Salt-tolerant Triticum×Lophopyrum derivatives limit the accumulation of sodium and chloride ions under saline-stress

Abstract. Cultivars of hexaploid wheat ( Triticum aestivum cvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt-tolerant species ( Lophopyrum elongatum or L. ponticum ) were compared to determine differences in growth, ion transport and ion accumulation under salt-stress. Two experiments were conducted in which plants were grown under saline and non-saline conditions and harvested at various lime intervals throughout ontogeny. Under salt-stress the growth rate of the cultivars, as compared to the growth rate of the derivatives, decreased more rapidly later in development. Transport rates from root to shoot of Na⁺ and Cl⁻ reached higher levels in the cultivars. The cultivars accumulated more Na⁺ and Cl⁻ and relatively less K⁺ in the shoot. The K⁺/Na⁺ ratio was higher in the derivatives than in the cultivars from which they were derived. The addition of chromosomes from Lophopyrum species into wheat altered ion accumulation, growth rates, and ion transport rates from root to shoot.     

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.     

ENERGETICS OF AMINO ACID TRANSPORT INTO BRAIN SLICES: EFFECTS OF K+ DEPLETION AND Rb+ OR Cs+ SUBSTITUTION ON AMINO ACID UPTAKE

Abstract— Mouse brain slices were depleted of K⁺ by three 10-min incubations-in oxygenated HEPES-buffered medium lacking glucose and K⁺. Addition of K⁺ or Rb⁺ (or Cs⁺, to a smaller degree) with glucose, or with succinate, malate, and pyruvate (SMP) before incubation at 37°C with ¹⁴C-amino acids restored active low-affinity transport of d -Glu, α-aminoisobutyrate (AIB), GABA, Gly, His, Val, Leu, Lys, and Orn. Ouabain at 1–2μ m with Rb⁺ was more inhibitory with SMP than with glucose, suggesting that the glycoside may affect specific energy coupling to transport. Valinomycin, in contrast, showed no specificity of inhibition of amino acid uptake with glucose or SMP and K⁺ or Rb⁺. Cs⁺ partially restored amino acid uptake, but Li⁺ was less effective than Cs ⁺. NaF at 10 m m with SMP + Rb⁺, or SMP + K⁺ did not inhibit amino acid uptake. Therefore, it was possible to dissociate glycolysis and Na⁺, K ⁺ -ATPase activity from amino acid transport. The ion replacements for K ⁺ that supported active amino acid transport indicate that the specificity of ions in possible ionic gradients for transport energetics should be reexamined.     

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.     

Potassium transport in wheat seedlings grown with different potassium supplies.

The K⁺(⁸⁶Rb) uptake into the roots and the translocation to the shoots of 11-day-old intact wheat seedlings ( Triticum aestivum L. cv. Martonvásári 8) were investigated using plants grown with different K⁺ supplies. The effects of environmental conditions (darkness, humidity) and of metabolic and transport inhibitors (oligomycin, disalicylidene-propanediamine, 2,4-dinitriphenol, diethylstilbestrol, colchicine) were also studied. Plants with K content of about 0.2 mmol/g dry weight in the root and 0.5 mmol/g dry weight in the shoot (low K status) showed high K⁺ uptake into the roots and high translocation rates to the shoots. Both transport processes were very low in plants with K content of more than 1.5 and 2.2 mmol/g dry weight in the root and shoot, respectively (high K status).
Darkness and a relative humidity of the air of 100% did not influence K⁺ uptake by roots, but did inhibit upward translocation and water transport. Inhibition of photosynthesis and treatments with diethylstilbestrol (10⁻⁵ mol/dm³), as well as with colchicine resulted in inhibition of translocation in plants of low K status, but these inhibitors had little effect on K⁺ uptake by the roots. Oligomycin, 2,4-dinitrophenol and diethylstilbestrol (10⁻⁴ mol/dm³), however, inhibited K⁺ uptake by the roots. In general, K⁺ transport processes were almost unchanged in plants of high K status. It is concluded that only plants of low K status operating with active K⁺ transport mechanisms are responsive to environmental factors. In high K⁺ plants the transport processes are passive and are uncoupled from the metabolic energy flow.     

