Developmental regulation of photosynthate distribution in leaves of rice

mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N_0.5, N_3.0). The relative gene expression patterns were similar in all leaves except for 9^th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS V_max, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS V_max was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5^th and 7^th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9^th and flag leaves). PEPC activity and SPS V_max decreased with declining leaf N content. After using ¹⁴CO₂ the ¹⁴C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more ¹⁴C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more ¹⁴C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status.     

Does carbon isotope discrimination correlate with biological nitrogen fixation?

It has recently been reported that N₂ fixation and carbon isotope discrimination (Δ) are negatively correlated. To further test this hypothesis, a greenhouse experiment was conducted to investigate if Δ is correlated with the efficiency of lentil (Lens culinaris cv Laird) in fixing atmospheric nitrogen. Lentil seed was inoculated with one of 10 Rhizobium leguminosarum strains that varied in their effectiveness in symbiotic N₂ fixation. Carbon-13 discrimination was positively correlated with N₂ fixation (r²=0.60^*). Although the amount of N₂ fixed ranged from 1.5 mg N to 13.5 mg N shoot⁻¹, the range of Δ values was only 25.8 to 26.6%.. It is unlikely that variability of such small magnitude could be of any practical use in selecting for N₂-fixing efficiency.     

Pyruvate metabolism in Helicobacter pylori

The metabolism of pyruvate by Helicobacter pylori was investigated employing one- and two-dimensional ¹H and ¹³C nuclear magnetic resonance spectroscopy. Generation of pyruvate from l-serine in incubations with whole cell lysates indicated the presence of serine dehydratase activity in the bacterium. Pyruvate was formed also in cell suspensions and lysates from phosphoenol pyruvate. Metabolically competent cells incubated aerobically with pyruvate yielded alanine, lactate, acetate, formate, and succinate. The production of alanine and lactate indicated the presence of alanine transaminase and lactate dehydrogenase activities, respectively. Accumulation of acetate and formate as metabolic products provided evidence for the existence of a mixed-acid fermentation pathway in the microorganism. Formation of succinate suggested the incorporation of the pyruvate carbon skeleton into the Kreb's cycle. Addition of pyruvate to various liquid culture media did not affect bacterial growth or loss of viability. The variety of products formed using pyruvate as the sole substrate showed the important role of this metabolite in the energy metabolism of H. pylori.     

C4 photosynthetic carbon metabolism in the leaves of aromatic tropical grasses — I. Leaf anatomy,CO2 compensation point and CO2 assimilation

A few species of Cymbopogon and Vetiveria are potentially important tropical grasses producing essential oils. In the present study, we report on the leaf anatomy and photosynthetic carbon assimilation in five species of Cymbopogon and Vetiveria zizanioides. Kranz-type leaf anatomy with a centrifugal distribution of chloroplasts and exclusive localization of starch in the bundle sheath cells were common among the test plants. Besides the Kranz leaf anatomy, these grasses displayed other typical C₄ characteristics including a low (0–5 µl/l) CO₂ compensation point, lack of light saturation of CO₂ uptake at high photon flux densities, high temperature (35°C) optimum of net photosynthesis, high rates of net photosynthesis (55–67 mg CO₂ dm^-2 leaf area h^-1), little or no response of net photosynthesis to atmospheric levels of O₂ and high leaf ¹³C/¹²C ratios. The biochemical studies with ¹⁴CO₂ indicated that the leaves of the above plant species synthesize predominantly malate during short term (5 s) photosynthesis. In pulse-chase experiments it was shown that the synthesis of 3-phosphoglycerate proceeds at the expense of malate, the major first formed product of photosynthesis in these plant species.     

Inorganic carbon acquisition by red seaweeds grown under dynamic light regimes

Palmaria palmata, which is able to use HCO _inf3 ^sup– as a carbon source for photosynthesis, and Lomentaria articulata, which is dependent on diffusive uptake of dissolved CO₂, were grown under constant light and light with sunflecks designed to model wave-induced fluctuations of near-shore underwater light. Both species exhibited significantly increased stable carbon isotope discrimination (more negative values of ¹³C relative to PDB) when grown with sunflecks. More negative ¹³C values were associated with decreased growth rate of P. palmata but not of L. articulata. The contrasting effects of sunflecks on the carbon-use characteristics of the two species are discussed in terms of the energetic cost of HCO _inf3 ^sup– use and the susceptibility of CO₂ diffusion-dependent species to photoinhibition.     

