Non-foliar photosynthesis and nitrogen assimilation influence grain yield in durum wheat regardless of water conditions.

There is a need to generate improved crop varieties adapted to the ongoing changes in the climate. We studied durum wheat canopy and central metabolism of six different photosynthetic organs in two yield-contrasting varieties. The aim was to understand the mechanisms associated with the water stress response and yield performance. Water stress strongly reduced grain yield, plant biomass, and leaf photosynthesis, and down-regulated C/N-metabolism genes and key protein levels, which occurred mainly in leaf blades. By contrast, higher yield was associated with high ear dry weight and lower biomass and ears per area, highlighting the advantage of reduced tillering and the consequent improvement in sink strength, which promoted C/N metabolism at the whole plant level. An improved C metabolism in blades and ear bracts and N assimilation in all photosynthetic organs facilitated C/N remobilization to the grain and promoted yield. Therefore, we propose that further yield gains in Mediterranean conditions could be achieved by considering the source-sink dynamics and the contribution of non-foliar organs, and particularly N assimilation and remobilization during the late growth stages. We highlight the power of linking phenotyping with plant metabolism to identify novel traits at the whole plant level to support breeding programmes.

Analysis of durum wheat photosynthetic organs during grain filling reveals the ear as a water stress-tolerant organ and the peduncle as the largest pool of primary metabolites.

MAIN CONCLUSION: The pool of carbon- and nitrogen-rich metabolites is quantitatively relevant in non-foliar photosynthetic organs during grain filling, which have a better response to water limitation than flag leaves. The response of durum wheat to contrasting water regimes has been extensively studied at leaf and agronomic level in previous studies, but the water stress effects on source-sink dynamics, particularly non-foliar photosynthetic organs, is more limited. Our study aims to investigate the response of different photosynthetic organs to water stress and to quantify the pool of carbon and nitrogen metabolites available for grain filling. Five durum wheat varieties were grown in field trials in the Spanish region of Castile and León under irrigated and rainfed conditions. Water stress led to a significant decrease in yield, biomass, and carbon and nitrogen assimilation, improved water use efficiency, and modified grain quality traits in the five varieties. The pool of carbon (glucose, glucose-6-phosphate, fructose, sucrose, starch, and malate) and nitrogen (glutamate, amino acids, proteins and chlorophylls) metabolites in leaf blades and sheaths, peduncles, awns, glumes and lemmas were also analysed. The results showed that the metabolism of the blades and peduncles was the most susceptible to water stress, while ear metabolism showed higher stability, particularly at mid-grain filling. Interestingly, the total metabolite content per organ highlighted that a large source of nutrients, which may be directly involved in grain filling, are found outside the blades, with the peduncles being quantitatively the most relevant. We conclude that yield improvements in our Mediterranean agro-ecosystem are highly linked to the success of shoots in producing ears and a higher number of grains, while grain filling is highly dependent on the capacity of non-foliar organs to fix CO2 and N. The ear organs show higher stress resilience than other organs, which deserves our attention in future breeding programmes.

Putrescine: A Key Metabolite Involved in Plant Development, Tolerance and Resistance Responses to Stress.

Putrescine (Put) is the starting point of the polyamines (PAs) pathway and the most common PA in higher plants. It is synthesized by two main pathways (from ornithine and arginine), but recently a third pathway from citrulline was reported in sesame plants. There is strong evidence that Put may play a crucial role not only in plant growth and development but also in the tolerance responses to the major stresses affecting crop production. The main strategies to investigate the involvement of PA in plant systems are based on the application of competitive inhibitors, exogenous PAs treatments, and the most efficient approaches based on mutant and transgenic plants. Thus, in this article, the recent advances in understanding the role of this metabolite in plant growth promotion and protection against abiotic and biotic stresses will be discussed to provide an overview for future research.

C and N metabolism in barley leaves and peduncles modulates responsiveness to changing CO2.

