Survival and death of Chara internodal cells in electrolyte solutions and calcium release from the cell wall

Abstract. Survival and death of Chara internodal cells were investigated in one of the alkali metal salts KCl, some of the alkali earth metal salts CaCl₂, Ca(NO₃)₂, MgCl₂, Mg(NO₃)₂, SrCl₂, Sr(NO₃)₂, BaCl₂ and Ba(NO₃)₂, potassium phosphate pH buffer solution (pH 7.0), Tris-maleate pH buffer solution (pH 7.0), HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid)-KOH (pH 7.0) pH buffer solution, calcium buffer solutions, and deionized water. Most of the internodal cells died within a day or a few days in KCl, MgCl₂, Mg(NO₃)₂, BaCl₂ and Ba(NO₃)₂ solutions of higher concentrations, calcium buffer solutions of pCa 6.0, 10.0 mol m^-3 potassium phosphate pH buffer solution and 10.0 mol m^-3 Trismaleate pH buffer solution. However, all of the internodal cells survived more than 10 d in deionized water, 80.0 mol m^-3 CaCl₂, 80.0 mol m^-3 Ca(NO₃)₂, 80.0 mol m^-3 SrCl₂, 80.0 mol m^-3 Sr(NO₃)₂ calcium buffer solutions of pCa 4.0 and pCa 5.0, and 10.0 mol m^-3 HEPES-KOH (pH 7.0) pH buffer solution. Addition of Ca²⁺ or Sr²⁺ to K⁺, Mg²⁺ and Ba²⁺ salt solutions increased the survival rates of the internodal cells. Calcium release from the internodal cell wall was measured in deionized water, KCl, NaCl, MgCl₂, CaCl₂, SrCl₂ and BaCl₂ solutions. Except in deionized water and CaCl₂ solution, most of the calcium binding to the cell wall was released within one or a few hours in respective electrolyte solutions. Thus, survival and death of the internodal cells in the electrolyte solutions tested were interpreted in terms of the calcium release from the cell wall and the cell membrane, and intrinsic ability of Sr²⁺ to maintain the cell membrane normal.     

THE MECHANISM BY WHICH TRIVALENT AND TETRAVALENT IONS PRODUCE AN ELECTRICAL CHARGE ON ISOELECTRIC PROTEIN

1. Experiments on anomalous osmosis suggested that salts with trivalent cations, e.g. LaCl₃, caused isoelectric gelatin to be positively charged, and salts with tetravalent anions, e.g. Na₄Fe(CN)₆, caused isoelectric gelatin to be negatively charged. In this paper direct measurements of the P.D. between gels of isoelectric gelatin and an aqueous solution as well as between solutions of isoelectric gelatin in a collodion bag and an aqueous solution are published which show that this suggestion was correct. 2. Experiments on anomalous osmosis suggested that salts like MgCl₂, CaCl₂, NaCl, LiCl, or Na₂SO₄ produce no charge on isoelectric gelatin and it is shown in this paper that direct measurements of the P.D. support this suggestion. 3. The question arose as to the nature of the mechanism by which trivalent and tetravalent ions cause the charge of isoelectric proteins. It is shown that salts with such ions act on isoelectric gelatin in a way similar to that in which acids or alkalies act, inasmuch as in low concentrations the positive charge of isoelectric gelatin increases with the concentration of the LaCl₃ solution until a maximum is reached at a concentration of LaCl₃ of about M/8,000; from then on a further increase in the concentration of LaCl₃ diminishes the charge again. It is shown that the same is true for the action of Na₄Fe(CN)₆. From this it is inferred that the charge of the isoelectric gelatin under the influence of LaCl₃ and Na₄Fe(CN)₆ at the isoelectric point is due to an ionization of the isoelectric protein by the trivalent or tetravalent ions. 4. This ionization might be due to a change of the pH of the solution, but experiments are reported which show that in addition to this influence on pH, LaCl₃ causes an ionization of the protein in some other way, possibly by the formation of a complex cation, gelatin-La. Na₄Fe(CN)₆ might probably cause the formation of a complex anion of the type gelatin-Fe(CN)₆. Isoelectric gelatin seems not to form such compounds with Ca, Na, Cl, or SO₄. 5. Solutions of LaCl₃ and Na₄Fe(CN)₆ influence the osmotic pressure of solutions of isoelectric gelatin in a similar way as they influence the P.D., inasmuch as in lower concentrations they raise the osmotic pressure of the gelatin solution until a maximum is reached at a concentration of about M/2,048 LaCl₃ and M/4,096 Na₄Fe(CN)₆. A further increase of the concentration of the salt depresses the osmotic pressure again. NaCl, LiCl, MgCl₂, CaCl₂, and Na₂SO₄ do not act in this way. 6. Solutions of LaCl₃ have only a depressing effect on the P.D. and osmotic pressure of gelatin chloride solutions of pH 3.0 and this depressing effect is quantitatively identical with that of solutions of CaCl₂ and NaCl of the same concentration of Cl.     

