Plant regeneration from mesophyll and suspension protoplasts of Silybum marianum

Mesophyll protoplasts of six lines of Silybum marianum were enzymatically isolated from young leaves, embedded in sodium alginate, and cultivated in KM-medium. Division frequencies observed after ten days were strongly influenced by the protoplast density. When 5 x 10 (4)/ml protoplasts were plated, division frequencies of about 35% were obtained, with a protoplast population density of 1 x 10 (5)/ml division frequencies of about 75% resulted. Plant regeneration experiments undertaken with the protocalluses on medium containing BAP led to shoot formation in only two lines with regeneration frequencies of less than 1% in one (M 24) and up to 7% in a second line (M 2), respectively. However, when the protocalluses from line M 2 were treated with thidiazuron (TDZ) in a first culture step, and with BAP in a second step, the shoot formation frequency rose to 22%. Shoots were rooted on hormone free MS agar medium and transferred into soil where plants grew to maturity. Similar results were obtained when protoplasts of the line M 2, isolated from a suspension culture, were cultivated.