Incorporation of radioactive molybdenum into protein during nitrate reductase formation and effect of molybdenum on nitrate reductase and diaphorase activities of spinach (Spinacea oleracea L.)

Spinach plants grown without molybdenum lack nitrate reductaseand when plants are deprived of nitrate existing activity islost. Transfer of molybdenum-deficient plants to a solutioncontaining (NH₄)₂⁹⁹MoO₄) or nitrate-starved plants to NaNO₃solution induced enzyme activity in 24 hr. After purificationby selective adsorption, precipitation and disc electrophoresis,the protein from molybdenum-deficient plants given ⁹⁹Mo showedradioactivity only where nitrate reductase was revealed on theacrylamide gel. Molybdenum was similarly selectively concentratedinto the enzyme as a result of induction by nitrate in plantsgrown with sub-optimal molybdenum supply in order to minimizeeffects of isotope dilution on measurement of ⁹⁹Mo incorporation. There was no exchange in vitro between ⁹⁹Mo and purified activeenzyme in the resting state over 18 hr at 4°C, or with functioningenzyme held at room temperature for 24 hr. There was evidenceeither for possible in vivo exchange of ⁹⁹Mo andenzyme boundMo or for slight synthesis of fresh enzyme under conditionsof net loss of enzyme in nitrate starved plants. Five NADH₂ and two NADPH₂ reactive diaphorases which could beseparated by electrophoresis were present in extracts. Onlyone of these having strong NADH₂ and weak NADPH₂ activity wasdirectly associated with nitrate reductase. The same complexalso showed the only benzyl viologen (BV.) reactive nitratereductase. Nitrate reductase in spinach is therefore considered to be amolybdenum-dependant and molybdenum-containing protein in whichNADH₂ (with weak NADPH₂) and BVelectron donor functions anddiaphorase/reductase activities remain closely associated duringpurification and electrophoresis. The techniques provide a simple means for the production andpurification of enzyme containing radioactively labelled Moapplicable to investigations on the structure of the enzyme. (Received January 16, 1971; )     

Stimulatory Effect of Chloride Ions on NADP Malic Enzyme from Leaves of two C4 Species of Cyperus

NADP malic enzyme (EC 1.1.1.40 [EC] ) from leaves of two C₄ speciesof Cyperus (C. rotundus and C. brevifolius var leiolepis) exihibiteda low level of activity in an assay mixture that contained lowconcentrations of Cl^–. This low level of activity wasmarkedly enhanced by increases in the concentration of NaClup to 200 mM. Since the activity of NADP malic enzyme was inhibitedby Na₂SO₄ and stimulated by relatively high concentration ofTris-HCl (50–100 mM, pH 7–8), the activation ofthe enzyme by NaCl appears to be due to Cl^–. Variationsin the concentration of Mg²⁺ affected the K_A (the concentrationof activator giving half-maximal activation) for Cl^–,which decreased from 500 mM to 80 mM with increasing concentrationsof Mg²⁺ from 0.5 mM to 7 mM. The K_m for Mg²⁺ was decreased from7.7 mM to 1.3 mM with increases in the concentration of NaClfrom zero to 200 mM, although the increase of V_max was not remarkable.NADP malic enzyme from Cyperus, being similar to that from otherC₄ species, was able to utilize Mn²⁺. The K_m for Mn²⁺ was 5mM, a value similar to that for Mg²⁺. The addition of 91 mMNaCl markedly decreased the K_m for Mn²⁺ to 20 +M. NADP malicenzyme from Setaria glauca, which contains rather less Cl^–than other C₄ species, was inactivated by concentrations ofNaCl above 20 mM, although slight activation of the enzyme wasobserved at low concentrations of NaCl at pH7.6. (Received February 20, 1989; Accepted June 12, 1989)     

Characterization of the vacuolar-type H+-ATPase from guard cell protoplasts of Commelina