Wall appositions induced by ionophore A 23187, CaCl2, LaCl3, and nifedipine in characean cells

Summary The formation of wall appositions (plugs) by ionophore A 23187, CaCl₂, LaCl₃, and nifedipine was studied in mature internodal cells of characeaen algae. CaCl₂ at concentrations above 10^–2M induces thick fibrillar plugs without callose inNitella flexilis. InChara corallina andNitella flexilis ionophore A 23187 (1.25×10^–5 to 5×10^–5M) and LaCl₃ (7.5×10^–5 to 2.5×10^–4M) cause flat appositions which contain callose and have a more granular structure. Plug formation by ionophore A 23187, CaCl₂, and LaCl₃ is pH-dependent and occurs beneath the alkaline regions of the cell. Nifedipine (10^–4 to 10^–5M) induces plugs inNitella flexilis after previous injury. These callose-containing wall appositions consist of a heterogeneous granular core which is covered by a fibrillar layer. The results of this work are compared with previous studies on wound wall formation and chlortetracycline (CTC)-induced plug formation which reveal that abundant coated vesicles occur only when a thick fibrillar wall layer is formed. Neither LaCl₃ nor nifedipine inhibit the formation of CaCl₂- or CTC-plugs. The unusual effects of these substances, which normally act as Ca²⁺ antagonists and therefore should prevent and not induce plug formation, are discussed. It is suggested that La³⁺ mimicks the effects of calcium and that nifedipine binding to the Ca²⁺ channels is altered in the alkaline regions of characean internodes and allows an influx of Ca²⁺.Abbreviations AFW artificial fresh water - CTC chlortetracycline - DCMU dichlorphenyldimethylurea - DMSO dimethylsulfoxide - EGTA ethyleneglycoltetraacetic acid - MES 2-(N-morpholino) ethanesulfonic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - TAPS N-tris[hydroxymethyl]methyl-3-aminopropanesulfonic acid     

Effects of Calcium and Calmodulin Antagonists on Chilling Stress-Induced Proline Accumulation in <Emphasis Type="Italic">Jatropha curcas</Emphasis> L.

Regulation of proline accumulation in plants under chilling stress remains unclear. In this paper, we treated Jatropha curcas seedlings under chilling stress with exogenous calcium chloride (CaCl₂), the plasma membrane Ca²⁺-channel blocker lanthanum chloride (LaCl₃), calmodulin antagonists, chlorpromazine (CPZ), and trifluoperazine (TFP) and investigated the effects of calcium and calmodulin (CaM) on proline accumulation and chilling tolerance. The results showed that CaCl₂ treatment significantly enhanced chilling stress-induced proline accumulation. CaCl₂ also induced an almost immediate and rapid increase of Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and glutamate dehydrogenase activities, the key enzymes in the glutamate pathway of proline biosynthesis, and up-regulated P5CS expression, but it decreased the activity of proline dehydrogenase (ProDH), a key enzyme of proline degradation, and inhibited ProDH expression. Treatment with LaCl₃, CPZ, and TFP exhibited the opposite effects to those by CaCl₂ treatment. Moreover, CaCl₂, LaCl₃, CPZ, and TFP had little effect on the activities of ornithine aminotransferase and arginase, the key enzymes in the ornithine pathway of proline biosynthesis. These results indicated that Ca²⁺-CaM might be involved in signal transduction events, leading to proline accumulation in J. curcas seedlings under chilling stress, and that Ca²⁺-induced proline accumulation is a combined result of the activation of the glutamate pathways of proline biosynthesis and the simultaneous inhibition of the proline degradation pathway. In addition, CaCl₂ treatment increased tissue vitality, decreased the content of the lipid peroxidation product malondialdehyde (MDA), and alleviated electrolyte leakage in J. curcas seedlings under chilling stress, indicating that exogenous Ca²⁺ can enhance chilling tolerance, and proline might be a key factor in this increased chilling tolerance.     

