Inhibition by 1-Aminocyclobutane-l-Carboxylate of the Activity of 1-Aminocyclopropane-l-Carboxylate Oxidase Obtained from Senescing Petals of Carnation {Dianthus caryophyllus L.) Flowers

We partially purified 1-aminocyclopropane-l-carboxy-late (ACC)oxidase from senescing petals of carnation {Dianthus caryophyllusL. cv. Nora) flowers and investigated its general characteristics,and, in particular, the inhibition of its activity by ACC analogs.The enzyme had an optimum pH at 7-7.5 and required Fe²⁺, ascorbateand NaHCO₃ for its maximal activity. The K_m for ACC was calculatedas 111-125 µM in the presence of NaHCO₃. Its M_r was estimatedto be 35 and 36 kDa by gel-filtration chromatography on HPLCand SDS-PAGE, respectively, indicating that the enzyme existsin a monomeric form. These properties were in agreement withthose reported previously with ACC oxidases from different planttissues including senescing carnation petals. Among six ACCanalogs tested, l-aminocyclobutane-l-carboxylate (ACBC) inhibitedmost severely the activity of ACC oxidase from carnation petals.ACBC acted as a competitive inhibitor with the K_i of 20-31 µM.The comparison between the K_m for ACC and the K_i for ACBC indicatedthat ACBC had an affinity which was ca. 5-fold higher than thatof ACC. Whereas ACC inactivated carnation ACC oxidase in a time-dependentmanner during incubation, ACBC did not cause the inactiva-tionof the enzyme. Preliminary experiments showed that ACBC andits N-substituted derivatives delayed the onset of senescencein cut carnation flowers. (Received August 19, 1996; Accepted November 26, 1996)     

Carbonic Anhydrase from the Blue-Green Alga (Cyanobacterium) Anabaena variabilis

Carbonic anhydrase (CA) activity was detected in homogenatesfrom Anabaena variabilis ATCC 29413, M-2 and M-3, but not inthe suspension of the intact cells. Activity was higher in cellsgrown in ordinary air (low-CO₂ cells) than in those grown inair enriched with 2–4% CO₂ (high-CO₂ cells). Fractionationby centrifugation indicated that the CA from A. variabilis ATCC29413 is soluble, whereas both soluble and insoluble forms existin A. variabilis M-2 and M-3. The addition of dithiothreitoland Mg^{2 $} greatly decreased the CA activity of A. variabilisATCC 29413. The specific activity of the CA from A. variabilis ATCC 29413was increased ca. 200 times by purification with ammonium sulfate,DEAE-Sephadex A-50 and Sephadex G-100. Major and minor CA peaksin Sephadex G-100 chromatography showed respective molecularweights of 48,000 and 25,000. The molecular weight of the CAdetermined by polyacrylamide disc gel electrophoresis was 42,000?5,000.The activity of CA was inhibited by ethoxyzolamide (I₅₀=2.8?10^-9M), acetazolamide (I₅₀=2.5?10^-7 M) and sulfanilamide (I₅₀=2.9?10^-6M). (Received January 5, 1984; Accepted April 26, 1984)     

Influence of subantarctic Macrocystis bed metabolism in diel changes of marine bacterioplankton and CO2 fluxes

The significance of bacterial communities in the fluxes of carbonand energy in giant kelp beds (Macrocystis pyrifera) in KerguelenArchipelago, subantarctica, was estimated by measuring bacterioplanktonbiomass and production over diel cycles in surface seawaterslocated inside and outside of Macrocystis beds. Several physicochemicalparameters [temperature, solar radiation, tide level, dissolvedoxygen, total inorganic carbon (TCO₂), partial pressure of CO₂(pCO₂) and dissolved organic carbon (DOC)] were simultaneouslyrecorded in order to establish possible relationships with observedchanges in bacterial parameters. Bacterial biomass and productionwere significantly higher inside the kelp bed than in the surroundingarea. Furthermore, the results showed large and clear diel variationsof all parameters measured inside the kelp bed. Changes in dissolvedoxygen, TCO₂ and pCO₂ paralleled those of solar radiation, andwere obviously related to the metabolic activity of the kelp.Mean cell volumes and saprophytic bacterial abundance variedover the diel cycles in the same way as photosynthetic activity,while DOC, bacterioplankton production and the frequency ofdividing cells varied in an opposite way with maximal valuesat night-time.     