Effect of K+ and H+ stress and role of Ca2+ in the regulation of intracellular K+ concentration in mung bean roots

The effects of external K⁺, H⁺ and Ca2⁺ concentrations on the intracellular K+ concentration, [K⁺]i, and the K⁺-ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K⁺]i, in mung bean roots was markedly decreased by external K⁺ or H⁺ stress and did not recover the initial value even after the stress was removed. This decrease in [K⁺]i, gradually disappeared with the addition of (Ca2⁺. Ca2⁺ may offset the harmful effects of ion stress. Ca2⁺ seems to have two effects on K+ transport; control of K⁺ permeability and activation of K⁺ uptake, although K⁺-ATPase activity was inhibited by Ca2⁺ concentrations higher than 10–4 M. We suggest that Ca2⁺ activates K⁺ uptake indirectly through the acidification of the cytoplasm.     

K/Na selectivity at the plasmalemma of cortical root cells and preferential release of sodium to the xylem vessels in roots of Atriplex hortensis

Using excised roots of Atriplex hortensis L., cv. Gelbe Gartenmelde, the uptake, accumulation and xylem transport of K⁺ and Na⁺ have been measured. Influx as well as xylem transport proved to discriminate little between K⁺ and Na⁺, when considered in relation to the external solution. Both K⁺ and Na⁺ inhibited the uptake and xylem transport of each other to about the same degree. Measurements of intracel-lular Na⁺ fluxes by means of compartment analysis indicated that the low degree of K/Na discrimination during uptake was due to low influx selectivity. Moreover, K⁺/Na⁺ exchange at the plasmalemma was not very efficient in Atriplex roots. In order to establish the basis of the low K/Na discrimination in xylem transport, the rates of K⁺ and Na⁺ transport were related to the cytoplasmic K⁺ and Na⁺ concentrations to yield the selectivity ratio of transport, S(transport) = (φ_cx(K) × [Na⁺]_c)/(φ_cx(Na) × [K⁺]_c). Under all conditions this ratio was far below one indicating that Na⁺ was favoured during xylem release in excised roots of Atriplex at low external concentrations. The implications of this discrimination in favour of Na+ are discussed with respect to salt tolerance of A. hortensis .     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

Potassium utilization and fluxes in wild salt-tolerant relatives of the cultivated tomato

The growth of the wild tomato species Lycopersicon peruvianum (L.) Mill, and L. pennellii (Correll) D'Arcy, was compared with that of the cultivated tomato, L. esculentum Mill. cv. VE 234, under conditions of reduced K⁺ supply. Growth was impaired less in the wild than in the cultivated species. The higher efficiency of K⁺ utilization in the wild species was not associated with more efficient JC uptake from the medium. The rate of K⁺ uptake by whole plants was similar in the three species, but the rate of uptake by detached root tips was lower in the wild species. The permeability of the plasma membrane to K+ was apparently similar in root tips of the three species, but the tonoplast permeability was much lower in the wild than in the cultivated species.     

ɛ-(γ-Glutamyl)lysine cross-links of spore coat proteins and transglutaminase activity in Bacillus subtilis

Abstract The capacity to transport potassium and to discriminate between the different alkali cations has been found to affect sodium tolerance in Saccharomyces cerevisiae . Mutants with a defective capacity to transport K⁺ were more sensitive to high concentrations of Na⁺ because they accumulated more Na⁺ and less K⁺ than wild-type cells which showed high discrimination between K⁺ and Na⁺.     

