Uptake and efflux of succinic acid by uninduced mycelium of Claviceps purpurea.

Claviceps purpurea PRL 1980 grew on partially dissociated succinic acid (pH 4) but not on fully dissociated succinic acid (pH 7.2). Myeclium suspended in 42 mM solution of partially ionized succinic acid (pH 4; 60.1% nonionized, 39% monoanion, and 0.9% dianion, K+ salt) over a period of 25 min accumulated more succinic acid carbon than mycelium suspended in highly ionized solution (pH 6.8; 0.01% nonionized, 4.8% monoanion, and 95% dianion). The greater accumulation from partially ionized solution was not attributable solely to metabolism of succinic acid nor to the lower external concentration of potassium ion. Rate of uptake by sodium azide and iodoacetate-treated mycelium was proportional to external concentration at least up to 200 mumol/ml. External potassium or sodium ion was not required for uptake by inhibited or uninhibited mycelium and external sodium ion and glucose did not allow concentration of succinic acid. The internal concentrations of succinic acid carbon expressed as succinic acid in cell water were about the same as the external concentrations. Uptake was not appreciably affected by extent of ionization of external succinic acid but accumulation was markedly affected. A plot of accumulated succinic acid carbon against external pH produced a bimodal curve with the two maxima corresponding to the maximal concentrations of nonionized and monoanion succinic acid. The bimodal curve probably results from overlapping of two separate curves; the nonionized form accumulating efficiently because of one interaction with the cell and the monoanion form accumulating efficiently because of another interaction. Uptake from concentrated solution is by diffusion and efflux is rapid but not complete. Efflux is not retarded by presence of phosphate in the external solution.     

pH dependence of adenosine 5'-triphosphate synthesis and hydrolysis catalyzed by reconstituted chloroplast coupling factor

The purified ATP-synthesizing complex from chloroplasts has been reconstituted into phospholipid vesicles with bacteriorhodopsin by use of octyl glucoside. Phosphorylation rates up to 90 mmol of ATP (mg of protein)-1 min-1 have been achieved. The dependence of the steady-state kinetic parameters on external and internal pH for both synthesis and hydrolysis was determined. The Michaelis constants are independent of the magnitude of the pH gradient at external pH values of 6.6 and 8.0. The dependence of the maximum velocity for ATP synthesis on the external pH is bell shaped at a constant pH gradient with a maximum at about pH 6.7. The variation of the maximum velocity with external pH is not dependent on the magnitude of the pH gradient. At external pH values of 6.6 and 8.0, the maximum velocity for ATP synthesis varies with approximately the 2.3 power of the internal hydrogen ion concentration. The maximum velocity for ATP hydrolysis also is dependent on the external pH, with a maximum at about pH 8.4; however, most of the ATPase activity is not coupled to the proton flux. Both Mg2+ and Mn2+ are good cofactors for ATP synthesis and hydrolysis whereas Ca2+ is completely ineffective for synthesis and only about 10% as effective as Mg2+ and Mn2+ for hydrolysis. The results obtained suggest that ATP synthesis or hydrolysis may be coupled to proton pumping indirectly, as, for example, by conformational changes.     

H+/ATP ratio of proton transport-coupled ATP synthesis and hydrolysis catalysed by CF0F1-liposomes

The H(+)/ATP ratio and the standard Gibbs free energy of ATP synthesis were determined with a new method using a chemiosmotic model system. The purified H(+)-translocating ATP synthase from chloroplasts was reconstituted into phosphatidylcholine/phosphatidic acid liposomes. During reconstitution, the internal phase was equilibrated with the reconstitution medium, and thereby the pH of the internal liposomal phase, pH(in), could be measured with a conventional glass electrode. The rates of ATP synthesis and hydrolysis were measured with the luciferin/luciferase assay after an acid-base transition at different [ATP]/([ADP][P(i)]) ratios as a function of deltapH, analysing the range from the ATP synthesis to the ATP hydrolysis direction and the deltapH at equilibrium, deltapH (eq) (zero net rate), was determined. The analysis of the [ATP]/([ADP][P(i)]) ratio as a function of deltapH (eq) and of the transmembrane electrochemical potential difference, delta micro approximately (H)(+) (eq), resulted in H(+)/ATP ratios of 3.9 +/- 0.2 at pH 8.45 and 4.0 +/- 0.3 at pH 8.05. The standard Gibbs free energies of ATP synthesis were determined to be 37 +/- 2 kJ/mol at pH 8.45 and 36 +/- 3 kJ/mol at pH 8.05.     