Changes in Photosynthetic Characteristics Induced by Transferring Air-Grown Cells of Chlorococcum littorale to High-CO2 Conditions

When air-grown cells of Chlorococcum littorale was enrichedwith CO₂, growth was enhanced after a lag period of one to twodays at 20% CO₂, and 3 to 6 days at 40% CO₂. Changes in therate of photosynthesis measured as oxygen evolution and CO₂fixation, were similar to those observed for growth. Duringthe initial inhibition of photosynthesis in 40% CO₂, the activityof PSII was suppressed. In contrast, PSI activity was greatlyenhanced. Air-grown cells of C. littorale possessed comparatively highcarbonic anhydrase (CA) activity which was localized insidethe cells and on the cell surface. Under high CO₂ concentrationsextracellular CA activity was greatly suppressed and intracellularactivity almost completely abolished. Phosphoenol pyruvate carboxylaseactivity was also suppressed in high CO₂-grown cells. Ribulose-l,5-bisphosphatecarboxylase activity was higher in high-CO₂ grown cells thanin air-grown cells. The above results indicated that the lagphase induced by 40% CO₂ was due to suppression of PSII activity. ¹Part of this work was reported in the International PhotosynthesisCongress, Nagoya, 1992.     

The Effects of Exogenous Amino Acid on Acetylene Reduction Activity of Vicia faba L. cv. Fiord

The feed back control mechanism proposed to explain the inhibitionof N₂ fixation by N was investigated using Vicia faba cv. Fiord.Plants were grown under controlled conditions without mineralN in coarse river sand. Asparagine was supplied to plants activelyfixing N₂ by absorption through cut roots and via a wick ordirect injection into the stem just above the bottom leaf. Responsesin N₂ fixation were measured by acetylene reduction (AR). Feedingplants with [¹⁴C]-labelled asparagine showed that the amidewas taken up when exogenously applied. Asparagine (10 mM) suppliedby the above procedures resulted in a 50-70% inhibition of ARby 48 h. Glutamine produced a similar effect. The cut root methodallowed higher levels of these amides to be supplied but theinhibition observed with 10 mM asparagine was only increasedslightly with higher levels of the amide. The antibiotic Securopenprevented bacterial contamination of root solutions of asparagineand glutamine and had no effect on nodule activity. It is concludedthat accumulation of asparagine of glutamine or the resultantincrease in the pool of soluble N in the plant cause a feedbackeffect on the activity of nitrogenase.Copyright 1993, 1999 AcademicPress Vicia faba, faba bean, asparagine, inhibition of N₂ fixation     

Endogenous Cytokinins in Developing Fruits of Seeded and Seedless Citrus Cultivars

This report describes the isolation and identification of endogenouscytokinins from Citrus ovaries. Cytokinin active fractions wereobtained by extraction with 80% (v/v) ethanol, followed by purificationwith hexane, n-butanol and a polyvinylpyrrolidone and SephadexLH-20 column chromatography. Five fractions with cytokinin activity were found in the organicphase, using the tobacco callus assay. The main active compoundsin these fractions were separated by HPLC, bioassayed and identifiedby GC—MS as ribosyl zeatin, zeatin and isopentenyl adenosine.Hydrolysis of the first fraction with B-glucosidase gave cytokininactive compounds that in paper chromatography had R_F's similarto those of zeatin and ribosyl zeatin. Treating the aqueousphase with alkaline phosphatase produced a cytokinin activecompound that in paper chromatography had the same R_F as isopentenyladenosine indicating that their ribotide was probably the majorphosphorylated cytokinin present in Citrus ovaries. Key words: Citrus, cytokinin fruit set and development     

