Freezing of isolated thylakoid membranes in complex media

Chloroplast thylakoid membranes isolated from spinach leaves (Spinacia oleracea L. cv. Monatol) were subjected to a freeze-thaw treatment in a buffered medium containing 70 mM KCl, 30 mM NaNO₃ and 20 mM K₂SO₄ in different combinations. In the presence of the three predominant inorganic electrolytes, inactivation of photophosphorylation was mainly caused by a decrease in the capacity of the photosynthetic electron transport; release of proteins from the membranes was not manifest and light-induced H⁺ gradient and proton permeability were largely unaffected. Omission of nitrate from the medium had little effect. When either sulfate or chloride or both were omitted prior to freezing, inactivation of photophosphorylation was correlated with stimulation of the phosphorylating electron flow, marked increase in H⁺ permeability and loss of the ability of the thylakoids to accumulate protons in the light. In the absence of sulfate, uncoupling was mainly a consequence of the dissociation of chloroplast coupling factor (CF₁). Partial restoration of proton impermeability and pH gradient occurred upon the addition of N,N-dicyclohexylcarbodiimide (DCCD). When sulfate was present but chloride omitted, CF₁ remained attached to the membranes and the addition of DCCD had no effect, indicating that the increase in proton efflux was caused by a different mechanism. It is concluded that sulfate stabilizes the CF₁ and prevents its release from the membranes, but KCl is also necessary for maintaining the low permeability of the membranes to protons. The importance of complex media for investigations on isolated biomembrane systems is stressed.Abbreviations CF₁ chloroplast coupling factor - DCCD N,N-dicyclohexylcarbodiimide - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid I=Santarius 1986 b     

Growth and mineral content of coriander (<Emphasis Type="Italic">Coriandrum sativum</Emphasis> L.) plants under mild salinity with different salts

Soil salinity is a complex issue in which various anions and cations contribute to have a general adverse effect on plant growth. In the present study, effects of salinity from various salts including sodium chloride (NaCl), potassium chloride?+?sodium chloride?+?calcium chloride (KCl?+?NaCl?+?CaCl₂), potassium sulfate?+?magnesium nitrate (K₂SO₄?+?Mg(NO₃)₂) at two electric conductivities (EC) of 2 and 4 dS m^?1 of irrigation water, and a distilled water control were evaluated on coriander plants (Coriandrum sativum L.). At EC?=?2, all salts increased plant yield (shoot fresh weight) than control. Most growth traits including plant height, shoot fresh and dry weight, leaf SPAD value and vitamin C, leaf K, Mg and P concentrations were increased by K₂SO₄?+?MgNO₃, and remained unchanged by KCl?+?NaCl?+?CaCl₂ treatment (except reduced plant height). Leaf’s zinc concentration reduced by either treatment. Even sodium chloride at EC?=?2 showed some beneficial effects on leaf chlorophyll index, root fresh weight, leaf’s calcium and phosphorus concentration; however, most traits remained unchanged than control. Treatment of plants with NaCl or KCl?+?NaCl?+?CaCl₂ at either EC increased the number of flowered shoots and leaf proline content than control. Most growth and quality traits including leaf minerals and vitamin C content were reduced by NaCl at EC?=?4; however, shoot fresh and dry weights remained unchanged than control. Plant root fresh weight increased by NaCl at EC?=?2 and decreased at EC?=?4 than control. At EC?=?4, shoot dry weight was increased and leaf Ca, P, Zn and Mn were decreased by KCl?+?NaCl?+?CaCl₂, whereas shoot dry weight, leaf SPAD value and vitamin C content, leaf Mg and P were increased and leaf Zn was decreased by K₂SO₄?+?MgNO₃ than control. The results indicate that in contrast to sodium chloride, the salinity effects of other salts can not be detrimental on coriander plant growth.     

