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2.
Shizhu Zhang Hailin Zheng Nanbiao Long Natalia Carbó Peiying Chen Pablo S. Aguilar Ling Lu 《Eukaryotic cell》2014,13(2):295-303
Calcium-mediated signaling pathways are widely employed in eukaryotes and are implicated in the regulation of diverse biological processes. In Saccharomyces cerevisiae, at least two different calcium uptake systems have been identified: the high-affinity calcium influx system (HACS) and the low-affinity calcium influx system (LACS). Compared to the HACS, the LACS in fungi is not well known. In this study, FigA, a homolog of the LACS member Fig1 from S. cerevisiae, was functionally characterized in the filamentous fungus Aspergillus nidulans. Loss of figA resulted in retardant hyphal growth and a sharp reduction of conidial production. Most importantly, FigA is essential for the homothallic mating (self-fertilization) process; further, FigA is required for heterothallic mating (outcrossing) in the absence of HACS midA. Interestingly, in a figA deletion mutant, adding extracellular Ca2+ rescued the hyphal growth defects but could not restore asexual and sexual reproduction. Furthermore, quantitative PCR results revealed that figA deletion sharply decreased the expression of brlA and nsdD, which are known as key regulators during asexual and sexual development, respectively. In addition, green fluorescent protein (GFP) tagging at the C terminus of FigA (FigA::GFP) showed that FigA localized to the center of the septum in mature hyphal cells, to the location between vesicles and metulae, and between the junctions of metulae and phialides in conidiophores. Thus, our findings suggest that FigA, apart from being a member of a calcium uptake system in A. nidulans, may play multiple unexplored roles during hyphal growth and asexual and sexual development. 相似文献
3.
Growth, development, virulence and secondary metabolism in fungi are governed by heterotrimeric G proteins (G proteins). A Gβ-like protein called Gib2 has been shown to function as an atypical Gβ in Gpa1-cAMP signaling in Cryptococcus neoformans. We found that the previously reported CpcB (cross pathway control B) protein is the ortholog of Gib2 in Aspergillus nidulans and Aspergillus fumigatus. In this report, we further characterize the roles of CpcB in governing growth, development and toxigenesis in the two aspergilli. The deletion of cpcB results in severely impaired cellular growth, delayed spore germination, and defective asexual sporulation (conidiation) in both aspergilli. Moreover, CpcB is necessary for proper expression of the key developmental activator brlA during initiation and progression of conidiation in A. nidulans and A. fumigatus. Somewhat in accordance with the previous study, the absence of cpcB results in the formation of fewer, but not micro-, cleistothecia in A. nidulans in the presence of wild type veA, an essential activator of sexual development. However, the cpcB deletion mutant cleistothecia contain no ascospores, validating that CpcB is required for progression and completion of sexual fruiting including ascosporogenesis. Furthermore, unlike the canonical GβSfaD, CpcB is not needed for the biosynthesis of the mycotoxin sterigmatocystin (ST) as the cpcB null mutant produced reduced amount of ST with unaltered STC gene expression. However, in A. fumigatus, the deletion of cpcB results in the blockage of gliotoxin (GT) production. Further genetic analyses in A. nidulans indicate that CpcB may play a central role in vegetative growth, which might be independent of FadA- and GanB-mediated signaling. A speculative model summarizing the roles of CpcB in conjunction with SfaD in A. nidulans is presented. 相似文献
4.
