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1.
Seed is a developmental stage that is highly protective against external stresses in the plant life cycle. In this study, we analyzed toxicity of essential (Cu2+ and Zn2+) and non-essential heavy metals (Hg2+, Pb2+ and Cd2+) on seed germination and seedling growth in the model species Arabidopsis. Our results show that seedling growth is more sensitive to heavy metals (Hg2+, Pb2+, Cu2+ and Zn2+) in comparison to seed germination, while Cd2+ is the exception that inhibited both of these processes at similar concentrations. To examine if toxicity of heavy metals is altered developmentally during germination, we incubated seeds with Hg2+ or Cd2+ only for a restricted period during germination. Hg2+ displayed relatively strong toxicity at period II (12–24 h after imbibition), while Cd2+ was more effective to inhibit germination at period I (0–12 h after imbibition) rather than at period II. The observed differences are likely to be due in part to selective uptake of different ions by the intact seed, because isolated embryos (without seed coat and endosperm) are more sensitive to both Hg2+ and Cd2+ at period I. We assessed interactive toxicity between heavy metals and non-toxic cations, and found that Ca2+ was able to partially restore the inhibition of seedling growth by Pb2+ and Zn2+. 相似文献
2.
Summary Cadmium ion (Cd++) significantly increased potential difference (PD) and short-circuit current (SCC) across isolated frog skin when added to the outside Ringer's solution at 10–4, 10–3 and 5×10–3
m concentration. Resistance was reduced by 10–4
m Cd++ but not significantly changed by the higher concentrations. When SCC was first stimulated by vasopressin, 10–4 and 10–3
m Cd++ produced additive stimulation which was reversible by washing with Cd++-free Ringer's. If SCC was first stimulated by Cd++, further stimulation by vasopressin was additive with 10–4
m Cd++ but completely inhibited by 10–3
m Cd++. Elevating the calcium ion (Ca++) concentration of the outer Ringer's from 10–3
m to 5×10–3
m or 10–2
m prior to Cd++ treatment did not reduce the magnitude of SCC stimulation by Cd++. Removal of Ca++ from the outside Ringer's with 2×10–3
m EDTA increased SCC as predicted. Subsequent addition of 5×10–3
m Cd++ drastically reduced SCC below control levels while equimolar concentrations of Cd++ and EDTA reduced SCC only to control levels. These results suggest that Cd++ interacts with the components of the apical plasma membranes of epithelial cells which are associated with the stimulation of SCC by vasopressin and Ca++ removal and may be a useful probe for elucidating these components. 相似文献
3.
Role of external calcium in sodium and chloride transport in the gills of seawater-adaptedMugil capito 总被引:1,自引:1,他引:0
Pierre Pic Jean Maetz 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1981,141(4):511-521
Summary When the mulletMugil capito is transferred to medium lacking Ca++ (either Ca++-free seawater or distilled water) the passive permeability of the gill to Na+ and Cl– is increased and the activating effect of external K+ on the Na+ and Cl– effluxes in hyposaline media is inhibited. The permeability of the gill increases progressively in proportion to the time of Ca++ deprivation; it declines when Ca++ is added again to the external medium. The active mechanisms for ion excretion are not reversible. At external Ca++ concentrations from 0.1 to 10 mM the Na+ permeability is constant but the activation of Na+ efflux by K+ shows a maximum at a Ca++ concentration of about 1 mM. For activation of Cl– efflux external bicarbonate must be present, in addition to Ca++, suggesting the existence of a Cl–/HCO
3
–
exchange. The mechanism by which Ca++ controls the passive branchial permeability is thus probably different from that involved in K+ activation of ion excretion. The Ca++ effect on the K+ sensitive ionic excretory mechanisms seems to be related to intracellular Ca++ movements. Thus, on the one hand, substances such as Ruthenium Red and La+++ which both inhibit Ca++ exchange, in media containing Ca++ and HCO
3
–
also inhibit K+ activation of Na+ and Cl– effluxes; on the other hand, the ionophore A 23187, a stimulator of Ca++ exchange, when added to these media, activates the Na+ and Cl– effluxes; its maximal effect on the Na+ flux occurs at 2 mM Ca++.Abbreviations
ASW-Ca
artificial seawater minus calcium
-
DW
deionised water
-
DWCa
deionised water with 1 mM Ca++ added
-
DWCaHCO
3
DW with calcium plus bicarbonate
-
DWHCO
3
DW with 1 mM sodium bicarbonate added
-
FW
freshwater (tap water)