Control Mechanisms at the Level of FDP-Aldolases in Algae

Abstract

The FDP-aldolase I from Euglena gracilis is a four-chain enzyme, as shown by the amino acid analysis of the C and N terminals. The protein is dissociated by acid pH to a monomer. The reassociation-dissociation process goes through a dimer stage. The enzyme, inhibited either by mercurials or by ATP, is dissociated to a dimer. This process is readly reversible either by mercaptoethanol and by AMP.     

Quantitation of methylmalonic acid and other dicarboxylic acids in normal serum and urine using capillary gas chromatography-mass spectrometry

Methylmalonic acid, succinic acid, and other dicarboxylic acids have been extracted and partially purified from serum and urine using ether extraction and high-performance liquid chromatography. The t-butyldimethylsilyl derivatives were prepared and analyzed using capillary gas chromatography-mass spectrometry with selected ion monitoring. The addition of [methyl-2H3]methylmalonic acid and [1,4-13C2]succinic acid to the starting samples made it possible to quantitate these two dicarboxylic acids. Normal ranges for methylmalonic acid and succinic acid were determined in human and rat serum and in human urine. The utilization of other internal standards would make it possible to quantitate malonic, dimethylmalonic, ethylmalonic, methylsuccinic, glutaric, and other dicarboxylic acids.     

Adaptive evolution improves acid tolerance and succinic acid production in Actinobacillus succinogenes

Fermentation at low pH is an efficient way to improve the competitiveness of biological succinic acid-producing process. Actinobacillus succinogenes shows good performance of succinic acid production under anaerobic conditions, but its succinic acid production capability at the low-pH is inefficient due to the poor acid resistance. Herein, a mutant A. succinogenes BC-4 with improved cell growth and succinic acid production under weak acid conditions was obtained by adaptive evolution. The specific growth rate and succinic acid production of BC-4 reached 0.13 g/L/h and 20.77 g/L, which were increased by 3.25- and 2.95- fold, respectively compared with the parent strain under anaerobic condition at pH 5.8. The activities of specific enzymes with ATP generation were significantly enhanced under weak acidic conditions, resulting in 1.28-fold increase in the maximum ATP level. Membrane fatty acid composition analysis demonstrated that the ratio of saturated to unsaturated fatty acids was decreased from 1.62 to 1.44 in mutant BC-4, leading to improved intracellular pH homeostasis. Furthermore, the change from long-chain to median-chain fatty acid might lower the permeability of H⁺ into cytoplasm for survival under acid stress. These results indicated that A. succinogenes BC-4 is a promising candidate for succinic acid production under weak acid condition.     

Organic Acid specificity for Acid-induced ATP synthesis by isolated chloroplasts

A study has been made of the structural requirements for organic acids that increase the yield of ATP formed by spinach chloroplasts in the dark due to an acid-base transition. Dicarboxylic acids of 4 and 5 carbon atoms with 1 pKa in the range of 4.2 to 4.4 and the second at 5.3 to 5.5 are most effective. A fairly good correlation was found between the fraction of the acid completely undissociated at the test pH and the final yield. Other considerations are also important, however, since introducing hydroxyl groups or excessive chain length decreased yields in spite of pKa considerations. Aromatic acids, except for the dicarboxylic phthalic acids, were inhibitory. The diversity of organic acids having some effect makes it unlikely that they serve as substrate for a chloroplast enzyme system.     

Conformational changes in coupling factor 1 may control the rate of electron flow in spinach chloroplasts.

