Carbon-nitrogen Balance Research Articles

Promoter Recognition and Activation by the Global Response Regulator CbrB in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the CbrA/CbrB two-component system is instrumental in the maintenance of the carbon-nitrogen balance and for growth on carbon sources that are energetically less favorable than the preferred dicarboxylate substrates. The CbrA/CbrB system drives the expression of the small RNA CrcZ, which antagonizes the repressing effects of the catabolite repression control protein Crc, an RNA-binding protein. Dicarboxylates appear to cause carbon catabolite repression by inhibiting the activity of the CbrA/CbrB system, resulting in reduced crcZ expression. Here we have identified a conserved palindromic nucleotide sequence that is present in upstream activating sequences (UASs) of promoters under positive control by CbrB and σ(54) RNA polymerase, especially in the UAS of the crcZ promoter. Evidence for recognition of this palindromic sequence by CbrB was obtained in vivo from mutational analysis of the crcZ promoter and in vitro from electrophoretic mobility shift assays using crcZ promoter fragments and purified CbrB protein truncated at the N terminus. Integration host factor (IHF) was required for crcZ expression. CbrB also activated the lipA (lipase) promoter, albeit less effectively, apparently by interacting with a similar but less conserved palindromic sequence in the UAS of lipA. As expected, succinate caused CbrB-dependent catabolite repression of the lipA promoter. Based on these results and previously published data, a consensus CbrB recognition sequence is proposed. This sequence has similarity to the consensus NtrC recognition sequence, which is relevant for nitrogen control.

Microbiological, colour and sensory properties of fresh beef steaks in low carbon monoxide concentration

AbstractSteaks from gluteus medius m. (GM) and longissimus dorsi m. (LD) were packaged in atmospheres containing two low levels of CO (0.2 and 0.4%) in combination with 21% O2 or without oxygen. The other components of the modified atmosphere packaging systems were carbon dioxide (30%) and nitrogen (balance). Steaks were evaluated on 0, 7, 14 and 21 days of storage at about 2oC to investigate the effects of the gas mixtures on the microflora, instrumental (CIE L*a*b*) and visual colour and odour. The preservation of colour and odour of GM and LD steaks packaged under low carbon monoxide was best achieved using anoxic mixtures containing 0.2% CO and 30% CO2. Steaks packaged without oxygen retained a desirable colour and practically did not present a visible discoloration or perceptive off‐odour along the entire storage time. Colour stabilization with 0.2% CO and 30% CO2, without O2, following storage up to 21 days at 2°C did not increase microbial risk of products. The increase in CO from 0.2 to 0.4% had a negative effect on the colour of LD steaks which was regarded as ‘artificial’ by some panellists. The higher stability achieved in this study using 0.2% CO may result from increased stability of the colour from Bos indicus × Bos Taurus cross. Discoloration and off‐odour were evident in the GM and LD steaks packaged aerobically after 14 days of storage when the counts of deteriorant bacteria achieved approximately 6.5 to 9.7 log CFU/g. Highest bacteriostatic effect could be obtained if the volume of injected CO2 was sufficient to saturate the meat and keep in balance around the product during storage. Copyright © 2010 John Wiley & Sons, Ltd.

New insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through a plastidic invertase

Since the photosynthetic apparatus of plants contains a massive amount of nitrogen, the regulation of its development by sugar signals is important to the maintenance of the carbon-nitrogen balance. Recently, we isolated a new Arabidopsis mutant, sicy (sugar-inducible cotyledon yellow)-192, whose cotyledons were prevented from greening by treatment with sucrose. On treatment with sucrose, the expression of photosynthesis- and nitrogen assimilation-related genes was respectively weaker and stronger in the mutant seedlings than the wild-type seedlings. In the mutants, the gene encoding plastidic alkaline/neutral (A/N) invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y). These findings provide new insights into the regulation of greening and carbon-nitrogen balance by sugar metabolism through INV-E in plastids. In this addendum, we describe the phenotypes of sicy-192 on treatment with sucrose in more detail, and propose a possible relationship among sugar metabolism through INV-E, plastid-to-nucleus retrograde signaling, and ethylene, a plant hormone, in the regulation of plant development and metabolism.

