Regulation of biosynthesis of pesticidal metabolic complexes inStreptomyces griseus

The complex of pesticidal metabolites produced byStreptomyces griseus LKS-1 consists of a peptide antibiotic (A), nonactic acids (B), macrotetrolides (C), pyrrolizines (D), and of cycloheximide. The latter unwanted phytotoxic compound was eliminated by treatment with mutagens. Combined approaches, including both genetic and physiological manipulations, resulted in the following alterations in the biosynthetic capacity: (1) A more than 80-fold increase in the production of C under a substantial decrease in the yields ofA, B andD, the ratio of the components ofC being steered toward the required more active ones; (2) a more than 300-fold increase in the production ofB under suppression of the formation ofA andC: (3) a 10-fold increase in the yields ofD under suppression ofA andC; (4 a significant increase in the yields ofA with eliminatingB, C andD. The level of inorganic phosphate in fermentation media and the sensitivity of the organism to carbon catabolite repression were important factors participating in the regulation of the above biosynthetic processes.     

Foliar physiology of yellow-poplar ( Liriodendron tulipifera L.) exposed to O3 and elevated CO2 over five seasons.

The chronic effects of ozone (O₃) alone or combined with elevated carbon dioxide (CO₂) on the foliar physiology of unfertilized field-grown yellow-poplar ( Liriodendron tulipifera L.) seedlings were studied from 1992 to 1996. Within open-top chambers, juvenile trees were exposed to the following: charcoal-filtered air (CF); 1× ambient ozone (1XO₃); 1.5× ambient ozone (1.5XO₃); 1.5× ambient ozone plus 700 ppm carbon dioxide (1.5XO₃+CO₂); or chamberless open-air (OA). Seasonal 24-h mean ambient O₃ concentrations ranged from 32 to 46 ppm over the five seasons. Averaged over 5 years, midseason net photosynthesis at saturating light ( A _sat) was reduced by 14% ( P =0.029) and stomatal conductance ( g _s) was reduced, albeit non-significant, by 13% ( P =0.096) in upper canopy foliage exposed to 1.5XO₃-air relative to CF controls. There were no significant differences over the 5 years in A _sat and g _s between trees grown in 1XO₃- and 1.5XO₃-air. Our results support the hypothesis that the magnitude of O₃ effects on A _sat and g _s decreases as saplings age. When averaged over the five seasons of exposure, total chlorophyll concentration ( chl) was not significantly affected by exposure to elevated O₃; however, in 1.5XO₃+CO₂-air, foliar chl was reduced by 33% relative to all others ( P <0.001). In 1.5XO₃+CO₂-air, A _sat was 1.4–1.9 times higher ( P <0.001) and g _s was 0.7 times lower ( P =0.022) than all others. O₃ uptake in juvenile trees exposed to elevated O₃ plus elevated CO₂ (1.5XO₃+CO₂-air) was most comparable to trees exposed to ambient air (1XO₃) throughout the study. These findings suggest that elevated CO₂ may minimize the negative effects of O₃ by reducing O₃ uptake through decreased stomatal conductance.     

EMG-biofeedback reduction of tension headache

The biofeedback literature affirms the therapeutic efficacy of EMG-biofeedback-assisted relaxation for the treatment of tension headache. However, this form of therapy has failed to focus on the role of cognitive variables in the control and perception of tension headache. The present case study provides a prototype treatment combining cognitive behavior-modification procedures with EMG-biofeedback training to treat a subject with chronic tension headache. Phase I, baseline, involved collecting mean EMG and daily headache activity, emphasizing specification of environmental stressors. Phase II, cognitive skills-training, focused on:(1) identifying negative self-statements(cognitions) related to stressors, and(2) training the subject to replace negative self-statements with coping self-instructions. This treatment resulted in a 33% headache reduction over baseline, with no concomitant changes in frontalis EMG. Phase III, EMG-biofeedback training, resulted in a 38% reduction in mean EMG level and a 66% reduction in mean headache activity when compared to baseline. The results suggest the importance of attending to cognitive factors in the treatment of tension headache.This paper was presented at the 6th annual meeting of the Biofeedback Research Society, Monterey, California, 1975.     

