Effects of growth temperature on photosynthetic carbon metabolism in green plants II. Photsoynthetic 14CO2-incorporation in plants acclimatized to varied temperatures

During photosynthetic ¹⁴CO₂-fixation, leaves of plants suchas wheat, the broad bean and spinach, which had been acclimatizedto high temperature (20–25?C), incorporated much moreradioactivity into sucrose, and less into glycine and serinein comparison with similar plants grown in the cold (mean temperature,5–7?C). Radioactivities incorporated into glycine and serine greatlydescreased on the addition of -hydroxyethylsulfonate or on theremoval of oxygen from the atmosphere, indicating that thesecompounds are synthesized through the glycolate pathway. In leaves of wheat grown under low temperatures, relativelyhigh radioactivity was detected in ribulose 1,5-diphosphateamong the photosynthetic ¹⁴CO₂-fixation products, whereas practicallyno radioactivity was detected in this compound in leaves ofwheat which had been acclimatized to high temperatures. We assumedthat the carboxylation reaction of ribulose 1,5-diphosphateis suppressed in plants acclimatized to low temperatures. It was further inferred that the C-2 and C-2 moiety of ribulose1,5-diphosphate accumulating as a result of suppression of carboxylationis converted to glycine and serine through the glycolate pathway. The possibility was also discussed that during photosyntheticCO₂-fixation in wheat leaves at least a part of the C₆-compoundformed by the carboxylation of ribulose 1,5-diphosphate is directlyconverted to sugar phosphate. ¹Part of this investigation was reported at the 2nd InternationalCongress on Photosynthesis Research at Stresa, Italy, June 1971.This paper is based on a dissertation submitted by S.S. to theFaculty of Science, the University of Tokyo, in partial fulfilmentof the requirements for a Ph.D. degree. ²Present address: Department of Botany, Faculty of Science,University of Tokyo, Tokyo, Japan. (Received July 20, 1973; )     

Effects of growth temperture on photosynthetic carbon metabolism in green plants I. Photosynthetic activites of various plants acclimatized to varied temperatures

In wheat, pea, barley, broad bean and rape, the photosyntheticcapacities in the leaves of plants acclimatized to a highertemperature (20–25?C) were much higher than those in thesame plants grown at low outdoor temperatures in winter (meanairtemperature, 5–7?C). On transferring the cold-grown wheat plants (vats, 5–7?C)to the higher temperature (25/20?C), the Photosynthetic rateof laves remained unchanged for the first 8 hr, then graduallyincreased to attain after 16 hr a maximum level which was thesame as that in wheat plants grown at the higher temperature(growth box, 20–25?C). When intact wheat without soilwas taken from the cold winter field and the attached leaveswere placed in the chamber at 25?C, the Photosyntheic rate ofthe attached leaves increased sluggishly for 2 hr, then remarkablyincreased to attain the maximum level 9 hr afer transferralto the chamber. When the leaves detached from wheat grown inthe winter field were transferred to the assimilation chamberkept at 25?C, the rate started to increase without a lag periodand attained the maximum level within 3 hr. The optimum temperaturefor photosynthesis shifted in parallel with the rise of airtemperature under which the wheat had been grown. The slopes of increase in the photosynthetic rates with increasingintensity of illumination wwere practically the same in wheatgrown under different temperatures. It was found that the total amount of sucrose in wheat grownat low temperatures in the winter was higher than that in thosegrown at the high temperature. ¹Present address: Department of Botany, Faculty of Science,University of Tokyo, Tokyo, Japan. (Received July 19, 1973; )     

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.     

Reactions of birch leaves to changes in light during early ontogeny: comparison between in vivo and in vitro techniques to measure carbon uptake

