AMINO-ACID CARRIERS OF RICINUS-COMMUNIS EXPRESSED DURING SEEDLING DEVELOPMENT - MOLECULAR-CLONING AND EXPRESSION ANALYSIS OF 2 PUTATIVE AMINO-ACID TRANSPORTERS, RCAAP1 AND RCAAP2

This study reports on the isolation of two putative amino acid carrier cDNAs, RcAAP1 and RcAAP2, from Ricinus communis. Northern analysis sh ows that RcAAP1 and RcAAP2 are expressed abundantly in the cotyledon a nd root tissues of developing seedlings and at lower levels in the end osperm and hypocotyl. In the mature plant low expression was observed in the source and sink leaves. We have further characterized the expre ssion of RcAAP1 in Ricinus roots by in situ hybridization. The transcr ipts are localized in many cell types of the root tip region, includin g the epidermal and cortical cells, but the highest expression was obs erved in the cells of the stele situated adjacent to the xylem poles. This is the first report describing the cellular expression of an amin o acid transporter in roots, and the results are discussed in relation to the physiological role of this transporter.