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.     

The Effect of Dichlorophenyldimethylurea on Light-Stimulated 22Na+, 42K+ and 86Rb+ Absorption in Different Tissues of Phaseolus vulgaris Leaves

The light-stimulated absorption of ⁸⁶Rb⁺ by Phaseolus vulgaris L. leaf slices was found to be sensitive to dichlorophenyldimethylurea in air as well as in nitrogen, whereas light-stimulated ²²Na⁺ absorption in nitrogen was not sensitive to this inhibitor. The absorption of ²²Na⁺ is not affected by light in air. The absorption of ⁴²K⁺ is enhanced by a dichlorophenyldimethylurea-insensitive light effect under anaerobic conditions and further increased by light in the absence of the inhibitor. Light-enhanced ⁴²K⁺ absorption in air was also inhibited by dichlorophenyldimethylurea. Previous work showed that light-stimulated ⁸⁶Rb⁺ and ⁴²K⁺ absorption by Phaseolus vulgaris leaf slices is restricted to the guard cells. The present results are discussed with reference to the effect of light on stomatal opening.     

Short term 22Na+ and 42K+ uptake in intact, mid-vegetative plants

Spergularia marina (L.) Griseb. is. a rapidly growing, annual, coastal halophyte. Because of its small size, it is suitable for isotope studies of ion transport well beyond the seedling stage. The purpose of this report is to establish the similarities and differences between ²²Na⁺ and ⁴²K⁺ uptake in S. marina and in more commonly used mesophytic crop species. Vegetative plants were used 18 days after transfer to solution culture. Plants were grown either on Na⁺-free medium or on 0.2 × sea water. ²²Na⁺ uptake was linear with time for several hours. The rate was relatively insensitive to external concentration between 1 and 180 mol Na⁺ m?³, particularly in Na⁺-free plants. Transport to the shoot accounted for 40 to 70% of the total uptake, dependent on salinity but largely independent of time. ⁴²K⁺ uptake decreased with increasing salinity in Na⁺-free plants and increased in 0.2 × sea water plants. Both uptake and transport to the shoot were non-linear with time, upward concavity suggesting recovery from a manipulative and/or osmotic injury. Steady state root contents were compared with predicted contents based on cortical cell electrical potentials using the Nernst equation. Reasonable agreement was found in all cases except Na⁺ content of 0.2 × sea water plants, in which active efflux was indicated. Uptake studies conducted in the presence of chemical modifiers (dicyclohexylcarbodiimide, dinitrophenol and fusicoccin) showed responses of ⁴²K⁺ uptake as expected from studies on agronomic species, and implied the presence of a similar active uptake here despite the appearance of equilibrium. Active Na⁺ uptake was suggested at low Na⁺ levels. We conclude that S. marina is a promising experimental system combining the rapid nutrient acquisition strategy of agionomically important annuals with a high degree of salt tolerance.     

Mechanism for Cd2+ inhibition of (K++ Mg2+)ATPase activity and K+ (86Rb+) uptake join roots of sugar beet (Beta vulgaris)

Steady state kinetics were used to examine the influence of Cd²⁺ both on K⁺ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K⁺(⁸⁶Rb⁺) uptake in intact or excised beet roots. The in vitro effect of Cd²⁺ was studied both on a 12000–25000 g root fraction of the (Na⁺+K⁺+Mg²⁺)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd²⁺ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd²⁺ at concentrations <100 μM inhibits the specific K⁺ activation at both high and low affinity sites for K⁺. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K⁺ <5 mM, the inhibition by Cd²⁺ with respect to K⁺ is uncompetitive. In the presence of MgATP and K⁺ >10 μM, the inhibition by Cd²⁺ is competitive. 3) At the low concentrations of K⁺, Cd²⁺ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K⁺(⁸⁶Rb⁺) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K⁺(⁸⁶Rb⁺) uptake is little influenced by Cd²⁺. As Cd²⁺ inhibits the metabolic uptake of K⁺(⁸⁶Rb⁺) and the K⁺ activation of the ATPase in the same way at low concentrations of K⁺, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K⁺ is low, the presence of Cd²⁺ could be disadvantageous.     

