Nitrogen assimilation and translocation in Arabidopsis seeds

In plants, assimilated nitrogen travels mostly as amino acids. Amino acids travel from sources to sink tissues through cellular and organelle membranes such as plasma membrane, chloroplast membrane, mitochondrial membrane, and tonoplast membrane via facilitated or active transport. Membrane transporter proteins such as amino acid transporters mediate the transport. These transporters, as they facilitate the movement of amino acids through membranes, also regulate the distribution of amino nitrogen. Understanding the organ and tissue-specific distribution of amino acid transporters, their substrate affinity, and transport mechanism can help us understand the source-sink distribution of amino nitrogen in plants. With advancements in plant science research, we understand the amino acid distribution route in theory, but we have yet to identify many of the necessary amino acid transporters that enable this route. This chapter discusses the source-sink distribution of amino acids with a specific focus on seeds and lists the amino acid transporters in this route, characterized to date, in the model plant system, Arabidopsis thaliana.