The relative effectiveness of three techniques to induce the trophotropic response

The purpose of this study was to examine the relative effectiveness of electromyographic biofeedback training(EMG BFT), remeditation, and progressive muscle relaxation(PMR) in eliciting a relaxation or trophotropic response as measured by frontalis muscle tension, heart rate, electrodermal response, respiration rate, and skin temperature. Fifty-four college students were randomly assigned to one of five groups:(1) control,(2) placebo control,(3) EMG BFT,(4) meditation,(5) PMR. After baseline measures were obtained subjects were trained in 10 30-minute training sessions and posttested. Comparisons by ANOVAs indicated there was a significant decrease in muscle tension in the EMG BFT and meditation groups and significant decreases in respiration rate in the meditation and PMR groups. No other changes were attributed to treatment.     

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.     

The Structure of Gibberellin A23 and the Biological Properties of 3,13-Dihydroxy C20-Gibberellins

Two aldehydic C₂₀-gibberellins, L-2 and L-4, were isolated from the immature fruits of yellow lupine (Lupinus luteus L.). L-2 was shown to have the structure II and named gibberellin A₂₃. L-4 was identified as gibberellin A₁₉(VI). Two new C₂₀-gibberellins, tentatively called 3,13-dihydroxy GA₁₅(IV) and 13-hydroxy GA₁₅(VIII), were derived from gibberellins, A₂₃ and A₁₉, respectively. The biological activities of four 3,13-dihydroxy C₂₀-gibberellins-GA₁₈(I), GA₂₃(II), GA₂₈(III) and 3,13-dihydroxy GA₁₅(IV), which were isolated from the fruits except for 3,13-dihydroxy GA₁₅—were compared in six gibberellin bioassays.     

Aerobic oxygenation of organic sulfides using diruthenium activators

Diruthenium compounds supported by carboxylate or mixed carboxylate/carbonate bridging ligands were found to be active catalysts for aerobic oxygenation of organic sulfides. Ru₂(OAc)₃(CO₃) (A), Ru₂(O₂CCF₃)₃(CO₃) (B) and Ru₂(OAc)₄Cl (C) promote the conversion of organic sulfide to sulfoxide, and subsequently sulfone in an oxygen atmosphere at ca. 90 °C. The order of catalytic activity is A > B ? C. Catalytic reactions are operative in a number of 1:1 co-solvent-H₂O combinations, and the highest reactivity was found in aqueous media.     

Crystallographic characterization of the α,γ C12 helix in hybrid peptide sequences

The solid‐state conformations of two αγ hybrid peptides Boc‐[Aib‐γ⁴(R)Ile]₄‐OMe 1 and Boc‐[Aib‐γ⁴(R)Ile]₅‐OMe 2 are described. Peptides 1 and 2 adopt C₁₂‐helical conformations in crystals. The structure of octapeptide 1 is stabilized by six intramolecular 4 → 1 hydrogen bonds, forming 12 atom C₁₂ motifs. The structure of peptide 2 reveals the formation of eight successive C₁₂ hydrogen‐bonded turns. Average backbone dihedral angles for αγ C₁₂ helices are peptide 1 , Aib; φ (°) = ?57.2 ± 0.8, ψ (°) = ?44.5 ± 4.7; γ⁴(R)Ile; φ (°) = ?127.3 ± 7.3, θ₁ (°) = 58.5 ± 12.1, θ₂ (°) = 67.6 ± 10.1, ψ (°) = ?126.2 ± 16.1; peptide 2 , Aib; φ (°) = ?58.8 ± 5.1, ψ (°) = ?40.3 ± 5.5; ψ⁴(R)Ile; φ (°) = ?123.9 ± 2.7, θ₁ (°) = 53.3 θ 4.9, θ ₂ (°) = 61.2 ± 1.6, ψ (°) = ?121.8 ± 5.1. The tendency of γ⁴‐substituted residues to adopt gauche–gauche conformations about the C^α–C^β and C^β–C^γ bonds facilitates helical folding. The αγ C₁₂ helix is a backbone expanded analog of α peptide 3₁₀ helix. The hydrogen bond parameters for α peptide 3₁₀ and α‐helices are compared with those for αγ hybrid C₁₂ helix. Copyright © 2016 European Peptide Society and John Wiley & Sons.     

