Genetic studies of the ribosomal proteins in Escherichia coli. I. Mutants and strains having 30s ribosomal subunit with altered protein components

Summary Two 30s ribosomal protein components, 30-4_K and 30-7_K, from E. coli K12 strain were clearly distinguished on the CMC column chromatogram from the corresponding protein components, 30-4_B and 30-7_B, from B strain. The 30-7_K component was shown to correspond to the K-character.A mutant strain of K12, W3637, had an altered 30s ribosomal protein component, 30-9_W3637.The characters of 30-4_K, 30-7_K, 30-9_W3637 and str ^r were found to be cotransduced from W3637 to B strain by Plke phage in 16 out of 20 str ^r transductants. The 30-9_W3637 and 30-4_K components were separated from str ^r in 4 str ^r transductants. These results indicate that (1) neither 30-4 nor 30-9 is the protein whose mutational change leads to str ^r, and (2) the genes specifying the 30s ribosomal proteins, 30-4, 30-7, 30-9 and str are linked on the chromosome.Abbreviations used CMC carboxymethyl cellulose - str streptomycin     

Optimal temperature and concentration profiles in a cascade of CSTR's performing Michaelis-Menten reactions with first order enzyme deactivation

A necessary condition is found for the intermediate temperatures and substrate concentrations in a series of CSTR's performing an enzyme-catalyzed reaction which leads to the minimum overall volume of the cascade for given initial and final temperatures and substrate concentrations. The reaction is assumed to occur in a single phase under steady state conditions. The common case of Michaelis-Menten kinetics coupled with first order deactivation of the enzyme is considered. This analysis shows that intermediate stream temperatures play as important a role as intermediate substrate concentrations when optimizing in the presence of nonisothermal conditions. The general procedure is applied to a practical example involving a series of two reactors with reasonable values for the relevant five operating parameters. These parameters are defined as dimensionless ratios involving activation energies (or enthalpy changes of reaction), preexponential factors, and initial temperature and substrate concentration. For negligible rate of deactivation, the qptimality condition corresponds to having the ratio of any two consecutive concentrations as a single-parameter increasing function of the previous ratio of consecutive concentrations.List of Symbols C _E,0 mol.m^–3 Initial concentration of active enzyme - C _E,i mol.m^–3 Concentration of active enzyme at the outlet of the i-th reactor - C _S,0 mol.m^–3 Initial concentration of substrate - C _S,i mol.m^–3 Concentration of substrate at the outlet of the i-th reactor - Da _i Damköhler number associated with the i-th reactor ((V _i.k_v,0.C_E,0)/(Q.C_S,0)) - Da _min Minimum value of the overall Damköhler number - Da _tot Overall Damköhler number - E _d J.mol^–1 Activation energy of the step of deactivation of the enzyme - E _m J.mol^–1 Standard enthalpy change of the step of binding of substrate to the enzyme - E _v J.mol^–1 Activation energy of the step of enzymatic transformation of substrate - i Integer variable - j Dummy integer variable - k Dummy integer variable - k _d,i s^–1 Kinetic constant associated with the deactivation of enzyme in the i-th reactor (k _d,o·exp{–E _d/(R.T _i}) - k _d,0 s^–1 Preexponential factor of the kinetic constant associated with the deactivation of the enzyme - K _m,i mol.m^–3 Equilibrium constant associated with the binding of substrate to the enzyme in the i-th reactor, (k _m,o·exp{–E _m}(R.T _i}) - K _m,0 mol.m^–3 Preexponential factor of the Michaelis-Menten constant associated with the binding of substrate to the enzyme - k _v,i s^–1 Kinetic constant associated with the transformation of the substrate by the enzyme in the i-th reactor (k _v,o·exp{–E _v/(R.T _i})) - k _v,0 s^–1 Preexponential factor of the kinetic constant associated with the transformation of the substrate by the enzyme - N Number of reactors in the series - Q m³.s^–1 Volumetric flow rate of reacting liquid through the reactor network - R J.K^–1.mol^–1 Ideal gas constant - T _i K Absolute temperature at the outlet of the i-th reactor - T ₀ K Initial absolute temperature - V _i m³ Volume of the i-th reactor - v _max mol.m^–3.s^–1 Maximum rate of reaction under saturation conditions of substrate - x _i Normalized concentration of substrate (C_S,i/C_{S, 0}) - x _i,opt Optimum value of the normalized concentration of substrate - y _i Dimensionless temperature (exp{–T ₀/T _i}) - y _i,opt Optimum value of the dimensionless temperature Greek Symbols Dimensionless preexponential factor associated with the Michaelis-Menten constant (K _m,0/C_s,0) - Dimensionless activation energy of the step of enzymatic transformation of substrate (E _v/R.T₀)) - Dimensionless standard enthalpy change of the step of binding of substrate to the enzyme (E _m/(R.T₀)) - Dimensionless activation energy of the step of deactivation of the enzyme (E _d/(R.T₀)) - Dimensionless deactivation preexponential factor ((k _d,0.C_S,0)/(k_v,0.C_E,0)     

