Growth energetics in relation to temperature of the larvae of Rhopaea verreauxi (Coleoptera: Scarabaeidae)

Summary Instantaneous energy budgets were constructed at a range of constant temperatures (7.5°–27.5°C) for the larval stages of the scarabaeid Rhopaea verreauxi. It was found that as larvae increased in size the temperature optima/maxima for the components of the energy budget shifted to lower temperatures. Also, as larvae increased in size the instantaneous assimilation efficiency (A/C) decreased and the temperature range over which energy could be assimilated narrowed. Within this narrowing range, temperature was found to have an increasingly greater influence upon A/C. This was attributed to its influence upon the post-consumption energetics processes rather than upon consumption itself. The instantaneous net production efficiency (P/A) also decreased with increasing body size. Also, the temperature range over which assimilated energy could be partitioned to growth production became narrower as body size increased. These findings are discussed in relation to those of other energy budget studies. Some comment is made on the importance of temperature acclimation in studies such as this, and on the relation of energetics conversion efficiencies to ectothermy and endothermy and to trophic status. It was concluded that in terms of instantaneous conversion efficiences R. verreauxi could be described as a typical ectothermic herbivore, a moderately efficient converter.     

Selectively 13C-enriched DNA: Evidence from 13C1′ relaxation rate measurements of an internal dynamics sequence effect in the lac operator

Summary In order to study some internal dynamic processes of the lac operator sequence, the ¹³C-labeled duplex 5d(C₀G₁C₂T₃C₄A₅C₆A₇A₈T₉T₁₀) · d(A₁₀A₉T₈T₇G₆T₅G₄A₃G₂C₁G₀)3 was used. The spreading of both the H1 and C1 resonances brought about an excellent dispersion of the ¹H1-¹³C1 correlations. The spinlattice relaxation parameters R(C_z), R(C_x,y) and R(H_zC_z) were measured for each residue of the two complementary strands, except for the 3-terminal residues which were not labeled. Variation of the relaxation rates was found along the sequence. These data were analyzed in the context of the model-free formalism proposed by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546–4570] and extended to three parameters by Clore et al. [(1990) Biochemistry, 29, 7387–7401; and (1990) J. Am. Chem. Soc., 112, 4989–4991]. A careful analysis using a least-squares program showed that our data must be interpreted in terms of a three-parameter spectral density function. With this approach, the global correlation time was found to be the same for each residue. All the C1-H1 fragments exhibited both slow (_s = 1.5) and fast (_f = 20 ps) restricted libration motions (S _inf2 ^sups =0.74 to 1.0 and S _inf2 ^supf =0.52 to 0.96). Relaxation processes were described as governed by the motion of the sugar relative to the base and in terms of bending of the whole duplex. The possible role played by the special structure of the AATT sequence is discussed. No evident correlation was found between the amplitude motions of the complementary residues. The 5-terminal residues showed large internal motions (S²=0.5), which describe the fraying of the double helix. Global examination of the microdynamical parameters S _inf2 ^supf and S _inf2 ^sups along the nucleotide sequence showed that the adenine residues exhibit more restricted fast internal motions (S _inf2 ^supf =0.88 to 0.96) than the others, whereas the measured relaxation rates of the four nucleosides in solution were mainly of dipolar origin. Moreover, the fit of both R(C_z) and R(HzC_z) experimental relaxation rates using an only global correlation time for all the residues, gave evidence of a supplementary relaxation pathway affecting R(C_x,y) for the purine residues in the (53) G₄A₃ and A₁₀A₉T₈T₇ sequences. This relaxation process was analyzed in terms of exchange stemming from motions of the sugar around the glycosidic bond on the millisecond time scale. It should be pointed out that these residues gave evidence of close contacts with the protein in the complex with the lac operator [Boelens et al. (1987) J. Mol. Biol., 193, 213–216] and that these motions could be implied in the lac-operator-lac-repressor recognition process.     

