Decrease of polypeptides in the PS I antenna complex with increasing growth irradiance in the red alga Porphyridium cruentum

Thylakoids isolated from cells of the red alga Porphyridium cruentum exhibit an increased PS I activity on a chlorophyll basis with increasing growth irradiance, even though the stoichiometry of Photosystems I and II in such cells shows little change (Cunningham et al. (1989) Plant Physiol 91: 1179–1187). PS I activity was 26% greater in thylakoids of cells acclimated at 280 mol photons · m^–2 · s^–1 (VHL) than in cells acclimated at 10 mol photons · m^–2 · s^–1 (LL), indicating a change in the light absorbance capacity of PS I. Upon isolating PS I holocomplexes from VHL cells it was found that they contained 132±9 Chl/P700 while those obtained from LL cells had 165±4 Chl/P700. Examination of the polypeptide composition of PS I holocomplexes on SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 and 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptides belong to a novel LHC I complex, recently discovered in red algae (Wolfe et al. (1994a) Nature 367: 566–568), that lacks Chl b and includes at least six different polypeptides. We suggest that the decrease in PS I Chl antenna size observed with increasing irradiance is attributable to changes occurring in the LHC I-antenna complex. Evidence for a Chl-binding antenna complex associated with PS II core complexes is lacking at this point. LHC II-type polypeptides were not observed in functionally active PS II preparations (Wolfe et al. (1994b) Biochimica Biophysica Acta 1188: 357–366), nor did we detect polypeptides that showed immunocross-reactivity with LHC II specific antisera (made to Chlamydomonas and Euglena LHC II).Abbreviations Bis-Tris bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane - DCPIP 2,6-dichlorophenol indophenol - -dm dodecyl--d-maltoside - HL high light of 150 mol photons · m^–2 · s^–1 - LGB lower green band - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - LL low light of 10 mol photons · m^–2 · s^–1 - ML medium light of 50 mol photons · m^–2 · s^–1 - MES 2-(N-morpholino) ethanesulfonic acid - P700 reaction center of PS I - PFD photon flux density - Trizma tris(hydroxymethyl)aminomethane - UGB upper green band - VHL very high light of 280 mol photons · m^–2 · s^–1     

Structural characterization and reactivity of gamma-octamolybdate functionalized by proline

The reaction of molybdate and dl-proline at pH 3.4 results in the formation of a Na₄[Mo₈O₂₆(proO)₂] · 22H₂O complex (pro = proline) in which two proline ligands are attached to molybdenum(VI) ions via monodentate coordination of the carboxylate groups. The structure of the complex was determined by single crystal X-ray diffraction and by combination of ¹H, ¹³C and ⁹⁵Mo NMR spectroscopy techniques in solution. The structure of the complex is strongly dependant on the pH. At native pH 3.4 the octamolybdate-type structure seems to be present in solution, but the increase of pH to 5.8 resulted in a rearrangement of the structure to a heptamolybdate-type structure. At physiological pH, the polyoxometalate framework was completely dissociated into the monomeric unit. The reactivity of the Na₄[Mo₈O₂₆(proO)₂] · 22H₂O towards the hydrolysis of ATP was tested at different pH values. While in solution at pH 3.4 the hydrolysis proceeded to yield AMP (adenosine monophosphate) and ADP (adenosine diphosphate) in nearly equal amounts, reaction mixture at pH 5.8 gave ADP as the only product of hydrolysis after 24 h of reaction. At neutral pH, the hydrolysis of ATP was slower, but it proceeded to yield 75% of ADP after 48 h of reaction.     

Enhanced production of scopolin bySolanum aviculare cells immobilised within Ca-alginate gel beads

Summary Different matrices, obtained by varying calcium (0.1 to 1.5M) and alginate (1 to 1.5%) concentrations, were used to study the influence of immobilisation parameters on the behaviour ofS. aviculare. A significant modulation of cell growth, cell release, and scopolin production and excretion has been observed. Physiological and morphological characteristics ofSolanum aviculare cells immobilised within Ca-alginate beads were notably different from those of suspended cells. ImmobilisedS. aviculare have accumulated scopolin (up to 120 g·g^–1 FWB) within beads and excreted it into the culture medium (up to 8 g·g^–1 FWB). Contrary to suspended cells which have accumulated only traces of this metabolite within intracellular compartments (1 g·g^–1 FWB), no scopolin has been found into the culture medium.Abbreviations ANA -Naphthaleneacetic acid - HPLC high performance liquid chromatography - FWB fresh weight biomass - LS medium Linsmaier and Skoog medium - MS mass spectroscopy - NMR nuclear magnetic resonance - r² coefficient of determination - s standard deviation     

