Effect of Ammonia on Dark CO2 Fixation by Anabaena Cells Treated with Methionine Sulfoximine

Dark CO₂ fixation by Anabaena cylindrica was stimulated aboutthree-fold by the addition of NH₄Cl to the cells. The ¹⁴CO₂incorporation experiments showed that ¹⁴C is most rapidly incorporatedinto aspartate and then glutamine by adding NH4CI. Glutamineaccumulated predominantly after the addition of NH₄Cl showingthat NH₄ is incorporated into glutamine by glutamine synthetase.The stimulating effect of NH4Cl on CO₂ fixation and amino acidsynthesis was suppressed by methionine sulfoximine, an inhibitorof glutamine synthetase. It was suggested that dark CO₂ fixationwas stimulated by the action of glutamine synthesis which isenhanced by ammonia. (Received February 10, 1981; Accepted April 2, 1981)     

A Mutant of Arabidopsis thaliana That Defines a New Locus for Glycine Decarboxylation

A novel photorespiratory mutant of Arabidopsis thaliana, designatedgld2, was isolated based on a growth requirement for abnormallyhigh levels of atmospheric CO₂. Photosynthetic CO₂ fixationwas inhibited in the mutant following illumination in air butnot in atmosphere containing 2% O₂. Photosynthetic assimilationof ¹⁴CO₂ in an atmosphere containing 50% O₂ resulted in accumulationof 48% of the soluble label in glycine in the mutant comparedto 9% in the wild type. The rate of glycine decarboxylationby isolated mitochondria from the mutant was reduced to 6% ofthe wild type rate. In genetic crosses, the mutant complementedtwo previously described photorespiratory mutants of A. thalianathat accumulate glycine during photosynthesis in air due todefects in glycine decarboxylase (glyD, now designated gld1)and serine transhydroxymethylase (stm). Because glycine decarboxylaseis a complex of four enzymes, these results are consistent witha mutation in a glycine decarboxylase subunit other than thataffected in the gld1 mutant. The two gld loci were mapped tochromosomes 2 and 5, respectively. ³Present address: Department of Crop and Soil Sciences, MichiganState University, East Lansing, MI 48824, U.S.A. ⁴Present address: Department of Applied Bioscience, Facultyof Agriculture, Hokkaido University, Kita-Ku, Sapporo, 060 Japan ⁵Present address: Department of Biology, Carnegie Institutionof Washington, 290 Panama Street, Standford, CA 94305, U.S.A.     

Effects of Ammonia on Respiration, Adenylate Levels, Amino Acid Synthesis and CO2 Fixation in Cells of Chlorella vulgaris 11h in Darkness

The effects of NH₄Cl on respiration, adenylate and free aminoacid levels as well as dark CO₂ fixation were investigated usingnitrogen-starved Chlorella vulgaris 11h cells with or withoutaddition of methionine sulfoximine (MSX), an inhibitor of glutaminesynthetase. Upon addition of NH₄Cl (1 mM) to the cells not treatedwith MSX, respiration was stimulated and the level of ATP droppedrapidly, while the levels of ADP and AMP increased. NH₄Cl alsostimulated amino acid synthesis, especially of glutamine, andmarkedly enhanced dark CO₂ fixation. Addition of NH₄Cl to MSX-treatedcells stimulated respiration and lowered the level of ATP, butdid not enhance glutamine synthesis and only slightly stimulateddark CO₂ fixation. ⁴On leave from Institute of Medical Science, Advance R &D Co. Minami-Hashimoto, Sagamihara, Kanagawa-ken 220, Japan (Received January 28, 1984; Accepted April 19, 1984)     

Relationship between Inhibition of CO2 Fixation and Glutamine Synthetase Inactivation in Lemna gibba L. Treated with L-Methionine-D,L-Sulphoximine (MSO)