Trends in several photosynthetic parameters and their responseto changed growth light were followed for 15 d in leaves ofyoung birch saplings using a rapid-response gas exchange measuringequipment. These in vivo measurements were compared to biochemicalassays that were made from the same leaves after the gas exchangestudies. The measurements were made on leaves that were selectedprior to the study and were at that time of similar age. Forthe first 7 d the photosynthetic parameters were followed fromthe growth conditions of moderate light (200 µmol m^–2s^–1; referred to as controls later in the text). On day7 some of the saplings were transferred to grow either underhigh (450 µmol m^–2 s^–1; referred to as highlight plants) or low (75 µmol m^–2 s^–1; referredto as low light plants) light and the capability of the preselectedleaves for acclimation was followed for 6 d. For comparison,at the end of the experiment the measurements were made on bothcontrols and on young leaves that had developed under high andlow light. Generally the in vivo measured rate of CO₂ uptake (gross photosynthesis)both at 310 ppm CO₂ and 2000 ppm CO₂ corresponded very wellto the biochemically determined CO₂ fixation capacity in vitroafter rapid extraction (measured as the initial and total activityof Rubisco, respectively). However, if the flux of CO₂ intothe chloroplasts was limited by the closure of the stomata,as was the case of the high light plants, then the in vitromeasured Rubisco activity was greater than the in vivo measuredCO₂ uptake. V_max, calculated from the mesophyll conductanceat 1% O₂, exceeded the initial activity of Rubisco (assayedat saturating RuBP and CO₂) constantly by 60%. The catalyticactivity of Rubisco in birch leaves was overall very low, evenwhen calculated from the total activity of Rubisco (K_cat 0.63–1.18 s^–1), when compared to herbaceous C₃ species. Signs of light acclimation were not observed in most of thephotosynthetic parameters and in chloroplast structure whenmature birch leaves were subjected to changes in growth lightfor 6 d. However, the change of the growth light either to highor low light caused day-to-day fluctuations in most of the measuredphotosynthetic parameters and in the case of the high lightplants signs of photoinhibition and photodestruction were alsoobserved (decrease in the amount of chlorophyll and increasein chlorophyll a/b ratio). As a result of these fluctuationsthese plants achieved a new and lower steady-state conditionbetween the light and dark reactions, as judged from the molarratio of RuBP to Rubisco binding site. Key words: Acclimation, photosynthesis, light, Rubisco, birch     

Photosynthesis by Flag Leaves of Wheat in Relation to Protein, Ribulose Bisphosphate Carboxylase Activity and Nitrogen Supply

The effects of nitrate supply on the composition (cell numbers,protein and chlorophyll contents) of flag leaves of winter wheatgrown with two amounts of N fertilizer and of spring wheat grownin the glasshouse under controlled nitrate supply are describedand related to photosynthesis. Nitrogen deficiency decreasedthe size of leaves, mainly by reducing cell number and, to asmaller extent, by decreasing cell volume. Protein content perunit leaf area, per cell and per unit cell volume was largerwith abundant N. Total soluble protein, ribulose bisphosphatecarboxylase-oxygenase (RuBPc-o) protein and chlorophyll changedin proportion irrespective of nitrogen supply and leaf age.Photosynthesis per unit area of flag leaf and carboxylationefficiency in both winter and spring wheat were proportionalto the amount of total soluble protein up to 7.0 g m^–2and to the amount of RuBPc-o protein up to 4.0 g m^–2.However, photosynthesis did not increase in proportion to theamount of total soluble or RuBPc-o protein above these amounts.In young leaves with a high protein content the measured ratesof photosynthesis were lower than expected from the amount andactivity of RuBPc-o. Carboxylation per unit of RuBPc-o protein,measured in vitro, was slightly greater in N-deficient leavesof winter wheat but not of spring wheat. RuBPc-o activity perunit of RuBPc-o protein was similar in winter and spring wheatleaves and remained approximately constant with age, but increasedin leaves showing advanced senescence. RuBPc-o protein fromN-deficient leaves migrated faster on polyacrylamide gels thanprotein from leaves with high N content. Regulation of the rateof photosynthesis in leaves and chloroplasts with a high proteincontent is discussed. The conductance of the cell to the fluxof CO₂ from intercellular spaces to RuBPc-o active sites iscalculated, from cell surface areas and CO₂ fluxes, to decreasethe CO₂ partial pressure at the active site by less than 0.8Pa at an internal CO₂ partial pressure of 34 Pa. Thus the decreasein partial pressure of CO₂ is insufficient to account for theinefficiency of RuBPc-o in vivo at high protein contents. Otherlimitations to the rate of photosynthesis are considered. Key words: Wheat, photosynthesis, nitrogen, ribulose, bisphosphate carboxylase     

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; )     

Photosynthetic Characteristics of Chloroplasts Isolated from Euglena gracilis Z Grown Photoautotrophically

