THE EFFECT OF EXOGENOUSLY-APPLIED PHYTOHORMONES ON GENE-TRANSFER EFFICIENCY IN SUGAR-BEET (BETA-VULGARIS L)

Cellular competence for regeneration and transformation has been monit ored in a recalcitrant crop, i.e, sugarbeet (Beta vulgaris L.). Explan ts for Agrobacterium inoculation were taken from the transition zone b etween hypocotyl and cotyledonary petioles. De novo generation of adve ntitious shoots was very efficient (60%-70%) from these cotyledonary n ode explants. Regeneration could not be further stimulated by manipula tion of cytokinin type or concentration. The mode of regeneration was direct, without a callus phase. Dedifferentiation, as induced by a pre culture period on 2,4-D, gave significantly higher gene transfer frequ encies, but regeneration was irreversibly impaired. NAA mimicked the e ffect of 2,4-D on gene transfer. However, explants retained their rege nerative capacity upon pretreatment with NAA. Using the procedure desc ribed here, transgenic sugarbeet plants were obtained after selecting on 250 mg/l kanamycin at a frequency of 1%.