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1.
The rate of photosynthesis by the freshwater alga Lemanea mamillosais proportional to CO2 concentration, virtually to the pointof saturation, and inversely proportional to the radius of thethallus. By contrast, the CO2 response curve of very thin slicesof the thallus is a rectangular hyperbola with a (lower) halfsaturation concentration of 10 mmol m–3. For the intactplant, the kinetics of CO2 fixation are strongly masked by internalCO2 transport limitations, although the maximum rate of photosynthesisis probably determined by the rate of supply of ribulose bisphosphate(RuBP). The flow of water over the alga becomes turbulent atwater velocities greater than about 90 mm s–1 and thethallus stretches significantly at higher water velocities.In its natural habitat, therefore, the external unstirred layerwill be thin (< 10 µm) and the thallus will be stretched,leading to rapid external and increased internal rates of CO2transport from the bulk solution. The estimated maximum rateof CO2 transport is commensurate with the maximum rate of photosynthesis(i.e. the rate of supply of RuBP). Key words: Transport limitations, Kinetics of CO2 fixation  相似文献   

2.
The carbon dioxide compensation point of the unicellular greenalga, Chloretla saccharophila, was determined in aqueous mediumby a gas chromatographic method. Compensation points decreasedmarkedly from 63 cm3 m–3 at an external pH of 4.0 to 3.2cm3 m–3 at pH 8.0 and were not affected by the O2 concentrationof the medium. The calculated CO2 concentration required tosupport the half-maximum photosynthetic rate of the algal cellsranged from 6.0 mmol m–3 at an external pH of 60 to 1.5mmol m–3 at pH 8.0 and these values were not affectedby O2 concentration. The Km(CO2) of nbulose-l,5-bisphosphatecarboxylase isolated from cells grown either at pH 4.0 or pH8.0 was determined to be 64 mmol m–3. These results indicatethat loss of CO2 by photorespiration does not occur in C. saccharophilacells at acid pH and the disparity between the apparent affinityfor CO2 of the intact cells and that of the carboxylase indicatesthe operation of a ‘CO2 concentrating mechanism’in this alga at acid pH. Key words: Acidophilic alga, bicarbonate transport, Chlorella saccharophila, compensation point, CO2 affinity, PH, RuBP carboxylase  相似文献   

3.
Lehnherr, B., Mächler, F. and Nösberger, J. 1985.Influence of temperature on the ratio of ribulose bisphosphatecarboxylase to oxygenase activities and on the ratio of photosynthesisto photorespiration of leaves.—J. exp. Bot. 36: 1117–1125. Rates of net and gross photosynthesis of intact white cloverleaves were measured by infrared gas analysis and by short termuptake of 14CO2 respectively. Ribulose bisphosphate carboxylaseoxygenase (RuBPCO) was purified from young leaves and kineticproperties investigated in combined and separate assays. Theratio of carboxylase to oxygenase activities was compared withthe ratio of photosynthesis to photorespiration at various temperaturesand CO2 concentrations. The ratio of photosynthesis to photorespiration at 30 Pa p(CO2)was consistent with the ratio of carboxylase activity to oxygenaseactivity when each was measured above 20 °C. However, theratio of photosynthesis to photorespiration increased with decreasingtemperature, whereas the ratio of carboxylase to oxygenase activitywas independent of temperature. This resulted in a disagreementbetween the measurements on the purified enzyme and intact leafat low temperature. No disagreement between enzyme and leafat low temperature occurred, when the ratio of photosynthesisto photorespiration was determined at increased CO2 concentrations. The results suggest an effect of low temperature and low CO2concentration on the ratio of photosynthesis to photorespirationindependent of the enzyme. Key words: Ribulose bisphosphate carboxylase oxygenase, photorespiration, temperature  相似文献   