-
FWK
freshwater with K+ added
-
P. D.
potential difference
-
SW
seawater
The experiments reported in this paper were done with Jean Maetz who tragically died in August 1977. It is the last report about several years of friendly collaboration 相似文献
4.
Steven C. Hebert Peter A. Friedman Thomas E. Andreoli 《The Journal of membrane biology》1984,80(3):201-219
Summary This paper reports experiments designed to assess the relations between net salt absorption and transcellular routes for ion conductance in single mouse medullary thick ascending limbs of Henle microperfusedin vitro. The experimental data indicate that ADH significantly increased the transepithelial electrical conductance, and that this conductance increase could be rationalized in terms of transcellular conductance changes. A minimal estimate (G
c
min
) of the transcellular conductance, estimated from Ba++ blockade of apical membrane K+ channels, indicated thatG
c
min
was approximately 30–40% of the measured transepithelial conductance. In apical membranes, K+ was the major conductive species; and ADH increased the magnitude of a Ba++-sensitive K+ conductance under conditions where net Cl– absorption was nearly abolished. In basolateral membranes, ADH increased the magnitude of a Cl– conductance; this ADH-dependent increase in basal Cl– conductance depended on a simultaneous hormone-dependent increase in the rate of net Cl– absorption. Cl– removal from luminal solutions had no detectable effect onG
e
, and net Cl– absorption was reduced at luminal K+ concentrations less than 5mm; thus apical Cl– entry may have been a Na+,K+,2Cl– cotransport process having a negligible conductance. The net rate of K+ secretion was approximately 10% of the net rate of Cl– absorption, while the chemical rate of net Cl– absorption was virtually equal to the equivalent short-circuit current. Thus net Cl– absorption was rheogenic; and approximately half of net Na+ absorption could be rationalized in terms of dissipative flux through the paracellular pathway. These findings, coupled with the observation that K+ was the principal conductive species in apical plasma membranes, support the view that the majority of K+ efflux from cell to lumen through the Ba++-sensitive apical K+ conductance pathway was recycled into cells by Na+,K+,2Cl– cotransport. 相似文献
5.
Response of sugarcane to different types of salt stress 总被引:2,自引:0,他引:2
Summary Due to climatic conditions and prevailing water regime the yield and sucrose recovery in sugarcane are high in South Western India. However, excessive irrigation, poor drainage and luxuriant use of fertilizers have resulted in conversion of large fertile areas into saline lands. The salinity is due to the excess of Na+, Ca++, Mg++, SO4
– and Cl– ions. Individual salts of NaCl, Na2SO4, MgCl2 and MgSO4 were employed in culture experiments to study salt stress effect on sugarcane variety Co 740. It was observed that sulphate salinity was more toxic to sugarcane than the chloride one. Sulphate salts caused more inhibition of growth, chlorophyll synthesis, PEPCase activity, decreased the uptake of K+ and Ca++ ions but stimulated nitrate reductase. The stress did not result in proline accumulation in the sugarcane cultivar Co 740. The degree of toxicity of different ions in decreasing order in sugarcane cultivar Co 740 is SO4
–>Na+>Cl–>Mg++. 相似文献
6.