Point Mutation of a Plastidic Invertase Inhibits Development of the Photosynthetic Apparatus and Enhances Nitrate Assimilation in Sugar-treated Arabidopsis Seedlings

Because the photosynthetic apparatus contains a massive amount of nitrogen in plants, the regulation of its development by sugar signals is important to the maintenance of the carbon-nitrogen balance. In this study we isolated an Arabidopsis mutant (sicy-192) whose cotyledon greening was inhibited by treatments with sugars such as sucrose, glucose, and fructose. In the mutant, the gene encoding plastidic alkaline/neutral invertase (INV-E) was point-mutated at codon 294, with Tyr substituted for Cys (C294Y). Interestingly, the greening of cotyledons in the knock-out INV-E lines was not inhibited by treatment with the sugars. In addition, the knock-out INV-E lines expressing an INV-E:C294Y or INV-E:C294A gene had the same phenotype as sicy-192 mutants, whereas the lines expressing a wild-type INV-E gene had the same phenotype as wild-type plants. A recombinant INV-E:C294Y protein had the same enzymatic activity as a recombinant INV-E protein, suggesting that the Cys-294 residue of INV-E is important for its functions in the chloroplasts. On treatment with sucrose, the expression of photosynthesis-related genes was weaker in seedlings of mutant plants than wild-type seedlings, whereas the activity of nitrate reductase was stronger in the mutant plants than wild-type plants. These findings suggest that Cys-294 of INV-E is associated with the development of the photosynthetic apparatus and the assimilation of nitrogen in Arabidopsis seedlings to control the ratio of sucrose content to hexose content.

Small RNA as global regulator of carbon catabolite repression in Pseudomonas aeruginosa

In the metabolically versatile bacterium Pseudomonas aeruginosa , the RNA-binding protein Crc is involved in catabolite repression of a range of degradative genes, such as amiE (encoding aliphatic amidase). We found that a CA-rich sequence (termed CA motif) in the amiE translation initiation region was important for Crc binding. The small RNA CrcZ (407 nt) containing 5 CA motifs was able to bind the Crc protein with high affinity and to remove it from amiE mRNA in vitro. Overexpression of crcZ relieved catabolite repression in vivo, whereas a crcZ mutation pleiotropically prevented the utilization of several carbon sources. The sigma factor RpoN and the CbrA/CbrB two-component system, which is known to maintain a healthy carbon–nitrogen balance, were necessary for crcZ expression. During growth on succinate, a preferred carbon source, CrcZ expression was low, resulting in catabolite repression of amiE and other genes under Crc control. By contrast, during growth on mannitol, a poor carbon source, elevated CrcZ levels correlated with relief of catabolite repression. During growth on glucose, an intermediate carbon source, CrcZ levels and amiE expression were intermediate between those observed in succinate and mannitol media. Thus, the CbrA–CbrB–CrcZ–Crc system allows the bacterium to adapt differentially to various carbon sources. This cascade also regulated the expression of the xylS ( benR ) gene, which encodes a transcriptional regulator involved in benzoate degradation, in an analogous way, confirming this cascade's global role.

Small RNA as global regulator of carbon catabolite repression in Pseudomonas aeruginosa

In the metabolically versatile bacterium Pseudomonas aeruginosa, the RNA-binding protein Crc is involved in catabolite repression of a range of degradative genes, such as amiE (encoding aliphatic amidase). We found that a CA-rich sequence (termed CA motif) in the amiE translation initiation region was important for Crc binding. The small RNA CrcZ (407 nt) containing 5 CA motifs was able to bind the Crc protein with high affinity and to remove it from amiE mRNA in vitro. Overexpression of crcZ relieved catabolite repression in vivo, whereas a crcZ mutation pleiotropically prevented the utilization of several carbon sources. The sigma factor RpoN and the CbrA/CbrB two-component system, which is known to maintain a healthy carbon-nitrogen balance, were necessary for crcZ expression. During growth on succinate, a preferred carbon source, CrcZ expression was low, resulting in catabolite repression of amiE and other genes under Crc control. By contrast, during growth on mannitol, a poor carbon source, elevated CrcZ levels correlated with relief of catabolite repression. During growth on glucose, an intermediate carbon source, CrcZ levels and amiE expression were intermediate between those observed in succinate and mannitol media. Thus, the CbrA-CbrB-CrcZ-Crc system allows the bacterium to adapt differentially to various carbon sources. This cascade also regulated the expression of the xylS (benR) gene, which encodes a transcriptional regulator involved in benzoate degradation, in an analogous way, confirming this cascade's global role.

