---

The importance of nitrogen partitioning processes for plant performance

Nitrogen (N) is an essential nutrient that plants need in large amounts for growth and development. It is required for the synthesis of amino acids, proteins, nucleic acids and many essential metabolites. In industrial countries, extensive N fertilizer use guarantees high crop yield. However, this level of fertilizer production and application is not sustainable because of costly high-energy inputs and negative effects on human health and the environment through greenhouse gas emissions and water pollution. In developing countries, on the other hand, access to N fertilizer is limited and insufficient N nutrition results in low crop productivity and ultimately in reduced food supply. A solution to these issues could be the production of crops that use N more efficiently and require less N fertilizer. One potential strategy for improving N use efficiency in plants is to regulate N allocation to specific plant organs for optimum growth.

In general, partitioning of N within plants occurs in the form of amino acids. Transport proteins in cellular membranes are necessary to move amino acids into cells and over long distances. Our lab has identified transporters that play central roles in allocation of amino acids to growing plant organs. We found that manipulation of amino acid transporter expression in Arabidopsis and pea plants results in improved seed yields under high N conditions. In this study, it is hypothesized that the transgenic Arabidopsis and pea plants continue to outperform non-transgenic plants under reduced N fertilization, and that alteration of N transport processes leads to more efficient N use. The transgenic lines were grown under a deficient, limiting or sufficient N fertilization regime, and physiological, biochemical and molecular analyses were used to determine plant N use efficiency and nutritional status. Results showed that the transgenic plants display increased N use efficiency under all N conditions tested. Additionally, Arabidopsis and pea plants with modified N transport required half the amount of N to produce as many fruits and seeds as their non-transgenic counterparts. Overall, it was demonstrated that altering amino acid allocation presents an effective strategy to improve plant yields, while reducing the input of N fertilizer.