Influence of medium parameters on somatic embryogenesis from hypocotyl explants of flax (Linum usitatissimum L.) - Effect of carbon source, total inorganic nitrogen and balance between ionic forms and interaction between calcium and zeatin

The effects of different carbon sources, total inorganic nitrogen concentra tion, nitrate to ammonium ratio and the interaction between calcium and zea tin (ZEA) levels on somatic embryogenesis from flax hypocotyl explants were studied in three independent factorial experiments. MS medium supplemented with the monosaccharides glucose or fructose at high concentrations (4 %) gave consistently highly embryogenic cultures, with higher somatic embryo f requencies and higher growth rates when compared with media supplemented wi th sucrose or maltose. Although media with maltose had performed well in a 1-4% concentration range, media supplemented with sucrose at 4 %, appeared to inhibit the induction and development of somatic embryos. Independently of the effect of the nitrogen content, the balance between both ionic forms (NO3- and NH4+) played a dramatic role on the induction of somatic embryog enesis and somatic embryo growth. Nitrate is important for calli differenti ation and growth, and a high ammonium content increased somatic embryo freq uency. The embryogenic vs. undifferentiated cell growth commitment of flax explants was determined by an interaction between calcium and ZEA levels, a high calcium/low ZEA affording very low embryogenic potential and high cal li biomass. A high ZEA concentration was essential for the normal developme nt of somatic embryos.