Physiological and agronomical responses of common bean subjected to tryptophol

With the increasing global demand for food, fuel and fibre, the use of plant growth regulators in agriculture has become an agricultural practice aimed to improve physiological and productive responses. Our work aimed to evaluate the effect of tryptophol (Tol), a precursor of auxin, on common bean (Phaseolus vulgaris L.). The experiment was conducted in pots under greenhouse conditions, where we evaluated the Tol effect on bean crop under two different application forms: T_Soil – soil application of Tol (4.10^?4 mg L^?1) and T_Leaf – leaf tryptophol application (4.10^?4 mg L^?1), plus a reference treatment (0 mg L^?1 of Tol). We analysed the variables: shoot fresh and dry matter; root dry matter, area and volume; leaf macro and micronutrients; CO₂ net assimilation rate (A); stomatal conductance (g_S); internal CO₂ concentration (C_I); foliar transpiration (E); photosynthetic pigment content and some crop production attributes. The application of Tol through the foliar pathway proved to be more advantageous because it improved the shoot fresh and dry matter, increased the root volume and area, favoured less foliar transpiration and improved the length of pods, while the application of Tol in soil induced higher nitrogen accumulation in leaves. Our observations allow the characterization of Tol as a bioactive metabolite, suggesting an important potential for use in agricultural systems.     

Hydrophobicity of biosurfaces as shown by chemoreceptive Thresholds inTetrahymena,Physarum andNitella

Summary Responses (chemotaxis and changes in membrane potential) ofTetrahymena, Physarum, andNitella against aqueous solution of homologous series ofn-alcohols,n-aldehydes andn-fatty acids were studied for clarifying the hydrophobic character of chemoreceptive membranes. Results were: (1) All organisms studied responded to homologous compounds examined when the concentration of these chemicals exceeded their respective threshold,C _th , and the response,R, were expressed approximately asR= log (C/C _th ) forC>C _th , (2) Increase of the length of hydrocarbon chain in homologues decreasedC _th . Plots of logC _th against the number of carbon atoms,n, inn-alcohols,n-aldehydes andn-fatty acids showed linear relationships as represented by logC _th =–An+B. A andB are positive constants for respective functional end groups of the chemicals and biological membranes used. The above empirical equation was interpreted in terms of the partition equilibrium of methylene groups between bulk solution and membrane phase. ParameterA was shown to be a measure of hydrophobicity of the membrane, andB represented the sensitivity of chemoreception of the membrane. (3) Thresholds,C _th , for various hydrophobic reagents were compared with those of human olfactory reception,T. Plots of logT against logC _th fell on straight lines for respective organisms with different slopes which were proportional to parameterA.     

Ribonuclease activities in bean roots

Vicia faba meristematic and elongating root cells (zones 0–4 and 10–20 mm) contained one nuclease (A₁) and four ribonucleases (A₂, A₃, C₁, C₂). When the overall activity of each enzyme was expressed per cell, the elongating cells contained 4-, 4-, 4-, 10- and 17-fold more activity than meristematic cells for A₁, C₁, C₂, A₂ and A₃, respectively.     

The utility and performance of near-infra red spectroscopy in simultaneous monitoring of multiple components in a high cell density recombinant Escherichiacoli production process

Bioprocess optimisation is often limited by an inability to measure biomass, nutrient and by-product concentrations in a time frame which allows process adjustments. Near-infrared (near-IR) spectroscopy can potentially be used to measure each of these components within 2 minutes of sampling, using an unprocessed whole broth sample. In the present study the use of near-IR spectroscopy for at-line (rapid off-line) monitoring of biomass, glycerol, ammonium, and acetate in a recombinant Escherichia coli fed batch process was investigated. The following robust correlation models were developed for these analytes using multiple least squares linear regression (MLR): [Glycerol],gl^?1 =15.957 ? 2219.270^* A(λ₂₂₇₄)?1705.041^* A(λ₂₁₇₂); [Acetate],gl^?1=27.683 ?1757.258^* A(λ₂₂₅₄)+296.903^* A(λ₂₃₄₀)?21.325^* A (λ₆₂₀); [Ammonium],gl^?1=?1310.502?47912.960^* A (λ₂₁₄₈)?135149.300^* A(λ₁₇₈₂)?27636.200^* A (λ₈₃₀); and [Biomass],gl^?1=14.034?3.548^* A(λ₆₀₂/λ₁₁₃₄) ?4286.050^* A(λ₉₂₈). Using these models permitted rapid simultaneous analysis of all four analytes. This improved monitoring capability was used to develop a high cell density recombinant E. coli fed-batch process in which ammonium and acetate accumulation were minimised leading to higher cell densities. By manipulation of the C?:?N ratio in the complex feed, the toxic effects of ammonium accumulation upon the organism were minimised, thereby facilitating the application of a carbon limited feeding strategy. The effect of these C?:?N ratio medium changes, upon the near-IR measurement capability, was investigated. In this process, near-IR spectroscopy has been shown to be a powerful, accurate and precise method for simultaneously measuring several key process variables. Its accuracy, precision and utility for at-line measurement and control are evaluated, particularly in reference to processes where the initial medium composition may vary, leading to changes in the chemical matrix. The potential of near-infra red for online analysis and control is discussed.     