The rate of net CO₂ fixation in Lemna gibba L. was decreasedto 50% by 100–150 min incubation in the presence of 0•5mol m^–3 L-methionine-D,L-Sulphoximine (MSO), an irreversibleinhibitor of glutasnine synthetase (GS). The pattern of inhibitionwas similar in both 21% O₂ and 2% O₂. The inhibition was accompaniedby increased intracellular levels. Incubation with 10 mol m^–3 under the same conditions, but without MSO, resulted in even higher levels but the rate of CO₂ fixation was unaffected. Additions of glutamine, glutamate, glycine or serine delayedthe MSO-induced inhibition of CO₂ fixation. The same amino acidsdelayed the inactivation of GS by MSO. Thus inhibition of CO₂ fixation by MSO in Lemna is neither causedby elevated levels nor closely related to photorespiration. Possibly, MSO causes shortage of amino-N formaintenance of the functional integrity of the photosyntheticapparatus. Key words: Methionine sulphoximine, CO₂, fixation, Lemna     

Comparison of carbon dioxide fixation and the fine structure in various assimilatory tissues of Amaranthus retroflexus L

The pattern for primary products of CO₂-fixation and the chloroplaststructure of Amaranthus retrqflexus L., a species which incorporatescarbon dioxide into C₄ dicarboxylic acids as the primary productof photosynthesis, were compared in various chlorophyll containingtissues,i.e., foliage leaves, stems, cotyledons and pale-greencallus induced from stem pith. Despite some morphological differencesin these assimilatory tissues, malate and aspartate were identifiedas the major compounds labelled during a 10 sec fixation of¹⁴CO₂ in all tissues. Whereas, aspartate was the major componentin C₄-dicarboxylic acids formed in foliage leaves, malate predominatedas the primary product in stems, cotyledons and the pale-greencallus. The percentage of ¹⁴C-radioactivity incorporated intoPGA and sugar-P esters increased and ¹⁴C-sucrose was detectedin the prolonged fixation of ¹⁴CO₂ in the light, not only infoliage leaves, but also in stems and cotyledons. ¹ This work was supported by a Grant for Scientific ResearchNo. 58813, from the Ministry of Education, Japan. ² Present address: Institute of Applied Microbiology, Universityof Tokyo, Tokyo, Japan. ³ Present address: Department of Biochemistry, University ofGeorgia, Athens 30601. Georgia, U. S. A. (Received July 10, 1971; )     

Photosynthetic Nitrogen Metabolism in High and Low CO2-adapted Scenedesmus: I. INORGANIC CARBON-DEPENDENT O2 EVOLUTION, NITRATE UTILIZATION AND NITROGEN RECYCLING

Larsson, M., Larsson, C.-M. and Guerrero, M. G. 1985. Photosyntheticnitrogen metabolism in high and low CO₂-adapted Scenedesmus.I. Inorganic carbon-dependent O2 evolution, nitrate utilizationand nitrogen recycling.—J. exp Bot. 36: 1373–1386 Scenedesmus obtusiusculus Chod. was grown on an inorganic mediumflushed with either air or air supplemented with 3% CO₂. Inair-grown cells, O₂ evolution dependent on low, but not high,HCO^–₃ concentrations was strongly inhibited by the carbonicanhydrase inhibitor acetazolamide. Cells grown with 3% CO² exhibitedlow rates of O2 evolution at low external inorganic C; however,after 30 min in air O2 evolution rates at low inorganic C approachedthose of air-grown cells. These results are compatible withthe view that Scenedesmus develops a ‘CO² concentratingmechanism’ in air, with carbonic anhydrase as an importantconstituent When 3% CO²-grown cells were subjected to air-level of CO²,just a transient decline in NO^–₃ utilization was observed,but in the presence of acetazolamide the rate of the processdecreased drastically in response to the decrease in the CO²level. In CO²-free air NO₃^– was taken up at high ratesbut in a deregulated manner, leading to release of NH₄⁺. A portionof the NO₃^– taken up in the absence of CO² was apparentlyassimilated Cellular nitrate reductase (NR) activity initially decreasedbut subsequently recovered after a transition from 3% CO² toair. In the presence of acetazolamide, a persistent decreasein NR activity was observed. Cellular glutamine synthetase (GS)activity increased after transition from 3% CO² to air, theactivity increase being unaffected by acetazolamide. NH₄⁺ releaseto the medium in the presence of L-methionine-D, L-sulphoximine(MSO) transiently increased in 3% CO²-grown cells in responseto a transfer to air. MSO-induced NH₄⁺ release was in fact higherin air-grown cells than in 3% CO²-grown cells. Glycollate wasinitially released after transition from 3% CO² to air, butthere was no difference in glycollate release between MSO-treatedand untreated cells. In air-adapted Scenedesmus, N recyclingseems to be of minor importance in comparison to primary N assimilation Key words: CO²-fixation, N recycling, nitrate uptake, Scenedesmus     