Synthesis and anticoagulant activity of the quaternary ammonium chitosan sulfates

Quaternary ammonium chitosan sulfates with diverse degrees of substitution (DS) ascribed to sulfate groups between 0.52 and 1.55 were synthesized by reacting quaternary ammonium chitosan with an uncommon sulfating agent (N(SO₃Na)₃) that was prepared from sodium bisulfite (NaHSO₃) through reaction with sodium nitrite (NaNO₂) in the aqueous system homogeneous. The structures of the derivatives were characterized by FTIR, ¹H NMR and ¹³C NMR. The factors affecting DS of quaternary ammonium chitosan sulfates which included the molar ratio of NaNO₂ to quaternary ammonium chitosan, sulfated temperature, sulfated time and pH of sulfated reaction solution were investigated in detail. Its anticoagulation activity in vitro was determined by an activated partial thromboplastin time (APTT) assay, a thrombin time (TT) assay and a prothrombin time (PT) assay. Results of anticoagulation assays showed quaternary ammonium chitosan sulfates significantly prolonged APTT and TT, but not PT, and demonstrated that the introduction of sulfate groups into the quaternary ammonium chitosan structure improved its anticoagulant activity obviously. The study showed its anticoagulant properties strongly depended on its DS, concentration and molecular weight.     

Influence de differentes salinités (Sels de sodium et sels de chlorure) sur la germination deRaphanus sativus

Résumé La germination des semences de radis (Raphanus sativus) est étudiée en fonction de la salinité exercée, d'une part, par les sels de sodium (organique ou minéraux), et d'autre part, par des sels de chlorure (de K, Ca ou Na). Les sels minéraux de sodium (comme les sel de chlorure ou de nitrate) apparaissent moins toxiques à la germination de la plante, par rapport à un sel organique (barbital ou salicylate). Par comparison, un milieu contenant NaCl est plus sélectif à la germination qu'un milieu contenant CaCl₂ ou KCl (ce dernier étant le moins nocif). Dans tous les cas, les sels agissent plus du point de vue toxicité que du point de vue stimulation de germination: l'action toxique de l'anion d'accompagnement (pour les sels organiques ou minéraux de sodium) ou des cations (pour les sels de chlorure) est supérieure à l'effet de la pression osmotique.

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Germination of radish (Raphanus sativus) seeds is studied as a function of salinity caused by sodium (organic or mineral) and chloride salts (K, Ca or Na chloride). Mineral salts of sodium (chloride or nitrate for exemple) seem to be less toxic for germination than organic salts (barbital or salicylate). A NaCl medium is more toxic for germination than the CaCl₂ or KCl medium, this last being the last toxic of the salts tested. In all cases, salts have a more toxic than stimulatory effect on germination. The toxic action of the accompanying anion (for organic and mineral salts) or cation (for chloride salts) is greater than the osmotic pressure effect.

     

Further photophysical and photochemical characterization of flavins associated with single-shelled vesicles

Summary In order to investigate whether the loop diuretic sensitive, sodium-chloride cotransport system described previously in shark rectal gland is in fact a sodium-potassium chloride cotransport system, plasma membrane vesicles were isolated from rectal glands ofSqualus acanthias and sodium and rubidium uptake were measured by a rapid filtration technique. In addition, the binding of N-methylfurosemide to the membranes was investigated. Sodium uptake into the vesicles in the presence of a 170mm KCl gradient was initially about five-fold higher than in the presence of a 170mm KNO₃ gradient. In the presence of chloride, sodium uptake was inhibited 56% by 0.4mm bumetanide and 40% by 0.8mm N-methylfurosemide. When potassium chloride was replaced by choline chloride or lithium chloride, sodium uptake decreased to the values observed in the presence of potassium nitrate. Replacement of potassium chloride by rubidium chloride, however, did not change sodium uptake. Initial rubidium uptake into the membrane vesicles was about 2.5-fold higher in the presence of a 170mm NaCl gradient than in the presence of a 170mm NaNO₃ gradient. The effect of chloride was completely abolished by 0.4mm bumetanide. Replacement of the sodium chloride gradient by a lithium chloride gradient decreased rubidium uptake by about 40%; replacement by a choline chloride gradient reduced the uptake even further. Rubidium uptake was also strongly inhibited by potassium. Sodium chloride dependence and bumetanide inhibition of rubidium flux were also found in tracer exchange experiments in the absence of salt gradients. The isolated plasma membranes bound³[H]-N-methylfurosemide in a dose-dependent manner. In Scatchard plots, one saturable component could be detected with an apparentK _D of 3.5×10^–6 m and a number of sitesn of 104 pmol/mg protein. At 0.8 m, N-methylfurosemide binding decreased 51% when sodium-free or low-potassium media were used. The same decrease was observed when the chloride concentration was increased from 200 to 600mm or when 1mm bumetanide or furosemide were added to the incubation medium. These studies indicate that the sodium-chloride cotransport system described previously in the rectal gland is in fact a sodium-potassium chloride cotransport system. It is postulated that this transport system plays an essential role in the secondary active chloride secretion of the rectal gland.     