Compartmental analysis of efflux of K+(86Rb+) and Rb+(86Rb+) from roots of intact plants of barley (Hordeum vulgare) of high and low K+ status, and after excision of the shoot

The classic compartment analysis of ion efflux from roots is often applied with the assumption that there is a system of 3 compartments in series. However, complex ion transport across the root tissues, as well as influences from the shoot, may complicate the picture. The present experiments were performed to study the immediate effects that excision of the shoot before the experiment exerts on the efflux of Rb⁺(⁸⁶Rb⁺) and of K⁺(⁸⁶Rb⁺) from 9-day-old roots of plants of barley (Hordeum vulgare L. cv. Salve). The efflux from high K⁺ and low K⁺ roots of intact and detopped plants were compared. After excision of the shoot of high K⁺ plants, a marked increase in efflux was observed after 2.5 h with a maximum at about 7 h. The increase in efflux was seen as a peak in plots of efflux versus time. Excision of the shoot from low K⁺ roots did not give rise to a consistent increase in efflux. Regular K⁺ ion efflux curves were observed from roots of intact plants of high or low K⁺ status. Furthermore, after a pulse treatment of 9-day-old roots of intact plants of high or low K⁺ status with a solution containing Rb⁺(⁸⁶Rb⁺), the Rb⁺(⁸⁶Rb⁺) transport to the shoots was not reduced during the following 3 h in unlabelled solution. It is suggested that both the peak appearing in the efflux plots and the maintained tracer transport to the shoots after transfer of the roots to an unlabelled solution indicate the existence of a K⁺/Rb⁺ transport system in the symplasm of the roots that has only a slow exchange with the bulk cytoplasm and vacuoles.     

Passive uptake of K+(86Rb+) in sunflower roots at low external K+ concentrations

Passive fluxes of K⁺ (⁸⁶Rb) into roots of sunflower ( Helianthus annuus L. cv. Uniflorus) were determined at low K⁺ concentration (0.1 and 1.0 mM K⁺) in the ambient solution. Metabolic uptake of K⁺ was inhibited by 10⁻⁴M 2,4-dinitrophenol (DNP). K⁺ (⁸⁶Rb) fluxes were studied both continuously and by time differentiation of uptake. In high K⁺ roots passive uptake was directly proportional to the K⁺ concentration of the uptake solution, indicating free diffusion. This assumption was supported by the fact that passive Rb⁺ uptake was not affected by high K⁺ concentrations. In low K⁺ roots the passive uptake of K⁺ was higher than in high K⁺ roots. The increase was possibly due to carrier-mediated K⁺ transport. As K⁺ effluxes were quantitatively similar to influxes, it is suggested that passive K⁺ fluxes represent exchange diffusion without relation to net K⁺ transport.     

Accumulation of metal-binding peptides in fission yeast requires hmt2+

The fission yeast Schizosaccharomyces pombe detoxifies cadmium by synthesizing phytochelatins, peptides of the structure (gamma-GluCys)nGly, which bind cadmium and mediate its sequestration into the vacuole. The fission yeast protein HMT2, a mitochondrial enzyme that can oxidize sulphide, appears to be essential for tolerance to multiple forms of stress, including exposure to cadmium. We found that the hmt2- mutant is unable to accumulate normal levels of phytochelatins in response to cadmium, although the cells possess a phytochelatin synthase that is active in vitro. Radioactive pulse-chase experiments demonstrated that the defect lies in two steps: the synthesis of phytochelations and the upregulation of glutathione production. Phytochelatins, once formed, are stable. hmt2- cells accumulate high levels of sulphide and, when exposed to cadmium, display bright fluorescent bodies consistent with cadmium sulphide. We propose that the precipitation of free cadmium blocks phytochelatin synthesis in vivo, by preventing upregulation of glutathione production and formation of the cadmium-glutathione thiolate required as a substrate by phytochelatin synthase. Thus, although sulphide is required for phytochelatin-mediated metal tolerance, aberrantly high sulphide levels can inhibit this pathway. Precise regulation of sulphur metabolism, mediated in part by HMT2, is essential for metal tolerance in fission yeast.     

Chronological Changes in the Accumulation of Poly(A)+ RNA in Developing Cells of Xenopus laevis, with Special Reference to Primordial Germ Cells

Chronological changes in the accumulation of poly(A)⁺RNA in developing cells of Xenopus laevis were traced by in situ hybridization with ³H-poly(U) as a probe. Almost all the somatic cells acquired ³H-poly(U) binding sites by 3.5 days after fertilization (stage 44). At this stage, the primordial germ cells (PGCs), which had just moved to the genital ridges from the deep endodermal cell mass showed moderate ³H-poly(U) binding activity. The silver grains disappeared from the PGCs after stage 47 (6 days after fertilization), while the somatic cells, which constituted the neural tube, genital ridges, kidney and intestine exhibited strong ³H-poly(U) binding activity. Activity for ³H-poly(U) binding reappeared in the FGCs after stage 52 (21 days after fertilization) when sexual differentiation of gonads became detectable morphologically. The chronological accumulation and disappearance of ³H-poly(U) binding activity in the PGCs in contrast to the constant activity in somatic cells is discussed.     