The relationship between the rate of electron flow, internal H⁺ concentration and the magnitude of the H⁺ concentration gradient (ΔpH) in chloroplasts illuminated at various light intensities has been examined. At an external pH of 7.0, the internal H⁺ concentration is a linear function of the rate of electron flow except at saturating light intensity. In contrast, at pH 8.1, this relationship between electron flow and internal H⁺ concentration holds only at values of ΔpH below about 2.8 – 2.9 units. At higher ΔpH values, the rate of electron flow increases much more dramatically than the internal H⁺ concentration. ATP (0.1 mM) prevents this increase. It is suggested that at pH 8.1 but not at pH 7.0, the conformation of coupling factor 1 is altered at high ΔpH values. Its altered conformation may result in an increased efflux of H⁺ from the chloroplasts. This notion is supported by the effects of ATP on electron flow and ΔpH as well as the effect of external pH and light intensity on the reactivity of coupling factor 1 to N-ethylmaleimide.     

Introduction of a carboxyl group in the loop of the F0 c-subunit affects the H+/ATP coupling ratio of the ATP synthase from Synechocystis 6803

The proton translocation stoichiometry (H⁺/ATP ratio) was investigated in membrane vesicles from a Synechocystis 6803 mutant in which the serine at position 37 in the hydrophilic loop of the c-subunit from the wild type was replaced by a negatively charged glutamic acid residue (strain plc37). At this position the c-subunit of chloroplasts and the cyanobacterium Synechococcus 6716 already contains glutamic acid. H⁺/ATP ratios were determined with active ATP synthase in thermodynamic equilibrium between phosphate potential (G _p ) and the proton gradient ( _H ⁺) induced by acid–base transition. The mutant displayed a significantly higher H⁺/ATP ratio than the control strain (wild type with kanamycin resistance) at pH 8 (4.3 vs. 3.3); the higher ratio also being observed in chloroplasts and Synechococcus 6716. Furthermore, the pH dependence of the H⁺/ATP of strain plc37 resembles that of Synechococcus 6716. When the pH was increased from 7.6 to 8.4, the H⁺/ATP of the mutant increased from 4.2 to 4.6 whereas in the control strain the ratio decreased from 3.8 to 2.8. Differences in H⁺/ATP between the mutant and the control strain were confirmed by measuring the light-induced phosphorylation efficiency (P/2e), which changed as expected, i.e., the P/2e ratio in the mutant was significantly less than that in the wild type. The need for more H⁺ ions used per ATP in the mutant was also reflected by the significantly lower growth rate of the mutant strain. The results are discussed against the background of the present structural and functional models of proton translocation coupled to catalytic activity of the ATP synthase.     

Influence of adenosine phosphates and magnesium on photosynthesis in chloroplasts from peas, sedum, and spinach

¹⁴CO₂ photoassimilation in the presence of MgATP, MgADP, and MgAMP was investigated using intact chloroplasts from Sedum praealtum, a Crassulacean acid metabolism plant, and two C₃ plants: spinach and peas. Inasmuch as free ATP, ADP, AMP, and uncomplexed Mg²⁺ were present in the assays, their influence upon CO₂ assimilation was also examined. Free Mg²⁺ was inhibitory with all chloroplasts, as were ADP and AMP in chloroplasts from Sedum and peas. With Sedum chloroplasts in the presence of ADP, the time course of assimilation was linear. However, with pea chloroplasts, ADP inhibition became progressively more severe, resulting in a curved time course. ATP stimulated assimilation only in pea chloroplasts. MgATP and MgADP stimulated assimilation in all chloroplasts. ADP inhibition of CO₂ assimilation was maximal at optimum orthophosphate concentrations in Sedum chloroplasts, while MgATP stimulation was maximal at optimum or below optimum concentrations of orthophosphate. MgATP stimulation in peas and Sedum and ADP inhibition in Sedum were not sensitive to the addition of glycerate 3-phosphate (PGA).

PGA-supported O₂ evolution by pea chloroplasts was not inhibited immediately by ADP; the rate of O₂ evolution slowed as time passed, corresponding to the effect of ADP on CO₂ assimilation, and indicating that glycerate 3-phosphate kinase was a site of inhibition. Likewise, upon the addition of AMP, inhibition of PGA-dependent O₂ evolution became more severe with time. This did not mirror CO₂ assimilation, which was inhibited immediately by AMP. In Sedum chloroplasts, PGA-dependent O₂ evolution was not inhibited by ADP and AMP. In chloroplasts from peas and Sedum, the magnitude of MgADP and MgATP stimulation of PGA-dependent O₂ evolution was not much larger than that given by ATP, and it was much smaller than MgATP stimulation of CO₂ assimilation. Analysis of stromal metabolite levels by anion exchange chromatography indicated that ribulose 1,5-bisphosphate carboxylase was inhibited by ADP and stimulated by MgADP in Sedum chloroplasts.

