A Mutant of Chlamydomonas reinhardtii with Reduced Rate of Photorespiration

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

Isolation and Characterization of Temperature-Sensitive, High-CO2 Requiring Mutant of Anacystis nidulans R2

Temperature-sensitive (ts), high-CO₂ requiring mutants of Anacystisnidulans R2 were isolated by N-methyl-N'-nitro-N-nitrosoguanidine(MNNG) mutagenesis and ampicillin enrichment. One of these mutantswas able to grow under ordinary air enriched with 5% CO₂, butnot under ordinary air at 40?C. At 40?C, the concentration ofCO₂ at which the rate of oxygen evolution reached half the maximumvelocity (apparent Km(CO₂) in photosynthesis) was 1,000 timeshigher in mutant cells than in wild type cells, whereas therewas no significant difference in the maximum rate of photosynthesis. When wild type and mutant cells were incubated with 55 µmNaHC0₃ under illumination at 40?C, the initial rate of inorganiccarbon (IC) transport from the medium into the cells and themaximum internal IC accumulation were significantly higher inwild type cells than in mutant cells. These results indicate that the isolated high-CO₂ requiringmutant lacks the ability in transporting IC into the cells at40?C. Furthermore, the finding that the mutant cells which aredefective in IC transport cannot grow under ordinary air suggeststhe importance of IC concentrating system(s) in photosynthesisof cyanobacteria. Present address: Department of Molecular Biology, The Universityof Wyoming, Laramie, Wyoming 82071, U.S.A. To whom reprints should be requested. (Received April 28, 1988; Accepted September 14, 1988)     

Photosynthetic carbon metabolism in wild, primitive and cultivated forms of wheat at three levels of ploidy: Role of the glycolate pathway

¹⁴CO₂ assimilation was studied with diploid, tetraploid, hexaploidspecies of the genera Triticum and their wild relatives Aegilops.Attached mature leaves of 3–4 weekold plants were allowedto undergo photosynthesis under air at ambient temperature.The pattern of distribution of ¹⁴C was notably similar in Triticumand Aegilops species whatever the level of ploidy. Sucrose wasthe sink for photosynthetic carbon. ¹⁴C for sucrose synthesis was supplied either through the glycolatepathway by glycolate, the product of the photorespiration orby the Calvin cycle intermediates exported into the cytoplasm.Depending on the species, the glycolate pathway provided 40to 75%of the sucrose ¹⁴C. The higher labeling of sucrose was associated with the greaterparticipation of the glycolate pathway in the wild diploid (DD)A. squarrosa and in the cultivated hexaploid (AABBDD) T. aestivum.The results suggest that the expression of the male D genomeis dominant over the female AB genome in T. aestivum. In T. aestivum under ambient conditions lowering (low temperature)or hindering (1% O₂ ) photorespiration, sucrose labeling decreased,but serine and glycine labeling was favoured. We propose thatin wheat leaves, the role of photorespiration is to drain artof the carbon exported from the chloroplast as glycolate, towardssucrose synthesis. (Received March 16, 1979; )     

Active uptake of inorganic carbon by Chlorella saccharophila is not repressed by growth in high CO2

Regulation of transport of dissolved inorganic carbon (DIC)in response to CO₂ concentration in the external medium hasbeen compared in two closely-related green algae, Chlorellaellipsoidea and Chlorella saccharophila. C. ellipsoidea, whengrown in high CO₂, had reduced activities of both CO₂ and transport and DIC transport activitieswere increased after the cells had acclimated to air. However,high CO₂-grown C. saccharophila had a comparable level of photosyntheticaffinity for DIC to that of air-grown C. ellipsoidea and thiswas accompanied by a capacity to accumulate high internal concentrationsof DIC. The high photosynthetic affinity and the high intracellularDIC accumulation did not change in cells grown in air exceptthat the occurrence of external carbonic anhydrase (CA) in air-grownC. saccharophila stimulated the intracellular DIC accumulationin the absence of added CA. These data indicate that activeDIC transport is constitutively expressed in C. saccharophila,presumably because this alga is insensitive to the repressiveeffect of high CO₂ on DIC transport. This strongly supportsthe existence of a direct sensing mechanism for external CO₂in Chlorella species, but also indicates that external CA isregulated independently of DIC transport in Chlorella species. Key words: Carbonic anhydrase, Chlorella, CO₂-insensitive, DIC transport, wild type     