Ion Homeostasis in Chloroplasts under Salinity and Mineral Deficiency : I. Solute Concentrations in Leaves and Chloroplasts from Spinach Plants under NaCl or NaNO(3) Salinity

Spinach (Spinacia oleracea var “Yates”) plants in hydroponic culture were exposed to stepwise increased concentrations of NaCl or NaNO₃ up to a final concentration of 300 millimoles per liter, at constant Ca²⁺-concentration. Leaf cell sap and extracts from aqueously isolated spinach chloroplasts were analyzed for mineral cations, anions, amino acids, sugars, and quarternary ammonium compounds. Total osmolality of leaf sap and photosynthetic capacity of leaves were also measured. For comparison, leaf sap from salt-treated pea plants was also analyzed. Spinach plants under NaCl or NaNO₃ salinity took up large amounts of sodium (up to 400 millimoles per liter); nitrate as the accompanying anion was taken up less (up to 90 millimoles per liter) than chloride (up to 450 millimoles per liter). Under chloride salinity, nitrate content in leaves decreased drastically, but total amino acid concentrations remained constant. This response was much more pronounced (and occurred at lower salt concentrations) in leaves from the glycophyte (pea, Pisum sativum var “Kleine Rheinländerin”) than from moderately salt-tolerant spinach. In spinach, sodium chloride or nitrate taken up into leaves was largely sequestered in the vacuoles; both salts induced synthesis of quarternary ammonium compounds, which were accumulated mainly in chloroplasts (and cytosol). This prevented impairment of metabolism, as indicated by an unchanged photosynthetic capacity of leaves.     

Production of aflatoxin by Aspergillus parasiticus NRRL-2999 during growth in the presence of curing salts

Aspergillus parasiticus NRRL-2999 was inoculated into meat mixtures with curing salts and into yeast extractsucrose (YES) and sucrose-ammonium salts (SAS) broth with and without curing salts to determine if the presence of curing salts significantly affected growth and aflatoxin production by the mold. The effect of individual curing salts or curing salt mixtures on growth and toxin elaboration by the aspergillus was substrate dependent. When YES broth contained 100 ppm of NaNO₂, 2% NaCl, or 1 or 2% NaCl plus 200 ppm of NaNO₂ or 200 ppm of NaNO₃, growth and/or aflatoxin production was depressed. Biosynthesis of aflatoxin B₁ was enhanced by presence of 1 and 4% NaCl in YES broth. The SAS broth containing only NaCl or NaCl combined with nitrite or nitrate yielded less aflatoxin than did control broth or no aflatoxin at all. When compared to the control, an increase in growth and amount of aflatoxin occurred in SAS broth which contained 200 ppm of NaNO₃. Sausages containing 100 and 200 ppm NaNO₂ and no NaCl supported more mold growth and aflatoxin production than did control sausage with 3 % NaCl and 100 ppm of NaNO₂. Addition of 2 and 3 % NaCl and no nitrite to sausage resulted in less aflatoxin than in control sausage.     