Role of carbonic anhydrase in photosynthetic CO2 fixation in Chlorella

Chlorella vulgaris 11h cells grown in air enriched with 4% CO₂(high-CO² cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO₂, low-CO₂ cells). The CO₂ concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO₂. When high-CO₂ cells were transferred to low CO₂ conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic¹⁴CO₂ fixation under ¹⁴CO₂-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic ¹⁴CO₂fixation at low ¹⁴CO₂ concentrations decreased when low-CO₂cells were transferred to high CO₂ conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO₂ cells at high CO₂ concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO₂ concentrations, and the lowerthe CO₂ concentration, the greater was the inhibition. Consequently,the CO₂ concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO₂ concentration was higher than 1%, the photosyntheticrate in low-CO₂ cells decreased, while that in high-CO₂ cellsincreased. Fractionation of the low-CO₂ cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO₂-limiting conditions, but inhibits it at CO₂ concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed. ¹This work was reported at the International Symposium on PhotosyntheticCO₂-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; )     

Ferric chelate reduction by sunflower (Helianthus annuus L.) leaves: influence of light, oxygen, iron-deficiency and leaf age

The presence of ferric chelate reducing activity in sunflower[Helianthus annuus L.) leaves has been studied by submergingleaf discs in a solution with Fe(III)-ethylenediaminetetra-acetate(FeEDTA), batho-phenanthroline disulphonate (BPDS) and vacuuminfiltration. The effect of different factors on the Fe(III)reduction rate was studied. Ferric reduction rate was about10-fold higher in the light than in darkness. The light effectwas greatly inhibited by 3-(3,4-dichloro-phenyl)-1,1-dimethylurea(DCMU), a photosystem II inhibitor. Several inhibitors of redoxsystems [cis-platinum (II) diamine dichloride (cis-platin),p-nitro-phenylacetate (p-NPA) and p-hydroxymercuribenzoic acid(pHMB)] decreased the FeEDTA reduction rate. The greatest inhibitionwas produced by the - SH group reagent pHMB (17% of control,in light). The FeEDTA reduction rate was much higher in theabsence of O₂ than with air or 100% O₂. Superoxide dismutase(SOD) decreased FeEDTA reduction with air in the light. Youngleaves reduced Fe(III)-chelate at a higher rate than did olderleaves. In iron-deficient plants, leaves did not exhibit enhancedferric chelate-reducing activity as was observed in roots. Itis suggested that at least two different redox systems or twostates of the same redox system work in the light and in darkness. Key words: Iron, leaves, plasma membrane-redox, light, oxygen level     

Effects of hydroxylamine and molybdate on the formation of nitrate reductase in the yeast Rhodotorula

NADPH-nitrate reductase (NR) and NADPH-cytochrome c reductase(CR) activities of Rhodotorula glulinis var. salinaria cellsgrown in nitrate medium supplied with hydroxylamine (0.2 mM)were respectively 1.6- and 3.1-fold higher than those of cellsgrown without hydroxylamine. NR formed in nitrate plus hydroxylaminemedium is almost totally in an inactive form which is reactivatedin vitro by K₃Fe(CN)₆. When molybdate (10^–7 M) was suppliedto this medium, total (active plus inactive) NR activity increasedfurther about twofold but CR activity somewhat decreased. Inordinary nitrate medium, such molybdate effects were small.Most of the CR derepressed (induced) excessively in the nitrateplus hydroxylamine medium had a molecular size similar to NRon the basis of Bio-Gel A 1.5 m chromatography. Some other propertiesof CR formed in this medium were the same as those of the CRmoiety of NR. Adding molybdate to the nitrate plus hydroxylamine medium aftergrowing the cells for 20 hr induced the development of NR activitywithout any increase in CR activity. This induction was completelyblocked by cycloheximide, puromycin and L-canavanine but notcompletely by 6-methylpurine. Ammonium repressed this inductionwith markedly decreasing CR activity. The roles of hydroxylamine and molybdate in the formation ofNR are discussed. (Received May 26, 1980; )     

