Differential CO2 effect on primary carbon metabolism of flag leaves in durum wheat (Triticum durum Desf.)

C sink/source balance and N assimilation have been identified as target processes conditioning crop responsiveness to elevated CO. However, little is known about phenology-driven modifications of C and N primary metabolism at elevated CO in cereals such as wheat. Here, we examined the differential effect of elevated CO 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 N labelling. Our results show that growth at elevated CO 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 CO 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 CO was larger and less N rich, suggesting that nitrogen use efficiency rather than photosynthesis is an important target for improvement, even in good CO-responsive cultivars.This work was funded by the Spanish National Research and Development Programme (AGL2011-30386-C02-2 and AGL2013-44147-R, Ramón y Cajal program) and the European Molecular Biology Organization (EMBO). Aranjuelo, Iker et al.Peer Reviewe