ATP production from polyphosphate in Acinetobacter strain 210A

In cell-free extracts of Acinetobacter strain 210A polyphosphate: AMP phosphotransferase and adenylate kinase activity was measured. Polyphosphate glucokinase and polyphosphate dependent NAD kinase were not detected. The specific activity of polyphosphate: AMP phosphotransferase was found to be 43 nmol · min^-1 · mg^-1 protein in presence of 1 mmol · l^-1 AMP. The adenylate kinase reaction had an equilibrium constant ([ATP] [AMP] [ADP]^-2) of 0.7, an activity of 54 nmol · min^-1 · mg^-1 protein, and was almost completely inhibited by 0.3 mM P¹,P⁵-di(adenosine-5)-pentaphosphate. ATP was formed through the combined action of polyphosphate: AMP phosphotransferase and adenylate kinase in cell-free extracts from bacterial polyphosphate and from chemically prepared polyphosphate (Graham's salt). A spectrophotometric method for the continuous monitoring of polyphosphate: AMP phosphotransferase is also presented.Abbreviations Ap₅A P¹,P⁵-di(adenosine-5)-pentaphosphate - G6P-DH D-glucose-6-phosphate dehydrogenase - HK hexokinase - AEC adenylate energy charge - U units (converting 1 mol · min^-1)     

Acetate oxidation to CO2 via a citric acid cycle involving an ATP-citrate lyase: a mechanism for the synthesis of ATP via substrate level phosphorylation in Desulfobacter postgatei growing on acetate and sulfate

Desulfobacter postgatei is an acetate-oxidizing, sulfate-reducing bacterium that metabolizes acetate via the citric acid cycle. The organism has been reported to contain a si-citrate synthase (EC 4.1.3.7) which is activated by AMP and inorganic phosphate. It is show now, that the enzyme mediating citrate formation is an ATP-citrate lyase (EC 4.1.3.8) rather than a citrate synthase. Cell extracts (160,000xg supernatant) catalyzed the conversion of oxaloacetate (apparent K _m=0.2 mM), acetyl-CoA (app. K _m=0.1 mM), ADP (app. K _m=0.06 mM) and phosphate (app. K _m=0.7 mM) to citrate, CoA and ATP with a specific activity of 0.3 mol·min^-1·mg^-1 protein. Per mol citrate formed 1 mol of ATP was generated. Cleavage of citrate (app. K _m=0.05 mM; V _max=1.2 mol · min^-1 · mg^-1 protein) was dependent on ATP (app. K _m=0.4 mM) and CoA (app. K _m=0.05 mM) and yielded oxaloacetate, acetyl-CoA, ADP, and phosphate as products in a stoichiometry of citrate:CoA:oxaloacetate:ADP=1:1:1:1. The use of an ATP-citrate lyase in the citric acid cycle enables D. postgatei to couple the oxidation of acetate to 2 CO₂ with the net synthesis of ATP via substrate level phosphorylation.     

Syntheses, crystal structures, and magnetic properties of two new 1D molecular solids based on Ni(mnt)2 ion

Two novel ion-pair complexes, 1-(4′-bromo-2′-fluorobenzyl)isoquinolinium-bis(maleonitrile dithiolato)nickel(III), [BrFBzIQl] · Ni(mnt)₂ · 0.5MeCN (1) and 1-(4′-bromo-2′-flourobenzyl)-quinolinium-bis(maleonitriledithiolato)nickel(III), [BrFBzQl] · Ni(mnt)₂ (2) have been characterized structurally and magnetically. The anions and cations of 1 stack into columns in the solid state, respectively; and the Ni(III) ions form uniform stacking column with the Ni?Ni distances 4.061 Å within a column through intermolecular Ni?S, S?S, Ni?Ni or π?π interactions, while 2 forms 1D column of alternating between cations and anions via the hydrogen bonds, C?N, C?N, N?C, and π?π interactions. The changes of coupling constants were observed in these two complexes at 85 K for 1 and 70 K for 2. It is interesting that 1 undergoes a transition from antiferromagnetic to ferromagnetic phase and 2 does counter to that of 1.     