Two mathematical models for the development of a single microbial pellet

A mathematical model for pellet development of filamentous microorganisms is presented, which simulates in detail location and growth of single hyphal elements. The basic model for growth, septation and branching of discrete hyphae is adopted from Yang et al. [2, 23]. Exact solutions to the intracellular mass-balance equations of a growth-limiting key component is given for two types of either branched or unbranched cellular compartments. Furthermore, the growth model was extended in regard to the external mass-balance equations of limiting substrates (oxygen, glucose) under the assumption that the substrates can enter the denser regions of the pellet only diffusively. Penetration of the substrates into the more porous outer regions of the pellet occurs more easily due to microeddies in the surrounding fluid. Chipping of hyphae from the pellet surface by shear forces was included in the model as well. The application of shear forces leads to a marked smoothing of the simulated pellet surface. The development of pellets from spore germination up to late stages with cell-lysis due to shortage of substrates in the pellet centre can be described. The effects of various model parameters are discussed.List of Symbols A _i algebraic coefficient (i = 1, 2,..., 6) - B _i algebraic coefficient (i = 1, 2,..., 6) - C _i mass-concentration of component i (i = O₂, S) (gl^–1) - C _i,crit concentration of substance i critical for lysis (i=O₂, S) (gl^–1) - C _i,stop concentration of substance i below which cells are inactivated (gl^–1) - C(l _i,t) intracellular concentration of the key component at site l _i and time t (gl^–1) - C _m maximal intracellular concentration of the key component (gl^–1) - C _X Concentration of dry biomass (gl^–1) - D intracellular diffusion coefficient of the key component (m² h^–1) - D _max,i maximal molecular diffusion coefficient of substrate i (i = O₂, S) (m² h^–1) - D _eff,i effective diffusion coefficient of component i (i = O₂) (m² h^–1) - d _h cross-sectional diameter of hyphae (m) - k production coefficient for the key component (h^–1) - K _s Monod coefficient for glucose (gl^–1) - k ₀ Monod coefficient for oxygen (gl^–1) - L _c total length of a compartment (m) - L _i total length of branch i (i=1, 2, 3) (m) - l _i position on branch i (i=1, 2, 3) - L _m maximal length of a segment (m) - m _i maintenance coefficient of substrate i (h^–1) - N _m maximal number of segments in a compartment - n _iR number of tips of type i in layer R, i=1, 2 - p auxiliary variable (see Eq. (7)) - P _Br probability that a hypha is chipped off (%h^–1) - pO ₂ partial pressure of oxygen in the liquid phase (%) - Q auxiliary variable (see Eq. (8)) - Q _i uptake rate of substrate i (i = O₂, S) (gl^–1 h^–1) - q auxiliary variable (see Eq. (7)) - R index of radial layer (R=1, 2, 3,..., R _max) - r radius (m) - r _crit critical radius, Eq. (15) (m) - r _max pellet radius (m) - r _tip distance from the pellet centre to the tip position (m) - r _thr threshold radius (m) - s auxiliary variable (see Eq. (7)) - S index for glucose - t time (h) - v _R volume of layer R (1) - Y _Mi observable yield coefficient of biomass on substrate i (gg^–1) - Y _Xi yield coefficient of biomass on substrate i (gg^–1) Greek Letters _i actual tip expansion rate (m h^–1) - _i,m actual maximal extension rate of tip i (i=1, 2) (m h^–1) - _1y lysis rate (h^–1) - _m maximal tip extension rate (m h^–1) - auxiliary variable in Eq. (2) - auxiliary variable in Eq. (3) - auxiliary variable defined in Eq. (4) (m^–1) - _shear shear force parameter - _R overall specific growth rate in layer R (h^–1) - _m maximal specific hyphal growth rate (h^–1) - cell volume density (l cell volume per 1) - _crit critical cell volume density in Eq. (15) - _S shear force parameter - _X cell mass density (g dry weight per 1 wet cells) - (C _i) growth kinetics on substrate i - proportional factor in Eq. (34) (l g^–1) We thank the Deutsche Forschungsgemeinschaft (DFG) for financially supporting parts of this work.We thank the Deutsche Forschungsgemeinschaft (DFG) for financially supporting parts of this work.     