The appearance of label in the medium was measured when [U-¹⁴C] ADP-loaded Sedum chloroplasts were challenged with ATP, ADP, or AMP and their Mg²⁺ complexes. The rate of back exchange was stimulated by the presence of Mg²⁺. This suggests that ATP, ADP, and AMP penetrate the chloroplast slower than their Mg²⁺ complexes. A portion of the CO₂ assimilation and O₂ evolution data could be explained by differential penetration rates, and other proposals were made to explain the remainder of the observations.

     

Role of the Interchangeable Cations on the Sorption of Fumaric and Succinic Acids on Montmorillonite and its Relevance in Prebiotic Chemistry

It has been proposed that clays could have served as key factors in promoting the increase in complexity of organic matter in primitive terrestrial and extraterrestrial environments. The aim of this work is to study the adsorption–desorption of two dicarboxylic acids, fumaric and succinic acids, onto clay minerals (sodium and iron montmorillonite). These two acids may have played a role in prebiotic chemistry, and in extant biochemistry, they constitute an important redox couple (e.g. in Krebs cycle) in extant biochemistry. Smectite clays might have played a key role in the origins of life. The effect of pH on sorption has been tested; the analysis was performed by UV–vis and FTIR-ATR spectroscopy, X-ray diffraction and X-ray fluorescence. The results show that chemisorption is the main responsible of the adsorption processes among the dicarboxylic acids and clays. The role of the ion, present in the clay, is fundamental in the adsorption processes of dicarboxylic acids. These ions (sodium and iron) were selected due to their relevance on the geochemical environments that possibly existed into the primitive Earth. Different mechanisms are proposed to explain the sorption of dicarboxylic acids in the clay. In this work, we propose the formation of complexes among metal cations in the clays and dicarboxylic acids. The organic complexes were probably formed in the prebiotic environments enabling chemical processes, prior to the appearance of life. Thus, the data presented here are relevant to the origin of life studies.

     

Mechanisms of Fatty Acid Toxicity for Yeast.

Neal, A. L. (Rutgers, The State University, New Brunswick, N.J.), Joan O. Weinstock, and J. Oliver Lampen. Mechanisms of fatty acid toxicity for yeast. J. Bacteriol. 90:126-131. 1965.-The internal pH of stationary- and log-phase yeast cells dropped quite rapidly when the cells were exposed to acetate buffers at pH 4 and 3, whereas no, or much less, acidification occurred with pyruvate or phosphate. Although inhibition of respiration and glycolysis was almost instantaneous when the cells were exposed to 0.2 m acetate at pH 4, the effect was not permanent and could be reversed by washing them with water or phosphate buffer. Irreversible inhibition did occur, however, at 0.5 m acetate under the same conditions; there was a marked decrease in several glycolytic enzyme systems, which undoubtedly contributed to the irreversible nature of the inhibition. In cell-free homogenates, various low-molecular-weight monocarboxylic acids exhibited about the same inhibitory effect on glycolysis; structural differences such as branching or unsaturation did not cause a marked change in their inhibitory effect. Also, glycolysis was much more sensitive to dicarboxylic acids such as succinate and phthalate than to acetate; phthalate was more inhibitory than succinate. This is in contrast with the noninhibitory nature of succinate and phthalate to whole cells, even at pH 4. Pyruvic acid decarboxylation was inhibited by phthalate but not by succinate. The greater toxic effect of phthalic acid may be due to the fixed steric configuration of its carboxyl groups, as compared with those of succinic acid.     

