Plant Biotechnology 23, 75–83 (2006)

With the purpose of enhancing environmental stress tolerance of sweet potato (Ipomoea batatas, cv. Kokei 14), we transformed this plant with spermidine synthase genes derived from Cucurbita ficifolia (FSPD1). The FSPD1-transgenic plants showed twice as high spermidine content as the wild type (WT) counterpart in both leaves and storage roots. One of the most characteristic features of the transgenic plants was the increase in the number of storage roots formed under both non-stress and stressful environments. Salt and drought stresses suppressed storage root growth, but the transgenic plants were less affected producing significantly larger mass of storage roots and starches than WT plants under either stress. The transgenic plants also showed increased tolerance to chillingand heat-mediated damage to photosynthesis compared to the WT plants. Thus, sweet potato was made more tolerant to environmental stresses through introduction of the FSPD1 genes. This improved tolerance may involve enhanced oxidative stress tolerance at least partially because the transgenic plants were more tolerant to paraquat, a potent oxidative stress inducer, than the WT plants. From these results, the FSPD1 gene is considered useful for gene transfer technology aiming at improving environmental stress tolerance of sweet potato.