Effects of trypsin and bivalent cations on P-680+-reduction,fluorescence induction and oxygen evolution in Photosystem II membrane fragments from spinach

Laser-flash-induced absorption changes at 830 nm, fluorescence-induction curves and the average oxygen yield per flash have been measured in spinach Photosystem II membrane fragments as a function of trypsin treatment and its modification by CaCl₂. The following was found. (i) The relative contribution of the nanosecond relaxation to the overall decay kinetics of 830 nm absorption changes reflecting the P-680⁺-reduction decreases as a function of incubation time with trypsin. Simultaneously, mild treatment at pH = 6.0 markedly increases the extent of 200 μs kinetics that highly revert back to nanosecond kinetics by CaCl₂ addition. After harsher trypsin treatment (pH = 7.5) pH-dependent 2–20 μs kinetics appear that cannot be reverted to nanosecond kinetics by CaCl₂. (ii) The CaCl₂-induced restoration of nanosecond kinetics is mainly due to a Ca²⁺-induced effect rather than to a functional role of Cl⁻. Sr²⁺ can substantially substitute for Ca²⁺, whereas Mg²⁺, Mn²⁺ and monovalent ions are almost inefficient. (iii) A quantitative correlation between the extent of the nanosecond kinetics and the average oxygen yield per flash was not observed. (iv) If CaCl₂ is present in the assay medium for trypsin treatment the samples are markedly protected to proteolytic degradation. This effect mainly refers to the reaction pattern of the acceptor side. Other bivalent cations can substitute Ca²⁺ for its protective function. (v) The CaCl₂-induced protection to proteolytic attack is extremely sensitive to a very short trypsin pretreatment that does hardly affect the shape of the fluorescence induction curve. The results are discussed in relation to the functional and structural organization of Photosystem II.     

THE INFLUENCE OF ELECTROLYTES ON THE CATAPHORETIC CHARGE OF COLLOIDAL PARTICLES AND THE STABILITY OF THEIR SUSPENSIONS : II. EXPERIMENTS WITH PARTICLES OF GELATIN,CASEIN, AND DENATURED EGG ALBUMIN.

1. This paper gives measurements of the influence of various electrolytes on the cataphoretic P.D. of particles of collodion coated with gelatin, of particles of casein, and of particles of boiled egg albumin in water at different pH. The influence of the same electrolyte was about the same in all three proteins. 2. It was found that the salts can be divided into two groups according to their effect on the P.D. at the isoelectric point. The salts of the first group including salts of the type of NaCl, CaCl₂, and Na₂SO₄ affect the P.D. of proteins at the isoelectric point but little; the second group includes salts with a trivalent or tetravalent ion such as LaCl₃ or Na₄Fe(CN)₆. These latter salts produce a high P.D. on the isoelectric particles, LaCl₃ making them positively and Na₄Fe(CN)₆ making them negatively charged. This difference in the action of the two groups of salts agrees with the observations on the effect of the same salts on the anomalous osmosis through collodion membranes coated with gelatin. 3. At pH 4.0 the three proteins have a positive cataphoretic charge which is increased by LaCl₃ but not by NaCl or CaCl₂, and which is reversed by Na₄Fe(CN)₆, the latter salt making the cataphoretic charge of the particles strongly negative. 4. At pH 5.8 the protein particles have a negative cataphoretic charge which is strongly increased by Na₄Fe(CN)₆ but practically not at all by Na₂SO₄ or NaCl, and which is reversed by LaCl₃. the latter salt making the cataphoretic charge of the particles strongly positive. 5. The fact that electrolytes affect the cataphoretic P.D. of protein particles in the same way, no matter whether the protein is denatured egg albumin or a genuine protein like gelatin, furnishes proof that the solutions of genuine proteins such as crystalline egg albumin or gelatin are not diaphasic systems, since we shall show in a subsequent paper that proteins insoluble in water, e.g. denatured egg albumin, are precipitated when the cataphoretic P.D. falls below a certain critical value, while water-soluble proteins, e.g. genuine crystalline egg albumin or gelatin, stay in solution even if the P.D. of the particles falls below the critical P.D.     