Promotion of crown-gall tumor initiation on primary pinto bean leaves by certain inorganic salts

Crown-gall tumor initiation by Agrobacterium tumefaciens (SMITHand TOWN.) CONN, strain B6, on Phaseolus vulgaris L. var. "Pinto"was found to be sensitive to the addition of various salts tothe freshly inoculated primary leaves. Calcium, magnesium, zincand ammonium sulfates, cobalt and nickel chlorides and potassiumnitrate increased the number of tumors on inoculated leavesby 100 to 200 percent. Maximal promotions were obtained at concentrationsof 10^–7 to 10^–5 M with all of these salts exceptpotassium nitrate which was most active at 10^–2M. Sodium,potassium, calcium, magnesium and aluminum chlorides, and sodium,potassium and nickel sulfates had little or no effect on tumorinitiation. The combination of sodium sulfate with magnesiumchloride gave promotions comparable to those obtained with magnesiumsulfate, indicating that both the magnesium and sulfate ionswere necessary for the promotion obtained with this latter salt.Combining any two of the active salts at their optimum concentrationsfor promotion resulted in a reciprocal inhibition of the promotionobtained with either salt alone, suggesting these salts to beactive by different and potentially antagonistic mechanisms.The possible nature of these promotions is discussed, but theyremain too obscure to warrant a specific proposal for theirmode of action. ¹Present adress: Department of Botany, University of Khartoum,Khartoum, Sudan.     

Proton Transport in Plasma Membrane and Tonoplast Vesicles from Red Beet (Beta vulgaris L.) Storage Tissue : A Comparative Study of Ion Effects on DeltapH and DeltaPsi

The proton transport properties of plasma membrane and tonoplast vesicles isolated from red beet (Beta vulgaris L.) storage tissue were examined and compared. Membrane vesicles isolated with 250 millimolar KCl in the homogenization media and recovered at low density following sucrose density gradient centrifugation displayed characteristics of proton transport (nitrate inhibition, no inhibition by orthovanadate, pH optimum of 7.75, pyrophosphate-driven proton transport) which were consistent with a tonoplast origin. When the KCl in the homogenization medium was replaced by 250 millimolar KI, sealed membrane vesicles were recovered at higher densities in sucrose gradients and displayed properties (orthovanadate sensitivity, no inhibition by nitrate, pH optimum of 6.5) consistent with a plasma membrane origin. A comparison of anion effects (potassium salts) upon ΔpH and ΔΨ revealed a direct correspondence between the relative ability of anions to stimulate proton transport and reduce ΔΨ. For tonoplast vesicles, the relative order for this effect was KI > KBr ≥ KCl > KClO₃ > K₂SO₄ while for plasma membrane vesicles, a different order KI > KNO₃ ≥ KBr ≥ KClO₃ > KCl > K₂SO₄ was observed. Proton transport in plasma membrane and tonoplast vesicles was inhibited by fluoride; however, plasma membrane vesicles appeared to be more sensitive to this anion. In order to correlate anion effects in the two vesicle fractions with anion transport, the kinetics of anion stimulation of steady-state pH gradients established in the absence of monovalent ions was examined. Anions were added as potassium salts and the total potassium concentration (100 millimolar) was maintained through the addition of K⁺/Mes. For plasma membrane vesicles, chlorate and nitrate displayed saturation kinetics while chloride displayed stimulation of proton transport which followed a linear profile. For tonoplast vesicles, the kinetics of chloride stimulation of proton transport displayed a saturable component. The results of this study indicate differences in proton transport properties of these two vesicle types and provide information on conditions where proton transport in the two fractions can be optimized.     

Protection of Pyruvate,Pi Dikinase from Maize against Cold Lability by Compatible Solutes

Most C₄ species are chilling sensitive and certain enzymes like pyruvate,Pi dikinase of the C₄ pathway are also cold labile. The ability of cations and compatible solutes to protect maize (Zea mays) dikinase against cold lability was examined. The enzyme in desalted extracts at pH 8 from preilluminated leaves could be protected against cold lability (at 0°C) by the divalent cations Mn²⁺, Mg²⁺, and Ca²⁺. There was substantial protection by sulfate based salts but little protection by chloride based salts of potassium or ammonium (concentration 250 millimolar). The degree of protection against cold lability under limiting MgCl₂ (5 millimolar) was pH sensitive (maximum protection at pH 8), but independent of ionic strength (up to 250 millimolar by addition of KCl). In catalysis Mg²⁺ is required and Mn²⁺ could not substitute as a cofactor. Several compatible solutes reduced or prevented the cold inactivation of dikinase (in desalted extracts and the partially purified enzyme), including glycerol, proline, glycinebetaine and trimethylamine-N-oxide (TMAO). TMAO and Mg²⁺ had an additive effect in protecting dikinase against cold inactivation. TMAO could largely substitute for the divalent cation and addition of TMAO during cold treatment prevented further inactivation. Cold inactivation was partially reversed by incubation at room temperature; with addition of TMAO reversal was complete. The temperature dependence of inactivation at pH 8 and 3 millimolar MgCl₂ was evaluated by incubation at 2 to 17°C for 45 minutes, followed by assay at room temperature. At preincubation temperatures below 11°C there was a progressive inactivation which could be prevented by TMAO (450 millimolar). The results are discussed relative to possible effects of the solutes on the quaternary structure of this enzyme, which is known to dissociate at low temperatures.     

