An Experimental Study of Calcium Acquisition and its Effects on the Calcifuge Moss Pleurozium schreberi

In a field experiment to investigate the sources and effectson growth of Ca in the calcifuge moss Pleurozium schreberi,significant quantities of Ca reached the growing shoot apicesfrom a CaCO₃ layer placed on the mineral soil surface Top applicationsof 0.5 and 5 mol m^–3 CaCl₂ raised the exchangeable andintracellular Ca concentrations and displaced natural exchangeableK and Mg The 5 mol m^–3 CaCl₂ treatment also caused a significantreduction in intracellular Mg indicating that Mg uptake is dependenton an initial exchange step No growth differences were notedbetween treatments, possibly because ionic changes had not reacheda detrimental level within the 28 weeks of the experiment ina second experiment, shoot apices of Pleurozium schreberi, Pseudoscleropodiumpurum and Calliergon cuspidatum were grown on nylon gauze underintermittent distilled-water mist At weekly intervals the shootswere saturated with CaCl₂ solutions providing factorial combinationsof Ca and pH Growth of C cuspidatum and P purum from chalk soilwas reduced at high (0.01) Ca concentration whereas Pleuroziumschreberi and Pseudoscleropodium purum from acidic clay wereunaffected The pH treatments did not significantly affect mossgrowth Initial tissue levels of K and Mg were lower in the mossesfrom chalk and it is suggested that the CaCl₂ treatments causednutrient deficiencies in these plants Mosses from acidic soilcontained less exchangeable Ca than the chalk plants and grewpoorly in the absence of CaCl₂, perhaps due to the developmentof Ca deficiency Bryophyte growth, calcium uptake, pH, mineral nutrition, Pleurozium schreberi, Pseudoscleropodium purum, Calliergon cuspidatum     

Salsola arbusculiformis, a C3-C4Intermediate in Salsoleae (Chenopodiaceae)

Salsola arbusculiformis is identified as a C₃–C₄intermediatespecies based on anatomical, biochemical and physiological characteristics.This is the first report of a naturally occurring intermediatespecies in the Chenopodiaceae, the family with the largest numberof C₄species amongst the dicots. In the genus Salsola, mostspecies have Salsoloid anatomy with Kranz type bundle sheathcells and C₄photosynthesis, while a few species have Sympegmoidanatomy and were found to have non-Kranz type bundle sheathcells and C₃photosynthesis. In the cylindrical leaves of C₄Salsolawith Salsoloid type anatomy, there is a continuous layer ofdistinct, chlorenchymatous Kranz type bundle sheath cells surroundedby a single layer of mesophyll cells; whereas species with Sympegmoidtype anatomy have an indistinct bundle sheath with few chloroplastsand multiple layers of chlorenchymatous mesophyll cells. However,S. arbusculiformis has intermediate anatomical features. Whileit has two-to-three layers of mesophyll cells, characteristicof Sympegmoid anatomy, it has distinctive, Kranz-like bundlesheath cells with numerous chloroplasts and mitochondria. Measurementsof its CO₂compensation point and CO₂response of photosynthesisshow S. arbusculiformis functions as an intermediate specieswith reduced levels of photorespiration. The primary means ofreducing photorespiration is suggested to be by refixing photorespiredCO₂in bundle sheath cells, since analysis of photosyntheticenzymes (activity and immunolocalization) and¹⁴CO₂labellingof initial fixation products suggests minimal operation of aC₄cycle. Copyright 2001 Annals of Botany Company Immunolocalization, photosynthetic enzymes, C₃–C₄intermediate, C₄-plants, leaf anatomy, Chenopodiaceae, Salsola arbusculiformis     

Studies on the Development of the Air Pores and Air Chambers of Marchantia paleacea: 1. Light Microscopy