Evidence that a light-accelerated abrupt change in membrane characteristics of bovine rod outer segment fragments takes place at acidic pH

Changes in the turbidity of suspensions of bovine rod outer segment fragments induced by rhodopsin bleaching were measured in the presence of various concentrations of divalent cations at acidic pH (4.7–5.4). Unlike the situation at neutral pH, the turbidity of the suspensions increased drastically by bleaching at acidic pH. It was found that the extent of turbidity change became maximum at a particular concentration of divalent cations (i.e., 5 mM CaCl₂, 5 mM MgCl₂, or 5 mM mixed divalent cations). However, the turbidity increment in the presence of 5 mM MgCl₂ was greatly enhanced by the addition of a minute amount of CaCl₂. These results evidently show that the membrane characteristic is abruptly changed by bleaching at acidic pH in particular. It is also suggested that there are two kinds of binding sites for Ca ions: one is a Ca²⁺ specific site, and the other is a nonspecific site to which Mg²⁺ can also bind.     

The calcium requirement in GnRH-stimulated LH release is not mediated through a specific action on receptor binding

A radioligand receptor assay was used to determine the effect of Ca⁺² and other cations on the binding of D-Ser-(t-Bu)⁶-desGly¹⁰EA GnRH (Buserelin acetate, Hoechst) to the gonadotropin releasing hormone receptor in rat pituitary membrane. Specific binding was reduced in the presence of CaCl₂, BaCl₂, MnCl₂, Co(CH₃COO)₂, MgCl₂, NaCl, or LaCl₃, although these salts have markedly different effects on receptor mediated gonadotropin release from intact cells. Consistent with this finding, compounds which chelate cations increased specific binding of the ligand. The decreased binding is explained solely by an effect on receptor affinity, which was reduced from 4 × 10⁹ M^?1 in the presence of 10 mM CaCl₂. Total receptor number was unchanged. These data suggest that the requirement for Ca⁺² in GnRH-stimulated LH release is not mediated through a specific action of this ion at the level of receptor binding.     

Myelin protein changes with digestion of whole sciatic nerve in trypsin.

Whole mouse sciatic nerves were split and incubated in phosphate buffered saline (PBS) and in PBS containing various amounts of trypsin. After 24 hours of exposure to PBS alone there were no changes in the gel electrophoresis pattern of myelin proteins. During the same period of time, trypsin digested major amounts ofboth the main myelin protein (P_O) and the two basic proteins of myelin (P₁, P₂). The basic proteins were undetectable after 24 hours of 1% trypsin digestion while the main myelin protein was not completely digested. The amount of digestion of the myelin proteins was related to the concentration of trypsin and the time of digestion. Myelin proteins were demonstrated by staining with Coomassie blue, periodic acid Schiff (PAS) and by special indirect lighting techniques.     

