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1.
Shuichi Sakaguchi Kyoko Shibuya Hidetoshi Iida Yasuhiro Anraku Takahito Suzuki 《Mycoscience》1997,38(2):215-225
The dimorphic fungusCandida albicans has both a yeast form and a hyphal form. When yeast-form cells were starved and then transferred to aN-acetylglucosamine medium, the formation of true hyphae from the unbudded yeast-form cells was induced. Removal of Ca2+ from the medium with EGTA inhibited hyphal formation by 50%, resulting in only thin and short hyphae. Externally applied
excess Ca2+ (>10−2M) also affected the hyphal formation, resulting in formation of pseudohyphae. This effect required a high concentration of
Ca2+ but was Ca2+-specific. Deprivation of Ca2+ also inhibited yeast-form growth. Interestingly, such cells had abnormally wide bud necks and became defective in cell separation.
To measure cytosolic free Ca2+, fura-2 was introduced into hyphal cells by electroporation. Its normal value was estimated to be about 100 nM. The electroporation
caused transient elevation of cytosolic free Ca2+ concentration and transient cessation of hyphal growth. There was a close correlation between the timing of recovery of Ca2+ concentration and that of the resumption of hyphal growth. Our results demonstrate the importance of extracellular and intracellular
free Ca2+ for the growth ofC. albicans. 相似文献
2.
Role of Internal Potassium in Maintaining Growth of Cultured Citrus Cells on Increasing NaCl and CaCl(2) Concentrations 总被引:1,自引:0,他引:1
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Shamouti orange (Citrus sinensis L. Osbeck) salt-tolerant cells were grown under low water potential conditions induced by polyethylene glycol (PEG), NaCl, and CaCl2. On the basis of equal osmotic potentials, PEG was the least inhibitory, NaCl next, and CaCl2 the most inhibitory. The relation between growth capacity and ion content can be summarized as follows. (a) Internal K+ concentration was a major factor which changed in the presence of PEG, NaCl, and CaCl2 and probably played a key role in determining growth capacity. (b) Internal concentrations of Na+, Ca2+, or Cl− could not be directly correlated with growth. (C) Internal Mg2+ concentration could be significant only in the presence of high external Ca2+ concentrations. (d) The contribution of nitrate and phosphate to the internal osmoticum was negligible. The ratio of external (Ca2+)/(Na+)2 concentration is crucial for growth. Ratios above 0.5 × 10−4 per millimolar gave maximal protection from adverse effects of NaCl. Growth capacity was found to be determined by the combination of (Ca2+)/(Na+)2 ratio and the absolute external concentration of NaCl. However, a correlation between internal K+ concentration and growth capacity seemed independent of external NaCl concentration. 相似文献
3.
Tijs Ketelaar Harold J.G. Meijer Marjolein Spiekerman Rob Weide Francine Govers 《Fungal genetics and biology : FG & B》2012,49(12):1014-1022
The actin cytoskeleton is conserved in all eukaryotes, but its functions vary among different organisms. In oomycetes, the function of the actin cytoskeleton has received relatively little attention. We have performed a bioinformatics study and show that oomycete actin genes fall within a distinct clade that is divergent from plant, fungal and vertebrate actin genes. To obtain a better understanding of the functions of the actin cytoskeleton in hyphal growth of oomycetes, we studied the actin organization in Phytophthora infestans hyphae and the consequences of treatment with the actin depolymerising drug latrunculin B (latB). This revealed that latB treatment causes a concentration dependent inhibition of colony expansion and aberrant hyphal growth. The most obvious aberrations observed upon treatment with 0.1 μM latB were increased hyphal branching and irregular tube diameters whereas at higher concentrations latB (0.5 and 1 μM) tips of expanding hyphae changed into balloon-like shapes. This aberrant growth correlated with changes in the organization of the actin cytoskeleton. In untreated hyphae, staining with fluorescently tagged phalloidin revealed two populations of actin filaments: long, axially oriented actin filament cables and cortical actin filament plaques. Two hyphal subtypes were recognized, one containing only plaques and the other containing both cables and plaques. In the latter, some hyphae had an apical zone without actin filament plaques. Upon latB treatment, the proportion of hyphae without actin filament cables increased and there were more hyphae with a short apical zone without actin filament plaques. In general, actin filament plaques were more resilient against actin depolymerisation than actin filament cables. Besides disturbing hyphal growth and actin organization, actin depolymerisation also affected the positioning of nuclei. In the presence of latB, the distance between nuclei and the hyphal tip decreased, suggesting that the actin cytoskeleton plays a role in preventing the movement of nuclei towards the hyphal tip. 相似文献
4.