Prokaryotic K(+) channels: from crystal structures to diversity

The deep roots and wide branches of the K⁺-channel family are evident from genome surveys and laboratory experimentation. K⁺-channel genes are widespread and found in nearly all the free-living bacteria, archaea and eukarya. The conservation of basic structures and mechanisms such as the K⁺ filter, the gate, and some of the gate's regulatory domains have allowed general insights on animal K⁺ channels to be gained from crystal structures of prokaryotic channels. Since microbes are the great majority of life's diversity, it is not surprising that microbial genomes reveal structural motifs beyond those found in animals. There are open-reading frames that encode K⁺-channel subunits with unconventional filter sequences, or regulatory domains of different sizes and numbers not previously known. Parasitic or symbiotic bacteria tend not to have K⁺ channels, while those showing lifestyle versatility often have more than one K⁺-channel gene. It is speculated that prokaryotic K⁺ channels function to allow adaptation to environmental and metabolic changes, although the actual roles of these channels in prokaryotes are not yet known. Unlike enzymes in basic metabolism, K⁺ channel, though evolved early, appear to play more diverse roles than revealed by animal research. Finding and sorting out these roles will be the goal and challenge of the near future.     

Intracellular ion levels in erythrocytes and hepatocytes isolated from three teleost species

Intracellular concentrations of Na⁺ and K⁺ were similar (∼75 mmol l⁻¹) in rainbow trout Oncorhynchus mykiss hepatocytes directly following isolation by collagenase digestion, but partial recovery occurred over 6 h with K⁺ levels increasing to 110 mmol l⁻¹ and Na⁺ levels decreasing to 42 mmol l⁻¹. Black bullhead Ameiurus melas hepatocytes exhibited higher intracellular concentrations of K⁺ (90 mmol l⁻¹) than Na⁺ (55 mmol l⁻¹) with no recovery occurring over 6 h following cell isolation. Concentrations of Na⁺, K⁺ and Cl⁻ in eel Anguilla rostrata hepatocytes were similar (∼ 55 mmol l⁻¹) following isolation, with no recovery occurring over time. Erythrocytes from all species apparently did not experience an intracellular ion imbalance following isolation as indicated by high K⁺ levels (<140 mmol l⁻¹) and low Na⁺ levels (<40 mmol l⁻¹) during the entire 24-h monitoring period. Although hepatocytes from all species exhibited an ion imbalance post-isolation, comparison of their in vitro intracellular Na⁺ and K⁺ concentrations with those in plasma demonstrated that directionally correct ion gradients still exist across the cell membrane, albeit differing from those that would be found in the tissue in vivo .     

Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells

Potassium ions (K⁺) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K⁺ transport system. In this study, we investigated the role of K⁺ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker -like outward K⁺ channel gene, NTORK1 , under cell-division conditions, whereas the inward K⁺ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K⁺ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K⁺ uptake is not required for cell division. In contrast, K⁺ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K⁺ or the cytoplasmic alkalizing reagent (NH₄)₂SO₄ increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K⁺ taken up into cells is used to regulate cytoplasmic pH during cell division.     

Regulation of haemolymph sodium and potassium during dehydration in the cricket Teleogryllus oceanicus

ABSTRACT. Male crickets ( Teleogryllus oceanicus ) when dehydrated for 3 days lost 51% of their body water, and 65% of their haemolymph volume. Haemolymph osmolality rose from 391 to 572mOs/kg; [Na⁺] from 149 to 289 HIM; and [K⁺] from 13.0 to 26.3 mM. During dehydration 385 μig Na (expressed as NaCl) and 41 μug K (expressed as KCI) were removed from the haemolymph. Rehydration of the dehydrated insects failed to restore the Na⁺ and K⁺ concentrations to near their original levels. Approximately 62% of the missing Na⁺ was excreted, whilst five times the amount of K⁺ removed from the haemolymph was excreted. It is presumed that the excess represents K⁺ removed from intracellular fluid.     

