TRANSIENT GENE-EXPRESSION IN SUNFLOWER (HELIANTHUS-ANNUUS L) FOLLOWING MICROPROJECTILE BOMBARDMENT

Transient expression of the uidA gene, coding for beta-glucuronidase ( GUS) and driven by different promoters, has been induced in sunflower cotyledonary explants and immature zygotic embryos of different develo pmental stages using two particle delivery systems. Explants were eval uated for expression of beta-glucuronidase activity 3 days, 2, and 4 w eeks post bombardment. Immature embryos were more suitable for transfo rmation than cotyledons derived from mature seeds, The highest level o f transient GUS expression after 3 and 14 days was obtained with embry os (less than or equal to 1.5 mm) precultured for 3 days in the presen ce of NAA and BAP. After 2 and 4 weeks of culture, increased GUS activ ities were determined following bombardment with plasmids harboring a doubled CaMV 35S and a stress inducible promoter, respectively. In cot yledons, GUS-expressing cells were mostly observed in the epidermal la yer, while in immature embryos they were located between the epidermis and the fourth mesophyll layer. The performance of the two biolistic equipments was comparable, Under any condition, GUS expression decline d with increasing culture time.