The actin cytoskeleton is a dynamic but well‐organized intracellular framework that is essential for proper functioning of eukaryotic cells. Here, we use the actin binding peptide Lifeact to investigate the in vivo actin cytoskeleton dynamics in the oomycete plant pathogen Phytophthora infestans. Lifeact–eGFP labelled thick and thin actin bundles and actin filament plaques allowing visualization of actin dynamics. All actin structures in the hyphae were cortically localized. In growing hyphae actin filament cables were axially oriented in the sub‐apical region whereas in the extreme apex in growing hyphae, waves of fine F‐actin polymerization were observed. Upon growth termination, actin filament plaques appeared in the hyphal tip. The distance between a hyphal tip and the first actin filament plaque correlated strongly with hyphal growth velocity. The actin filament plaques were nearly immobile with average lifetimes exceeding 1 h, relatively long when compared to the lifetime of actin patches known in other eukaryotes. Plaque assembly required ~30 s while disassembly was accomplished in ~10 s. Remarkably, plaque disassembly was not accompanied with internalization and the formation of endocytic vesicles. These findings suggest that the functions of actin plaques in oomycetes differ from those of actin patches present in other organisms. 相似文献
5.
Marianne C. Cilluffo Nasser A. Farahbakhsh Gordon L. Fain 《In vitro cellular & developmental biology. Animal》1997,33(7):546-552
Summary We have examined the effect of alteration in cell shape on promoting differentiated morphology and physiology in cultured
nonpigmented epithelial cells from the ciliary body. We have grown pure populations of nonpigmented cells on collagen gels
released from the culture dish to create collagen rafts. Shortly after the gels were detached, the cells shrank in diameter
and increased in height while they contracted the gel. Concurrently, the actin cytoskeleton reorganized to the cell cortex
as found in vivo. After this differentiated morphology developed, large changes in intracellular Ca2+ could be elicited by simultaneous activation of acetylcholine and epinephrine or acetylcholine and somatostatin receptors
as seen in intact tissue. Explant cultures of isolated nonpigmented cell layers maintained their actin distribution and also
showed synergistic Ca2+ increases. Spread cells, grown on rigid substrates, had a disorganized cytoskeleton and rarely showed synergism. These data
suggest that the mechanism underlying synergistic Ca2+ responses in the ciliary body is functional in nonpigmented cells grown on collagen rafts. In addition, this pathway appears
to be sensitive to the disposition of the cell’s cytoarchitecture. 相似文献
6.
Effects of NaCl and CaCl(2) on Cell Enlargement and Cell Production in Cotton Roots 总被引:8,自引:2,他引:6
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In many crop species, supplemental Ca2+ 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 Ca2+, 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 Ca2+ 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 Ca2+. Our observations suggest Ca2+-dependent effects of salinity on the cytoskeleton. The rate of cell production declined with increasing salinity at 0.4 millimolar Ca2+ but at 10 millimolar Ca2+ was not affected by salinities up to 150 millimolar NaCl. 相似文献
7.
Sara Torralba I. Brent Heath F. Peter Ottensmeyer 《Fungal genetics and biology : FG & B》2001,33(3):181
Tip-growing organisms maintain an apparently essential tip-high gradient of cytoplasmic Ca2+. In the oomycete Saprolegnia ferax, in pollen tubes and root hairs, the gradient is produced by a tip-localized Ca2+ influx from the external medium. Such a gradient is normally dispensable for Neurospora crassa hyphae, which may maintain their Ca2+ gradient by some form of internal recycling. We localized Ca2+ in N. crassa hyphae at the ultrastructural level using two techniques (a) electron spectroscopic imaging of freeze-dried hyphae and (b) pyroantimoniate precipitation. The results of both methods support the presence of Ca2+ in the wall vesicles and Golgi body equivalents, providing a plausible mechanism for the generation and maintenance of the gradient by Ca2+ shuttling in vesicles to the apex, without exogenous Ca2+ influx. Ca2+ sequestration into the vesicles seems to be dependent on Ca2+–ATPases since cyclopiazonic acid, a specific inhibitor of Ca2+ pumps, eliminated all Ca2+ deposits from the vesicles of N. crassa. 相似文献
8.
