A full-length cDNA clone encoding deoxyhypusine synthase (DHS) was isolated from a cDNA expression library prepared from senescing leaves of Arabidopsis thaliana. Southern blot analysis indicated that DHS is encoded by a single-copy gene in Arabidopsis. During leaf development, the abundance of DHS mRNA in the third pair of rosette leaves peaked at days 14 and 35 after emergence coincident with the initiation of bolting and the later stages of leaf senescence, respectively. These changes in DHS expression were paralleled by corresponding changes in transcript abundance for eIF-5A1, one of three isoforms of eIF-5A in Arabidopsis. Levels of DHS transcript also increased in detached leaves coincident with post-harvest senescence. DHS was suppressed in transgenic plants by introducing antisense full-length or 3'-untranslated Arabidopsis DHS cDNA under the regulation of the constitutive cauliflower mosaic virus (CaMV-35S) promoter. Plants expressing the antisense transgenes had reduced levels of leaf DHS protein and, depending on the level of DHS suppression, exhibited delayed natural leaf senescence, delayed bolting, increased rosette leaf and root biomass, and enhanced seed yield. Suppression of DHS also delayed premature leaf senescence induced by drought stress resulting in enhanced survival in comparison with wild-type plants. In addition, detached leaves from DHS-suppressed plants exhibited delayed post-harvest senescence. These pleiotropic effects of DHS suppression indicate that the protein plays a central role in plant development and senescence.