Continuous penicillin G hydrolysis in an electro-membrane reactor with immobilized penicillin G acylase

Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml^–1). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from –600 to +600 A/m² with a substrate residency of 1 h. Symbols and abbreviations c _j ^p & concentration of component j in product stream (M) c _j ^s & concentration of component j in substrate stream (M) c _s ^o & substrate concentration at reactor inlet (M) C _j ^p=c _j ^p/c _S ⁰ & scaled concentration of component j in product stream C _j ^s=c _j ^s/c _S ⁰ & scaled concentration of component j in substrate stream i & electric current density (A/m²) j & reaction component, j P, Q or S P & main reaction product (6-aminopenicillanic acid) PGA & penicillin G acylase Q & side reaction product (phenylacetic acid) S & substrate (penicillin G) Y _s=C _P ^s+C _P ^p & substrate conversion & mean residence time of substrate and product streams in reactor (h) =C _Q ^s+C _Q ^p+C _S ^s+C _S ^s & check-sum of scaled concentrations =C _P ^p/(C _P ^s+C _P ^p) & separation factor of 6-aminopenicillanic acid (0 1)     

Membrane bending energy and shape determination of phospholipid vesicles and red blood cells

A procedure is developed to calculate red blood cell and phospholipid vesicle shapes within the bilayer couple model of the membrane. The membrane is assumed to consist of two laterally incompressible leaflets which are in close contact but unconnected. Shapes are determined by minimizing the membrane bending energy at a given volume of a cell (V), given average membrane area (A) and given difference of the areas of two leaflets (A). Different classes of shapes exist in parts of the v/a phase diagram, where v and a are the volume and the leaflet area difference relative to the sphere with area A. The limiting shapes are composed of sections of spheres with only two values allowed for their radii. Two low energy axisymmetrical classes, which include discocyte and stomatocyte shapes are studied and their phase diagrams are analyzed. For v=0.6, the discocyte is the lowest energy shape, which transforms by decreasing a continuously into a stomatocyte. The spontaneous membrane curvature (C ₀) and compressibility of membrane leaflest can be incorporated into the model.A model, where A is free and C ₀ determines the shapes at given V and A, is also studied. In this case, by decreasing C ₀, a discocyte transforms discontinuously into an almost closed stomatocyte.     

Specific Status of Propithecus spp.

Controversial taxonomic relationships within Propithecus have consistently made conservation and management decisions difficult. We present a multidisciplinary phylogenetic analysis of Propithecus supporting the elevation of 4 subspecies to specific status: P. diadema perrieri P. perrieri, P. diadema candidus P. candidus, P. diadema edwardsi P. edwardsi, and P. verreauxi coquereliP. coquereli; leaving P. diadema diadema as P. diadema and P. verreauxi verreauxi as P. verreauxi.     

Estimation of the canopy-gap size using two photographs taken at different heights

A new, convenient method to estimate canopy-gap size using a camera is proposed. Canopy-gap size was estimated from two images taken with a vertically mounted, digital camera at high and low points (P_h and P_l) beneath a canopy gap. The actual (A_OBS) and estimated (A_1.0) canopy-gap sizes were highly correlated (R² > 0.93) for 16 canopy gaps in the Cryptomeria japonica D. Don. plantations, and the relationship between A_1.0 and A_OBS was expressed as A_1.0 = 1.16A_OBS. Thus, the method overestimated actual canopy-gap size by an average of 16%.     

Cytogenetic studies in the genus Zea

Summary New cytological evidence supporting x = 5 as the basic chromosome number of the genus Zea has been obtained as a consequence of our analysis of the meiotic configurations of Zea mays ssp. mays, Z. diploperennis, Z. perennis and of four F₁ artificial interspecific hybrids. Z. mays ssp. mays (2n = 20) presents regular meiosis with 10 bivalents (II) and is considered here as a typical allotetraploid (A₂A₂B₂B₂). In Z. diploperennis (2n = 20) 10II are formed in the majority of the cells, but the formation of 1III + 8II + 1I or 1III + 711 + 3I in 4% of the cells would indicate its segmental allotetraploid nature (A₁A₁B₁B₁). Z. perennis (2n = 40) had 5IV + 10II in 55% of the cells and would be considered as an auto-allooctoploid (A₁A₁A'₁A'₁C₁C₁C₂C₂). Z. diploperennis x Z. mays ssp. mays (2n = 20) presents 10II in ca. 70% of the cells and no multivalents are formed. In the two 2n = 30 hybrids (Z. mays ssp. mays x Z. perennis and Z. diploperennis x Z. perennis) the most frequent meiotic configuration was 5III + 5II + 5I and in 2n = 40 hybrid (Z. diploperennis x Z. perennis) was 5IV + 10II. Moreover, secondary association was observed in the three abovementioned tetraploid taxa (2n = 20) where one to five groups of two bivalents each at diakinesis-metaphase I was formed showing the affinities between homoeologous genomes. The results, as a whole, can be interpreed by assuming a basic x = 5 in this polyploid complex. The main previous contributions that support this working hypothesis are reviewed and its phylogenetic implications studied are discussed.     