Importance of myo-inositol,calcium, and ammonium for the viability and division of tomato (Lycopersicon esculentum) protoplasts

Plants from four cultivars of Lycopersicon esculentum were grown under different conditions, in controlled environment chambers. Low light intensity, long photoperiod (16 h), 25° C/17°C temperature alternance (day/night) were found to be the most convenient conditions for obtaining viable protoplasts. The use of myo-inositol as an osmoticum in the digestion medium and the adjustment of the pH to 6.5, instead of the usual 5.8, for this medium increased the yield of viable protoplasts and enhanced their stability. Under these conditions neither pretreatment (dark and cold treatments), nor preplasmolysis of leaf tissues, were required before protoplast isolation. The concentrations of ammonium nitrate, calcium chloride, myo-inositol, and sucrose were found to be critical for the success of protoplast culture. A medium containing 5 mM ammonium nitrate, 40 mM calcium chloride, 10 mg l^-1 adenine sulfate, 0.5% myo-inositol and 6% sucrose gave sustained protoplast divisions. Under these conditions, plating efficiency ranged from 5% for the cultivar Lukulus to 15% for the cultivar Golden Sunrise.Abbreviations BA benzylaminopurine - CaCl₂ calcium chloride, 2,4,-D-2,4-dichlorophenoxyacetic acid - EDTA ethylene diamine tetraacetic acid - KCl potassium chloride - MES-2-N morpholino ethane sulfonic acid - MgCl₂ magnesium chloride - NH₄NO₃ ammonium nitrate - NAA naphthalene acetic acid, p-protoplasts     

Level nitric oxide (NO) and growth of roots of etiolated pea seedlings

Data regarding the interrelation of nitric oxide (NO) content in roots of 3-day-old etiolated pea seedlings and their growth under different concentrations of N-containing compounds were obtained. The concentration of exogenous compounds (sodium nitroprusside SNP, KNO₃, NaNO₂, L-arginine) rendering an inhibiting effect on the growth of roots were established, and the NO content in roots was determined at these concentration. It was shown that the inhibition of growth and highest NO content in the roots was determined with SNP (4 mM) and NaNO₂ (2 mM) during 24 h exposition of seedlings. This dependence was not established in combinations with KNO₃ (20 mM) and L-arginine (4 mM). We established that a NO scavenger, hemoglobin (4 μM), fully or partially removed the toxic effect of SNP, nitrate, and nitrite on growth. The effect of NO on the growth and the participation of N-containing compounds in generation of NO in roots of pea seedlings is discussed.     

Decrease in nitrate reductase activity in extracts of Trichoderma viride Incubated with chlorides.

Reduced nicotinamide adenine dinucleotide phosphate-dependent nitrate reductase activity in crude extracts of Trichoderma virde was significantly inhibited by physiological concentrations of ammonium chloride, sodium chloride, and potassium chloride, but not by ammonium or sodium sulfate. The chloride inhibition of nitrate reductase activity increased in a linear manner with chloride concentration.     