Balancing of leaf carbohydrates is a key process for maximising crop performance in elevated CO2 environments. With the aim of testing the role of the carbon sink-source relationship under different CO2 conditions, we performed two experiments with two barley genotypes (Harrington and RCSL-89) exposed to changing CO2. In Experiment 1, the genotypes were exposed to 400 and 700 ppm CO2. Elevated CO2 induced photosynthetic acclimation in Harrington that was linked with the depletion of Rubisco protein. In contrast, a higher peduncle carbohydrate-storage capacity in RSCL-89 was associated with a better balance of leaf carbohydrates that could help to maximize the photosynthetic capacity under elevated CO2. In Experiment 2, plants that were grown at 400 ppm or 700 ppm CO2 for 5 weeks were switched to 700 ppm or 400 ppm CO2, respectively. Raising CO2 to 700 ppm increased photosynthetic rates with a reduction in leaf carbohydrate content and an improvement in N assimilation. The increase in nitrate content was associated with up-regulation of genes of protein transcripts of photosynthesis and N assimilation that favoured plant performance under elevated CO2. Finally, decreasing the CO2 from 700 ppm to 400 ppm revealed that both stomatal closure and inhibited expression of light-harvesting proteins negatively affected photosynthetic performance and plant growth.

Surfing the Hyperbola Equations of the Steady-State Farquhar-von Caemmerer-Berry C3 Leaf Photosynthesis Model: What Can a Theoretical Analysis of Their Oblique Asymptotes and Transition Points Tell Us?

The asymptotes and transition points of the net CO2 assimilation (A/Ci) rate curves of the steady-state Farquhar-von Caemmerer-Berry (FvCB) model for leaf photosynthesis of C3 plants are examined in a theoretical study, which begins from the exploration of the standard equations of hyperbolae after rotating the coordinate system. The analysis of the A/Ci quadratic equations of the three limitation states of the FvCB model-abbreviated as Ac, Aj and Ap-allows us to conclude that their oblique asymptotes have a common slope that depends only on the mesophyll conductance to CO2 diffusion (gm). The limiting values for the transition points between any two states of the three limitation states c, j and p do not depend on gm, and the results are therefore valid for rectangular and non-rectangular hyperbola equations of the FvCB model. The analysis of the variation of the slopes of the asymptotes with gm casts doubts about the fulfilment of the steady-state conditions, particularly, when the net CO2 assimilation rate is inhibited at high CO2 concentrations. The application of the theoretical analysis to extended steady-state FvCB models, where the hyperbola equations of Ac, Aj and Ap are modified to accommodate nitrogen assimilation and amino acids export via the photorespiratory pathway, is also discussed.

Metabolic and Transcriptional Analysis of Durum Wheat Responses to Elevated CO2 at Low and High Nitrate Supply.

Elevated [CO2] (eCO2) can lead to photosynthetic acclimation and this is often intensified by low nitrogen (N). Despite intensive studies of plant responses to eCO2, the regulation mechanism of primary metabolism at the whole-plant level in interaction with [Formula: see text] supply remains unclear. We examined the metabolic and transcriptional responses triggered by eCO2 in association with physiological-biochemical traits in flag leaves and roots of durum wheat grown hydroponically in ambient and elevated [CO2] with low (LN) and high (HN) [Formula: see text] supply. Multivariate analysis revealed a strong interaction between eCO2 and [Formula: see text] supply. Photosynthetic acclimation induced by eCO2 in LN plants was accompanied by an increase in biomass and carbohydrates, and decreases of leaf organic N per unit area, organic acids, inorganic ions, Calvin-Benson cycle intermediates, Rubisco, nitrate reductase activity, amino acids and transcripts for N metabolism, particularly in leaves, whereas [Formula: see text] uptake was unaffected. In HN plants, eCO2 did not decrease photosynthetic capacity or leaf organic N per unit area, but induced transcripts for N metabolism, especially in roots. In conclusion, the photosynthetic acclimation in LN plants was associated with an inhibition of leaf [Formula: see text] assimilation, whereas up-regulation of N metabolism in roots could have mitigated the acclimatory effect of eCO2 in HN plants.

Temporal kinetics of the transcriptional response to carbon depletion and sucrose readdition in Arabidopsis seedlings.

