Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 3. Time-course Study on 13C Incorporation into Soluble Metabolites and Respiratory Evolution of 13CO2 from Roots and Nodules

Well-nodulated soya bean (Glycine max L.) plants were allowedto assimilate ¹³CO₂ for 10 h in the light, under steady-stateconditions in which CO₂ concentration and ¹³C abundance wereboth strictly controlled at constant levels. The respiratoryevolution of ¹³CO₂ from roots and nodules and ¹³C incorporationinto various metabolic fractions were measured during the ¹³CO₂feeding and subsequent 48 h chase period. CO₂ respired from nodules was much more rapidly labelled with¹³C than that from roots. The level of labelling (percentageof carbon currently assimilated during the ¹³COM₂ feeding period)of CO₂ respired from nodules reached a maximum of about 87 percent after 4 h of steady-state ^l3CO₂ assimilation and thereafterremained fairly constant. The absolute amount of labelled carbonevolved by the respiration of the nodules during the 10 h ¹³CO₂feeding period was 1·5-fold that of root respiration.These results demonstrated that the currently assimilated (labelled)carbon was preferentially used to support nodule respiration,while root respiration relied considerably on earlier (non-labelled)carbon reserved in the roots. Sucrose pools were mostly composed of currently assimilatedcarbon in all tissues of the plants, since the levels of labellingaccounted for 86–91 per cent at the end of the ¹³CO₂ feeding.In the nodules, the kinetics and levels of sucrose labellingwere in fairly good agreement with those of respired CO₂, whilein the roots, the level of labelling of respired CO₂ was significantlylower than that of sucrose. Succinate and malate were highly labelled in both roots andnodules but they were labelled much more slowly than sucroseand respired CO₂. The kinetics and levels of labelling of theseKrebs cycle intermediates resembled those of major amino acidswhich are derived directly from Krebs cycle intermediates. Itis suggested that large fractions of organic acids in noduleswere physically separate from the respiration site. Glycine max L., Soya bean, ¹³CO₂ assimilation, respiratory evolution of ¹³CO₂, carbon metabolism in root nodules     

Antagonism Between Malate and Ethylene in the Regulation of Avena sativa Coleoptile Elongation

Etiolated Avena sativa L. coleoptile sections were used to determinethe influence of C₂H₄ on in vivo and in vitro rates of CO₂ fixation,and to measure the influence of various permutations of C₂H₄,CO₂, and malate on growth. Whereas 1 mM malate or 320 µI^-1 CO₂ stimulated growth by approximately 100 per cent, inhibitionof growth by 10-8 µ I_-1 C₂H₄ was substantial only in thepresence of malate or CO₂ The increase in growth rate in responseto these two agents was eliminated by the simultaneous applicationof C₂H₄. The in vivo rate of dark [¹⁴C]bicarbonate fixationand in vitro enzymic assays of fixation were not measurablyinhibited by C₂H₄. These results are discussed in the lightof evidence which indicates that CO₂-stimulated growth is mediatedby dark fixation. The data do not support the view that C₂H₄inhibition of growth results from an inhibition of fixation,but suggests that C₂H₄ may inhibit some step in the processby which malate stimulates growth.     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Overcoming Incompatibility in Brassica campestris L. by Carbon Dioxide, and Dark Fixation of the Gas by Self- and Cross-pollinated Pistils

Supplementing pollen suspension cultures with CO₂ (3–5per cent) caused a marked increase in germination and tube growthin vitro in Brassica campestris L. cv. toria. A weakening ofself-incompatibility by increased CO₂ levels from 3–5per cent was observed. The percentage of pollen tubes whichpenetrated the cuticle layer of stigmatic papilla cells in self-pollinatedpistils was high when CO₂ level was 5 per cent. Phosphoenolpyruvate (PEP) carboxylase activity was greater in the pollengerminated in 4 per cent CO₂ as compared to air (0.03 per cent).A possible role of CO₂ for self-recognition and control of pollentube growth is proposed, proposed. Brassica campestris L., carbon dioxide, self-incompatibility, phosphoenol pyruvate carboxylase     

Defoliation in White Clover: Nodule Metabolism, Nodule Growth and Maintenance, and Nitrogenase Functioning During Growth and Regrowth

