Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues1: XVII. THE EFFECT OF IODOACETATE ON THE CO2 OUTPUT, PATHWAYS OF GLUCOSE RESPIRATION AND CONTENTS OF PHOSPHATE ESTERS IN STRAWBERRY LEAVES

When specifically labelled glucose was fed to strawberry leaves,the C₆/C₁, quotient (rate of release of ¹⁴CO₂ from glucose-6-¹⁴C/rateof release of ¹⁴CO₂ from glucose-1¹⁴C ranged from 0.27 to 0.35in leaves in water and from 0.46 to 0.96 in leaves fed withiodoacetate. These quotients indicate that both the glycolyticand the pentose phosphate pathways participate in the respirationof strawberry leaves, with a greater contribution from the formerin the iodoacetate increased CO₂ output. Concurrently with the increase of CO² output in iodoacetate,the contents of glucose-6-phosphate (G6P), fructose-6 (F6P)and fructose-1,6-diphosphate (FDP) increased greatly; therewas a smaller increase of phosphoenol-pyruvate (PEP). The increasein the CO₂ output in iodoacetate may be explained solely onthe basis that the increases of G6P and FDP accelerate the ratesrespectively of the pentose phosphate pathway and of glycolysisand traffic into the tricarboxylic acid cycle. The increasein content of G6P and FDP is attributed to an increase in theaccessibility of enzymes and substrates caused by iodoacetate.Alternatively the increased CO₂ output in iodoacetate may bepartly due to uncoupling of oxidative phosphorylation.     

Studies on the effect of certain enzymic poisons on the metabolism of storage organs IV. Respiration and nitrogen assimilation by radish root slices in relation to feeding with KCN

At low and high concentrations, respectively, KCN stimulatedand inhibited the CO₂ output of radish root slices. Analysisof tissue slices showed that CO₂ production is nearly accountedfor by the loss in carbohydrates. After 48 hr, the content ofprotein-N was slightly changed in all the cyanide-treated tissues;whereas, that of soluble-N decreased markedly at high cyanideconcentrations and hardly changed at low concentrations. Leakageof soluble-N occurred at high concentrations of cyanide. The nitrogen compounds taken up were incorporated into the nitrogenpool of radish slices. KCN retarded uptake of nitrogen compounds,inhibited their utilization and led to excessive leakage ofsoluble-N from the tissues into the media. Increased CO₂ outputof slices in nitrogen media was largely accounted for by theloss in carbohydrates from the tissues. High concentrations of cyanide are thought to inhibit CO₂ outputthrough inhibition of the oxidase system and accompanying phosphorylations.The present results with low concentrations further substantiatethe uncoupling theory as a main factor involved in respiration. ¹Permanent address: Department of Botany, Faculty of Science,University of A'in Shams, Abbassia, Cairo, Egypt, U.A.R. (Received October 3, 1969; )     

Studies on the effect of certain enzymic poisons on the metabolism of storage organs III. Uptake and utilization of sucrose by radish root slices in presence of iodoacetate

Iodoacetate greatly retarded the uptake of sucrose and slightlyaffected its inversion by radish root slices. Carbohydrate content of the samples decreased substantiallyboth in water and in iodoacetate. Feeding with sucrose led tomarked accumulation of carbohydrates and supplemental additionof iodoacetate induced less accumulation of carbohydrates. Iodoacetate caused exudation of nitrogen fractions into theculture media. Protein synthesis via amino acids seems to beoperative in iodoacetate treated slices. It is also suggestedthat nitrate-N, in presence of sucrose, is converted into peptidesand proteins. Addition of iodoacetate to sucrose media inhibitedthis pathway of protein synthesis. Both sucrose and iodoacetate (4 x 10^–4M) stimulated theCO₂ output whereas 25 x 10^–4M iodoacetate did not changethe CO₂ output when compared with that of controls. Sucroseand iodoacetate (4 x 10^–4 M) when joined together maskedthe accelerating effect of each other. ¹Present address: Department of Botany, Faculty of Science,University of A'in Shams, Abbassia, Cairo, Egypt, U. A. R. (Received November 6, 1968; )     

Operation of the reductive pentose phosphate cycle daring the induction period of photosynthesis in Chlorella