Aminergic Receptors in Drosophila melanogaster: Properties of [3H]Dihydroergocryptine Binding Sites

Abstract: [³H]Dihydroergocryptine ([³H]DHE) binds to a particulate preparation from Drosophila melanogaster heads at a level of 2.4 ± 0.4 pmol/mg protein, with an apparent dissociation constant of 2.0 ± 0.5 n M . The binding sites are inactivated by heat, pronase treatment, detergents, and sulfhydryl and disulfide reagents. [³H]DHE binding is inhibited by low concentrations of serotonergic and α-adrenergic ligands. The specificity of the binding sites, as revealed by displacement studies, differs from that of [³H]DHE binding sites in various vertebrate tissues. The [³H]DHE binding sites may correspond to serotonergic receptors, and possibly, to additional classes of receptors for putative neurotransmitters in Drosophila .     

Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots

Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K⁺ levels (0.25 and 2.5 m M ) were used to study the effect of K⁺ content in the root on uptake and transport of K⁺ to the exuding stream of decapitated plants. Roots of plants grown in low K⁺ gave higher exudation flux, higher K⁺ concentration in exudate and higher K⁺ flux than high K⁺ roots. After 6 h of uptake the K⁺ flux in low K⁺ roots was about three times that in high K⁺ roots. When the roots were kept in a nutrient solution in which Rb⁺ replaced K⁺, low K⁺ roots exuded much more Rb⁺ than K⁺ after the first 2 h, whereas high K⁺ roots exuded about similar amounts of K⁺ and Rb⁺. In intact plants grown at three different K⁺ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K⁺ level in the nutrient solution and the Rb⁺ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.     

Carbon Isotope Ratios (13C/12C) in Fractions of Field-Grown Grape

The carbon isotope ratio (δ¹³C%) in leaves and berries of Vitis vinifera L. was determined during the fruiting season. The δ¹³C was from ?24.6 to ?26.3 in total leaf tissue, while it is from ?22.7 to ?24.3 in the aqueous extract of leaves. The δ¹³C in the berries was more stable, around ?24, with no change during ripening. Malic and tartaric acid, isolated from the berries at the onset of ripening, showed a δ¹³C of ?23.5 and ?23.0 respectively. It was concluded that malic acid accumulated in the berries at the onset of ripening is not formed directly through β-carboxylation.     

Effect of Fatty Acids on [3H]Ouabain Binding to Cerebromicrovascular (Na++ K+)-ATPase

The effects of short- and long-chain fatty acids on the cerebromicrovascular (Na+ + K+)-ATPase were investigated using specific [3H]ouabain binding to the enzyme. Specific binding increased linearly with total microvessel protein (37-110 micrograms) and was time-dependent with maximum binding obtained by 10 min. Arachidonic acid, but not palmitic acid, stimulated [3H]ouabain binding in a dose-dependent manner, with a 105% increase over basal levels at 100 microM arachidonic acid. Preincubation of the microvessels with arachidonic acid did not alter the stimulation observed. 4-Pentenoic acid stimulated [3H]ouabain binding only at high concentrations (10 mM). Scatchard analysis of [3H]ouabain binding to untreated microvessels yielded a single class of "high-affinity" binding sites with an apparent binding affinity (KD) of 64.7 +/- 2.0 nM and a binding capacity (Bmax) of 10.1 +/- 1.5 pmol/mg protein. In the presence of 100 microM arachidonic acid, a monophasic Scatchard plot also was obtained, but the KD significantly decreased to 51.9 +/- 2.7 nM (p less than 0.01), whereas the Bmax remained virtually unchanged (12.5 +/- 1.2 pmol/mg protein). The stimulation of [3H]ouabain binding in the presence of arachidonic acid was potentiated by 4-pentenoic acid, but not by indomethacin or eicosatetraynoic acid. These data suggest that long-chain polyunsaturated fatty acids may be involved in the regulation of blood-brain barrier (Na+ + K+)-ATPase and may play a role in the cerebral dysfunction associated with diseases in which plasma levels of nonesterified fatty acids are elevated.     