Possible Involvement of K^＋/Na^＋ in Assessing the Seed Vigor Index

More substances leaked from a higher-vigor seed sample than from a lower-vigor sample. This indicates that, in some cases, electric conductivity does not represent seed vigor level very well, especially for high-vigor seeds. Results from germination, germination index, leachate conductivity, and the ratio of K^＋/Na^＋ from three-seed lots of Chinese cabbage （Brassica pekinensis （Louv.） Rupr） showed that K^＋/Na^＋ correlated well with germination and germination index. The ability of K^＋/Na^＋ to indicate well changes in vigor was further supported by investigation in soybean （Glycine max （L.） Merr.） seeds and another cultivar of Chinese cabbage seeds. Thus, seed leakage of K^＋/Na^＋ can accurately indicate seed vigor, whereas the conductivity test failed to do so. Furthermore, K^＋/Na^＋ showed up bigger quantitative differences in vigor level than did the conductivity test. This findings provide a more sensitive and accurate index for the assessment of seed vigor. The mechanisms of Na^＋ and K^＋ ion transport are also discussed.     

Adaptation of Escherichia coli to high osmolarity environments: Osmoregulation of the high-affinity glycine betaine transport system ProU

Abstract: A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Fscherichia coli and Salmonella typhimurium since it triggers a rapid efflux of water from the cell, resulting in a decreased turgor. Changes in the external osmolarity must therefore be sensed by the microorganisms and this information must be converted into an adaptation process that aims at the restoration of turgor. The physiological reaction of the cell to the changing environmental condition is a highly coordinated process. Loss of turgor triggers a rapid influx of K⁺ ions into the cell via specific transporters and the concomitant synthesis of counterions, such as glutamate. The increased intracellular concentration of K⁺-glutamate allows the adaptation of the cell to environments of moderately high osmolarities. At high osmolarity, K⁺-glutamate is insufficient to ensure cell growth, and the bacteria therefore replace the accumulated K⁺ ions with compounds that are less d eleterious for the cell's physiology. These compatible solutes include polyoles such as trehalose, amino acids such as proline, and methyl-amines such as glycine betaine. One of the most important compatible solutes for bacteria is glycine betaine. This potent osmoprotectant is widespread in nature, and its intracellular accumulation is achieved through uptake from the environment or synthesis from its precursor choline. In this overview, we discuss the properties of the high-affinity glycine betaine transport system ProU and the osmotic regulation of its structural genes.     

Cd2+ uptake, Cd2+ binding and loss of cell K+ by a Cd-sensitive and a Cd-resistant strain of Saccharomyces cerevisiae

Abstract Uptake of Cd²⁺ into Cd-resistant cells was approximately four times lower than in Cd-sensitive cells of Saccharomyces cerevisiae . Binding of Cd²⁺ to the yeast cells increased during incubation of the cells in the presence of Cd²⁺. The increase in the binding was much higher for wild-type cells than for Cd-resistant cells. This increased binding is ascribed to permeabilization of part of the cells. There is no single relation between the relative rate of K⁺ efflux and the cellular Cd content as has been found previously for wild-type cells. The rates of K⁺ efflux were much less than those found for the wild-type cells. Only with short incubation periods of the cells with Cd²⁺ was the same dependence found between the efflux of K⁺ and the cellular Cd content for both types of cell. The discrepancies found after extended incubation of the cells with Cd²⁺ are ascribed to the fact that Cd-provoked K⁺ release proceeds via an all-or-nothing process and that K⁺ released from permeabilized cells can be reaccumulated in still intact cells. The latter proceeds more efficiently in Cd-resistant cells than in wild-type cells.     

All-or-none K+ efflux from yeast cells induced by calmodulin antagonists

Abstract Three calmodulin antagonists, trifluoperazin, compound 48/ 80 and calmidazolium provoke K⁺ efflux from metabolizing yeast cells. This K⁺ efflux is accompanied by a shrinkage of the cells. Part of the cells show a gradual shrinkage whilst the remainder of the cells shrink via an all-or-none process. Cells shrunken via an all-or-none process have the same size as cells which have been completely permeabilized by a cationic detergent with loss of all their K⁺.