When Chlorella oulgaris ll h cells grown in air containing 4%CO₂ (high-CO₂ cells) were given low concentrations of¹⁴CO₂ (<150ppm), the initial rate of photosynthetic ¹⁴CO₂ fixation wasvery low and linear ¹⁴CO₂ fixation was observed after an inductionperiod which lasted for ca. 45 min. No such induction period was observed when high-CO₂ cells weregiven high concentrations of ¹⁴CO₂ (10,000 ppm) or when IOW-CO₂cells were given either low or high concentrations of ¹⁴CO₂,supporting the observations by Briggs and Whittingham (l). However,irrespective of CO₂ concentrations during growth and of ¹⁴CO₂concentrations during the experiments, most of the ¹⁴C was incorporatedinto phosphate esters during the initial periods of photosynthetic¹⁴CO₂ fixation. These results are in sharp contrast to the reportby Graham and Whittingham (4). ¹ Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received June 30, 1979; )     

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; )     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

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     

Stimulation of Malate Synthesis by Glycolate in Tomato Leaves in Relation to CO2 Concentration

The mechanism by which malate synthesis from CO2 is increasedunder low concentrations of CO₂ was investigated in C₃ plants.A number of metabolites were administered to illuminated tomatoleaves, and their effects on the incorporation of ¹⁴CO₂ intomalate were determined. Compared with water as a control, glycolate,glyoxylate, D,L-glycerate, glycine, phosphoglycolate and L-serineincreased malate synthesis by factors of 6.8, 3.8, 3.3, 2.5,2.3 and 2.2, respectively. The effect of exogenous glycolateon malate synthesis from CO₂ was dependent on its concentrationup to 100 mu, but was independent of ambient CO₂ concentration.The feeding of l-¹⁴C-glycolate in the light indicated that glycolatestimulated the carbon flow from CO₂ to malate. The analysis of the products of ¹⁴CO₂ fixation in illuminatedleaves supplied with glycolate showed increases in malate andsugar and decreases in serine and phosphate esters. However,this stimulated malate synthesis ceased when malonate was suppliedsimultaneously with glycolate. Treatment with glycolate didnot affect the dark ¹⁴CO₂-fixation, but increased the ¹⁴C-malatesynthesis, with a corresponding decrease in ¹⁴C-aspartate and14^C-glutamate. These results suggest that exogenous glycolateactivates malate dehydrogenase in leaves, and that the increasedglycolate formation at low CO₂ concentrations is associatedwith the increased malate synthesis from CO₂. (Received January 12, 1981; Accepted May 20, 1981)     

Carbon Dioxide Effects on Carbohydrate Status and Partitioning in Rice

The atmospheric carbon dioxide (CO₂) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO₂ concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO₂ concentrations of 160, 250, 330, 500, 660, and 900µmolCO₂ mol¹ air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO₂ concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO₂ concentration but tended to level off above 500µmolmol^–1 CO₂. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol^–1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO₂ concentration. At maturity, increasing CO₂ concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO₂concentrations below 330µmol mol^–1 than for treatmentsat concentrations above ambient Increasing CO₂ concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO₂ enrichment, starch, sucrose     

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.     

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; )     

Influence of Elevated CO2 and Temperature on the Photosynthesis and Respiration of White Clover Dependent on N2 Fixation

Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N₂ fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO₂, and temperature 23/18 °C day/night temperaturesat 680 µmol mol^–1 CO₂, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol^–1 CO₂ (C340)After 3–4 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO₂ and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 17–29%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO₂ mol H₂O^–1)was also significantly increased Plants acclimated to elevatedCO₂, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves ‘instantaneously’exposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO₂, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO₂ at 23 °C increased graduallyfrom approx 10 % at 100 µmol m^–1 s^–1 to >27 % at 1170 µmol m^–2 s^–1 In parallel, wateruse efficiency increased by 20–40 % at 315 µmolm^–2 s^–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m^–2 s^–1 In parallel,water use efficiency increased by 20–40 % at 315 µmolm^–2 s^–1 In parallel, water use efficiency increasedby 20–40 % at 315 µmol m^–2 s^–1 to approx100 % at the highest irradiance Elevated CO₂, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO₂ and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N₂, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO₂, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO₂, elevated temperature, water use efficiency, N₂ fixation     

Effects of Elevated Carbon Dioxide Concentration in the Dark on the Growth of Soybean Seedlings