Characteristics of the vacuolar-type (V-type) H⁺-ATPase fromguard cell protoplasts of Commelina communis L. were investigatedusing a linked enzyme assay and nitrate inhibition as a diagnosticindicator of the enzyme activity. ATPase activity was completelyinhibited by about 50 mol m^–3 nitrate and activity wasoptimal near pH 8.0. The temperature optimum for activity wasabout 37 C and an Arrhenius plot indicated changes in activationenergy for the ATPase at 15C and possibly at about 30 C. Theenzyme was stimulated by Cl^– while Ca²⁺ inhibited activity(l₅₀ = 1.5 mol m^–3). The apparent K_m (MgATP) was 0.62mol m^–3. Incubation of guard cell protoplasts for up to 5 h in 50 µMabscisic acid (ABA) or 25µM fusicoccin (FC) did not affectsubsequent ATPase activity. In vitro assays with FC or ABA alsodid not affect enzyme activity. Activity was not affected bylight or potassium ferricyanide, two factors which are knownto influence stomatal activity. Beticoline was a potent inhibitorof activity (l₅₀ = 50 µM) while DCCD was less effective(l₅₀ = 90µM). On chlorophyll, protein and protoplast bases, V-type ATPaseactivity was greater in guard cell protoplasts than mesophyllcell protoplasts by 66, 13.9 and 1.9, respectively. On atonoplast surface area basis the enzyme activity was 5.6 timeshigher in guard cell protoplasts than in mesophyll cell protoplasts Thus, although the characteristics of the V-type, H ⁺-ATPaseof GCP are very similar to those found in other cell types,rates of activity and probably tonoplast enzyme density aremuch greater in guard cell protoplasts than mesophyll cell protoplastsof C. communis which corresponds with the large and rapid ionfluxes across the tonoplast associated with stomatal movements Key words: Guard cell protoplasts, stomata, V-type H ⁺-ATPase     

Activation of Ribulose Bisphosphate Carboxylase Purified from Wheat Leaves

A stable freeze-dried powder was prepared of partly purifiedribulose bisphosphate carboxylase from wheat leaves. As withpreparations from other leaves it is necessary to incubate theenzyme with Mg^2$ and CO₂ to achieve maximum activity. At 25°C this activity was 0.75 IU mg^–1 protein for a preparationactivated at 50 °C for 10 min; the K_m for CO₂ was 15 µM. The time for reactivation of enzyme that had been inactivatedthrough the absence of CO₂ and Mg^2$ was influenced by the lengthof the inactivating treatment. After a short inactivation periodthe enzyme was reactivated within a few minutes, whereas aftera longer period several hours were needed. Enzyme in the latterstate had some properties in common with enzyme inactivatedby lower temperatures but in the presence of CO₂ and Mg^2$. Theenzyme kinetic characteristics are similarly affected by bothkinds of inactivation; the maximum velocity is decreased butthe affinity for CO₂ is not affected. Reactivation following a long inactivating treatment becomesmore dependent on Mg^2$ concentration as the temperature is increasedfrom 0 to 20 °C.     

RNA Polymerase Activity During Breakage of Seed Dormancy by Low Temperature Treatment of Fruits of Acer platanoides (Norway Maple)

Slater, R. J. and Bryant, J. A. 1987. RNA polymerase activityduring breakage of seed dormancy by low temperature treatmentof fruits of Acer platanoides (Norway maple).—J. exp.Bot. 38:1026–1032. Endogenous RNA polymerase activity has been characterized innuclei isolated from embryo axes of Acer platanoides. Optimalactivity was recorded at 4·0 mol m^–3 MgCl₂ and50 mol m^–3 (NH₄)₂SO₄ and total activity could be inhibitedby up to 30% by -amanitin. Stratification of fruits leads toa stimulation of RNA polymerase activity. A minimum of 3 d coldtreatment is required with at least 3-fold stimulation recordedafter 10 d at 4°C. The increased enzyme activity is resistantto -amanitin suggesting an effect on RNA polymerase I. Key words: Acer platanoides, RNA polymerase, seed dormancy     

Germination of Sporangia of Phytophthora palmivora (Butl.) Butl.