Tension headaches

In order to assess the effectiveness of verbal relaxation instructions and EMG relaxation training on the relief of tension headaches, 18 medically documented tension-headache sufferers were randomly assigned to one of three conditions:(1) Jacobson-Wolpe autogenic-relaxation training,(2) EMG relaxation training, or(3) EMG relaxation training combined with Jacobson-Wolpe autogenic instructions. The two EMG-assisted groups showed significantly better results, compared to the verbal group, in terms of reduction of headache activity and the rate at which reduction took place. Thus, EMG-assisted relaxation procedures seem the treatment method of choice for relief of tension headaches.     

Scandium and yttrium complexes of a heteroscorpionate [N,N,O]-donor-set ligand: Synthesis, characterization and catalytic activity in ethylene polymerization

New scandium and yttrium complexes ScL₂(bpzmp)(THF) {L = Cl (1); L = CH₂Si(CH₃)₃ (3)}, YL₂(bpzmp) {L = Cl (2); L = OTf (5)} and Y(CH₂SiMe₃)₂(bpzmp)(THF) (4) bearing the heteroscorpionate bpzmp ligand {bpzmp = (3,5-^tBu₂-2-phenoxo)bis(3,5-Me₂-pyrazol-1-yl)methane} have been synthesized and characterized by means of NMR and Mass spectroscopy. The tridentate monoanionic ligand resulted κ³-coordinated to the metal via the oxygen and both the sp² nitrogen atoms of the heterocycles, producing complexes in C_S symmetry.The behavior of 1-4 in ethylene polymerization was investigated after proper activation with different activating agents. Complex 4, in combination with the Brönsted or Lewis acids [PhNMe₂H][B(C₆F₅)₄] or [Ph₃C][B(C₆F₅)₄], produced linear high molecular weight polyethylene in good yield.     

FOUR PROTEIN POLYMORPHISMS IN PIGEON BRAIN EXTRACTS DETECTED BY TWO-DIMENSIONAL GEL ELECTROPHORESIS

Abstract— Proteins of the brain extracts of 85 individual pigeons (Columba livia) were mapped by two-dimensional gel electrophoresis. The method is a modification of O'Farrell 'S technique and separates proteins first by charge and then by molecular weight. There were three proteins, A, B and D which had each a variant form. The positions of these six proteins on the gel corresponded to the following pH values and molecular weight values: protein A₁, 6.4/43,000; A₂, 6.6/43,000; B₁, 5.7/41,000; B₂, 5.8/40,000; D₁, 6.2/22,000; D₂, 6.2/21,000. The variants are genetically determined, since protein A, B and D each occurred in three phenotypes (A₁, A₁A₂ and A₂; B₁, B₁B₂ and B₂; D₁, D₁D₂ and D₂) corresponding to the three possible genotypes. From the observed frequencies of the phenotypes the following allele frequencies were calculated: allele A₁, 72%; A₂, 28%; B₁, 15%; B₂, 85%; D₁, 74%; D₂, 26%. A fourth protein named C occurred in four different forms (C₁, 7.2/37,000; C₂, 7.2/36,000; C₃, 7.1/37,000; C₄, 7.1/36,000) and six phenotypes (C₁, C₁C₂, C₂, C₁C₃, C₂C₃ and C₄C₃). This polymorphism is also interpreted as being genetically determined. The four alleles coding for the four protein C forms had the following frequencies: allele C₁, 62%; C₂, 27%; C₃, 10.5%; C₄, 0.5%.     

