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A Läuchli

Publications and source records attributed to A Läuchli.

At least 19 recordsLinked to original sources
PubMed2005

Two-step restoration of SU(2) symmetry in a frustrated ring-exchange magnet.

We demonstrate the existence of a spin-nematic, moment-free phase in a quantum four-spin ring-exchange model on the square lattice. This unusual quantum state is created by the interplay of frustration and quantum fluctuations that lead to a partial restoration of SU(2) symmetry when going from a four-sublattice orthogonal biaxial Néel order to this exotic uniaxial magnet. A further increase of frustration drives a transition to a fully gapped SU(2) symmetric valence bond crystal.

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PubMed2004

d-Mott phases in one and two dimensions.

We use exact diagonalization to determine the spectrum of reduced Hamiltonians based on renormalization group flows to strong coupling. For the half-filled two-leg Hubbard ladder we reproduce the known insulating d-Mott ground state with spin and charge gaps. For the saddle point regions of the two-dimensional Hubbard model near half filling we find a crossover to a similar strong coupling state, which truncates the Fermi surface near the saddle points. At lower scales d-wave superconductivity appears on the remaining Fermi surface.

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PubMed2000

Light-induced pH and K+ changes in the apoplast of intact leaves.

The K +-sensitive fluorescent dye benzofuran isophthalate (PBFI) and the pH-sensitive fluorescein isothiocyanate dextran (FITC-Dextran) were used to investigate the influence of light/dark transitions on apoplastic pH and K+ concentration in intact leaves of Vicia faba L. with fluorescence ratio imaging microscopy. Illumination by red light led to an acidification in the leaf apoplast due to light-induced H+ extrusion. Similar apoplastic pH responses were found on adaxial and abaxial sides of leaves after light/dark transition. Stomatal opening resulted only in a slight pH decrease (0.2 units) in the leaf apoplast. Gradients of apoplastic pH exist in the leaf apoplast, being about 0.5-1.0 units lower in the center of the xylem veins as compared with surrounding cells. The apoplastic K+ concentration in intact leaves declined during the light period. A steeper light-induced decrease in apoplastic K+, possibly caused by higher apoplastic K+, was found on the abaxial side of leaves concentration. Simultaneous measurements of apoplastic pH and K+ demonstrated that a light-induced decline in apoplastic K- concentration indicative of net K+ uptake into leaf cells occurs independent of apoplastic pH changes. It is suggested that the driving force that is generated by H+ extrusion into the leaf apoplast due to H+-ATPase activity is sufficient for passive K+ influx into the leaf cells.

Cytosol↗
PubMed1992

Growth and Deposition of Inorganic Nutrient Elements in Developing Leaves of Zea mays L.

Spatial distributions of growth and of the concentration of some inorganic nutrient elements were analyzed in developing leaves of maize (Zea mays L.). Growth was analyzed by pinprick experiments with numerical analysis to characterize fields of velocity and relative elemental elongation rate. Inductively coupled plasma and atomic emission spectroscopy were used to measure nutrients extracted from segments of leaf tissue collected by position. Leaves 7 and 8, both elongating 3 millimeters per hour had maximum relative elemental growth rates of 0.06 to 0.08 millimeters per hour with maximum rates 20 to 50 millimeters from the node and cessation of growth by 90 millimeters from the node. Spatial distribution of dry weight density revealed that the rate of biomass deposition was maximum in the most rapidly expanding region and continued beyond the elongation zone. The nutrient elements K, Cl, Ca, Mg, and P showed different distribution patterns of ion density (on a dry weight basis). K and Cl had minimal density in the leaf tips; K density was maximum in the growing region, whereas Cl density was maximum at the region of growth cessation. Ca, Mg, and P had relatively high densities at the base of the elongation zone near the node and also in the tip regions. Near the node, P and Mg densities were higher in the young, growing leaves, whereas Ca density near the node was higher in older leaves that had completed elongation. Deposition rates of all nutrients were greatest in the region of maximum elongation rate.

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PubMed1989

Salinity stress increases cytoplasmic ca activity in maize root protoplasts.

High concentrations of NaCl immediately elevated cytoplasmic Ca activity in maize (Zea Mays L. cv Pioneer 3377) root protoplasts, as measured with the fluorescent probe Indo-1. The effect of salinity was inhibited by Li pretreatment but restored by inositol, suggesting that phosphoinositides mediate the stress response.

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PubMed1988

Salinity affects intracellular calcium in corn root protoplasts.

