Cultivar variability in the Agrobacterium-rice cell interaction and plant regeneration

Thirteen cultivars of rite (Oryza sativa) were tested for plant regeneratio n from calli initiated from the scutella of mature seeds by water stress tr eatment using a high concentration of agarose, and examined for their respo nse Agrobacterium tumefaciens LBA4404, carrying a plasmid pTOK233, harborin g genes for kanamycin resistance (nptII), hygromycin resistance (hpt) and b eta-glucuronidase (gus). Plant regeneration frequency was considerably incr eased in most of the cultivars when the calli were treated with water stres s, as compared with untreated controls. In particular, the cultivars Dongji nbyeo, IR43, Nagdongbyeo and Sinseonchalbyeo showed an increased frequency of shoot regeneration, Expression of GUS was detected in an of the co-culti vated cultivars. Based on GUS expression at 3 days after co-cultivation wit h A, tumefaciens, three rice cultivars (Dongjinbyeo, Hwayoungbyeo and Nagdo ngbyeo) were judged highly susceptible to A. tumefaciens, while Milyang 23, Nonganbyeo and Samgangbyeo cultivars were weakly susceptible. Plantlets a; ere readily regenerated when the hygromycin-resistant calli were transferre d to a regeneration medium containing hygromycin. Intense blue staining was observed in GUS assays of leaf segments, roots and flower organs from rege nerated plants, Stable integration and expression of the introduced hpt and gus genes were confirmed by Southern blot analysis of the transformants, T herefore, Dongjinbyeo and Nagdongbyeo cultivars proved to be both highly su sceptible to A. tumefaciens and highly responsive to plant regeneration.