Photosynthetic activity of isolated spinach mesophyll cells

Cells were isolated from spinach leaves on a large scale. Photosyntheticactivity and the effects of CO₂, KCN, DNP and DCMU were examinedwith an oxygen electrode. The cells showed rapid response toCO₂ and inhibitors in photosynthetic O₂ evolution. (Received October 1, 1973; )     

Mechanisms of the acido- and thermo-phily of Cyanidium caldarium Geitler I. Effects of temperature, pH and light intensity on the photosynthetic oxygen evolution of intact and treated cells

Photosynthetic oxygen evolution in an acido- and thermo-philicunicellular alga, Cyanidium caldarium, was measured under variousconditions, using a Clark-type oxygen electrode. 1). Maximum Hill reaction activity with p-benzoquinone as theHill oxidant was obtained at 45°C in a wide pH range from1.0 to 7.0. 2) The pH activity curve showed two peaks at pH3.0 and 7.0. The Hill activity had an optimum at pH 3.0 in cellspreilluminated under strong light (300,000 lux, 30 min, 40°C).Sonication of algal cells abolished the pH 3.0 component ofthe Hill reaction producing an activity maximum at pH 7.0. 3)Endogenous O₂ evolution in the absence of the Hill oxidant,which lasted for several minutes after illumination, had a maximumat pH 7.0. 4) This endogenous O₂ evolution was abolished bysonication. 5) KCN inhibited endogenous O₂ evolution, but notthe Hill reaction in the presence of p-benzoquinone. (Received August 19, 1974; )     

Changes in the Carbonic Anhydrase Activity and the Rate of Photosynthetic O2 Evolution during the Cell Cycle of Chlorella ellipsoidea C-27

Rhythmical changes in carbonic anhydrase activity(CA) and inphotosynthesis were observed during the cell cycle of Chlorellaellipsoidea C-27 synchronized at various concentrations of dissolvedCO₂ (dCO₂ with a regime of 16 h of light and 8 h of darkness.At a constant low concentration of dCO₂ (11 {diaeresis}M), intracellularCA activity showed obvious fluctuations with a peak at 8 h afterthe initiation of illumination, while extracellular CA activity,located on the cell surface, showed only minor fluctuationsalthough the activity was as high as the maximum activity ofintracellular CA. In contrast, obvious changes in the activitiesof intra- and extracellular CA activities were not observedat a high concentration of dCO₂ (520 {diaeresis}M). The ratioof photosynthetic activity at limiting versus saturating concentrationsof dCO₂, which is indicative of the affinity of cells for CO₂,showed clear rhythmical changes during the cell cycle and theratio was higher in low-CO₂ cells than in high-CO₂ cells. Thechanges in the ratio seemed to reflect the changes in CA activity. When the cells that had been synchronized under high CO₂ conditionswere transferred to low CO₂ conditions at any given stage inthe cell cycle, CA activity was induced in every case but thecapacity for induction of CA was greater in young cells thanin mature cells. This result suggests that the capacity of cellsto induce CA over the course of the cell cycle is closely relatedto endogenous aging of the cell. (Received August 29, 1988; Accepted December 28, 1988)     

2,4-D-Sustained Photomixotrophic Growth of a Chlorophyllous Cell Suspension Culture of Nicotiana tabacum