4.
A stable freeze-dried powder was prepared of partly purifiedribulose bisphosphate carboxylase from wheat leaves. As withpreparations from other leaves it is necessary to incubate theenzyme with Mg2$ and CO2 to achieve maximum activity. At 25°C this activity was 0.75 IU mg–1 protein for a preparationactivated at 50 °C for 10 min; the Km for CO2 was 15 µM. The time for reactivation of enzyme that had been inactivatedthrough the absence of CO2 and Mg2$ was influenced by the lengthof the inactivating treatment. After a short inactivation periodthe enzyme was reactivated within a few minutes, whereas aftera longer period several hours were needed. Enzyme in the latterstate had some properties in common with enzyme inactivatedby lower temperatures but in the presence of CO2 and Mg2$. Theenzyme kinetic characteristics are similarly affected by bothkinds of inactivation; the maximum velocity is decreased butthe affinity for CO2 is not affected. Reactivation following a long inactivating treatment becomesmore dependent on Mg2$ concentration as the temperature is increasedfrom 0 to 20 °C.  相似文献   

5.
Rintamäki, E. and Aro, E.-M. 1985. Photosynthetic and photorespiratoryenzymes in widely divergent plant species with special referenceto the moss Ceratodon purpureus: Properties of ribulose bisphosphatecarboxylase/oxygenase, phosphoenolpyruvate carboxylase and glycolateoxidase.—J. exp. Bot. 36: 1677–1684. Km(CO2) values and maximal velocities of ribulose bisphosphatecarboxylase/oxygenase (E.C. 4.1.1.39 [EC] ) were determined for sixplant species growing in the wild, consisting of a moss, a fernand four angiosperms. The maximum velocities of the RuBP carboxylasesvaried from 0.13 to 0.;62 µmol CO2 fixed min–1 mg–1soluble protein and the Km(CO2) values from 15 to 22 mmol m–3CO2. The highest Km(CO2) values found were for the moss, Ceratodonpurpureus, and the grass, Deschampsia flexuosa. These plantsalso had the highest ratios of the activities of RuBP carboxylaseto RuBP oxygenase. Glycolate oxidase (E.C. 1.1.3.1 [EC] ) activitieswere slightly lower in D.flexuosa, but not in C. purpureus,than for typical C3 species. Phosphoenolpyruvate carboxylase(E.C. 4.1.1.31 [EC] ) was not involved in the photosynthetic carboxylationby these two plants. However, another grass, Phragmites australis,was intermediate in PEP carboxylase activity between C3 andC4 plants The properties of RuBP carboxylase/oxygenase are discussedin relation to the activities of PEP carboxylase and glycolateoxidase and to the internal CO2 concentration. Key words: RuBP carboxylase, oxygenase, Km(CO2), moss  相似文献   

6.
The rates of photosynthetic 14CO2 fixation by Chlorella vulgarisllh, grown under high CO2, were determined between 4 to 37°Cwith air containing from 300 to 13,000 ppm 14CO2. When the CO2level was increased, both the rate of photosynthesis and theoptimum temperature for maximum photosynthesis increased. Themaximum photosynthetic rate was reached at 12°C with 300ppm l4CO2. Among the photosynthetic products fromed at 300 ppm 14CO2, glycolatedecreased greatly when the temperature was raised from 20 to30°C. At 3,000 ppm 14CO2 an insignificant amount of glycolatewas formed at all temperatures, whereas 14C-incorporation intothe insoluble fraction, sucrose, and the lipid fraction wassignificantly higher than at 300 ppm 14CO2. The 14C in sucrosewas greatly increased and the radioactivity in the insolublefraction decreased when the temperature was raised from 28 to36°C. (Received April 8, 1980; )  相似文献   

7.
Seeds of apple cv. Golden Delicious were germinated and cultivatedin the greenhouse until the third leaf emerged. Respirationofgerminating seeds or photosynthesis of the first leaves wasmeasured by infra-red gas analysis and porometry, respectively.To study the role of phosphoenolpyruvate carboxylase (PEPC),the dominant carboxylase in the carbon economy, its CO2 refixationpotentialwas related to the amount of CO2 lost in respiration. With arange of 0.2 (dry seeds) to 18 (cotyledons) µmol CO2 h–1g–1 PEPC activity resembled or exceeded the amount ofC02 lost in respiration before the third leaf developed. Itis concludedthat PEPC largely contributes to economize the carbonmetabolism of apple seedlings before they become photosyntheticallycompetent. Key words: Apple (Malus pumila Mill.) seedling, carbon economy, phosphoenolpyruvate carboxylase, photosynthesis, respiration  相似文献   