Previous work with the fluorescent Ca probe chlorotetracycline (CTC) showed that salinity displaces Ca from membranes of root cells. Using a variety of indirect approaches, we studied whether salinity displaces Ca from the cell surface or from internal membranes of corn (Zea mays L. cv Pioneer 3377) root protoplasts. Preloading the cells with supplemental Ca counteracted subsequent NaCl effects on CTC fluorescence. CTC quenching by exogenous EGTA was not competitive with CTC quenching by NaCl. The Ca channel reagent (+)-202-791 had significant interactions with the effect of NaCl on CTC fluorescence. The effect of NaCl on CTC fluorescence was attenuated by pretreatment with Li, but was restored by inositol. Salinity increased Na influx, decreased Ca influx, and increased Ca efflux from the cells. Fluorescence anisotropy indicated that NaCl decreased the fluidity of the external face of the plasmalemma but increased the fluidity of cell membranes in general. Our results suggest that salinity displaces Ca associated with intracellular membranes through activation of the phosphoinositide system and depletion of intracellular Ca pools.

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PubMed1988

Incorporation of [C]Glucose into Cell Wall Polysaccharides of Cotton Roots: Effects of NaCl and CaCl(2).

Cotton (Gossypium hirsutum L. cv Acala SJ-2) seedlings were grown in nutrient solutions with four combinations of NaCl (0.1 and 150 millimolar) and CaCl(2) (1 and 10 millimolar) for 7 days, and then exposed to [(14)C]glucose for 5 hours. Uptake and incorporation of [(14)C]glucose into various cell wall fractions of the root tips were determined. At 1 millimolar Ca(2+), treatment with 150 millimolar NaCl slightly stimulated uptake but considerably inhibited glucose incorporation into noncellulosic and cellulosic polysaccharides. Supplemental Ca(2+) did not affect incorporation of glucose into the noncellulosic fraction (regardless of NaCl treatment) but completely alleviated the inhibitory effect of NaCl on glucose incorporation into cellulose. We suggest that high Na(+) concentrations reduce synthesis of cellulose in cotton roots via disturbance of plasma membrane integrity and that supplemental Ca(2+) counteracts this effect. The effects on cellulose biosynthesis are proposed to be related to Ca(2+) displacement from the plasma membrane.

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PubMed1987

Salinity reduces membrane-associated calcium in corn root protoplasts.

Calcium is an important factor in the ability of plants to resist salt stress, possibly because of its role in maintaining membrane integrity. We studied the effects of NaCl stress on membrane-associated Ca in corn root protoplasts (Zea mays L. cv Pioneer 3377) using the fluorescent Ca probe chlorotetracycline (CTC). Protoplasts were isolated from the cortex of primary roots of corn seedlings (Gronwald and Leonard, Plant Physiol 1982 70: 1391-1395). After a 30 minute incubation in 50 micromolar CTC, the protoplasts were exposed to isosmotic treatment solutions containing various concentrations of NaCl just before fluorimetric analysis. Increasing NaCl concentrations caused a progressive reduction in net CTC fluorescence, to 50% of control values at 150 mm NaCl. NaCl did not displace CTC from the cells, nor did it directly interfere with Ca-CTC binding. Tests with CsCl, RbCl, KCl, LiCl, Na(2)SO(4), NaNO(3), and NaBr indicated that the reduction in CTC fluorescence was not specific to either Na or Cl, but may have been due to increased ionic strength of the treatment solutions. Like CTC fluorescence, root growth of intact corn seedlings was not specifically sensitive to Na, but was inhibited by several monovalent cations in the order Li > Cs >> Rb > Na > K. CTC fluorescence at 100 mm NaCl was restored to unstressed levels by increasing Ca concentrations. Since our salt treatments were isosmotic, we conclude that the ionic component of salt stress displaces Ca from membranes of corn root cells.

Journal Article↗
PubMed1987

Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca.

High Na(+) concentrations may disrupt K(+) and Ca(2+) transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca(2+) levels often counteract these consequences of salinity. The effect of supplemental Ca(2+) on influx of Ca(2+), K(+), and Na(+) in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca(2+). Sodium influx increased proportionally to increasing salinity. At high external Ca(2+), Na(+) influx was less than at low Ca(2+). Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, (45)Ca(2+) influx increased in proportion to salt concentrations, especially with high Ca(2+). Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca(2+). The rate of K(+) uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca(2+) is related to improved Ca-status and maintenance of K(+)/Na(+) selectivity.

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PubMed1986

Effects of NaCl and CaCl(2) on Ion Activities in Complex Nutrient Solutions and Root Growth of Cotton.