Sulphate influx in wheat and barley roots becomes more sensitive to specific protein-binding reagents when plants are sulphate-deficient

When young wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) plants were deprived of an external sulphate supply (-S plants), the capacity of their roots to absorb sulphate, but not phosphate or potassium, increased rapidly (derepression) so that after 3–5 d it was more than tenfold that of sulphate-sufficient plants (+S plants). This increased capacity was lost rapidly (repression) over a 24-h period when the sulphate supply was restored. There was little effect on the uptake of L-methionine during de-repression of the sulphate-transport system, but S input from methionine during a 24-h pretreatment repressed sulphate influx in both+S and-S plants.Sulphate influx of both+S and-S plants was inhibited by pretreating roots for 1 h with 4,4-diisothiocyanatostilbene-2,2-disulphonic acid (DIDS) at concentrations > 0.1 mol · m^-3. This inhibition was substantially reversed by washing for 1 h in DIDS-free medium before measuring influx. Longer-term pretreatment of roots with 0.1 mol·m^-3 DIDS delayed de-repression of the sulphatetransport system in-S plants but had no influence on+S plants in 3 d.The sulphydryl-binding reagent, n-ethylmaleimide, was a very potent inhibitor of sulphate influx in-S roots, but was much less inhibitory in +S roots. Its effects were essentially irreversible and were proportionately the same at all sulphate concentrations within the range of operation of the high-affinity sulphate-transport system. Inhibition of influx was 85–96% by 300 s pretreatment by 0.3 mol·m^-3 n-ethylmaleimide. No protection of the transport system could be observed by including up to 50 mol·m^-3 sulphate in the n-ethylmaleimide pre-treatment solution. A similar differential sensitivity of-S and+S plants was seen with p-chloromercuriphenyl sulphonic acid.The arginyl-binding reagent, phenylglyoxal, supplied to roots at 0.25 or 1 mol·m^-3 strongly inhibited influx in-S wheat plants (by up to 95%) but reduced influx by only one-half in+S plants. The inhibition of sulphate influx in-S plants was much greater than that of phosphate influx and could not be prevented by relatively high (100 mol·m^-3 sulphate concentrations accompanying phenylglyoxal treatment. Effects of phenylglyoxal pretreatment were unchanged for at least 30 min after its removal from the solution but thereafter the capacity for sulphate influx was restored. The amount of new carrier appearing in-S roots was far greater than in+S roots over a 24-h period.The results indicate that, in the de-repressed state, the sulphate transporter is more sensitive to reagents binding sulphydryl and arginyl residues. This suggests a number of strategies for identifying the proteins involved in sulphate transport.Abbreviations DIDS 4,4-diisothiocyanatostilbene-2,2-disulphonic acid - NEM n-ethylmaleimide - PCMBS p-chloromercuriphenyl sulphonic acid     

Flight of the honeybee

Summary Drag forces and lift forces acting on honeybee trunks were measured by using specially built sensitive mechanical balances. Measurements were made on prepared bodies in good and in bad flight position, with and without legs, at velocities between 0.5 and 5m·s^-1 (Reynolds numbers between 4·10² and 4·10³) and at angles of attack between-20° and +20°. From the forces drag coefficients and lift coefficients were calculated. The drag coefficient measured with a zero angle of attack was 0.45 at 3v5m·s^-1, 0.6 at 2m·s^-1, 0.9 at 1m·s^-1 and 1.35 at 0.5m·s^-1, thus demonstrating a pronounced effect of Reynolds number on drag. These values are about 2 times lower (better) than those of a drag disc with the same diameter and attacked at the same velocity. The drag coefficient (related to constant minimal frontal area) was minimal at zero angle of attack, rising symmetrically to larger (+) and smaller (-) angles of attack in a non-linear fashion. The absolute value is higher and the rise is steeper at lower speeds or Reynolds numbers, but the incremental factors are independent of Reynolds number. For example, the drag coefficient is 1.44±0.05 times higher at an angle of attack of 20° than at one of 0°. On a double-logarithmic scale the slope of the drag versus Reynolds number plot was 1.5: with decreasing Reynolds number the relationship between drag and velocity changes from quadratic (Newton's law) to linear (viscous flow). Trunk drag was not systematically increased by the legs at any velocity or Reynolds number or any angle of attack. The legs appear to shape the trunk aerodynamically, to form a relatively low-drag trunk-leg system. The body is able to generate dynamic lift. Highly significant positive linear correlations between lift coefficient and angle of attack were determined for the trunk-leg system in the typical flight position. Lift coefficient was +0.05 at zero angle of attack (possibly attained during very fast flight), +0.1 at 5° (attained during fast flight), +0.25 at +20° (attained during slow flight) and +0.55 at 45° (attained whilst changing over to hovering). Average slope c_L was 0.66±0.07, and average profile efficiency was 0.10. Non-wing lift contribution due to body form and banking only accounts for a few percent of body weight during fast flight. A non-wing lift contribution due to the legs has been demonstrated. The legs increase trunk lift by 23–24%. Reynolds number lift effects are present but of no biological significance. Force and power calculations do not support maximum flight speeds substantially higher than approximately 7m · s^-1 relative to the ambient air. At this speed body drag attains 35% and body lift 8.4% of the body weight, and parasite power is 5% of the maximum metabolic power.Abbreviations angle of attack - A area - c drag coefficient - c_L lift coefficient - D drag - F force - L lift - P power - Q quotient - Re Reynolds number - density - dliding number - O₂ oxygen consumption - W work - v kinematic viscosity - efficiency - v velocity     