Carbonic Anhydrase of a Unicellular Red Alga Porphyridium cruentum R-l. I. Purification and Properties of the Enzyme

Cells of Porphyridium cruentum R-l, a unicellular red alga,grown under ordinary air (0.04% CO₂) showed much higher activityof carbonic anhydrase (CA) than those grown under CCvenrichedair (2% CO₂). CA activity was not detected in a suspension ofintact cells, and was detectable only after the cells had beenhomogenized, indicating that this enzyme was localized onlywithin the algal cells. After partial purification of Porphyridium CA, its mol wt wasestimated as 59 kDa by SDS-PAGE and 55 kDa by gelfiltration.This suggests that the native enzyme is a monomer. Its activitywas not affected by benzensulfonamides, potent inhibitors ofCAs isolated from Chlamydomonas and other organisms. Chloride(or bromide) ions was essential for CA activity. CA activitymarkedly decreased when the cell extract had been incubatedat pH lower than 7 before assay. Upon readjusting the pH ofthe preincubation medium to 9 or higher, the enzyme activitywas restored, indicating that the inactivation is reversible. (Received April 17, 1987; Accepted July 21, 1987)     

Preliminary Characterization of Glutathione S-Transferases That Accumulate in Callus Cells of Pumpkin (Cucurbita maxima Duch.)

Glutathione S-transferases (GSTs; EC 2.5.1.18 [EC] ) in sarcocarptissue of pumpkin (Cucurbita maxima Duch.) fruit and in callusinduced from the tissue were examined. The specific activityof GST in the callus was 6.9-fold higher than that in the tissue.The specific activity in the callus remained constant duringcultivation. Column chromatography on DEAE-cellulose, hydroxylapatite,and S-hexylglutathione-agarose was used to fractionate solubleproteins that were precipitated by ammonium sulfate at 30% to70% saturation from homogenates of the sarcocarp tissue of pumpkinfruit and the callus and GST activity was monitored. Two andseven isozymes of GST were identified in the tissue and in thecallus, respectively. Furthermore, column chromatography onSephadex G-200 and SDS-polyacrylamide gel electrophoresis, indicatedthat these GST isozymes were homo- and heterodimers of subunitsof M_r 22,000 (Puga), and 23,000 (Pugb), 24,000 (Pugc) or 24,500(Pugd). Puga and Pugb were predominant in the sarcocarp tissueand in the callus, respectively. Puga, Pugb, Pugc and Pugd hadacidic pI values of 5.45, 5.00, 5.35 and 5.75, respectively.Rabbit antiserum against Pugb did not cross-react with the threeother subunits of GST during immunoblotting. (Received July 15, 1993; Accepted December 14, 1993)     

Effect of Potassium Deficiency on C3 and C4 Cereals

C₄ cereals (Zea maya L. and Sorghum bicolor L. Moench) and C₃cereals (Triticum aestivum L. and Hordeum vulgare L) were grownin nutrient solutions with constant, interrupted, or absentpotassium supply. The lack of potassium retarded shoot growthand depressed the chlorophyll accumulation in all species ina similar way. After the renewal of potassium, the differencesin the compensation for growth retardation were not correlatedwith the photosynthetic system, but with the recovery of chlorophyllaccumulation in younger leaves. As important for the compensationof shoot growth retardation was a slower senescence of old leavescompared to plants with a constant potassium supply. This wasshown by the chlorophyll content and PEP carboxylase activity.In contrast to C₃ cereals, the C₄ cereals did not react withhigher chlorophyll contents to the same extent after the renewalof the postassium supply. The PEP carboxylase activity, however,was immediately raised higher than in control leaves. Chlorophylland PEP carboxylase activity increased simultaneously only inless aged leaves.     