Improvement of α-Amylase Production by Modulation of Ribosomal Component Protein S12 in Bacillus subtilis 168

The capacity of ribosomal modification to improve antibiotic production by Streptomyces spp. has already been demonstrated. Here we show that introduction of mutations that produce streptomycin resistance (str) also enhances α-amylase (and protease) production by a strain of Bacillus subtilis as estimated by measuring the enzyme activity. The str mutations are point mutations within rpsL, the gene encoding the ribosomal protein S12. In vivo as well as in vitro poly(U)-directed cell-free translation systems showed that among the various rpsL mutations K56R (which corresponds to position 42 in E. coli) was particularly effective at enhancing α-amylase production. Cells harboring the K56R mutant ribosome exhibited enhanced translational activity during the stationary phase of cell growth. In addition, the K56R mutant ribosome exhibited increased 70S complex stability in the presence of low Mg²⁺ concentrations. We therefore conclude that the observed increase in protein synthesis activity by the K56R mutant ribosome reflects increased stability of the 70S complex and is responsible for the increase in α-amylase production seen in the affected strain.     

Identification of the tautomeric form of formycin A in its complex with<Emphasis Type="Italic"> Escherichia coli</Emphasis> purine nucleoside phosphorylase based on the effect of enzyme–ligand binding on fluorescence and phosphorescence

Fluorescence and phosphorescence emission spectroscopy were employed to study the interaction of Escherichia coli purine nucleoside phosphorylase (PNP) with its specific inhibitor, formycin A (FA), a close structural analogue of adenosine (natural substrate), in the absence and presence of phosphate (P_i, substrate). Formation of enzyme–FA complexes led to marked quenching of enzyme tyrosine intrinsic fluorescence and phosphorescence, with concomitant increases in fluorescence and phosphorescence of FA. Fluorescence resonance energy transfer from the protein Tyr160 residue to the FA base moiety was identified as a major mechanism of protein fluorescence quenching, increased by addition of P_i. The effects of enzyme–FA interactions on the nucleoside excitation and emission spectra for fluorescence and phosphorescence revealed shifts in the tautomeric equilibrium of the bound FA, i.e. from the N(1)–H tautomer (predominant in solution) to the N(2)–H form, enhanced by the presence of P_i. The latter was confirmed by enzyme–ligand dissociation constant (K _d) values of 5.9±0.4 and 2.1±0.3 M in the absence and presence of P_i, respectively. Addition of glycerol (80%, v/v) led to a lower enzyme affinity (K _d70 M), without changes in binding stoichiometry. Enzyme–FA complex formation led to a higher increase of the fluorescence than the phosphorescence band of the ligand, consistent with the fact that the N(2)–H tautomer is characterized by a weaker phosphorescence than the N(1)–H tautomeric form. These results show, for the first time, the application of phosphorescence spectroscopy to the identification of the tautomeric form of the inhibitor bound by the enzyme.Abbreviations Ado adenosine - FA formycin A [3-(-d-ribofuranosyl)-7-aminopyrazolo[4,3-d]pyrimidine] - FB formycin B - FRET fluorescence resonance energy transfer - Guo guanosine - Hepes N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfonic acid) - Ino inosine - m¹FA N(1)-methylformycin A - m²FA N(2)-methylformycin A - m⁴FA N(4)-methylformycin A - m⁶FA N(6)-methylformycin A - m⁷Guo N(7)-methylguanosine - P_i orthophosphate - PNP purine nucleoside phosphorylase - Xao xanthosine     

To what extent is a constant volume design worse than a minimum volume design for a series of CSTR's?