The role of lipid and antioxidant exchanges in cell division synchronization (mathematical model)

Cell-cycle synchronization of two diffusecoupled cells has been studied in the framework of the membrane model for the cell division cycle, proposed by Chernavskii et al. (1977). It has been shown semianalytically (using the averaging principle) and by computer stimulation that a) if the duration of theG1-phase (T _G1 ) for two identical cells is comparable with the duration of the remaining cycle (T _S+G2+M ), the lipid (L)-exchange results in a synchronization with phase difference =0. The antioxidant (A)-exchange leads to a phase-locking with =T ₀/2 (whereT ₀ is the cell cycle period; b) ifT _G1 T _S+G2+M (orT _G1 T _S+G2+M ) theL-exchange makes synchronization possible both with =0 and =T ₀/2 while theA-exchange results in phase-locking with confined to the region 0 toT ₀/2; c) for non-identical cells differing in the values of kinetic parameters, the locking band narrows as the population density increases (when some model parameters are close to the bifurcation thresholds). We expect that the cells selected artificially at a definite phase of cycle might maintain the synchronous division for a long time if the lipid exchange between cells were stimulated.     

Analysis of gas exchange in seedlings of Acer saccharum: integration of field and laboratory studies

In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m^-2 s^-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m^-2 s^-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO₂ response. At PPFD-saturation CE was 0.018 mol m^-2 s^-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO₂ was 0.05–0.08 mol/mol. and PPFD-saturated CO₂ exchange was 6–8 mol m^-2 s^-1. The ratio of internal CO₂ concentration to external (C _i /C _a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C _i /C _a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO₂ exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m^-2 s^-1) - A _m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO₂ and 21% (v/v) O₂ (mol m^-2 s^-1) - C constant in equation of Smith (1937, 1938) - C _a CO₂ concentration in the air (l/l) - C _i CO₂ concentration in the intercellular air space (l/l) - C _i ^/* C _i corrected for CO₂ compensation point, i.e., C _i -I ^*, (l/l) - CE initial slope of the CO₂ response of photosynthesis (mol m^-2 s^-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m^-2 s^-1) - F predicted photosynthetic rate (mol m^-2 s^-1) - G leaf conductance to H₂O (mol m^-2 s^-1) - I photosynthetic photon flux density (mol m^-2 s^-1) - N number of data points - P _m predicted photosynthetic rate at saturating CO₂ and given PPFD (mol m^-2 s^-1) - P _ml predicted photosynthetic rate at saturating CO₂ and PPFD (mol m^-2 s^-1) - R _d residual respiratory rate (mol m^-2 s^-1) - T _a air temperature (°C) - T _l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V _max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO₂ (mol CO₂/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO₂ and 21% (v/v) O₂ (mol CO₂/mol quanta) - I ^* CO₂ compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m^-2 s^-1)     

Stable carbon and oxygen isotopic compositions of recent charophyte oosporangia and water from Malham Tarn,U.K.: palaeontological implications

Charophyte oosporangia and water samples from a highly calcareous lake were measured for stable carbon and oxygen isotopic composition. The time period over which the oosporangia calcify is short, thus any biochemical relationship between the water and oosporangia"s calcite represents only one time window (late Summer in Malham Tam). This important temporal restraint must also apply to interpretations of all fossil material measured. The ¹⁸O_c of the charophyte oosporangia is deduced to be in equilibrium with the ¹⁸O of the water for a given temperature. The ¹³ C_c of the charophyte oosporangia was approximately 2.5 per mil lower than the ¹³C_DIC in the water we measured. With the release Of CO₂ with phosphoric acid from the charophyte oosporangia, there was no significant difference in the ¹⁸O_c values obtained, regardless of whether or not the carbonate was separated from the organic center, however ¹³C_c values were marginally lower for carbonate plus organic center measurements. Our results indicate that fossil charophyte gyrogonites can be used to elucidate the geochemistry of the ancient water body in which they lived.     

