cultivar, probably because Al interferes less with the Ca²⁺ fluxes and because this cultivar actively excludes phosphate in the presence of Al. Thus Al-phosphate precipitation within the plant could be avoided.     

Specific drug sensitive transport pathways for chloride and potassium ions in steady-state ehrlich mouse ascites tumor cells

A major aim of this investigation was to determine whether, in steady-state ascites cells, Cl^? transport can be partitioned into a furosemide-sensitive cotransport with K⁺ and a separate 4,4′-isothiocyanostilbene-2,2′-disulfonic acid (DIDS) sensitive self-exchange. Both Cl^? and K⁺ fluxes were studied. The furosemide- and Cl^? sensitive K⁺ fluxes were equivalent, both in normal ionic media and when the external K⁺ concentration, [K⁺]_o, was varied from 4 to 30 mM. The stoichiometry of the furosemide-sensitive Cl^? and K⁺ fluxes was 2 Cl^?: 1 K⁺ at 0.1 and 0.5 mM drug levels but increased to 3 Cl^? : 1 K⁺ at 1.0 mM furosemide. DIDS at 0.1 mM had no effect on the K⁺ exchange rate but inhibited Cl^? exchange by $\text{39\% ± 2}$ (S.E.). The effects of DIDS and 0.5 mM furosemide on Cl^? transport were additive but 1.0 mM furosemide and DIDS had overlapping inhibitory actions. Thus furosemide acts on components of K⁺ and Cl^? transport which are linked to each other, but the drug also inhibits an additional DIDS-sensitive Cl^? pathway, when present at higher concentrations. The dependence of the furosemide-sensitive K⁺ and Cl^? transport on [K⁺]_o was also studied; both fluxes fell as the [K⁺]_o increased. The latter results recall those in an earlier study by Hempling (Hempling, H.G. (1962) J. Cell. Comp. Physiol. 60, 181–198).     

Hormonal Regulation of Ca2+ Stimulated K+ Influx and Ca2+, K+- ATPase in Rice Roots: in vivo and in vitro Effects of Auxins and Reconstitution of the ATPase

The role of natural and synthetic auxins in regulation of ion transport and ATPase activity was studied in rice roots (Oryza sativa L. cv. Dunghan Shah). In vivo treatment of seedlings with 2,4-dichlorophenoxyacetic acid at 2 × 10^?6M for a short period enhanced subsequent Ca²⁺ stimulated K⁺ influx and ATPase activity, while a longer treatment diminished both K⁺ influx and ATPase activity. Indoleacetic acid at 10^?10–10^?8M induced ATPase activity. In in vitro experiments both 2,4-dichloro phenoxyacetic acid and indoleacetic acid (10^?10–10^?8M) stimulated Ca²⁺, K⁺-ATPase activity of a plasmalemma rich micro somal fraction from the roots. Acetone extracted ATPase preparations lost their activity. The enzyme regained its activity and its sensitivity towards ions (Ca²⁺+ K⁺) when reconstituted with phosphatidyl choline. Addition of auxins also indicated that the presence of the lipid was necessary in the interaction between the ATPase and auxins. Auxins and ions probably interact with the intact ATPase lipoprotein complex, which may possess a receptor site for the auxins, possibly as a sub unit.     

Changes in Ion Transport in Spring Wheat during Ontogenesis

The 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 SO^2-₄ free space uptake was divided into a Water Free Space (WFS) fraction and a labile-bound fraction. The labile-bound SO^2-₄ 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.