To investigate whether the transcriptional response to carbon (C) depletion and sucrose resupply depends on the duration and severity of the C depletion, Arabidopsis seedlings were grown in liquid culture and harvested 3, 6, 12, 24, 48 and 72 h after removing sucrose from the medium and 30 min after resupplying sucrose at each time. Expression profiling revealed early transcriptional inhibition of cell wall synthesis and remodelling of signalling, followed by induction of C recycling and photosynthesis and general inhibition of growth. The temporal sequence differed from the published response to progressive exhaustion of C during a night and extended night in vegetatively growing plants. The response to sucrose readdition was conserved across the C-depletion time course. Intriguingly, the vast majority of rapidly responding transcripts decreased rather than increased. The majority of transcripts that respond rapidly to sucrose and many transcripts that respond during C depletion also decrease after treating seedlings with the transcriptional inhibitor cordycepin A. Comparison with published responses to overexpression of otsA, AKIN10 and bZIP11 revealed that many genes that respond to C depletion, and especially sucrose resupply, respond to one or more of these C-signalling components. Thus, multiple factors contribute to C responsiveness, including many signalling components, transcriptional regulation and transcript turnover.

Quantitative RT-PCR Platform to Measure Transcript Levels of C and N Metabolism-Related Genes in Durum Wheat: Transcript Profiles in Elevated [CO2] and High Temperature at Different Levels of N Supply.

Only limited public transcriptomics resources are available for durum wheat and its responses to environmental changes. We developed a quantitative reverse transcription-PCR (qRT-PCR) platform for analysing the expression of primary C and N metabolism genes in durum wheat in leaves (125 genes) and roots (38 genes), based on available bread wheat genes and the identification of orthologs of known genes in other species. We also assessed the expression stability of seven reference genes for qRT-PCR under varying environments. We therefore present a functional qRT-PCR platform for gene expression analysis in durum wheat, and suggest using the ADP-ribosylation factor as a reference gene for qRT-PCR normalization. We investigated the effects of elevated [CO(2)] and temperature at two levels of N supply on C and N metabolism by combining gene expression analysis, using our qRT-PCR platform, with biochemical and physiological parameters in durum wheat grown in field chambers. Elevated CO(2) down-regulated the photosynthetic capacity and led to the loss of N compounds, including Rubisco; this effect was exacerbated at low N. Mechanistically, the reduction in photosynthesis and N levels could be associated with a decreased transcription of the genes involved in photosynthesis and N assimilation. High temperatures increased stomatal conductance, and thus did not inhibit photosynthesis, even though Rubisco protein and activity, soluble protein, leaf N, and gene expression for C fixation and N assimilation were down-regulated. Under a future scenario of climate change, the extent to which C fixation capacity and N assimilation are down-regulated will depend upon the N supply.

Singlet Oxygen and Superoxide Anion Radical Detection by EPR Spin Trapping in Thylakoid Preparations.

Reactive oxygen species (ROS) are produced by energy transfer and electron transport in plant chloroplast thylakoids at non-toxic levels under normal growth conditions, but at threatening levels under adverse or fluctuating environmental conditions. Among chloroplast ROS, singlet oxygen and superoxide anion radical, respectively, produced by photosystem II (PSII) and PSI, are known to be the major ROS under several stress conditions. Both are very unlikely to diffuse out of chloroplasts, but they are instead capable of triggering ROS-mediated chloroplast operational retrograde signalling to activate defence gene expression in concert with hormones and other molecular compounds. Therefore, their detection, identification and localization in vivo or in biological preparations is a priority for a deeper understanding of their role in (concurrent) regulation of plant growth and defence responses. Here, we present two EPR spin traps, abbreviated as TEMPD-HCl and DEPMPO, to detect and identify ROS in complex systems, such as isolated thylakoids, together with some hints and cautions to perform reliable spin trapping experiments.

Source-Sink Dynamics in Field-Grown Durum Wheat Under Contrasting Nitrogen Supplies: Key Role of Non-Foliar Organs During Grain Filling.