Actin cytoskeleton modulates calcium signaling during maturation of starfish oocytes 总被引:2,自引:0,他引:2
Kyozuka K Chun JT Puppo A Gragnaniello G Garante E Santella L 《Developmental biology》2008,320(2):426-435
Before successful fertilization can occur, oocytes must undergo meiotic maturation. In starfish, this can be achieved in vitro by applying 1-methyladenine (1-MA). The immediate response to 1-MA is the fast Ca2+ release in the cell cortex. Here, we show that this Ca2+ wave always initiates in the vegetal hemisphere and propagates through the cortex, which is the space immediately under the plasma membrane. We have observed that alteration of the cortical actin cytoskeleton by latrunculin-A and jasplakinolide can potently affect the Ca2+ waves triggered by 1-MA. This indicates that the cortical actin cytoskeleton modulates Ca2+ release during meiotic maturation. The Ca2+ wave was inhibited by the classical antagonists of the InsP3-linked Ca2+ signaling pathway, U73122 and heparin. To our surprise, however, these two inhibitors induced remarkable actin hyper-polymerization in the cell cortex, suggesting that their inhibitory effect on Ca2+ release may be attributed to the perturbation of the cortical actin cytoskeleton. In post-meiotic eggs, U73122 and jasplakinolide blocked the elevation of the vitelline layer by uncaged InsP3, despite the massive release of Ca2+, implying that exocytosis of the cortical granules requires not only a Ca2+ rise, but also regulation of the cortical actin cytoskeleton. Our results suggest that the cortical actin cytoskeleton of starfish oocytes plays critical roles both in generating Ca2+ signals and in regulating cortical granule exocytosis. 相似文献
9.
Mayura Veerana Sarmistha Mitra Se-Hoon Ki Soo-Min Kim Eun-Ha Choi Taek Lee Gyungsoon Park 《Microbial biotechnology》2021,14(1):262-276
Technical bottlenecks in protein production and secretion often limit the efficient and robust industrial use of microbial enzymes. The potential of non-thermal atmospheric pressure plasma to overcome these technical barriers was examined. Spores of the fermenting fungus Aspergillus oryzae (A. oryzae) were submerged in potato dextrose broth (PDB) (5 × 106 per ml) and treated with micro dielectric barrier discharge plasma at an input voltage of 1.2 kV and current of 50 to 63 mA using nitrogen as the feed gas. The specific activity of α-amylase in the broth was increased by 7.4 to 9.3% after 24 and 48 h of plasma treatment. Long-lived species, such as NO2− and NO3−, generated in PDB after plasma treatment may have contributed to the elevated secretion of α-amylase. Observations after 24 h of plasma treatment also included increased accumulation of vesicles at the hyphal tip, hyphal membrane depolarization and higher intracellular Ca2+ levels. These results suggest that long-lived nitrogen species generated in PDB after plasma treatment can enhance the secretion of α-amylase from fungal hyphae by depolarizing the cell membrane and activating Ca2+ influx into hyphal cells, eventually leading to the accumulation of secretory vesicles near the hyphal tips. 相似文献
10.
Moccia F 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2007,148(4):845-852
Depolymerization of the actin cytoskeleton may liberate Ca2+ from InsP3-sensitive stores in some cell types, including starfish oocytes, while inhibiting Ca2+ influx in others. However, no information is available on the modulation of membrane potential (Vm) by actin. The present study was aimed to ascertain whether the widely employed actin depolymerizing drug, latrunculin A (Lat A), affects Vm in mature oocytes of the starfish Astropecten aranciacus. Lat A induced a membrane depolarization which was mimicked by cytochalasin D, another popular actin disruptor, and prevented by jasplakinolide, a stabilizer of the actin network. Lat A-elicited depolarization consisted in a positive shift in Vm which reached the threshold of activation of voltage-gated Ca2+ channels (VGCC), thus triggering an action potential. Lat A-promoted depolarization lacked the action potential in Ca2+-free sea water, while it was abolished upon removal of external Na+. Moreover, membrane depolarization was prevented by pre-injection of BAPTA and heparin, but not ryanodine. These data indicate that Lat A induces a membrane depolarization by releasing Ca2+ from InsP3Rs. The Ca2+ signal in turn activates a Ca2+-dependent Na+ entry, which causes the positive shift in Vm and stimulates the VGCC. 相似文献
11.