Increasing sucrose uptake capacity of wheat grains stimulates storage protein synthesis.

Increasing grain sink strength by improving assimilate uptake capacity could be a promising approach toward getting higher yield. The barley (Hordeum vulgare) sucrose transporter HvSUT1 (SUT) was expressed under control of the endosperm-specific Hordein B1 promoter (HO). Compared with the wild type, transgenic HOSUT grains take up more sucrose (Suc) in vitro, showing that the transgene is functional. Grain Suc levels are not altered, indicating that Suc fluxes are influenced rather than steady-state levels. HOSUT grains have increased percentages of total nitrogen and prolamins, which is reflected in increased levels of phenylalanine, tyrosine, tryptophan, isoleucine, and leucine at late grain development. Transcript profiling indicates specific stimulation of prolamin gene expression at the onset of storage phase. Changes in gene expression and metabolite levels related to carbon metabolism and amino acid biosynthesis suggest deregulated carbon-nitrogen balance, which together indicate carbon sufficiency and relative depletion of nitrogen. Genes, deregulated together with prolamin genes, might represent candidates, which respond positively to assimilate supply and are related to sugar-starch metabolism, cytokinin and brassinosteroid functions, cell proliferation, and sugar/abscisic acid signaling. Genes showing inverse expression patterns represent potential negative regulators. It is concluded that HvSUT1 overexpression increases grain protein content but also deregulates the metabolic status of wheat (Triticum aestivum) grains, accompanied by up-regulated gene expression of positive and negative regulators related to sugar signaling and assimilate supply. In HOSUT grains, alternating stimulation of positive and negative regulators causes oscillatory patterns of gene expression and highlights the capacity and great flexibility to adjust wheat grain storage metabolism in response to metabolic alterations.

Contribution of chloroplast biogenesis to carbon–nitrogen balance during early leaf development in rice

Chloroplast biogenesis is most significant during the changes in cellular organization associated with leaf development in higher plants. To examine the physiological relationship between developing chloroplasts and host leaf cells during early leaf development, we investigated changes in the carbon and nitrogen contents in leaves at the P4 developmental stage of rice, during which leaf blade structure is established and early events of chloroplast differentiation occur. During the P4 stage, carbon content on a dry mass basis remained constant, whereas the nitrogen content decreased by 30%. Among carbohydrates, sucrose and starch accumulated to high levels early in the P4 stage, and glucose, fructose and cellulose degradation increased during the mid-to-late P4 stage. In the chloroplast-deficient leaves of the virescent-1 mutant of rice, however, the carbon and nitrogen contents, as well as the C/N ratio during the P4 stage, were largely unaffected. These observations suggest that developing rice leaves function as sink organs at the P4 stage, and that chloroplast biogenesis and carbon and nitrogen metabolism in the leaf cell is regulated independently at this stage.

The effect of altered sink-source relations on photosynthetic traits and matter transport during the phase of reproductive growth in the annual herb Chenopodium album

Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO2 concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant’s ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.

Ozone responsive genes in Medicago truncatula: Analysis by suppression subtraction hybridization

Acute ozone is a model abiotic elicitor of oxidative stress in plants. In order to identify genes that are important for conferring ozone resistance or sensitivity we used two accessions of Medicago truncatula with contrasting responses to this oxidant. We used suppression subtraction hybridization (SSH) to identify genes differentially expressed in ozone-sensitive Jemalong and ozone-resistant JE154 following exposure to 300 nLL(-1) of ozone for 6h. Following differential screening of more than 2500 clones from four subtraction libraries, more than 800 clones were selected for sequencing. Sequence analysis of these clones identified 239 unique contigs. Fifteen novel genes of unknown functions were identified. A majority of the ozone responsive genes identified in this study were present in the Medicago truncatula EST collections. Genes induced in JE154 were associated with adaptive responses to stress, while in Jemalong, the gene ontologies for oxidative stress, cell growth, and translation were enriched. A meta-analysis of ozone responsive genes using the Genvestigator program indicated enrichment of ABA and auxin responsive genes in JE154, while cytokinin response genes were induced in Jemalong. In resistant JE154, down regulation of photosynthesis-related genes and up regulation of genes responding to low nitrate leads us to speculate that lowering carbon-nitrogen balance may be an important resource allocation strategy for overcoming oxidative stress. Temporal profiles of select genes using real-time PCR analysis showed that most of the genes in Jemalong were induced at the later time points and is consistent with our earlier microarray studies. Inability to mount an early active transcriptional reprogramming in Jemalong may be the cause for an inefficient defense response that in turn leads to severe oxidative stress and culminates in cell death.

