Effects of glycerol on somatic embryogenesis in Cichorium leaves

Direct somatic embryogenesis was induced in leaf cells of a Cichorium hybri d (Cichorium intybus L var, sativum x Cichorium endivia L. var. latifolia) through a two-step procedure. Leaf tissue explants were cultured for 5 days in M17 liquid medium supplemented with 30 mM sucrose and 330 mM glycerol ( M17S30Gly330 medium). Synchronised divisions of embryogenic cells occurred after transfer for 7 days onto glycerol free-medium (M17S30). By doubling t he sucrose concentration (60 mM) in the presence of glycerol (M17S60Gly330) during the induction step, embryogenesis increased and the length of the i nduction step was reduced from 5 to 4 days. Compared to sucrose, glycerol a s carbon source during the induction and the expression steps had an inhibi tory effect on the embryogenic response. During culture, glycerol was not d etected in M17S60 medium and was at a low level in leaf fragments incubated in this medium. Initially supplied as an osmoticum, glycerol disappeared F rom M17S60Gly330 medium during the 4-day induction period and penetrated in to the tissues where most of was metabolised. Furthermore, glycerol modifie d it carbohydrate metabolism, particularly during the induction period of e mbryogenesis. Sucrose hydrolysis was affected in the medium and sucrose and hexose contents in tissues were higher than in glycerol-free medium. The e ffects of glycerol as osmoticum and as a molecule itself are discussed.