Photosynthesis and photorespiration in soybean [Glycine max (L.) Merr.] chronically exposed to elevated carbon dioxide and ozone

The effects of elevated carbon dioxide (CO₂ and ozone (O₃) onsoybean (Glycine max (L.) Merr.] photosynthesis and photorespiration-relatedparameters were determined periodically during the growing seasonby measurements of gas exchange, photorespiratory enzyme activitiesand amino acid levels. Plants were treated in open-top fieldchambers from emergence to harvest maturity with seasonal meanconcentrations of either 364 or 726 µmol mol^–1 CO₂in combination with either 19 or 73 nmol mol^–1 O₃ (12h daily averages). On average at growth CO₂ concentrations,net photosynthesis (A) increased 56% and photorespiration decreased36% in terminal mainstem leaves with CO₂ enrichment. Net photosynthesisand photorespiration were suppressed 30% and 41%, respectively,by elevated O₃ during late reproductive growth in the ambientCO₂ treatment, but not in the elevated CO₂ treatment. The ratioof photorespiration to A at growth CO₂ was decreased 61% byelevated CO₂ There was no statistically significant effect ofelevated O₃ on the ratio of photorespiration to A. Activitiesof glycolate oxidase, hydroxypyruvate reductase and catalasewere decreased 10–25% by elevated CO₂ and by 46–66%by elevated O₃ at late reproductive growth. The treatments hadno significant effect on total amino acid or glycine levels,although serine concentration was lower in the elevated CO₂and O₃ treatments at several sampling dates. The inhibitoryeffects of elevated O₃ on photorespiration-related parameterswere generally commensurate with the O₃-induced decline in A.The results suggest that elevated CO₂ could promote productivityboth through increased photoassimilation and suppressed photorespiration. Key words: Photorespiration, CO₂-enrichment, ozone, climate change, air pollution     

Salsola arbusculiformis, a C3-C4Intermediate in Salsoleae (Chenopodiaceae)

Salsola arbusculiformis is identified as a C₃–C₄intermediatespecies based on anatomical, biochemical and physiological characteristics.This is the first report of a naturally occurring intermediatespecies in the Chenopodiaceae, the family with the largest numberof C₄species amongst the dicots. In the genus Salsola, mostspecies have Salsoloid anatomy with Kranz type bundle sheathcells and C₄photosynthesis, while a few species have Sympegmoidanatomy and were found to have non-Kranz type bundle sheathcells and C₃photosynthesis. In the cylindrical leaves of C₄Salsolawith Salsoloid type anatomy, there is a continuous layer ofdistinct, chlorenchymatous Kranz type bundle sheath cells surroundedby a single layer of mesophyll cells; whereas species with Sympegmoidtype anatomy have an indistinct bundle sheath with few chloroplastsand multiple layers of chlorenchymatous mesophyll cells. However,S. arbusculiformis has intermediate anatomical features. Whileit has two-to-three layers of mesophyll cells, characteristicof Sympegmoid anatomy, it has distinctive, Kranz-like bundlesheath cells with numerous chloroplasts and mitochondria. Measurementsof its CO₂compensation point and CO₂response of photosynthesisshow S. arbusculiformis functions as an intermediate specieswith reduced levels of photorespiration. The primary means ofreducing photorespiration is suggested to be by refixing photorespiredCO₂in bundle sheath cells, since analysis of photosyntheticenzymes (activity and immunolocalization) and¹⁴CO₂labellingof initial fixation products suggests minimal operation of aC₄cycle. Copyright 2001 Annals of Botany Company Immunolocalization, photosynthetic enzymes, C₃–C₄intermediate, C₄-plants, leaf anatomy, Chenopodiaceae, Salsola arbusculiformis     

Inhibition of Photosynthesis in Barley with Decreased Levels of Chloroplastic Glutamine Synthetase Activity

