Abstract: The wounded cotyledon and hypocotyl explants from sunflower seedlings grown in vitro were soaked in suspension cultures of wild type strain B6S3 or T37 of A. tumefaciens which were at logarithmic growth phage. After 20-30 min the infected explants were transfered into MS medium lacking hormones and co-cultivated for three days at 25°C and weak light. The non-attached bacteria were then removed by washing the infected explants for 8-10 times. The selection for hormone-independent growth and elimination for the rest of the free bacteria were made in hormone-free medium supplemented with 500 mg/l carbenicillin. Transformed tumor tissues from infected both cotyledon and hypocotyl explants haev been induced by A. tumefaciens with the in vitro transformation system. Frequencies of transformation were ca. 60-96. Transformants were confirmed by their ability to proliferate tumor callus in hormone-free medium and to contain opine synthase activities in their tissues. In the process of subculture the isolated tumor tissues retained their growth trait of homone autonomy. In addition the growth rate of tumor tissues was much higher than that of normal callus cultures induced by hormones in hormone-free conditions.

Key words: In vitro transformation