Studies on photophosphorylation II. Uncoupling of chloroplasts by anions at low temperatures and at acidic pH values

Photophosphorylation of spinach chloroplasts was uncoupled bypreincubation at 0°C in the presence of a neutral salt atpH 6.0 to 6.5 ("cold-anion uncoupling"). Preincubation at 20°Ccaused some depression in both photophosphorylation and theHill reaction, but the efficiency of photophosphorylation wasnot depressed much. Low pH values accelerated uncoupling. Theeffectiveness of anions tested as sodium salts in inducing uncouplingwas of the order: SCN->>NO₃^–>Cl^–>SO₄^2–There was little difference in effectiveness among monovalentcations; LiCl, NaCl, KCl, RbCl and CsCl. 10^–4M ATP orADP largely protected chloroplasts from cold-anion uncoupling.Addition of EDTA-extract or dicyclohexylcarbodiimide to uncoupledchloroplasts partially restored photophosphorylation. Theseobservations suggest that inactivation of chloroplast ATPaseis one cause of cold-anion uncoupling. At low light intensities, the time lag and the depression ofthe efficiency of photophosphorylation were more pronouncedin cold-anion uncoupled chloroplasts than in the control chloroplasts. (Received February 15, 1972; )     

Mutagenicity of five food additives in Ames/Salmonella/microsome test

The mutagenic activity of five food additives (K₂S₂O₅: potassium metabisulphite, KMB; K₂SO₄: potassium sulphate, KS; Na₂SO₃: sodium sulphite, SS; KNO₃: potassium nitrate, KN; NaNO₃: sodium nitrate, SN) were investigated using histidin auxotrophs TA98 and TA100 strains ofSalmonella typhimurium in the presence or absence of S9 mix. The test substance were investigated for their mutagenic effects at non toxic concentrations of 0.83, 1.66, 3.33 and 5.00 mg/plate with and without S9 mix. All the test substances were not mutagenic on TA98 and TA100 strains ofSalmonella typhimurium in the presence or absence of S9 mix except KS and SN. KS and SN showed a weak mutagenic effect on TA100 strain in the absence of S9 mix.     

Better conditions for mammalian in vitro splicing provided by acetate and glutamate as potassium counterions

We demonstrate here that replacing potassium chloride (KCl) with potassium acetate (KAc) or potassium glutamate (KGlu) routinely enhances the yield of RNA intermediates and products obtained from in vitro splicing reactions performed in HeLa cell nuclear extract. This effect was reproducibly observed with multiple splicing substrates. The enhanced yields are at least partially due to stabilization of splicing precursors and products in the KAc and KGlu reactions. This stabilization relative to KCl reactions was greatest with KGlu and was observed over an extended potassium concentration range. The RNA stability differences could not be attributed to heavy metal contamination of the KCl, since ultrapure preparations of this salt yielded similar results. After testing various methods for altering the salts, we found that substitution of KAc or KGlu for KCl and MgAc₂ for MgCl₂ in splicing reactions is the simplest and most effective. Since the conditions defined here more closely mimic in vivo ionic concentrations, they may permit the study of more weakly spliced substrates, as well as facilitate more detailed analyses of spliceosome structure and function.     

Nitrification inhibition of added nitrogenous fertilisers by potassium chloride in soil

Summary Inhibitory effect of potassium chloride on nitrification of ammonium sulfate and urea in acid, neutral and calcareous soils was observed in an incubation study. In acidic soil, NO ₃ ^– –N production in soil treated with urea was retarded by addition of KCl. NO ₃ ^– –N concentration was much less even in comparison to control where ammonium sulfate and KCl were added together which might be due to cumulative effect of Cl^– and SO ₄ ^–2 ions. In neutral and calcareous soils, nitrification inhibition was less conspicuous.     

Role of potassium and malate in nitrate uptake and translocation by wheat seedlings

Wheat seedlings (Triticum vulgare) treated with 1 mm KNO₃ or NaNO₃, in the presence of 0.2 mm CaSO₄, were compared during a 48-hour period with respect to nitrate uptake, translocation, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlings treated with KNO₃ absorbed and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO₃. Within seedlings of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO₃-treated seedlings had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO₃-treated seedlings. NADP-malic enzyme levels increased only slightly in leaves and roots of both KNO₃- and NaNO₃-treated seedlings. The effects of K⁺ and Na⁺ on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phosphoenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO₃ treatment, and increased only slightly in the KCl control.     