Sugijanto Kartosentono Sinar Suryawati Gunawan Indrayanto Noor Cholies Zaini 《Biotechnology letters》2002,24(9):687-690
Cell suspension cultures of Agave amaniensis and Costus speciosus were grown in media containing Cd2 + up to 25 and 20 mg l–1, respectively, and Pb2+ up to 40 mg l–1. The cultures hyper-accumulated Cd2+ up to 900 and 530 g g–1 and Pb2+ up to 1390 and 1170 g g–1 dry wt. in their respective biomasses. Increasing Pb2+ up to 30 mg l–1 increased the biomass production and total sitosterol content of Costus speciosus by up to 1.7- and 1.3-fold, respectively. 相似文献
7.
Maryanne R. Hughes David Kojwang Tania Zenteno-Savin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(7):625-631
Summary The intestinal caeca reabsorb urinary sodium chloride (NaCl) and water (Rice and Skadhauge 1982). Free water may be generated if the reabsorbed NaCl is secreted via salt gland secretion (Schmidt-Nielsen et al. 1958). Therefore ceacal ligation should (a) reduce hingut NaCl and water reabsorption, (b) enhance the increase in plasma osmolality during saline acclimation, and (c) affect drakes more than ducks. Twelve Pekin drakes and 13 Pekin ducks, Anas platyrhynchos, were caecally ligated or sham operated before acclimation to 450 mmol · 1 NaCl. Body mass, hematocrit, plasma osmolality, and inonic concentrations of plasma, cloacal fluid, and salt gland secretion were measured after each increase in drinking water salinity. Osmoregulatory organ masses were determined. Caecal ligation did not effect plasma osmolality or ion concentrations of plasma, cloacal fluid, or salt gland secretion, but reduced salt gland size in ducks. Drakes and ducks drinking fresh water had the same hematocrit, plasma osmolality, and plasma concentrations of Na+ and Cl–. In both sexes exposure to 75 mmol · 1-1 NaCl significantly decreased plasma [Na+] and doubled cloacal fluid [Na+]. Exposure to 450 mmol · 1-1 NaCl decreased body mass and increased hematocrit, plasma [Na+], [Cl–], and plasma osmolality (more in drakes than in ducks); cloacal fluid osmolality nearly doubled compared to freshwater-adapted ducks, due mainly to osmolytes other than Na+ and Cl–. The [Cl–] in salt gland secretion only slightly exceeded drinking water [Cl–].Abbreviations
AVT
antiduretic hormone
-
CF
cloacal fluid
-
ECFV
extraoellular fluid volume
-
FW
freshwater acclimated
-
Hct
hematocrit
-
MDWE
mean daily water flux
-
[Na
+]cf
cloacal fluid sodium concentration
-
[Na
+]pl
plasma sodium concentration
-
Osm
cf
cloacal fluid osmolality
-
Osm
pl
plasma osmolality
-
SGS
salt gland secretion
-
TBW
total body water 相似文献
8.
Summary Internodal cells ofChara australis were made tonoplast-free by replacing the cell sap with EGTA-containing media; then the involvement of internal Cl– and K+ in the excitation of the plasmalemma was studied.[Cl–]
i
was drastically decreased by perfusing the cell interior twice with a medium lacking Cl–. The lowered [Cl–]
i
was about 0.01mm. Cells with this low [Cl–]
i
generated action potential and showed anN-shapedV–I curve under voltage clamped depolarization like Cl–-rich cells containing 13 or 29mm Cl–.E
m at the peak of the action potential was constant at [Cl–]
i
between 0.01 and 29mm. The possibility that the plasmalemma becomes as permeable to other anions as to Cl– during excitation is discussed.At [Cl–]
i
higher than 48mm, cells were inexcitable. When anions were added to the perfusion medium to bring the K+ concentration to 100mm, NO
3
–
, F–, SO
4
2–
, acetate, and propionate inhibited the generation of action potentials like Cl–, while methane sulfonate, PIPES, and phosphate did not inhibit excitability.The duration of the action potential depended strongly on the intracellular K+ concentration. It decreased as [K+]
i
(K-methane sulfonate) increased. Increase in [Na+]
i
(Na-methane sulfonate) also caused its decrease, although this effect was weaker than that of K+. The action of these monovalent cations on the duration of the action potential is the opposite of their action on the membrane from the outside (cf. Shimmen, Kikuyama & Tazawa, 1976,J. Membrane Biol.