The ontogeny of the air pores and air chambers of Marchantiapaleacea begins with the schizogenous development of protodermalintercellular spaces of the initial apertures, and is completedwith the formation of the air pores and giant sub-epidermalair chambers bearing numerous photosynthetic filaments. Intercellularspace formation commences from the thallus surface and proceedsinwards to the first internal layer of cells. The cells amongwhich spaces develop do not originate from one mother cell.Spaces are formed only in the regions of the intersection ofthe anticlinal walls of three, four, or sometimes more successivederivatives of S₁, S₃ and S₄ segments of the apical cell, oneor two of which have been divided periclinally and the restanticlinally. Protodermal intercellular spaces appear in mostor all the corners of these cells, the anticlinal walls of whichexhibit an opposite disposition. The S₁, S₂, S₃ and S₄ segmentsare produced by definite divisions of a five-sided apical celland by a series of divisions give rise to initial cells of theinternal layers of the thallus and initial cells of the protodermaland sub-protodermal layers. The concept of a quiescent apicalcell cannot be accepted, since dividing apical cells have beenobserved, and the pattern of wall disposition of the thallusapex cannot be explained without the active participation ofthe apical cell. The air chambers are apparently of exogenous origin. They resultfrom the broadening of the bottom of the initial apertures bythe coordination of the rate of anticlinal divisions and growthof the protodermal and sub-protodermal cells surrounding theintercellular spaces of the initial apertures. The ontogenyof the pore rings starts at an advanced stage of air chamberformation not from a mother cell but from the cells which surroundthe closed entrance of the air chamber, by a shift of the planeof division from anticlinal to periclinal. Before the periclinaldivisions a new axis of growth perpendicular to the thallussurface is established in the mother cells of the pore. By a polarized growth into the air chamber followed by periclinaldivisions, the cells of the floor form initial cells of thephotosynthetic filaments. The latter divide again to form singleor branched photosynthetic filaments. Marchantia paleacea, air pore, air chamber     

Ultrastructural Investigation of Tension Wood Fibre in Fraxinus mandshurica Rupr. var. japonica Maxim.

The ultrastructure of the fibre wall in Fraxinus mandshuricaRupr. var. japonica Maxim. was investigated by electron microscopy.The trees had been inclined artificially at an angle of 30°to the vertical at the beginning of the initiation of cambialgrowth in early spring. The secondary walls of tension woodfibres were of the outer (S₁) layer and gelatinous (G) layertype. The microfibrils in the gelatinous (G) layer were orientedas a steep Z-helix relative to the fibre axis with a deviationthat ranged from 0° to 25° but was mainly between 5°and 10°. The cross-sectional surface of tension wood fibresrevealed the relatively strong attachment of the G-layer tothe S₁ layer. The G-layer stained weakly with potassium permanganate.The S₁ layer of tension wood fibres stained less strongly thanthat of the normal and opposite wood fibres. These results indicatethat the tension wood in F. mandshurica var. japonica is nottypical and is somewhat anomalous. The secondary walls of normaland opposite wood fibres were composed of two layers, S₁ andS₂, and lacked an S₃ layer. Microfibrils in the S₃ layer ofjuvenile stems were extremely variable in orientation and weresparsely distributed without forming a layer. By contrast, avery thin S₃ layer was present in the wood fibres of maturestems. The variations in the formation of the S₃ layer in thefibre walls were probably due to the differences in the cambialage of the stems of F. mandshurica Rupr. var. japonica.Copyright1995, 1999 Academic Press Fraxinus mandshurica Rupr. var. japonica Maxim., Japanese ash, tension wood, fibre wall, G-layer, microfibrillar orientation, normal and opposite wood, juvenile stem, field-emission scanning electron microscopy, low accelerating voltage     

Maitotoxin and P2Z/P2X7 purinergic receptor stimulation activate a common cytolytic pore

The effects ofmaitotoxin (MTX) on plasmalemma permeability are similar to thosecaused by stimulation of P2Z/P2X₇ionotropic receptors, suggesting that1) MTX directly activatesP2Z/P2X₇ receptors or2) MTX andP2Z/P2X₇ receptor stimulationactivate a common cytolytic pore. To distinguish between these twopossibilities, the effect of MTX was examined in1) THP-1 monocytic cells before andafter treatment with lipopolysaccharide and interferon-, a maneuverknown to upregulate P2Z/P2X₇receptor, 2) wild-type HEK cells andHEK cells stably expressing theP2Z/P2X₇ receptor, and3) BW5147.3 lymphoma cells, a cellline that expresses functional P2Z/P2X₇ channels that are poorlylinked to pore formation. In control THP-1 monocytes, addition of MTXproduced a biphasic increase in the cytosolic freeCa²⁺ concentration([Ca²⁺]_i);the initial increase reflects MTX-inducedCa²⁺ influx, whereas the secondphase correlates in time with the appearance of large pores and theuptake of ethidium. MTX produced comparable increases in[Ca²⁺]_iand ethidium uptake in THP-1 monocytes overexpressing theP2Z/P2X₇ receptor. In bothwild-type HEK and HEK cells stably expressing theP2Z/P2X₇ receptor, MTX-inducedincreases in[Ca²⁺]_iand ethidium uptake were virtually identical. The response of BW5147.3cells to concentrations of MTX that produced large increases in[Ca²⁺]_ihad no effect on ethidium uptake. In both THP-1 and HEK cells, MTX- andBz-ATP-induced pores activate with similar kinetics and exhibit similarsize exclusion. Last, MTX-induced pore formation, but not channelactivation, is greatly attenuated by reducing the temperature to22°C, a characteristic shared by theP2Z/P2X₇-induced pore. Together,the results demonstrate that, although MTX activates channels that aredistinct from those activated byP2Z/P2X₇ receptor stimulation, thecytolytic/oncotic pores activated by MTX- and Bz-ATP are indistinguishable.