Sodium displaces Ca(2+) from membranes (GR Cramer, A Läuchli, VS Polito Plant Physiol 1985 79: 207-211) and this can be related to the (Ca(2+))/(Na(+))(2) activity ratio in the external solution (GR Cramer, A Läuchli 1986 J Exp Bot 37: 321-330). Supplemental Ca(2+) is known to mitigate the adverse effects of salinity on plant growth. In this report we investigated the effects of NaCl (0-250 millimolar) and Ca(2+) (0.4 and 10 millimolar) on the ion activities in solution and on root growth of cotton (Gossypium hirsutum L.). Ion activities were analyzed using the computer program, GEOCHEM. Most ion activities in a 0.1 modified Hoagland solution were significantly reduced by both NaCl and supplemental Ca(2+). Ion-pair formation and precipitation were significant for some ions, especially phosphate. Root growth of 6-day-old seedlings was stimulated by low NaCl concentrations (25 millimolar). At higher NaCl concentrations, root growth was inhibited; the concentration at which this occurred depended on the Ca(2+) concentration and the growth index used. Supplemental Ca(2+) mitigated the inhibition of root growth caused by NaCl. There was a curvilinear relationship between root growth and the (Ca(2+))/(Na(+))(2) ratio in the nutrient solution. The mechanisms by which Na(+) and Ca(2+) may affect root growth are discussed.

Journal Article↗
PubMed1986

Effects of NaCl and CaCl(2) on Cell Enlargement and Cell Production in Cotton Roots.

In many crop species, supplemental Ca(2+) alleviates the inhibition of growth typical of exposure to salt stress. In hydroponically grown cotton seedlings (Gossypium hirsutum L. cv Acala SJ-2), both length and weight of the primary root were enhanced by moderate salinities (25 to 100 millimolar NaCl) in the presence of 10 millimolar Ca(2+), but the roots became thinner. Anatomical analysis showed that the cortical cells of these roots were longer and narrower than those of the control plants, while cortical cells of roots grown at the same salinities but in the presence of only 0.4 millimolar Ca(2+) became shorter and more nearly isodiametrical. Cell volume, however, was not affected by salinities up to 200 millimolar NaCl at either 0.4 or 10 millimolar Ca(2+). Our observations suggest Ca(2+)-dependent effects of salinity on the cytoskeleton. The rate of cell production declined with increasing salinity at 0.4 millimolar Ca(2+) but at 10 millimolar Ca(2+) was not affected by salinities up to 150 millimolar NaCl.

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PubMed1985

Oxygen-Dependent Exclusion of Sodium Ions from Shoots by Roots of Zea mays (cv Pioneer 3906) in Relation to Salinity Damage.

Using radio-tracers, we measured Na(+) and K(+) accumulation in roots and transport to shoots in Zea mays (cv Pioneer 3906) as a function of NaCl concentration and O(2) partial pressure in the nutrient solution. Under fully aerobic conditions, roots partially excluded Na(+) from the shoots over a wide range of NaCl concentration (0.2-200 millimolar). With root anoxia, the exclusion mechanism broke down so that much greater amounts of Na(+) reached the shoots, with simultaneous inhibition of K(+) transport. The ratio Na(+)/K(+) entering the shoot consequently increased 90 to 200 times. Increases in Na(+) transport were first detected when the O(2) partial pressure was reduced from ambient (21% v/v) to 15%, whereas K(+) transport was not inhibited until O(2) concentrations were <5%. Since soil O(2) deficiency can often accompany high salinity in irrigation agriculture, failure of the Na(+) exclusion mechanism may be a contributory factor in salinity damage of salt-sensitive glycophytes.

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PubMed1985

Displacement of ca by na from the plasmalemma of root cells : a primary response to salt stress?

A microfluorometric assay using chlorotetracycline (CTC) as a probe for membrane-associated Ca(2+) in intact cotton (Gossypium hirsutum L. cv Acala SJ-2) root hairs indicated displacement of Ca(2+) by Na(+) from membrane sites with increasing levels of NaCl (0 to 250 millimolar). K(+)((86)Rb) efflux increased dramatically at high salinity. An increase in external Ca(2+) concentration (10 millimolar) mitigated both responses. Other cations and mannitol, which did not affect Ca(2+)-CTC chelation properties, were found to have no effect on Ca(2+)-CTC fluorescence, indicating a Na(+)-specific effect. Reduction of Ca(2+)-CTC fluorescence by ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid, which does not cross membranes, provided an indication that reduction by Na(+) of Ca(2+)-CTC fluorescence may be occurring primarily at the plasmalemma. The findings support prior proposals that Ca(2+) protects membranes from adverse effects of Na(+) thereby maintaining membrane integrity and minimizing leakage of cytosolic K(+).

Journal Article↗
PubMed1984

Influx and efflux of p in roots of intact maize plants : double-labeling with p and p.

