Growth Delay and Intracellular Changes in Chlorella ellipsoidea C-27 as a Result of Deuteration

The effects of deuterium (D) on Chlorella ellipsoidea C-27 wereinvestigated. Cells grown in a medium prepared with deuteriumoxide (D₂O) showed pronounced delays in cell growth and division;the length of a cell cycle in medium with 100 mol% D₂O was morethan 5 times longer than that in medium prepared in H₂O Thedelay caused by D₂O was not overcome by either indoleaceticacid or kinetin. The biological and ultrastractural characteristicsof deuterated .Chlorella (D-Chlorella) cells were examined.The responses of D-Chlorella to cell wall-digesting enzymesdid not differ from those of normal (H-Chlorella) cells. D-Chlorellacells were enlarged, and cellular components, such as proteins,nucleic acids, lipids and ATP, were present in larger quantitiesthan those in H-cells. The chloroplast of D-Chlorella was enlarged,but the levels of component photosynthetic pigments were significantlyreduced. By contrast, mitochondria of D-Chlorella were smallerthan those of H-cells. These changes in levels of cellular componentsand in the sizes of organelles seem to be unique to deuteration. (Received May 13, 1992; Accepted July 28, 1992)     

Role of carbonic anhydrase in photosynthesis in Chlorella derived from kinetic analysis of 14CO2 fixation1

Time courses of photosynthetic ¹⁴CO₂ fixation and its simulationare presented for Chlorella cells grown under low CO₂ concentration(low-CO₂ cells) and subsequently exposed to 0.2 mM NaH¹⁴CO₃or 130 ppm ¹⁴CO₂ in the presence or absence of carbonic anhydrase(CA) in the suspending medium. It was shown that Chlorella cells utilized only free CO₂ whenNaHCO₃ was given in the presence or absence of CA, or when CO₂was bubbled in the absence of CA. However, the present simulationindicated that both CO₃ and HCO₃^– were utilized when CO₂was given in the presence of CA. Based on these results, weconcluded that 1) Chlorella cells absorb only free CO₂ and 2)this gas is provided to algal cells in two ways, i.e., by directand indirect CO₂ supply. Usually, the dissolved CO₂ is directlyutilized by the algal cells (direct supply of CO₂). However,when the concentration of dissolved CO₂ is extremely low andwhen there is CA, CO₂ reconverted from HCO₃^– is also utilizedby Chlorella cells (indirect supply of CO₂). The utilizationof HCO₃^– indicated by the above simulation was explainedby the indirect supply of CO₂. We further assumed that the indirectsupply of CO₂ to ribulose 1,5-bisphosphate carboxylase occursmainly in the chloroplasts of low-CO₂ cells containing highCA. Thus, under low CO₂ concentrations, low-CO₂ cells can carryout more efficient CO₂ fixation than high-CO₂ cells, resultingin the lower apparent Km(CO₂). ³Department of Biology, Faculty of Science, Niigata University,Niigata, Japan. (Received April 2, 1980; )     

Effect of gaseous composition on cell growth and secondary metabolite production in suspension culture of Stizolobium hassjoo cells

The gaseous composition is an important factor affecting the performance of plant cell cultures. Gaseous metabolites, especially O₂, CO₂ and C₂H₄, play important roles in cell physiology. Forced aeration in bioreactors usually results in poor cell growth and secondary metabolite production. In this work, the effects of gaseous metabolites on cell growth, secondary metabolite formation as well as PPO activity were investigated with respect to Stizolobium hassjoo cell culture producing l-DOPA (3,4-dihydroxyphenylalanine). A device allowing the control of the partial pressures of gaseous metabolites in shake flasks was designed. In addition, a recirculating gas system with a P_O2 controller was designed for a bioreactor. This device could maintain constant P_O2 and P_CO2 in the bioreactor headspace. The results showed that the highest l-DOPA content was attained at P_O2=0.30 atm. Higher P_O2 values retarded cell growth and increased the pH of the culture broth. High P_O2 also enhanced the formation of ethylene and inhibited l-DOPA formation. Carbon dioxide concentrations lower than 5% enhanced cell growth and l-DOPA formation. Cell growth was retarded by 0.3 ppm of ethylene in 2~5 carbon dioxide. Oxygen concentration and D.O. in the broth could be controlled at constant levels in the recirculating culture system. Enrichment of P_O2 up to 0.3 atm during the later stage of cultivation facilitated l-DOPA formation. The interaction among the gaseous metabolites and their influences on cell metabolism and l-DOPA formation were elucidated. This information will facilitate the rational operation of plant cell culture systems producing secondary metabolites.     