Expanded thermodynamic true yield prediction model: adjustments and limitations

Bacterial yield prediction is critical for bioprocess optimization and modeling of natural biological systems. In previous work, an expanded thermodynamic true yield prediction model was developed through incorporating carbon balance and nitrogen balance along with electron balance and energy balance. In the present work, the application of the expanded model is demonstrated in multiple growth situations (aerobic heterotrophs, anoxic, anaerobic heterotrophs, and autolithotrophs). Two adjustments are presented that enable improved prediction when additional information regarding the environmental conditions (pH) or degradation pathway (requirement for oxygenase- or oxidase-catalyzed reactions) is known. A large data set of reported yields is presented and considered for suitability in model validation. Significant uncertainties of literature-reported yield values are described. Evaluation of the model with experimental yield values shows good predictive ability. However, the wide range in reported yields and the variability introduced into the prediction by uncertainty in model parameters, limits comprehensive validation. Our results suggest that the uncertainty of the experimental data used for validation limits further improvement of thermodynamic prediction models.

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon–nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

Expanded thermodynamic model for microbial true yield prediction

Thermodynamic methods to predict true yield and stoichiometry of bacterial reactions have been widely used in biotechnology and environmental engineering. However, yield predictions are often inaccurate for certain simple organic compounds. This work evaluates an existing method and identifies the cause of prediction errors for compounds with low degree of reductance of carbon. For these compounds, carbon, not energy or reducing equivalents, constrains growth. Existing thermodynamically-based models do not account for the potential of carbon-limited growth. The improved method described here consists of four balances: carbon balance, nitrogen balance, electron balance, and energy balance. Two efficiency terms, K1 and K2 are defined and estimated from a priori analysis. The results show that K1 and K2 are nearly the same in value so that only one coefficient, K = 0.41 is used in the modified model. Comparisons with observed yields show that use of the new model and parameters results in significantly improved yield estimation based on inclusion of the carbon balance. The average estimation error is less than 6% for the data set presented.

Mitochondria-Driven Changes in Leaf NAD Status Exert a Crucial Influence on the Control of Nitrate Assimilation and the Integration of Carbon and Nitrogen Metabolism

The Nicotiana sylvestris mutant, CMS, lacks the mitochondrial gene nad7 and functional complex I, and respires using low-affinity NADH (alternative) mitochondrial dehydrogenases. Here, we show that this adjustment of respiratory pathways is associated with a profound modification of foliar carbon-nitrogen balance. CMS leaves are characterized by abundant amino acids compared to either wild-type plants or CMS in which complex I function has been restored by nuclear transformation with the nad7 cDNA. The metabolite profile of CMS leaves is enriched in amino acids with low carbon/nitrogen and depleted in starch and 2-oxoglutarate. Deficiency in 2-oxoglutarate occurred despite increased citrate and malate and higher capacity of key anaplerotic enzymes, notably the mitochondrial NAD-dependent isocitrate dehydrogenase. The accumulation of nitrogen-rich amino acids was not accompanied by increased expression of enzymes involved in nitrogen assimilation. Partitioning of (15)N-nitrate into soluble amines was enhanced in CMS leaf discs compared to wild-type discs, especially in the dark. Analysis of pyridine nucleotides showed that both NAD and NADH were increased by 2-fold in CMS leaves. The growth retardation of CMS relative to the wild type was highly dependent on photoperiod, but at all photoperiod regimes the link between high contents of amino acids and NADH was observed. Together, the data provide strong evidence that (1) NADH availability is a critical factor in influencing the rate of nitrate assimilation and that (2) NAD status plays a crucial role in coordinating ammonia assimilation with the anaplerotic production of carbon skeletons.

Biomass allocation and leaf chemical defence in defoliated seedlings of Quercus serrata with respect to carbon-nitrogen balance.