30:249). 相似文献
9.
A salt-tolerant callus line of Lycopersicon peruvianum has been obtained by exposing the cells, in suspension cultures and then in callus, to increasing concentrations of NaCl (50–350mM). This selected line grew better than the nonselected line at all levels of NaCl. Moreover, this selected line grew better in media containing salt than in those without it. It retained its tolerance after subculture for 3 passages (3 months) on salt-free medium. The growth of the selected line in mannitol was similar to that of the nonselected line, which suggested that the superiority of the selected line under salt stress was not due to osmotic stress tolerance. The ions SO
4
––
and K+ were highly toxic to L. peruvianum root callus, while Na+, Mg++ and Cl– were less toxic. 相似文献
10.
Stanley D. Hillyard Ronald Sera Harvey C. Gonick 《The Journal of membrane biology》1979,46(4):283-294
Summary Cadmium ion (Cd++) was found not to inhibit active sodium transport across the isolated frog skin when added in 10–3
m concentration to the basal-lateral surface. The same Cd++ concentration similarly had no effect on Na+ transport across the isolated epithelial cell layer from the frog skin, although this dose of Cd++ did inhibit Na+ transport across the frog urinary bladder and large intestine. When 10–3
m Cd++ was added to the apical surface of the isolated frog skin or to the isolated epithelial cells from the frog skin, sodium transport was reversibly stimulated, in contrast to the irreversible inhibition noted above. If equimolar cysteine was added with Cd++ to the apical surface of the skin, however, active Na+ transport was irreversibly inhibited. In conjunction with the inhibition produced by equimolar Cd++ and cysteine, isotopic Cd++ permeation into the tissue was three times higher when added with cysteine than in the absence of cysteine. Thus, the effects of Cd++ on epithelial Na+ transport is variable according to the epithelium studied and the presence of potential carrier molecules. 相似文献
11.
M. J. Beilby 《The Journal of membrane biology》1981,62(3):207-218
Summary The changes in the cytoplasmic Cl– concentration, [Cl–]
c
, are monitored at the time of withdrawal (starvation) and subsequent replacement of Cl– in the outside medium. The measurement technique exploits the involvement of Cl– inChara excitation. The transient clamp current due to Cl–,I
Cl, is separated from other excitation transients through Hodgkin-Huxley (HH) equations, which have been adjusted toChara. TheI
Cl amplitude depends on HH parameters, [Cl–]
c
and the maximum membrane conductance to Cl–,
. The results are discussed in terms of these quantities.I
Cl and
were found to fall after 6–10 hr of Cl– starvation, thus supporting the hypothesis that [Cl–
c
decreases in Cl–-free medium. The best HH fit to starved data was obtained with [Cl–
c
=3.5mm. The time-course forI
Cl decline is considerably slower than the time-course of the rise of the starvation-stimulated influx. As cells starved for periods longer than 24 hr are re-exposed to Cl–, it is revealed that while [Cl–]
c
remains low during long starvation,
increases to values greater than those of the normal cells. Such differences among cells starved for various lengths of time have not been detected previously. 相似文献
12.