Photosynthetic carbon metabolism during leaf ontogeny in Zea mays L.: Enzyme studies

The activities of several enzymes, including ribulose-1,5-diphosphate (RuDP) carboxylase (EC 4.1.1.39) and phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured as a function of leaf age in Z. mays. Mature leaf tissue had a RuDP-carboxylase activity of 296.7 mol CO₂ g^-1 fresh weight h^-1 and a PEP-carboxylase activity of 660.6 mol CO₂ g^-1 fresh weight h^-1. In young corn leaves the activity of the two enzymes was 11 and 29%, respectively, of the mature leaves. In senescent leaf tissue, RuDP carboxylase activity declined more rapidly than that of any of the other enzymes assayed. On a relative basis the activities of NADP malic enzyme (EC 1.1.1.40), aspartate (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2), and NAD malate dehydrogenase (EC 1.1.1.37) exceeded those of both PEP and RuDP carboxylase in young and senescent leaf tissue. Pulse-chase labeling experiments with mature and senescent leaf tissue show that the predominant C₄ acid differs between the two leaf ages. Labeling of alanine in senescent tissue never exceeded 4% of the total ¹⁴C remaining during the chase period, while in mature leaf tissue alanine accounted for 20% of the total after 60 s in ¹²CO₂. The activity of RuDP carboxylase during leaf ontogeny in Z. mays parallels the development of the activity of this enzyme in C₃ plants.Abbreviations RuDP ribulose-1,5-diphosphate - PEP phosphoenol pyruvate - PGA 3-phosphoglycerate     

Relationship between net photosynthesis and leaf respiration in Mediterranean evergreen species

The relationship between net photosynthetic (P _N) and leaf respiration (R) rates of Quercus ilex, Phillyrea latifolia, Myrtus communis, Arbutus unedo, and Cistus incanus was monitored in the period February 2006 to February 2007. The species investigated had low R and P _N during winter, increasing from March to May, when mean air temperature reached 19.2 °C. During the favourable period, C. incanus and A. unedo had a higher mean P _N (16.4±2.4 μmol m⁻² s⁻¹) than P. latifolia, Q. ilex, and M. communis (10.0±1.3 μmol m⁻² s⁻¹). The highest R (1.89±0.30 μmol m⁻² s⁻¹, mean of the species), associated to a significant P _N decrease (62 % of the maximum, mean value of the species), was measured in July (mean R/P _N ratio 0.447±0.091). Q₁₀, indicating the respiration sensitivity to short-term temperature increase, was in the range 1.49 to 2.21. Global change might modify R/P _N determining differences in dry matter accumulation among the species, and Q. ilex and P. latifolia might be the most favoured species by their ability to maintain sufficiently higher P _N and lower R during stress periods.     

Elevated CO<Subscript>2</Subscript> Effects on Peatland Plant Community Carbon Dynamics and DOC Production

Northern peatlands are important stores of carbon and reservoirs of biodiversity that are vulnerable to global change. However, the carbon dynamics of individual peatland plant species is poorly understood, despite the potential for rising atmospheric CO₂ to affect the vegetation’s contribution to overall ecosystem carbon function. Here, we examined the effects of 3 years exposure to elevated CO₂ (eCO₂) on (a) peatland plant community composition and biomass, and (b) plant carbon dynamics and the production of dissolved organic carbon (DOC) using a ¹³CO₂ pulse–chase approach. Results showed that under eCO₂, Sphagnum spp. cover declined by 39% (P < 0.05) and Juncus effusus L. cover increased by 40% (P < 0.001). There was a concurrent increase in above- and belowground plant biomass of 115% (P < 0.01) and 96% (P < 0.01), respectively. Vascular species assimilated and turned over more ¹³CO₂-derived carbon than Sphagnum spp. (49% greater turnover of assimilated ¹³C in J. effusus and F. ovina L. leaf tissues compared with Sphagnum, P < 0.01). Elevated CO₂ also produced a 66% rise in DOC concentrations (P < 0.001) and an order of magnitude more ‘new’ exudate ¹³DOC than control samples (24 h after ¹³CO₂ pulse-labelling 2.5 ± 0.5 and 0.2 ± 0.1% in eCO₂ and control leachate, respectively, P < 0.05). We attribute the observed increase in DOC concentrations under eCO₂ to the switch from predominantly Sphagnum spp. to vascular species (namely J. effusus), leading to enhanced exudation and decomposition (litter and peat). The potential for reduced peatland carbon accretion, increased DOC exports and positive feedback to climate change are discussed.     