Mutant barley plants containing only 8%, 16% or 38% of the wildtype level of glutamine synthetase activity have been isolated.The level of glutamine synthetase activity in the roots of themutant containing only 8% leaf activity was not affected bythis mutation. The plants accumulated high levels of ammoniain leaves exposed to air and although they were able to carryout photosynthetic CO₂fixation normally at low levels of atmosphericO₂, they were unable to maintain wild type rates of CO₂fixationin air. The extent of this inhibition and the extent to whichammonia accumulated in the leaves was dependent on the photonfluence rate intercepted by the plant. When leaves from themutant plant were fed glutamine under non-photorespiratory conditionsfor 40 min before they were transferred to air, the plants exhibitedwild type rates of CO₂ fixation in air but the ammonia contentof the leaves increased to an even higher level. At least inthe short term, therefore, ammonia accumulation was not responsiblefor the dramatic decline in the fixation rate of these mutantsin air. The most probable explanation is that as the supplyof potential amino donors diminished on transfer to air, therewas a restriction on the return of glycerate to the Calvin cyclewithin the chloroplast. Key words: Ammonia toxicity, photorespiration, photosynthesis, GS-deficient barley     

Role of Carbonic Anhydrase in Photosynthesis of Blue-Green Alga (Cyanobacterium) Anabaena variabilis ATCC 29413

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 K_m(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 K_m(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)     

Effect of Oxygen on Photosynthetic 14CO2 Fixation in Chroomonas sp. (Cryptophyta) I. Some Characteristics of the Oxygen Effect

The effect of oxygen on photosynthetic ¹⁴CO₂ fixation in theair-grown freshwater flagellate Chroomonas sp. (Cryptophyta)was studied. Considerable inhibition by anaerobiosis was observedonly under light-saturated conditions with no effect from theCO₂ concentration. This inhibition was reversed by 2% O₂. With,more than 2% O₂, the rate of ¹⁴CO₂ fixation was inhibited; 100%O₂ caused about 20% inhibition which could be reversed by 2%O₂. The degree of inhibition was only slightly higher at lowconcentrations (less than 0.43 mM NaHCO₃) than at high CO₂ concentrations,indicating that photorespiration is not a main cause of thisinhibition. Possible causes of the inhibitions by anaerobiosisand by oxygen are discussed. (Received June 29, 1983; Accepted January 23, 1984)     

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; )     

The Effect of External pH on the Apparent CO2 Affinity of Chlorella saccharophila

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 K_m(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     

Effects of Temperature and CO2 Concentration on Induction of Carbonic Anhydrase and Changes in Efficiency of Photosynthesis in Chlorella vulgaris 11h

The increase in carbonic anhydrase (CA) activity and the decreasein apparent K_m(CO₂) for photosynthesis induced by reducing CO₂concentration during the growth of Chlorella vulgaris 11h cellswere followed under different temperatures. Both changes wereaccelerated by raising the temperature and reached an optimumat 32–37?C. When the CO₂ concentration was lowered from3 to 0.04%, the rate of photosynthetic O₂ evolution at limitingCO₂ concentrations increased and reached a stationary levelafter 3 h. Under such conditions, the concentration of CO₂ dissolvedin the algal suspension decreased logarithmically (t_1/2=10 min)and reached a concentration in equilibrium with 0.04% CO₂ inair after ca. 2 h. When high-CO₂ cells grown with 3% CO₂ in air were transferredto various lower CO₂ concentrations, CA activity and apparentK_m(CO₂) for photosynthesis changed depending on the CO₂ concentration.The CO₂ concentration which gives one-half the maximum valuefor K_m(CO₂) and one-half minimum value foi CA activities wasabout 0.5%. The inverse relationship observed for the changesin CA activity and the affinity for CO₂ in photosynthesis supportsthe theory that CA loweres the apparent K_m(CO₂) for photosynthesisin Chlorella vulgaris 11h. (Received August 27, 1984; Accepted February 8, 1985)     

Carbonic Anhydrase in Chlamydomonas reinhardtii II. Requirements for Carbonic Anhydrase Induction

Carbonic anhydrase (CA) activity in wild type cells of Chlamydomonasreinhardtii was low when cells were cultured under 2% CO₃ inthe light. When the gas phase was changed to air, CA activityincresaed as much as 20 fold over the next 24 hours. In contrast,CA activity did not change markedly in cells of the mutantspet 20-8 (PS II-negative), lip 10-2 (photophosphorylation-negative),and F60 (phosphoribulokinase-negative), when they were subjectedto the same induction regimen. DCMU (10^–5 M) and cydoheximide(3 µg/ml) severely inhibited the induction in wild typecells. No induction occured when CO₂ concentration was loweredin darkness. ³Present adress: Photoconversion Research Branch, Solar EnergyResearch Institute, Golden, Colorado 80401, USA. (Received June 7, 1982; Accepted December 25, 1982)     