Carbon-isotope discrimination by leaves of Flaveria species exhibiting different amounts of C3-and C4-cycle co-function

Carbon-isotope ratios were examined as ¹³C values in several C₃, C₄, and C₃–C₄ Flaveria species, and compared to predicted ¹³C, values generated from theoretical models. The measured ¹³C values were within 4 of those predicted from the models. The models were used to identify factors that contribute to C₃-like ¹³C values in C₃–C₄ species that exhibit considerable C₄-cycle activity. Two of the factors contributing to C₃-like ¹³C values are high CO₂ leakiness from the C₄ pathway and pi/pa values that were higher than C₄ congeners. A marked break occurred in the relationship between the percentage of atmospheric CO₂ assimilated through the C₄ cycle and the ¹³C value. Below 50% C₄-cycle assimialtion there was no significant relationship between the variables, but above 50% the ¹³C values became less negative. These results demonstrate that the level of C₄-cycle expression can increase from, 0 to 50% with little integration of carbon transfer from the C₄ to the C₃ cycle. As expression increaces above 50%, however, increased integration of C₃- and C₄-cycle co-function occurs.Abbreviations and symbols RuBP carboxylase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - PEP carboxylase phosphoenolpyruvate carboxylase (EC 4.1.1.31) - pa atmospheric CO₂ partial pressure - pi intercellular CO₂ partial pressure - isotope ratio - quantum yield for CO₂ uptake     

Optimal acclimation of the C3 photosynthetic system under enhanced CO2

A range of studies of C₃ plants have shown that there is a change in both the carbon flux and the pattern of nitrogen allocation when plants are grown under enhanced CO₂. This paper examines evidence that allocation of nitrogen both to and within the photosynthetic system is optimised with respect to the carbon flux. A model is developed which predicts the optimal relative allocation of nitrogen to key enzymes of the photosynthetic system as a function of CO₂ concentration. It is shown that evidence from flux control analysis is broadly consistent with this model, although at high nitrogen and under certain conditions at low nitrogen experimental data are not consistent with the model. Acclimation to enhanced CO₂ is also assessed in terms of resource allocation between photosynthate sources and sinks. A means of assessing the optimisation of this source-sink allocation is proposed, and several studies are examined within this framework. It is concluded that C₃ plants probably possess the genetic feedback mechanisms required to efficiently smooth out any imbalance within the photosynthetic system caused by a rise in atmospheric CO₂.Abbreviations A net rate of CO₂ assimilation - c _i intercellular CO₂ concentration - C_R ^A flux control coefficient for Rubisco with respect to flux A - FBPase fructose 1,6-bisphosphatase - k_app apparent catalytic rate constant - PCO photorespiratory carbon oxidation - PCR photosynthetic carbon reduction - PPFD photosynthetically active photon flux density - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose 1,5-bisphosphate - Ru5P ribulose 5-phosphate - SBPase sedoheptulose 1,7-bisphosphatase     

Transport of auxin (indoleacetic acid) through lipid bilayer membranes

Summary Diffusion of auxin (indole-3-acetic acid) through planar lipid bilayer membranes was studied as a function of pH and auxin concentration. Membranes were made of egg or soybean lecithin or phosphatidyl serine inn-decane (25–35 mg/ml). Tracer and electrical techniques were used to estimate the permeabilities to nonionized (HA) and ionized (A^–) auxin. The auxin tracer flux is unstirred layer limited at low pH and membrane limited at high pH, i.e., when [A^–][HA]. The tracer flux is not affected by the transmembrane voltage and is much higher than the flux predicted from the membrane conductance. Thus, only nonionized auxin crosses the membrane at a significant rate. Auxin transport shows saturation kinetics, but this is due entirely to unstirred layer effects rather than to the existence of an auxin carrier in the membrane. A rapid interconversion of A^– and HA at the membrane surface allows A^– to facilitate the auxin flux through the unstirred layer. Thus, the total flux is higher than that expected for the simple diffusion of HA alone. The relation between flux (J _A), concentrations and permeabilities is: 1/J _A=1/P ^UL([A^–]+[HA])+1/P _HA ^M [HA]. By fitting this equation to our data we find thatP ^UL=6.9×10^–4 cm/sec andP _HA ^M =3.3×10^–3 cm/sec for egg lecithin-decane bilayers. Similar membrane permeabilities were observed with phosphatidyl serine or soybean lipids. Thus, auxin permeability is not affected by a net surface charge on the membrane. Our model describing diffusion and reaction in the unstirred layers can explain the anomolous relationship between pH and weak acid (or weak base) uptake observed in many plant cells.     