Epr detection of endogenous nitric oxide in postischemic heart using lipid and aqueous-soluble dithiocarbamate-iron complexes

Spin-trapping techniques combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (·NO) production were compared in the ischemic-reperfused myocardium for the first time, using both aqueous-soluble and lipophilic complexes of reduced iron (Fe) with dithiocarbamate derivatives. The aqueous-soluble complex of Fe and N-methyl-D-glucamine dithiocarbamate (MGD) formed MGD2-Fe-NO complex with a characteristic triplet EPR signal (a_N12.5 G and g_iso = 2.04) at room temperature, in native isolated rat hearts following 40 min global ischemia and 15 min reperfusion. Diethyldithiocarbamate (DETC) and Fe formed in ischemic-reperfused myocardium the lipophilic DETC2-Fe-NO complex exhibiting an EPR signal (g = 2.04 and g = 2.02 at 77K) with a triplet hyperfine structure at g. Dithiocarbamate-Fe-NO complexes detected by both trapping agents were abolished by the ·NO synthase inhibitor, N^G-nitro-L-arginine methyl ester. Quantitatively, both trapping procedures provi ded similar values for tissue ·NO production, which were observed primarily during ischemia. Postischemic hemodynamic recovery of the heart was not affected by the trapping procedure. (Mol Cell Biochem 175: 91–97, 1997)     

Ozone detoxification in the apoplasm and symplasm of spinach,broad bean and beech leaves at ambient and elevated concentrations of ozone in air

Spinach (Spinacia oleracea L.), broad bean (Vicia faba L.) and beech (Fagus sylvatica L.) plants were exposed to ozone at concentrations often measured in air during the summer months (120–300 g·m^–3) and antioxidants were determined in the leaf tissue and in the aqueous phase of the cell wall, the apoplasm. Concentrations of both reduced ascorbate (AA) and its oxidized form, dehydroascorbate (DHA), showed the tendency to increase transiently in the apoplasm of spinach leaves 6–24 h after starting fumigation with ozone. In beech leaves, apoplasmic AA and DHA increased 3–7 d after beginning of treatment. At the very high concentration of 1600 g O₃·m^–3, an increase of apoplasmic AA was already measured after 1 d in beech leaves. Apparently, spinach and beech leaves respond to oxidative stress by increasing AA transport into the apoplasm and by accelerating DHA export. In contrast to these observations, DHA accumulated during 3 d of fumigation with only 120 g O₃·m^–3 in the apoplasm of broad bean leaves, while AA contents did not increase. After termination of fumigation, the extracellular redox state of ascorbate normalized within 1 d. Glutathione could not be detected in the apoplasm of any of the three leaf species. Intracellular AA changed its redox state in response to exposure to elevated concentrations of ozone. After 4–6 weeks of fumigation with 200–300 g O₃·m^–3 an increase of intracellular DHA was measured in beech leaves. At the same time, chlorophyll contents decreased and characteristic symptoms of ozone damage could be observed. However, no significant change in the redox state of apoplasmic ascorbate could be detected in beech leaves. Evidently, detoxification of ozone by apoplasmic AA was insufficient to protect the leaf tissue. Fumigation with a high ozone concentration (1600 g·m^–3) caused an appreciable increase in the cellular contents of the oxidized forms of ascorbate and glutathione in beech leaves. Whereas in spinach leaves intracellular antioxidant contents and redox states were not altered during fumigation with 120–240 g O₃·m^–3, in broad bean leaves the intracellular DHA concentration increased and intracellular ascorbate became more oxidized after fumigation of the plants with 120 g O₃·m^–3. Apparently, broad bean leaves are more sensitive to ozone than beech and spinach leaves.Abbreviations AA ascorbate, reduced form - DHA ascorbate, oxidized form (dehydroascorbate) - FW fresh weight - GSH glutathione, reduced form - GSSG glutathione, oxidized form - IWF intercellular washing fluid - V_air intercellular air space volume of leaves - V_apo apoplasmic water volume of leaves This work was supported within the Sonderforschungsbereich 251 of the University of Würzburg.     