A chlorophyllous, photomixotrophic cell suspension culture oftobacco (Nicotiana tabacum L.) was established using mediumcontaining 30 g/liter of sucrose and 1.5 µM 2,4-D. The2,4-D-sustained photomixotrophic line was able to show rapidregreening in the light after bleaching in the dark and characterizedwith a much slower and longer growth cycle than a heterotrophicline derived from the same original callus (cell doubling timeof 100 h vs. 40 h and duration of logarithmic phase of 17 daysvs. 7 days). The photomixotrophic line took up sucrose morerapidly than the heterotrophic line and accumulated starch duringthe early logarithmic phase when it showed a maximum photosyntheticcapacity on a chlorophyll basis (6.3µmol O₂/min/mg Chl).Chlorophyll content and photosynthetic capacity on a per cellbasis and on a cell fresh weight basis, on the other hand, decreasedduring this phase and reincreased later to reach maximum levels(310 µg Chl/g fr wt; 1.4 µmol O₂/min/g fr wt) whenthe line exhibited the highest activities of dark respiration(1.0 µmol; O₂/min/g fr wt) and cell division (mitoticindex of 3.0%). These characteristics of the photomixotrophicline were lost if it was grown in the dark to become non-chlorophyllous.Although net O₂ evolution could not be detected in the photomixotrophicline throughout the growth cycle when assayed under suboptimumlight intensity, reaccumulation of starch and a marked increasein cell fresh weight upon addition of minerals, vitamins and2,4-D without sucrose at the late logarithmic phase indicatedthe development of photosynthetic activity under the cultureconditions. ¹The investigations reported were included in the thesis submittedto the Graduate School, Faculty of Agriculture, Kobe University,in partial fulfillment of the requirement for M. Agr. degree. (Received May 30, 1988; Accepted October 5, 1988)     

Photoautotrophic and Photomixotrophic Culture of Green Tobacco Cells in a Jar-Fermenter

Green tobacco cells were cultured photomixotrophically and photoautotrophicallyin a jar-fermenter (working volume, 5 liters). Optimum aerationand agitation, i.e. the type of impeller (marine), agitationspeed (200 rpm), and aeration rate [1 aeration volume/mediumvolume/min (wm)], and light intensity (8,000 lux) were determinedin order to get high cell growth. Under these conditions, tobaccocells increased about ten fold after 17 days of photomixotrophicculture. In the photoautotrophic culture that had aeration with1% CO₂ enriched air, the mass of the tobacco cells did not increasebecause stimulated cell respiration compensated for photosyntheticactivity. A low oxygen supply was essential for photoautotrophicculture in a jar-fermenter. The fresh weight of green tobaccocells increased twice under photoautotrophy, after 17 days ofculture with an agitation of 200 rpm, aeration of 0.8 vvm, withair containing 1% CO₂, 14% O₂ and 85% N₂, and an illuminationof 8,000 lux. ¹Present address: Botanical Institute, PL-Women's College, Tondabayashi,Osaka 584, Japan. (Received April 2, 1981; Accepted June 15, 1981)     

The photoautotrophic culture of chlorophyllous cells

Photosynthesis in chlorophyllous cells in heterotrophic cultureswas investigated. Chlorophyllous cells from the amur cork-tree,scotch broom and tobacco, all of which had relatively high chlorophyllcontents (70 to 120 µg/g fresh weight) were selected throughoutcallus induction and cell subculture. When cultured under variouslight intensities, growth was stimulated by increases in lightintensity. This stimulation depended on the chlorophyll contentsof the cells. It disappeared on the addition of photosynthesisinhibitors (DCMU or 2-chloro-4,6-bis(ethylamino)-s-triazine).These phenomena indicate that photosynthesis accounted for athird to a half of cell growth under strong illumination. These heterotrophic cultures were then developed as autotrophiccultures. When these chlorophyllous cells were cultured withaeration using CO₂-enriched air in the light condition, thescotch broom and tobacco chlorophyllous cells grew photoautotrophically.Nearly the same amount of growth as with 3% sucrose in the darkwas observed in an autotrophic culture with aeration using aircontaining 1% CO₂. The green tobacco cells have been subculturedautotrophically for about one year. (Received November 28, 1977; )     

C3和C4植物光合途径的适应性变化和进化

 高等植物大多为C₃植物, C₄植物和景天酸代谢(Crassulacean acid metabolism, CAM)植物是由C₃植物进化而来的。C₄途径的多源进化表明, 光合途径由C₃途径向C₄途径的转变相对简单。该文分析研究了植物光合途径的进化前景, 指出C₄植物是从C₃植物进化而来的高光效种类, 且地质时期以来降低的大气CO₂浓度和升高的大气温度以及干旱和盐渍化是C₄途径进化的外部动力。C₃植物的C₄途径的发现说明植物的光合途径并非是一成不变的, C₃和C₄植物的光合特征具有极大的可塑性, 某些环境的变化会引起植物光合途径在C₃和C₄途径之间转变。C₃植物具有的C₄途径是环境调控的产物, 是对逆境的适应性进化结果, 因而光合途径的转变也适用于干旱地区植被的适应性生存机理研究。该文还利用国外最新的C₄光合进化模型介绍了植物在进化C₄途径中所经历的7个重要时期(从分子基础到形态基础、结构基础, 再到物质代谢水平、光合酶活水平, 直到C3和C4途径协调运转时期, 最后达到形态与功能最优化阶段), 并结合全球气候变化的特点对国内外相关领域的研究进行了分析, 总结了植物光合途径的适应性转变和进化的研究成果, 为今后的相关工作提出建议。     