Occurrence of C3 and C4 photosynthesis in cotyledons and leaves of Salsola species (Chenopodiaceae)

Most species of the genus Salsola (Chenopodiaceae) that have been examined exhibit C₄ photosynthesis in leaves. Four Salsola species from Central Asia were investigated in this study to determine the structural and functional relationships in photosynthesis of cotyledons compared to leaves, using anatomical (Kranz versus non-Kranz anatomy, chloroplast ultrastructure) and biochemical (activities of photosynthetic enzymes of the C₃ and C₄ pathways, ¹⁴C labeling of primary photosynthesis products and ¹³C/¹²C carbon isotope fractionation) criteria. The species included S. paulsenii from section Salsola, S. richteri from section Coccosalsola, S. laricina from section Caroxylon, and S. gemmascens from section Malpigipila. The results show that all four species have a C₄ type of photosynthesis in leaves with a Salsoloid type Kranz anatomy, whereas both C₃ and C₄ types of photosynthesis were found in cotyledons. S. paulsenii and S. richteri have NADP- (NADP-ME) C₄ type biochemistry with Salsoloid Kranz anatomy in both leaves and cotyledons. In S. laricina, both cotyledons and leaves have NAD-malic enzyme (NAD-ME) C₄ type photosynthesis; however, while the leaves have Salsoloid type Kranz anatomy, cotyledons have Atriplicoid type Kranz anatomy. In S. gemmascens, cotyledons exhibit C₃ type photosynthesis, while leaves perform NAD-ME type photosynthesis. Since the four species studied belong to different Salsola sections, this suggests that differences in photosynthetic types of leaves and cotyledons may be used as a basis or studies of the origin and evolution of C₄ photosynthesis in the family Chenopodiaceae.This revised version was published online in October 2005 with corrections to the Cover Date.     

Does Bienertia cycloptera with the single-cell system of C(4) photosynthesis exhibit a seasonal pattern of delta (13)C values in nature similar to co-existing C (4) Chenopodiaceae having the dual-cell (Kranz) system?

Family Chenopodiaceae is an intriguing lineage, having the largest number of C₄ species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C₄ functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (δ¹³C values) of leaves deviated from C₄ to C₃−C₄ intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species usually co-occurs with several Kranz type C₄ annuals. The development of B. cycloptera morphologically and δ¹³C values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a salt flat in north central Iran, along with eight Kranz type C₄ species and one C₃ species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf anatomy and C₄ biochemical subtype. Among the nine C₄ species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C₄ anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in the δ¹³C values found in plants grown in the natural habitat. The nine C₄ species had average seasonal δ¹³C values of −13.9‰ (with a range between species from −11.3 to −15.9‰). The measurements of δ¹³C values over a complete growing season show that B. cycloptera performs C₄ photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average δ¹³C value of −15.2‰. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Adaptive photosynthetic strategies of the Mediterranean maquis species according to their origin

In consideration of their origin the adaptive strategies of the evergreen species of the Mediterranean maquis were analysed. Rosmarinus officinalis L., Erica arborea L., and Erica multiflora L. had the lowest net photosynthetic rate (P_N) in the favourable period [7.8±0.6 mol(CO₂) m^–2s^–1, mean value], the highest P_N decrease (on an average 86 % of the maximum) but the highest recovery capacity (>70 % of the maximum) at the first rainfall in September. Cistus incanus L. and Arbutus unedo L. had the highest P_N during the favourable period [15.5±5.2 mol(CO₂) m^–2s^–1, mean value], 79 % decrease during drought, and a lower recovery capacity (on an average 54 %). Quercus ilex L., Phillyrea latifolia L., and Pistacia lentiscus L. had an intermediate P_N in the favourable period [9.2±1.3 mol(CO2) m^–2s^–1, mean value], a lower reduction during drought (on an average 63 %), and a range from 62 % (Q. ilex and P. latifolia) to 39 % (P. lentiscus) of recovery capacity. The Mediterranean species had higher decrease in P_N and stomatal conductance during drought and a higher recovery capacity than the pre-Mediterranean species. Among the pre-Mediterranean species, P. latifoliahad the best adaptation to long drought periods also by its higher leaf mass per area (LMA) which lowered leaf temperature thus decreasing transpiration rate during drought. Moreover, its leaf longevity determined a more stable leaf biomass during the year. Among the Mediteranean species, R. officinalis was the best adapted species to short drought periods by its ability to rapidly recover. Nevertheless, R. officinalis had the lowest tolerance to high temperatures by its P_N dropping below half its maximum value when leaf temperature was over 33.6°C. R. officinalismay be used as a bioindicator species of global change.This revised version was published online in March 2005 with corrections to the page numbers.     