Since the first demonstration of sperm entry into the fertilized eggs of Mediterranean sea urchin Paracentrotus lividus by Hertwig (1876), enormous progress and insights have been made on this topic. However, the precise molecular mechanisms
underlying fertilization are largely unknown. The two most dramatic changes taking place in the zygote immediately after fertilization
are: (i) a sharp increase of intracellular Ca2+ that initiates at the sperm interaction site and traverses the egg cytoplasm as a wave, and (ii) the concomitant dynamic
rearrangement of the actin cytoskeleton. Traditionally, this has been studied most extensively in the sea urchin eggs, but
another echinoderm, starfish, whose eggs are much bigger and transparent, has facilitated experimental approaches using microinjection
and fluorescent imaging methodologies. Thus in starfish, it has been shown that the sperm-induced Ca2+ increase in the fertilized egg can be recapitulated by several Ca2+-evoking second messengers, namely inositol 1,4,5-trisphosphate (InsP3), cyclic ADP-ribose (cADPr) and nicotinic acid adenine
dinucleotide phosphate (NAADP), which may play distinct roles in the generation and propagation of the Ca2+ waves. Interestingly, it has also been found that the dynamic rearrangement of the actin cytoskeleton in the fertilized eggs
plays pivotal roles in guiding monospermic sperm entry and in the fine modulation of the intracellular Ca2+ signaling. As it is well known that Ca2+ regulates the structure of the actin cytoskeleton, our finding that Ca2+ signaling can be reciprocally affected by the state of the actin cytoskeleton raises an intriguing possibility that actin
and Ca2+ signaling may form a ‘positive feedback loop’ that accelerates the downstream events of fertilization. Perturbation of the
cortical actin networks also inhibits cortical granules exocytosis. Polymerizing actin bundles also compose the ‘acrosome
process,’ a tubular structure protruding from the head of fertilizing sperm. Hence, actin, which is one of the most strictly
conserved proteins in eukaryotes, modulates almost all major aspects of fertilization. 相似文献
12.
The cellular and Ca2+ responses to physiological stimuli of different nature were studied in the experiments with the strain Aspergillus awamori 66A containing recombinant aequorin, a Ca2+-dependent photosensitive protein. The relationship between the cellular response registered by changes in the development
of the mycelial fungus (colony growth, hyphal branching, and the rate of spore formation) and the level and duration of calcium
flares in the cytosol was assessed. The physical or chemical stimuli (mechanical effect, osmotic shock) inducing short-time
calcium flares in the cytosol did not influence significantly the development of A. awamori grown in liquid or on solid nutrient media. The action on the 24-h A. awamori culture of the Ca2+-selective ionophore (A23187) inducing long-term changes in calcium homeostasis caused disorders in the fungus development
and morphology (hyperbranching of mycelial hyphae, formation of spherical cells, and inhibition of colony growth and spore
formation). Thus, it was established that the development of cellular response in the micromycete correlated with the duration
of the calcium flare in the cytosol. 相似文献
13.
Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca
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High Na+ concentrations may disrupt K+ and Ca2+ transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca2+ levels often counteract these consequences of salinity. The effect of supplemental Ca2+ on influx of Ca2+, 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 Ca2+. Sodium influx increased proportionally to increasing salinity. At high external Ca2+, Na+ influx was less than at low Ca2+. 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, 45Ca2+ influx increased in proportion to salt concentrations, especially with high Ca2+. Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca2+. 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 Ca2+ is related to improved Ca-status and maintenance of K+/Na+ selectivity. 相似文献
14.
Summary We examined the ionic regulation of tip growth inNeurospora crassa by a combination of electrophysiology and confocal microscopy. To determine if transmembrane ionic fluxes are required for tip growth, we voltage clamped the membrane from –200 to +50 mV. In this voltage range, transmembrane ionic fluxes would either reverse (e.g., K+) or change dramatically (e.g., Ca2+ influx) but had no effect on hyphal growth rates. Therefore, ionic fluxes (including Ca2+ influx) may not be required for tip growth. However, intracellular Ca2+ may still play an obligatory role in tip growth. To assess this possibility, we first increased cytosolic Ca2+ directly by ionophoresis. Elevated Ca2+ induced subapical branch initiation, often multiple tips. At hyphal tips, fluorescence ratio imaging using fluo-3 and fura-red revealed a pronounced tip-high Ca2+ gradient within 10 m of the tip in growing hyphae which was not observed in nongrowing hyphae. Injection of the Ca2+ chelator 1,2-bis(ortho-aminophenoxy)ethane-N,N,N,N-tetrapotassium acetate consistently inhibited growth concomitantly with a depletion of intracellular Ca2+ and dissipation of the tip-high gradient. We conclude that Ca2+ plays a regulatory role in tip initiation and the maintenance of tip growth. Because plasma membrane ionic fluxes do not play a role in tip growth, we suggest that the tip-high Ca2+ gradient is generated from intracellular Ca2+ stores in the ascomyceteN. crassa.Abbreviations BAPTA
1,2-bis(ortho-aminophenoxy)ethane-N,N,N,N-tetrapotassium acetate
- [Ca2+]i
intracellular Ca2+ concentration
- fluo-3
2,7-dichloro-6-hydroxy-3-oxo-9-xanthenyl-4-methyl-2,2-(ethylenedioxy)dianiline-N,N,N,N-tetraacetic acid 相似文献
15.