Translocation Profiles of [11C] and [13N]-Labelled Metabolites after Assimilation of 11CO2 and [13N]-Labelled Ammonia Gas by Leaves of Helianthus annuus L. and Lupinus albus L.

Tracer amounts of atmospheric [¹³N]-Iabelled ammonia gas, wereabsorbed by leaves of Lupinus albus and Helianthus annuus inboth the light and the dark. Exogenous [¹³N]-ammonia was onlyabsorbed in the dark when the feeding occurred shortly aftera period of illumination and the tissue was not depleted ofits carbohydrate reserves (e.g. starch). Incorporation of the[¹³N]-ammonia appeared to occur via the leaf glutamine synthetase/glutamatesynthase (GS/GOGAT) cycle since 2.0 mol m^–3 MSX, an inhibitorof the GS reduced uptake in both the light and dark. Photosyntheticincorporation of ¹¹CO₂ was not affected by this treatment Therate of movement of [¹³N]-assimilates in the petiole of attachedleaves of Helianthus and Lupinus was similar to that of the¹¹Cl-photo assimilates. Export of both [¹³N] and [¹¹C]-Iabelledassimilates from the leaf and movement in the petiole in boththe light and the dark was inhibited by source leaf anoxia (i.e.nitrogen gas). Translocation was re-established at the samerate when the feed leaf was exposed to gas containing more than2% O₂ which permitted dark respiration to proceed. After aninitial feeding of either ¹¹CO₂ or [¹³N]-ammonia at ambient(21%) O₂ exposure of the source leaf to 2% O2, or 50% O² didnot alter the rates of translocation, indicating that changesin photosynthetic activity in the source leaf due to photorespiratoryactivity need not markedly alter, at least during the shortperiod, the loading and translocation of either [¹¹C ] or [¹³N]-labelledleaf products. Key words: Translocation, CO₂, NH₃, Leaves, Helianthus annuus, Lupinus albus     

Studies on the change of the respiratory system in roots in relation to the growth of plants II. Activity of iron-containing oxidases in roots of cereal crops with the aging of plants

Distribution of iron-containing oxidases in aging nodal rootsof rice and wheat was studied. Activities of cytochrome c oxidase(1.9.3.1 [EC] , cytochrome c : O₂ oxidoreductase), catalase (1.11.1.6 [EC] ,H₂O₂: H₂O₂ oxidoreductase) and peroxidase (1.11.1.7 [EC] , donor:H₂O₂ oxidoreductase) in wheat roots were comparatively higherthan were those in rice roots at corresponding stages. Cytochromec oxidase in roots remained active throughout the lives of therice and wheat crops. In rice roots, catalase seemed to playa distinct role around the panicle formation stage. Decay ofcatalase activity took place earlier than did that of peroxidaseand cytochrome c oxidase activities. In wheat roots similarenzyme activity changes were not observed. Data may suggestthat the high activity of iron containing oxidases at the panicleformation stage (I) may be chiefly due to catalase activityin rice roots. ¹Paper presented at the 14th Annual Meeting of the Society ofthe Science of Soil and Manure, Japan (1968). (Received November 21, 1968; )     