The multifunctional regulator VelB physically interacts with other velvet regulators and the resulting complexes govern development and secondary metabolism in the filamentous fungus Aspergillus nidulans. Here, we further characterize VelB’s role in governing asexual development and conidiogenesis in A. nidulans. In asexual spore formation, velB deletion strains show reduced number of conidia, and decreased and delayed mRNA accumulation of the key asexual regulatory genes brlA, abaA, and vosA. Overexpression of velB induces a two-fold increase of asexual spore production compared to wild type. Furthermore, the velB deletion mutant exhibits increased conidial germination rates in the presence of glucose, and rapid germination of conidia in the absence of external carbon sources. In vivo immuno-pull-down analyses reveal that VelB primarily interacts with VosA in both asexual and sexual spores, and VelB and VosA play an inter-dependent role in spore viability, focal trehalose biogenesis and control of conidial germination. Genetic and in vitro studies reveal that AbaA positively regulates velB and vosA mRNA expression during sporogenesis, and directly binds to the promoters of velB and vosA. In summary, VelB acts as a positive regulator of asexual development and regulates spore maturation, focal trehalose biogenesis and germination by interacting with VosA in A. nidulans. 相似文献
5.
Perng-Kuang Chang Leslie L. Scharfenstein Brian Mack Kenneth C. Ehrlich 《Applied and environmental microbiology》2012,78(21):7557-7563
The fluG gene is a member of a family of genes required for conidiation and sterigmatocystin production in Aspergillus nidulans. We examined the role of the Aspergillus flavus fluG orthologue in asexual development and aflatoxin biosynthesis. Deletion of fluG in A. flavus yielded strains with an approximately 3-fold reduction in conidiation but a 30-fold increase in sclerotial formation when grown on potato dextrose agar in the dark. The concurrent developmental changes suggest that A. flavus FluG exerts opposite effects on a mutual signaling pathway for both processes. The altered conidial development was in part attributable to delayed expression of brlA, a gene controlling conidiophore formation. Unlike the loss of sterigmatocystin production by A. nidulans fluG deletion strains, aflatoxin biosynthesis was not affected by the fluG deletion in A. flavus. In A. nidulans, FluG was recently found to be involved in the formation of dehydroaustinol, a component of a diffusible signal of conidiation. Coculturing experiments did not show a similar diffusible meroterpenoid secondary metabolite produced by A. flavus. These results suggest that the function of fluG and the signaling pathways related to conidiation are different in the two related aspergilli. 相似文献
6.
The velvet regulators VosA and VelB are primarily involved in spore maturation and dormancy. Previous studies found that the VosA-VelB hetero-complex coordinates certain target genes that are related to fungal differentiation and conidial maturation in Aspergillus nidulans. Here, we characterized the VosA/VelB-inhibited developmental gene vidD in A. nidulans. Phenotypic analyses demonstrated that the vidD deleted mutant exhibited defect fungal growth, a reduced number of conidia, and delayed formation of sexual fruiting bodies. The deletion of vidD decreased the amount of conidial trehalose, increased the sensitivity against heat stress, and reduced the conidial viability. Moreover, the absence of vidD resulted in increased production of sterigmatocystin. Together, these results show that VidD is required for proper fungal growth, development, and sterigmatocystin production in A. nidulans. 相似文献
7.
Point mutations in the barley HvHAK1 potassium transporter lead to improved K+-nutrition and enhanced resistance to salt stress 总被引:1,自引:0,他引:1
Members of group I KT-HAK-KUP transporters play an important role in K+ acquisition by plant roots, a process that is strongly affected by salt stress. A PCR-based random mutagenesis approach on HvHAK1 allowed identification of V366I and R591C substitutions, which confer enhanced K+-capture, and improved NaCl, LiCl and NH4Cl tolerance, to yeast cells. Improved K+-capture was linked to an enhanced Vmax. Results reveal an intrinsic protective effect of K+, and assign an important role to the 8th transmembrane domain, as well as the C-terminus, in determining the maximum capacity for the transport of K+ in KT-HAK-KUP transporters. 相似文献
8.