The Relation Between Activity of Phosphoenolpyruvate Carboxykinase and Photosynthesis in Aloe vera Leaves

The chlorophyllous layer of leaf of a PEP-CK type CAM plant Aloe vera was stripped tiff from the colorIess water storage tissue and used to stuly the interrelation between the activity of decarboxylating enzyme phosphoenolpyruvate carboxykinase (PEPCK) and photosynthesis. Oxaloacetate, malate+ADP, and NaHCO3 were found to stimulate photosynthetic oxygen evolution. During the period from 6:00 to 18:00 of the day time, a diurnal fluctuation was observed in both PEPCK activity and the rate of oxygen evolution. The maximum of photosynthesis appeared at 10-12:00, but the maximum PEPCK activity appeared at 14:00. The PEPCK activity and photosynthetic rate in leaf discs increased with temperature from 10 to 35℃, then decreased at 45℃. Similar decline of both parameters was found in the leaf discs stressed by different concentration of PEG-6000 solution for 4.5 h. At light intensity of 900 mol m-2 s-1 and 25℃, the PEPCK activity and photosynthetic rate of leaf discs rised with the illumination time, then a slight inhibition followed at the time of 30 min (Pn) or 40 min (PEPCK). The strong response of PEPCK activity to high light intensity in leaf discs, and a progressive increase of PEPCK activity in direct illumination of crude enzyme extractm the range of 0-55 min, indicated that light s likely to be an activator for PEPCK. Leaf discs were infiltrated with 3-(3,4-dichlorophenyl)-l, 1-dimethylurea, DL-glyceraldehyde and 2,4-dimitrophenol resulted in the partial inhibition of light-ependent photosynthesis and decarboxylation of C4 acid. The activity of PEPCK was also stimulated by Mg2+ or Mg2++ATP infiltrated into the leaf discs in the dark. The evidence presented here suggested that PEPCK activity of CAM plants showed a close interrelation with photosynthesis. Both of them were regulated by the environmental changes. The activity of PEPCK might be coupled to electron trsnsport and photophosphorylatiou.     

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)     

Developing embryos of Sesbania sesban have unique potential to photosynthesize under high osmotic environment

This study has been carried out to investigate the photosynthetic activities in developing embryos of Sesbania sesban under a highly osmotic environment. In S. sesban, the embryo turns green/chlorophyllous at the early heart shape stage. Interestingly, despite being deeply embedded within the supporting tissues (several layers of pod wall, seed coat and endosperm) and developing in a highly osmotic environment, the growing embryo of the developing seed showed the presence of various components of photosynthetic machinery besides being chlorophyllous. The shade-adaptive nature of the photosynthetic machinery of the embryo is evident from (a) low chlorophyll a/b ratio, (b) photosystem (PS) II attaining maximal activity at low photon flux density and (c) lesser plastoquinone pool. The photosynthetic potential of the growing embryo seems to contribute towards seed filling as it has the potential not only to harvest light energy but also to fix CO2 as efficiently as other photosynthetic parts of S. sesban. In fact, ribulose-1,5 bisphosphate carboxylase purified from embryos manifested subunit composition similar to that of leaves. The PS II activity in leaves, cotyledonary leaves and pod wall declined sharply with increase in the level of NaCl and sucrose above 150 and 300 mmol, respectively. Amazingly, PS II activity in developing embryos was maximal in the presence of 250 mmol NaCl or 500 mmol sucrose and remained high even when NaCl and sucrose levels were increased to 500 and 1000 mmol, respectively. We hypothesize that the developing embryos have some factor(s) which protect(s) the photosynthetic machinery in an environment of high osmotic strength.     

