Transient expression of -glucuronidase gene in indica and japonica rice (Oryza sativa L.) callus cultures after different stages of co-bombardment

Rapidly growing embryogenic calli of different ages derived from the scutellum of mature seed embryos of indica rice (Rasi) and mature seeds of japonica rice (Taipei 309) was biolistically transformed. Plasmid pUCGUS containing the uidA gene encoding -glucuronidase was used to optimize transformation conditions using various combinations of helium pressure, target distance and gap distance. Plasmid pHX4 carrying hygromycin phosphotransferase (hph) gene and pUCGUS was used for co bombardment. Resistant calli were selected in the presence of hygromycin B. Successful co-transfer of DNAs to cells was monitored by analyzing transient gus expression 24 h after bombardment and 24 days after selection. Maximum level of gus expression was observed if calli were selected for transformation after 44 days in maintenance medium. Maximum callus transformation frequency of 37.5 was observed for Taipei 309 as compared to 24.2 for indica rice cv. Rasi.