Form of Inorganic Carbon Utilized for Photosynthesis in Chlamydomonas reinhardtii1

The effect of carbonic anhydrase (CA) on time courses of photosynthetic¹⁴C incorporation in the presence of ¹⁴CO₂ or NaH¹⁴CO₃ was studiedwith cells of Chlamydomonas reinhardtii which had been grownunder ordinary air (low-CO₂ cells) or air enriched with 4% CO₂(high-CO₂ cells). Experimental data obtained at 20°C andpH 8.0 suggested that the major form of inorganic carbon utilizedby high-CO₂ cells was CO₂, while that utilized by low-CO₂ cellswas HCO₃^–. The cell suspension showed CA activity which was comparableto that observed in the sonicate of cells. Both activities werehigher in low-CO₂ cells than in high-CO₂ cells. The mechanism by which HCO₃^– is utilized by low-CO₂ cellsof C. reinhardtii is discussed. ³Present address: Department of Biology, Faculty of Science,University of Niigata, Niigata 950-21, Japan. (Received August 4, 1982; Accepted January 19, 1983)     

Control of Glutamate Dehydrogenase from Green Tobacco Callus Mitochondria by Ca2$ and pH

Glutamate dehydrogenase (GDH) (EC 1.4.1.3 [EC] .) purified from greentobacco callus mitochondria was activated markedly by Ca^2$ inthe amination reaction. This activation was detectable evenat concentrations below 5 µM Ca^2$. Saturation curves for the three substrates of the aminationreaction showed normal Michaelis-Menten kinetics in the presenceof 1 mM of Ca^2$, but pronounced substrate inhibition occurredwithout Ca^2$. The effect of Ca^2$ was chiefly on the maximalvelocity. The saturation curve for NH₄Cl in the presence of Ca^2$ was modulatedby a change in pH. The apparent K_m value for NH₄Cl markedlydecreased whereas that for -ketoglutarate increased slightlywhen the pH was raised from 7.3 to 9.0. In contrast, the K_mfor NADH was little affected by raising the pH. The characteristicof GDH which increases its affinity for NH₄Cl when the pH israised may be compatible with the detoxification of ammonia. ¹ Present address: Mochida Pharmaceutical Co., Ltd. (Received August 24, 1981; Accepted November 28, 1981)     

A comparative study on the effect of O2 on photosynthetic carbon metabolism by Chlorobium thiosulfatophilum and Chromatium vinosum

The reductive carboxylic acid cycle appears to be the majorcarbon assimilation pathway in green sulfur bacteria, Chlorobiumthiosulfatophilum. While cyanide was relatively ineffectivein inhibiting the bacterial photosynthetic CO₂ fixation, photosynthesiswas strongly impaired in an O₂-containing atmospheric environment.No glycolate formation was detected in Chlorobium under an O₂atmosphere. In the purple sulfur bacteria, Chromatium vinosum,however, photosynthesis was highly sensitive to cyanide, andin a short-term incubation (up to 10 min) photosynthetic CO₂fixation was found to be relatively indifferent to an O₂-containingatmosphere of up to 100% O₂. Significant formation of glycolatewas demonstrated upon a very brief exposure to O₂, whereas thetotal photosynthetic CO₂ fixation was slightly affected. However,ribulose-1,5-bisphosphate carboxylase activity in Chromatiumextract was competitively inhibited by O₂ in a similar mannerto the higher plant enzyme, K¹(O₂) value being 0.7 mM at pH8.2. The percentage of incorporation of ¹⁴CO₂ into glycolateand glycine under an O₂-containing atmosphere declined withincreasing levels of bicarbonate concentrations in the medium.The Warburg effect and biosynthetic mechanisms involving glycolatein photosynthetic bacteria are discussed. ¹ This is paper XXXIX in the series "Structure and Functionof Chloroplast Proteins". Paper XXXVIII is reference (6) Asamiand Akazawa (1977). This research was supported in part by grantsfrom the Ministry of Education of Japan (111912), the TorayScience Foundation (Tokyo), and the Japan Securities ScholarshipFoundation (Tokyo). (Received January 28, 1977; )     