Sporangia of Phytophthora palmivora germinated by either forminggerm tubes or producing zoospores. Two distinct modes of germ-tubedevelopment have been described. Sporangia in distilled waterformed zoospores at 10–34°C with an optimum at 22°Cbut germinated by means of germ tubes at 30 and 34°C only.Zoospore formation was inhibited to varying degrees by cocoapod extract, I.0 per cent (w/v) peptone and yeast extract, 100–500µg1^-1 thiamine, and by very low concentrations of severalamino acids, carbohydrates, and inorganic salts. Germ-tube formation was encouraged at 22°C by 1'0 per cent(w/v) peptone and yeast extract, by cocoa pod extract and exudate,10mM CaCl2, 1–10 mM MgSO₄. 7H₂O, 0.5 per cent (w/v) fructose,galactose, glucose, lactose, maltose, and sucrose, by 100 ppmarginine, aspartic acid, glutarnic acid, glycine, leucine, andtryptophane, and by 100–500 µg 1^-1 thiamine.     

Preliminary characterization of 1-aminocyclopropane-1-carboxylate oxidase properties from embryonic axes of chick-pea (Cicer arietinum L.) seeds

For a deeper understanding of the germination of chick–pea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS0₄, 6 mM Na–ascorbate,1 mM ACC, 20% 0₂, 3% CO₂ , and 10%glycerol) this enzyme was5–fold more active than under the conditions we used initiallyin the present work. The enzyme has the following K_m: 28 µMfor ACC (approximately 4–fold less than in vivo), 1.2%for O₂ (in the presence of an optimal CO₂ concentration of 3%),and 1% for CO₂ in the presence of O₂ (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K₁, =0.5 mM) by 2–aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO₂. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn²⁺> CO²⁺>Ni²⁺>Cu²⁺>Mn²⁺>Mg²⁺) and by salicylic acid, propylgallate, carbonyl cyanidem–chlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Na–benzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 80–85%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

The NADP$-specific isocitrate dehydrogenase of Rhodospirillum rubrum

The NADP^$-specific isocitrate dehydrogenase was partially purifiedfrom photosynthetically-grown Rhodospirillum rubrum. The pHoptimum is between 7.5 and 9.0 in phosphate buffer. The apparentKm is 3.1x10^–5 M for isocitrate, 5.1x10^–5 M forNADP^$, 1.7x10^–5 M for manganese, 1.5x10^–4 M formagnesium, and 3.5x10^–3 M for inorganic orthophosphate.Arsenate exerts a slight inhibition. The Q₁₀ between 17.5°Cand 40°C is 1.62, and the energy of activation at 25°Cis 9.74 Kcal/mole. Glyoxylate and oxalacetate cause concertedinhibition of the enzyme activity. Various nucleotides inhibitthe activity. The kinetics of inhibition by ATP was found tobe mixed type with respect to NADP^$ and isocitrate, the K_i valuesbeing 1.17x10^–3 M and 1.10x10^–3 M respectively.The inhibition between ATP and orthophosphate is competitivewith a K_i of 10^–4M. Thiol binding reagents are inhibitory;this inhibition is reversed by cysteine or reduced glutathione. (Received October 1, 1971; )     

RNA Synthesis in Phaseolus Chloroplasts: I. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLAST PREPARATIONS FROM PHASEOLUS VULGARIS L. LEAVES AND SOLUBILIZATION OF THE RNA POLYMERASE

Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg^–1 chlorophyll h^–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl₂. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl₂. The simultaneouspresence of MnCl₂ and MgCl₂ resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg^–1 DNA h^–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.     

Studies in the Physiology of Parasitism: XXII. The Production of Pectolytic Enzymes by Pythium de Baryanum Hesse

