Sink/Source Balance of Leaves Influences Amino Acid Pools and Their Associated Metabolic Fluxes in Winter Oilseed Rape (Brassica napus L.)

Abstract

Nitrogen remobilization processes from source to sink tissues in plants are determinant for seed yield and their implementation results in a complete reorganization of the primary metabolism during sink/source transition. Here, we decided to characterize the impact of the sink/source balance on amino acid metabolism in the leaves of winter oilseed rape grown at the vegetative stage. We combined a quantitative metabolomics approach with an instationary 15N-labeling experiment by using [15N]L-glycine as a metabolic probe on leaf ranks with a gradual increase in their source status. We showed that the acquisition of the source status by leaves was specifically accompanied by a decrease in asparagine, glutamine, proline and S-methyl-l-cysteine sulphoxide contents and an increase in valine and threonine contents. Dynamic analysis of 15N enrichment and concentration of amino acids revealed gradual changes in the dynamics of amino acid metabolism with respect to the sink/source status of leaf ranks. Notably, nitrogen assimilation into valine, threonine and proline were all decreased in source leaves compared to sink leaves. Overall, our results suggested a reduction in de novo amino acid biosynthesis during sink/source transition at the vegetative stage.

Manipulating Amino Acid Metabolism to Improve Crop Nitrogen Use Efficiency for a Sustainable Agriculture

“…Therefore, the further development of 15 N-based fluxomics to explore AA metabolism in crops would be highly beneficial. For instance, the recent use of scalable metabolic flux modeling after 15 N-glycine labeling showed that metabolic fluxes associated with de novo biosynthesis of proline and valine were strongly affected by leaf sink/source balances in Brassica napus (Dellero et al, 2020b). Future work should focus on developing more detailed and complete isotopic models of compartmented AA metabolism in crops under normal and low N conditions to identify new targets to improve NUE (and abiotic stress tolerance).…”

The Impact of Photorespiratory Glycolate Oxidase Activity on Arabidopsis thaliana Leaf Soluble Amino Acid Pool Sizes during Acclimation to Low Atmospheric CO2 Concentrations

“…This can happen because either they are being used less or being produced more. It should be noted that variations of amino acid pool sizes are clearly not always correlated with intuitive variations of their associated metabolic fluxes [ 39 ].…”

Appropriate Activity Assays Are Crucial for the Specific Determination of Proline Dehydrogenase and Pyrroline-5-Carboxylate Reductase Activities

“…El Moukhtari et al, 2020). Multi-level analyses and flux modeling demonstrated that different plant species rely on different regulatory mechanisms of either transcriptional regulation or modulation of enzyme activities to shift the balance between proline biosynthesis, consumption, and degradation toward proline accumulation (AbdElgawad et al, 2015;Hildebrandt, 2018;Dellero et al, 2020). Proline is synthesized from glutamate and also degraded to glutamate via the common intermediate glutamate-5-semialdhyde (GSA), which is in spontaneous equilibrium with pyrroline-5-carboxylate (P5C, Figure 1).…”

“…Therefore, in order to improve crop performance under stress conditions, a lot of research has been dedicated to understand the molecular basis of proline accumulation and the role of this amino acid in plant acclimation and stress tolerance ( Szabados and Savoure, 2010 ; Forlani et al, 2019 ; El Moukhtari et al, 2020 ). Multi-level analyses and flux modeling demonstrated that different plant species rely on different regulatory mechanisms of either transcriptional regulation or modulation of enzyme activities to shift the balance between proline biosynthesis, consumption, and degradation toward proline accumulation ( AbdElgawad et al, 2015 ; Hildebrandt, 2018 ; Dellero et al, 2020 ). Proline is synthesized from glutamate and also degraded to glutamate via the common intermediate glutamate-5-semialdhyde (GSA), which is in spontaneous equilibrium with pyrroline-5-carboxylate (P5C, Figure 1 ).…”