Plant regeneration from leaf mesophyll protoplasts of the tropical woody plant, passionfruit (Passiflora edulis fv flavicarpa Degener.): the importance of the antibiotic cefotaxime in the culture medium

Abstract

Enzymatic digestion of newly expanded leaves of glasshouse-grown seedlings of passionfruit released protoplasts which exhibited highest division frequency (38.6%) when plated at a density of 1.5×10⁵ ppts ml⁻¹ in agarose-solidified droplets of KM8P medium containing the antibiotic cefotaxime (250 μg ml⁻¹). Cefotaxime was essential for sustained cell division. Protoplast-derived calli were cultured on agarsolidified MS medium with 5.0 mg H NAA, 0.25 mg l⁻¹ BAP and additional vitamins. These calli regenerated shoots on transfer to MS medium with 1.0 mg l⁻¹ BAP. Regenerated shoots were rooted in half-strength MS medium with 3.0 mg l⁻¹ IBA and 0.5 mg l⁻¹ NAA (7 d), followed by sub-culture to MS medium lacking growth regulators. The ability to regenerate plants from protoplasts of passionfruit is discussed in relation to the application of somatic cell techniques for the genetic improvement of this economically important tropical woody plant.