Photosynthetically competent chloroplasts were isolated fromcells of Euglena gracilis Z grown photoautotrophically in 1.5%CO₂. The isolated chloroplasts were intact and substantiallyfree from cytosolic, mitochondrial and microbody materials.The effects of some compounds on the activity of photosynthetic¹⁴CO₂ fixation were examined. The optimal pH and sorbitol concentrationwere 8.0 and 0.33 M, respectively. The chloroplasts requireda high level of P, (5 to 20 mM) for the maximal rate of photosynthesis.They were insusceptible to 10 mM of free Mg²⁺. ATP, ADP andAMP at 1 to 5 mM notably stimulated photosynthesis, althoughhigh concentrations of AMP were unfavorable. In the assay mediumdeveloped for this study, the chloroplasts exhibited photosyntheticactivity of 120µmoles-mg^–1 Chl-h^–1 at 30?C. Chloroplasts could also be isolated from cells grown under ordinaryair. The rate of photosynthetic ¹⁴CO₂ fixation at 1 mM NaH^l4CO₃was higher in these chloroplasts than in those isolated fromcells grown in 1.5% CO₂, whereas at 10 mM NaH^l4CO₃, the ratesof the two types of chloroplasts were nearly the same. Theseresults suggest that the CO₂ concentration given during growthof the algal cells affects the affinity for dissolved inorganiccarbon at the chloroplast level. (Received March 30, 1987; Accepted August 17, 1987)     

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     

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     

Fatty acid synthesis by spinach chloroplasts I. Property of fatty acid synthesis from acetate

Intact chloroplasts (about 70% Class I chloroplasts) isolatedfrom spinach leaves incorporated 150 nmoles of [1-¹⁴C] acetateinto fatty acids per mg chlorophyll in 1 hr at pH 8.3, 25°Cand 25,000 lux. On electron and phase-contrast microscopiescombined with hypotonic treatment of chloroplasts, this syntheticactivity was shown to be proportional to the percentage of ClassI chloroplasts in the preparation. Light was necessary for thesynthesis, the activity in the complete reaction mixture inthe dark being only 2% of that in the light. The synthetic activityincreased with increasing intensities of light to reach saturationat 6,000 lux. CoA and ATP were most effective as cofactors,HCO₃^–, HPO₄^2–, Mg^2$ and Mn^2$ were less effective.ATP could be replaced by ADP in the presence of Pi, suggestingpossible supply of ATP by photophosphorylation. Omission ofthe NADPH-generation system and NADH did not affect the synthesis,indicating sufficient provision of endogenous NADPH and NADHin intact chloroplasts under light. Addition of DTE did notcause recovery of the synthetic activity of intact chloroplastsin the dark. ¹ Present address: Radioisotope Centre, University of Tokyo,Yayoi, Bunkyo, Tokyo 113, Japan. (Received August 26, 1974; )     

Flag Leaf Photosynthesis of Triticum aestivum and Related Diploid and Tetraploid Species

Rates of net photosynthesis of the flag leaves of 15 genotypesof wheat and related species were measured throughout theirlife, using intact leaves on plants grown in the field. At thestage when rates were maximal, they were in general highestfor the diploid species, intermediate for the tetraploidspeciesand lowest for Triticum aestivum (means of 38, 32 and 28 mgCO₂ dm^–2 h^–1 respectively). Rates were stronglynegatively correlated with leaf area, leaf width and the meanplan area per mesophyll cell and positvely correlated with stomatalfrequency and number of veins per mm of leaf width. The differencesamong species in these attributes were mainly related to ploidylevel. It was not possible to determine the relative importanceof each anatomical feature, though the changes in stomatal frequencyhad only slight effects on stomatal conductance and the observeddifferences in rates of photosynthesis were much greater thanwould be expected from those in stomatal conductance alone. There was genetic variation in rates of light dependent oxygenevolution of isolated protoplasts and intact chloroplasts butno difference attributable to ploidy. The mean rate, 91 µmolO₂ mg^–1 chlorophyll h^–1, equivalent to 3.9 mg CO₂mg^-1chlorophyll h^-1 was considerably less than the rate of photosynthesisin comparable intact leaves, which was 7.2 mg CO₂ mg^–1chlorophyll h^–1. The total above-ground dry matter yields were least for thewild diploids T. urartu and T. thauodar and the wild tetraploidT. dicoccoides, but the other wild diploids produced as muchdry matter as the hexaploids. The prospects of exploiting differences in photosynthetic ratein the breeding of higher yielding varieties are discussed. Triticum aestivum L., wheat, Aegilops spp, photosynthesis, stomatal conductance, stomatal frequency, polyploidy     

The Extent of Starch Turnover in Mature Pepper Leaves in the Light

The extent of starch turnover in pepper leaves in the lighthas been estimated. After leaves were labelled with ¹⁴CO₂ atconstant specific activity for 4–7 h, the irradiance wasreduced to a level which caused no net change in the starchcontent of the leaf, and the supply of ¹⁴CO₂ was removed. Therewas no significant change in specific activity of starch overthe following 6–10 h, thus there was no exchange of ¹⁴C-starchwith ¹²C-assimilates entering the chloroplasts. Starch, turnover, ¹⁴C-labelling, pepper, Capsicum annuum L.     

