Stable transformation of papaya (Carica papaya L.) has been achieved following DNA delivery via high velocity microprojectiles. Three types of embryogenic tissues, including immature zygotic embryos, hypocotyl sections, and somatic embryos derived from both, were bombarded with tungsten particles carrying chimeric genes coding for NPT II, GUS, and the coat protein of a mild mutant strain HA 5-1 of papaya ringspot virus. All tissue types were cultured prior to and following particle bombardment on half-strength.MS medium supplemented with 10 mg/1-1 2,4-D, 400 mg/lrI glutamine, and 6% sucrose. Upon transfer to 2,4-D-free medium containing 150 mg/l-1 kanamycin sulfate, 12 isolates regenerated somatic embryos, and five of these produced leafy shoots six to nine months following bombardment. Tissues from 11 isolates were assayed for NPTII activity, and nine were positive. Five out of 12 isolates assayed for GUS expression were positive. Three isolates were positive for both NPTII and GUS