A new technique for continuous measurement of the heat of fermentation

Summary A special temperature control system has been developed and applied to continuous measuring of the heat evolved during a fermentation process. In this system, the fermentation broth was overcooled by a given constant cooling water flow. The excess heat removed from the fermentor was then made up by an immersion electrical heater. The action of the temperature controller was precisely monitored as it varied in response to the amount of heat produced by the microbial activities.The technique was used for determining the heat evolution byEscherichia coli grown on glucose. The ratio between quantities of total heat release and total oxygen consumption has been determined to be 0.556 MJ/mol O₂.The newly developed technique can be employed as an online sensor to monitor the microbial activities of either aerobic or anaerobic fermentation systems.Symbols C_c Heat capacity of cooling water (MJ/kg · °C) - C_p Heat capacity (MJ/kg · °C) - I Current of immersion heater (A) - K Constant in Equation (2) (h) - K Constant in Equation (13) (m³ · h · °C/MJ) - Q_c Flow rate of cooling water (m³/h) - Heat of agitation (MJ/m³ · h) - Heat dissipated by the bubbling gas (MJ/m³ · h) - Heat removal by the action of controller (MJ/m³ · h) - Heat of fermentation (MJ/m³ · h) - Heat loss to the surroundings (MJ/m³ · h) - Q_pass Constant average power dissipated by the immersion heater (MJ/m³ · h) - Fluctuating power dissipated by the immersion heater (MJ/m³ · h) - Power dissipated by the immersion heater (MJ/m³ · h) - T Temperature of fermentation broth (°C) - Constant average temperature of fermentation broth (°C) - Fluctuating temperature of fermentation broth (°C) - T_a Temperature of the ambient air (°C) - T_c Inlet temperature of cooling water (°C) - U₁A₁ Specific heat transfer coefficient for determination of heat loss to the surroundings (MJ/m³ · h · °C) - U₂A₂ Specific heat transfer coefficient for cooling surfaces (MJ/m³ · h · °C) - U₃A₃ Constant in Equation (16) (MJ/m³ · h · °C) - V Voltage of immersion heater (V) - V_L Liquid volume (m³) - OUR Oxygen uptake rate (mol O₂/m³ · h) Greek Letters H_fo The ratio between the total heat release and the total oxygen uptake (MJ/mol O₂) - _c Density of cooling water (kg/m³) - Time constant defined in Equation (6) (h) - _iM_iC_pi Heat capacity of system components (fermentation broth + fermentor jar + stainless steel) (MJ/m³ · °C)     

Photosynthetic recovery in the resurrection plant Selaginella lepidophylla after wetting

Summary Photosynthetic recovery (PR) in a southwest Texas, USA population of Selaginella lepidophylla (Hook and Grev.) (Selaginellaceae), a poikilohydric spikemoss, was examined in the laboratory. Infrared CO₂ gas analysis and ribulose 1,5-bisphosphate (RuBP) carboxylase activity measurements indicated that optimal temperature for PR was near 25°C in terms of: (1) rapidity of net CO₂ uptake after hydration (5.4 h), (2) maximum net photosynthetic rate at 2000 E·m^-2·s^-1 (2.44 mg CO₂·g(DWT)^-1·h^-1), and (3) maximum net CO₂ assimilation per 30 h hydration event (43.8 mg CO₂·g(DWT)^-1·30 h^-1). The PR was much slower at both 15° and 35° C, with lower photosynthetic rates and net carbon gains per hydration event. High respiratory costs were incurred at 45°C and no net photosynthesis was observed. Increases in RuBP carboxylase activity and chlorophyll content during 24 h hydration were also greatest near 25°C. Dry plants had 60% of the enzyme activity of fully recovered (24 h hydration) plants, indicating enzyme conservation. Actinomycin D and cycloheximide did not appear to inhibit PR, but chloramphenicol appeared to totally inhibit RuBP carboxylase activity increases over levels conserved in dry plants. Therefore, rapid PR in S. lepidophylla was achieved by both rapid increase in RuBP carboxylase activity, possibly via de novo synthesis, and conservation of the photosynthetic enzyme. Both mechanisms are essential to maximize assimilation in S. lepidophylla in an environment where hydrated periods are rare and of short duration.     