Stimulation or inhibition of K+(86Rb+)influx in wheat roots depending on different ABA treatments

The regulatory role of abscisic acid (ABA) and kinetin on influx of K+(86RB+) IN tools of 7day old intact winter wheat which plant (Fritieun aestivum I ass starke 1 and 11) Was studied the inhibitory effect of 40,80 μM ABA in the uptake solution on K+(86RB+)influx was transiently stipulated pretreatment of the plants with ABA kinetin content enacted inhibitors effect caused by ABA. At low water potential in the uptake solution (05MPa)K+(86RB+) influx was slights higher in the presence of ABA than in is absence High humidity 123kpa ca 100% relative humidity (RID)around the shoots counteracted the inhibitory effect on k+(86RB+) influx caused by A,B,A IN the uptake solution the present data contain the hypothesis that when plants are subjected to conditions such as low water potential and low temperature. ABA stimulates K influx to facilitate water uptake.     

Effects of ionic strength and relative humidity on the efflux of K+ (86Rb) and Ca2+ (45Ca) from roots of intact seedlings of cucumber, oat and wheat

Spring wheat (Triticum aestivum L. cv. Svenno), oat (Avena sativa L. cv. Brighton) and glasshouse cucumber (Cucumis sativus L. cv. Bestseller F1) were cultured for a week after germination on complete nutrient solutions of three different dilutions (1, 25 and 50% of the full strength medium). K⁺(⁸⁶Rb) and ⁴⁵Ca were present during the whole culture period. Relative humidity (RH) was 50% except during the last day, when half the material was transferred to 90% RH. Efflux of labelled ions was then followed during eight hours on unlabelled solutions of the same composition as before, and at both 50% and 90% RH in the atmosphere. – Uptake of K⁺(⁸⁶Rb) during growth tended to be saturated in the 25% medium. Contrariwise, the level of Ca²⁺ in the roots increased continuously with strength of the medium. At low concentrations cucumber roots were higher in Ca²⁺ than roots of oat or wheat, whereas all three species showed similar levels of Ca²⁺ in 50% medium. – At the lowest ionic strength, smooth efflux curves were obtained that could be resolved according to the three-compartment theory. At higher ionic strength, irregularities were observed, and more for Ca²⁺ than for K⁺; but for practical purposes compartment analysis with the same time constants could be applied as for the lowest concentration. – Discrimination between K⁺ and Rb⁺ differed between the roots, but not much between the shoots of different species. The roots of oat and wheat took up Rb⁺ preferentially over K⁺ in the 25% and 50% media; whereas K⁺ was preferred over Rb⁺ or little discrimination made in 1% medium and for cucumber. The shoots generally showed less discrimination than the roots. The main variability in discrimination between K⁺ and Rb⁺ thus appears to be localized in the tonoplasts of the roots cells. – Low RH around the shoots increased efflux of K⁺(⁸⁶Rb) from the cytoplasm and vacuoles of the root cells as compared to the efflux at high RH. DNP (2,4-dinitrophenol) in the medium had the same effect as high RH around the shoots. The signal system that must exist between shoots and roots is discussed as a response to “drought” conditions. In relation to investigations of others, it is assumed that the effect of DNP may indicate that part of the chain between roots and shoots consists of metabolically influenced sites, whose output is influenced by the rate of water transport.     

Distribution of Soluble 14C-Labelled Assimilates as Related to Distribution of 14C-Benzyladenine in Shoot Tips of Hedera helix

The relationship between benzyladenine and assimilate distributions in shoot tips of English Ivy (Hedera helix L.) was studied. Exogenous applications of benzyladenine resulted in small amounts of the hormone moving to the apical meristem. The large part of the recovered benzyladenine was found in the young leaves of the shoot tip. Benzyladenine increased the amount of ¹⁴C-labelled assimilates in the shoot tip, but the distribution pattern of those assimilates within the tip was like that of the untreated control.     

Incorporation of 35S-Sulfate into Yolk Platelets of Xenopus laevis Embryos

Inorganic ³⁵S-sulfate was injected into Xenopus laevis embryos before first cleavage to study incorporation of the label into the yolk platelets in order to localize glycosaminoglycan synthesis. Electron microscope autoradiography of embryonic thin sections from blastulae and gastrulae revealed that the primary site of label incorporation is at the edge of the yolk platelets, and, to a lesser extent, in their interiors. Autoradiography of isolated yolk platelets, lacking unit membranes, indicated the absence of label. Thus, edge associated label comes from the yolk platelets membrane, and interior label is solubilized in the glycerol-water gradient during yolk platelets isolation.
Ruthenium red staining of yolk platelet in situ shows heavy deposits of the dye on the yolk platelet membrane surface facing the cytoplasmic surface. The crystalline main body of isolated yolk platelets does not take up the dye.
It appears that continuous synthesis or sulfation of glycosaminoglycan occurs primarily at the outer surface yolk platelet membranes during early development, providing a novel site for this process.