Alkalization of the Medium by Unicellular Green Algae during Uptake Dissolved Inorganic Carbon

When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO₃,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O₂ evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO^-₃, and algae grown or adapted to a low, air-levelCO₂ in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO₂ in air. Photosynthetic O₂ evolutionwithout alkalization occurred using either internal DIC or externalCO₂ at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO^–₃ into CO₂ plus OH^– during photosynthesisby cells with a high affinity for CO₂ uptake. Cells grown onhigh CO₂ to suppress the DIC pump, when given low levels ofHCO^–₃ in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO^–₃ pump, aswell as a CO₂ pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O₂ evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H₂CO₃ to HCO^–₃ and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO₂ concentrating process. ¹Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.     

A Mutant of Chlamydomonas reinhardtii with Reduced Rate of Photorespiration

Photorespiration rates under air-equilibrated conditions (0.04%CO₂ and 21% O₂) were measured in Chlamydomonas reinhardtii wild-type2137, a phosphoglycolate-phosphatase-deficient (pgp1) mutantand a suppressor double mutant (7FR2N) derived from the pgp1mutant. In both cells grown under 5% CO₂ and adapted air for24 h in the suppressor double mutant, the maximal rate of photorespiration(phosphoglycolate synthesis) was only about half of that ineither the wild type or the pgp1 mutant (18-7F) cells. In theprogeny, the reduced rate of photorespiration was accompaniedby increased photosynthetic affinity for inorganic carbon andthe capacity for growth under air whether accompanied by thepgp1 background or not. Tetrad analyses suggested that thesethree characteristics all resulted from a nuclear single-genemutation at a site unlinked to the pgp1 mutation. The decreasein photorespiration was, however, not due to an increase inthe CO₂/O₂ relative specificity of ribulose-1,5-bisphosphatecarboxylase/oxygenase of 7FR2N or of any other suppressor doublemutants tested. The relationship between the decrease in therate of photorespiration and the CO₂-concentrating mechanismis discussed. ³ Current address: Institute of Botany, Academy of Sciences,Patamdar Shosse, 40, Baku, 370073, Azerbaijan. ⁴ Current address: Department of Management and InformationScience, Jobu University, 270-1, Shinmachi, Tano, Gunma, 370-1393Japan.     