Enzymatic Properties of Phosphoenolpyruvate Carboxylase Isoforms in the CAM Plant Kalanchoe daigremontiana

Three isoforms (Types 1, 2 and 3) of phosphoenolpyruvate (PEP)carboxylase in young leaves of the Crassulacean acid metabolism(CAM) plant Kalanchoe daigremontiana were separated by DEAE-cellulosecolumn chromatography and preparative polyacrylamide-agarosegel electrophoresis, and their enzymatic properties were characterized. All three isoforms had similar molecular weights of about 234,000.At pH 8.0 Type 1 showed a high affinity to PEP, (K_m=0.08 mM),whereas Type 3 showed a low affinity (K_m=1.0mM). K_m values forMgCl₂ were 0.26 HIM in Types 1 and 3 and 0.5 nut in Type 2.All three types exhibited the same pH optimum at 8.0, but Type1 showed relatively low activity below pH 6.0, whereas Type3 showed high activity. Type 3 was more acid stable than theother forms. In the presence of glucose-6-phosphate, the K_mvalues of Types 1, 2 and 3 for PEP lowered to 0.027, 0.037 and0.044 mu at pH 8.0, respectively. Inhibition of activity byorganic acids such as malate and pyruvate was pronounced inType 3. Type 2 exhibited properties intermediate to Types 1and 3 with regard to pH curve, affinity to PEP and its effectof various metabolites. The physiological significance of PEPcarboxylase isoforms in CAM plants is discussed on the basisof these findings. ¹Present address: Agricultural Chemicals Research Lab., SankyoCo., Ltd., Yasu-cho, Yasugun, Shiga 520-23, Japan. (Received November 30, 1983; Accepted March 24, 1984)     

岩木瓜化学成分的分离、结构鉴定与杀虫活性

为明确岩木瓜Ficus tsiangii Merr. ex Corner的杀虫活性成分及杀虫活性,利用活性跟踪分离技术,通过硅胶柱层析、薄层层析及葡聚糖凝胶等手段对岩木瓜茎和根皮的化学成分进行了分离、纯化,结合化合物理化性质和波谱数据对其结构进行了鉴定.结果表明,从岩木瓜中分离得到4个生物活性化合物,分别为β-香树脂醇乙酸酯、蒲公英赛酮、柯依利素及齐墩果酸.利用胃毒法测定了这些化合物（500μg/g糖）对家蝇Musca domestica成虫的生物活性,其中蒲公英赛酮处理试虫48 h后的校正死亡率达到83.33%,表现出较强杀虫活性,并进一步测定了其对试虫的毒力.结果表明,蒲公英赛酮处理家蝇成虫48 h后表现出较强毒力,其LC₅₀值为89.82μg/g糖,略低于对照药剂鱼藤酮毒力（LC₅₀值为67.58μg/g糖）.因此,蒲公英赛酮值得进一步深入研究.     

Plasma Membrane H+-ATPase in Guard-Cell Protoplasts from Vicia faba L.

The activity of plasma membrane H⁺-ATPase was measured withmembrane fragments of guard-cell protoplasts isolated from Viciafaba L. ATP hydrolytic activity was slightly inhibited by oligomycinand ammonium molybdate, and markedly inhibited by NO₃^–and vanadate. In the presence of oligomycin, ammonium molybdateand NO₃^–, the ATP-hydrolyzing activity was strongly inhibitedby vanadate. It was also inhibited by diethylstilbestrol (DES),p-chloromercuribenzoic acid (PCMB) and Ca²⁺, but slightly stimulatedby carbonyl cyanide m-chlorophenylhydrazone (CCCP). The acitivityhad higher specificity for ATP as a substrate than other phosphoricesters such as ADP, AMP, GTP and p-nitrophenylphosphate; theK_m was 0.5 mM for ATP. The activity required Mg²⁺ but was notaffected by K⁺, and it was maximal around pH 6.8. When guard-cellprotoplasts were used instead of membrane fragments, the ATPaseactivity reached up to 800µmol Pi.(mg Chl)^–1.h^–1in the presence of lysolecithin. These results indicate thatthe guard cell has a high plasma membrane H⁺-ATPase activity. (Received December 23, 1986; Accepted April 28, 1987)     

