No abstract

The expression of the green-fluorescent protein (GFP) gene from Aequorea victoria (jellyfish) was analyzed by transient and stable expression in sweet potato Ipomoea batatas L. (Lam.) cv. Beauregard tissues by electroporation and particle bombardment. Leaf and petiole segments from in vitro-raised young plantlets were used for protoplast isolation and electroporation. Embryogenic callus was also produced from leaf segments for particle bombardment experiments. A buffer solution containing 1 Â 10 6 protoplasts ml 21 was mixed with plasmid DNA containing the GFP gene, and electroporated at 375 V cm 21 . Approximately 25±30% of electroporated mesophyll cell protoplasts subsequently cultured in KM8P medium regenerated cell walls after 48 h. Of these, 3% emitted bright green fluorescence when exposed to UV-blue light at 395 nm. Transformed cells continued to grow after embedding in KM8P medium solidified with 1.2% SeaPlaque agarose. Stable expression of GFP was observed after 4 wk of culture in approximately 1.0% of the initial GFP positive cells (27.5 GFP positive micro calluses out of 3024 cells which transiently expressed GFP 48 h after electroporation). In a separate experiment, 600±700 bright green spots were observed per plate 48 h after bombarding leaf segments or embryogenic callus. In bombarded cultures, several stable GFP-expressing sectors were observed in leafderived embryogenic callus grown without selection for 4 wk. These results show that GFP gene expression can occur in various sweet potato tissues, and that it may be a useful screenable marker to improve transformation efficiency and obtain transgenic sweet potato plants.