Effects of lanthanum chloride on glutamate level, intracellular calcium concentration and caspases expression in the rat hippocampus

Lanthanum chloride (LaCl₃) can affect neurobehavioral development and impair cognitive abilities. The mechanism underlying LaCl₃-induced neurotoxic effects is still unknown. The purpose of this research was to investigate the neuronal impairment induced by LaCl₃ and discuss the possible mechanism from the aspects of the alteration of glutamate level, intracellular calcium concentration ([Ca²⁺]_i), Bax, Bcl-2 and caspases expression in the hippocampus. Lactational rats were exposed to 0, 0.25, 0.50 and 1.0 % LaCl₃ in drinking water, respectively. Their offspring were exposed to LaCl₃ by parental lactation and then administrated with 0, 0.25, 0.50 and 1.0 % LaCl₃ in drinking water for 1 month. The results showed that 0.25, 0.50 and 1.0 % LaCl₃ exposure induced neuronal impairment in the hippocampus of young rat. Hippocampal glutamate level, [Ca²⁺]_i and ratio of Bax and Bcl-2 expression increased significantly after LaCl₃ exposure. Besides, LaCl₃ exposure increased GRP78, GRP94, GADD153 and p-JNK expression, promoted the activation of caspase-3, caspase-9 and caspase-12, induced PARP cleavage and caused excessive apoptosis. These results indicate that LaCl₃ increases glutamate level, [Ca²⁺]_i and ratio of Bax and Bcl-2 expression, which cause excessive apoptosis by the mitochondrial and endoplasmic reticulum stress-induced pathway, and thus neuronal damages in the hippocampus.     

SODIUM CHLORIDE AND SELECTIVE DIFFUSION IN LIVING ORGANISMS

1. It is shown that NaCl acts like CaCl₂ or LaCl₃ in preventing the diffusion of strong acids through the membrane of the egg of Fundulus with this difference only that a M/8 solution of NaCl acts like a M/1,000 solution of CaCl₂ and like a M/30,000 solution of LaCl₃. 2. It is shown that these salts inhibit the diffusion of non-dissociated weak acid through the membrane of the Fundulus egg but slightly if at all. 3. Both NaCl and CaCl₂ accelerate the diffusion of dissociated strong alkali through the egg membrane of Fundulus and CaCl₂ is more efficient in this respect than NaCl. 4. It is shown that in moderate concentrations NaCl accelerates the rate of diffusion of KCl through the membrane of the egg of Fundulus while CaCl₂ does not.     

IONIZING INFLUENCE OF SALTS WITH TRIVALENT AND TETRAVALENT IONS ON CRYSTALLINE EGG ALBUMIN AT THE ISOELECTRIC POINT

1. While crystalline egg albumin is highly soluble in water at low temperature at the pH of its isoelectric point, it is coagulated by heating. It has long been known that this coagulation can be prevented by adding either acid or alkali, whereby the protein is ionized. 2. It is shown in this paper that salts with trivalent or tetravalent ions, e.g. LaCl₃ or Na₄Fe(CN)₆, are also able to prevent the heat coagulation of albumin at the isoelectric point (i.e. pH 4.8), while salts with a divalent ion, e.g. CaCl₂, BaCl₄, Na₂SO₄, or salts like NaCl, have no such effect. 3. This is in harmony with the fact shown in a preceding paper that salts with trivalent or tetravalent ions can cause the ionization of proteins at its isoelectric point and thus give rise to a membrane potential between micellæ of isoelectric protein and surrounding aqueous solution, while the above mentioned salts with divalent and monovalent ions have apparently no such effect.     

Polar lobe formation and cytokinesis in fertilized eggs of Ilyanassa obsoleta. II. Large bleb formation caused by high concentrations of exogenous calcium ions

