In-vitro regeneration of sunflower plants: effects of a Metylobacterium strain on organ development

Under natural conditions, plant surfaces are colonized by a variety of microorganisms. It has been postulated that non-pathogenic methylobacteria promote plant growth via the secretion of phytohormones. In order to study the putative role of these prokaryotic epiphytes during plant development we established a sterile regeneration system, using sunflower (Helianthus annnuus L.) as model organism. Apical hypocotyl segments, excised from 4-day-old etiolated seedlings, were placed into a shoot induction medium. Half of them were inoculated by immersing the hypocotyl segments in a bacterial suspension, containing a Methybacterium strain that was isolated from a ligulate flower of a field-grown plant. After 14 days of cultivation in darkness (followed by 14 days in a light/dark-regime), regenerated shoots were excised from the hypocotyl seggments. After 20 days on vitamin medium, juvenile plantlets were rooted on rooting medium. Regenerated sunflower plantlets started to flower after about 50 days of growth in glass jars. In the presence of the methylobacteria a promotion in the number of shoots and roots regenerated in-vitro was recorded, but no enhancement in growth occured.