The relation of the alteration of photosystem. II. Activity to the inhibition of energy transfer and the proton pump in tris-washed chloroplasts

Washing of spinach chloroplasts with high concentrations of Tris³ induces pH-dependent changes in chloroplast reactions. At high pH (8.4) Tris washing causes the inhibition of Photosystem 2 activity which can be prevented by the maintenance of reducing conditions during washing. Washing at low pH (7.2) causes an enhancement of oxygen evolution and increased rate of ferricyanide photoreduction which is not influenced by the presence of reducing conditions. The increased rate of electron flow is accompanied by the inhibition of light mediated phosphorylating activity, acid-induced ATP synthesis, light-induced proton uptake and light triggered Mg²⁺ ATPase activity. Tris treatment at low pH also causes a sensitization of Photosystem 2 activity such that oxygen evolution is inhibited by low concentrations of tris at high pH. This inhibition of the stimulated electron flow is not accompanied by a reconstitution of the photophosphorylation activity. A detailed analysis of the effect of tris treatment on Photosystem II activity and membrane dependent energy conversion shows that the treatment of chloroplasts causes an inhibition of the energy conversion process which is independent of the effect on oxygen evolution. Determination of the presence of coupling factor (as determined by ATPase activity) and membrane osmotic properties reveal normal levels of enzyme activity and osmotic response in treated chloroplasts. The inhibition of the energy conversion process is accompanied by reduced capacity to maintain a proton gradient. Kinetic analysis of the proton uptake reaction reveals that Tris treatment renders the grana membranes more permeable to protons.     

The rate of ATP synthesis as a function of ΔpH in normal and dithiothreitol-modified chloroplasts

The rate of ATP synthesis catalyzed by normal and by dithiothreitol-modified ATPases is investigated as a function of ΔpH in spinach chloroplasts at constant pH_out. The transmembrane ΔpH was generated by an acid-base transition and the reaction time was limited to 150 ms by using a rapidly mixing quenched-flow apparatus. The result was that the functional dependence of the rate on ΔpH is shifted to lower ΔpH values and that the shape of this curve is altered after dithiothreitol modification. The maximal rate (400 ATP / CF₁ per s) is the same under both conditions.     

Equilibration of the ATPase reaction of chloroplasts at transition from strong light to weak light

Broken chloroplasts activated by preillumination in the presence of dithiothreitol were supplied with phosphate and with a limited concentration of ADP. On re-illumination, ATP was formed until a steady state was attained. If after reaching the steady state light intensity was reduced to 20–50 W · m⁻², net ATP hydrolysis took place, but after some time in weak light the level of ATP re-increased. Similarly, a drop of transmembrane ΔpH followed by a slow recovery was observed. Further data indicate that the reversible changes of ATP level and ΔpH are the result of partial uncoupling induced by ATP during the preceding strong light period and of restoration of coupling within a few minutes in weak light. Since similar changes of endogenous ATP level were found when intact chloroplasts were subjected to a strong-light/weak-light transition, it is proposed that ATP-induced partial uncoupling may play a role in regulation of photosynthetic energy conservation as a means to dissipate abundant transmembrane electrochemical energy and to permit flexibility of the stoichiometry of ATP-to-NADPH production.     

Activation of carboxyl group with cyanate: peptide bond formation from dicarboxylic acids

The reaction of cyanate with C-terminal carboxyl groups of peptides in aqueous solution was considered as a potential pathway for the abiotic formation of peptide bonds under the condition of the primitive Earth. The catalytic effect of dicarboxylic acids on cyanate hydrolysis was definitely attributed to intramolecular nucleophilic catalysis by the observation of the ¹H-NMR signal of succinic anhydride when reacting succinic acid with KOCN in aqueous solution (pH 2.2–5.5). The formation of amide bonds was noticed when adding amino acids or amino acid derivatives into the solution. The reaction of N-acyl aspartic acid derivatives was observed to proceed similarly and the scope of the cyanate-promoted reaction was analyzed from the standpoint of prebiotic peptide formation. The role of cyanate in activating peptide C-terminus constitutes a proof of principle that intramolecular reactions of adducts of peptides C-terminal carboxyl groups with activating agents represent a pathway for peptide activation in aqueous solution, the relevance of which is discussed in connexion with the issue of the emergence of homochirality.     