     

THE RATIO OF CALCAREOUS AND ORGANIC SHELL COMPONENTS OF FRESHWATER SPHAERIID CLAMS IN RELATION TO WATER HARDNESS AND TROPHIC CONDITIONS

Shells from 14 populations of sphaeriid clams including Sphaeriumstriatinum, S. simile, Pisidium walkeri, Musculim partumeiumand M. iransversum were analyzed for organic carbon (µgCmg^–1 shell), nitrogen (µg,N mg^–1 shell) andCaCO_s (%CaCO₃ of total clam dry weight). Habitat waters wereassessed for total hardness (expressed as ppm CaCo₃), ppm Ca,ppm Mg, conductivity (µmho) and suspended organic Carbon(µgCl^–1). For all populations, shell organic C andN are positively correlated and there is an inverse relationshipbetween the amounts of shell CaCO₃ and shell organic carbon.Trophic considerations give the best correlation with shelltype at the generic level of consideration since species ofMusculium are found at the opposite end of the trophic scale(eutrophic) from all other populations studied. For S. striatinum,the most extensively studied species, the amount of shell CaCO₃is inversely related to water hardness. The selection of shellsin the Sphaeriidae is discussed in relation to structural-functionalneeds and habitat conditions ¹ Present Address: Department of Biology, Syracuse University,Syracuse, New York 13210, U.S.A. ² Present Address: Department of Zoology, Miami University,Oxford, Ohio 45056, U.S.A. (Received 5 December 1978;     

Neuronal swelling and surface area regulation: elevated intracellular calcium is not a requirement

Neurons aremechanically robust. During prolonged swelling, molluscan neurons cantriple their apparent membrane area. They gain surface area andcapacitance independent of extracellular Ca concentration([Ca]_e), but it isunknown if an increase in intracellular Ca concentration([Ca]_i) isnecessary. If Ca for stimulating exocytosis is unnecessary, it ispossible that swelling-induced membrane tension changes directlytrigger surface area readjustments. If, however, Ca-mediated but nottension-mediated membrane recruitment is responsible for surface areaincreases, swelling neurons should sustain elevated levels of[Ca]_i. The purpose ofthis investigation is to determine if the[Ca]_i in swellingneurons attains levels high enough to promote exocytosis and if anysuch increase is required. Lymnaeaneurons were loaded with the Ca concentration indicator fura 2. Calibration was performed in situ using 4-bromo-A-23187 and Ca-ethyleneglycol-bis(-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA), with free Ca concentration ranging from 0 to 5 µM. Swelling perturbations (medium osmolarity reduced to 25% for 5 min)were done at either a standard[Ca]_e or very low[Ca]_e level (0.9 mM or0.13 µM, respectively). In neither case did the[Ca]_i increase tolevels that drive exocytosis. We also monitored osmomechanically drivenmembrane dynamics [swelling, then formation and reversal ofvacuole-like dilations (VLDs)] with the[Ca]_i clamped below 40 nM via1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). [Ca]_idid not change with swelling, and VLD behavior was unaffected,consistent with tension-driven,[Ca]_i-independent surface area adjustments. In addition, neurons with[Ca]_i clamped at 0.1 µM via an ionophore could produce VLDs. We conclude that, undermechanical stress, neuronal membranes are compliant by virtue ofsurface area regulatory adjustments that operate independent of[Ca]_i. The findingssupport the hypothesis that plasma membrane area is regulated in partby membrane tension.

