Improved responses to elevated CO in durum wheat at a low nitrate supply associated with the upregulation of photosynthetic genes and the activation of nitrate assimilation.

Elevated CO often leads to photosynthetic acclimation, and N availability may alter this response. We investigated whether the coordination of shoot-root N assimilation by elevated CO may help to optimize the whole-plant N allocation and maximize photosynthesis in hydroponically-grown durum wheat at two NO supplies in interaction with plant development. Transcriptional and biochemical analyses were performed on flag leaves and roots. At anthesis, the improved photosynthetic acclimation response to elevated CO at low N was associated with increased Rubisco, chlorophyll and amino acid contents, and upregulation of genes related to their biosynthesis, light reactions and Calvin-Benson cycle, while a decrease was recorded at high N. Despite the decrease in carbohydrates with elevated CO at low N and the increase at high N, a stronger upward trend in leaf NR activity was found at low rather than high N. The induction of N recycling-related genes was accompanied by an amino acids decline at high N. At the grain-filling stage, the photosynthetic acclimation to elevated CO at high N was associated with the downregulation of both N assimilation, mainly in roots, and photosynthetic genes. At low N, enhanced root N assimilation partly compensated for slower shoot N assimilation and maximized photosynthetic capacity.