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.
Highlights
Winter oilseed rape (Brassica napus L.) is a major oleaginous crop ranked the 3rd most essential source of plant oil in the world
In order to characterize modifications to nitrogen fluxes occurring at cellular level within amino acid metabolism during nitrogen remobilization in oilseed rape leaves, we decided first to quantify changes in physiology and amino acid pools that occurred during the acquisition of the source status in leaves
Since nutrient remobilization processes are known to affect the contents of both fresh weight (FW) and dry weight (DW), we first analyzed these parameters in order to find a good way to normalize our data when comparing the different leaf ranks
Summary
Winter oilseed rape (Brassica napus L.) is a major oleaginous crop ranked the 3rd most essential source of plant oil in the world. Oilseed rape production is highly demanding for mineral nitrogen (N) inputs (150–250 kg N/ha) compared with other crops, and is characterized by a strong. Oilseed rape has a low nitrogen remobilization efficiency (NRE), leading to a low nitrogen use efficiency and a low recovery of initial N input in the seeds (50% of losses) [2,4]. Since oilseed rape breeding progress in the last 20 years has essentially improved nitrogen uptake efficiency, the optimization of nitrogen use efficiency, and NRE in oilseed rape, is still a promising target for future crop improvement [7,8,9]
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