Oscillations in photosynthesis are initiated and supported by imbalances in the supply of ATP and NADPH to the Calvin cycle

Oscillations in the rate of photosynthesis of sunflower (Helianthus annuus L.) leaves were induced by subjecting leaves, whose photosynthetic apparatus had been activated, to a sudden transition from darkness or low light to high-intensity illumination, or by transfering them in the light from air to an atmosphere containing saturating CO₂. It was found that at the first maximum, light-and CO₂-saturated photosynthesis can be much faster than steady-state photosynthesis. Both Q_A in the reaction center of PS II and P₇₀₀ in the reaction center of PS I of the chloroplast electron-transport chain were more oxidized during the maxima of photosynthesis than during the minima. Maxima of P₇₀₀ oxidation slightly preceded maxima in photosynthesis. During a transition from low to high irradiance, the assimilatory force F_A, which was calculated from ratios of dihydroxyacetone phosphate to phosphoglycerate under the assumption that the reactions catalyzed by NADP-dependent glyceraldehydephosphate dehydrogenase, phosphoglycerate kinase and triosephosphate isomerase are close to equilibrium, oscillated in parallel with photosynthesis. However, only one of its components, the calculated phosphorylation potential (ATP)/(ADP)(P_i), paralleled photosynthesis, whereas calculated NADPH/NADP ratios exhibited antiparallel behaviour. When photosynthetic oscillations were initiated by a transition from low to high CO₂, the assimilatory force F_A declined, was very low at the first minimum of photosynthesis and increased as photosynthesis rose to its second maximum. The observations indicate that the minima in photosynthesis are caused by lack of ATP. This leads to overreduction of the electron-transport chain which is indicated by the reduction of P₇₀₀. During photosynthetic oscillations the chloroplast thylakoid system is unable to adjust the supply of ATP and NADPH rapidly to demand at the stoichiometric relationship required by the carbonreduction cycle.Abbreviations PGA 3-phosphoglycerate - DHAP dihydroxyacetone phosphate - P₇₀₀ electron-donor pigment in the reaction enter of PS I - Q_A quinone acceptor in the reaction center of PS II This work received support from the Estonian Academy of Sciences, the Bavarian Ministry of Science and Art and the Sonderforschungsbereich 251 of the University of Würzburg. We are grateful for criticism by D.A. Walker, Robert Hill Institute, University of Sheffield, U.K. and by Mark Stitt, Institute of Botany, University of Heidelberg, FRG.     

Weak field influence on biomolecular changes

Model equations for the kinetics of the synthesis and decay of molecular aggregates are used to show the high sensitivity of equilibrium concentrations of high-molecular aggregates to external radiation. This phenomenon is used to explain the effects of low-intensity microwave fields on the functioning of biological systems. The experimental results on the influence of SHF-radiation on ferricyanide reduction by erythrocytes are interpreted in detail.     

Dissimilatory hexaheme c nitrite reductase of “Spirillum” strain 5175: purification and properties

When grown with nitrate as terminal electron acceptor both the soluble (periplasm, cytoplasm) and the membrane fraction of Spirillum strain 5175 exhibited high nitrite reductase activity. The nitrite reductase obtained from the soluble fraction was purified 76-fold to electrophoretical homogeneity. The enzyme reduced nitrite to ammonia with a specific activity of 723 mol NO _inf2 ^sup- × (mg protein × min)^-1. The molecular mass was 58±1 kDa by SDS-PAGE compared to 59±2 kDa determined by size exclusion chromatography under nondenaturing conditions. The enzyme (as isolated) contained 5.97±0.15 heme c molecules/M_r 58 kDa. The absorption spectrum was typical for c-type cytochrome with maxima at 280, 408, 532 and 610 nm (oxidized) and at 420, 523 and 553 nm (dithionite-reduced). The enzyme (as isolated) exhibited a complex set of high-spin and lowspin ferric heme resonances with g-values at 9.82, 3,85, 3.31, 2.95, 2.30 and 1.49 in agreement with data reported for electron paramagnetic resonance spectra of nitrite reductases from Desulfovibrio desulfuricans, Wolinella succinogenes and Escherichia coli.Abbreviations DNRA dissimilatory nitrate reduction to ammonia - EPR electron paramagnetic resonance - PAGE polyacrylamide gel electrophoresis - NaP_i sodium phosphate - SDS sodium dodecylsulfate     

Identification of an insertion sequence, IS1081, in Mycobacterium bovis

Abstract: An insertion sequence, IS1081, in the genome of Mycobacterium bovis has been identified and sequenced. It is 1324 bp long with 15 bp inverted repeat ends and contains a large ORF. There are six copies of IS1081 in the genome of M. bovis and the element is also present in Mycobacterium tuberculosis . IS1081 is not closely related to other DNA elements described in actinomycetes but its putative transposase bears some resemblance to that of IS256 from Staphylococcus aureus . IS1081 may be useful for genetic manipulations and for developing a diagnostic test for bovine tuberculosis based on the polymerase chain reaction.     

Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment

Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method.     

