(724g) Isotope-Assisted Metabolic Flux Analysis Reveals Metabolic Landscape Alterations in Poplar Induced By Carbon-Nitrogen Interactions

Nitrogen is an indispensable element for life because it is present in numerous biochemical compounds including amino acids, nucleotides and cofactors such as NAD(P)H. However, nitrogen is usually supplied in the form of fertilizers that are produced mainly by high-energy industrial processes. Fortunately, most trees are capable of conserving and recycling nitrogen. Poplar, specifically, is capable of efficiently managing its nitrogen reserves by recycling nitrogen from leaves during senescence in fall, storing this recycled nitrogen in the form of a protein (bark storage protein [BSP]) during winter and mobilizing this stored nitrogen for de novo protein synthesis in spring. Previous research shows that this nitrogen recycling mechanism is strongly correlated with carbon availability that influences BSP accumulation. Therefore, it is desirable to study how carbon and nitrogen nutrient levels affect metabolic landscapes in poplar.

Isotope-assisted metabolic flux analysis (MFA) is a powerful tool in understanding metabolism with its ability to accurately quantify intracellular chemical reaction rates (fluxes). We performed isotope-assisted MFA to calculate fluxes of central carbon metabolism in cells from poplar trees under different carbon and nitrogen nutrient levels. Besides, in order to improve the statistical quality of the flux results, we employed multiple types of labeled carbon sources in parallel experiments and consolidated the ensuing mass isotopomer data into a single flux evaluation. Moreover, we conducted transcriptome analysis to measure the expression levels of all metabolic genes and compared them with the flux map obtained from MFA. The consistency of fluxome and transcriptome clearly shows the metabolic significance of the availability of carbon and nitrogen sources. We anticipate that this study can shed light on future research on nitrogen recycling mechanism and experiment design in poplar plants.