Developmental changes of plant affecting primary photosynthate distribution in rice leaves

Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the ¹⁴CO₂ tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5^th leaf than in the 6^th one. Correspondingly, the V_max of PEPC was significantly higher in the 5^th than in the 6^th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the V_max of SPS and PEPC was lower in the 5^th than in the 6^th leaf. As the 5^th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6^th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6^th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of ¹⁴C was transiently changed in the 5^th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage.     

C-NMR analysis of Aspergillus mutants disturbed in pyruvate metabolism

The metabolic consequences of two defects in pyruvate metabolism of the hyphal fungus Aspergillus nidulans have been investigated by natural abundance ¹³C-NMR spectroscopy. A pyruvate dehydrogenase complex (pdh) mutant, grown on acetate, accumulates alanine upon starvation which is derived from mannitol reserves. The -alanine level increases further upon incubation with the non-permissive substrate -glucose. -Glutamate is absent from these spectra as it is required both for the transamination of pyruvate and as a reaction on an impaired energy metabolism in such a pdh-deficient strain. A pyruvate carboxylase (pyc) mutant, grown upon acetate, only starts to accumulate alanine after a long incubation period with -glucose, due to the long-lasting presence of phosphoenolpyruvate carboxykinase and malic enzyme, which are both induced by growth on acetate. When this strain is grown on -fructose and -glutamate, alanine also accumulates within 3 h upon transfer to -glucose.     

Differential inhibition of photosynthesis under drought stress in <Emphasis Type="Italic">Flaveria</Emphasis> species with different degrees of development of the C<Subscript>4</Subscript> syndrome

The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C₃), F. floridana (C₃–C₄), F. brownii (C₄-like), and F. trinervia (C₄) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in the C₃ species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient to interpret the net photosynthetic rates (P _N), but, from the decreases in P _N values under high CO₂ (C _a = 700 μmol mol^{− 1}) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C₃ species. The observed decline in the photosynthesis capacity of the C₃–C₄ species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum P _N observed in the C₄-like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate (RuBP or PEP) regeneration rates. In the C₄ species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS plants.     

Acetyl CoA,a central intermediate of autotrophic CO2 fixation in Methanobacterium thermoautotrophicum

The pathway of autotrophic CO₂ fixation in Methanobacterium thermoautotrophicum has been investigated by long term labelling of the organism with isotopic acetate and pyruvate while exponentially growing on H₂ plus CO₂. Maximally 2% of the cell carbon were derived from exogeneous tracer, 98% were synthesized from CO₂. Since growth was obviously autotrophic the labelled compounds functioned as tracers of the cellular acetyl CoA and pyruvate pool during cell carbon synthesis from CO₂. M. thermoautotrophicum growing in presence of U-¹⁴C acetate incorporated ¹⁴C into cell compounds derived from acetyl CoA (N-acetyl groups) as well as into compounds derived from pyruvate (alanine), oxaloacetate (aspartate), -ketoglutarate (glutamate), hexosephosphates (galactosamine), and pentosephosphates (ribose). The specific radioactities of N-acetylgroups and of the three amino acids were identical. The hexosamine exhibited a two times higher specific radioactivity, and the pentose a 1.6 times higher specific radioactivity than e.g. alanine. M. thermoautotrophicum growing in presence of 3-¹⁴C pyruvate, however, did not incorporate ¹⁴C into cell compounds directly derived from acetyl CoA. Those compounds derived from pyruvate, dicarboxylic acids and hexosephosphates became labelled. The specific radioactivities of alanine, aspartate and glutamate were identical; the hexosamine had a specific radioactivity twice as high as e.g. alanine.The finding that pyruvate was not incorporated into compounds derived from acetyl CoA, whereas acetate was incorporated into derivatives of acetyl CoA and pyruvate in a 1:1 ratio demonstrates that pyruvate is synthesized by reductive carboxylation of acetyl CoA. The data further provide evidence that in this autotrophic CO₂ fixation pathway hexosephosphates and pentosephosphates are synthesized from CO₂ via acetyl CoA and pyruvate.     