Both nutrient availability and defoliation affect the carbon-nutrient balance in plants, which in turn influences biomass allocation (e.g. shoot-to-root ratio) and leaf chemical composition (concentration of nitrogen and secondary compounds). In this study it is questioned whether defoliation alters biomass allocation and chemical defence in a similar fashion to the response to nutrient deficiency. Current-year seedlings of Quercus serrata were grown with or without removal of all leaves at three levels of nutrient availability. Plant nitrogen concentration (PNC), a measure of the carbon-nutrient balance in the plant, significantly decreased immediately after defoliation because leaves had higher nitrogen concentrations than stems and roots. However, PNC recovered to levels similar to or higher than that of control plants in 3 or 6 weeks after the defoliation. Nitrogen concentration of leaves produced after defoliation was significantly higher than leaf nitrogen concentration of control leaves. Leaf mass per plant mass (leaf mass ratio, LMR) was positively correlated with PNC but the relationship was significantly different between defoliated and control plants. When compared at the same PNC, defoliated plants had a lower LMR. However, the ratio of the leaf to root tissues that were newly produced after defoliation as a function of PNC did not differ between defoliated and control plants. Defoliated plants had a significantly lower concentration of total phenolics and condensed tannins. Across defoliated and control plants, the leaf tannin concentration was negatively correlated with the leaf nitrogen concentration, suggesting that the amount of carbon-based defensive compounds was controlled by the carbon-nutrient balance at the leaf level. Defoliation alters biomass allocation and chemical defence through the carbon-nutrient balance at the plant and at the leaf level, respectively.

Consequences of manipulations in carbon and nitrogen supply for concentration of anti-herbivore defence compounds in Salix polaris

The concentration of carbon-based anti-herbivore defence compounds is key to herbivore utilization of forage. Production of phenolics and condensed tannins in boreal woody plants is known to reduce grazing pressure. Their production depends, among other things, on the availability of nutrient resources, especially nitrogen, relative to the availability of assimilates. The carbon-nutrient balance (CNB) hypothesis (Bryant, Chapin & Klein, 1983) predicts a decrease in the concentration of carbon-based defence compounds with increased availability of nutrients. In a High Arctic heath, I manipulated the carbon-nitrogen balance of polar willow (Salix polaris) in a factorial, multi-level fertilizing and shading experiment. Other plots were subject to elevated temperature. After 2 years, shading and, to a lesser extent, fertilization had caused an increase in nitrogen concentrations in the leaves, which were highly and negatively correlated with lower total phenolic and condensed tannin concentrations. Elevated temperature caused no such effects, but increased growth significantly, while shading reduced shoot biomass, and fertilization had no detectable effect. These results are consistent with the CNB hypothesis. On the basis of this study it seems unlikely, however, that environmental modifications due to global climate change will have a major impact on defence chemistry, as very high shading (>70%) and fertilization levels (>1.5 g m–2 year–1) were needed to produce significant deviations from controls.

Effect of Elevated CO2 and Nitrogen Nutrition on Photosynthesis, Growth and Carbon‐Nitrogen Balance in Brassica juncea

The response of Brassica juncea var. Bio‐183‐92 to elevated CO2 under increased nitrogen treatment was studied. There was an interactive effect of CO2 and nitrogen nutrition, indicating that, on the addition of more nitrogen, the plants sustained the positive effect of CO2 enrichment by utilizing additional carbohydrates for the development of new sinks. Excess carbohydrate enables plants to be flexible and responsive to additional nitrogen application to sustain the CO2 enrichment effect.

Effect of conjugated linoleic acid on energy metabolism in growing‐finishing pigs

SummaryThe effect of conjugated linoleic acid (CLA) on energy metabolism was studied in a respiration experiment with 20 growing pigs. From 70 kg liveweight onwards the animals received isoenergetic rations containing 0 or 3% CLA on the basis of metabolic bodyweight. Between 95 and 100 kg liveweight the gas exchange of each animal was measured over 48 h in a respiration chamber. This was preceded by a 5‐day quantitative determination of faeces and urine. The heat production and energy retention of the animals were determined by the carbon–nitrogen balance technique and the RQ method. Additionally several parameters of blood serum were determined. CLA had no effect on digestibility and metabolizability of energy, nor were gas exchange and heat production (HP) of the animals affected by the treatment. Average heat production across all measurements was 628 kJ/kg W0.75 in the control group and 636 kJ/kg W0.75 in the CLA group. No difference in fat deposition was observed (control 386, CLA group 379 kJ/kgW0.75). The N balance on the other hand was 2.2 g/day higher in the CLA‐supplemented animals. This caused retained protein energy, as a proportion of total energy retention, to increase from 24.2 to 25.8%. The ratio of retained protein energy to fat energy was 10% higher in the CLA‐treated animals than in the controls. Body mass increase over the trial as a whole was unaffected (control 27.6, CLA group 28.1 kg, equivalent to daily gains of 931 and 946 g, respectively). Blood serum lipoproteins exhibited few CLA‐induced changes. The greatest effects were observed in triacylglycerols, which were raised in the CLA animals compared with the controls. The ratio of cholesterol‐low‐density lipoprotein to cholesterol‐high‐density lipoprotein rose by 17% as a result of CLA treatment. Serum concentrations of albumin, creatinine, urea and glucose were unchanged. In conclusion, the study showed that supplementation with CLA under isoenergetic feeding conditions with a strongly positive energy balance has no marked effect on total metabolism, although a slightly enhanced deposition of protein was evident.