The integration of high-throughput phenotyping and metabolic approaches is a suitable strategy to study the genotype-by-environment interaction and identify novel traits for crop improvement from canopy to an organ level. Our aims were to study the phenotypic and metabolic traits that are related to grain yield and quality at canopy and organ levels, with a special focus on source-sink coordination under contrasting N supplies. Four modern durum wheat varieties with contrasting grain yield were grown in field conditions under two N fertilization levels in north-eastern Spain. We evaluated canopy vegetation indices taken throughout the growing season, physiological and metabolic traits in different photosynthetic organs (flag leaf blade, sheath, peduncle, awn, glume, and lemma) at anthesis and mid-grain filling stages, and agronomic and grain quality traits at harvest. Low N supply triggered an imbalance of C and N coordination at the whole plant level, leading to a reduction of grain yield and nutrient composition. The activities of key enzymes in C and N metabolism as well as the levels of photoassimilates showed that each organ plays an important role during grain filling, some with a higher photosynthetic capacity, others for nutrient storage for later stages of grain filling, or N assimilation and recycling. Interestingly, the enzyme activities and sucrose content of the ear organs were positively associated with grain yield and quality, suggesting, together with the regression models using isotope signatures, the potential contribution of these organs during grain filling. This study highlights the use of holistic approaches to the identification of novel targets to improve grain yield and quality in C3 cereals and the key role of non-foliar organs at late-growth stages.

Physiological and Antioxidant Response to Different Water Deficit Regimes of Flag Leaves and Ears of Wheat Grown under Combined Elevated CO2 and High Temperature.

Triticum aestivum L. cv. Gazul is a spring wheat widely cultivated in Castilla y León (Spain). Potted plants were grown in a scenario emulating the climate change environmental conditions expected by the end of this century, i.e., with elevated CO2 and high temperature under two water deficit regimes: long (LWD) and terminal (TWD). Changes in biomass and morphology, the content of proline (Pro), ascorbate (AsA) and glutathione (GSH), and enzymatic antioxidant activities were analyzed in flag leaves and ears. Additionally, leaf gas exchange was measured. LWD caused a decrease in biomass and AsA content but an increase in Pro content and catalase and GSH reductase activities in flag leaves, whereas TWD produced no significant changes. Photosynthesis was enhanced under both water deficit regimes. Increase in superoxide dismutase activity and Pro content was only observed in ears under TWD. The lack of a more acute effect of LWD and TWD on both organs was attributed to the ROS relieving effect of elevated CO2. Gazul acted as a drought tolerant variety with anisohydric behavior. A multifactorial analysis showed better adaptation of ears to water deficit than flag leaves, underlining the importance of this finding for breeding programs to improve grain yield under future climate change.

Does ear C sink strength contribute to overcoming photosynthetic acclimation of wheat plants exposed to elevated CO2?

Wheat plants (Triticum durum Desf., cv. Regallo) were grown in the field to study the effects of contrasting [CO(2)] conditions (700 versus 370 µmol mol(-1)) on growth, photosynthetic performance, and C management during the post-anthesis period. The aim was to test whether a restricted capacity of sink organs to utilize photosynthates drives a loss of photosynthetic capacity in elevated CO(2). The ambient (13)C/(12)C isotopic composition (δ(13)C) of air CO(2) was changed from -10.2‰ in ambient [CO(2)] to -23.6‰ under elevated [CO(2)] between the 7th and the 14th days after anthesis in order to study C assimilation and partitioning between leaves and ears. Elevated [CO(2)] had no significant effect on biomass production and grain filling, and caused an accumulation of C compounds in leaves. This was accompanied by up-regulation of phosphoglycerate mutase and ATP synthase protein content, together with down-regulation of adenosine diphosphate glucose pyrophosphatase protein. Growth in elevated [CO(2)] negatively affected Rubisco and Rubisco activase protein content and induced photosynthetic down-regulation. CO(2) enrichment caused a specific decrease in Rubisco content, together with decreases in the amino acid and total N content of leaves. The C labelling revealed that in flag leaves, part of the C fixed during grain filling was stored as starch and structural C compounds whereas the rest of the labelled C (mainly in the form of soluble sugars) was completely respired 48 h after the end of labelling. Although labelled C was not detected in the δ(13)C of ear total organic matter and respired CO(2), soluble sugar δ(13)C revealed that a small amount of labelled C reached the ear. The (12)CO(2) labelling suggests that during the beginning of post-anthesis the ear did not contribute towards overcoming flag leaf carbohydrate accumulation, and this had a consequent effect on protein expression and photosynthetic acclimation.