In two experiments, the functioning and metabolism of nodulesof white clover, following a defoliation which removed abouthalf the shoot tissue, were compared with those of undefoliatedplants. In one experiment, the specific respiration rates of nodulesfrom undefoliated plants varied between 1160 and 1830 µmolCO₂ g^–1h^–1, of which nodule ‘growth and maintenance’accounted for 22 ± 2 per cent, or 27 ± 3.6 percent, according to method of calculation. Defoliation reducedspecific nodule respiration and nodule ‘growth and maintenance’respiration by 60–70 per cent, and rate of N₂ fixationby a similar proportion. The original rate of nodule metabolismwas re-established after about 5 d of regrowth; during regrowthnodule respiration was quantitatively related to rate of N₂,fixation: 9.1 µmol CO₂ µmol^–1N₂. With the possible exception of nodules examined 24 h after defoliation,the efficiency of energy utilization in nitrogenase functioningin both experiments was the same in defoliated and undefoliatedplants: 2.0±0.1 µmol CO₂ µmol^–1 C₂H₄;similarly, there was no change in the efficiency of nitrogenasefunctioning as rate of N₂ fixation increased with plant growthfrom 1 to 22 µmol N₂ per plant h^–1. Exposure of nodulated white clover root systems to a 10 percent acetylene gas mixture resulted in a sharp peak in rateof ethylene production after 1.5–2.5 min; subsequently,rate of ethylene production declined rapidly before stabilisingafter 0.5–1 h at a rate about 50 per cent of that initiallyobserved. Regression of ‘peak’ rate of ethyleneproduction on rate of N₂ fixation indicated a value of 2.9 µmolC₂H₄ µmol^–1 N₂, for rates of N₂ fixation between1 and 22 µmol N₂ per plant h^–1. The relationshipsbetween nitrogenase respiration, acetylene reduction rates andN₂ fixation rates are discussed. Trifolium repens, white clover, defoliation, nodule respiration, N₂, fixation, nitrogenase     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

Respiratory Efflux of Carbon Dioxide from Mature and Meristematic Tissue of Uniculm Barley During Eighty Hours of Continuous Darkness

Young plants of uniculm barley were grown singly in pots ina growth room at 23/21 °C, and an irradiance of 655 µEm^–2s^–1 during each 12 h photoperiod. At the fifth leaf stage,they were subjected to 80 h of continuous darkness during whichthe rates of CO₂ efflux of vegetative shoot meristems, and maturefully expanded leaves, were separately monitored. Respiratoryefflux from the meristematic tissue was initially high, 12–15mg CO₂ g^–1 h^–1, equivalent to a daily loss in weightof 20–25 per cent. It remained high, or even rose slightly,during what would have been the normal dark period, but thenfell sharply. Even so, it was still three times that of themature tissue at the end of the experimental period. The rateof CO₂ efflux of the mature tissue began low, and fell evenfurther during the first 12 h of darkness. It then levelledoff at a rate of 2·0–2·5 mg CO2 g^–1h^–1, equivalent to a daily loss in weight of about 3 percent. It is suggested that the rate of ‘mature tissue’respiration, established after 12–24 h of darkness, mightbe a useful selection criterion to employ in attempts to increasethe total dry matter yield of the grass crop by breeding. Hordeum vulgare L., barley, respiration, synthetic respiration, maintenance respiration, meristem, mature tissue respiration, simulated sward     

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.     

Dynamics of Carbon Photosynthetically Assimilated in Nodulated Soya Bean Plants under Steady-state Conditions 1. Development and Application of 13CO2 Assimilation System at a Constant 13C Abundance

A long-term, steady-state ¹³CO₂ assimilation system at a constantCO₂ concentration with a constant ¹³C abundance was designedand applied to quantitative investigations on the allocationof photoassimilated carbon in nodulated soya bean (Glycine maxL.) plants. The CO₂ concentration in the assimilation chamberand its ¹³C abundance were maintained constant with relativevariances of less than ±0.5 per cent during an 8-h assimilationperiod. At the termination of 8-h ¹³CO₂ assimilation by plantsat early flowering stage, the currently assimilated carbon relativeto total tissue carbon (measured by the degree of isotopic saturation)were for young leaves (including flower buds), 13.9 per cent;mature leaves, 15.7 per cent; stems+petioles, 5.9 per cent;roots, 5.4 per cent and nodules, 6.9 per cent, 48 h after theend of the ¹³CO₂ assimilation period, they were 12.3, 7.5, 7.4,6.8 and 6.1 per cent, respectively. The treatment with a highconcentration of nitrate in the nutrient media significantlydecreased the allocation of ¹³C into nodules. Experiments on¹³CO₂ assimilation by plants at the pod-filling stage were alsoconducted. Labelling by ¹³C was weaker than at the early floweringstage, but an intense accumulation of ¹³C into reproductiveorgans was observed. Glycine max L., nodulated soya bean plants, ¹³CO₂ assimilation, carbon dynamics     