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; )     

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     

Factors Controlling Induction of Carbonic Anhydrase and Efficiency of Photosynthesis in Chlorella vulgaris llh Cells

When Chlorella vulgaris llh cells which had been grown in airenriched with 2–4% CO₂ (high-CO₂ cells) were bubbled withair containing ca. 400 ppm CO₂, illumination at an intensityas low as the light compensation point (350 lux) was sufficientto increase the photosynthetic rate under limiting CO₂ concentrations.The same treatment induced carbonic anhydrase (CA) activity.The induction of CA activity and increase in photosyntheticrate at limiting CO₂ concentrations were observed in the presenceof 10 µM DCMU which completely inhibits photosynthesis.These results indicate that photosynthetic electron transportis not involved in CA induction in Chlorella vulgaris llh cells.The parallelism between the changes in CA activity and the rateof photosynthesis under limiting CO₂ concentrations agree withthe previous conclusion that the transport of CO₂ from outsideto the site of CO₂ fixation is facilitated by CA and hence lowersthe apparent K_m(CO₂) for photosynthesis. (Received December 24, 1982; Accepted May 10, 1983)     

Alterations in the Heat Response of Chlorella ellipsoidea by Deuteration

For the elucidation of the isotope effect on cell functionsof deuterium (D) incorporated into cell constituents, alterationsin the heat response of D-exchanged Chlorella ellipsoidea (D-Chlorella)were investigated. D-Chlorella cells obtained by culture inmedium that contained 60 mol% D₂O were assayed for their responseto heat in H₂O medium to rule out the solvent isotope effectof D₂O. Upon heating at 41–45?C, the heat sensitivityof D-Chlorella was greater than that of ordinary (H-Chlorella)cells; at 43?C, the heat sensitivity of D-Chlorella was 1.5–1.6times higher than that of H-Chlorella. For the induction ofresistance to heating, preheating of the cells at a lower temperaturethan that used for heat treatment was effective in the caseof both D- and H-Chlorella. However, the optimum temperaturefor preheating of D-Chlorella (34?C) was lower than for H-Chlorella(36–37?C). With preheating at 34?C, heat-shock proteins(HSPs), in particular proteins of 62 and 79 kDa, were inducedsimilarly in both types of cell. However, the gel-electrophoreticpatterns of HSPs induced at 37?C were differed somewhat betweenD- and H-Chlorella. These results suggest that the responseof cells to heat, in particular the induction of resistanceto heating and the synthesis of HSPs, was altered by deuterationof cell constituents. (Received June 11, 1990; Accepted November 24, 1990)     

Ammonia Induces Starch Degradation in Chlorella Cells

When ammonia was added to cells of Chlorella which had fixed¹⁴CO₂ photo synthetically, ¹⁴C which had been incorporated intostarch was greatly decreased. A similar effect was observedwhen potassium nitrate and sodium nitrite were added. The ammonia-induceddecrease in ¹⁴C-starch was observed in all species of Chlorellatested. With cells of C. vulgaris 11h, most of the radioactivityin starch was recovered in sucrose, indicating that ammoniainduces the conversion of starch into sucrose. The percent of¹⁴C recovered in sucrose differed from species to species andpractically no recovery in sucrose was observed in C. pyrenoidosa.In most species tested, the enhancing effects of blue lightand ammonia on O₂ uptake as well as the ammonia effect on starchdegradation were greater in cells which had been starved inphosphate medium in the dark than in non-starved cells. In contrast,the enhancing effect of ammonia on dark CO₂ fixation was muchgreater in non-starved cells. C. pyrenoidosa was unique in thatblue light did not show any effect on its O₂ uptake. (Received August 15, 1984; Accepted November 16, 1984)     

Transport and Fixation of Inorganic Carbon during Photosynthesis of Anabaena Grown under Ordinary Air. I. Active Species of Inorganic Carbon Utilized for Photosynthesis