Screening for Higher Grain Yield and Biomass among Sixty Bread Wheat Genotypes Grown under Elevated CO2 and High-Temperature Conditions.

Global warming will inevitably affect crop development and productivity, increasing uncertainty regarding food production. The exploitation of genotypic variability can be a promising approach for selecting improved crop varieties that can counteract the adverse effects of future climate change. We investigated the natural variation in yield performance under combined elevated CO2 and high-temperature conditions in a set of 60 bread wheat genotypes (59 of the 8TH HTWSN CIMMYT collection and Gazul). Plant height, biomass production, yield components and phenological traits were assessed. Large variations in the selected traits were observed across genotypes. The CIMMYT genotypes showed higher biomass and grain yield when compared to Gazul, indicating that the former performed better than the latter under the studied environmental conditions. Principal component and hierarchical clustering analyses revealed that the 60 wheat genotypes employed different strategies to achieve final grain yield, highlighting that the genotypes that can preferentially increase grain and ear numbers per plant will display better yield responses under combined elevated levels of CO2 and temperature. This study demonstrates the success of the breeding programs under warmer temperatures and the plants' capacity to respond to the concurrence of certain environmental factors, opening new opportunities for the selection of widely adapted climate-resilient wheat genotypes.

Genotypic Variability on Grain Yield and Grain Nutritional Quality Characteristics of Wheat Grown under Elevated CO2 and High Temperature.

The progressive rise in atmospheric CO2 concentrations and temperature associated with climate change is predicted to have a major impact on the productivity and quality of food crops. Therefore, food security is highly dependent on climate change. Following a survey with 60 bread wheat genotypes, here we investigated the genetic variation in grain yield and nutritional quality among 10 of these genotypes grown under elevated CO2 and temperature. With this purpose, the biomass production, grain yield-related traits, the grain concentration of starch, total protein, phenolic compounds, and mineral nutrients, together with the total antioxidant capacity, were determined. Variation among genotypes was found for almost all the studied traits. Higher grain and ear numbers were associated with increased grain yield but decreased grain total protein concentration and minerals such as Cu, Fe, Mg, Na, P, and Zn. Mineral nutrients were mainly associated with wheat biomass, whereas protein concentration was affected by plant biomass and yield-related traits. Associations among different nutrients and promising nutrient concentrations in some wheat genotypes were also found. This study demonstrates that the exploration of genetic diversity is a powerful approach, not only for selecting genotypes with improved quality, but also for dissecting the effect of the environment on grain yield and nutritional composition.

Theoretical and Experimental Considerations for a Rapid and High Throughput Measurement of Catalase In Vitro.

A rapid and high throughput protocol to measure the catalase activity in vitro has been designed. Catalase is an enzyme with unusual kinetic properties because it does not follow the standard Michaelis-Menten model and is inactivated by H2O2. This makes the analysis of the two rate equations of the second-ordered reactions of the kinetic model rather complex. A two-degree polynomial fitting of the experimental data is proposed after transforming the exponential form of the integrated rate equation of the [H2O2] into a polynomial using the Taylor series. The fitting is validated by establishing an experimental linear relationship between the initial rate of the H2O2 decomposition and the protein concentration, regardless of the suicide inactivation that catalase might undergo beyond t > 0. In addition, experimental considerations are taken into account to avoid statistical bias in the analysis of the catalase activity. ANOVA analyses show that the proposed protocol can be utilized to measure the initial rate of the H2O2 decomposition by catalase in 32 samples in triplicates if kept below 8 mM min-1 in the microplate wells. These kinetic and statistical analyses can pave the way for other antioxidant enzyme activity assays in microplate readers at small scale and low cost.

Differential Flag Leaf and Ear Photosynthetic Performance Under Elevated (CO2) Conditions During Grain Filling Period in Durum Wheat.