The incorporation of sodium chloride in a synthetic medium stimulatedthe pectolytic activity of cultures of Pythium de Baryanum.The Cl^– ion appeared to be mainly responsible for thiseffect; on the other hand, presence of the Ca⁺⁺ ion depressedenzymic activity. Glucose, fructose, and mannose were about equally suitable forgrowth and enzyme production. Sucrose, if used as sole carbohydratesource, gave good mycelial growth but poor enzyme production,but if a small proportion was replaced by glucose, enzyme productionwas as good as on glucose itself. Galactose gave very poor growthand negligible enzyme production. For optimum production of pectolytic enzyme, glucose (or fructoseor mannose) requires to be autoclaved in a somewhat alkalinemedium—very conveniently with the K₂HPO₄ or K₃PO₄ of thenutrient medium. A yellow to brown coloration (due to caramelization)is produced in the process, but the stimulating factor is notbound up with the colouring substance. The same stimulatingeffect on enzyme production was obtained by adding to the nutrientmedium a small quantity of glucose which had been dry heatedat 150° C. for 20 minutes. Chromatographic analysis suggestedthat the stimulating substance was probably glyceraldehyde,though it is not excluded that other breakdown products of sugarsmay also play a part.     

Isocitrate Lyase from Germinating Soybean Cotyledons: Purification and Characterization

Ruchti, M. and Widmer, F. 1986. Isocitrate lyase from germinatingsoybean cotyledons: purification and characterization.—J.exp. Bot. 37: 1685–1690. Isocitrate lyase (E.C. 4.1.3.1 [EC] ) was purified from the cotyledonsof 7-d-old soybean seedlings. Three molecular forms were detectedwith pi values of 6·46, 6·25 and 6·0. Themain form (pl = 6·46) had an approximate Mr of 130000,a pH optimum of 8·0, a K_m (isocitrate) close to 2·0mol m^–3 and a molecular activity of 615 min ^–1 at25 °C. The purified enzyme is not a glycoprotein and isheat labile. Key words: Isocitrate lyase, soybean     

Biological and Cultural Characteristics of the Effective Frankia Strain HFPCcl3 (Actinomycetales) from Casuarina cunninghamiana (Casuarinaceae)

From homogenates prepared from surface-sterilized nodules ofseedlings of Casuarina cunninghamiana grown aeroponically, astrain of Frankia designated HFPCc13 was isolated and has beengrown in pure filamentous culture in a defined synthetic nutrientmedium. Vesicle and sporangium formation can be induced by removalof combined nitrogen from the medium.Frankia strain HFPCc13nodulates young seedlings of C. cunninghamiana and C. equisetifoliawithin three weeks of inoculation with an optimum root mediumpH of 6–7 for nodulation and optimum temperature of 30–35^°C. The presence of combined nitrogen in the root mediuminhibits nodulation with NH₄⁺ more inhibitory than NO₃^–.Frankia HFPCc13 does not nodulate Allocasuarina species withinthe same family nor several other possible actinorhizal plantstested. Thus this strain is quite precise in its host specificity.The rate of acetylene reduction was greater in C. cunninghamianathan the closely related species C. equisetifolia. In neitherof these host species were vesicles observed to occur withinthe infected root nodules which had been demonstrated to beactively fixing dinitrogen. Root nodules were shown to be activein acetylene reduction over a range of O₂ concentration in thegaseous environment with an optimum at about 20 per cent O₂,the ambient P_O2 of the air. The mechanism(s) for oxygen protectionof nitrogenase within the filamentous form of Frankia withinthese nodules remains to be explained. Casuarina, Frankia, nodulation, nitrogen fixation     

Photosynthesis in Panicum milioides, a Species with Reduced Photorespiration

The capacity for C₄ photosynthesis in Panicum milioides, a specieshaving reduced levels of photorespiration, was investigatedby examining the activity of certain key enzymes of the C₄ pathwayand by pulse-chase experiments with ¹⁴CO₂. The ATP$P₁ dependentactivity of pyruvate,P₁ dikinase in the species was extremelylow (0.14–0.18 µmol mg chlorophyll^–1 min^–1).Low activity of the enzyme was also found in Panicum decipiensand Panicum hians (related species with reduced photorespiration)and in Panicum laxum (a C₃ species). The antibody to pyruvate,P₁dikinase caused about 70% inhibition of the ATP$P₁ dependentactivity of the enzyme in P. milioides. The activity of NAD-malicenzyme and NADP-malic enzyme in ^P. ^milioides was equally low(approximately 0.1–0.2 µmol mg chlorophyll^–1min^–1) and similar to the activity in P. decipiens, P.hians and P. laxum. Photosynthetic pulse-chase experiments underatmospheric conditions showed a typical C₃-like pattern of carbonassimilation including the labelling of glycine and serine asexpected during photorespiration. During the pulse with ¹⁴CO₂only about 1% of the labelled products appeared in malate and2–3% in aspartate. During a chase in atmospheric levelsof CO₂ for up to 6 min there was a slight increase in labellingin the C₄ acids. The amount of label in carbon 4 of aspartatedid not change during the chase, indicating little or no turnoverof the C₄ acid via decarboxylation. The results indicate thatunder atmospheric conditions P. milioides assimilates carbondirectly through the C₃ pathway. Photorespiration as indicatedby the CO₂ compensation point may be repressed in the speciesby a more efficient recycling of photorespired CO₂. (Received June 8, 1982; Accepted July 22, 1982)     