In liver homogenate the biosynthesis ofN-acetylneuraminic acid usingN-acetylglucosamine as precursor can be followed stepwise by applying different chromatographic procedures. In this cell-free system 16 metal ions (Zn2+, Mn2+, La3+, Co2+, Cu2+, Hg2+, VO
3
–
, Pb2+, Ce3+, Cd2+, Fe2+, Fe3+, Al3+, Sn2+, Cs+ and Li+) and the selenium compounds, selenium(IV) oxide and sodium selenite, have been checked with respect to their ability to influence a single or possible several steps of the biosynthesis ofN-acetylneuraminic acid. It could be shown that the following enzymes are sensitive to these metal ions (usually applied at a concentration of 1 mmoll–1):N-acetylglucosamine kinase (inhibited by Zn2+ and vandate), UDP-N-acetylglucosamine-2-epimerase (inhibited by zn2+, Co2+, Cu2+, Hg2+, VO
3
–
, Pb2+, Cd2+, Fe3+, Cs+, Li+, selenium(IV) oxide and selenite), andN-acetylmannosamine kinase (inhibited by Zn2+, Cu2+, Cd2+, and Co2+). Dose dependent measurements have shown that Zn2+, Cu2+ and selenite are more efficient inhibitors of UDP-N-acetylglucosamine-2-epimerase than vanadate. As for theN-acetylmannosamine kinase inhibition, a decreasing inhibitory effect exists in the following order Zn2+, Cd2+, Co2+ and Cu2+. In contrast, La3+, Al3+ and Mn2+ (1 mmoll–1) did not interfere with the biosynthesis ofN-acetylneuraminic acid. Thus, the conclusion that the inhibitory effect of the metal ions investigated cannot be regarded as simply unspecific is justified.Dedicated to Professor Theodor Günther on the occasion of his 60th birthday 相似文献
13.
Can elevated CO(2) improve salt tolerance in olive trees? 总被引:2,自引:0,他引:2
We compared growth, leaf gas exchange characteristics, water relations, chlorophyll fluorescence, and Na+ and Cl− concentration of two cultivars (‘Koroneiki’ and ‘Picual’) of olive (Olea europaea L.) trees in response to high salinity (NaCl 100 mM) and elevated CO2 (eCO2) concentration (700 μL L−1). The cultivar ‘Koroneiki’ is considered to be more salt sensitive than the relatively salt-tolerant ‘Picual’. After 3 months of treatment, the 9-month-old cuttings of ‘Koroneiki’ had significantly greater shoot growth, and net CO2 assimilation (ACO2) at eCO2 than at ambient CO2, but this difference disappeared under salt stress. Growth and ACO2 of ‘Picual’ did not respond to eCO2 regardless of salinity treatment. Stomatal conductance (gs) and leaf transpiration were decreased at eCO2 such that leaf water use efficiency (WUE) increased in both cultivars regardless of saline treatment. Salt stress increased leaf Na+ and Cl− concentration, reduced growth and leaf osmotic potential, but increased leaf turgor compared with non-salinized control plants of both cultivars. Salinity decreased ACO2, gs, and WUE, but internal CO2 concentrations in the mesophyll were not affected. eCO2 increased the sensitivity of PSII and chlorophyll concentration to salinity. eCO2 did not affect leaf or root Na+ or Cl− concentrations in salt-tolerant ‘Picual’, but eCO2 decreased leaf and root Na+ concentration and root Cl− concentration in the more salt-sensitive ‘Koroneiki’. Na+ and Cl− accumulation was associated with the lower water use in ‘Koroneiki’ but not in ‘Picual’. Although eCO2 increased WUE in salinized leaves and decreased salt ion uptake in the relatively salt-tolerant ‘Koroneiki’, growth of these young olive trees was not affected by eCO2. 相似文献
14.
