Somatic embryogenesis and in vitro secondary metabolite production from common mallow (Malva sylvestris L.) collected in Greece

The effect of plant growth regulators (PGRs) and culture conditions on somatic embryogenesis and secondary metabolite production from stem explants of common mallow (Malva sylvestris L.), a herb naturally found in marginal lands and roadsides, was investigated. Numerous spherical somatic embryos could be induced on explants within only three days of culture on a Murashige and Skoog (MS) medium supplemented with 1.8-18 mu M 1-naphthalenacetic acid (NAA) and 6-benzyladenine (BA). The type and concentration of PGRs, together with the value of the photosynthetic photon flux density (PPFD) (250 or 50 mu mol m(-2) s(-1)) significantly affected callus growth, as well as the number of somatic embryos over a culture period of four weeks. Somatic embryogenesis was favored by higher light intensities. Heart and torpedo-shaped embryos (1-1.5 mm long) were observed two weeks after continuous culture on the induction medium. The secondary metabolite production from mallow tissues cultured on 1.8 mu M NAA and 1.8 mu M BA was investigated over a culture period of four weeks. Substances were extracted with warm water and partitioned against ethyl acetate. The constituents of the concentrated extracts were separated by thin-layer chromatography (9.5 toluene: 0.5 ethyl acetate (v/v)) and their total concentration was determined spectrophotometrically at 257 nm. A total of at least seven constituents were detected in tissues cultured in vitro, while only one constituent could be detected in stems received from plants growing in vivo. Differences were observed between tissues cultured under different PPFDs. Neither of the detected substances was psoralen, bergapten or 8-methoxypsoralen, which were co-analysed as standard furanocoumarines.