《BBA》2022,1863(8):148908
Mitochondria play an important role not only in producing energy for the cell but also for regulating mitochondrial and cell function depending on the cell's needs and environment. Uptake of cations, anions, and substrates requires a stable, polarized transmembrane charge potential (ΔΨm). Chemiosmosis requires ion exchangers to remove Na+, K+, Ca2+, PO43?, and other charged species that enter mitochondria. Knowledge of the kinetics of mitochondrial (m) cation channels and exchangers is important in understanding their roles in regulating mitochondrial chemiosmosis and bioenergetics. The influx/efflux of K+, the most abundant mitochondrial cation, alters mitochondrial volume and shape by bringing in anions and H2O by osmosis. The effects of K+ uptake through ligand-specific mK+ channels stimulated/inhibited by agonists/antagonists on mitochondrial volume (swelling/contraction) are well known. However, a more important role for K+ influx is likely its effects on H+ cycling and bioenergetics facilitated by mitochondrial (m) K+/H+ exchange (mKHE), though the kinetics and consequences of K+ efflux by KHE are not well described. We hypothesized that a major role of K+ influx/efflux is stimulation of respiration via the influx of H+ by KHE. We proposed to modulate KHE activity by energizing guinea pig heart isolated mitochondria and by altering the mK+ cycle to capture changes in mitochondrial volume, pHm, ΔΨm, and respiration that would reflect a role for H+ influx via KHE to regulate bioenergetics. To test this, mitochondria were suspended in a 150 mM K+ buffer at pH 6.9, or in a 140 mM Cs+ buffer at pH 7.6 or 6.9 with added 10 mM K+, minimal Ca2+ and free of Na+. O2 content was measured by a Clark electrode, and pHm, ΔΨm, and volume, were measured by fluorescence spectrophotometry and light-scattering. Adding pyruvic acid (PA) alone caused increases in volume and respiration and a rapid decrease in the transmembrane pH gradient (ΔpHm = pHin–pHext) at pHext 6.9> > 7.6, so that ΔΨm was charged and maintained. BKCa agonist NS1619 and antagonist paxilline modified these effects, and KHE inhibitor quinine and K+ ionophore valinomycin depolarized ΔΨm. We postulate that K+ efflux-induced H+ influx via KHE causes an inward H+ leak that stimulates respiration, but at buffer pH 6.9 also utilizes the energy of ΔpHm, the smaller component of the overall proton motive force, ΔμH+. Thus ΔpHm establishes and maintains the ΔΨm required for utilization of substrates, entry of all cations, and for oxidative phosphorylation. Thus, K+ influx/efflux appears to play a pivotal role in regulating energetics while maintaining mitochondrial ionic balance and volume homeostasis. 相似文献
9.
Evan J. Wiens Judith L. Winogrodzki Craig T. Resch George L. Orriss Jörg Stetefeld Pavel Dibrov 《Molecular and cellular biochemistry》2014,389(1-2):51-58
In this work, we report the phenotypic and biochemical effects of deleting the C-terminal cytoplasmic portion of the NhaP2 cation/proton antiporter from Vibrio cholerae. While the deletion changed neither the expression nor targeting of the Vc-NhaP2 in an antiporter-less Escherichia coli strain, it resulted in a changed sensitivity of the host to sodium ions at neutral pH, indicating an altered Na+ transport through the truncated variant. When assayed in inside-out sub-bacterial vesicles, the truncation was found to result in greatly reduced K+/H+ and Na+/H+ antiport activity at all pH values tested and a greater than fivefold decrease in the affinity for K+ (measured as the apparent K m) at pH 7.5. Being expressed in trans in a strain of V. cholerae bearing a chromosomal nhaP2 deletion, the truncated nhaP2 gene was able to complement its inability to grow in potassium-rich medium at pH 6.0. Thus the residual K+/H+ antiport activity associated with the truncated Vc-NhaP2 was still sufficient to protect cells from an over-accumulation of K+ ions in the cytoplasm. The presented data suggest that while the cytoplasmic portion of Vc-NhaP2 is not involved in ion translocation directly, it is necessary for optimal activity and substrate binding of the Vc-NhaP2 antiporter. 相似文献
10.