Summary Enhanced cellular cAMP levels have been shown to increase apical membrane Cl– and HCO
3
–
conductances in epithelia. We found that the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (IBMX) increases cAMP levels inNecturus gallbladder. We used conventional open-tip and double-barreled Cl–-selective microelectrodes to study the effects of IBMX on membrane conductances and intracellular Cl– activities in gallbladders mounted in a divided chamber and bathed with Ringer's solutions at 23°C and pH 7.4. In HCO
3
–
-free media, 0.1mM IBMX added to the mucosal medium depolarized the apical membrane potentialV
a
, decreased the fractional resistanceF
R
, and significantly reduced intracellular Cl– activity (a
Cl
i
). Under control conditions,a
Cl
i
was above the value corresponding to passive distribution across the apical cell membrane. In media containing 25mM HCO
3
–
, IBMX caused a small transient hyperpolarization ofV
a
followed by a depolarization not significantly different from that observed in HCO
3
–
-free Ringer's. Removal of mucosal Cl–, Na+ or Ca2+ did not affect the IBMX-induced depolarization inV
a
. The basolateral membrane ofNecturus gallbladder is highly K+ permeable. Increasing serosal K+ from 2.5 to 80mM, depolarizedV
a
. Mucosal IBMX significantly reduced this depolarization. Addition of 10mM Ba2+, a K+ channel blocker, to the serosal medium depolarizedV
a
and, essentially, blocked the depolarization induced by IBMX. These results indicate that mucosal IBMX increases apical HCO
3
–
conductance and decreases basolateral K+ conductance in gallbladder epithelial cells via a cAMP-dependent mechanism. The latter effect, not previously reported in epithelial tissues, appears to be the major determinant of the IBMX-induced depolarization ofV
a
. 相似文献
15.
Zusammenfassung Die Lumineszenz wÄ\riger Tl+-Lösungen unter Einwirkung von 8,5-keVeff-Röntgenstrahlen wird untersucht, und zwar 1. in neutraler Lösung, 2. in saurer Lösung, 3. in alkalischer Lösung, 4. bei Zusatz von NaCl.Bei Änderung des pH-Wertes nimmt die Lichtausbeute sowohl auf der sauren Scite (beipH=3,4) als auch auf der alkalischen Scite (beipH=12) ein Maximum an; sie erreicht dort den 2- bis 3fachen Wert der Ausbeute in neutraler Lösung. Andererseits ist bei Zusatz von 1 M NaCl in neutraler Lösung die Ausbeute fünfmal höher als bei Abwesenheit von NaCl; die Maxima im sauren und alkalischen Bereich verschwinden jedoch bei 1 M NaCl vollkommen, und man erhÄlt bei gro\en und bei kleinen pH-Werten lediglich eine Löschung der Lumineszenz.Die Lumineszenz kommt durch Bildung von Tl+* bei der Anlagerung von eaq an Tl++ zustande. Tl++ entsteht jedoch nicht unmittelbar gemÄ\ Tl+ + OH Tl++ + OH–, sondern zunÄchst bildet sich Tl+OH, und dieses dissoziiert erst nach einer Verzögerung von > 10–7 sec in Tl++ und OH–. Die Sensibilisierung durch H+ wird durch die Reaktion Tl+OH + H+ Tl++ + H2O und die durch OH– durch Tl+OH + OH– Tl++O– + H2O erklÄrt. Die Reaktion der Komplexe Tl+Cl– und Tl+Cl2
– mit OH erfolgt offenbar ohne zeitliche Verzögerung, d. h. Tl++Cl–– bzw. Tl++Cl2
–– wird dabei innerhalb einer Zeit 10–7 sec gebildet.
Chemiluminescences of aqueous TlI solutions produced by irradiation with 8.5-keV-X-rays
Summary The luminescence of aqueous solutions of Tl+ during irradiation with 8.5-keV-X-rays has been investigated. In particular we have studied the Tl+-luminescence in 1. neutral solutions, 2. acid solutions, 3. alkaline solutions, 4. solutions containing various concentrations of NaCl.Varying thepH the luminescence yield passes a maximum on the acid side as well as on the alkaline side (atpH=3.4 respectivelypH=12). Compared with neutral solutions the luminescence yield is increased by a factor 2 to 3 at these pH-values.By adding 1 M NaCl to neutral Tl+-solutions the luminescence yield is enhanced by a factor five, however in dependence ofpH no further increase has been observed, but only quenching of the luminescence at low and highpH.The luminescence origins from the formation of Tl+* by the reaction of eaq with Tl++ formed by oxidation of Tl+ by OH. However, Tl++ is not formed directly by Tl++OH Tl++ + OH– but via dissociation of the intermediate Tl+OH after a delay > 10–7 sec.We explain the increase of the luminescence yield in acid solutions by the reaction Tl+OH + H+ Tl++ + H2O and in alkaline solutions by the reaction Tl+OH + OH– Tl++O– + H2O. In alkaline solutions the luminescence spectrum shifts to longer wavelengths; we conclude, that this spectrum is attributed to Tl+*O–. Evidently the reaction of Tl+Cl– and Tl+Cl2 –– with OH leads to formation of Tl++Cl– and Tl++Cl2 –– without any efficient delay.相似文献
16.