Development of Photorespiration during Chloroplast Biogenesis in Wheat Leaves

Tobin, A. K., Sumar, N., Patel, M., Moore, A. L. and Stewart,G. R. 1988. Development of photorespiration during chloroplastbiogenesis in wheat leaves.—J. exp. Bot. 39: 833–843. The rate of light-dependent ammonia accumulation in L-methioninesulphoximine (MSO: glutamine synthetase inhibitor)-treated wheat(Triticum aestivum L. cv. Maris Huntsman) primary leaf sectionsincreased with mesophyll cell maturity. Ammonia production inthe more mature sections (beyond 2.0 cm from the basal meristem)was inhibited by elevated CO₂ concentrations and by incubationwith 10 mol m^–3 pyrid-2-yl hydroxymethane sulphonate (HPMS).In contrast, the low levels of ammonia which accumulated inthe immature sections (0 to 2.0 cm from the base) were unaffectedby such treatments. This indicates that the ammonia producedin mature wheat leaf sections is of photorespiratory originand that the capacity of this pathway increases with mesophyllcell and chloroplast development. Rates of CO₂-dependent oxygenevolution by leaf sections (under saturating CO₂) increasedin parallel with ammonia production. Levels of endogenous nitratewere relatively high and increased from 5.15 mol x 10^–13mesophyll cell^–1 in meristematic cells to 6.6 mol x 10^–12mesophyll cell^–1 in mature tissue. There was no significantchange in leaf nitrate level during 30 min light incubationof the wheat leaf sections, indicating that the majority ofthe nitrate was metabolically inactive and stored in the vacuole.Activities of key enzymes of photorespiration (glutamine synthetase,glycollate oxidase), nitrogen metabolism (nitrate reductase,glutamate dehydrogenase, glutamine synthetase) and mitochondrialrespiration (cytochrome oxidase), showed specific and distinctpatterns of development during leaf growth. Chloroplast glutaminesynthetase (GS₂) and peroxisomal glycollate oxidase developedin apparent synchrony with the major increase in activity occurringin regions beyond4.0 cm from the leaf base, i.e. where photorespirationwas developing. Cytosolic glutamine synthetase (GS₁) and nitratereductase (in vivo) activities were identical throughout leafgrowth, reaching maximum rates at 4.0 cm from the base and thenremaining constant. Activities of the mitochondrial enzymesglutamate dehydrogenase (GDH) and cytochrome oxidase were highin meristematic cells and increased in parallel, attaining amaximum towards the leaf tip. This indicated a respiratory,as opposed to a photorespiratory, role for GDH in wheat leafmetabolism. The evidence for controlled, co-ordinated synthesisof pathway enzymes at specific stages of organelle biogenesisis discussed. Key words: Photorespiration, organelle biogenesis     

Impact of elevated atmospheric CO2 and O3 on gas exchange and chlorophyll content in spring wheat (Triticum aestivum L.)

Stands of spring wheat grown in open-top chambers (OTCs) wereused to assess the individual and interactive effects of season-longexposure to elevated atmospheric carbon dioxide (CO₂ and ozone(O₃) on the photosynthetic and gas exchange properties of leavesof differing age and position within the canopy. The observedeffects were related to estimated ozone fluxes to individualleaves. Foliar chlorophyll content was unaffected by elevatedCO₂ but photosynthesis under saturating irradiances was increasedby up to 100% at 680 µmol mol^–1 CO₂ relative tothe ambient CO₂ control; instantaneous water use efficiencywas improved by a combination of increased photosynthesis andreduced transpiration. Exposure to a seasonal mean O₃ concentration(7 h d^–1) of 84 nmol mol^–1 under ambient CO₂ acceleratedleaf senescence following full expansion, at which time chlorophyllcontent was unaffected. Stomatal regulation of pollutant uptakewas limited since estimated O₃ fluxes to individual leaves werenot reduced by elevated atmospheric CO₂, A common feature ofO₃-treated leaves under ambient CO₂ was an initial stimulationof photosynthesis and stomatal conductance for up to 4 d and10 d, respectively, after full leaf expansion, but thereafterboth variables declined rapidly. The O₃-induced decline in chlorophyllcontent was less rapid under elevated CO₂ and photosynthesiswas increased relative to the ambient CO₂ treatment. A/C_i analysessuggested that an increase in the amount of in vivo active RuBisCOmay be involved in mitigating O₃-induced damage to leaves. Theresults obtained suggest that elevated atmospheric CO₂ has animportant role in restricting the damaging effects of O₃ onphotosynthetic activity during the vegetative growth of springwheat, and that additional direct effects on reproductive developmentwere responsible for the substantial reductions in grain yieldobtained at final harvest, against which elevated CO₂ providedlittle or no protection. Key words: Elevated CO₂ and O₃, gas exchange, O₃ flux, stomata, chlorophyll, Triticum aestivum     

Ammonia emission from young barley plants: influence of N source, light/dark cycles and inhibition of glutamine synthetase

