The Impact of Nitrogen Fertilization and the Overexpression of Alanine Aminotransferase on Populus Tremula X Alba

It has been well established that increased nitrogen fertilization can increase yield and growth of plants; however, broad scale fertilizer application also causes detrimental impacts to the environment. By manipulating trees to better utilize lower levels of nitrogen it may be possible to grow biomass for biofuel without increasing fertilization. This study aims to determine how altered nitrogen metabolism impacts the growth and secondary cell wall (SCW) characteristics of Populus tremula x alba. Specifically, this study looks at how the overexpression of alanine aminotransferase (AlaAT1.1) impacts growth parameters and the SCW of poplar trees grown under three different nitrogen conditions. AlaAT1.1 was transformed into wild type Populus tremula x alba under the control of two different promoters. The transgenic plants were then grown under three nitrogen treatments, Hocking\u27s solution with supplemental N as 0mM NH₄NO₃ (low), 1.5mM NH₄NO₃ (medium), and 15mM NH₄NO₃ (high), in the greenhouse. Measurements for growth, gene expression, and secondary cell wall components were taken and analyzed. The results show that despite evidence of integration of the AlaAT1.1 construct into the plant genome, there was no evidence of altered expression as assessed by transcript expression in the developing xylem and no phenotypic changes as a result of transformation with AlaAT1.1 However, increased available nitrogen impacted secondary cell wall components, leaf area, leaf count, biomass accumulation, and structural carbohydrates. While the impact of AlaAT1.1 overexpression could not be assessed here, altered N availability impacted growth parameters of poplar trees. It is possible that AlaAT expression is tightly regulated preventing high expression levels