Environmental gradients,plant distribution,and species richness in arctic salt marsh near Prudhoe Bay,Alaska 总被引:2,自引:0,他引:2
Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca2+, Mg2+, Na+, K+, SO4
= and Cl– were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca2+, Mg2+, Na+, K+, SO4
= and Cl–. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments. 相似文献
17.
A. Diez de los Rios N. E. DeRose W. McD Armstrong 《The Journal of membrane biology》1981,63(1-2):25-30
Summary Open-tip and liquid ion-exchanger microelectrodes were used to study the effects of cAMP (6mm, added to the serosal medium) on apical membrane potential (E
m
) and intracellular sodium, potassium, and chloride activities (a
Na
i
,a
K
i
,a
Cl
i
) inNecturus gallbladder under open-circuit conditions. Transepithelial potential difference (E
Tr
) was also measured. In the presence of cAMP,a
Cl
i
fell from about 1.5 times its equilibrium value to a level that corresponded to electrochemical equilibrium across the apical and basolateral cell membranes. Under these conditionsa
Na
i
decreased anda
K
i
increased,E
m
was unchanged andE
Tr
increased from virtually zero to a small but significant serosal positive value. The cAMP-induced increase ina
K
i
was abolished when Cl–-free incubation media were used. Addition of the Ca++-ionophore A23187 (0.5 g/ml) to the serosal medium had no effect onE
m
,E
Tr
, ora
Cl
i
. When A23187 was added to the mucosal medium,E
m
and the basolateral membrane potential hyperpolarized by about 20 mV and an increase in the outwardly directed electrochemical driving force for Cl– was observed. These results indicate that cAMP inhibits coupled transapical Na–Cl entry into epithelial cells ofNecturus gallbladder and suggest that this inhibition may not be mediated by an increase in intracellular Ca++ concentration. 相似文献
18.
The first analysis of chloride fluxes and compartmentation in a non-excised plant system is presented, examining ten ecologically pertinent conditions. The short-lived radiotracer couple 38Cl/39Cl was used as a Cl– tracer in intact barley (Hordeum vulgare L. cv. Klondike) seedlings, which were cultured and investigated under four external [Cl–], from abundant (0.1 mM) to potentially toxic (100 mM). Chloride–nitrogen interactions were investigated by varying N source (NO3
– or NH4
+) and strength (0.1 or 10 mM), in order to examine, at the subcellular compartmentation level, the antagonism, previously documented at the influx level, between Cl– and NO3
–, and the potential role of Cl– as a counterion for NH4
+ under conditions in which cytosolic [NH4
+] is excessive. Cytosolic [Cl–] increased with external [Cl–] from 6 mM to 360 mM. Cl– influx, fluxes to vacuole and shoot, and, in particular, efflux to the external medium, also increased along this gradient. Efflux reached 90% of influx at the highest external [Cl–]. Half-times of cytosolic Cl– exchange decreased between high-affinity and low-affinity influx conditions. The relationship between cytosolic [Cl–] and shoot flux indicated the presence of a saturable low-affinity transport system (SLATS) responsible for xylem loading of Cl–. N source strongly influenced Cl– flux to the vacuole, and moderately influenced Cl– influx and shoot flux, whereas efflux and half-time were insensitive to N source. Cytosolic pool sizes were not strongly or consistently influenced by N source, indicating the low potential for Cl– to act as a counterion to hyperaccumulating NH4
+. We discuss our results in relation to salinity responses in cereals.Abbreviations [Cl–]cyt
cytosolic chloride concentration
- [Cl–]o
external chloride concentration 相似文献
19.