Control of electron flow in intact chloroplasts by the intrathylakoid pH,not by the phosphorylation potential

In the presence of nitrite or oxaloacetate, intact chloroplasts evolved oxygen at a significant rate for the initial 1 to 2 min of illumination. Subsequently, oxygen evolution was suppressed progressively. The suppressed oxygen evolution was stimulated strikingly by NH₄Cl. The results indicate that coupled electron flow in intact chloroplasts is controlled in the light, and the control is released by NH₄Cl. However, at low concentrations, NH₄Cl was not an effective uncoupler of photophosphorylation in intact chloroplasts. Intrachloroplast ATP levels and ATP/ADP ratios were not significantly influenced by NH₄Cl. In contrast, the quenching of 9-aminoacridine fluorescence, which can be used to indicate the intrathylakoid pH in intact chloroplasts, was reduced drastically even by low concentrations of NH₄Cl. This suggests that the chloroplast phosphorylation potential is not in equilibrium with the proton gradient. In coupled chloroplasts, the intrathylakoid pH was lower in the light with nitrite than with oxaloacetate as electron acceptor. Electron flow was also more effectively controlled in chloroplasts illuminated with nitrite than with oxaloacetate. It is concluded that the intrathylakoid pH, not the phosphorylation potential, is a factor in the control of the rate of electron flow in intact chloroplasts.Abbreviations CCCP carbonylcyanide-m-chlorophenylhydrazone - OAA oxalo-acetate - MES 2-(N-morpholino)-ethanesulfonic acid - HEPES N-2-hyroxyethylpiperazine-N-2-ethanesulfonic acid Postal address     

Photosynthesis by isolated protoplasts, protoplast extracts, and chloroplasts of wheat: influence of orthophosphate, pyrophosphate, and adenylates

Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat (Triticum aestivum) have rates of photosynthesis as measured by light-dependent O₂ evolution of about 100 to 150 micromoles of O₂ per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO₃ with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O₂ per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset.

Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5′-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5′-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP.

Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO₃ and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed.

     

La Cellula: Aspetti Morfologici e Metabolici Dei Suoi Organuli

Abstract

The cell: morphologic and metabolic aspects of its organelles. — Some aspects of the mechanism of the chloroplasts movement induced by light, it has been studied in «Elodea canadensis» leaves. Red, yellow and blue light induce the movement of the chloroplasts. Green light does not promote the movement. 5.10—⁵M CMU completely inhibits cyclosis. Photosynthesis is required for cyclosis. ATP alone, does not Substitute photosynthesis, however in the presence of green light, 5.10—³M ATP, pH 6.5, promotes cyclosis movement. It has been concluded that light has dual role in promoting the movement in «Elodea» leaves: first, inducing photosynthesis and consequently the ATP production; second, light is necessary to start the movement exciting a photo-receptor, visualized like a System Controlling the induction-repression of enzymes. It has been postulated that ATP produced by illuminated chloroplasts, saturated a «SSS» system, connected with another System, «SAV», lowering the plasma viscosity; ATP in this action is not necessarily used as energetic Compound. Successively, by means an unknow photoreceptor, the mechano-enzyme-system, «SEM», promotes cyclosis utilizing ATP as energic source. The movement stop when ATP is exausted or immediately, in the presence of ATP, when the photoreceptor is not working, like happens in the dark.     

Exudation of low molecular weight organic acids by germinating seeds of two edaphic ecotypes of Silene nutans L.

Two parapatric ecotypes of Silene nutans, exhibiting distinct allozyme patterns, morphology and autecology were investigated for differences in exudation of low molecular weight organic acids from germinating seeds, and for differences in seed phosphorus content. The calcicolous ecotype is restricted to calcareous soils, and the silicicolous one predominantly occurs on acid soils, and sometimes, although less frequently, on neutral to alkaline soils. No clear difference was found between ecotypes. However, within the silicicolous ecotype seed samples showed marked differences in exudation pattern and seed phosphorus content depending on origin along the soil acidity gradient. Seeds of low-pH origin exuded more dicarboxylic acids (malic + succinic acid, oxalic acid) and had a lower phosphorus content than seeds of high pH origin. The exudation of dicarboxylic acids from seeds of low pH origin is probably an adaptation to adverse conditions (aluminium toxicity) on acid soils. The pattern is similar to that found among different cultivars of wheat. It is contrasted to the pattern found on comparison of a suite of calcifugous and calcicolous species, where exudation of di- and tricarboxylic acids is associated with solubilisation of recalcitrantly bound phosphorus and iron in calcareous soils.