Effects of 1-MCP on the vase life and ethylene response of cut flowers

Pretreatment for 6 h with low concentrations of 1-MCP (1-Methylcyclopropene, formerly designated as SIS-X), a cyclic ethylene analog, inhibits the normal wilting response of cut carnations exposed continuously to 0.4 l·l^–1 ethylene. The response to 1-MCP was a function of treatment concentration and time. Treatment with 1-MCP was as effective in inhibiting ethylene effects as treatment with the anionic silver thiosulfate complex (STS), the standard commercial treatment. Other ethylene-sensitive cut flowers responded similarly to carnations. In the presence of 1 l·l^–1 ethylene, the vase life of 1-MCP-treated flowers was up to 4 times that of the controls.Abbreviations 1-MCP 1-Methylcyclopropene - STS silver thiosulfate     

Photoinhibition and repair in Dunaliella salina acclimated to different growth irradiances

The light-dependent rate of photosystem-II (PSII) damage and repair was measured in photoautotrophic cultures of Dunaliella salina Teod. grown at different irradiances in the range 50–3000 mol photons · m^–2· s^–1. Rates of cell growth increased in the range of 50–800 mol photons·m^–2·s^–1, remained constant at a maximum in the range of 800–1,500 mol photons·m^–2 ·s^–1, and declined due to photoinhibition in the range of 1500–3000 mol photons·m^–2·s^–1. Western blot analyses, upon addition of lincomycin to the cultures, revealed first-order kinetics for the loss of the PSII reaction-center protein (D1) from the 32-kDa position, occurring as a result of photodamage. The rate constant of this 32-kDa protein loss was a linear function of cell growth irradiance. In the presence of lincomycin, loss of the other PSII reaction-center protein (D2) from the 34-kDa position was also observed, occurring with kinetics similar to those of the 32-kDa form of D1. Increasing rates of photodamage as a function of irradiance were accompanied by an increase in the steady-state level of a higher-molecular-weight protein complex ( 160-kDa) that cross-reacted with D1 antibodies. The steady-state level of the 160-kDa complex in thylakoids was also a linear function of cell growth irradiance. These observations suggest that photodamage to D1 converts stoichiometric amounts of D1 and D2 (i.e., the D1/D2 heterodimer) into a 160-kDa complex. This complex may help to stabilize the reaction-center proteins until degradation and replacement of D1 can occur. The results indicated an intrinsic half-time of about 60 min for the repair of individual PSII units, supporting the idea that degradation of D1 after photodamage is the rate-limiting step in the PSII repair process.Abbreviations Chl chlorophyll - PSI photosystem I - PSII photosystem II - D1 the 32-kDa reaction-center protein of PSII, encoded by the chloroplast psbA gene - D2 the 34-kDa reactioncenter protein of PSII, encoded by the chloroplast psbD gene - Q_A primary electron-accepting plastoquinone of PSII The work was supported by grant 94-37100-7529 from the US Department of Agriculture, National Research Initiative Competitive Grants Program.     

Movement and compartmentation of abscisic acid in guard cells of Valerianella locusta: Effects of osmotic stress,external H+-concentration and fusicoccin

Epidermal peels of Valerianella locusta were acid-treated for 1 h at pH 3.9 to kill all cells other than guard cells. These guard-cell preparations were used to explore the steady-state one-way fluxes and the cytoplasmic and vacuolar contents of abscisic acid (ABA). The method of compartmental analysis has been applied. The intracellular ABA concentrations were surprisingly high. At an external pH of 5.8 the cytoplasm contained 1.28 mmol·dm^-3 of ABA, twice of the amount which accumulated in the vacuoles (0.57 mmol·dm^-3). The fluxes of ABA at the plasmalemma (_oc=_oc=0.43 fmol · cell ^–1 · h ^–1) were higher than those at the tonoplast (_cv=_vc=0.12 fmol · cell ^–1 · h ^–1). Moderate stress (0.1 and 0.3 mol·dm^-3 sorbitol in the medium) caused a change in the kinetics of ABA movement. The rate constants of the fluxes from the cytoplasm into the vacuole (_cv) and into the apoplast (_co) were increased while the rate constant of the flux from the vacuoles into the cytoplasm (_vc) was decreased. As a consequence the amount of ABA sequestered in the vacuole remained unchanged; the cytoplasmic ABA content, however, was reduced to only 20% of that found in the control treatments (no sorbitol in the medium). Under moderate stress, one Valerianella guard cell released rapidly about 0.36 fmol·cell^-1 to its direct cell-wall space. This surprising result is discussed in regard to rapid stomatal closure under reduced water supply.Abbreviations ABA abscisic acid - FC fusicoccin     