Mutationsversuche an Kulturpflanzen

Zusammenfassung Die im Jahre 1951 zunächst allgemein gegen die RassenA undD nachgewiesene Mehltauresistenz von 8 röntgeninduzierten Wintergerstenmutanten ist differenziert und erweitert worden. Mut. 501 ist gegen 10 von 14 untersuchten Rassen der RassengruppenA, D, B undC resistent (A ₁,A ₂,A ₃,A ₄,D ₁,D ₃,B ₂,B ₃,C ₂,C ₃) und gegen vier anfällig (B ₅,B ₆,C ₄,C ₅). Die übrigen 7 Mutanten 511, 512, 513, 514, 515, 520 und 525a zeigen übereinstimmendes Resistenzverhalten: Von den 16 untersuchten Rassen der RassengruppenA, D, B, C sind die Mutanten gegen acht resistent (A ₂,A ₅,D ₁,B ₂,B ₃,B ₇,C ₂,C ₄) und für die anderen acht anfällig (A ₁,A ₃,A ₄,D ₃,B ₅,B ₆,C ₃,C ₅). Die Mutanten stellen durch diese ihnen eigentümliche, bisher nicht bekannte Kombination der Resistenz gegen verschiedene Rassen vonErysiphe graminis hordei wertvolle Differentialwirte dar.Die Genetik der Mehltauresistenz ist bei den acht Mutanten für die RasseA ₂ untersucht worden. Zwei unabhängige Gene sind nachgewiesen: eines bedingt die Resistenz von Mut. 501 (Obsistens) und ein zweites diejenige der übrigen sieben Mutanten 511, 512, 513, 514, 515, 520, 525a (Resistens). Diese sieben Mutanten sind also bzgl. der Mehltauresistenz genetisch identisch, während Mut. 501 heterogen ist. Vererbt wird die Mehltauresistenz bei allen acht Mutanten monogen und vollständig bzw. unvollständig dominant. Lediglich Mut. 520 scheint sich labil zu verhalten. alle Mutanten zeigen zusätzliche Merkmalsänderungen.     

Gene analysis in rye

A number of recessive characters in rye were studied, seven of which in detail: anthocyanin-less (a); waxless (w); brittle (b); canary (c); yellow-green (yg) and two dwarfs (d ₁ end ₂). All are inherited monofactorially against the normal dominant character.Yellow-green showed a small but significant shortage of homozygous recessives, ascribed mainly to classification difficulties.For the study of the linkage relationships many, though not all combinations were made. Linkage betweend ₁ andyg, although seemingly significant, was considered unproven and improbable. Linkage betweend ₁ and a gene for prostrate growth was found probable. Linkage betweend ₁ andc was established, with a crossover percentage of 31. Here the situation was complicated by apparent absence of double recessives, best explained by cryptomeric masking (recessive epistasy) of the segregationD ₂-d ₂ bycc. If lethality of the double recessive class is assumed, the crossover percentage is 23.7.     

Models of the bis-histidine-coordinated ferricytochromes: Mössbauer and EPR spectroscopic studies of low-spin iron(III) tetrapyrroles of various electronic ground states and axial ligand orientations

