Nitrogen Partitioning and Remobilization in Arabidopsis Under Sufficient and Depleted Conditions

Abstract

Nitrogen is the essential nutrient most limiting to plant productivity. Two of the critical steps limiting the efficient use of nitrogen are the ability of plants to acquire it from applied fertilizers followed by the efficient remobilization of accumulated nitrogen from source to sink tissues. In order to characterize the contributions of these processes to nitrogen utilization by plants and how the expression of certain genes may influence these steps, a hydroponic-based nitrogen depletion method was developed to evaluate genetic efficacy of both phases of nitrogen metabolism , accumulation , and remobilization , in Arabidopsis thaliana. The method was tested under short and long days and it was found that short-day (10 h) conditions were effective in increasing nitrogen storage in source tissues more than long day, allowing differences in as low as 1 week of treatment initiation of nitrogen depletion to show exponential changes in seed yield . Under these conditions, plants were grown for seven weeks in sufficient N solution, where a subset of the population was harvested to determine basal N allocation. Half of the remaining plants remained in N sufficient conditions, while the rest were subjected to progressive N depletion conditions to determine the ability to remobilize nitrogen when supply is eliminated. At growth stage (GS) 9.7, effect of N treatments on total N, nitrate, seed yield , and biomass allocation was evaluated under N sufficient and N depletion conditions. Plants transformed with one of two genes [12S seed storage globulin precursor as antisense orientation (At1g07750) and a hypothetical protein as sense orientation (At3g49550)], that were previously identified among others to impact Arabidopsis tolerance to insufficient nitrogen levels, were characterized by the hydroponic method for their impact on nitrogen accumulation and remobilization in Arabidopsis. Phenotypic and metabolic analysis showed that the gene encoding the 12S seed storage globulin precursor has improved accumulation , assimilation , and remobilization , leading to increased seed yield under N depletion conditions. Conversely, the hypothetical protein has improved accumulation in vegetative tissues, but reduced assimilation and remobilization , leading to reduced seed yield . The results from this research help improve our understanding of how plants improve their efficiency to assimilate and translocate nitrogen when they face environmental stress factors that affect their ability to accumulate nitrogen from the surrounding environment .