K stimulation of ATPase activity associated with the chloroplast inner envelope 总被引:1,自引:0,他引:1
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Studies were conducted to characterize ATPase activity associated with purified chloroplast inner envelope preparations from spinach (Spinacea oleracea L.) plants. Comparison of free Mg2+ and Mg·ATP complex effects on ATPase activity revealed that any Mg2+ stimulation of activity was likely a function of the use of the Mg·ATP complex as a substrate by the enzyme; free Mg2+ may be inhibitory. In contrast, a marked (one- to twofold) stimulation of ATPase activity was noted in the presence of K+. This stimulation had a pH optimum of approximately pH 8.0, the same pH optimum found for enzyme activity in the absence of K+. K+ stimulation of enzyme activity did not follow simple Michaelis-Menton kinetics. Rather, K+ effects were consistent with a negative cooperativity-type binding of the cation to the enzyme, with the Km increasing at increasing substrate. Of the total ATPase activity associated with the chloroplast inner envelope, the K+-stimulated component was most sensitive to the inhibitors oligomycin and vanadate. It was concluded that K+ effects on this chloroplast envelope ATPase were similar to this cation's effects on other transport ATPases (such as the plasmalemma H+-ATPase). Such ATPases are thought to be indirectly involved in active K+ uptake, which can be facilitated by ATPase-dependent generation of an electrical driving force. Thus, K+ effects on the chloroplast enzyme in vitro were found to be consistent with the hypothesized role of this envelope ATPase in facilitating active cation transport in vivo. 相似文献
11.
Betim Karahoda Lakhansing Pardeshi Mevlut Ulas Zhiqiang Dong Niranjan Shirgaonkar Shuhui Guo Fang Wang Kaeling Tan
zlem Sarikaya-Bayram Ingo Bauer Paul Dowling Alastair B Fleming Brandon
T Pfannenstiel Dianiris Luciano-Rosario Harald Berger Stefan Graessle Mohamed M Alhussain Joseph Strauss Nancy P Keller Koon Ho Wong
zgür Bayram 《Nucleic acids research》2022,50(17):9797
12.
Swelling of nonenergized heart mitochondria suspended in acetate salts appears to depend on the activity of an endogenous cation/H+ exchanger. Passive swelling in acetate shows a characteristic cation selectivity sequence of Na+ >Li+ >K+, Rb+, Cs+, or tetramethylammonium, a sharp optimum at pH 7.2–7.3, activation by Ca2+, and loss of activity on aging which can be related to loss of endogenous K+. The reaction is nearly insensitive to either addition of exogenous Mg2+ or removal of membrane Mg2+ with EDTA. Each of these characteristics of passive swelling in acetate salts is duplicated in chloride media when tripropyltin is added to induce Cl?/OH? exchange. In contrast to nonenergized mitochondria, swelling of respiring mitochondria has been postulated to depend on electrophoretic uptake of cations in response to an interior negative membrane potential. Respiration-dependent swelling in acetate shows an indistinct cation selectivity sequence with Li+ and Na+ supporting higher rates of swelling at higher efficiency than K+, Rb+, and Cs+. The high rates of respiration-dependent swelling in Li+ and Na+ are inhibited by low levels of exogenous Mg2+ (Ki of 5–10 μm), but a significant swelling with almost no cation selectivity persists in the presences of 2 mm Mg2+. Removal of membrane Mg2+ by addition of EDTA strongly activates the rate of respiration-dependent swelling and converts a sigmoid dependency of swelling rate on Li+ concentration to a hyperbolic one with a Km of about 14 mm Li+. The cation selectivity and Mg2+ dependence of the reaction induced in chloride salts by tripropyltin are identical to these properties in acetate. Energy-dependent swelling in acetate shows optimum activity at pH 6.5 which appears related to the availability of free acetic acid, since the corresponding reaction induced in chloride shows a broad optimum at about pH 7.5. These studies support the concept that monovalent cations enter nonenergized mitochondria by electroneutral exchange with protons but penetrate respiring mitochondria by electrophoretic movement through one or more uniport pathways. They further suggest that both a Mg2+-sensitive uniport with high activity for Na+ and Li+ and a Mg2+-insensitive pathway with little cation discrimination are available in the membrane. 相似文献
13.