Interconversion of F430 derivatives of methanogenic bacteria

F₄₃₀ is the prosthetic group of the methylcoenzyme M reductase of methanogenic bacteria. The compound isolated from Methanosarcina barkeri appears to be identical to the one obtained from the only distinctly related Methanobacterium thermoautotrophicum. F₄₃₀ is thermolabile and in the presence of acetonitrile or C10 _in4 ^sup- two epimerization products are obtained upon heating; in the absence of these compounds F₄₃₀ is oxidized to 12, 13-didehydro-F₄₃₀. The latter is stereoselectively reduced under H₂ atmosphere to F₄₃₀ by cell-free extracts of M. barkeri or M. thermoautotrophicum. H₂ may be replaced by the reduced methanogenic electron carrier coenzyme F₄₂₀.Abbreviations CH₃S-CoM methylcoenzyme M, 2-methylthioethanesulfonic acid - HS-CoM coenzyme M, 2-mercaptoethanesulfonic acid - F₄₃₀ Ni(II) tetrahydro-(12, 13)-corphin with a uroporphinoid (III) ligand skeleton - 13-epi-F₄₃₀ and 12,13-di-epi-F₄₃₀ the 12, 13- and 12, 13-derivatives of F₄₃₀ - 12, 13-didehydro-F₄₃₀ F₄₃₀ oxidized at C-12 and C-13 - coenzyme F₄₂₀ 7,8-didemethyl-8-hydroxy-5-deazaflavin derivative - coenzyme F₄₂₀H₂ reduced coenzyme F₄₂₀ - MV⁺ methylviologen semiquinone - HPLC high-performance liquid chromatography     

Effects of oxygen partial pressure and combined nitrogen on N2-fixation (C2H2) associated withZea mays and other gramineous species

Summary The objectives of this investigation were to determine the effects of oxygen partial pressure (pO₂) and combined nitrogen (NH ₄ ⁺ ) on rates of acetylene reduction (AR) associated with roots of intact corn, sorghum, and pearl millet plants. Soil-grown plants were carefully removed from soil and incubated hydroponically with the root system enclosed in a plastic cylinder; the tops were left exposed to ambient conditions. Oxygen concentrations around the root systems were controlled by sparging the nutrient solution with known quantities of O₂ in N₂. Ammonium nitrogen was added to the nutrient solution following establishment of AR rates to determine its effect on rates of N₂-fixation (AR). Substantial AR rates (0.1–1.5 mol C₂H₄ g dry wt^–1 h^–1) were associated with roots exposed to 0–2% O₂ (v/v) (0.0–2.02 kPa) in N₂ following at 12–24 h period of exposure to the reduced oxygen tension. Root systems exposed to air failed to demonstrate AR while those exposed to 100% N₂ showed lower activity than those at reduced pO₂ values. Addition of NH ₄ ⁺ (10–20 g N ml^–1 of nutrient solution) reduced AR by 75–90% within 24 h after addition. Oxygen uptake by roots exposed to low pO₂ was substantially reduced.     

The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply

Abstract Growth-chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m^?3 (NO^?₃) in a balanced nutrient solution, the oldest leaves (eight-leaf stage) accumulated 2.5% NO^?₃-nitrogen (NO₃-N) in their lamina, and almost 5% NO₃-N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol^?3 m^?3 concentration of NO^?₃ in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO^?₃ uptake, NO^?₃ fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO^?₃ uptake by roots and mesophyll cells was greater in the light than in the dark. The NO^?₃ concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO^?₃ was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty-four per cent of the NO^?₃ influx was turned into organic nitrogen, with the remaining NO^?₃ accumulating in both the light and the dark.     

Isolation and characterization of an anaerobic benzoate-degrading spore-forming sulfate-reducing bacterium, Desulfotomaculum sapomandens sp. nov.

Abstract Spore-forming sulfate-reducing bacteria (SRB) were enriched selectively from various kinds of aerobic soils with fatty acids as the sole carbon and energy source. A Gram-negative motile rod-shaped bacterium, which produced gas vacuoles during sporulation was isolated. It degraded alcohols, aromatic and n-fatty acids (up to C₁₈) except for propionate, completely to CO₂. Sulfate, sulfite, thiosulfate or elemental sulfur served as electron acceptors. Because of its sensitivity to H₂S, the isolate never produced more than 8 mM dissolved sulfide at pH 7.0. G + C-content of the DNA was 48.0 mol %. The isolated strain Pato is described as a new species Desulfotomaculum sapomandens .     

光呼吸代谢物乙醇酸、乙醛酸和草酸对烟草叶片硝酸还原的影响

乙醇酸、乙醛酸和草酸能明显促进烟草(Nicotiana rustica)叶片在黑暗中的硝酸还原,光呼吸抑制剂a-羟基吡啶甲烷磺酸能消除前二者的促进作用而不能完全消除草酸的作用。草酸+NAD~+能显著促进离体的硝酸还原。烟叶提取液加入草酸和NAD~+后生成NADH和CO_2认为活体内由乙醛酸氧化生成的草酸是经脱氢生成NADH供硝酸还原之用。未能证明在烟叶内存在乙醇酸脱氨酶,因此排除由乙醇酸直接脱氢以还原硝酸的可能。