Ashbya gossypii has been an ideal system to study filamentous hyphal growth. Previously, we identified a link between polarized hyphal growth, the organization of the actin cytoskeleton and endocytosis with our analysis of the A. gossypii Wiskott-Aldrich Syndrome Protein (WASP)-homolog encoded by the AgWAL1 gene. Here, we studied the role of AgSAC6, encoding a fimbrin in polarized hyphal growth and endocytosis, and based on our functional analysis identified genetic interactions between AgSAC6 and AgWAL1. SAC6 mutants show severely reduced polarized growth. This growth phenotype is temperature dependent and sac6 spores do not germinate at elevated temperatures. Spores germinated at 30 °C generate slow growing mycelia without displaying polarity establishment defects at the hyphal tip. Several phenotypic characteristics of sac6 hyphae resemble those found in wal1 mutants. First, tips of sac6 hyphae shifted to 37 °C swell and produce subapical bulges. Second, actin patches are mislocalized subapically. And third, the rate of endocytotic uptake of the vital dye FM4-64 was reduced. This indicates that actin filament bundling, a conserved function of fimbrins, is required for fast polarized hyphal growth, polarity maintenance, and endocytosis in filamentous fungi. 相似文献
16.
Summary Growing hyphae of the oomyceteSaprolegnia ferax wounded by impalement with a ca. 0.2 m diameter glass microelectrode normally respond within seconds with an apically directed cytoplasmic contraction followed by production of a plug which encases the electrode and occludes its recording of transmembrane potentials. This plug contains callose and Ca2+-associated membranes. To characterize the rapid wounding response, we disrupted specific filamentous (F) actin populations and Ca2+ regulation. Plug formation is inhibited by disruption of F-actin populations and low exogenous Ca2+ but not by inhibition of stretch-activated Ca2+ channels with Gd3+. Therefore, stretch-activated channels are not the immediate sensor. Instead, sensing may involve strain on the actin cytoskeleton which triggers the occlusion response. This wound response is qualitatively similar to the production of septa which isolate developing sporangia and seal severed hyphae, indicating the use of a normal basic cellular developmental system as a protective mechanism against environmental damage. The wound response is essential, since an inability to seal sites of mechanical damage is potentially catastrophic in acellular coenocytic organisms.Abbreviations APW
artificial pond water
- BAPTA
1,2-bis(orthzo-aminophenoxy)ethane-N,N,N,N-tetrapotassium acetate
- CTC
chlortetracycline
- DIC
Nomarski differential interference contrast microscopy
- F-actin
filamentous actin
- LatB
latrunculin B
- PM
plasma membrane
- RP
rhodamine-labeled phalloidin
- SA
channels stretch-activated channels 相似文献
17.
A large-conductance, Ca2+-activated K+ channel was identified and characterized in embryonic chick hepatocytes using the patch-electrode voltage-clamp technique. The channel conductance was 213 pS in excised patches bathed in symmetrical 145 mM KCl and 1 mM Ca2+. Current-voltage relationships were linear with high K+ on both sides of the membrane but showed constant field rectification as the K+ gradient was increased. The reversal potential shifted 58 mV per 10-fold change in the ratio of external to internal K+. Channel openings occurred at potentials higher than +50 mV in cell-attached patches. The open probability × voltage relationship shifted to more negative potentials in excised, inside-out patches exposed to a solution containing high Ca2+. The voltage sensitivity of the channel was not significantly affected by changes in internal Ca2+ concentration. Conversely, channel gating, reflected in the half-activation potential, shifted 118 mV per 10-fold change in internal Ca2+ at concentrations less than ∼2 μM, although at higher Ca2+, this parameter was Ca2+ insensitive. Channel open probability in cell-attached patches increased significantly following exposure of the cells to either the Ca2+ ionophore A-23187 or L-alanine, a cell-volume modulator. Channel density increased with time spent in culture from no observations in 10-hr cells, through 13 and 80% of patches in 24-and 48-hr cultured cells, respectively. The implications of delayed functional expression for ion channel studies in acutely dissociated cells is discussed. J. Cell. Physiol. 171:87–94, 1997. © 1997 Wiley-Liss, Inc. 相似文献
18.