     

Influence of Soil Moisture on Soil Solution Chemistry and Concentrations of Minerals in the Calcicoles Phleum phleoides and Veronica spicata Grown on a Limestone Soil

Veronica spicata and Phleum phleoides are calcicole plants,mainly occurring on neutral or alkaline soil. An experimentof 16 weeks duration was performed in a glasshouse with theobjective of elucidating the influence of soil moisture levelon soil solution chemistry, and biomass concentrations and uptakeof mineral nutrients by the plants. Seven levels of moisture,corresponding to 35–85% of the water holding capacity(WHC) of the soil, were tested. Soil solution HCO₃, P and Mnconcentrations, and pH, increased, whereas Ca, Mg and Zn concentrationsdecreased, with increasing soil moisture. Concentrations ofK were highest at 50–70% WHC. Concentrations and amountsof P, Zn and Mn in the two species were usually related to soilsolution concentrations; these are elements with low solubilityand availability in calcareous soils. Concentrations of nutrientsin biomass were more influenced by soil moisture in V. spicatathan inP. phleoides . This indicates that P. phleoides is morecapable of controlling its uptake of mineral nutrients, whereasV. spicata is sensitive to variations in soil moisture. It isconcluded that variation in soil moisture regime may greatlyinfluence concentrations of mineral nutrients in calcareoussoil solutions and their uptake by plants. Species able to utilizethese solubility fluctuations may have an advantage in competitionfor nutrients. Variation in soil moisture content might evenbe a prerequisite for adequate acquisition of mineral nutrientsand growth of plants on limestone soils, thereby influencingthe field distribution of native plants among habitats. Copyright1999 Annals of Botany Company Calcareous, calcicole, concentration, mineral, moisture, nutrient, Phleum phleoides, soil, soil solution, uptake, Veronica spicata, water.     

Morphological studies on the calcification process in the fresh-water mussel Amblema

Light microscopy, transmission electron microscopy, scanning electron microscopy, various histochemical procedures for the localization of mineral ions, and analytical electron microscopy have been used to investigate the mechanisms inherent at the mantle edge for shell formation and growth in Amblema plicata perplicata, Conrad. The multilayered periostracum, its component laminae formed from the epithelia lining either the periostracal groove or the outer mantle epithelium (of the periostracal cul de sac), appears to play the major regulatory and organizational role in the formation of the component mineralized layers of the shell. Thus, the inner layer of the periostracum traps and binds calcium and subsequently gives rise to matricial proteinaceous fibrils or lamellar extensions which serve as nucleation templates for the formation and orientation of the crystalline subunits (rhombs) in the forming nacreous layer. Simultaneously, the middle periostracal layer furnishes or provides the total ionic calcium pool and the matricial organization necessary for the production of the spherical subunits which pack the matricial ‘bags’ of the developing prismatic layer. The outer periostracal layer appears to be a supportive structure, possibly responsible for the mechanical deformations which occur in the other laminae of the periostracum. The functional differences in the various layers of the periostracum are related to peculiar morphological variables (foliations, vacuolizations, columns) inherent in the structure and course of this heterogeneous (morphologically and biochemically) unit. From this study, using the dynamic mantle edge as a morphological model system, we have been able to identify at least six interrelated events which culminate in the production of the mature mineralized shell layers (nacre, prisms) at the growing edge of this fresh-water mussel.     

Proteins of the Crustacean Exoskeleton

We describe here some of the components of the exoskeleton ofthe decapod crustacean with emphasis on the constituent proteins,including both structural and enzymatic. All four layers, butparticularly the inner three, of the exoskeletons of four brachyuranscontain high concentrations of proteins 31 kDa; the innermostmembranous layer is especially rich in such proteins. A numberof crab exoskeletal proteins resemble insect cuticle proteinsin size (M_r) and isoelectric point (pI). A further similarityis the cross reactivity of crab exoskeletal proteins with fourdifferent antibodies against cuticular proteins of two speciesof insects. One of the small M_r exoskeletal proteins in theBermuda land crab Gecarcinus lateralis has a similar distributionas a protein of similar size in the cuticle of the tobacco hornworm Manduca sexta. The partial dissolution of an old exoskeletonand formation of the two outer layers of a new exoskeleton aremajor events in readying a crustacean for the increase in sizethat occurs at each molt. Expressing both parallel and sequentialactivation of a number of genes, a single layer of epidermalcells that bounds a crustacean such as G. lateralis synthesizesspecific proteins at different stages of the intermolt cycleas the outermost epicuticle and exocuticle are formed duringproecdysis and as the endocuticle and membranous layer are formedduring metecdysis. Finally, two sets of proteinases isolatedfrom integumentary tissues of land crabs degrade the same exoskeletalproteins in vitro as are degraded in vivo during proecdysis.     