Previous work has shown that elevated carbon dioxide (CO₂) concentrationsin the dark reversibly reduce the rate of CO₂ efflux from soybeans.Experiments were performed exposing soybean plants continuallyto concentrations of 350 or 700 cm³ m^-3 for 24 h d^-1, or to350 during the day and 700 cm³ m^-3 at night, in order to determinethe importance of the reduced rate of dark CO₂ efflux for plantgrowth. High CO₂ applied only at night conserved carbon andincreased dry mass during initial growth compared with the constant350 cm³ m^-3 treatment. Long-term net assimilation rate was increasedby high CO₂ in the dark, without any increase in daytime leafphotosynthesis. However, leaf area ratio was reduced by thedark CO₂ treatment to values equal to those of plants continuallyexposed to the higher concentration. From days 14-21, leaf areawas less for the elevated night-time CO₂ treatment than foreither the constant 350 or 700 cm³ m^-3 treatments. For the days7-21-period, relative growth rate was significantly reducedby the high night CO₂ treatment compared with the 350 cm³ m^-3continuous treatment. The results indicate that some functionallysignificant component of respiration was reduced by the elevatedCO₂ concentration in the dark.Copyright 1995, 1999 AcademicPress Glycine max L. (Merr.), carbon dioxide, plant growth, respiration     

Transport and Fixation of Inorganic Carbon during Photosynthesis in the Cells of Anabaena Grown under Ordinary Air. II. Effect of Sodium Concentration during Growth on the Induction of Active Trasport System for IC

The requirement of sodium for growth of Anabaena variabilisM3 was investigated under low (0.04%) and high (1.5 or 5%) CO₂conditions. The growth rates under both conditions were stronglyaffected by NaCl concentrations up to 0.5 mM in the medium.In the presence of 40 µM NaCl, the cells were not ableto grow under a low CO₂ condition, but were able to grow undera high CO₂ condition. The sodium requirement for growth wasdependent on pH: in the Na⁺-deficient condition, cells couldgrow at pH6.8, while no growth occurred at pH 8.2, suggestingthat the requirement of Na⁺ for growth observed in the low CO₂condition can be substituted for by a lower pH. In the presence of 20 mM NaCl at pH 7.8, ¹⁴CO₂ as well as H¹⁴CO₃^–were actively transported into the cells which had been grownin air. In contrast, the transport of both of these inorganiccarbon (IC) species was suppressed under the Na⁺-deficient condition.These results suggest that sodium is required for the stimulationof transport of IC during photosynthesis. This is one of thereasons why Na⁺ is required for the growth of Anabaena underordinary air and alkaline conditions. (Received September 27, 1986; Accepted March 26, 1987)     

The Effects of CO2 Enrichment and Nutrient Supply on Growth Morphology and Anatomy of Phaseolus vulgaris L. Seedlings

Plants of Phaseolus vulgaris were grown from seed in open-topgrowth chambers at the present (P, 350 µmol mol^–1)atmospheric CO₂ concentration and at an elevated (E, 700 µmolmol^–1) CO₂ concentration, and at low (L, without additionalnutrient solution) and high (H, with additional nutrient solution)nutrient supply for 28 d The effects of CO₂ and nutrient availabilitywere examined on growth, morphological and biochemical characteristics Leaf area and dry mass were significantly increased by CO₂ enrichmentand by high nutrient supply Stomatal density, stomatal indexand epidermal cell density were not affected by elevated CO₂concentration or by nutrient supply Leaf thickness respondedpositively to CO₂ increasing particularly in mesophyll areaas a result of cell enlargement Intercellular air spaces inthe mesophyll decreased slightly in plants grown in elevatedCO₂ Leaf chlorophyll content per unit area or dry mass was significantlylower in elevated CO₂ grown plants and increased significantlywith increasing nutrient availability The content of reducingcarbohydrates of leaves, stem, and roots was not affected byCO₂ but was significantly increased by nutrient addition inall plant parts Starch content in leaves and stem was significantlyincreased by elevated CO₂ concentration and by high nutrientsupply Phaseolus vulgaris, elevated atmospheric CO₂, CO₂-nutrient interaction, stomatal density, leaf anatomy, chlorophyll, carbohydrates, starch     

Photosynthetic carbon metabolism in photoautotrophically and photomixotrophically cultured tobacco cells

Labeling patterns of light and dark ¹⁴CO₂-fixation in photoautotrophicallyand photomixotrophically cultured tobacco cells were determined.During short term ¹⁴CO₂ fixation under light, malate(C₃–C₃carboxylation) was heavily labeled as were phosphoglyceric acidand sugar phosphates(C₁–C₅ carboxylation). Dark fixationcould not account for this high ¹⁴CO₂ incorporation into theC₄ compounds linked to PEPCase. Two carboxylation pathways linkedto the RuBPCase and PEPCase were indicated in ¹⁴CO₂-fixationin light in photoautotrophically and photomixotrophically culturedcells. (Received October 25, 1979; )     

Responses of Noogoora Burr (Xanthium occidentale Bertol.) to Nitrogen Supply and Carbon Dioxide Enrichment