Solid-phase extraction of cytokinins from aqueous solutions with C18 cartridges and their use in a rapid purification procedure

Eleven cytokinins-including bases, ribosides, glucosides, and ribotides-were tested for their retention on C₁₈ cartridges that were washed with 40 mL of water or a dilute acid at pH 3. Cytokinins were then eluted with methanol and analyzed by high performance liquid chromatography (HPLC). All pure cytokinin were well retained when the cartridge was washed with water, but Z and (diH)Z were less well retained at pH 3. The ribotides required 80% methanol for elution. Cotton leaf tissue (500 mg dry wt) was spiked with cytokinins, extracted with 80% methanol, and the extract bulk purified with hexane, insoluble polyvinylpyrrolidone, and minicolumns (strong anion exchange, amino, and C₁₈ cartridges). Ribotides, added to leaf tissue, could not be recovered as ribotides; it was necessary to hydrolyze and purify them as ribosides. The cytokinins were separated and analyzed by HPLC on strong cation exchange and C₁₈ columns. Recoveries through the entire procedure averaged 70%.Cytokinin abbreviations (diH)Z Dihydrozeatin - (diH)Z dihydrozeatin riboside - (diH)[9R]Z trans-zeatin - Z t-zeatin riboside - [9R]Z t-zeatin-O-glucoside - (OG)Z t-zeatin riboside-O-glucoside - (OG)[9R]Z t-zeatin riboside-5-monophosphate - [9R-5P]Z N6(^2-isopentenyl)adenine - iP N6(^2-isopentenyl)adenosine - [9R]iP N6(^2-isopentenyl)adenosine-5-monophosphate-[9R-5P]iP     

Observations on phase-locking within the response of primary muscle spindle afferents to pseudo-random stretch

In order to uncover encoder properties of primary muscle spindle afferent fibers, time coupling (phase-locking) of action potentials on cyclic muscle stretch was studied by means of pseudo-random noise. In cats Ia action potentials were recorded from dorsal root filaments and the gastrocnemius muscles of one hind leg were stretched. The stimulus time course was a determined sequence of randomly varying muscle length which could be applied repeatedly (sequence duration 0.6 or 20 s). The noise amplitude (standard deviation of displacements) was varied between 5 and 300 m, the upper cut-off frequency of noise f _c was varied between 20 and 100 Hz. The responses to the consecutive pseudo-random noise cycles were displayed as raster diagrams and cycle histograms. Phaselocking characterized the responses at all noise amplitudes outside the near threshold range (>10 m). The higher and f _c , the stronger was the phase-locking of impulses on the stretch. When and f _c were selected to achieve high mean stretch velocities of about 500 mm/s, phase-locking was as precise as 0.15 ms, measured as the variability of spike occurrences with respect to stretch. The rasters obtained with low noise amplitudes (<40 m) showed a loose phase-locking and this gave insight into underlying mechanisms: The elicitation of action potentials caused by dynamic stretch can be prevented by a post-spike depression of excitability. This disfacilitation was very effective in counteracting weak stretch components within the random sequence and less effective or even missing when relatively strong stretch components could force the spike elicitation. This led to the reestablishment of phase-locked patterns. The results were discussed in relation to the known encoder models.     

Interrelationships Between Nitrogen Supply and Photosynthetic Parameters in Vicia faba L.