Effects of Light Quality on Photosynthetic Carbon Metabolism in C4 and C3 Plants: Rapid Movements of Photosynthetic Intermediates Between Mesophyll and Bundle Sheath Cells

The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C₃ plant),Setaria italica (a malate-formingC₄ plant), and Amaranthus paniculatus(an aspartate-forming C₄ plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C₄ acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C₄-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein ¹⁴CO₂ for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in ¹²CO₂. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells.     

Bio-electric Potentials of Intact Green Plants: III. EFFECTS OF JACKETING A REGION OF THE PLANT TISSUE 3

When measuring the potential difference between two regionsof an oat seedling the P.D. may change if a region of the tissuebetween the measuring contacts is surrounded by a mineral saltsolution. This change is shown to be equal to (E₂—E₁)/(1+R₂/R₁)where E₁ is the E.M.F. generated by the shunted tissue and R₁its resistance, and E₂ is the net E.M.F. generated at the shuntingsolution and the tissue interfaces and R₂ the shunt resistance,expected to be proportional to the specific resistance of theshunting solution. However, in these experiments R₂/R₁ was closeto unity because of a large resistance from tissue to shuntingsolution and there was no relationship between the P.D. changeand the resistance of the shunt. Where the shunt was appliedbetween two dissimilar regions of the plant (coleoptile andprimary leaf) E₂ changed with the concentration of the shuntingsolution, and hence the measured potential difference was changedby varied amounts. When the shunt was applied to a primary leafalone, E₂ was independent of solution concentration, and thechange in P.D. was constant.     

Primary production in lakes Huron and Michigan: in vitro and in situ comparisons

Oxygen- and carbon-14-based primary production estimates from9–16 h in vitro incubations were compared in lakes Huronand Michigan. For surface mixing layer compansons, gross O₂/¹⁴Cphotosynthetic quotients (gross PQ) averaged 2.2, and net O₂/¹⁴Cphotosynthetic quotients (net PQ) averaged 1.4. The mean grossPQ is consistent with a theoretical P0 based on the CO₂ andNO₃ assimilation ratio. However, within the deep chlorophylllayer, gross PQ and net PQ averaged 4.9 and 2.8 respectively.These higher values were likely due to excess NO₃ reductionat the expense of CO₂ uptake. Thus, during short experimentsunder low light conditions, oxygen evolution and CO₂ uptakemay not be tightly coupled. In vitro and in situ O₂ productionestimates were compared in four diurnal (dawn to dusk) experimentsin Lake Huron. In situ production estimates were determinedby measuring water-mass oxygen changes and oxygen transfer acrossthe air-water interface. In situ production estimates were approximatelytwice in vitro production estimates for both surface mixinglayer and deep chlorophyll layer comparisons. The differencebetween estimates was attributable to containment effects manifestin 13–16 h bottle incubations. Short-term (1–2 h)in vitro production was also compared to diurnal in vitro production.Rates of short-term production were {small tilde}1.6 times higherthan rates of diurnal production, suggesting that short-termin vitro production experiments may provide reasonable estimatesof in situ primary production.     

Distribution of enzymes related to C3 and C4 pathway of photosynthesis between mesophyll and bundle sheath cells of Panicum hians and Panicum milioides

Enzymes of the C₄, C₃ pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C₄species, RuDP carboxylase is typical of C₃ species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C₃ and C₄. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C₄-acid decarboxylatingenzymes may limit the capacity for C₄ photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO₂ fixation via C₃ pathway in these two species. ¹ This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; )     

Inhibition of the Production of Phenolic Compounds in Brassica napus 2-Amino-oxyacetic Acid