We studied the responses of Xanthium occidentale (Bertol.) (cockleburor Noogoora burr), a noxious weed, to atmospheric CO₂ enrichmentand nitrate-N concentrations in the root zone ranging from 0.5to 25 mM. CO₂ enrichment (1500 cm³ m^–3) increased dry-matterproduction to about the same extent (18 per cent) at all levelsof supplied N: most of the increment in dry matter was distributedequally between leaves and roots so that there was little effecton shoot-to-root dry-weight ratios. Growth was stimulated greatlyby N and plateaued at 12 mM supplied N. Shoot-to-root dry-weightand total N ratios increased with increasing N supply. CO₂ enrichmenthad no effect on the total amount of N accumulated by plants,but increased the N-use efficiency of leaves. Enriched plantshad lower concentrations and quantities of N in their leavesthan controls, and therefore lower shoot-to-root total N ratios.Little free NO₃^– accumulated in organs of control or enrichedplants. NO₃^– was the major form of N in xylem sap fromdetopped plants at low supplied NO₃-N, but amino N was equalin importance at high supplied NO₃-N in control and enrichedplants. Concentrations of NO₃^– were lower in the xylemsap of CO₂ enriched plants. It was concluded that the betterN-use efficiency of CO₂ enriched plants could result in increasedgrowth of X. occidentale in regions of marginal soil fertilityas atmospheric levels of CO₂ increase. CO₂ enrichment, nitrogen, Xanthium, Noogoora burr, cocklebur     

Effect of Light Intensity, Carbon Dioxide Concentration, and Leaf Temperature on Gas Exchange of Spray Carnation Plants

The rates of CO₂ assimilation by potted spray carnation plants(cv. Cerise Royalette) were determined over a wide range oflight intensities (45–450 W m^–2 PAR), CO₂ concentrations(200–3100 vpm), and leaf temperatures (5–35 °C).Assimilation rates varied with these factors in a way similarto the response of single leaves of other temperate crops, althoughthe absolute values were lower. The optimal temperature forCO₂ assimilation was between 5 and 10 °C at 45 W m^–2PAR but it increased progressively with increasing light intensityand CO₂ concentration up to 27 °C at 450 W m^–2 PARand 3100 vpm CO₂ as expressed by the equation TOpt = –6.47-h 2.336 In G + 0.031951 where C is CO₂ concentration in vpmand I is photo-synthetically active radiation in W m^–2.CO₂ enrichment also increased stomatal resistance, especiallyat high light intensities. The influence of these results on optimalization of temperaturesand CO₂ concentrations for carnation crops subjected to dailylight variation, and the discrepancy between optimal temperaturesfor growth and net photosynthesis, are discussed briefly     

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; )     

Response of Photosynthesis, Stomatal Conductance and Water Use Efficiency to Elevated CO2 and Nutrient Supply in Acclimated Seedlings of Phaseolus vulgaris L.

Plants of Phaseolus vulgaris L were grown from seed in open-topgrowth chambers at present day (350 µmol mol^–1)and double the present day (700 µmol mol^–1) atmosphericCO₂ concentration with either low (L, without additional nutrientsolution) or relatively high (H, with additional nutrient solution)nutrient supply Measurements of assimilation rate, stomatalconductance and water use efficiency were started 17 d aftersowing on each fully expanded, primary leaf of three plantsper treatment Measurements were made in external CO₂ concentrations(C₂) of 200, 350, 450, 550 and 700 µmol mol^–1 andrelated to both C_a and to C₁, the mean intercellular space CO₂concentration Fully adjusted, steady state measurements weremade after approx 2 h equilibration at each CO₂ concentration The rate of CO₂ assimilation by leaves increased and stomatalconductance decreased similarly over the range of C_a or C₁ inall four CO₂ and nutrient supply treatments but both assimilationrate and stomatal conductance were higher in the high nutrientsupply treatment than in the low nutrient treatment The relationbetween assimilation rate or stomatal conductance and C₁ wasnot significantly different amongst plants grown in present-dayor elevated CO₂ concentration in either nutrient supply treatment,i e there was no evidence of down regulation of photosynthesisor stomatal response Increase in CO₂ concentration from 350to 700 µmol mol^–1 doubled water use efficiency ofindividual leaves in the high nutrient supply treatment andtripled water use efficiency in the low nutrient supply treatment The results support the hypothesis that acclimation phenomenaresult from unbalanced growth that occurs after the seed reservesare exhausted, when the supply of resources becomes growth limiting CO₂ enrichment, Phaseolus vulgaris L., net CO₂ assimilation rate, stomatal conductance, water use efficiency