Inorganic carbon transport during photosynthesis of cyanobacteriumAnabaena variabilis grown under ordinary air was investigatedby supplying ¹⁴CO₂ or H¹⁴CO₃^– solution to three differentstrains. Both CO₂ and HCO₃^– were accumulated within thealgal cells. In the cell suspension from which dissolved inorganiccarbon had been depleted by pre-illumination, CO₂ was transportedand accumulated faster than HCO₃^–. When the concentrationof HCO₃^– injected into the cell suspension of A. variabilisM3 was 25 times as high as that of CO2 (the expected ratio atequilibrium at pH 7.8), the initial rates of fixation of bothinorganic carbon species were practically the same. On the otherhand, when ¹⁴CO₂ or H¹⁴CO₃^– was added under steady statephotosynthetic conditions, both carbon species were transportedat similar rates. The ratio of fixed to transported carbon measuredafter the initial 5 s was only 23–27% regardless of thecarbon species supplied. This percentage is much lower thanthat reported for Chlorella cells. ¹ To whom reprint requests should be addressed (Received June 30, 1986; Accepted December 16, 1986)     

The Heterotrophic Nutrition of Chlorella vulgaris (Brannon No. 1 Strain): With two Figures In the Text

A range of sugars, sugar alcohols, sugar phosphates, organicacids, and monohydric alcohols have been tested as carbon sourcesfor growth and as respiratory substrates using Chlorella vulgaris,Brannon I, grown in darkness. Much higher rates of growth and respiration were obtained withd-glucose than with any other substance tested. Ethanol (at0·005 M.) sustained both growth and respiration at c.50 per cent, of the level with glucose (0·028 M. or higher).Evidence was obtained that the organism can become ‘adapted’to utilize d-galactose and sucrose as effective carbon sources.Sustained growth was not obtained with any of the other substancestested. The glucose monophosphates, methanol and certain organic acids(oxalacetate, -ketoglutarate, cis-aconitate, and pyruvate) clearlystimulated oxygen uptake but to a less extent than ethanol.The other substances tested were either inhibitory to respirationor inactive or of very low activity as substrates. The growth in darkness and in liquid culture of Chlorella whensupplied with d-glucose was insensitive to pH over the range4·5 to 7·0 and was markedly enhanced by a highlevel of aeration. Gains in cellular dry weight ranging from45 to 90 per cent, of the weight of d-glucose disappearing fromthe culture medium were recorded in growth experiments; measurementsof CO₂ evolution in the Warburg indicated retention of up totwo-thirds of the glucose-C in cell material.     

Micropropagation of Potato: Evaluation of Closed, Diffusive and Forced Ventilation on Growth and Tuberization

Different types of ventilation of the culture vessel headspace,each with and without the ethylene inhibitor AgNO₃(3.0 µM)or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid(ACC) (2.0 µM) in the culture medium, were investigatedin terms of their effects on the growth of potato cuttings (Solanumtuberosum L. ‘cara’). Concentrations of CO₂ , O₂andethylene in the culture vessel headspaces were monitored duringthe study. Growth was substantially enhanced and vitrification(stunting and epinasty of leaves and hooking of stem apices)was reduced by increasing the efficiency of ventilation, theeffects being greatest with forced ventilation. In the conventionaldiffusive treatment (via a polypropylene membrane), leaf epinastyoccurred but the leaves were not stunted unless ACC had beenadded. AgNO₃prevented vitrification in the latter case and reducedit in the sealed treatment. On the other hand, with all forcedventilation treatments, even with the addition of ACC, the plantletsgrew well and some of the growth parameters exceeded those inthe diffusive + AgNO₃treatment. Ethylene removal was clearlyan important factor contributing to the better growth foundwith diffusive and especially with the forced ventilation treatment;with the latter, ethylene concentrations in the culture vesselswere virtually zero. In addition, enhanced CO₂supply probablycontributed to the better performance under forced ventilationcompared to diffusive ventilation. Callus developed on the stembases in all sealed (airtight) and diffusive treatments exceptwhere AgNO₃was used. No callus was observed in any treatmentwhere forced ventilation was applied and in vitro tuberization(tuber size) was considerably improved by this treatment. Copyright2001 Annals of Botany Company Callus, ethylene, potato, tuberization, vitrification     

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.     