Role of carbonic anhydrase in photosynthetic CO2 fixation in Chlorella

Chlorella vulgaris 11h cells grown in air enriched with 4% CO₂(high-CO² cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO₂, low-CO₂ cells). The CO₂ concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO₂. When high-CO₂ cells were transferred to low CO₂ conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic¹⁴CO₂ fixation under ¹⁴CO₂-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic ¹⁴CO₂fixation at low ¹⁴CO₂ concentrations decreased when low-CO₂cells were transferred to high CO₂ conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO₂ cells at high CO₂ concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO₂ concentrations, and the lowerthe CO₂ concentration, the greater was the inhibition. Consequently,the CO₂ concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO₂ concentration was higher than 1%, the photosyntheticrate in low-CO₂ cells decreased, while that in high-CO₂ cellsincreased. Fractionation of the low-CO₂ cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO₂-limiting conditions, but inhibits it at CO₂ concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed. ¹This work was reported at the International Symposium on PhotosyntheticCO₂-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; )     

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

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

Estimation of Photorespiration of Green Plants and of their Mesophyll Resistance to CO2 Uptake

An estimate of photorespiration is obtained from the relationshipbetween the net exchange of CO₂ of the leaf and the internalCO₂ concentration, i.e. within the mesophyll intercellular spaces.The latter is obtained by calculation, taking into account thecombined epidermal and boundary-layer resistances between thebulk atmosphere and the mesophyll intercellular spaces. Thelinear part of this relationship (at low CO₂ concentrations)is extrapolated to zero internal concentration, at which noneof the intercellular photorespired CO₂ is available for reassimilation.The calculated output of CO₂ under such conditions providesan estimate of photorespiration, but, by failing to take intoaccount intracellular reassimilation of photorespired CO₂ underestimatesactual photorespiration. As the slope of this linear relationshiprepresents the mesophyll (intracellular) resistance to CO₂ uptake,this procedure was used to recalculate published data on effectsof light intensity and of oxygen concentration on net photosynthesis.The analysis showed that increased oxygen concentration anddecreased light intensity reduced photosynthesis largely byincreasing mesophyll resistance to CO₂ uptake. It is suggestedthat the CO₂ compensation point () is a function of both photorespiration(L) and mesophyll resistance (r_m): = L. r_m.     

Form of inorganic carbon utilized for photosynthesis in Chlorella vulgaris 11 h cells

The rate of photosynthetic ¹⁴CO₂ fixation in Chlorella vulgaris11h cells in the presence of 0.55 mM NaH¹⁴CO₃ at pH 8.0 (20?C)was greatly enhanced by the addition of carbonic anhydrase (CA).However, when air containing 400 ppm ¹⁴CO₂ was bubbled throughthe algal suspension, the rate of ¹⁴CO₂ fixation immediatelyafter the start of the bubbling was suppressed by CA. Theseeffects of CA were observed in cells which had been grown inair containing 2% CO₂ (high-CO₂ cells) as well as those grownin ordinary air (containing 0.04% CO₂, low-CO₂ cells). We thereforeconcluded that, irrespective of the CO₂ concentration givento the algal cells during growth, the active species of inorganiccarbon absorbed by Chlorella cells is free CO₂ and they cannotutilize bicarbonate. The effects observed in the high-CO₂ cellswere much more pronounced than those in the high-CO₂ cells.This difference was accounted for by the difference in the affinityfor CO₂ in photosynthesis between the high- and low-CO₂ cells. (Received May 19, 1978; )     

Factors Controlling Induction of External Carbonic Anhydrase and Change in K?(CO2) of Photosynthesis in Chlorella regularis