8.
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  相似文献   

9.
Equipment is described which delivers air with concentrationsof CO2 and water vapour closely controlled in the ranges 0 to2500 ppm and 5 to 15 mb respectively, at flow rates of up to10 1 min-1, to each four leaf chambers. The leaf temperatureis controlled to ±0.5 °C and, with a light intensityof 0.3 cal cm-2 min-1 visible radiation (0.4 to 0.7 µm)leaf temperature can be maintained at 17.5 °C.The apparatusused to measure the concentration differences between the watervapour and CO2 entering and leaving the leaf chamber (used tocalculate transpiration, photosynthetic, and respiration rates)is described in detail.Results of tests, which show the necessityfor mounting a fan within the leaf chamber, are reported.Typicallight- and CO2-response curves are given for kale leaves (Brassicaoleracca var. acephala) and an attempt is made to quantify theerrors in the measurement of photosynthesis and transpiration.  相似文献   

10.
Mächler, F., Lehnherr, B., Schnyder, H. and Nösberger,J. 1985. A CO2 concentrating system in leaves of higher C3-plantspredicted by a model based on RuBP carboxylase/oxygenase kineticsand 14CO2/12CO2 exchange.–J. exp. Bot. 36: 1542–1550. A model is presented which compares the ratio of the two activitiesof the enzyme nbulose bisphosphate carboxylase/oxygenase asdetermined in vitro with the ratio of photosynthesis to photorespirationin leaves as determined from differential 14CO2/12CO2 uptakeor from CO2 compensation concentration. Discrepancies betweenmeasurements made in vitro and in vivo are attributed to theeffect of a CO2 concentrating system in the leaf cells. Interferencefrom dark respiration is discussed. A CO2 concentrating systemis postulated which is efficient mainly at low temperature andlow CO2 concentration. Key words: —Photosynthesis, photorespiration, ribulose bisphosphate carboxylase/oxygenase  相似文献   

11.
Pascopyrum smithii (C3) andBouteloua gracilis (C4) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO2enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO2concentrations (380 and 750 µmol mol-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol-1CO2. Leaf CO2exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO2concentrationsof approx. 380 and 700 µmol mol-1. Long-term CO2enrichmentstimulated CER in both species, although the response was greaterin the C3,P. smithii . Doubling the [CO2] from 380 to 750 µmolmol-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO2-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO2], indicating photosynthetic acclimation to CO2growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO2] were generally less evident.Temperatures considered optimal for growth (C3: 20 °C; C4:35 °C) sometimes led to CO2-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO2-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)  相似文献   

12.
Diurnal temperature fluctuations induced change in soya bean-pod[Glycine max (L.) Merr.] carbon exchange rate (CER, where positiveCER represents CO2 evolution). CER appeared to depend linearlyon temperature. Linear regressions of CER on temperature interceptedthe temperature axis at 5°C (i.e. zero CER at 5°C).Slopes of these regressions (i.e. temperature sensitivity) changedover the season. The CER-temperature sensitivity coefficient,K, (calculated from observed values of CER. pod temperatureand temperature intercept) rose from less than 0·02 mgCO2 h–1 pod–1 °C–1 during early pod-flll,peaked at over 0·04 mg CO2 h–1 pod–1 °C–1at mid pod-fill, and then declined during late pod-fill andmaturation. Glycine max (L.) Merr., Soya bean, carbon exchange rate, temperature  相似文献   