Barley (Hordeum vulgare L. cv. Golf) plants were grown at twodifferent relative addition rates; 0.1 and 0.2 d^–1 ofnitrate. Three to five days before measurements started theplants were transferred to a nutrient solution with 2 mM nitrateor ammonium. The ammonium-grown plants showed increased ammoniumlevels in both shoots and roots and also increased ammoniumconcentrations in xylem sap. Ammonia emission measured in cuvettes connected to an automaticNH₃ monitor was close to zero for nitrate-grown plants but increasedto 0.59 and 0.88 nmol NH₃ m^–2 S^–1 for plants transferredto ammonium after growing at RA=0.2 and 0.1 d^–1, respectively.In darkness, NH₃ emission decreased together with photosynthesisand transpiration, but increased rapidly when the light wasturned on again. Addition of 0.5 mM methionine sulphoximine (MSO) to the plantscaused an almost complete inhibition of both root and shootglutamine synthetase (GS) activity after 24 h. Ammonia emissionincreased dramatically and photosynthesis and transpirationdecreased in both nitrate- and ammonium-grown plants as a resultof the GS inhibition. At the same time plant tissue and xylemsap ammonium concentrations increased, indicating the importanceof GS in controlling plant ammonium levels and thereby NH₃ emissionfrom the leaves. Key words: Hordeum vulgare, ammonia emission, ammonium, glutamine synthetase, nitrogen nutrition, photosynthesis, transpiration     

Wavelength effects on photosynthetic carbon metabolism in Chlorella

To study the wavelength-effect on photosynthetic carbon metabolism,¹⁴C-bicarbon-ate was added to Chlorella vulgaris 1 lh suspensionunder monochromatic blue (456 nm) and red (660 nm) light. Thelight intensities were so adjusted that the rates of ¹⁴CO₂ fixationunder blue and red light were practically equal. Analysis of¹⁴C-fixation products revealed that the rates of ¹⁴CO₂ incorporationinto sucrose and starch were greater under red light than underblue light, while blue light specifically enhanced ¹⁴CO₂ incorporationinto alanine, aspartate, glutamate, glutamine, malate, citrate,lipid fraction and alcohol-water insoluble non-carbohydratefraction. Pretreatment of the algal cells in phosphate mediumin the dark, which was essential for the blue light enhancementof PEP carboxylase activity, was not necessary to induce theabove wavelength effects. Superimposition of monochromatic bluelight at low intensity (450 erg.cm^–2.sec^–1) on thered light at saturating intensity caused a significant decreasein the rate of ¹⁴CO₂ incorporation into sucrose and increasein incorporation into alanine, lipid-fraction, aspartate andother related compounds, indicating that the path of carbonin photosynthesis is regulated by short wavelengdi light ofvery low intensity. Possible effects of wavelength regulationof photosynthetic carbon metabolism in algal cells are discussed. ¹ Part of this investigation was reported at the XII InternationalBotanical Congress, Leningrad, 1975 and the Japan-US CooperativeScience Seminar "Biological Solar Energy Conversion", Miami,1976. Requests for reprints should be addressed to S. Miyachi,Radioisotope Centre, University of Tokyo, Bunkyo-ku, Tokyo 113,Japan. ⁴ Present address: Department of Chemistry, Faculty of PharmaceuticalSciences, Teikyo Univ., Sagamiko, Kanagawa, Japan. (Received August 6, 1977; )     

Changes in Photosystem Stoichiometry in Response to Environmental Conditions for Cell Growth Observed with the Cyanophyte Synechocystis PCC 6714