The Damping and Reinitiation of the Circadian Rhythm of CO2 Output in Bryophyllum Leaves in Relation to their Malate Content

The circadian rhythm of CO₂ output in leaves of Bryophyllumfedtschenkoi damps out after 3–4 d in continuous darknessand a CO₂-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 3–4 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO₂ outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO₂ fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m^–3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m^–3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO₂ output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO₂ output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO₂-fixation, malate metabolism     

Respiratory Loss of Recently Assimilated Carbon in Wheat

A series of experiments was undertaken to assess the amountof respiration associated with the growth of wheat at differentstages. Plants (or in some cases just the flag leaf) were labelledwith ¹⁴CO₂ and the amount of ¹⁴CO₂ respired during the subsequent48 or 72 h was measured. The evolution of ¹⁴C, expressed asa percentage of the amount initially assimilated (referred toas the R/A value) was used as a measure of the overall efficiencyof dry matter production. Respiratory ¹⁴CO₂ evolution from labelledplants was most rapid in the first 12 h after labelling, thereafterdeclining rapidly. Evolution was also more rapid following labellingsat the end of the light period (dusk) than at the beginningof it (dawn). The R/A values were greatest (42 and 50 per centrespectively for dawn- and dusk-labelled plants) for young plantsand least (13 and 28 per cent respectively) for plants duringmid grain filling. When flag leaves, as distinct from wholeplants, were labelled, R/A values were lower still (9 and 21per cent respectively), indicating that flag leaf assimilatewas used efficiently in grain production. The calculated minimum R/A for the formation of grain material(10 per cent protein, 90 per cent starch) was 6.2 per cent.That the experimentally determined values were greater thanthis is attributed to the turnover of carbon in enzymes, toother maintenance processes, and possibly to the operation ofthe pentose phosphate pathway of glucose oxidation. R/A valueswere lower in those plants labelled at the beginning than thoseat the end of the photoperiod. This was considered to be a consequenceof refixation of respiratory ¹⁴CO₂ during the light. The higherR/A values found for young plants were considered to be a consequenceof the greater percentage of ¹⁴C translocated to the roots (rootsbeing unable to refix respired CO₂) and of greater turnoverof enzymes associated with more active metabolism. Triticum, wheat, respiration, carbon assimilation, carbon loss, grain-filling     

Metabolism of Barley Leaves Inoculated with Erysiphe graminis Merat

Inoculating Proctor barley leaves with Erysiphe graminis decreasedrates of photosynthesis, after an initial lag period, and increasedrespiration. Increasing the area inoculated progressively decreased ratesof photosynthesis, but the effects cannot be attributed to asimple loss of leaf area. When less than 30 per cent of a leafwas inoculated, decreases were equivalent to area losses greaterthan those inoculated; when more than 30 per cent was inoculatedthe photo-synthetic losses were equivalent to area losses lessthan those inoculated. Although the relative effects of E. graminis on photosynthesisand respiration were of the same order, the absolute effectson photosynthesis were greater than those on respiration. Inoculating30 per cent of a leaf decreased photosynthesis by 5–6mg CO₂/dm²/hr from 12.9 in the uninoculated controls to 7.3.Respiration increased by 0.6 mg CO₂/dm/hr, from 1.7 to 2.3-     

The Incorporation of 14CO2 into Green Peas in the Dark

Shelled green peas (ripening seeds of Pisum sativum var. Onward)were kept in the dark for 2 or 3 days in an atmosphere, eitherof air or 10 per cent carbon dioxide in air, containing ¹⁴CO₂.Samples were removed at intervals, the acids of the T.C.A.C.extracted, estimated, and their content of ¹⁴C measured. Incorporationof ¹⁴C was mainly into the carboxyl carbon atoms of the acidswhich, with the exception of citrate, rose in specific activityrapidly for the first 4–6 h and then levelled off androse slowly for the rest of the experiment. The final valuesattained, again with the exception of C-6 of citrate, were muchbelow that of the tissue carbon dioxide. The cause of this failureto equilibrate with tissue carbon dioxide is discussed. Twomain carboxylation reactions are proposed, one from pyruvate(or other three carbon acid) to malate and the other from -oxoglutarateto oxalsuccinate and so to C-6 of citrate. The value of thevelocity constant of the first of these reactions was shownto be markedly decreased by increase in tissue carbon dioxidewhile that for the second carboxylation was unaffected. ¹⁴Cmoved into soluble amino-acids rapidly at first and then moreslowly; protein received ¹⁴C at a high rate throughout the experimentsmainly by isotopic exchange reactions. Calculations were madeof the rate of movement of carbon in the T.C.A.C. which wouldhave been required to give the observed changes in specificactivity of the metabolites but no scheme tested fitted allthe results satisfactorily.     

