PLANT-REGENERATION AT HIGH-FREQUENCY FROM MATURE SUNFLOWER COTYLEDONS

Methods for sunflower (Helianthus annuus L.) tissue culture and transformation are to date characterized by a low degree of efficiency, reliability and reproducibilty. The most widely used approach for regeneration of plants from somatic cells makes use of immature embryos, a material laborious to obtain. We describe here an efficient regeneration system using cotyledons of young plantlets, yielding up to ten shoots per cotyledon. Factors found to influence quantitative aspects (frequency of response) and qualitative aspects (response type) include hormonal balance and nitrogen supply in the medium, as well as explant type, age and genotype. Physical culture conditions, while exerting a certain effect, appear to be of minor importance. A number of regenerated plants have been transferred to the greenhouse and seeds were obtained from each plant. The total time required from isolation of the explant to harvest of seeds was 4-6 months.