13.
The affinity for NaHCO3 (CO2) in photosynthesis of Anabaenavariabilis ATCC 29413 was much higher in the cells grown underordinary air (low-CO2 cells) than in those grown in air enrichedwith 2–4% CO2 (high-CO2 cells) (pH 8.0, 25?C). Ethoxyzolamide(50 µM) increased the Km(NaHCO3 in low-CO2 cells aboutnine times (from 14.3 to 125), while the maximum rate of photosynthesisdecreased about 20%. When high-CO2 cells were transferred tolow-CO2 conditions, carbonic anhydrase (CA) activity increased,while Km(NaHCO3) in photosynthesis decreased from 140 to 30µM within about 5 h. The addition of CA to the suspensionof both high- and low-CO2 cells enhanced the rates of photosyntheticO2 evolution under CO2-limiting conditions. The rate of 14CO2fixation was much faster than that of H14CO3 fixation.The former reaction was greatly suppressed, while the latterwas enhanced by the addition of CA. These results indicate thatthe active species of inorganic carbon utilized for photosynthesiswas free CO2 irrespective of the CO2 concentration given duringgrowth. It is suggested that CA plays an active role in increasingthe affinity for CO2 in photosynthesis of low-CO2 cells of thisblue-green alga. (Received January 24, 1984; Accepted October 22, 1984)  相似文献   

14.
The effect of high light and root chilling on gas exchange,chlorophyll fluorescence, and bulk shoot water potential (shoot)was examined for Pinus sylvestris seedlings. Transferring plantsfrom low light (200 µmol m–2s–1, PAR) anda soil temperature of 15 °C to high light (850 µmolm–2 s–1) and 1 °C caused >90% decrease innet photosynthesis and leaf conductance measured at 350 mm3dm-3 CO2, and a decrease in the ratio of variable to maximumfluorescence (Fv/Fm) from 0.83 to 0.63. The decrease in Fv/Fmwas, however, only marginally greater than when seedlings weretransferred from low to high light but kept at a soil temperatureof 15 °C. Thus, photoinhibition was a minor component ofthe substantial decrease observed for net photosynthesis at1 °C soil temperature. The decrease in net photosynthesisand shoot at 1 °C was associated with an increase in calculatedintracellular CO2 concentration, suggesting that non-stomatalfactors related to water stress were involved in inhibitingcarbon assimilation. Measurements at saturating external CO2concentration, however, indicate that stomatal closure was thedominant factor limiting net photosynthesis at low soil temperature.This interpretation was confirmed with additional experimentsusing Pinus taeda and Picea engelmannii seedlings. Decreasesin gas-exchange variables at 5 °C soil temperature werenot associated with changes in shoot Thus, hormonal factors,localized decreases in needles or changes in xylem flux maymediate the response to moderate root chilling.  相似文献   

15.
The nature of the lack of oxygen inhibition of C3-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO2), 21 kPa p(O2), balance N2) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O2). At 20°C, lowering p(O2) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O2) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O2). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O2) suggestingthat RuBP regeneration was reduced at low p(O2) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O2) was 24% higherthan at 21 kPa p(O2). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O2). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase  相似文献   

16.
Acclimation of Lolium temulentum to enhanced carbon dioxide concentration   总被引:2,自引:0,他引:2  
Acclimation of single plants of Lolium temulentum to changing[CO2] was studied on plants grown in controlled environmentsat 20°C with an 8 h photoperiod. In the first experimentplants were grown at 135 µ;mol m–2 s–1 photosyntheticphoton flux density (PPFD) at 415µl l–1 or 550µll–1 [CO2] with some plants transferred from the lowerto the higher [CO2] at emergence of leaf 4. In the second experimentplants were grown at 135 and 500 µmol m–2 s–1PPFD at 345 and 575 µl l–1 [CO2]. High [CO2] during growth had little effect on stomatal density,total soluble proteins, chlorophyll a content, amount of Rubiscoor cytochrome f. However, increasing [CO2] during measurementincreased photosynthetic rates, particularly in high light.Plants grown in the higher [CO2] had greater leaf extension,leaf and plant growth rates in low but not in high light. Theresults are discussed in relation to the limitation of growthby sink capacity and the modifications in the plant which allowthe storage of extra assimilates at high [CO2]. Key words: Lolium, carbon dioxide, photosynthesis, growth, stomatal density  相似文献   