A Model for the Interaction of Low Temperature, ABA, IAA, and CO2 in the Control of Stomatal Behaviour

In the chilling sensitive (C.S.) species Phaseolus vulgarisit was found that at 22 ?C ABA induced stomatal closure butthis effect was dependent on the presence of CO₂. In the absenceof CO₂ the effect of ABA was completely lost. In contrast toABA, the effect of IAA at 22 ?C was to increase stomatal openingas the IAA concentration increased from 10^–2 to 10 molm^–3, and this effect was dependent upon the presence ofCO₂. However, at 5 ?C the action of ABA was reversed and itwas found to induce stomatal opening when fed via the transpirationstream in excised leaves. Similarly, the CO₂ response characteristicswere reversed at low temperatures as removal of CO₂ from theatmosphere caused stomatal closure. However, the effect of IAAat 5 ?C in the presence of CO₂ and with or without ABA was toincrease stomatal aperture with increasing IAA concentration.Significantly, ABA was found to have no effect upon aperturein the presence of CO₂ when IAA was added. The interactive effectsof ABA, IAA, CO₂ and low temperature are discussed in relationto a model proposed by the authors. Key words: IAA, ABA, CO₂, Stomata     

The duration and rate of grain growth, and harvest index, of wheat (Triticum aestivum L.) in response to temperature and CO2

Winter wheat (Triticum aestivum L. cv. Hereward) was grown inthe field inside polyethylene-covered tunnels at a range oftemperatures at either 380 or 684 µmol mol^–1 CO₂.Serial harvests were taken from anthesis until harvest maturity.Grain yield was reduced by warmer temperatures, but increasedby CO₂ enrichment at all temperatures. During grain-filling,individual grain dry weight was a linear function of time fromanthesis until mass maturity (attainment of maximum grain dryweight) within each plot. The rate of progress to mass maturity(the reciprocal of time to mass maturity) was a positive linearfunction of mean temperature, but was not affected by CO₂ concentration.The rate of increase in grain dry weight per ear was 2.0 mgd^–1 greater per 1 C rise, and was 8.0 mg d^–1 greaterat 684 compared with 380 µmol mol^–1 CO₂ at a giventemperature. The rate of increase in harvest index was 1.0%d^–1 in most plots at 380 µmol mol^–1 CO₂ andin open field plots, compared with 1.18% d^–1 in all plotsat 684 µmol mol^–1 CO₂. Thus, the increased rateof grain growth observed at an elevated CO₂ concentration couldbe attributed partly to a change in the partitioning of assimilatesto the grain. In contrast, the primary effect of warmer temperatureswas to shorten the duration of grain-filling. The rate of graingrowth at a given temperature and the rate of increase in harvestindex were only independent of the number of grains per earabove a critical grain number of 23–24 grains per ear({small tilde}20 000 grains m^–2). Key words: Winter wheat, grain growth, temperature, CO₂, harvest index, critical grain number     

Effects of CO2 concentration during growth on subsequent photosynthetic CO2 fixation in Chlorella1

The maximum rate of photosynthetic ¹⁴CO₂ fixation (V_max) aswell as the concentration of CO₂ at which the rate of photosynthetic¹⁴CO₂ fixation attains one-half its maximum velocity (K_m) inChlorella vulgaris 11h cells was strongly dependent on the concentrationof CO₂ continuously provided during the algal growth. The V_max (µmoles ¹⁴CO₂ fixed/ml pcv?min) and K_m (% CO₂)of the algal cells which had been grown in air containing 4%CO₂ (by volume) were ca. 10 and 0.15–0.17, while thosein the cells which had been grown in ordinary air (containing0.04% CO₂) were 7 and 0.05–0.06, respectively. When the concentration of CO₂ in the bubbling gas was loweredfrom 4 to 0.04% during the algal growth, their photosynthetickinetics attained the respective lower steady levels after 5–10hr. On the other hand, when the photosynthetic kinetics weredetermined 24 hr after raising the concentration of CO₂ from0.04 to 4%, the V_max and K_m-values were found to have alreadyattained the respective higher levels. (Received October 15, 1976; )     

Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass

Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO₂ concentration of either 340 or680µI 1^–1 CO₂. Following complete acclimation tothe environmental regimes, leaf and whole plant CO₂ effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO₂ increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI^–1 CO₂ reduced rates of photosynthesis in bothCO₂ regimes, compared with plants acclimated to 340µll^–1. There was no significant effect of CO₂ regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO₂ exhibited generally lower ratesthan those developed in 340µI I^–1 CO₂. Initially the seedling plants in elevated CO₂ grew faster thantheir counterparts in 340µI I^–1 CO₂, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO₂ regime, specific leaf area was persistently13–40% lower in elevated CO₂ while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO₂reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO₂ on plant growthwas primarily due to the fact that CO₂ concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO₂, photosynthesis, respiration, growth, development     

Photosynthesis by developing embryos of oilseed rape (Brassica napus L.)