Fertilized eggs of the mollusk Ilyanassa obsoleta (Nassarius obsoletus) form large blebs resembling polar lobes within 12 min of exposure to solutions of isotonic CaCl₂, whereas control eggs in sea water remain spherical. Under identical conditions, fertilized eggs of the sea urchin, Strongylocentrotus purpuratus, an organism which normally does not form polar lobes, do not form blebs upon exposure to solutions of isotonic CaCl₂. The calcium-induced blebbing in Ilyanassa still occurs if other cations such as Na⁺, Mg²⁺, or Mn²⁺ are present in addition to Ca²⁺, but not if comparable concentrations of K⁺ are present. Cytochalasin B prevents the calcium-induced blebbing, whereas colchicine does not. Cytokinesis in both Ilyanassa and Strongylocentrotus and normal polar lobe formation in Ilyanassa appear to require exogenous K⁺ but not exogenous Ca²⁺. Preliminary electron microscopy of Ilyanassa eggs exposed to isotonic solutions of CaCl₂ has shown microfilaments in the cortical cytoplasm in the region of the bleb constriction but no microfilaments in spherical control eggs in sea water. These data suggest that high concentrations of exogenous Ca²⁺ trigger the polymerization and contraction of a ring of microfilaments in the cortical cytoplasm of the Ilyanassa egg which results in the formation of a lobelike bleb of cytoplasm. The observation that K⁺ antagonizes this Ca²⁺-induced blebbing has led to the formulation of a theory which postulates that the ratio of intracellular Ca²⁺ to intracellular K⁺ is critical in the control of polar lobe formation and cytokinesis.     

Atypical incorporation of single amino acids into myelin proteins.

—Purified myelin incorporated l -[¹⁴C]leucine and l -[¹⁴C]lysine into myelin proteins in an enzymatic process similar to that of renal brush border membranes. The system was not inhibited by cycloheximide or puromycin or by pretreatment with ribonuclease; the reaction was inhibited by cetophenicol. ATP was an effector, shifting the optimal pH from 7.2 to 8.3. In the presence of ATP, myelin was less dense in a sucrose gradient. Ammonia was released from the membrane during the incorporation of amino acids. Myelin preloaded with cold leucine did not incorporate [¹⁴C]leucine but did incorporate [¹⁴C]lysine; there was no cross inhibition between the two amino acids. The incorporation was into or onto proteins of the Wolfgram proteolipid fraction of myelin. The incorporation was of the high affinity type with a K_m of 10^?7m and was restricted to the natural amino acids.     

Tentacle contraction and ultrastructure inDiscophrya collini: The response to cations

Summary Discophrya collini is a suctorian protozoan with contractile tentacles containing a microtubule-lined canal and microfilaments. The effects of a range of cations on tentacle contraction and ultrastructure have been determined. Treatment with 80 mM CaCl₂ and 95 mM MgCl₂ causes contraction to 28% and 57% of the control length respectively. Re-extension takes over 4 hours in the culture medium, but CaCl₂-treated tentacles are re-extended after a 5 minutes treatment with 10^–2 M EDTA or 5 × 10^–3 M EGTA. CuCl₂ causes a significant contraction at 10^–5 M (to 77%); LaCl₃ at 10^–4 M (to 65%); ZnCl₂ at 10^–2 M (to 65%), but BaCl₂, CoCl₂, MnCl₂, NiCl₂, and SrCl₂ cause significant changes only at 10^–1 M.The cytoplasm of CaCl₂-treated cells contains two forms of membraneous structures when viewed in TEM; that of MgCl₂-treated cells reveals granular areas of medium electron density. None of these features are seen in control cells. The microtubules of the tentacle canal appear to be intact upon its retraction into the cell with no change occurring in the numbers or relative positions of the microtubules. The tentacle cortex is wrinkled. It is suggested from this and previous work that tentacle contraction may be mediated by a microfilament-based mechanism, and that calcium may be involved.     

Magnetic fields alter electrical properties of solutions and their physiological effects

Calcium chloride and snail physiological salt solutions were exposed to static magnetic fields (2.3–350 mT), and the physical properties of the solutions as well as their biologic effects were studied. Our preliminary observations show that these fields alter physicochemical properties of CaCl₂ solutions and the functional effects of physiological solutions. Experiments on CaCl₂ solutions demonstrated field-dependent changes of electrical conductivity, with the magnitude and the direction of conductivity change being a function of both concentration and field intensity. The changes in conductivity were maintained for periods in excess of 1 h after exposure. Conductivity changes were not found after exposure of physiological solutions to static magnetic fields, but changes of biological consequence did occur. Other experiments showed that there were several changes in cellular function observed in ganglia and isolated neurons of Helix pomatia when the perfusing medium was changed from the normal physiologic solution to the same solution after exposure to magnetic fields. These changes include membrane depolarization and increased action potential discharge, reduced uptake of Ca into cells, altered content of cyclic nucleotides in ganglia, and increased volume of isolated cell bodies. A change in hydration of calcium ions may be one of the consequences of magnetic-field exposure, and in physiological solutions this change may have functional consequences. © 1994 Wiley-Liss, Inc.     