Interactions between cyanobacterium and fungus during 15N2-incorporation and metabolism in the lichen Peltigera canina

On following N₂-incorporation and subsequent metabolism in the lichen Peltigera canina using ¹⁵N as tracer, it was found, over a 30 min period, that greatest initial labelling was into NH ₄ ⁺ followed by glutamate and the amide-N of glutamine. Labelling of the amino-N of glutamine, aspartate and alanine increased slowly. Pulse-chase experiments using ¹⁵N confirmed this pattern. On inhibiting the GS-GOGAT pathway using l-methionine-dl-sulphoximine and azaserine, ¹⁵N enrichment of glutamate, alanine and aspartate continued although labelling of glutamine was undetectable. From this and enzymic data, NH ₄ ⁺ assimilation in the P. canina thallus appears to proceed via GS-GOGAT in the cyanobacterium and via GDH in the fungus; aminotransferases were present in both partners. The cyanobacterium assimilated 44% of the ¹⁵N₂ fixed; the remainder was liberated almost exclusively as NH ₄ ⁺ and then assimilated by fungal GDH.Abbreviations ADH alanine dehydrogenase - APT aspartate-pyruvate aminotransferase - AOA aminooxyacetate - GDH glutamate dehydrogenase - GOT glutamate-oxaloacetate aminotransferase - GOGAT glutamate synthase - GPT glutamate-pyruvate aminotransferase - GS glutamine synthetase - HEPES 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid - MSX l-methionine-dl-sulphoximine     

Formation of l-alanine as a reduced end product in carbohydrate fermentation by the hyperthermophilic archaeon Pyrococcus furiosus

The hyperthermophilic archaeon Pyrococcus furiosus was found to form substantial amounts of l-alanine during batch growth on either cellobiose, maltose or pyruvate. Acetate, CO₂ and H₂ were produced next to alanine. The carbon- and electron balances were complete for all three substrates. Under standard growth conditions (N₂/CO₂ atmosphere) an alanine/acetate ratio of about 0.3 was found for either substrate. The alanine /acetate ratio was influenced, however, by the hydrogen partial pressure. In the presence of S⁰ or in coculture with Methanococcus jannaschii this ratio was only 0.07, whereas under a H₂/CO₂ atmosphere this ratio could amount up to 0.8. Alanine formation was also aflected by the NH _inf4 ^sup+ concentration, i.e. below 4 mM, NH _inf4 ^sup+ becomes limiting to alanine formation. Alanine formation was shown to occur via an alanine aminotransferase, which exhibited a specific activity in cell-free extract of up to 6.0 U/mg (90°C; direction of pyruvate formation). The alanine aminotransferase probably cooperates with glutamate dehydrogenase (up to 23 U/mg; 90°C) and ferredoxin: NADP⁺ oxidoreductase (up to 0.7 U/mg, using methyl viologen; 90°C) to recycle the electron acceptors involved in catabolism. Thus, the existence of this unusual alanine-forming branch enables P. furiosus to adjust its fermentation, depending on the redox potential of the terminal electron acceptor.Abbreviations DTT dithiothreitol - MV methyl viologen - AAT alanine aminotransferase - GDH glutamate dehydrogenase - MV: NADP⁺ OR methyl viologen: NADP⁺ oxidoreductase     

Polyglucose synthesis in Chloroflexus aurantiacus studied by 13C-NMR

Chloroflexus aurantiacus OK-70 fl was grown photoautotrophically with hydrogen as electron source. The cultures were subjected to long term labelling experments with ¹³C-labelled acetate or alanine in the presence of sodium fluoroacetate. The presence of fluoroacetate caused the cells to accumulate large amounts of polyglucose which was hydrolysed and analysed by NMR. The labelling patterns of glucose were symmetric and in agreement with carbohydrate synthesis from acetate and CO₂ via pyruvate synthase. The content of carbon derived from added acetate was highest in C2 and C5 of glucose, at least 20% higher than in C1 and C6. About one third of the glucose carbon was derived from added acetate, the rest being from CO₂. Contrary to expectations, in glucose formed in the presence of C1-labelled acetate C1 and C6 contained more label than C2 and C5, and with C2-labelled acetate as the tracer glucose was mainly labelled in C2 and C5. Labelled CO₂ was formed from acetate labelled at either position. The labelling data indicate a new metabolic pathway in C. aurantiacus. It is suggested that the cells form C1-labelled acetyl-CoA from C2-labelled acetyl-CoA and vice versa by a cyclic mechanism involving concomitant CO₂ fixation and that this cycle is the part of the autotrophic CO₂ fixation pathways in C. aurantiacus in which acetyl-CoA is formed from CO₂.The polyglucose of C. aurantiacus appears to have predominantly (1–4)-linked structure with about 10% (1–6)-linkages as revealed by ¹³C-NMR.     