The balance equations for substrate in a cascade of CSTR's undergoing an enzyme-catalyzed reaction following Michaelis-Menten kinetics are developed in dimensionless form. Analytical expressions relating the intermediate concentrations are independently obtained for the cases of minimum overall volume and constant volume. The fractional deviations between the overall volumes following these two design criteria are calculated and presented for several values of the relevant parameters. For situations of practical interest, the fractional deviation is below 10%. Increasing values of the Michaelis-Menten parameter, K _m(or decreasing values of the number of reactors in the cascade, N) lead to lower values of the maximum deviation; this maximum deviation is attained at lower conversions of substrate when K _mis increased or N decreased.List of Symbols C _{S, i}mol.m^–3 concentration of substrate at the outlet of the i-th reactor - C _* ^{S, i} normalized concentration of substrate at the outlet of the i-th reactor - C _* ^{S, i, eq} normalized concentration of substrate at the outlet of the i-th reactor using the design criterion of constant volume - C _* ^{S, i, opt} normalized concentration of substrate at the outlet of the i-th reactor using the design criterion of minimum overall volume - C _{S, 0} mol.m^–3 concentration of substrate at the inlet to the first reactor - Da _i Damköhler number for the i-th reactor - Da _eq constant Damköhler number for each reactor of the cascade - Da _{tot, eq} overall Damköhler number for the cascade assuming equal-sized reactors - Da _{tot, min} minimum overall Damköhler number for the cascade - Er fractional deviation between the overall volumes using the two different design criteria - K _mmol. m^–3 Michaelis-Menten constant - K _* ^M dimensionless Michaelis-Menten constant - N number of reactors of the cascade - Q m³. s^–1 volumetric flow rate - V _im³ volume of the i-th reactor - v _max mol. m^–3. s^–1 reaction rate under saturation conditions of the enzyme with substrate - V _{tot, opt} m³ minimum overall volume of the cascade - V _{tot, eq} m³ overall volume of the cascade assuming equal-sized reactors     

Cadmium-copper antagonism in the activation of periplasmic nitrous oxide reductase of copper-deficient cells fromPseudomonas stutzeri

Summary Copper-deficient cells ofPseudomonas stutzeri strain ZoBell synthesize catalytically inactive nitrous oxide (N₂O) reductase which is activated by added Cu(II) in the absence of de novo protein synthesis. The apparentK _m for the activation process is 0.13 M. Activation is temperature-dependent and is inhibited by Cd(II)(K _i 1.27 M) and less strongly by Zn(II), Ni(II), and Co(II). The same metal ions at 20 M have little or no effect on N₂O reduction of intact cells. Apo-N₂O reductase of transposon Tn5-inducednos ^– mutants with defective Cu-chromophore biosynthesis is not reactivated by Cu(II). N₂O reductase of Cu-sufficient and Cu-deficient wild type, and ofnos ^– mutants is localized in the periplasm, the latter providing the likely site of metal incorporation into the apoenzyme.     

Outdoor pond cultivation of the subtropical marine red algaGracilaria tenuistipitata in brackish water in Sweden. Growth,nutrient uptake,co-cultivation with rainbow trout and epiphyte control