Establishment and physiological analyses of photoautotrophic callus cultures of the fern Platycerium coronarium (Koenig) Desv. under CO2 enrichmen

Gametophyte-derived callus cultures of Platycerium coronariumcould be maintained under photoautotrophic conditions on Murashigeand Skoog medium supplemented with 2µM 2,4-dichlorophenoxyaceticacid (2,4-D) and with CO₂ enrichment. Progressive reductionof sucrose from the medium resulted in a reduction in growth,but an increase in total chlorophyll content. When subculturingwas delayed beyond 2 weeks, callus cells differentiated intogametophytes on the medium with 0.2 sucrose and no CO₂ enrichment.Enriching the photoautotrophic cultures on 2µM 2, 4-Dwith 1% CO₂ resulted in about 1.7-fold increase in fresh weightwithin 42 d. Total chlorophyll content was generally higherwith 1% CO₂ enrichment than with 10%. F_v/F_m ratio was higherfor callus on low levels of sucrose (>0.5%) than that onsucrose 1.0%. An increase in autofluorescence of chloroplasts,but not the size, was observed with decreasing sucrose levelsin the medium. Autofluorescence decreased with increase in CO₂from 0.03%. Our data are in agreement with the view that long-termexposure to high levels of decrease in photosynthetic capacity. Key words: Platycerium coronarium, stag's horn fern, autofluorescence of chloroplasts, confocal laser scanning microscope, F_v/F_m ratio, photoautotrophic callus     

Specificity and Reversibility of the Bicarbonate Effect on Hexose Uptake by Maize Root Tips

The inhibition of hexose uptake by bicarbonate ions was investigatedin detail in order to test the specificity and reversibilityof the effect and to compare it with those of other electrolytes.The degree of inhibition was similar at pH 7.0 and pH 8.0. AtpH 4.5 no influence of a high concentration of CO₂ on 3-O-methylglucoseuptake was found. Therefore, the inhibition of hexose uptakeby bicarbonate cannot be explained by consequences of CO₂ influx.The inhibition of sugar absorption by calcium and potassiumions was similar to that exerted by bicarbonate in so far asit was observed at higher pH only. The inhibition exerted bysodium salts of different monovalent weak acids was limitedto lower pH and needed some time to become established or reversed.The bicarbonate effect was independent of time and reversiblewithout a lag phase. Sodium salts of strong mineral monovalentacids did not differ significantly in their effect on sugaruptake. Bicarbonate inhibited phosphate uptake in a similarmanner to hexose uptake but strongly stimulated the absorptionof potassium. The bicarbonate effect is assumed to result froma change in the degree of coupling of secondary active transportto the proton pump. Key words: Inhibition, Transport coupling, pH, Proton pump     

Chaperonin-Repairable Subtle Incompleteness of Protein Assembly Induced by a Substitution of Hydrogen with Deuterium: Effect of GroE on Deuterated Ribulose 1,5-Bisphosphate Carboxylase

For investigating the effect of slight modification of proteinson their higher-ordered structure, and that of chaperonin onthe functional assembly of proteins, we prepared partially deuteratedribulose 1,5-bisphosphate carboxylase (Rubisco) by cultivatingChlorella ellipsoidea in 100 mol% D₂O medium. Chlorella cellsgrown in the D₂O medium (D-Chlorella) contained almost the sameamount of Rubisco (D-Rubisco) as the cells grown in H₂O medium(H-Chlorella) determined by Western blotting using Rubisco-specificantibody, whereas the activity of D-Rubisco determined by carbonfixation was only 28% of that of Rubisco from H-Chlorella (H-Rubisco).D-Rubisco, however, showed similar K_m and pH and temperatureoptima to those of H-Rubisco as well as similar antibody bindingcapability. The enzyme activity of D-Rubisco was recovered to84% of that of H-Rubisco by the addition of GroE proteins (GroEL,chaperonin 60, and GroES, chaperonin 10), members of the chaperoninfamily produced by Escherichia coli. These data suggest thatD-Rubisco has subtle incompleteness in terms of functional assembly,a situation that is correctable by chaperonin. (Received August 8, 1994; Accepted January 9, 1995)     

Studies on Dark Fixation of Carbon Dioxide in Kalanchoe: I. Effect of Water Stress and Growth Retardants

Rooted cuttings of Kalanchoë blossfeldiana cv. Feuer Bluteand K. crenatum failed to show a net dark CO₂ fixation whenraised in dilute nutrient solution. Dark CO₂ fixation (CAM)in these plants was initiated either by increasing the soluteconcentration or lowering the water potential of the nutrientsolution by addition of mannitol (0.11 M and 0.25 M) and carbowax4000 (0.16 M and 0.3 M). Initiation was also brought about byspraying the leaves with B-9 (N,dimethylamino-succinamicacid,300mg1^–1) or by addition of CCC (2 chloroethyl trimethylammonium chloride, 300 or 750 mg1^–1) to the nutrient medium.Failure of CAM in dilute solution was suggested to be due tolack of accumulation of photosynthates in the leaves. Waterstress and growth retardants brought about reduction of monilizationand/or translocation thereby leading to accumulation of assimilatesin the leaves and to initiation of dark CO₂ fixation.     

