Importance of media mineral composition on the induction of somatic embryogenesis en E. globulus Labill.

Eucalyptus globulus is one of the main species for the pulp industry and it is the third most important forest species in Portugal. As other Eucalyptus species it is an obvious target for in vitro propagation (e.g. somatic embryogenesis) and genetic manipulation. We have compared several published media (MS, 1/2MS, B5, WPM, DKW and JADS) both on the somatic embryogenesis induction and expression steps. MS, followed by B5, were the best induction media. Since different media induced heterogeneous responses, with MS being the best medium to induce somatic embryos, we compared its mineral composition with the mineral content of zygotic embryos (explants). Simultaneously, and as the secondary somatic embryos are routinely maintained on this medium and used to regenerate plants, we also compared the mineral composition of zygotic and secondary somatic (grown in MS media) embryos. Fresh samples were digested with HClO4 for Mg, Ca, Cu, Zn, Fe and Mn, and with H2SO4 for P, N and K analyses.. Preliminary results showed that zygotic embryos have different mineral proportions when compared to all basal media used, including the MS medium. Also, when compared to secondary somatic embryos, zygotic embryos showed higher levels of Mg (7.6:1), Cu (11.4:1), Zn (3.6:1), Fe (1.7:1), Mn (17.9:1), N (1.8:1), P (4.0:1) but less K (0.7:1), showing that SE induction conditions lead to changes in tissue mineral content relatively to zygotic embryos