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C sink/source balance and N assimilation have been identified as target processes conditioning crop responsiveness to elevated CO2. However, little is known about phenology-driven modifications of C and N primary metabolism at elevated CO2 in cereals such as wheat. Here, we examined the differential effect of elevated CO2 at two development stages (onset of flowering, onset of grain filling) in durum wheat ( Triticum durum, var. Sula) using physiological measurements (photosynthesis, isotopes), metabolomics, proteomics and 15 N labelling. Our results show that growth at elevated CO2 was accompanied by photosynthetic acclimation through a lower internal (mesophyll) conductance but no significant effect on Rubisco content, maximal carboxylation or electron transfer. Growth at elevated CO2 altered photosynthate export and tended to accelerate leaf N remobilization, which was visible for several proteins and amino acids, as well as lysine degradation metabolism. However, grain biomass produced at elevated CO2 was larger and less N rich, suggesting that nitrogen use efficiency rather than photosynthesis is an important target for improvement, even in good CO2-responsive cultivars. [ABSTRACT FROM AUTHOR]

Thioredoxins f (Trx f ) are chloroplastic proteins that have been shown to be essential for the redox-based regulation of several steps of carbon assimilation, such as the Calvin–Benson–Bassham cycle. However, the effective impact of Trx f activity on photosynthetic performance and carbon primary metabolism, including under varying CO 2 mole fraction, is not well documented. In this study, we provide a physiological and metabolomic characterization of leaves in transplastomic Trx f over-expressing tobacco ( Nicotiana tabacum L., cv. Petit Havana SR1) grown under either ambient or elevated CO 2 (400 or 800 μmol mol −1 ). Trx f overexpression strongly increased starch synthesis under both ambient and elevated CO 2 but was not accompanied by a stimulation of net photosynthetic CO 2 fixation. Rather, Trx f -overexpressing plants had a lower photorespiration rate due to an increase in internal (mesophyll) conductance for CO 2 (with the consequent increase in CO 2 mole fraction at the carboxylation site, c c ), and a higher decrease (compared with the wild-type) in total photosynthetic electron flux upon acclimation to elevated CO 2 . There were also changes in a number of metabolites, such as enrichment in sugar phosphates and free phosphate, and depletion in alanine, threonine and free sugars. Our results suggest that over-expressing Trx f has an influence on chloroplastic metabolism by simultaneously stimulating the carboxylation-to-oxygenation ratio and starch synthesis, with side effects on amino acid metabolism. The potential mechanisms involved are discussed. [ABSTRACT FROM AUTHOR]

Cold nights impact grapevine flower development and fruit set. Regulation at the female meiosis stepmay be of considerable importance for further understanding on how flower reacts to cold stress. In this study, the impact of chilling temperature (0 °C overnight) on carbon metabolism was investigated in the inflorescencesof two cultivars, Pinot noir (Pinot) and Gewurztraminer (Gewurtz.). Fluctuations in photosynthetic activity and carbohydrate metabolism were monitored by analyzing gas exchanges, simultaneous photosystem I and II activities, andcarbohydrate content. Further, the expression of PEPc , PC , FNR , ISO , OXO , AGPase , amylases and invertase genes, activities of various enzymes, as well as metabolomic analysis were attained. Results showed that the chilling night has different impacts depending on cultivars. Thus, in Gewurtz., net photosynthesis ( P n ) was transiently increased whereas, in Pinot, the P n increase was persistent and concomitant with an inhibition of respiration. However, during the days following the cold night, photosynthetic activity was decreased, and the cyclic electron flow was inhibited in Gewurtz., suggesting lower efficient energy dissipation. Likewise, metabolomic analysis revealed that several metabolites contents (namely alanine, GABA, lysine and succinate)were distinctly modulated in the two cultivars. Taking together, these results reflect a photosynthetic metabolism alteration or internal CO 2 conductance in Gewurtz. explaining partly why Pinot is less susceptible to cold stress. [ABSTRACT FROM AUTHOR]