To find out a simpler method that can directly transfer the aim gene into plant genomes, the purple medic seeds irradiated by ⁶⁰Co with 0.375 Gy were transformed by linear DNA containing a β-glucuronidase (GUS) gene (as an aim gene), a betaine aldehyde dehydrogenase (BADH) gene (as a selectable marker) and two pairs of both CaMV35S promoter and Nos terminator. Subsequently, the seeds were planted and grown in perlite media watered with NaCl solution as a kind of selective compound. The results showed that, positive frequency of PCR identification by the GUS gene or the BADH gene was higher than 53.2 and 89.5% in T₀ and T₁ generations, while GUS staining rate was higher than 50%; whereas five T₁ plants assayed by southern hybridization all showed positive reaction. In conclusion, by this method, transgenic plants may be easily obtained with the antibiotic markers for free; moreover, the plant regeneration-system must not be erected by directly transforming the seeds.

Key words: DNA transformation, irradiated seeds, purple medic, salt screening.