The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO₂-dependent O₂ evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO₂-dependentO₂ evolution, per unit chlorophyll, and CO₂ saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO₂-dependent O₂ evolution(90–100 mol mg^–1 chlorophyll h^–1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m^–2 s^–1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L.     

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     

Photoinhibition under Atmospheric O2, the Activation State of RuBP Carboxylase and the Content of Photosynthetic Intermediates in Soybean and Wheat

Ward, D. A. and Drake, B. G. 1987. Photoinhibition under atmosphericO₂, the activation state of RuBP carboxylase and the contentof photosynthetic intermediates in soybean and wheat.—J.exp. Bot. 38: 1937–1948. Associations between photosynthesis, the activation state ofRuBP carboxylase and the contents of photosynthetic intermediateswere compared in soybean and wheat leaves before and after exposureto photoinhibitory treatments in the presence of atmosphericO₂. Exposing attached leaves to a supra-saturating irradiance(3 800 µmol quanta m^{– 2} s^–1) for 2 h in CO_2-freeair decreased carboxylation efficiency and the light-saturatedphotosynthetic rate in air by approximately 50%. Exposure tothe photoinhibitory treatment for periods in excess of 2 h didnot cause a further decrease of photosynthesis in soybean. Althoughphotosynthesis was reduced, the initial and total (fully-activated)activities of ribulose 1,5-bisphosphate carboxylase (RuBPCase)in leaf extracts were unaltered in each species by the photoinhibitorytreatment. This was true for leaves sampled under both air andat a rate-limiting intercellular CO₂ partial pressure (C_i) of75 µPa Pa^–1. The contents of ribulose l,5-bisphosphate(RuBP) and 3-phosphoglyceric acid (3-PGA) were reduced by thephotoinhibitory treatment in soybean leaves sampled in air andat a rate-limiting C_i, although the RuBP/3-PGA ratio was unaffected.The relative reduction of RuBP content in soybean leaves atrate-limiting C₁ was similar to the corresponding reductionof carboxylation efficiency. For wheat,the relative reductionof RuBP content at rate-limiting C_i (–19%) caused by thephotoinhibitory treatment was considerably less than the correspondingdecrease of carboxylation efficiency (–49%).The RuBP/3-PGAratio of wheat was also increased significantly by the photoinhibitorytreatment The significance of these observations to the regulationof CO₂-limited photosynthesis in leaves experiencing photoinhibitionunder atmospheric oxygen is discussed. Consideration is alsogiven to the previous contention that contemporary measurementsof initial activity in crude extracts may provide a spuriousindication of the amount of the enzyme-CO₂-Mg_{2 +} form of RuBPcarboxylase present in the leaf. Key words: Carboxylation efficiency, RuBP carboxylase, photoinhibition, RuBP, 3-PGA     

Stomatal Responses to Applied ABA and CO2 in Epidermis Detached from Well-Watered and Water-Stressed Plants of Commelina communis L.

Epidermal strips from either well-watered or water-stressedplants of Commelina communis L. were subjected to a range ofABA concentrations (10^–6–10^–3 mol m^–3)in the presence (330 parts 10^–6 in air) or virtual absence(3 parts 10–6 in air) of CO₂. The stomatal response toCO₂ was greater in epidermis from water-stressed plants, althoughthere was a distinct CO₂ response in epidermis from well-wateredplants. Additions of ABA via the incubation medium had littleeffect on the relative CO₂ response. Stomata responded to ABAboth in the presence and virtual absence of CO₂, but the relativeresponse to ABA was greatest in the high CO₂ treatment. Whenwell-watered plants were sprayed with a 10^–1 mol m^–3ABA solution 1 d prior to use, the stomatal response of detachedepidermis to both CO₂ and ABA was very similar to that of epidermisdetached from water-stressed leaves. It is hypothesized thata prolonged exposure to ABA is necessary before there is anymodification of the CO₂ response of stomata.