Pond cultivation of the subtropical, euryhaline macroscopic red algaGracilaria tenuisipitata var.liui Zhanget Xia was carried out in brackish seawater (6–7) in the Gryt archipelago on the east coast of Sweden, using four outdoor tanks of 30–40 m³. Growth rate and nutrient uptake in batch culture were measured with the aim of estimating the water purification capacity ofG. tenuisipitata in outdoor conditions. Its ability to withstand epiphytic infections was also studied. An average growth rate of 4 biomass increase per day was recorded during two seasons with a maximum growth rate of 9 d^–1. The initial biomass was usually 1 kgFW m^–3 (FW, fresh weight). The nutrient uptake capacity was on average ca. 1 g N_i kgFW^–1 d^–1 and 0.08 g P_i kgFW^–1 d^–1 and the uptake rates for NH₄ ⁺-N were higher than those for NO₃ ^–-N. Both the growth rate and the nutrient uptake rate were highest at the highest water temperature. Co-cultivation with rainbow trout (Oncorhynchus mykiss) was tested: with trout fodder as the only nutrient inputG. tenuistipitata could grow and maintain low levels of N_i and P_i with optimum efficiency at a trout: alga ratio of 1:1 (w:w). Epiphytic growth of filamentous green and brown algae was limited, probably as a result of the high pH values caused by inorganic carbon uptake byG. tenuistipitata. The growth ofEnteromorpha intestinalis, the only significant epiphyte, was completely inhibited and the majority of plants died by a few days treatment with 100 µg 1^–1 Cu²⁺, a concentration that did not severely affectG. tenuistipitata. We conclude thatG. tenuistipitata can be cultivated in outdoor ponds in southern Sweden during 5–6 months of the year using aerated or unaerated batch cultures and that wastewater from trout cultivation may be used as a nutrient source, resulting in purification with respect to N and P.     

Determination of protein global folds using backbone residual dipolar coupling and long-range NOE restraints

We report the determination of the global fold of human ubiquitin using protein backbone NMR residual dipolar coupling and long-range nuclear Overhauser effect (NOE) data as conformational restraints. Specifically, by use of a maximum of three backbone residual dipolar couplings per residue (N_i-H^N _i, N_i-C_i–1, H^N _i - C_i–1) in two tensor frames and only backbone H^N-H^N NOEs, a global fold of ubiquitin can be derived with a backbone root-mean-square deviation of 1.4 Å with respect to the crystal structure. This degree of accuracy is more than adequate for use in databases of structural motifs, and suggests a general approach for the determination of protein global folds using conformational restraints derived only from backbone atoms.     

Spatial variability of symbiotic N2 fixation in grass-white clover pastures estimated by the 15N isotope dilution method and the natural 15N abundance method

Aiming at estimating the spatial variability in N₂ fixation, and to evaluate the appropriateness of the ¹⁵N isotope dilution (ID) method and the natural¹⁵N abundance (NA) method in reflecting spatial variability under the influence of cattle grazing, the symbiotic N₂ fixation in grass–white clover mixture was studied. At the Foulum site, where the ID method was used, differences in the climatic conditions between the two years of investigations caused a considerable difference in plant growth rates and proportion of clover. Consequently, the total N₂ fixation in ungrazed reference plots was significantly less in 1998 than in 1997, being 5.9 and 12.5 g N m^–2, respectively. In both years there was a wide range in concentration of inorganic N in the soil with coefficients of variance of approximately 60–190% for ammonium and 70–340% for nitrate. Significant negative correlations between pNdfa, determined by the ID method, and the log-transformed values of inorganic N and total N in grass were found. The NA method was applied on three nearby commercial dairy farms. They also showed high coefficients of variation. The coefficient of variance for NO₃ ^–-N ranged from 37 to 282% and for NH₄ ⁺-N from 29 to 237%. Average estimates of pNdfa values, which in the NA method were calculated using apparent B values ranging from –2.10 to –2.59, were generally lower (0.7–0.87) for these farms than for the Foulum site (0.89–0.95) using the ID method. For the NA method the ¹⁵N values, i.e. deviation in ¹⁵N concentration from atmospheric N₂, ranged from –7.0 to 5.7 for the grass N, which in several cases was lower than for clover N. Due to this high variability of the ¹⁵N values, probably caused by deposition and plant assimilation of ¹⁵N depleted urinary N in the pastures, the NA method was marginal for accurate determination of pNdfa. Consequently no significant correlation between the pNdfa determined by this method, and the log-transformed values of inorganic N in soil or total N in grass were found.     