Comparative glucose tolerance studies in the freshwater snail Biomphalaria glabrata: influence of starvation and infection with the trematode Schistosoma mansoni

Summary The dynamic reactions of B. glabrata on intravasal loads of 20–1000 g glucose·g live fresh wt^-1 were studied in standard fed snails (SFS). Starved snails (SS) and snails infected with S. mansoni (IS) were given 100–500 g glucose·g fresh live wt^-1. Mean hemolymph glucose level was 12.1 mg·100 ml^-1 in SFS. It was not significantly lower in SS (10.7 mg·100 ml^-1), but significantly reduced in IS (8.5 mg·100 ml^-1). Since hemolymph volumes were significantly increased in SS, the amount of circulating glucose (pool) did not change (75 g·g body weight^-1) compared to SFS (62 g·g^-1). It was, however, reduced to 41 g·g^-1 in IS. In SFS the circulating glucose pool had to be doubled to induce significantly elimination of the injected glucose. Tripled pools were eliminated with half-times of 45 min, whereas lower and higher glucose loads were eliminated significantly slower (half-times: 80–105 min). Glucose tolerance of SS was reduced: half-times were doubled, and metabolization of injected glucose was reduced. Since tissue fresh weights were lowered by 40%, absolute incorporation of ¹⁴C from labeled glucose was lowered, but specific incorporation (per mg) was higher than in SFS and IS. Glucose tolerance of IS was increased: metabolic clearance rates rose by 70% and half-times were shortened by 30%, though absolute and specific rates of ¹⁴C incorporation were lowered. However, IS lost 25% of the label to the water, whereas SFS lost 12% and SS only lost 8%. Using the antimetabolite 2-deoxyglucose, 80% of the losses proved to be glucose in IS, and 50% in SFS. The present results suggest the existence of a glucostatic regulation in B. glabrata with lower sensitivity and capacity than in mammals. As to glucose tolerance, the often reported parallelism in metabolic shifts induced by starvation and parasitic infection was not confirmed.Abbreviations SFS standard fed snails - SS starved snails - IS infected snails - MGG midgut-gland-gonad - RB rest of the bodymass - MCR metabolic clearance rate     

Mechanisms of sulphide tolerance in the peanut worm,Sipunculus nudus (Sipunculidae) and in the lugworm,Arenicola marina (Polychaeta)

Summary The peanut worm Sipunculus nudus and the lugworm Arenicola marina are inhabitants of intertidal flats. Both species may be exposed to H₂S within their habitat. Sulphide concentrations in the vicinity of A. marina burrows are as high as 340 mol · 1^-1, whereas the pore water in sipuncle areas contains much lower sulphide levels of 13 mol · 1^-1 at most. During in vivo sulphide incubations, H₂S increases within the coelomic fluid of both species. In S. nudus the concentration of total sulphide after 8 h is about 40% of that of the incubation medium containing 200 and 1000 mol · 1^-1, respectively, which is partly due to the acidification of the coelomic fluid by 0.2 pH units during anaerobiosis. After 8 h, the sulphide concentration in A. marina was only 15% of that in the incubation medium containing 1000 mol · 1^-1. When oxygen is available, both species oxidize sulphide to thiosulphate, but in A. marina this capability is more pronounced than in S. nudus. If sulphide is not completely oxidized internally both intertidal worms switch to an anaerobic metabolism as indicated by the accumulation of opines and succinate.Abbreviations ATP adenosine triphosphate - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - HPLC high-performance liquid chromatography - wwt wet weight     

Biological tertiary treatment of urban wastewaters with chitosan-immobilizedPhormidium