Rates of P influx and efflux were determined in whole plants at ambient P concentrations comparable to those found in soil solutions. Maize (Zea mays L. var NC+59) seedlings were trimmed (endosperm and adventitious roots removed) and grown in a greenhouse in solution cultures at P concentrations of approximately 0.4 and 1.8 micromolar. Roots of intact plants previously exposed to (32)P-labeled solutions at 0.2 and 2.0 micromolar P for 48 hours were rinsed 10 minutes in P-free solution and exposed to (33)P solutions at 0.2 and 2.0 micromolar for 10 minutes. Net depletion of (33)P from and appearance of (32)P in the ambient solution were used to measure influx and efflux. The ration of (32)P efflux to (33)P influx was about 0.68 at 0.2 micromolar and 0.08 at 2.0 micromolar. When plants were allowed to deplete P from solutions, the P concentration in the medium dropped to about 0.15 micromolar within 24 hours and 0.05 micromolar within 60 hours. Results indicate that P efflux is a substantial component of net P accumulation at P concentrations normally found in soil solutions.

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PubMed1981

Ion distribution in roots of barley seedlings measured by electron probe x-ray microanalysis.

The distribution of ions, particularly K and Na, was studied in roots of barley seedlings grown on various ionic solutions. Analyses were made by means of electron probe x-ray microanalysis using frozen, fractured bulk specimens. By this technique, it was demonstrated that there can be variability in the ratio K/Na measured in the vacuoles of cortical cells, with this ratio often being lower in epidermal cells of the root than in the inner cortex. A sharp difference in the K/Na ratio was also found between cells of the endodermis and those of the adjacent cortex, and generally higher ratios of K/Na occurred in the stele than in the cortex. Estimation of the concentrations in the cytoplasm was at the limit of resolution of this technique, but it can be shown that the K/Na ratio in the cytoplasm was higher than that in the vacuole. In low salt roots, the K concentration in the cytoplasm was higher than that in the vacuoles. The results with the x-ray microprobe confirm other measurements based on flux analysis or analysis of small samples of the root.

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PubMed1977

Cytochemical Localization of K-stimulated Adenosine Triphosphatase Activity in Xylem Parenchyma Cells of Barley Roots.

ATPase activity in xylem parenchyma cells of barley (Hordeum vulgare L.) roots was demonstrated cytochemically with a lead precipitation reaction. The methodical parameters of this cytochemical test were optimized for distinction between ATPase-specific and nonspecific precipitates. Optimum conditions were prefixation in 1% glutaraldehyde for 1 hour and incubation for 2 hours in a medium containing 2 mm each of ATP, Ca(2+), and Pb(2+) at pH 7 and 25 C. Problems of cytochemical localizations are discussed.ATPase activity occurred mainly at the plasmalemma, the endoplasmic reticulum nuclear envelope, and outer mitochondrial membranes of xylem parenchyma cells. The tonoplast of these cells showed only little ATPase activity. High K(+) concentrations stimulated ATPase activity, particularly at the plasmalemma. Diethylstilbestrol prevented the formation of ATPase-specific precipitates. The cytochemical demonstration of a K(+)-stimulated ATPase at the plasmalemma of xylem parenchyma cells is discussed in relation to the possible role of this membrane in ion transport to the vessels.

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PubMed1971

Lateral transport of ions into the xylem of corn roots: I. Kinetics and energetics.

A technique is described for study of the kinetics of lateral transport of ions across single roots of corn, Zea mays, in short term experiments under steady state conditions. The kinetics of chloride transfer to the vessels reflected the kinetics of absorption of chloride by the root cells. Efflux from the root vacuoles contributed to only a small extent to transport of chloride into the exudate. Lateral transport of chloride was inhibited by bromide at chloride concentrations in the ranges of both mechanisms 1 and 2 in a manner implicating competition. The uncoupler carbonylcyanide m-chlorophenylhydrazone used at 1 mum caused transfer of chloride to cease almost immediately at both low and high concentrations of chloride. Oligomycin depressed transport of chloride to the vessels within 10 to 15 minutes after application at 2 micrograms per milliliter. Inhibition by oligomycin was 75% at 0.5 mm chloride and 55% at 5 mm.It is concluded that lateral transport of chloride across corn roots is mediated by the dual mechanisms of ion absorption which reside in the plasmalemma. Transfer of chloride is inhibited by bromide and depends upon ATP as energy source. Chloride moves from the plasmalemma, the site of carriermediated absorption, to the xylem vessels by way of the symplasm. There is no evidence in these experiments that lateral transport of chloride in corn roots is governed by diffusion at any concentrations of chloride used in these experiments.

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