The EPR and magnetic Mössbauer spectra of a series of axial ligand complexes of tetrakis(2,6-dimethoxyphenyl)porphyrinatoiron(III), [(2,6-(OMe)₂)₄TPPFeL₂]⁺, where L=N-methylimidazole, 2-methylimidazole, or 4-(dimethylamino)pyridine, of one axial ligand complex of tetraphenylporphyrin, the bis(4-cyanopyridine) complex [TPPFe(4-CNPy)₂]⁺, and of one axial ligand complex of tetraphenylchlorin, [TPCFe(ImH)₂]⁺, where ImH=imidazole, have been investigated and compared to those of low-spin Fe(III) porphyrinates and ferriheme proteins reported in the literature. On the basis of this and previous complementary spectroscopic investigations, three types of complexes have been identified: those having (d_xy)²(d_xz,d_yz)³ electronic ground states with axial ligands aligned in perpendicular planes (Type I), those having (d_xy)²(d_xz,d_yz)³ electronic ground states with axial ligands aligned in parallel planes (Type II), and those having the novel (d_xz,d_yz)⁴(d_xy)¹ electronic ground state (Type III). A subset of the latter type, with planar axial ligands aligned parallel to each other or strong macrocycle asymmetry that yield rhombic EPR spectra, cannot be created using the porphyrinate ligand. Type I centers are characterized by "large g_max" EPR spectra with g>3.2 and well-resolved, widely spread magnetic Mössbauer spectra having A_zz/g_NN>680 kG, with A_xx negative in sign but much smaller in magnitude than A_zz, while Type II centers have well-resolved rhombic EPR spectra with g_zz=2.4–3.1 and also less-resolved magnetic Mössbauer spectra, and usually have A_zz/g_NN in the range of 440–660 kG (but in certain cases as small as 180 kG) and A_xx again negative in sign but only somewhat smaller (but occasionally larger in magnitude) than A_zz, and Type III centers have axial EPR spectra with g_┴2.6 or smaller and g_║<1.0–1.95, but often not resolved, and less-resolved magnetic Mössbauer spectra having A_zz/g_NN in the range of 270–400 kG, and A_xx again negative in sign but much smaller in magnitude than A_zz. An exception to this rule is [TPPFe(4-CNPy)₂]⁺, which has A_xx/g_NN=–565 kG, A_yy/g_NN=629 kG, and A_zz/g_NN=4 kG. A subset of Type II complexes (Type II) have rhombicities (V/) much greater than 0.67 and A_zz/g_NN ranging from 320 to 170 kG, with A_xx also negative but with the magnitude of A_xx significantly larger than that of A_zz. These classifications are also observed for a variety of ferriheme proteins, and they lead to linear correlations between A_zz and either A_xx, g_zz, or V/ for Types I and II (but not for A_zz versus V/ for Type II). Not enough data are yet available on Type III complexes to determine what, if any, correlations may be observed.Abbreviations CCP cytochrome c peroxidase - 4-CNPy 4-cyanopyridine - cyt cytochrome - EFG electric field gradient - ESEEM electron spin echo envelope modulation - ImH imidazole - Mb myoglobin - MCD magnetic circular dichroism - 2-MeImH 2-methylimidazole - N-MeIm N-methylimidazole - 3NH₂PzH 3-aminopyrazole - 4-NMe₂Py 4-(dimethylamino)pyridine - [2,6-(OMe)₂]₄TPP dianion of tetrakis(meso-2,6-dimethoxyphenyl)porphyrin - OEiBC dianion of octaethylisobacteriochlorin - OEP dianion of octaethylporphyrin - PPIX dianion of protoporphyrin IX - Py pyridine - TMP dianion of meso-tetramesitylporphyrin - TPC dianion of meso-tetraphenylchlorin - TPP dianion of meso-tetraphenylporphyrin - 2,6-XylylNC 2,6-xylyl isocyanide     

Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C3–C4 grassland

Atmospheric CO₂ (C_a) has risen dramatically since preglacial times and is projected to double in the next century. As part of a 4‐year study, we examined leaf gas exchange and photosynthetic acclimation in C₃ and C₄ plants using unique chambers that maintained a continuous C_a gradient from 200 to 550 µmol mol^?1 in a natural grassland. Our goals were to characterize linear, nonlinear and threshold responses to increasing C_a from past to future C_a levels. Photosynthesis (A), stomatal conductance (g_s), leaf water‐use efficiency (A/g_s) and leaf N content were measured in three common species: Bothriochloa ischaemum, a C₄ perennial grass, Bromus japonicus, a C₃ annual grass, and Solanum dimidiatum, a C₃ perennial forb. Assimilation responses to internal CO₂ concentrations (A/C_i curves) and photosynthetically active radiation (A/PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with C_a in all species (P < 0.05). S. dimidiatum and B. ischaemum had greater carboxylation rates for Rubisco and PEP carboxylase, respectively, at subambient than superambient C_a (P < 0.05). To our knowledge, this is the first published evidence of A up‐regulation at subambient C_a in the field. No species showed down‐regulation at superambient C_a. Stomatal conductance generally showed curvilinear decreases with C_a in the perennial species (P < 0.05), with steeper declines over subambient C_a than superambient, suggesting that plant water relations have already changed significantly with past C_a increases. Resource‐use efficiency (A/g_s and A/leaf N) in all species increased linearly with C_a. As both C₃ and C₄ plants had significant responses in A, g_s, A/g_s and A/leaf N to C_a enrichment, future C_a increases in this grassland may not favour C₃ species as much as originally thought. Non‐linear responses and acclimation to low C_a should be incorporated into mechanistic models to better predict the effects of past and present rising C_a on grassland ecosystems.