Light-induced changes of bioelectric potential in Chara

Experiments were performed on light-induced changes of the restingpotential in Chara under various conditions. In the dark-adaptedcells, a slow increase in resting potential, by about 60 mv,appeared in a solution containing 0.5 mM KCl, 0.2 mM NaCl and0.5 mM CaCl₂. On the contrary, a rapid decrease preceded bya small, sharp rise in potential was produced when the cellsbecame adapted to light. On the first illumination, the cellmembrane resistance decreased in dark-adapted cells, but a slightincrease was observed every time on subsequent illuminations.No parallel relation was found between the time course of thechanges of resistance and the potential difference. During severalilluminations, as well as during the short dark periods betweenthem, cells lost their sensitivity to change in a potassiumconcentration. The time courses of photosynthetic oxygen evolutionwere not in accordance with those of changes in the potential.However, 10µM 3-(3,4-dichlorophenyl)-l, l-dimethylureareversibly abolished both the oxygen evolution and the changesin potential. An enhancement of the photoelectric response wasobserved when bicarbonate ions were added in the external solution.On the other hand, the oxygen evolution was not affected bythe bicarbonate ions. On the basis of these observations itwas assumed that some assimilation products of photosynthesiswere responsible for the photoelectric response. (Received February 13, 1968; )     

The Effect of Photoautotrophy on Photosynthesis and Photoinhibition of Gardenia Plantlets during Micropropagation

We studied the relationships between the degree of photoautotrophy, photosynthetic capacity, and extent of photoinhibition of Gardenia jasminoides Ellis plantlets in vitro. Two successive micropropagation stages (shoot multiplication and root induction), and three culture conditions [tube cap closure, photosynthetic photon flux density (PPFD), and sucrose concentration] which may influence the development of photoautotrophy in vitro were assayed. The ratios of variable chlorophyll fluorescence to either maximal (F_v/F_m) or ground (F_v/F₀) values were low, irrespective of the culture stage or growing conditions. Incomplete development of the photosynthetic apparatus and permanent photoinhibition may be involved. However, F_v/F_m and F_v/F₀ increased from shoot multiplication to root induction owing to a decrease in F₀ and an increase in F_m. This suggests that photoinhibition decreases later during micropropagation, when the photoautotrophy of plantlets is more advanced. The low sucrose content and high PPFD increased the photoinhibition of plantlets, whereas growth in tubes with permeable caps showed the opposite effect. The only culture factor with a significant (positive) effect on maximum photosynthetic rate (P _max) was PPFD. At shoot multiplication net photosynthetic rate (P _N) was positively correlated with the half time of the increase from F₀ to F_m (t_1/2). Such association may be mainly due to a common response of both traits to higher PPFD in culture. Within each culture stage, no relationship was observed between P _N and the degree of photoautotrophy, which was positively correlated with F_v/F_m and F_v/F₀ during root induction. During shoot multiplication, these correlations were not significant, or were even negative. Hence during the last stage of micropropagation, plantlets with a higher degree of photoautotrophy are less photoinhibited, whereas they do not follow this pattern at the earlier stage.     

Photoautotrophic micropropagation

Summary Sugar in the medium is considered to be an essential cause for the high production costs of plantlets in conventional, heterotrophic micropropagation. Chlorophyllous explants, shoots, and plantlets in vitro have high photosynthetic ability to develop photoautotrophy, but their photosynthetic activity is restricted largely by the low CO₂ concentration in the vessel during the photoperiod and in part by the presence of sugar in the medium. The growth of plantlets in vitro is often greater under photoautotrophic conditions than under heterotrophic conditions, provided that the in vitro environment is properly controlled for promoting photosynthesis. The advantages and disadvantages of photoautotrophic micropropagation are discussed.     