Effects of Prolonged Darkness on the Sensitivity of Leaf Respiration to Carbon Dioxide Concentration in C3and C4Species

Predicting responses of plant and global carbon balance to theincreasing concentration of carbon dioxide in the atmosphererequires an understanding of the response of plant respirationto carbon dioxide concentration ([CO₂]). Direct effects of thecarbon dioxide concentration at which rates of respiration ofplant tissue are measured are quite variable and their effectsremain controversial. One possible source of variation in responsivenessis the energy status of the tissue, which could influence thecontrol coefficients of enzymes, such as cytochrome-c oxidase,whose activity is sensitive to [CO₂]. In this study we comparedresponses of respiration rate to [CO₂] over the range of 60to 1000 µmol mol^-1in fully expanded leaves of four C₃andfour C₄herbaceous species. Responses were measured near themiddle of the normal 10 h dark period, and also after another24 h of darkness. On average, rates of respiration were reducedabout 70% by the prolonged dark period, and leaf dry mass perunit area decreased about 30%. In all species studied, the relativedecrease in respiration rate with increasing [CO₂] was largerafter prolonged darkness. In the C₃species, rates measured at1000 µmol mol^-1CO₂averaged 0.89 of those measured at 60µmol mol^-1in the middle of the normal dark period, and0.70-times when measured after prolonged darkness. In the C₄species,rates measured at 1000 µmol mol^-1CO₂averaged 0.79 of thoseat 60 µmol mol^-1CO₂in the middle of the normal dark period,and 0.51-times when measured after prolonged darkness. In threeof the C₃species and one of the C₄species, the decrease in theabsolute respiration rate between 60 and 1000 µmol mol^-1CO₂wasessentially the same in the middle of the normal night periodand after prolonged darkness. In the other species, the decreasein the absolute rate of respiration with increase in [CO₂] wassubstantially less after prolonged darkness than in the middleof the normal night period. These results indicated that increasingthe [CO₂] at the time of measurement decreased respiration inall species examined, and that this effect was relatively largerin tissues in which the respiration rate was substrate-limited.The larger relative effect of [CO₂] on respiration in tissuesafter prolonged darkness is evidence against a controlling roleof cytochrome-c oxidase in the direct effects of [CO₂] on respiration.Copyright 2001 Annals of Botany Company Carbon dioxide, respiration, Abutilon theophrasti(L.), Amaranthus retroflexus(L.),Amaranthus hypochondriacus (L.), Datura stramonium(L.), Helianthus annuus(L.), Solanum melongena(L.), Sorghum bicolor(L. Moench), Zea mays     

Effect of Temperature on Photosynthesis and Photorespiration of Wheat Leaves

Wheat plants were grown in a controlled environment with daytemperatures of 18 ?C and with 500 µ Einsteins m^–28^–1 of photosynthetically active radiation for 16 h. Beforeanthesis and 2 to 3 weeks after, rates of net photosynthesiswere measured for leaves in 2 or 21% O₂ containing 350 vpm CO₂at 13, 18, 23, and 28 ?C and with 500 µEinsteins m^–2s^–1 of photosynthetically active radiation. Also, underthe same conditions of light intensity and temperature, therates of efflux of CO₂ into CO₂-free air were measured and,for mature flag leaves 3 to 4 weeks after anthesis, gross andnet photosynthesis from air containing 320 vpm ¹⁴CO₂ of specificactivity 39?7 nCi µmol^–1. When the O₂ concentration was decreased from 21 to 2% (v/v)the rate of net photosynthesis increased by 32 per cent at thelowest temperature and 54 per cent at the highest temperature.Efflux of CO₂ into CO₂-free air ranged from 38 per cent of netphotosynthesis at 13 ?C to 86 per cent at 28 ?C. Gross photosynthesis,measured by the ¹⁴C assimilated during 40 s, was greater thannet photosynthesis by some 10 per cent at 13 ?C and 17 per centat 28 ?C. These data indicate that photorespiration was relativelygreater at higher temperatures.     