Summary Chitosan:Phormidium aggregates (chitosan: algae=1:2, dry weight basis) were used as a biological tertiary treatment to remove the nitrogen (NH ₄ ⁺ , NO ₂ ^- , NO ₃ ^- ) and phosphorus (PO ₄ ^3- ) from a secondary effluent. In a batch system, 71 and 92% of P–PO ₄ ^3- were removed after 6 and 24 h, respectively. The orthophosphate removal rate was identical for all three concentrations of algae-chitosan tested (3.3, 4.6, 5.9 g d. wt.·l^-1), and was 90 g±2 g P–PO ₄ ^3- ·l^-1·h^-1, for a 90% removal. Under control conditions (chitosan flakes only added to the effluent) 73 and 78% of PO ₄ ^3- were removed after 6 and 24 h respectively. A 95% removal of inorganic nitrogen (NH ₄ ⁺ , NO ₂ ^- , NO ₃ ^- ) was attained after 4–6 h withPhormidium immobilized on chitosan flakes, as compared to 30% with chitosan flakes alone (5 g d. wt.·l^-1). The system gave a similar performance when operated semi-continuously over 5 days at a daily retention time of 1.0. In the presence of chitosan-immobilized algae, medium P–PO ₄ ^3- levels were reduced by 87.3%±6.4% after 24 h (61.1 g±7.0 g P·l^-1·h^-1). The reduction of inorganic nitrogen in the medium was 98% after 24 h (370 g±50 g N·l^-1·h^-1). In the presence of chitosan alone, some 60% orthophosphate removal was recorded, whereas no reduction of nitrogen was observed. Disappearance of orthophosphate was attributed to its co-precipitation with calcium released from the chitosan by abrasion. The presence of the algae protected the chitosan from abrasion andPhormidium directly assimilated the orthophosphate and inorganic nitrogen, thus reducing their levels in the effluent.     

Water stress,temperature, and light effects on the capacity for isoprene emission and photosynthesis of kudzu leaves

Kudzu (Pueraria lobata (Willd) Ohwi.) is a vine which forms large, monospecific stands in disturbed areas of the southeastern United States. Kudzu also emits isoprene, a hydrocarbon which can significantly affect atmospheric chemistry including reactions leading to tropospheric ozone. We have studied physiological aspects of isoprene emission from kudzu so the ecological consequences of isoprene emission can be better understood. We examined: (a) the development of isoprene emission as leaves developed, (b) the interaction between photon flux density and temperature effects on isoprene emission, (c) isoprene emission during and after water stress, and (d) the induction of isoprene emission from leaves grown at low temperature by water stress or elevated temperature. Isoprene emission under standard conditions of 1000 mol photons·m^-2·s^-1 and 30°C developed only after the leaf had reached full expansion, and was not complete until up to two weeks past the point of full expansion of the leaf. The effect of temperature on isoprene emission was much greater than found for other species, with a 10°C increase in temperature causing a eight-fold increase in the rate of isoprene emission. Isoprene emission from kudzu was stimulated by increases in photon flux density up to 3000 mol photons·m^-2·s^-1. In contrast, photosynthesis of kudzu was saturated at less than 1000 mol·m^-2·s^-1 photon flux density and was reduced at high temperature, so that up to 20% of the carbon fixed in photosynthesis was reemitted as isoprene gas at 1000 mol photons·m^-2·s^-1 and 35°C. Withholding water caused photosynthesis to decline nearly to zero after several days but had a much smaller effect on isoprene emission. Following the relief of water stress, photosynthesis recovered to the prestress level but isoprene emission increased to about five times the prestress rate. At 1000 mol photons·m^-2·s^-1 and 35°C as much as 67% of the carbon fixed in photosynthesis was reemitted as isoprene eight days after water stress. Leaves grown at less than 20°C did not make isoprene until an inductive treatment was given. Inductive treatments included growth at 24°C, leaf temperature of 30°C for 5 h, or witholding water from plants. With the new information on temperature and water stress effects on isoprene emission, we speculate that isoprene emission may help plants cope with stressful conditions.     

Does photorespiration protect the photosynthetic apparatus in french bean leaves from photoinhibition during drought stress?

Dithiothreitol (DTT), an inhibitor of violaxanthin de-epoxidation and zeaxanthin formation in chloroplasts, inhibited blue-light-stimulated stomatal opening in epidermal peels of Vicia faba L. in a concentration-dependent fashion. Complete inhibition was observed at 3 mM DTT. The DTT effect was specific for the stomatal response to blue light, and the red-light-stimulated opening, which depends on photosynthetic reactions in the guard cells, was unaffected. Preirradiation of stomata in epidermal peels with increasing photon fluence rates of red light, prior to an incubation in 10 mol·m^-2·s^-1 of blue light and 100 mol·m^-2·s^-1 red light, resulted in a DTT-sensitive, blue-light-stimulated opening that was proportional to the fluence rate of the red light pre-treatment. Guard cells in epidermal peels and guard-cell protoplasts irradiated with red light showed increases in their zeaxanthin content that depended on the fluence rate of red light, or on the incubation time. The increases in zeaxanthin concentration were inhibited by DTT. The obtained results indicate that zeaxanthin could function as a photoreceptor mediating the stomatal responses to blue light.Abbreviation DTT dithiothreitol This work was supported by grants from the National Science Foundation and the US Department of Energy to E.Z.