The present invention relates to unique isoforms of eukaryotic initiation Factor 5A ("eIF-5A"): senescence-induced eIF-5A; wounding/pathogen induced eIF-5A; stress eIF-5A and growth eIF-5A, as well as polynucleotides that encode these three factors. The present invention also relates to methods involving modulating the expression of these factors. The present invention also relates to deoxyhypusine synthase ("DHS"), polynucleotides that encode DHS, and methods involving modulating the expression of DHS.