The organization of filamentous actin (F-actin) in the synaptic pedicle of depolarizing bipolar cells from the goldfish retina was studied using fluorescently labeled phalloidin. The amount of F-actin in the synaptic pedicle relative to the cell body increased from a ratio of 1.6 ± 0.1 in the dark to 2.1 ± 0.1 after exposure to light. Light also caused the retraction of spinules and processes elaborated by the synaptic pedicle in the dark.Isolated bipolar cells were used to characterize the factors affecting the actin cytoskeleton. When the electrical effect of light was mimicked by depolarization in 50 mM K+, the actin network in the synaptic pedicle extended up to 2.5 μm from the plasma membrane. Formation of F-actin occurred on the time scale of minutes and required Ca2+ influx through L-type Ca2+ channels. Phorbol esters that activate protein kinase C (PKC) accelerated growth of F-actin. Agents that inhibit PKC hindered F-actin growth in response to Ca2+ influx and accelerated F-actin breakdown on removal of Ca2+.To test whether activity-dependent changes in the organization of F-actin might regulate exocytosis or endocytosis, vesicles were labeled with the fluorescent membrane marker FM1-43. Disruption of F-actin with cytochalasin D did not affect the continuous cycle of exocytosis and endocytosis that was stimulated by maintained depolarization, nor the spatial distribution of recycled vesicles within the synaptic terminal. We suggest that the actions of Ca2+ and PKC on the organization of F-actin regulate the morphology of the synaptic pedicle under varying light conditions. 相似文献
19.
Growth,photosynthesis and storage of carbohydrates and nitrogen in Phaseolus lunatus in relation to resource availability 总被引:13,自引:0,他引:13
External hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi were quantified over a growing season in a reconstructed tallgrass prairie and an ungrazed cool-season pasture. In both sites, hyphal lengths increased throughout the growing season. Peak external hyphal lengths were 111 m cm–3 of soil in the prairie and 81 m cm–3 of soil in the pasture. These hyphal lengths calculate to external hyphal dry weights of 457 g cm–3 and 339 g cm–3 of soil for prairie and pasture communities, respectively. The relationships among external hyphal length, root characteristics, soil P and soil moisture were also determined. Measures of gross root morphology [e.g., specific root length (SRL) and root mass] have a strong association with external hyphal length. Over the course of the study, both grassland communities experienced a major drought event in late spring. During this period a reduction in SRL occurred in both the pasture and prairie without a measured reduction in external hyphal length. Recovery for both the pasture and prairie occurred not by increasing SRL, but rather by increasing external hyphal length. This study suggests that growth is coordinated between VAM hyphae and root morphology, which in turn, are constrained by plant community composition and soil nutrient and moisture conditions. 相似文献
20.
《Cell calcium》2008,43(6):606-617
We have previously demonstrated a role for the reorganization of the actin cytoskeleton in store-operated calcium entry (SOCE) in human platelets and interpreted this as evidence for a de novo conformational coupling step in SOCE activation involving the type II IP3 receptor and the platelet hTRPC1-containing store-operated channel (SOC). Here, we present evidence challenging this model. The actin polymerization inhibitors cytochalasin D or latrunculin A significantly reduced Ca2+ but not Mn2+ or Na+ entry into thapsigargin (TG)-treated platelets. Jasplakinolide, which induces actin polymerization, also inhibited Ca2+ but not Mn2+ or Na+ entry. However, an anti-hTRPC1 antibody inhibited TG-evoked entry of all three cations, indicating that they all permeate an hTRPC1-containing store-operated channel (SOC). These results indicate that the reorganization of the actin cytoskeleton is not involved in SOC activation. The inhibitors of the Na+/Ca2+ exchanger (NCX), KB-R7943 or SN-6, caused a dose-dependent inhibition of Ca2+ but not Mn2+ or Na+ entry into TG-treated platelets. The effects of the NCX inhibitors were not additive with those of actin polymerization inhibitors, suggesting a common point of action. These results indicate a role for two Ca2+ permeable pathways activated following Ca2+ store depletion in human platelets: A Ca2+-permeable, hTRPC1-containing SOC and reverse Na+/Ca2+ exchange, which is activated following Na+ entry through the SOC and requires a functional actin cytoskeleton. 相似文献