Relationship of Cell Sap pH to Organic Acid Change During Ion Uptake

Excised roots of barley (Hordeum vulgare, var. Campana) were incubated in KCl, K₂SO₄, CaCl₂, and NaCl solutions at concentrations of 10⁻⁵ to 10⁻² n. Changes in substrate solution pH, cell sap pH, and organic acid content of the roots were related to differences in cation and anion absorption. The pH of expressed sap of roots increased when cations were absorbed in excess of anions and decreased when anions were absorbed in excess of cations. The pH of the cell sap shifted in response to imbalances in cation and anion uptake in salt solutions as dilute as 10⁻⁵ n. Changes in cell sap pH were detectable within 15 minutes after the roots were placed in 10⁻³ n K₂SO₄. Organic acid changes in the roots were proportional to expressed sap pH changes induced by unbalanced ion uptake. Changes in organic acid content in response to differential cation and anion uptake appear to be associated with the low-salt component of ion uptake.     

Changes in haemolymph ion concentrations of Astacus astacus L. and Pacifastacus leniusculus (Dana) after exposure to low pH and aluminium

During exposure to soft water, acidified to pH 4.0, the haemolymph concentrations of Na⁺, K⁺, and Cl^– decreased whereas the Ca²⁺ concentration fluctuated in Astacus astacus. The haemocyte content of K⁺ decreased from 9% to 2% of the total haemolymph K⁺ content after exposure to pH 3.7 for 3 days. Within 14 days, 250 µg Al³⁺ l^–1, as Al₂(SO₄)₃ at pH 5.0, reduced the haemolymph Na⁺ content in Astacus astacus and Pacifastacus leniusculus, however, the effects were less pronounced than earlier reported for fish. Disturbed ion regulation, mainly depending on low pH, is thought to contribute to the absence of these species in acid waters.     

Ionic processes underlying the decrease in osmotic potential of Chara L-cell fragments in dilute electrolyte solutions

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 SO^2?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⁺, SO^2?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.     

Crosstalk of nitric oxide with calcium induced tolerance of tall fescue leaves to high irradiance

Calcium ion (Ca²⁺) is essential secondary messenger in plant signaling networks. In this study, the effect of Ca²⁺ on oxidative damage caused by a high irradiance (HI) was investigated in the leaves of two cultivars of tall fescue (Arid3 and Houndog5). Pretreatment of the tall fescue leaves with a CaCl₂ solution significantly increased Ca²⁺ content and intrinsic HI tolerance due to a decreased ion leakage and content of malondialdehyde, hydrogen peroxide, and superoxide radicals. Moreover, the activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased in both the cultivars in the presence of Ca²⁺ under the HI stress. In contrast, treatments with a Ca²⁺ chelator ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA) or a plasma membrane Ca²⁺ channel blocker LaCl₃ reversed these effects. On the other hand, a pronounced increase in nitric oxide synthase-like activity and NO release by exogenous Ca²⁺ treatment was observed in the tolerant Arid3 plants after exposure to the HI, whereas only a small increase was observed in more sensitive Houndog5. Moreover, the inhibition of NO production by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide or N^ω-nitro-L-arginine blocked the protective effect of exogenous Ca²⁺, whereas the inhibition of Ca²⁺ by EGTA or LaCl₃ had no influence on the protective effect of NO. The results indicate that NO might be involved in the Ca²⁺-induced activities of antioxidant enzymes further protecting against HI-induced oxidative damage. This protective mechanism was found to be more efficient in Arid3 than in Houndog5.