Poster: Membrane Transport

Abs # 1237: Identification of an aspartic acid transporter associated with developing flowers

Presenter:	Lee, Yong-hwa , ylee1@mail.wsu.edu
Authors	Lee, Yong-hwa  (A)   Tegeder, Mechthild  (A)
Affiliations:	(A): School of Biological Sciences, Center for Reproductive Biology, Center of Integrated Biotechnology, Washington State University, Pullman

When plants enter their sexual reproductive phase, the development of flowers strongly relies on the availability of nitrogen transported to these sink organs. Transport of nitrogen to the reproductive organs occurs via the phloem, primarily in the form of amino acids and amides. Analysis of phloem sap for a number of plant species has shown that aspartate and glutamate are the dominant amino acids translocated to sinks. We are currently analyzing different amino acid transporters from Arabidopsis for their specificity for aspartate. Heterologous expression in a yeast mutant deficient in uptake of specific amino acids demonstrated that two Arabidopsis transport proteins mediate yeast growth on aspartate and glutamate but also on proline, citrulline, and GABA as sole nitrogen source. Uptake studies of radioactive aspartate by yeast cells showed for one of these transporters saturable kinetics with a Km value of 42 µM suggesting a high affinity transport system for aspartate. Northern blot analysis of this aspartate transporter demonstrated exclusive expression in flower buds. Tissue and cell level expression of the transporter gene is currently being studied by RNA in situ hybridization analysis. In this study we will provide new information on an amino acid transporter that recognizes aspartate efficiently and is probably exclusively involved in import of acidic amino acids into the flower bud for bud and microspore development.