Transfer of algal cells of Chlorella regularis from 3% CO₂ inair into ordinary air in the light increased external carbonicanhydrase (CA) activity as well as photosynthetic affinity forCO₂ by several-fold within 2 h. Since no noticeable differencewas observed in CA activity between intact cells and cell homogenates,CA seemed to be mainly localized on the cell surface. Changesin CA activity and K_?(CO₂) of photosynthesis were not observedin the dark. CA induction was 50%-inhibited by incubation with10 µM DCMU during adaptation of high-CO₂ cells to air,whereas it was considerably suppressed when high-CO₂ cells preincubatedwith DCMU in the light for 6 h or without DCMU in the dark for24 h were used. The change in K_?(CO₂) of photosynthesis wasonly slightly affected by DCMU. Uncoupler like carbonylcyanide-m-chlorophenyl-hydrazone(CCCP) and inhibitors of mitochondrial respiration (KCN plussalicylhydroxamic acid) suppressed CA induction during adaptationof high-CO₂ cells to low CO₂ conditions. These results suggest that photosynthesis is not essential forCA induction in Chlorella regularis when some amounts of photosyntheticproducts are previously stored in the cells and respirationis active. A decrease in K_?(CO₂) of photosynthesis during adaptationfrom high to low CO₂ was mostly independent on photosynthesis.However, light is essential for both phenomena. (Received July 16, 1990; Accepted January 21, 1991)     

C4荒漠植物猪毛菜与木本猪毛菜的叶片解剖结构及光合生理特征

 为了比较C₄荒漠植物猪毛菜(Salsola collina)和木本猪毛菜(S. arbuscula)的抗旱结构和适应环境的光合作用特征, 在二者混生的群落中, 选择代表性植株, 采集叶片进行叶片解剖结构分析, 在自然条件下测定了二者叶片的气体交换参数。研究结果表明：猪毛菜叶片具表皮毛, 具有更发达的薄壁贮水组织;木本猪毛菜叶片具有更厚的角质层, 表皮下有1层下皮细胞, 其栅栏组织细胞较长, 排列更紧密。猪毛菜的净光合速率明显高于木本猪毛菜, 日平均值分别为21.5和15.7 μmol CO₂·m^–2·s^–1。猪毛菜的蒸腾速率也明显高于木本猪毛菜, 日平均值分别为14.9和10.2 mmol·m^–2·s^–1。猪毛菜和木本猪毛菜的水分利用效率的日平均值分别为1.39和1.53 μmol CO₂·mmol^–1 H₂O, 特别是在14:00时分别为1.61和2.30 μmol CO₂·mmol^–1 H₂O, 木本猪毛菜高出猪毛菜约42%。猪毛菜的光补偿点低于木本猪毛菜, 而光饱和点和光量子效率较高, 具有更低的CO₂补偿点。这表明：二者的旱生结构不同, 木本猪毛菜具有更显著的荒漠植物特征;在适于二者混生的环境下, 猪毛菜比木本猪毛菜的光合能力更强, 而木本猪毛菜的水分利用效率更高。     

CO2-Fixation, Glycolate Formation, and Enzyme Activities of Photorespiration and Photosynthesis during Greening and Senescence of Sunflower Cotyledons

Time-courses of ¹⁴CO₂-fixation and of enzyme activities involvedin photorespiration and photosynthesis were determined duringthe life span of cotyledons from sunflower seedlings (Helianthusannuus L.). Glycolate formation in vivo was estimated from theresults of combined labelling and inhibitor experiments. NADPH-glyceraldehyde-3-phosphatedehydrogenase, NADPH-glyoxylate reductase and chlorophyll werewell correlated with the time-course of ¹⁴CO₂-fixation (photosynthesis).There was, however, a considerable discrepancy between the developmentalsequence of photosynthesis and that of both ribulose-l,5-bisphosphatecarboxylase and glycolate oxidase. Furthermore, time-coursesof glycolate oxidase activity in vitro and of glycolate formationin vivo differed significantly. Therefore, the use of glycolateoxidase as a marker for the activity of photorespiration ingreening sunflower cotyledons may be questionable. Results from¹⁴CO₂-labelling experiments with cotyledons treated with theglycolate oxidase inhibitor 2-hydroxy butynoic acid suggestthat glycolate formation relative to CO₂-fixation is reducedin senescent cotyledons. Key words: Development, glycolate oxidase, photorespiration, ribulose-l,5-bisphosphate carboxylase, oxygenase