Elevated concentrations of CO2 (CO2) in plants with C3 photosynthesis metabolism, such as wheat, stimulate photosynthetic rates. However, photosynthesis tends to decrease as a function of exposure to high (CO2) due to down-regulation of the photosynthetic machinery, and this phenomenon is defined as photosynthetic acclimation. Considerable efforts are currently done to determine the effect of photosynthetic tissues, such us spike, in grain filling. There is good evidence that the contribution of ears to grain filling may be important not only under good agronomic conditions but also under high (CO2). The main objective of this study was to compare photoassimilate production and energy metabolism between flag leaves and glumes as part of ears of wheat (Triticum turgidum L. subsp. durum cv. Amilcar) plants exposed to ambient [a(CO2)] and elevated [e(CO2)] (CO2) (400 and 700 µmol mol-1, respectively). Elevated CO2 had a differential effect on the responses of flag leaves and ears. The ears showed higher gross photosynthesis and respiration rates compared to the flag leaves. The higher ear carbohydrate content and respiration rates contribute to increase the grain dry mass. Our results support the concept that acclimation of photosynthesis to e(CO2) is driven by sugar accumulation, reduction in N concentrations and repression of genes related to photosynthesis, glycolysis and the tricarboxylic acid cycle, and that these were more marked in glumes than leaves. Further, important differences are described on responsiveness of flag leaves and ears to e(CO2) on genes linked with carbon and nitrogen metabolism. These findings provide information about the impact of e(CO2) on ear development during the grain filling stage and are significant for understanding the effects of increasing (CO2) on crop yield.

Acclimation to future atmospheric CO2 levels increases photochemical efficiency and mitigates photochemistry inhibition by warm temperatures in wheat under field chambers.

A study was conducted over 2 years to determine whether growth under elevated CO(2) (700 µmol mol(-1) ) and temperature (ambient + 4 °C) conditions modifies photochemical efficiency or only the use of electron transport products in spring wheat grown in field chambers. Elevated atmospheric CO(2) concentrations increased crop dry matter at maturity by 12-17%, while above-ambient temperatures did not significantly affect dry matter yield. In measurements with ambient CO(2) at ear emergence and after anthesis, growth at elevated CO(2) concentrations decreased flag leaf light-saturated carbon assimilation. The quantum yield of electron transport (Φ(PSII) ) measured at ambient CO(2) and higher irradiances increased at ear emergence and decreased after anthesis in plants grown at elevated CO(2) . At higher light intensities, but not in low light, photochemical quenching (qP) decreased after growth in elevated CO(2) conditions. Growth under CO(2) enrichment increased dark- (Fv:Fm) and light-adapted (Fv':Fm') photochemical efficiencies, and decreased the chlorophyll a:b ratio, suggesting an increase in light-harvesting complexes relative to PSII reaction centres. A relatively higher decrease in carbon assimilation than the decrease in Φ(PSII) pointed to a sink other than CO(2) assimilation for electron transport products at defined growth stages. With higher light intensities, warmer temperatures increased Φ(PSII) and Fv':Fm' at ear emergence and decreased Φ(PSII) after anthesis; in ambient-but not elevated-CO(2) , warmer temperatures also decreased qP after anthesis. CO(2) fixation increased or did not change with temperature, depending on the growth stage and year. We conclude that elevated CO(2) decreases the carbon assimilation capacity, but increases photochemistry and resource allocation to light harvesting, and that elevated levels of CO(2) can mitigate photochemistry inhibition as a result of warm temperatures.

De Novo Transcriptome Analysis of Durum Wheat Flag Leaves Provides New Insights Into the Regulatory Response to Elevated CO2 and High Temperature.