Comparative effects of growth irradiance on photosynthesis and leaf anatomy of Flaveria brownii (C4-like), Flaveria linearis (C3–C4) and their F1 hybrid

Photosynthetic rates and related anatomical characteristics of leaves developed at three levels of irradiance (1200, 300 and 80 umol · m^–2 · s^–1) were determined in the C₄-like species Flaveria brownii A.M. Powell, the C₃–C₄-intermediate species F. linearis Lag., and the F₁ hybrid between them (F. brownii × F. linearis). In the C₃–C₄ and F₁ plants, increases in photosynthetic capacity per unit leaf area were strongly correlated with changes in mesophyll area per unit leaf area. The C₄-like plant F. brownii, however, showed a much lower correlation between photosynthetic capacity and mesophyll area per unit leaf area. Plants of F. brownii developed at high irradiance showed photosynthetic rates per unit of mesophyll cell area 50% higher than those plants developed at medium irradiance. These results along with an increase in water-use efficiency are consistent with an increase of C₄ photosynthesis in high-irradiance-grown F. brownii plants, whereas in the other two genotypes such plasticity seems to be absent. Photosynthetic discrimination against ¹³C in the three genotypes was less at high than at low irradiance, with the greatest change occurring in F. brownii. Discrimination against ¹³C expressed as ¹³C was linearly correlated (r ² = 0.81; P<0.001) with the ratio of bundle-sheath volume to mesophyll cell area when all samples from the three genotypes were combined. This tissue ratio increased for F. brownii and the F₁ hybrid as growth irradiance increased, indicating a greater tendency towards Kranz anatomy. The results indicated that F. brownii had plasticity in its C₄-related anatomical and physiological characteristics as a function of growth irradiance, whereas plasticity was less evident in the F₁ hybrid and absent in F. linearis.Abbreviations A leaf surface area - A_ma, A_mn, A_lm total ma, mn or lm cell surface area - bs vascular bundle sheath - lm large spongy-mesophyll cells - ma mesophyll cells adjacent to bundle sheath - mn mesophyll cells not adjacent to bundle sheath - P_n net photosynthesis - (H, M, L) PPFD (high, medium, low) photosynthetic photon flux density - SLDW specific leaf dry wight - V_bs bs volume - V_{(ma + mn + bs)} total photosynthetic tissue volume - ¹³C ¹³C discrimination We thank Mrs. Lisa Smith for technical assistance in light microscopy and Dr. Ned Friedman (Department of Botany, University of Georgia, Athens, GA, USA) for the use of digitizing equipment. Participation of Dr. J.L. Araus in this work was supported by a grant Beca de Especialización para Doctores y Tecnólogos en el Extranjero, from Ministerio de Educatión y Ciencia, Spain.     

Redirecting Carbon Flux in Torulopsis glabrata from Pyruvate to α-Ketoglutaric Acid by Changing Metabolic Co-factors

The nutrition conditions needed to redirect the carbon flux in Torulopsis glabrata, a pyruvate hyper-production yeast, from pyruvate to α-ketoglutaric acid (KG) were investigated in a stirred fermentor. A minor amount of KG (1.3 gl⁻¹) was produced when NaOH was used to control the pH, while 12 g KG l⁻¹ was produced when CaCO₃ was used instead. When thiamine and biotin were included in the medium, 13 g KG l⁻¹ and 68 g pyruvate l⁻¹ were produced after 48 h when glucose was nearly consumed (approximately 5 gl⁻¹). With fermentation continuing for a further 16 h, the concentration of pyruvate decreased to 31 gl⁻¹, and KG increased to 30 gl⁻¹. KG thus accumulated at the expense of pyruvate consumption. Received 2 June 2005; Revisions requested 30 June 2005 and 1 September 2005; Revisions received 1 September 2005 and 28 October 2005; Accepted 28 October 2005