Changes in photosystem stoichiometry in response to shift ofenvironments for cell growth other than light regime were studiedwith the cyanophyte Synechocystis PCC 6714 in relation to thechange induced by light-quality shift. Following two environment-shiftswere examined: the shift of molecular form of inorganic carbonsource for photosynthesis from CO₂ to HCO₃^– (CO₂ stress)and the increase in salinity of the medium with NaCl (0.5 M)(Na⁺ stress). Both CO₂ and Na⁺ stresses induced the increasein PSI abundance resulting in a higher PSI/PSII stoichiometry.CO₂ stress was found to elevate simultaneously Cyt c oxidaseactivity (V_max). The feature was the same as that caused bylight-quality shift from preferential excitation of PSI to PSII(light stress) though the enhancement by either stress was smallerthan that by light stress. Under our experimental conditions,PSI/PSII stoichiometry appeared to increase at a fairly constantrate to the basal level even when the basal level had been differentlydetermined by the light-quality. Enhancing rates for PSI/PSIIstoichiometry and for Cyt c oxidase activity were also similarto each other. Since the two stresses affect the thylakoid electrontransport similarly to the shift of light-quality, we interpretedour results as follows: three environmental stresses, CO₂, Na⁺,and light stresses, cause changes in electron turnover capacityof PSI and Cyt c oxidase under a similar, probably a common,mechanism for monitoring redox state of thylakoid electron transportsystem. ¹On leave from Department of Biology, College of Natural Science,Kyngpook National University, Taegu 702-701, Korea. ₂Present address: Department of Marine Bioscience, Fukui Pre-fecturalUniversity, Obama, Fukui, 917 Japan.     

Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies

The effects of abscisic acid (ABA) on photosynthesis in leavesof Helianthus annuus L. were compared with those in leaves ofVicia faba L. After the ABA treatment, the response of photosyntheticCO₂ assimilation rate, A, to calculated intercellular partialpressure of CO₂, P_i, (A(p_i) relationship) was markedly depressedin H. annuus. A less marked depression was also observed inV.faba. However, when the abaxial epidermes were removed fromthese leaves, neither the maximum rate nor the CO₂ responseof photosynthetic oxygen evolution was affected by the applicationof ABA. Starch-iodine tests revealed that photosynthesis was not uniformover the leaves of H. annuus treated with ABA. The starch contentwas diffferent in each bundle sheath extension compartment (thesmallest subdivision of mesophyll by veins with bundle sheathextensions, having an area of ca. 0.25 mm² and ca. 50 stomata).In some compartments, no starch was detected. The distributionof open stomata, examined using the silicone rubber impressiontechniques, was similar to the pattern of starch accumulation.In V.faba leaves, which lack bundle sheath extensions, distributionof starch was more homogeneous. These results indicate that the apparent non-stomatal inhibitionof photosynthesis by ABA deduced from the depression of A(pⁱ)relationship is an artifact which can be attributed to the non-uniformdistribution of transpiration and photosynthesis over the leaf.Intercellular gaseous environment in the ABA-treated leavesis discussed in relation to mesophyll anatomy. ¹ Present address: Department of Botany, Duke University, Durham,NC 27706, U.S.A. (Received September 30, 1987; Accepted January 13, 1988)     

Effects of Oxygen on Metabolism by the Glycollate Pathway in Leaves

Segments of wheat leaves were supplied in the light with ¹⁴C-labelledserine or glucose in atmospheres containing different concentrationsof O₂ and zero or 350 parts/10⁶ CO₂. Some O₂ was necessary forsucrose synthesis from either serine or glucose but sucrosesynthesis from glucose depended on reactions with a high affinityfor O₂ whereas sucrose synthesis from serine depended both onreactions with high and low affinities for O₂. In the presenceof CO₂ sucrose synthesis from serine was decreased when theO₂ concentration was increased from 20 to 80% by volume andCO₂ was liberated; sucrose synthesis from glucose was almostunaffected by the same change in conditions. Also, in an atmospherecontaining 80% O₂ and 350 parts/10⁶ CO₂, radioactivity from[¹⁴C]serine, was incorporated into glycine. This was not truefor glucose feeding. Hence glucose provides a substrate forsucrose synthesis but not for photorespiration whereas serineis used for both processes in the presence of CO₂; in the absenceof CO₂ glucose provides substrate for both sucrose synthesisand photorespiration and serine metabolism to sucrose is restricted.