Chloride salinity reduces cadmium accumulation by the Mediterranean halophyte species Atriplex halimus L.

Soil salinity usually increases bioavailability of Cd on heavy metal polluted soils but its impact on Cd absorption and accumulation by plants remains largely unknown. Plants from the halophyte species Atriplex halimus were therefore exposed for 12 and 14 days to nutrient solution containing 50 μM CdCl₂ in the presence of NaCl, KCl or NaNO₃ 50 mM. Most Cd present in solution remained as Cd–EDTA and salinity had no impact on Cd speciation. Chloride salinity (NaCl and KCl) reduced Cd accumulation in shoots and roots while NaNO₃ increased Cd accumulation in leaves. More than 30% of accumulated Cd was found at the leaf surface and accumulated in trichomes but all tested salts decreased the proportion of excreted Cd. Cadmium induced a decrease in the leaf water content. External NaCl and KCl mitigated the deleterious impact of Cd by inducing osmotic adjustment while NaNO₃ and synthesis of protecting compounds such as soluble sugars and glycinebetaine. Free polyamines (putrescine, spermidine and spermine) increased in response to Cd, Cd + NaCl and Cd + KCl while only putrescine increased in response to Cd + NaNO₃. Proline exhibited maximal concentration in the leaves of Cd + NaCl and Cd + KCl-treated plants and was correlated with osmotic adjustment. Our results suggest that chloride salinity improved the resistance of A. halimus to Cd toxicity both by decreasing the absorption of heavy metal and by improving tissular tolerance through an increase in the synthesis of osmoprotective compounds.     

The effect of some ammonium salts on nitrate reductase level,onin vivo nitrate reduction and on nitrate content in excisedpisum sativum roots

The effect of some ammonium salts on nitrate reductase (NR) level, onin vivo nitrate reduction and on nitrate content was followed in the presence of nitrate in the medium, under changing experimental conditions, in excisedPisum sativum roots, and their effect was compared with that of KNO₃, Ca(NO₃)₂ and NaNO₃ at 15 mM NO₃ ^- concentration, i.e. at a concentration which considerably exceeded the level of saturation with nitrate with respect to nitrate reductase. The effect of ammonium salts on NR level is indirect and changes from a positive one to a strongly negative one which is dependent on the time of action of the salt, on the presence of other cations, on pH of the solution of the ammonium salt and on the nature of the anion of the ammonium salt. A positive effect on the enzyme level can be observed in the presence of other cations than NH₄ ⁺ at suitable concentrations of those ammonium salts, the solutions of which have their pH values in the acid region (i.e. NH₄H₂PO₄, (NH₄)₂SO₄ and NH₄NO₃). However their positive effect is independent of the presence of NH₄ ⁺ ions, and it is obviously the result of an increased concentration of H⁺ ions. A clear-cut negative effect on NR level can be observed after 24 h in one-salt NH₄NO₃ solution where NH₄ ⁺ is not balanced with other cations and thus certainly can adversely influence many metabolic processes, and in the solutions containing neutral (pH 6.2) and dibasic ammonium phosphates in which dissolved undissociated ammonia [(NH₃). (H₂O) which can also affect many metabolic processes incl. proteosynthesis] probably has a toxic influence. Thein vivo nitrate reduction is always depressed in excised pea roots in the presence of ammonium salts in the medium, regardless of the level of nitrate reductase. Under the described conditions, no relationship could be established between the enzyme level and the so-called metabolic NO₃ ^- pool (i.e. NO₂ ^- production under anaerobic conditions), nor between NR level and the total nitrate content in the roots. One-salt solutions of NaNO₃, Ca(NO₃)₂ and KNO₃ exert different effects on the level of nitrate reductase and on the content of NO₃ ^- in the roots, but the in vivo NO₃ ^- reduction shows the same trend as NR level in the roots influenced by these salts. Cl^- ions, supplied in NH₄C1, depress both NR level and NO₃ ^- content in the roots at higher concentrations, but they do not significantly affect the in vivo nitrate reduction in comparison with other ammonium salts. These results indicate that NR level,in vivo nitrate reduction, and nitrate uptake can be regulated in pea roots independently of each other.