Long-term Respiratory Cost of Maintenance and Growth of Field-grown Young Hinoki Cypress (Chamaecyparis obtusa)

Respiration rate of the entire above-ground parts of field-grown8-year-old hinoki cypress [Chamaecyparis obtusa(Sieb. et Zucc.)Endl.] was measured at monthly intervals over a 5-year period,to evaluate the trend in proportion of maintenance and growthcomponents of respiration with stand development. Representativesample trees were selected for respiration measurements. Theannual respiration rates of individual sample trees were combinedand partitioned into maintenance and growth components by regressingspecific respiration rate on mean relative growth rate. Maintenanceand growth respiration coefficients generated in this way were5.2 mol CO₂kg^-1year^-1and 39 mol  CO₂kg^-1, which are equivalentto 14.3 mg C kg^-1C h^-1(at mean annual air temperature of 15.1°C) and 0.94 kg C kg^-1C. Considering the maintenance andgrowth respiration coefficients, and phytomass and phytomassincrement of individual trees in the stand, the maintenanceand growth respiration rates of the stand were estimated. Theproportion of the maintenance respiration increased, whereasthat of the growth respiration decreased with stand development,due to decreasing relative growth rate.Copyright 1997 Annalsof Botany Company Chamaecyparis obtusa; growth respiration coefficient; hinoki; maintenance respiration coefficient; stand respiration     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

Development of Lipid Synthesis from CO2 in Avena Leaves during Greening of Etiolated Seedlings

The development of the lipid synthesizing system in Avena leafsections was examined in connection with carbon fixation duringthe greening of etiolated seedlings under light. During theinitial 2 h illumination there was a low level of CO₂ fixationby PEP carboxylation, but its products, malate and citrate,did not serve as a carbon source for lipid synthesis, althoughlipid synthesis from acetate had already been established. Withthe initiation of Calvin cycle activity after the initial 2h illumination, lipid synthesis began, with CO₂ fixed by RuBPcarboxylation serving exclusively as the carbon source. Fattyacid synthesis in the leaves during the initial 3 h illumination,unlike the fatty acid synthesis thereafter, was insensitiveto thiolactomycin, an inhibitor of type II fatty acid synthetasecontained in the plastids, and was not dependent on light, incontrast to light-dependent activity in greened leaves. The distribution of ¹⁴C incorporated into lipid molecules fromNaH¹⁴CO₃ showed an equal ratio of ¹⁴C in fatty acid, glyceroland choline moieties of labeled phosphatidylcholine, but a denserradioactivity in the galactose moiety than in the residual moietyof mono- and di-galactosyldiacylglycerols. This suggests a regulatedsupply of glycerol, choline and fatty acid moieties for phosphatidylcholinesynthesis, and an excess supply of galactose to diacylglycerolmoiety for galactosyldiacylglycerol synthesis in Avena leaves. (Received October 31, 1984; Accepted January 25, 1985)     

The Respiration of Mature Field Bean (Vicia faba L.) Leaves During Prolonged Darkness

Dark respiration in attached and detached mature leaves of thefield bean (Vicia faba L.) was studied whilst leaves experiencedup to 60 h of darkness. The results showed: (1) the initialrespiration rate to vary according to the irradiance duringthe previous photoperiod; (2) the dark respiration rate (perunit area) of attached leaves to be essentially constant duringa normal 12 h night although there was a rapid loss in leafd. wt during this time; (3) after 12 h, the respiration rateof attached leaves decayed to an asymptotic value at about 36h; (4) the respiration rate of leaves detached at the end ofthe photoperiod and maintained in the dark on deionised water,decayed only after 36 h of darkness; (5) there was no differencebetween the respiration rate of attached and detached leavesduring the normal 12 h night. It is concluded that the dark respiration of attached fieldbean leaves is intially related to the synthesis and translocationof sucrose in addition to maintenance. After about 36 h, whenthe rate of CO₂ efflux is more or less steady, the CO₂ effluxreflects the intensity of maintenance processes only. The maintenancerespiration rate (determined after 60 h in the dark) rangedfrom 062 to 151 mg CO₂ (g d. wt)^–1 h^–1 but wasrelatively unaffected by several applied treatments. Vicia faba L., field bean, respiration, maintenance, nitrate, non-structural carbohydrate, export     

STUDIES ON THE RE-ASSIMILATION OF RESPIRATORY CO2 IN ILLUMINATED LEAVES

Experiments were performed, using rice, barley and Hydrangealeaves, to examine the re-assimilation of respiratory ¹⁴CO₂while photosynthesis is going on in an open air flow system. It was found that the leaves which had assimilated ¹⁴CO₂ beforehandevolved, when kept under photosynthesizing conditions, threeto four tenths (variable according to plant species and externalconditions) of the amount of ¹⁴CO₂ to be produced in the dark.Such an incomplete re-utilization of ¹⁴CO₂ was observed alsoin spinach leaf homogenate as well as in the leaves which hadpreviously absorbed ¹⁴C-glucose. The ¹⁴CO₂ output in rice leaves was found to be acceleratedby the light of high intensity. A possibility of light stimulationon the respiration was suggested. (Received October 7, 1961; )