| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 93 === Nitrogen is the constituent of protein, nucleic acids, chlorophyll, some plant hormones, and also the important part of ATP. Therefore the acquisition and translocation of nitrogenous compounds are important for plant growth and development. As being sessile organisms, most of the plants have to absorb nitrogen from the soil. Because nitrification is pervasive in the soil, most of the nitrogen is taken up as nitrate. Since negatively charged nitrate cannot penetrate the membrane by diffusion, its absorption by root from the soil and translocation between various tissues should be accomplished by nitrate transporters. So far, two families of nitrate transporters, NRT1 and NRT2, have been identified. The Arabidopsis genome contains 53 NRT1 and 7 NRT2 genes. In the Part I of this dissertation, through the studies of phylogenetic analyses and expression pattern of NRT1 family members in Arabidopsis, we provide the genome-wide information of this family, and also point out the potential physiological roles of NRT1 genes. In Part II, I focus on a petiole-specific NRT1 gene, AtNRT1:4. Different from that the well-characterized nitrate transporters are all shown to be expressed in root and involved nitrate uptake, AtNRT1:4 is expressed is leaf petiole and involved in vacuolar nitrate storage. In addition, my study also shown that AtNRT1:4 is also involved in the regulation of leaf nitrate homeostasis.
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