L-Tyrosine carboxy-lyase of barley roots

_L-Tyrosine carboxy-lyase (E.C. 4. 1. 1. 25) was isolated fromroots of germinating barley (Hordeum vulgare). The enzyme requirespyridoxal phosphate for maximum activity. The optimum pH foractivity is about 7.0. The enzyme is inhibited by p-chloromercuribenzoateand hydroxylamine at 10^–3 M. Enzyme activity is foundin extracts from young roots, especially from those in earlystages of development, but not in extracts from shoots of thesame plant. Localization and changes in the amounts of _L-tyrosinecarboxy-lyase and aromatic amines in developing barley seedlingswere measured. Participation of carboxy-lyase in the formationof aromatic amines in barley roots is suggested. (Received July 17, 1970; )     

Influence of Environmental Stress on the Germination of Anabaena vaginicola Akinetes

Germination of akinetes of Anabeana vaginicola v. fertilissimaPrasad in response to environmental stress was studied. Additionof nitrate to the medium induced early and maximum germination(96 per cent), whereas less than half of the akinetes germinatedwhen either nitrate or phosphate was omitted from the medium.The pH range over which germination occurred was 7.0–9.0.The desiccated akinetes after rehydration germinated after acertain lag period, depending upon the dehydration state. Thetemperature optimum for germination and vegetative growth wasthe same (25 °C) and germination did not occur at 5 °Cor above 35 °C. The limit of heat shock tolerated was 55°C for 4 min. In addition to white light, only the red partof the visible spectrum induced germination. Ultraviolet radiationreduced germination rate presumably by inducing thymine dimersin DNA. The photoreactivating system (s) in akinetes is certainlynon-photosynthetic. LD₅₀ photon flux densities were 300 Jm^–2for akinetes and 240 Jm^–2 for vegetative cells. Anabaena vaginicola, blue-green alga, akinete, germination, environmental stress     

Purification and characterization of the enzymes of fructan biosynthesis in tubers of Helianthus tuberosus 'Colombia': I. Fructan: fructan fructosyl transferase

Fructan: fructan fructosyl transferase (FFT), one of the enzymesinvolved in the synthesis of ß-2,1 linked fructosepolymers has been purified 205-fold from tubers of Helianthustuberosus harvested in the accumulation phase. The molecularweight of the native as well as the SDS-denatured protein isapproximately 70 kDa. On IEF, the protein was separated intofive molecular species with pl values between pH 4.5–5.0.The optimum pH for fructosyl transfer activity was between 5.5–7.0.Temperature optimum was in the range of 25-35° C; the Q10value between 25 and 5° C was 1.14. FTT catalysed the self-transferof fructosyl groups with GF₂, GF₃, GF₄ or GF₅ as substrate andacceptor. The rate of elf-transfer with both GF₂ and GF₃ increasedlinearly with substrate concentration up to 100 mol m^–3and was still not saturated at 600 and 300 mol m^–3, respectively.FFT was unable to hydrolyse GF or to catalyse the self-transferwith GF but could mediate the transfer of fructosyl units frominulin on to GF. Key words: Fructan: fructan fructosyl transferase, Helianthus tuberosus, Jerusalem artichoke, purification, kinetics     