Ribosomal protein S12 as a site for streptomycin resistance in Nicotiana chloroplasts

Summary A streptomycin resistant Nicotiana plastome mutant, X/str ^R6, was subjected to molecular analysis. In this mutant, a single nucleotide transition, C » T, in the chloroplast gene for ribosomal protein S12 alters codon 90 from proline to serine while the nucleotide sequence of the chloroplast 16 S rRNA gene is identical to that of the wild type. Mutant X/str ^R6 thus differs from several previously reported streptomycin resistant chloroplast mutants which are altered in the gene for 16 S rRNA.     

Effect of Foliar Application of Chitin and Chitosan Oligosaccharides on Photosynthesis of Maize and Soybean

On the first day after foliar application, chitosan pentamer (CH5) and chitin pentamer (CHIT5) decreased net photosynthetic rate (P _N) of soybean and maize, however, on subsequent days there was an increase in P _N in some treatments. CH5 caused an increase in maize P _N on day 3 at 10^–5 and 10^–7 M; the increases were 18 and 10 % over the control plants. This increase was correlated with increases in stomatal conductance (g _s) and transpiration rate (E), while the intercellular CO₂ concentration (C _i) was not different from the control plants. P _N of soybean plants did not differ from the control plants except for treatment CH5 (10^–7 M) which caused an 8 % increase on day 2, along with increased g _s, E, and C _i. On days 5 and 6 the CHIT5 treatment caused a 6–8 % increase in P _N of maize, which was accompanied by increases in g _s, E, and C _i. However, there was no such increase for soybean plants treated with CHIT5. In general, foliar application of high molecular mass chitin (CHH) resulted in decreased P _N, particularly for 0.010 % treated plants, both in maize and soybean. Foliar applications of chitosan and chitin oligomers did not affect (p > 0.05) maize or soybean height, root length, leaf area, shoot or root or total dry mass.     

Cooperative control of translational fidelity by ribosomal proteins in Escherichia coli

Summary The effect on translational fidelity of a particular mutation in the gene coding for protein S5 (rpxE) has been investigated. This mutation has the opposite effect of a restrictive strA mutation; in vivo, it relieves the restriction imposed by strA on the suppression of T4 nonsense mutants and results in hypersensitivity to streptomycin; in vitro, the presence of the altered S5 protein in 30S ribosomes results in increased intrinsic misreading. It is concluded that this mutation, ramC₃₁₉, acts as a ribosomal ambiguity mutation similar to certain mutations of protein S4 (ramA).     

Enhancement of product selectivity via enzyme immobilization in sequential degradation reactions of polymeric substrates

The balance equations pertaining to the modelling of a slap-shaped bead containing immobilized enzyme uniformly distributed which catalyzes the sequential reactions of degradation of a polymeric substrate were written and analytically solved in dimensionless form. The effect of the Thiele modulus on the selectivity of consumption of each multimeric product was studied for a simple case. Whereas plain diffusional regime leads to lower selectivities than plain kinetic regime, improvements in selectivity of species A _i relative to species A_i+1 may be obtained at the expense of higher Thiele moduli within a limited range when the diffusivity of A _i is larger than that of A _i +1, or when the pseudo first order kinetic constant describing the rate of consumption of A _i is lower than that of A_i+1.List of Symbols A _i polymeric substrate containing i monomeric subunits - C _i mol·m^–3 normalized counterpart of C _i - C _i mol·m^–3 concentration of substrate A _i - C _i,0 mol·m^–3 initial concentration of substrate A _i - C _i,0 normalized counterpart of C _i,0 - D _ap,i m²·s^–1 apparent diffusivity of substrate A _i - k _i s^–1 pseudo-first order rate constant - K _m,i mol·m^–3 Michaelis-Menten constant associated with substrate A _i - L m half-thickness of the catalyst slab - N number of monomeric subunits of the largest substrate molecule - Th Thiele modulus - V _i mol·m^–3·s^–1 rate of rection of substrate A _i - V_max,i mol·m^–3·s^–1 maximum rate of reaction under saturating conditions of substrate A _i - x m longitudinal coordinate - S _i,i+1 selectivity of enzyme with respect to substrates with consecutive numbers of monomeric subunits Greek Symbols _i ratio of maximum rates of reaction - _i ratio of apparent diffusivities     

