The seminal roots of an upland rice variety, Azucena, showed accelerated elongation in response to a water deficit. The elongation of cortical cells in the elongation zone is rapidly stimulated within 16 h by the water deficit. cDNA-AFLP analysis was used to examine gene expression in seminal root tips at four time points (4, 16, 48 and 72h) during the water deficit. One hundred and six unique genes induced by the water deficit were obtained. The expression patterns of these genes were confirmed by Northern blot analysis based on 21 selected genesrepresenting different patterns. The 106 upregulated genes were composed of 60 genes of known function, 28 genes of unknown function and 18 novel genes. Sixty genes of known functions were involved in transport facilitation, metabolism and energy, stress-and defense-related proteins, cellular organization and cell-wall biogenesis, signal transduction, expression regulator and transposable element, suggesting that seminal root tips undergo a complex adaptive process in response to the water deficit. Expression of 22 genes reached a maximum within 16h of water deficit treatment. These included aquaporin (PIP2a), 9-cis-epoxycarotenoid dioxygenase (NCED1) and a negative regulator of gibberellin signal transduction (SPY); eight other genes participated in cell wall loosening or vesicle traffic.