Induction of somatic embryogenesis and genetic transformation of ohio buckeye (Aesculus glabra willd.)

Summary  Mature embryo axes of the Ohio buckeye were germinated on a medium containing 1 mg gibberellic acid (GA) per 1. Three wk following germination, stem, petiole, and leaf blade tissues were excised and placed on media containing either 1 mg (4.5 μM) 2,4-dichlorophenoxy acetic acid (2,4-D) per 1, 1 mg (4.7 μM) kinetin per 1, 1 mg of both 2,4-D (4.5 μM) and kinetin (4.7 μM per 1, or 2 mg of both 2,4-D (9.1 μM) and kinetin (9.3 μM) per 1. Embryogenic tissue was formed only from stem segments after 2–3 mo. of culture on media containing both 2,4-D and kinetin. Embryogenic tissue could be either maintained on solid medium for proliferation of embryogenic callus or placed in liquid medium for proliferation of embryogenic suspension cultures. For transformation of suspension cultures, tissues were inoculated with Agrobacterium EHA105 containing the binary plasmid Vec035, briefly sonicated, and cultured in the presence of 100 μM acetosyringone for 2 d. To eliminate Agrobacterium, tissues were washed and placed in liquid proliferation medium containing either 500 mg Cefotaxime per 1 or 400 mg TimentinŖ per 1. Selection on 20 mg hygromycin per 1 was initiated 2 wk after inoculation, and after an additional 10 wk, hygromycin-resistant tissue was isolated and separately cultured. Although some hygromycinresistant clones were recovered with no sonication treatment, four to five times more clones were obtained following sonication. Putative transformed clones were confirmed to be transgenic via both histochemical β-glucuronidase (GUS) assay and southern hybridization analyses. Development of transgenic embryos occurred on a growth regulator-free medium containing 3% sucrose. After 2 mo. of embryo development, the embryos were transferred to fresh medium for germination.