Mass Propagation of Eucalyptus camaldulensis in a Scaled-up Vessel Under In Vitro Photoautotrophic Condition

A scaled-up culture vessel was designed for the large-scalephotoautotrophic micropropagation of chlorophyllous plants.The culture vessel (volume 20 l) contained a plug cell traywith 448 plantlets, and had a forced ventilation system to supplyCO₂-enriched air. A nutrient-reservoir was connected to theculture vessel from which nutrient solution was circulated tothe culture vessel every 24 h. Nodal leafy cuttings of Eucalyptuscamaldulensis L. were cultured photoautotrophically in thissystem without sugar in the nutrient medium, but with an enrichedCO₂concentration and a high photosynthetic photon flux. Thegrowth and the net photosynthetic rate of the in vitro grownplantlets and the survival percentage of the plantlets aftertransplanting to ex vitro conditions were compared with thoseof plantlets grown photoautotrophically under natural ventilationin conventional small culture vessels (Magenta-type vessels;volume 0.4 l). Fresh and dry masses and net photosynthetic ratewere significantly higher in plantlets grown in the scaled-upvessel compared to plantlets grown in the conventional smallvessels (control). The environmental conditions created in thisscaled-up vessel (with forced ventilation) also facilitatedacclimatizationin vitro . Importantly, after transplanting tothe ex vitro condition, plantlets grew well without any specializedexvitro acclimatization treatment. Copyright 2000 Annals of BotanyCompany CO₂enrichment, Eucalyptus camaldulensis L., ex vitro, forced ventilation, natural ventilation, photoautotrophic, scaled-up vessel, survival percentage     

Glutamine Synthetase Isoenzymes of Striga hermonthica and other Angiosperm Root Parasites

The occurrence of multiple forms of glutamine synthetase inStriga hermonthica and other angiosperm root parasites was investigated.The facultative chlorophyllous parasite Melampyrum arvense exhibitedtwo isoenzymes in leaf tissue, the cytosolic component (GS₁)comprised less than 30% of total glutamine synthetase. In contrastGS₁ was the major component (<70%) in photosynthetic tissueof Striga hermonthica and S. gesnerioides. Only a single isoenzyme(GS₁) was detectable in the achlorophyllous root parasites Orobancheand Lathraea and in non-photosynthetic tissue of S. gesnerioides.The kinetic and physical properties of GS₁ and GS₂ of theseangiosperm parasites were similar to those of the isoenzymesin other non-parasitic angiosperms. Key words: Glutamine synthetase, Angiosperms, Root parasites     

Influence of Temperature and O2 Concentration on Photosynthesis and Light Activation of Ribulosebisphosphate Carboxylase Oxygenase in Intact Leaves of White Clover (Trifolium repens L.)

Detached leaves of white clover (Trifolium repens L.) were keptfor 1 h under various conditions of temperature, oxygen concentrationand light intensity. Rates of photosynthesis were measured whereappropriate and then ribulosebisphosphate carboxylase oxygenase(RuBPCO) was extracted rapidly and its initial activity measuredimmediately. The extracted activity increased with increased intensity ofillumination of the leaves. Where leaves were pretreated atlow light intensity, the lower the temperature of the leavesthe higher the extracted activity of RuBPCO. At high light intensitytemperature did not affect the activity of subsequently extractedRuBPCO but the light intensity which was necessary for maximumactivity increased with temperature. Activity of RuBPCO fromleaves pretreated in the dark was least when CO₂ was low andtemperature high. Leaves, pretreated at low temperatures andhigh light intensity in 20% O₂, yielded higher activity in extractsthan leaves pretreated under similar conditions but in 2% O₂.A relatively weak temperature response of photosynthesis atlow irradiances was associated with a decrease in extractableRuBPCO activity with increasing temperature. A strong temperaturedependence of the oxygen inhibition of photosynthesis was associatedwith lower extractable RuBPCO activity in leaves pretreatedat low oxygen concentration at low temperatures. With leavesfrom plants grown at low temperatures prior to treatment ofleaves, oxygen inhibition of photosynthesis was less temperaturedependent and activity of RuBPCO in extracts was not decreasedby low O₂ at low temperatures. Differences in the activationof RuBPCO appear to influence photosynthesis and account foran absence of oxygen inhibition of photosynthesis at low temperaturesin plants grown in warm conditions. Key words: Ribulosebisphosphate carboxylase oxygenase activation, Photosynthesis, Temperature, O₂ effect, White clover     