Phenolic compounds precipitated with caffeine were more widelydistributed in the cytoplasm and nucleus in the outermost layerof the columella of germinating Brassica napus root than inthe other layers. Amino-oxyacetic acid, an inhibitor of thebiosynthesis of the C₆C₃ part of phenolic compounds, inhibitedthe biosynthesis of phenolics, and made dark deposits less numerousin all three of the outermost layers of the columella. The firstlayer was the most responsive, because symptoms of inhibitionwere already visible after 3 h. After 24 h the inhibition inthe second and third layers was proportional to the concentration.The first layer contained less deposits than the control, butmore than the second and third layers, suggesting that manyof these compounds in the first layer were present at the outset.Copyright1995, 1999 Academic Press Phenolics, 2-amino-oxyacetic acid, Brassica, germination, cytoplasm, nucleus     

Are second messengers crucial for opening the pore associated with P2X7 receptor?

Stimulation of the P2X₇ receptor by ATP induces cell membrane depolarization, increase in intracellular Ca²⁺ concentration, and, in most cases, permeabilization of the cell membrane to molecules up to 900 Da. After the activation of P2X₇, at least two phenomena occur: the opening of low-conductance (8 pS) cationic channels and pore formation. At least two conflicting hypotheses have been postulated to reconcile these findings: 1) the P2X₇ pore is formed as a result of gradual permeability increase (dilation) of cationic channels, and 2) the P2X₇ pore represents a distinct channel, possibly activated by a second messenger and not directly by extracellular nucleotides. In this study, we investigated whether second messengers are necessary to open the pore associated with the P2X₇ receptor in cells that expressed the pore activity by using the patch-clamp technique in whole cell and cell-attached configurations in conjunction with fluorescent imaging. In peritoneal macrophages and 2BH4 cells, we detected permeabilization and single-channel currents in the cell-attached configuration when ATP was applied outside the membrane patch in a condition in which oxidized ATP and Lucifer yellow were maintained within the pipette. Our data support Ca²⁺ as a second messenger associated with pore formation because the permeabilization depended on the presence of intracellular Ca²⁺ and was blocked by BAPTA-AM. In addition, MAPK inhibitors (SB-203580 and PD-98059) blocked the permeabilization and single-channel currents in these cells. Together our data indicate that the P2X₇ pore depends on second messengers such as Ca²⁺ and MAP kinases. electrophysiology; pore formation     

长期施肥对麦田土壤微生物垂直分布的影响

应用微量热法研究了长期轮作下麦田不同土层中的微生物活性, 以及施肥对微生物垂直分布的影响。结果表明, 微生物活性基本随深度的增加而下降; 随着土层加深, 可培养细菌菌落数减少, 且可培养细菌菌落数目与最大时间(Peak time)P_t值(表示从微生物生长开始到达到峰值的时间)呈负相关; 热功率(P)-时间(t)曲线由陡变缓, 由规则变得起伏不定, 侧翼变得更短, 峰高也降低; 不同土层的微生物生长速率常数(Microbial growth rate constant) µ、峰高(Peak height)P_h值变化明显, 基本随深度增加而减小。施肥土样和不施肥土样的曲线形状不同, 特别是上层土样施肥后的曲线明显比不施肥的曲线陡, 侧翼也明显变短; 施肥土样的µ和P_h值都大于不施肥土样, 且施肥土样的P_t都小于对照。这说明, 在不同的土壤深度有不同的微生物群落结构, 长期的施肥处理改变了土壤微生物的垂直分布特征。     

Control of ascorbic acid efflux in rat luteal cells: role of intracellular calcium and oxygen radicals

In luteal cells, prostaglandin (PG)F_2a mobilizes intracellular calcium concentration ([Ca]_i), generates reactive oxygen species (ROS), depletes ascorbic acid (AA) levels, inhibits steroidogenesis, and ultimately induces cell death. We investigated the hypothesis that [Ca]_i mobilization stimulates ROS, which results in depletion of cellular AA in rat luteal cells. We used a self-referencing AA-selective electrode that noninvasively measures AA flux at the extended boundary layer of single cells and fluorescence microscopy with fura 2 and dichlorofluorescein diacetate (DCF-DA) to measure [Ca]_i and ROS, respectively. Menadione, a generator of intracellular superoxide radical (), PGF_2a, and calcium ionophore were shown to increase [Ca]_i and stimulate intracellular ROS. With calcium ionophore and PGF_2a, but not menadione, the generation of ROS was dependent on extracellular calcium influx. In unstimulated cells there was a net efflux of AA of 121.5 ± 20.3 fmol · cm^–1 · s^–1 (mean ± SE, n = 8), but in the absence of extracellular calcium the efflux was significantly reduced (10.3 ± 4.9 fmol · cm^–1 · s^–1; n = 5, P < 0.05). PGF_2a and menadione stimulated AA efflux, but calcium ionophore had no significant effect. These data suggest two AA regulatory mechanisms: Under basal conditions, AA efflux is calcium dependent and may represent recycling and maintenance of an antioxidant AA gradient at the plasma membrane. Under luteolytic hormone and/or oxidative stress, AA efflux is stimulated that is independent of extracellular calcium influx or generation of ROS. Although site-specific mobilization of calcium pools and ROS cannot be ruled out, the release of AA by PGF_2a-stimulated luteal cells may occur through other signaling pathways. luteolysis; apoptosis; self-referencing microelectrode     

LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport

An interactive computer program,LabHEART, was developed to simulate the action potential (AP), ioniccurrents, and Ca handling mechanisms in a rabbit ventricular myocyte.User-oriented, its design allows switching between voltage and currentclamp and easy on-line manipulation of key parameters to change theoriginal formulation. The model reproduces normal rabbit ventricularmyocyte currents, Ca transients, and APs. We also changed parameters to simulate data from heart failure (HF) myocytes, including reduced transient outward (I_to) and inward rectifying Kcurrents (I_K1), enhanced Na/Ca exchangeexpression, and reduced sarcoplasmic reticulum Ca-ATPase function, butunaltered Ca current density. These changes caused reduced Ca transientamplitude and increased AP duration (especially at lower frequency) asobserved experimentally. The model shows that the increased Na/Caexchange current (I_NaCa) in HF lowers theintracellular [Ca] threshold for a triggered AP from 800 to 540 nM. Similarly, the decrease in I_K1reduces the threshold to 600 nM. Changes in I_tohave no effect. Combining enhanced Na/Ca exchange with reducedI_K1 (as in HF) lowers the threshold to triggeran AP to 380 nM. These changes reproduce experimental results inHF, where the contributions of different factors are notreadily distinguishable. We conclude that the triggered APs thatcontribute to nonreentrant ventricular tachycardia in HF are dueapproximately equally (and nearly additively) to alterations inI_NaCa and I_K1. A freecopy of this software can be obtained athttp://www.meddean.luc.edu/lumen/DeptWebs/physio/bers.html.

     

Acid phosphatase role in chickpea/maize intercropping

• Background and aims Organic P comprises 30–80 %of the total P in most agricultural soils. It has been proventhat chickpea facilitates P uptake from an organic P sourceby intercropped wheat. In this study, acid phosphatase excretedfrom chickpea roots is quantified and the contribution of acidphosphatase to the facilitation of P uptake by intercroppedmaize receiving phytate is examined. • Methods For the first experiment using hydroponics, maize(Zea mays ‘Zhongdan No. 2’) and chickpea (Cicerarietinum ‘Sona’) were grown in either the sameor separate containers, and P was supplied as phytate, KH₂PO₄at 0·25 mmol P L^–1, or not at all. The second experimentinvolved soil culture with three types of root separation betweenthe two species: (1) plastic sheet, (2) nylon mesh, and (3)no barrier. Maize plants were grown in one compartment and chickpeain the other. Phosphorus was supplied as phytate, Ca(H₂PO₄)₂at 50 mg P kg^–1, or no P added. • Key results In the hydroponics study, the total P uptakeby intercropped maize supplied with phytate was 2·1-foldgreater than when it was grown as a monoculture. In the soilexperiment, when supplied with phytate, total P uptake by maizewith mesh barrier and without root barrier was 2·2 and1·5 times, respectively, as much as that with solid barrier.In both experiments, roots of both maize and chickpea suppliedwith phytate and no P secreted more acid phosphatase than thosewith KH₂PO₄ or Ca(H₂PO₄)₂. However, average acid phosphataseactivity of chickpea roots supplied with phytate was 2–3-foldas much as maize. Soil acid phosphatase activity in the rhizosphereof chickpea was also significantly higher than maize regardlessof P sources. • Conclusions Chickpea can mobilize organic P in both hydroponicand soil cultures, leading to an interspecific facilitationin utilization of organic P in maize/chickpea intercropping.