Membrane potential, Vm, and K+(86Rb+) fluxes have been measured simultaneously on individual cells of Acetabularia mediterranea. During resting state (resting potential approx. ?170 mV) the K+ influx amounts to 0.24–0.6 pmol · cm?2 · s?1 and the K+ efflux to 0.2–1.5 pmol · cm?2 s?1. According to the K+ concentrations inside and outside the cell (40 : 1) the voltage dependent K+ flux (zero at Vm = EK = ?90 mV) is stimulated approx. 40-fold for Vm more positive than EK.It is calculated that during one action potential (temporary depolarization to Vm more positive than EK) a cell looses the same amount of K+, which leaks in during 10–20 min in the resting state (Vm = ?170 mV). Since action potentials occur spontaneously in Acetabularia, they are therefore suggested to have a significant function for the K+ balance of this alga. 相似文献
14.
Characterization of a partially purified adenosine triphosphatase from a corn root plasma membrane fraction 总被引:19,自引:18,他引:1
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The (K+,Mg2+)-ATPase was partially purified from a plasma membrane fraction from corn roots (WF9 × Mol7) and stored in liquid N2 without loss of activity. Specific activity was increased 4-fold over that of the plasma membrane fraction. ATPase activity resembled that of the plasma membrane fraction with certain alterations in cation sensitivity. The enzyme required a divalent cation for activity (Co2+ > Mg2+ > Mn2+ > Zn2+ > Ca2+) when assayed at 3 millimolar ATP and 3 millimolar divalent cation at pH 6.3. When assayed in the presence of 3 millimolar Mg2+, the enzyme was further activated by monovalent cations (K+, NH4+, Rb+ Na+, Cs+, Li+). The pH optima were 6.5 and 6.3 in the absence and presence of 50 millimolar KCl, respectively. The enzyme showed simple Michaelis-Menten kinetics for the substrate ATP-Mg, with a Km of 1.3 millimolar in the absence and 0.7 millimolar in the presence of 50 millimolar KCl. Stimulation by K+ approached simple Michaelis-Menten kinetics, with a Km of approximately 4 millimolar KCl. ATPase activity was inhibited by sodium orthovanadate. Half-maximal inhibition was at 150 and 35 micromolar in the absence and presence of 50 millimolar KCl. The enzyme required the substrate ATP. The rate of hydrolysis of other substrates, except UDP, IDP, and GDP, was less than 20% of ATP hydrolysis. Nucleoside diphosphatase activity was less than 30% of ATPase activity, was not inhibited by vanadate, was not stimulated by K+, and preferred Mn2+ to Mg2+. The results demonstrate that the (K+,Mg2+)-ATPase can be clearly distinguished from nonspecific phosphohydrolase and nucleoside diphosphatase activities of plasma membrane fractions prepared from corn roots. 相似文献
15.