The Location of the Transporting System for Inorganic Carbon and the Nature of the Form Translocated in Chlamydomonas reinhardtii

The permeability of the plasmalemma of Chlamydomonas reinhardtiicells was increased by treatment with poly-L-lysine or dimethylsulphoxideas indicated by 3-phosphoglyceric acid dependent O₂ evolution.These treatments decreased the ability of the cells to accumulateinorganic carbon internally and hence their photosynthetic affinityfor inorganic carbon in the medium. With saturating light andinorganic carbon, the photosynthetic rate was less affectedby the poly-L-lysine and dimethylsulphoxide treatments. Thusthe poly-L-lysine and dimethylsulphoxide did not alter the activityof the chloroplasts but rather made the intracellular inorganiccarbon pool more freely exchangeable with the medium. It isconcluded that the transporting system for inorganic carbonis located at the plasmalemma. Treatment with Diamox, an inhibitor of carbonic anhydrase, didnot affect photosynthetic rate and accumulation of inorganiccarbon when CO₂ was supplied but strongly inhibited both parameterswhen HCO^–₃ was supplied. In a mutant of Chlamydomonasreinhardtii lacking a cell wall, carbonic anhydrase leaks tothe medium and uptake of inorganic carbon is much faster whenCO₂ is supplied than when HCO^–₃ is supplied. These resultssuggest that CO₂ rather than HCO^–₃ is the inorganic carbonspecies that is actively translocated across the plasmalemma. Key words: Chlamydomonas, Inorganic carbon uptake     

Oxygen enhancement of photosynthesis in Anacystis nidulans cells1

Oxygen enhanced photosynthetic ¹⁴CO₂ fixation in Anacystis nidulanscells. Results obtained under different conditions revealedthe following properties of the oxygen enhancement:

1. The enhancement was most significant at ca. 10% O₂. Furtherincrease in oxygen concentration decreased the enhancing effect.The rate under 100% O₂ was equivalent to or a little higherthan that under N₂ gas.
2. b) With the increase in CO₂ concentration,the magnitude ofthe enhancing effect decreased. No oxygen enhancementwas observedwhen the CO₂ concentration. was raised to 9,000ppm.
3. c) The enhancement was observed only at high light intensities.No enhancement was observed when the rate of photosynthesiswas limited by light intensity.
4. Ribulose 1,5-diphosphate (RuDP)carboxylase activity was demonstratedin the extract obtainedfrom A. nidulans cells. We also foundthat the RuDP carboxylaseactivity in this extract was competitivelyinhibited by oxygen.
5. Based on the above-mentioned results, the possible mechanismunderlying the observed enhancing effect of oxygen was discussed.

(Received May 10, 1976; )     

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.     

Increased activity of only an individual non-regulated enzyme fructose-1,6-bisphosphate aldolase in <Emphasis Type="Italic">Anabaena</Emphasis> sp. strain PCC 7120 stimulates photosynthetic yield

The goal of this study was to investigate the contribution of increased activity of individual non-regulated enzymes in the Calvin cycle to improve photosynthetic yield. Two non-regulated enzymes, rice fructose-1,6-bisphosphate aldolase (FBA) and spinach triosephosphate isomerase (TPI), were individually cloned and overexpressed in the cyanobacterium Anabaena sp. strain PCC 7120 cells. The enzyme activity and the photosynthetic yield, as reflected by the cell growth rate, photosynthetic oxygen evolution and dry cellular weight, were measured and compared between the wild-type and transgenic cells harboring either FBA or TPI. Though the activity of these two individual non-regulated enzymes was similarly increased in the corresponding transgenic cells, the contributions of each enzyme on the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), reflected by the levels of Rubisco large subunit, and the photosynthetic yield were different. Transgenic cells, carrying FBA, showed an evident increase in Rubisco amount and photosynthetic yield, while there was no increase in cells harboring TPI. This indicates that the contributions of non-regulated enzymes in the Calvin cycle on photosynthetic yield differed and firstly reveals that increased activity of only a single non-regulated enzyme in transgenic cells markedly improves the photosynthetic yield via stimulating the amount of Rubisco and consequently accelerating the ribulose-1,5-bisphosphate (RuBP) regeneration rate.