Maximal oxygen uptake, maximal voluntary isometric contraction and physical activity in young Danish adults

In a randomly selected sample of 88 men and 115 women, aged 23–27 years from Denmark, maximal oxygen uptake ( O_2max), maximal voluntary isometric contraction (MVC) in four muscle groups and physical activity were studied. The O_2max was 48.0 ml · min^–1 kg^–1 and 39.6 ml · min^–1 · kg^–1 for the men and the women, respectively. The MVC was 10% lower than in a comparable group of Danes of the same age and height studied 35 years ago. Only in men was sports activity directly related to O_2max (ml · min^–1 · kg^–1; r=0.31, P<0.01). The MVC of the knee extensors was related to O_2max in the men (r=0.31, P<0.01), but there was no relationship between the other measurements of MVC and O_2max. In the women O_2max (ml · min^–1 · kg^–1) was only related to body size, i.e. body mass index, percentage body fat and body mass [(r= –0.47, –0.48 (both P<0.001) and –0.34. (P<0.01), respectively)]. There were differences in O_2max in the men, according to education and occupation. Blue collar workers and subjects attending vocational or trade schools in 1983 had lower O_2max and more of them were physically inactive. In the women differences were also found, but there was no clear pattern among the groups. More of the women participated regularly in sports activity, but more of the men were very active compared to the women.     

Gas Exchange of Carrot Leaves in Response to Elevated CO2 Concentration

Short-term responses of four carrot (Daucus carota) cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) to CO₂ concentrations (C _a) were studied in a controlled environment. Leaf net photosynthetic rate (P _N), intercellular CO₂ (C _i), stomatal conductance (g _s), and transpiration rate (E) were measured at C _a from 50 to 1 050 mol mol^–1. The cultivars responded similarly to C _a and did not differ in all the variables measured. The P _N increased with C _a until saturation at 650 mol mol^–1 (C _i= 350–400 mol mol^–1), thereafter P _N increased slightly. On average, increasing C _a from 350 to 650 and from 350 to 1 050 mol mol^–1 increased P _N by 43 and 52 %, respectively. The P _N vs. C _i curves were fitted to a non-rectangular hyperbola model. The cultivars did not differ in the parameters estimated from the model. Carboxylation efficiencies ranged from 68 to 91 mol m^–2 s^–1 and maximum P _N were 15.50, 13.52, 13.31, and 14.96 mol m^–2 s^–1 for Cascade, CC, Oranza, and RCC, respectively. Dark respiration rate varied from 2.80 mol m^–2 s^–1 for Oranza to 3.96 mol m^–2 s^–1 for Cascade and the CO₂ compensation concentration was between 42 and 46 mol mol^–1. The g _s and E increased to a peak at C _a= 350 mol mol^–1 and then decreased by 17 and 15 %, respectively when C _a was increased to 650 mol mol^–1. An increase from 350 to 1 050 mol mol^–1 reduced g _s and E by 53 and 47 %, respectively. Changes in g _s and P _N maintained the C _i:C _a ratio. The water use efficiency increased linearly with C _a due to increases in P _N in addition to the decline in E at high C _a. Hence CO₂ enrichment increases P _N and decreases g _s, and can improve carrot productivity and water conservation.     

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.     

Intracellular chloride and potassium ions in relation to excitability ofChara membrane

Summary Internodal cells ofChara australis were made tonoplast-free by replacing the cell sap with EGTA-containing media; then the involvement of internal Cl^– and K⁺ in the excitation of the plasmalemma was studied.[Cl^–] _i was drastically decreased by perfusing the cell interior twice with a medium lacking Cl^–. The lowered [Cl^–] _i was about 0.01mm. Cells with this low [Cl^–] _i generated action potential and showed anN-shapedV–I curve under voltage clamped depolarization like Cl^–-rich cells containing 13 or 29mm Cl^–.E _m at the peak of the action potential was constant at [Cl^–] _i between 0.01 and 29mm. The possibility that the plasmalemma becomes as permeable to other anions as to Cl^– during excitation is discussed.At [Cl^–] _i higher than 48mm, cells were inexcitable. When anions were added to the perfusion medium to bring the K⁺ concentration to 100mm, NO ₃ ^– , F^–, SO ₄ ^2– , acetate, and propionate inhibited the generation of action potentials like Cl^–, while methane sulfonate, PIPES, and phosphate did not inhibit excitability.The duration of the action potential depended strongly on the intracellular K⁺ concentration. It decreased as [K⁺] _i (K-methane sulfonate) increased. Increase in [Na⁺] _i (Na-methane sulfonate) also caused its decrease, although this effect was weaker than that of K⁺. The action of these monovalent cations on the duration of the action potential is the opposite of their action on the membrane from the outside (cf. Shimmen, Kikuyama & Tazawa, 1976,J. Membrane Biol. 30:249).     