A Comparative Study of the Influence of Salt Type and Concentration on 14CO2 Fixation in Potato Slices at 25{degrees} C and 0{degrees} C

Dark fixation of ¹⁴CO₂ was followed in potato disks under varyingsalt treatments at 0° C and 25° C. It is shown thatthe specific activity of the ¹⁴CO₂ supplied is heavily dilutedby endogenously produced CO₂ and that the apparently greaterfixation of ¹⁴CO₂, at 0° C as compared with that at 25 °C is due to the lower respiration rate at 0° C, with consequentlyless dilution of the ¹⁴CO₂. supplied. At 25° C organic acidformation in response to different salt treatments fulfils thecommon expectation, ¹⁴CO₂ fixation increasing in the presenceof K₂SO₄ and decreasing in CaCl₂ relative to that in KCl. Therole of organic acids in maintaining ionic balance within thecell at 25° C is thereby indicated but at 0° C organicacid adjustments did not follow the normal pattern. At 25°C but not at o° C increasing external concentration of KCIresulted in an increased level of ¹⁴CO₂ fixation.     

STUDIES ON HOMOSERINE DEHYDROGENASE IN PEA SEEDLINGS

Partially purified homoserine dehydrogenase was prepared frompea seedlings. The optimum pH for this enzyme is approximately 5.4. The K_mvaluesfor ASA and TPNH are 4.6xl0^–4Af and 7.7xl0^–5M, respectively.This enzyme can also utilize DPNH but less effectively thanTPNH. In contrast with yeast homoserine dehydrogenase whichis insensitive to — SH reagents, the pea enzyme is inhibitedalmost completely by 10^–4MPCMB and 10^–5MHgCl₂, theinhibition being removed by 10^–2M thioglycolate. Homoserinedehydrogenase was found not only in decotylized seedlings, butalso in cotyledons. The significance of this enzyme in homoserine biosynthesis ingerminating pea seeds has been discussed. (Received February 20, 1961; )     

Growth and Partitioning in Pascopyrum smithii (C3) and Bouteloua gracilis(C4) as Influenced by Carbon Dioxide and Temperature

This study investigated how CO₂and temperature affect dry weight(d.wt) accumulation, total nonstructural carbohydrate (TNC)concentration, and partitioning of C and N among organs of twoimportant grasses of the shortgrass steppe,Pascopyrum smithiiRydb. (C₃) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C₄).Treatment combinations comprised two temperatures (20 and 35°C)at two concentrations of CO₂(380 and 750 µmol mol^-1),and two additional temperatures of 25 and 30°C at 750 µmolmol^-1CO₂. Plants were maintained under favourable nutrient andsoil moisture and harvested following 21, 35, and 49d of treatment.CO₂-induced growth enhancements were greatest at temperaturesconsidered favourable for growth of these grasses. Comparedto growth at 380 µmol mol^-1CO₂, final d.wt of CO₂-enrichedP.smithiiincreased 84% at 20°C, but only 4% at 35°C. Finald.wt ofB. graciliswas unaffected by CO₂at 20°C, but wasenhanced by 28% at 35°C. Root:shoot ratios remained relativelyconstant across CO₂levels, but increased inP. smithiiwith reductionin temperature. These partitioning results were adequately explainedby the theory of balanced root and shoot activity. Favourablegrowth temperatures led to CO₂-induced accumulations of TNCin leaves of both species, and in stems ofP. smithii, whichgenerally reflected responses of above-ground d.wt partitioningto CO₂. However, CO₂-induced decreases in plant tissue N concentrationswere more evident forP. smithii. Roots of CO₂-enrichedP. smithiihadgreater total N content at 20°C, an allocation of N below-groundthat may be an especially important adaptation for C₃plants.Tissue N contents ofB. graciliswere unaffected by CO₂. Resultssuggest CO₂enrichment may lead to reduced N requirements forgrowth in C₃plants and lower shoot N concentration, especiallyat favourable growth temperatures. Acclimation to CO₂; blue grama; Bouteloua gracilis ; carbohydrate; climate change; global change; grass; growth; growth temperature optima; nitrogen; N uptake; Pascopyrum smithii; western wheatgrass