Purification, Kinetic and Regulatory Properties of Phosphofructokinase from Chiorella pyrenoidosa

Phosphofructokinase was purified 585-fold from Chlorella pyrenoidosaby using a combination of ammonium sulphate fractionation, filtrationthrough Sepharose 4B and chromatography on DEAE-Sephacel. Enzymestability was maintained by the presence of 50 mM P_i at pH 6.6.The optimum pH for activity was 7.7. Concentrations of substratesrequired to achieve half maximal velocity in the standard assaywere 9 µM (ATP) and 0.2 mM (fructose-6-P). ATP above 0.5mM was inhibitory. Enzyme activity was inhibited by high concentrations(10–100 mM) of P_i but lower concentrations (1–5mM) were effective in relieving the influence of other inhibitorssuch as P enolpyruvate. Inhibition by P-enolpyruvate was greaterat lower pH and with less P_i in reaction mixtures: 50% inhibitioncould be attained with 0.1 mM P-enolpyruvate. Fructose-2,6-bisphosphate,which was shown to be present in Chlorella, had no effect onthe phosphofructokinase. Chlorella appeared to contain onlyone form of phosphofructokinase, possibly in the chloroplast.No pyrophosphate :D-fructose-6-P 1-phospho transferase activitycould be detected. (Received February 20, 1984; Accepted December 5, 1984)     

High Respiratory Activity of Guard Cell Protoplasts from Vicia faba L.

The rate of O₂ uptake was about 29 times higher in guard cellprotoplasts (GCPs) than in mesophyll protoplasts (MGPs) on aChi basis. The O₂ uptake was inhibited by respiratory inhibitors,but stimulated by respiratory uncouplers. On a Chi basis, theactivities of Cyt c oxidase and NADH-Cyt c reductase, mitochondrialenzymes, were about 27 and 35 times higher in GCPs than in MCPs.On a Chi basis, the ATP content was about 9 times higher inGCPs. The amount of ATP in GCPs was decreased by respiratoryinhibitors, an energy transfer inhibitor, and uncouplers ofoxidative phosphorylation. On a volume basis, GCPs had 8- to10-fold higher respiratory activities than MCPs, but had a lowChi content and lacked the activity of NADP-glyceraldehyde-3-phosphatedehydrogenase (NADP-GAPD), the Calvin cycle enzyme. From theseresults, we concluded that oxidative phosphorylation plays amain role in ATP production in guard cells and that guard cellshave a heterotrophic feature. Salicylhydroxamic acid (SHAM)in combination with KCN or NaN₃ strongly inhibited O₂ uptake,indicating the presence of cyanide-resistant respiration inguard cells. Phenylmercuric acetate (PMA), a potent inhibitorof stomatal opening, reduced the ATP content of GCPs by about90%, whereas it had a relatively small effect on the ATP levelof MCPs. The specific effect of PMA on GCPs is discussed. (Received March 24, 1983; Accepted June 8, 1983)     

Properties of the Cytochrome c Oxidase Activity of Cytochrome b561 from Photoanaerobically Grown Rhodopseudomonas sphaeroides