Characterization of the non-photochemical quenching of chlorophyll fluorescence that occurs during the active accumulation of inorganic carbon in the cyanobacterium Synechococcus PCC 7942

Previous work has shown that the maximum fluorescence yield from PS 2 of Synechococcus PCC 7942 occurs when the cells are at the CO₂ compensation point. The addition of inorganic carbon (C_i), as CO₂ or HCO₃ ^–, causes a lowering of the fluorescence yield due to both photochemical (q_p) and non-photochemical (q_N) quenching. In this paper, we characterize the q_N that is induced by C_i addition to cells grown at high light intensities (500 mol photons m^–2 s^–1). The C_i-induced q_N was considerably greater in these cells than in cells grown at low light intensities (50 mol photons m^–2 s^–1), when assayed at a white light (WL) intensity of 250 mol photons m^–2 s^–1. In high-light grown cells we measured q_N values as high as 70%, while in low-light grown cells the q_N was about 16%. The q_N was relieved when cells regained the CO₂ compensation point, when cells were illuminated by supplemental far-red light (FRL) absorbed mainly by PS 1, or when cells were illuminated with increased WL intensities. These characteristics indicate that the q_N was not a form of energy quenching (q_E). Supplemental FRL illumination caused significant enhancement of photosynthetic O₂ evolution that could be correlated with the changes in q_p and q_N. The increases in q_p induced by C_i addition represent increases in the effective quantum yield of PS 2 due to increased levels of oxidized Q_A. The increase in q_N induced by C_i represents a decrease in PS 2 activity related to decreases in the potential quantum yield. The lack of diagnostic changes in the 77 K fluorescence emission spectrum argue against q_N being related to classical state transitions, in which the decrease in potential quantum yield of PS 2 is due either to a decrease in absorption cross-section or by increased spill-over of excitation energy to PS 1. Both the C_i-induced q_p (t _0.5<0.5 s) and q_N (t _0.51.6 s) were rapidly relieved by the addition of DCMU. The two time constants give further support for two separate quenching mechanisms. We have thus characterized a novel form of q_N in cyanobacteria, not related to state transitions or energy quenching, which is induced by the addition of C_i to cells at the CO₂-compensation point.Abbreviations BTP- 1,3-bis[tris(hydroxymethyl)-methylaminopropane] - Chl- chlorophyll - C_i- inorganic carbon (CO₂+HCO₃ ^–+CO₃ ^2–) - DCMU- 3-(3,4-dichlorophenyl)-, 1-dimethylurea) - F- chlorophyll fluorescence measured at any time in the absence of a saturating flash - F_o- chlorophyll fluorescence with only the weak modulated measuring beam on - F_M'- chlorophyll fluorescence during a saturating flash - F_M- maximum chlorophyll fluorescence, measured in the presence of WL and FRL at the CO₂-compensation point or in the presence of DCMU - F_V- variable fluorescence (= F_M'–F₀) - FRL- supplemental illumination with far red light - MB- modulated measuring beam of the PAM fluorometer - MV- methyl viologen - PAM- pulse amplitude modulation - PFD- incident photon flux density - PS 1, 2- Photosystems 1 and 2 - Q_A- primary electron-accepting plastoquinione of PS 2 - q_N- non-photochemical quenching of chlorophyll fluorescence - q_p- photochemical quenching of chlorophyll fluorescence; rubisco-ribulose bisphosphate carboxylase/oxygenase - SF- saturating flash (600 ms duration) - WL- white light illumination