17.
Panicum hians and Panicum milioides were found to have characteristicsintermediate to those of C3 and C4 species with respect to CO2compensation point, percentage inhibition of photosynthesisby O2 at various O2/CO2 solubility ratios, and water use efficiency.C4 species have a higher carboxylation efficiency than eitherthe intermediate or C3 species. During photosynthesis, evenunder 2.5% O2, C4 species have a higher affinity for intercellularCO2 (Km 1.6 µM) apparently due to the initial carboxylationthrough PEP carboxylase. Under low O2 the intermediate and C3species had a similar affinity for intercellular CO2 duringphotosynthesis (Km 5–7 µM) consistent with carboxylationof atmospheric CO2 through RuDP carboxylase. There were considerablevariation in photosynthesis/unit leaf area at saturating CO2levels in the species examined which in part is due to differencesin RuDP carboxylase /unit leaf area. The highest rates of photosynthesis/unitleaf area under CO2-saturating conditions were with the C3 specieswhich had a correspondingly high level of RuDP carboxylase/unitleaf area. Possibilities for the greater efficiency of P. hiansand P. milioides in comparison to C3 species in utilizing lowlevels of CO2 in the presence of atmospheric O2 are discussed. 1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and theUniversity of Wisconsin Research Committee with funds from theWisconsin Alumni Research Foundation. (Received June 25, 1977; )  相似文献   

18.
The Carbon Economy of Rubus chamaemorus L. I. Photosynthesis   总被引:1,自引:0,他引:1  
MARKS  T. C.; TAYLOR  K. 《Annals of botany》1978,42(1):165-179
Studies on the photosynthetic activity of Rubus chamaemorusL. in controlled environment conditions are reported. Theseshow that material collected from Moor House National NatureReserve, England has a photosynthetic light saturation pointof 100 J m–2s–1 (380–720 nm) and a temperatureoptimum for photosynthesis between 10 and 15 °C. A markeddecline in net CO2 uptake is evident at temperatures in excessof 18 ° C; this persists for some time after return to anoptimum temperature regime. Leaves show rapid responses to changesin both light intensity and temperature, and show no evidenceof an endogenous rhythm in photosynthetic rate.  相似文献   

19.
The mechanism for utilization of dissolved inorganic carbon(DIC) was investigated in the marine unicellular calcareousalga Emiliania huxleyi, grown with constant aeration. The apparentK0.5 (DIC), the concentration of DIC which attains one-halfof the maximum velocity of apparent photosynthesis, for photosyntheticevolution of O2, measured under saturating light, was 5.5 mM(55 µM for CO2) at pH 8.0 and 25°C. The value of K0.5was not affected by inhibitors of carbonic anhydrase (CA), andan electrometric assay of CA showed that the enzyme was notinvolved in photosynthesis in this alga. The rate of photosyntheticfixation of 14C-DIC into acid-stable products was about 20 timeshigher than that into CaCO3, irrespective of the external concentrationof DIC. In short-term experiments, 14C-DIC was usually incorporatedinto the internal pool of DIC (IIC) to concentrations up to13 to 16 times higher than that of the external DIC. CO2 addedexternally was utilized mainly for fixation of CO2 and accumulationof IIC. By contrast, HCO-3 was utilized mainly for productionof CaCO3 and accumulation of IIC. Incorporation of 14C intoIIC was partially suppressed by DCMU or in darkness but itstransfer to CaCO3 was unaffected. These results suggest thataccumulation of IIC in this alga, even under ordinary circumstances,is only partially responsible for increasing the efficiencyof utilization of DIC by photosynthetic fixation but may bemost useful for the production of CaCO3. (Hydroxyethylidene) bisphosphonic acid, an inhibitor of thegrowth of CaCO3 crystals, completely suppressed production ofCaCO3. The accumulation of IIC was also partially suppressed,but photosynthetic fixation of CO2 was enhanced. In a pulse-chaseexperiment with 14CDIC, 14C incorporated into IIC and CaCO3in darkness was transferred to acid-stable products of photosynthesisin the light. These results suggest that 14C-DIC in IIC andpre-formed CaCO3 may be useful sources of carbon for fixationof CO2. (Received July 2, 1993; Accepted January 10, 1994)  相似文献   

20.
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 CO2-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 (Ci) 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 Ci, 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 Ci (–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-Mg2 + form of RuBPcarboxylase present in the leaf. Key words: Carboxylation efficiency, RuBP carboxylase, photoinhibition, RuBP, 3-PGA  相似文献   

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