Global warming is becoming a significant problem for food security, particularly in the Mediterranean basin. The use of molecular techniques to study gene-level responses to environmental changes in non-model organisms is increasing and may help to improve the mechanistic understanding of durum wheat response to elevated CO2 and high temperature. With this purpose, we performed transcriptome RNA sequencing (RNA-Seq) analyses combined with physiological and biochemical studies in the flag leaf of plants grown in field chambers at ear emergence. Enhanced photosynthesis by elevated CO2 was accompanied by an increase in biomass and starch and fructan content, and a decrease in N compounds, as chlorophyll, soluble proteins, and Rubisco content, in association with a decline of nitrate reductase and initial and total Rubisco activities. While high temperature led to a decline of chlorophyll, Rubisco activity, and protein content, the glucose content increased and starch decreased. Furthermore, elevated CO2 induced several genes involved in mitochondrial electron transport, a few genes for photosynthesis and fructan synthesis, and most of the genes involved in secondary metabolism and gibberellin and jasmonate metabolism, whereas those related to light harvesting, N assimilation, and other hormone pathways were repressed. High temperature repressed genes for C, energy, N, lipid, secondary, and hormone metabolisms. Under the combined increases in atmospheric CO2 and temperature, the transcript profile resembled that previously reported for high temperature, although elevated CO2 partly alleviated the downregulation of primary and secondary metabolism genes. The results suggest that there was a reprogramming of primary and secondary metabolism under the future climatic scenario, leading to coordinated regulation of C-N metabolism towards C-rich metabolites at elevated CO2 and a shift away from C-rich secondary metabolites at high temperature. Several candidate genes differentially expressed were identified, including protein kinases, receptor kinases, and transcription factors.

Future CO2 concentrations, though not warmer temperatures, enhance wheat photosynthesis temperature responses.

The temperature dependence of C3 photosynthesis is known to vary according to the growth environment. Atmospheric CO2 concentration and temperature are predicted to increase with climate change. To test whether long-term growth in elevated CO2 and temperature modifies photosynthesis temperature response, wheat (Triticum aestivum L.) was grown in ambient CO2 (370 micromol mol(-1)) and elevated CO2 (700 micromol mol(-1)) combined with ambient temperatures and 4 degrees C warmer ones, using temperature gradient chambers in the field. Flag leaf photosynthesis was measured at temperatures ranging from 20 to 35 degrees C and varying CO2 concentrations between ear emergence and anthesis. The maximum rate of carboxylation was determined in vitro in the first year of the experiment and from the photosynthesis-intercellular CO2 response in the second year. With measurement CO2 concentrations of 330 micromol mol(-1) or lower, growth temperature had no effect on flag leaf photosynthesis in plants grown in ambient CO2, while it increased photosynthesis in elevated growth CO2. However, warmer growth temperatures did not modify the response of photosynthesis to measurement temperatures from 20 to 35 degrees C. A central finding of this study was that the increase with temperature in photosynthesis and the photosynthesis temperature optimum were significantly higher in plants grown in elevated rather than ambient CO2. In association with this, growth in elevated CO2 increased the temperature response (activation energy) of the maximum rate of carboxylation. The results provide field evidence that growth under CO2 enrichment enhances the response of Rubisco activity to temperature in wheat.

New insights into the impacts of elevated CO2, nitrogen, and temperature levels on the regulation of C and N metabolism in durum wheat using network analysis.

The use of correlation networks and hierarchical cluster analysis provides a framework to organize and study the coordination of parameters such as genes, metabolites, proteins and physiological parameters. We have analyzed 142 traits from primary C and N metabolism, including biochemical and gene expression analyses, in a range of 32 different growth conditions (various [CO2] levels, temperatures, N supplies, growth stages and experimental methods). To test the integration of primary metabolism, particularly under climate change, we investigated which C and N metabolic traits and transcript levels are correlated in durum wheat flag leaves using a correlation network and a hierarchical cluster analysis. There was a high amount of positive correlation between traits involved in a wide range of biological processes, suggesting a close and intricate coordination between C-N metabolisms at the biochemical and transcriptional levels. Transcript levels for genes related to N uptake and assimilation were especially coexpressed with genes belonging to the respiratory pathway, highlighting the coordination between the synthesis of organic N compounds and provision of energy and C skeletons. Also involved in this coordination were Rubisco and nitrate reductase activities, which play a key role in the regulation of plant metabolism. Carbohydrate accumulation was linked with a down-regulation of photosynthetic and N metabolism genes and nitrate reductase activity. Based on the degree of connectivity between nodes, network exploration facilitated the identification of some traits that may be biologically relevant during plant abiotic stress tolerance, as most of them are involved in limiting steps of plant metabolism.