Ana Cristina Colabardini Laure Nicolas Annick Ries Neil Andrew Brown Marcela Savoldi Taísa Magnani Dinamarco Marcia Regina von Zeska Maria Helena S. Goldman Gustavo Henrique Goldman 《PloS one》2014,9(8)
In filamentous fungi, intracellular signaling pathways which are mediated by changing calcium levels and/or by activated protein kinase C (Pkc), control fungal adaptation to external stimuli. A rise in intracellular Ca2+ levels activates calcineurin subunit A (CnaA), which regulates cellular calcium homeostasis among other processes. Pkc is primarily involved in maintaining cell wall integrity (CWI) in response to different environmental stresses. Cross-talk between the Ca2+ and Pkc-mediated pathways has mainly been described in Saccharomyces cerevisiae and in a few other filamentous fungi. The presented study describes a genetic interaction between CnaA and PkcA in the filamentous fungus Aspergillus nidulans. Overexpression of pkcA partially rescues the phenotypes caused by a cnaA deletion. Furthermore, CnaA appears to affect the regulation of a mitogen-activated kinase, MpkA, involved in the CWI pathway. Reversely, PkcA is involved in controlling intracellular calcium homeostasis, as was confirmed by microarray analysis. Furthermore, overexpression of pkcA in a cnaA deletion background restores mitochondrial number and function. In conclusion, PkcA and CnaA-mediated signaling appear to share common targets, one of which appears to be MpkA of the CWI pathway. Both pathways also regulate components involved in mitochondrial biogenesis and function. This study describes targets for PkcA and CnaA-signaling pathways in an A. nidulans and identifies a novel interaction of both pathways in the regulation of cellular respiration. 相似文献
16.
Further Studies on the Roles of Sodium and Potassium in the Generation of the Electro-Olfactogram : Effects of mono-, di-, and trivalent cations 总被引:1,自引:1,他引:1
In the negative EOG-generating process a cation which can substitute for Na+ was sought among the monovalent ions, Li+, Rb+, Cs+, NH4+, and TEA+, the divalent ions, Mg++, Ca++, Sr++, Ba++, Zn++, Cd++, Mn++, Co++, and Ni++, and the trivalent ions, Al+++ and Fe+++. In Ringer solutions in which Na+ was replaced by one of these cations the negative EOG's decreased in amplitude and could not maintain the original amplitudes. In K+-Ringer solution in which Na+ was replaced by K+, the negative EOG's reversed their polarity. Recovery of these reversed potentials was examined in modified Ringer solutions in which Na+ was replaced by one of the above cations. Complete recovery was found only in the normal Ringer solution. Thus, it was clarified that Na+ plays an irreplaceable role in the generation of the negative EOG's. The sieve hypothesis which was valid for the positive EOG-generating membrane or IPSP was not found applicable in any form to the negative EOG-generating membrane. The reversal of the negative EOG's found in K+- , Rb+- , and Ba++-Ringer solutions was attributed to the exit of the internal K+. It is, however, not known whether or not Cl- permeability increases in these Na+-free solutions and contributes to the generation of the reversed EOG's. 相似文献
17.
The crystal structure of the Tl+ form of the G-quadruplex formed from the Oxytricha nova telomere sequence, d(G4T4G4), has been solved to 1.55 Å. This G-quadruplex contains five Tl+ ions, three of which are interspersed between adjacent G-quartet planes and one in each of the two thymine loops. The structure displays a high degree of similarity to the K+ crystal structure [Haider et al. (2002), J. Mol. Biol., 320, 189–200], including the number and location of the monovalent cation binding sites. The highly isomorphic nature of the two structures, which contain such a large number of monovalent binding sites (relative to nucleic acid content), verifies the ability of Tl+ to mimic K+ in nucleic acids. Information from this report confirms and extends the assignment of 205Tl resonances from a previous report [Gill et al. (2005), J. Am. Chem. Soc., 127, 16 723–16 732] where 205Tl NMR was used to study monovalent cation binding to this G-quadruplex. The assignment of these resonances provides evidence for the occurrence of conformational dynamics in the thymine loop region that is in slow exchange on the 205Tl timescale. 相似文献
18.