Alkalization of the Medium by Unicellular Green Algae during Uptake Dissolved Inorganic Carbon

When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO₃,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O₂ evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO^-₃, and algae grown or adapted to a low, air-levelCO₂ in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO₂ in air. Photosynthetic O₂ evolutionwithout alkalization occurred using either internal DIC or externalCO₂ at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO^–₃ into CO₂ plus OH^– during photosynthesisby cells with a high affinity for CO₂ uptake. Cells grown onhigh CO₂ to suppress the DIC pump, when given low levels ofHCO^–₃ in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO^–₃ pump, aswell as a CO₂ pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O₂ evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H₂CO₃ to HCO^–₃ and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO₂ concentrating process. ¹Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.     

Changes of Photosystem Stoichiometry during Cell Growth in Dunaliella salina Cultures

The photosystem stoichiometry in Dunaliella salina thylakoidswas measured during cell growth in a fully contained culture.In dilute cultures, obtained after inoculation of cells intofresh growth medium, the PS II/PS I stoichiometry was about2.2/1.0. This ratio was gradually lowered to about 1.2/1.0 inmature cultures. The decrease of the PS II/PS I ratio is discussedin terms of increasing self-shading in the culture and increasingpH in the growth medium. Changes in the pH occurred from 7.7in young cultures to 8.9 in mature ones and caused a significantdepletion of soluble CO₂ from the growth medium. A correlationof the CO₂/HCO₃^– ratio in the growth medium with the PSII/PS I ratio in the thylakoid membrane is presented. ¹ Permanent address: Department of Physics, Palacky University,tr. Svobody 26, 771 46 Olomouc, Czechoslovakia (Received September 12, 1990; Accepted April 4, 1991)     

Direct and Maternal Effects of Elevated CO2on Early Root Growth of GerminatingArabidopsis thalianaSeedlings

Individuals ofArabidopsis thaliana, collected in different naturalpopulations, were grown in controlled and elevated CO₂in a glasshouse.Following germination, root growth of progeny of different linesof these populations was studied in control and elevated atmosphericCO₂. No significant direct effect of atmospheric CO₂concentrationcould be demonstrated on root growth. An important parentaleffect was apparent, namely that root length and branching weredecreased in seeds collected from a mother plant which had beengrown in elevated CO₂. This was correlated with smaller seeds,containing less nitrogen. These parental effects were geneticallyvariable. We conclude that CO₂may affect plant fitness via parentaleffects on seed size and early root growth and that the geneticvariability shown in our study demonstrates thatArabidopsispopulationswill evolve in the face of this new selective pressure.Copyright1998 Annals of Botany Company Root growth, root branching, seed, elevated CO₂, natural population,Arabidopsis thaliana, parental effect.     

Characteristics of the Photosynthetic Metabolism of Carbon in Deuterated Chlorella ellipsoidea C-27

The photosynthetic metabolism of carbon in fully deuteratedcells of Chlorella ellipsoidea C-27 (D-Chlorella), obtainedby culture in medium prepared with 100 mol% D₂O, was characterizedby examining the activities of several enzymes and the levelsof metabolic regulators in a comparison with those of ordinarycells (H-Chlorella). The cellular content of starch in D-Chlorellawas more than twice that in H-Chlorella, whereas those of sucroseand glucose were significantly lower in D-Chlorella. Deuterationof Chlorella caused marked alterations in the activities ofenzymes involved in starch metabolism. There was a significantdecrease in the activity of phosphorylase, a catabolic enzyme,and a significant increase in the activity of starch synthase,an anabolic enzyme. These alterations are probably responsiblefor the increase in the amount of starch in cells. By contrast,no marked changes were observed in the activities of enzymesand the levels of metabolic inhibitors that are involved inthe synthesis of sucrose. It seems likely, therefore, that thedecrease in the amount of sucrose in D-Chlorella was causedmainly by a deficiency in sources of carbon in the cytoplasm,as a consequence of an increase in levels of starch in chloroplasts. (Received May 13, 1992; Accepted December 1, 1992)