Influence of resource availability on growth and foliar chemistry within and among young white spruce trees

We increased and decreased the growth of young white spruce through fertilization and root-pruning during three years in a manipulated field study to investigate the influence of variations in resource availability on shoot growth and foliar chemistry within and among trees. As predicted by the carbon/nitrogen balance (CNB) and by the growth differentiation balance (GDB) hypotheses, increases in growth rate caused by fertilization were generally associated with increases in foliar nitrogen and water content and decreases in most C-based secondary compounds (phenols and tannins but not monoterpenes). The CNB and GDB hypotheses also correctly predicted that decreases in growth rate caused by root-pruning would be associated with decreases in foliar N and water content and increases in phenols and tannins. A negative relationship between foliar nitrogen and water content and foliar phenol and tannin content was also observed within trees, again supporting the CNB and GDB hypotheses. In spring, foliar N and water content was highest and foliar content of phenols and tannins lowest, in the upper crown. However, this intra-tree variation changed seasonally, and the highest foliar N and water content and lowest phenol and tannin content was found in the lower crown in fall. Seasonal variations in foliar nutrient content can be best explained by the source/sink hypothesis, as larger buds in the upper crown probably import more nutrients from foliage than smaller buds in the lower crown, resulting in the lower foliar nutrient content in the upper crown in fall. Interactions between whorl and treatment did not significantly influence shoot length, but non-significant trends were in agreement with predictions from the source/sink hypothesis. Thus CNB and GDB hypotheses could adequately explain among-tree variations in growth rate and foliar chemistry when resource availability was manipulated, but only the source/sink hypothesis could explain between-season differences within trees.

Effect of CO2 enrichment on carbon and nitrogen interaction in wheat and soybean

Effect of CO2 enrichment on the carbon-nitrogen balance in whole plant and the acclimation of photosynthesis was studied in wheat (spring wheat) and soybean (A62-1 [nodulated] and A62-2 [non-nodulated]) with a combination of two nitrogen application rates (0 g N land area m-2 and 30 g N land area m-2) and two temperature treatments (30/20°C (day/night) and 26/16°C). Results were as follows. 1. Carbon (dry matter)-nitrogen balance of whole plant throughout growth was remarkably different between wheat and soybean, as follows: 1) in wheat, the relationship between the amount of dry matter (DMt) and amount of nitrogen absorbed (Nt) in whole plant was expressed by an exponential regression, in which the regression coefficient was affected by only the nitrogen application rate, and not by CO2 and temperature treatments, and 2) in soybean the DMt-Nt relationship was basically expressed by a linear regression, in which the regression coefficient was only slightly affected by the nitrogen treatment (at 0N, DMt-Nt balance finally converged to a linear regression). Thus, carbon-nitrogen interaction in wheat was strongly affected by the underground environment (nitrogen nutrition), but not by the above ground environment (CO2 enrichment and temperature), while that in soybean was less affected by both under and above ground environments. 2. The photosynthetic response curve to CO2 concentration in wheat and soybean was less affected by the CO2 enrichment treatment, while that in wheat and soybean (A62-2) was affected by the nitrogen treatment, indicating that nitrogen nutrition is a more important factor for the regulation of photosynthesis regardless of the CO2 enrichment. 3. Carbon isotope discrimination (..:1) in soybean was similar to that in wheat under ambient CO2, while lower than that in wheat under CO2 enrichment, suggesting that the carbon metabolism is considerably different between wheat and soybean under the CO2 enrichment conditions.