Little knowledge is available about the influence of cation competition and metal speciation on trivalent chromium (Cr(III)) toxicity. In the present study, the effects of pH and selected cations on the toxicity of trivalent chromium (Cr(III)) to barley (Hordeum vulgare) root elongation were investigated to develop an appropriate biotic ligand model (BLM). Results showed that the toxicity of Cr(III) decreased with increasing activity of Ca2+ and Mg2+ but not with K+ and Na+. The effect of pH on Cr(III) toxicity to barley root elongation could be explained by H+ competition with Cr3+ bound to a biotic ligand (BL) as well as by the concomitant toxicity of CrOH2+ in solution culture. Stability constants were obtained for the binding of Cr3+, CrOH2+, Ca2+, Mg2+ and H+ with binding ligand: log KCrBL 7.34, log KCrOHBL 5.35, log KCaBL 2.64, log KMgBL 2.98, and log KHBL 4.74. On the basis of those estimated parameters, a BLM was successfully developed to predict Cr(III) toxicity to barley root elongation as a function of solution characteristics. 相似文献
19.
《Plant Science Letters》1984,33(1):103-114
The effects of monovalent cations, inhibitors of metabolism dinitrophenol (DNP), carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), and KCN and temperature variations upon Ca2+ fluxes in intact roots of barley (Hordeum vulgare L. cv. Fergus and Herta) seedlings were investigated. 45Ca2+ influx was depressed in CaSO4-grown (low-salt) plants by the presence of NH4+, K+, or Na+ in the uptake medium. In contrast Ca2+ influx was slightly increased by Li+. In low-salt roots pretreated with KCN and in roots preloaded with K+ (high-K+ plants), the presence of K+ in the medium had no significant effect on Ca2+ influx, while in roots preloaded with Na+, the presence of K+ in the medium depressed Ca2+ influx. In absolute terms, Ca2+ influx was significantly greater in high-salt (both K+ or Na+ preloaded) than in low-salt roots.Patterns of 45Ca2+ efflux in the absence and in the presence of K+, NH4+, or Li+ in the external medium showed that these monovalent cations caused stimulation of 45Ca2+ efflux both from the cytoplasmic and vacuolar phases.It was noted that these modifications of Ca2+ fluxes by monovalent cations are transient and characteristic of a transitional stage of cation uptake by low-salt roots. We conclude that, together with stimulated active H+ efflux (another characteristic of this transitional stage), modifications of Ca2+ fluxes during monovalent cation uptake by low-salt roots is a response directed towards the maintenance of electrical neutrality.Determination of net fluxes revealed that the plants were close to Ca2+ flux equilibrium in the growth medium (0.5 mM CaSO4). Transfer of these plants to 0.5 mM CaSO4 + 0.25 mM K2SO4 caused a net release of CA2+ into the external medium. 相似文献
20.
Keitaro Kiyosawa 《Physiologia plantarum》1996,97(1):180-184
Movements of ions are considered to be governed by the electroneutrality rule. Therefore, a cation moving across the cell membrane into the cell either passively or actively should move together with its counterion, an anion, in equal amounts of charge or in exchange for another cation inside the cell. This means that the net influx of the cation in question should be affected by the permeability of its counterion and/or another cation inside the cell. To examine osmotic and ionic regulation in Chara cells, cell fragments of Chara having a lower osmotic pressure than normal (L-cell fragments) were prepared. The L-cell fragments were individually put into various dilute electrolyte solutions and their osmotic potentials were measured with a turgor balance. Concentrations of K+, Na+, Ca2+, Mg2+, Cl?, NO?3. and SO2?4. in the external electrolyte solutions in which L-cells had been incubated were also analysed by ion chromatography. The results showed that in 0.5 mM KCL + 0.1 mM CaCl2 solution, Chara L-cell fragments absorbed K+ and Cl? to maintain electroneutrality and then regained their osmotic potential very rapidly. When the anion was Cl, the cation absorbed at the highest rate was K+ On the other hand, when the cation was K, the anion absorbed at the highest rate was Cl, Other ions Ca2+, SO2?4 and NO?3 showed much less permeability than K+ and Cl ?for the Chara plasma membrane. The conclusion from these findings was that due to the constraint of electroneutral transport, the uptake rate of a salt into L-cells is limited by the permeability of the least permeable ion. 相似文献