Competitive adsorption of Pb, Cd and Zn ions onto Eichhornia crassipes in binary and ternary systems
A batch sorption technique was used to study the biosorption of Pb2+, Cd2+ and Zn2+ ions onto the vastly abundant water hyacinth weed, Eichhornia crassipes biomass in binary and ternary systems at a temperature of 30 °C and pH 4.84. Mutual interference effects were probed using equilibrium adsorption capacity ratios, , where the prime indicates the presence of one or two other metal ions. The combined action of the metals was found to be antagonistic, and the metal sorption followed the order Pb2+ Cd2+ Zn2+. The behaviour of competitive biosorption for Pb–Cd and Pb–Zn combinations were successfully described by the Langmuir Competitive Model (CLM), whilst the model showed poor fitting to the Cd–Zn data. In conclusion, Pb2+ ions could still be effectively removed from aqueous solution in the presence of both Cd2+ and Zn2+ ions, but removal of the Cd2+ and Zn2+ ions would be suppressed in the presence of Pb2+. 相似文献
20.
Christopher J. Winters W. Brian Reeves Thomas E. Andreoli 《The Journal of membrane biology》1992,128(1):27-39
Summary Cl– channels from basolaterally-enriched rabbit outer renal medullary membranes are activated either by increases in intracellular Cl– activity or by intracellular protein kinase A (PKA). Phosphorylation by PKA, however, is not obligatory for channel activity since channels can be activated by intracellular Cl– in the absence of PKA. The PKA requirement for activation of Cl– channels in certain secretory epithelia is, in contrast, obligatory. In the present studies, we examined the effects of PKA and intracellular Cl– concentrations on the properties of Cl– channels obtained either from basolaterally-enriched vesicles derived from highly purified suspensions of mouse medullary thick ascending limb (mTALH) segments, or from apical membrane vesicles obtained from two secretory epithelia, bovine trachea and rabbit small intestine. Our results indicate that the Cl– channels from mTALH suspensions were virtually identical to those previously described from rabbit outer renal medulla. In particular, an increase in intracellular (trans) Cl– concentration from 2 to 50 mm increased both channel activity (P
o) and channel conductance (g
Cl, pS). Likewise, trans PKA increased mTALH Cl– channel activity by increasing the activity of individual channels when the trans solutions were 2 mm Cl. Under the latter circumstance, PKA did not activate quiescent channels, nor did it affect g
Cl. Moreover, when mTALH Cl– channels were inactivated by reducing cis Cl– concentrations to 50 mm, cis PKA addition did not affect P
o. These results are consistent with the view that these Cl– channels originated from basolateral membranes of the mTALH.Cl– channels from apical vesicles from trachea and small intestine were completely insensitive to alterations in trans Cl– concentrations and demonstrated markedly different responses to PKA. In the absence of PKA, tracheal Cl– channels inactivated spontaneously after a mean time of 8 min; addition of PKA to trans solutions reactivated these channels. The intestinal Cl– channels did not inactivate with time. Trans PKA addition activated new channels with no effect on basal channel activity. Thus the regulation of Cl– channel activity by both intracellular Cl– and by PKA differ in basolateral mTALH Cl– channels compared to apical Cl– channels from either the tracheal or small intestine.We acknowledge the able technical assistance of Steven D. Chasteen. Clementine M. Whitman provided her customary excellent secretarial assistance. This work was supported by Veterans Administration Merit Review Grants to T.E. Andreoli and to W.B. Reeves. C.J. Winters is a Veterans Administration Associate Investigator. 相似文献