We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P _Nmax), quantum yield efficiency (), intercellular CO₂ concentration (C _i), and carboxylation efficiency (C _e). As leaf nitrogen content (N_L) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO₂) mol(quantum)^–1. Also, as N_L increased the C _i value fell to an asymptotic minimum of 115.80±1.59 mol mol^–1, and C _e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO₂) m^–2 s^–1 Pa^–1 and declined to zero at a N_L-intercept equal to 0.596±0.096 g(N) m^–2. fell to zero for an N_L-intercept of 0.660±0.052 g(N) m^–2. As N_L increased, the value of P _Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO₂) m^–2 s^–1. P _N fell to zero for an N_L-intercept of 0.710±0.035 g(N) m^–2. Under variable daily meteorological conditions the values for N_L, specific leaf area (_L), root mass fraction (R_f), P _Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. _L increased with increasing N supply or with increasing N_L.     

Energy requirements for growth and maintenance of Scenedesmus protuberans Fritsch in light-limited continuous cultures

Scenedesmus protuberans Fritsch was grown in light-limited continuous cultures with a light-dark cycle, at temperatures of 20° and 28° C. At 20° irradiances of 12 and 38 W m^–2 were used, at 28° 38 W m^–2.The relationships between growth rate and light uptake rate were of diphasic linear character. With the lower growth rates the relationships were defined with the parameters _e , i.e. the specific maintenance rate constant, and c, the true efficiency of light energy conversion into biomass. The _e -value was dependent on temperature, the c on irradiance.In cultures, incubated in prolonged darkness, decrease rates of biomass were comparable to the derived _e -values.Both diphasic linear relationships between growth rate and light uptake rate and the same order of magnitude of _e -values could be derived from literature data on other green algae.     

Biotransformation of cephalosporin C to 7-aminocephalosporanic acid with coimmobilized biocatalyst in a batch bioreactor

Biotransformation of cephalosporin C (CPS-C) to 7-aminocephalosporanic acid (7-ACA) was carried out with coimmobilized permeabilized cells of Trigonopsis variabilis and Pseudomonas species entrapped in Ca-pectate gel beads. Good aeration and stirring during the process was assured. The analysis of this complicated biochemical process in a heterogeneous system was based on the identification of individual effects (internal diffusion, reaction) running simultaneously. A spectrophotometric method was proposed for the determination of 7-(-ketoadipyl amido) cephalosporanic acid (CO-GL-7-ACA) and 7-ACA. The reaction-diffusion model containing dimensionless partial differential equations was solved by using the orthogonal collocation method. A good agreement between experimental values and values predicted by the mathematical model was obtained. Numerical simulations were performed on the basis of following the two assumptions:- several times higher activity of both cells,- hydrogen peroxide was continuously supplied in the bioreactor.List of Symbols A m² surface of the bead - c _i mol/dm³ concentration of component in the bead and/or in the solution - c _i0 mol/dm³ initial concentration of component in the solution - c _l0 mol/dm³ initial concentration of CPS-C in the solution - C _jl orthogonal collocation weights of the first derivation - D _ei m²/s effective diffusion coefficient of the components - D _jl orthogonal collocation weights of the second derivation - k ₅ dm³/(mol · s) kinetic parameter of non-enzyme reaction - K _inh mol/dm³ inhibition parameter for the first enzyme reaction - K _i dimensionless Michaelis constant for the first and second enzyme reaction, defined in Eq. (7) - K _l dimensionless inhibition parameter for the first enzyme reaction, defined in Eq. (7) - K _mi mol/dm³ Michaelis constant for the first and second enzyme reaction - n number of beads - P( _i ) symbol of dimensionless reaction rate, defined in Eq. (13) - r m radial coordinate inside the bead - R m radius of the bead - R(c _i ) mol/(dm³ · s) symbol for reaction rate, defined in Eq. (6) - t s time - V _max mol/(dm³ · s) max. reaction rate for the first and second enzyme reaction - V _L dm³ volume of solution excluding the space occupied by beads - voidage in batch bioreactor - _P porosity of the bead - i dimensionless effective diffusion coefficient of the components, defined in Eq. (7) - dimensionless time, defined in Eq. (7) - _mi Thiele modulus, defined in Eq. (7) - _i dimensionless concentration, defined in Eq. (7) - dimensionless radial position inside the bead, defined in Eq. (7) - _l0 initial dimension concentration of CPS-C, defined in Eq. (9), (10) - _i0 initial dimension concentration of component, defined in Eq. (9), (10) The authors wish to thank Dr. P. Gemeiner of Slovak Academy of Sciences for rendering of pectate gel. This work is supported by Ministry of Education (Grant No. 1/990 935/93).     