Cytochrome b₅₆₁ from Rhodopseudomonas sphaeroides had cytochromec (c2) oxidase activity and a pH optimum at 6.0 for this activity.The activity was affected by the ionic strength of the reactionmixture. The apparent K_m and maximal velocity (V_max) valuesin the absence of addea salts were 14 µM and 120 nmoloxidized per min per mg protein for horse heart cytochrome c.Reduced horse heart cytochrome c was reoxidized in first-orderkinetics by this cytochrome b₅₆₁. The specific activity was0.7 s^–1 per mg protein at 20°C at the concentrationof 30 µMM cytochrome c. Activity was inhibited by KCN and NaN₃, but not by antimycin.The addition of a low concentration of KCN to the cytochromeb₅₆₁ produced a change in the absorption spectrum, evidencethat KCN interacts with the heme moiety of cytochrome b₅₆₁.Results of this and preceeding studies show that the cytochromeoxidase (cytochrome "o") described earlier (Sasaki et al. 1970)is cytochrome b₅₆₁. (Received May 16, 1983; Accepted September 8, 1983)     

Phosphoglycolate Phosphatase-Defident Mutants of Chlamydomonas reinhardtii Capable of Growth under Air

Mutants deficient in phosphoglycolate phosphatase (PGPase) requireelevated levels of CO₂ for growth in the light and cannot growwhen photorespiration occurs. Revertants, namely, double mutantscapable of growth under air without restoration of the missingPGPase activity, might be expected to have secondary mutationsthat reduce or eliminate photorespiration. Nineteen revertantswere selected from a culture of a PGPase-deficient mutant ofChlamydomonas reinhardtii (pgp-1-18-7F) after a second mutagenesisthat involved treatment with 5-fluorodeoxyuridine and ethylmethanesulfonate. There were significant differences in thephotosynthetic affinity for CO₂ among revertant cells grownunder 5% CO₂. Eight revertants had five times higher photosyntheticaffinity for CO₂ than that of wild type 2137 cells grown under5% CO₂, resembling air-adapted wild-type cells, whereas fourrevertants had less than half the affinity for CO₂ of the wildtype. In all of the revertant cells with higher affinity grownin 5% CO₂, the rates of photosynthesis under levels of CO₂ belowthose in air were apparently higher than that of the wild type,whereas the rates under CO₂-saturating conditions were lowerthan that of wild type, indicating that the efficiency of photosynthesisunder air was significantly improved in these revertants. Inaddition, some revertants had a photosynthetic capacity anda growth rate higher than those of the wild type, without anyincreased photosynthetic affinity for CO₂. (Received July 7, 1994; Accepted November 5, 1994)     

Growth and Physiology of One-year old Poplar (Populus) Under Elevated Atmospheric CO2 Levels

The effects of elevated atmospheric CO₂ concentrations on theecophysiological responses (gas exchange, chlorophyll a fluorescence,Rubisco activity, leaf area development) as well as on the growthand biomass production of two poplar clones (i.e. Populus trichocarpax P. deltoides clone Beaupré and P. x euramericana cloneRobusta) were examined under open top chamber conditions. Theelevated CO₂ treatment (ambient + 350 µmol mol^-1) stimulatedabove-ground biomass of clones Robusta and Beaupré afterthe first growing season by 55 and 38%, respectively. This increasedbiomass production under elevated CO₂ was associated with asignificant increase in plant height, the latter being the resultof enhanced internode elongation rather than an increased productionof leaves or internodes. Both an increased leaf area index (LAI)and a stimulated net photosynthesis per unit leaf contributedto a significantly higher stem biomass per unit leaf area, andthus to the increased above-ground biomass production underthe elevated CO₂ concentrations in both clones. The larger LAIwas caused by a larger individual leaf size and leaf growthrate; the number of leaves was not altered by the elevated CO₂treatment. The higher net leaf photosynthesis was the resultof an increase in the photochemical (maximal chlorophyll fluorescenceFm and photochemical efficiency Fv/Fm) as well as in the biochemical(increased Rubisco activity) process capacities. No significantdifferences were found in dark respiration rate, neither betweenclones nor between treatments, but specific leaf area significantlydecreased under elevated CO₂ conditions.Copyright 1995, 1999Academic Press Biomass, chlorophyll a fluorescence, elevated CO₂, growth, Populus, poplar, photosynthesis, respiration, Rubisco