Analysis of inhibition of photosynthesis due to water stress in the C3 species Hordeum vulgare and Vicia faba: Electron transport, CO2 fixation and carboxylation capacity

A C₃ monocot, Hordeum vulgare and C₃ dicot, Vicia faba, were studied to evaluate the mechanism of inhibition of photosynthesis due to water stress. The net rate of CO₂ fixation (A) and transpiration (E) were measured by gas exchange, while the true rate of O₂ evolution (J _O2) was calculated from chlorophyll fluorescence analysis through the stress cycle (10 to 11 days). With the development of water stress, the decrease in A was more pronounced than the decrease in J _O2 resulting in an increased ratio of Photosystem II activity per CO₂ fixed which is indicative of an increase in photorespiration due to a decrease in supply of CO₂ to Rubisco. Analyses of changes in the J _O2 A ratios versus that of CO₂ limited photosynthesis in well watered plants, and RuBP pool/RuBP binding sites on Rubisco and RuBP activity, indicate a decreased supply of CO₂ to Rubisco under both mild and severe stress is primarily responsible for the decrease in CO₂ fixation. In the early stages of stress, the decrease in C _i (intercellular CO₂) due to stomatal closure can account for the decrease in photosynthesis. Under more severe stress, CO₂ supply to Rubisco, calculated from analysis of electron flow and CO₂ exchange, continued to decrease. However, C _i, calculated from analysis of transpiration and CO₂ exchange, either remained constant or increased which may be due to either a decrease in mesophyll conductance or an overestimation of C _i by this method due to patchiness in conductance of CO₂ to the intercellular space. When plants were rewatered after photosynthesis had dropped to 10–30% of the original rate, both species showed near full recovery within two to four days.Abbreviations A- net CO₂ assimilation rate - A ^*- net CO₂ assimilation rate plus dark respiration - ATP- adenosine triphosphate - CABP- carboxyarabinitol 1,5-bisphosphate - C _a- ambient CO₂ concentration - C _c- CO₂ concentration in the chloroplast - C _i- intercellular CO₂ concentration - E- transpiration rate - g _m- mesophyll conductance - g _s- stomatal conductance - J _O2 true rate of O₂ evolution - LSD- least significant difference - PPFD- photosynthetic photon flux density - PS II- Photosystem II - R _n- dark respiration rate - Rubisco- ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP- ribulose 1,5-bisphosphate - RWC- relative water content - _c- rate of carboxylation - _o- rate of oxygenation - _PSII- quantum yield of Photosystem II - - CO₂ compensation point in the absence of R _n - - water potential     

Dehalogenation of haloalkanes byRhodococcus erythropolis Y2

Phodococcus erythropolis Y2 produced two types of dehalogenase: a hydrolytic enzyme, that is an halidohydrolase, which was induced by C₃ to C₆ 1-haloalkane substrates, and at least one oxygenase-type dehalogenase induced by C₇ to C₁₆ 1-haloalkanes andn-alkanes. The oxygenase-type activity dehalogenated C₄ to C₁₈ 1-chloroalkanes with an optimum activity towards 1-chlorotetradecane. The halidohydrolase catalysed the dehalogenation of a wide range of 1- and ,-disubstituted haloalkanes and ,-substituted haloalcohols. In resting cell suspensions of hexadecane-grownR. erythropolis Y2 the oxygenase-type dehalogenase had a specific activity of 12.9 mU (mg protein)^–1 towards 1-chlorotetradecane (3.67 mU mg^–1 towards 1-chlorobutane) whereas the halidohydrolase in 1-chlorobutane-grown batch cultures had a specific activity of 44 mU (mg protein)^–1 towards 1-chlorobutane.The significance of the two dehalogenase systems in a single bacterial strain is discussed in terms of their contribution to the overall catabolic potential of the organism.