Stress induced somatic embryogenesis in carrot and its application to synthetic seed production

Abstract

When apical meristems of carrot (Daucus carota L. cv. US-Harumakigosun) seedlings were cultured on hormone-free Murashige and Skoog’s (MS) medium with 0.7 M sucrose or 0.25–1 mM cadmium ion, then transferred to hormone-free MS medium with 0.1 M sucrose, somatic embryos were formed on the surface of the explants without visible callus formation. Somatic embryos were also formed on malformed seedlings, when carrot seeds were treated with hypochlorite solution at a high concentration and sown on hormone-free MS medium with 0.09 M sucrose. These somatic embryos were fractionated by passing through stainless steel sieves with different pore sizes, encapsulated in calcium alginate gel, and placed in plastic petri dishes under sterile conditions. These synthetic seeds germinated 1 to 2 weeks after the beginning of the culture. In the case of synthetic seeds containing a single embryo, the frequency of the seeds which developed both a radicle and a green bud was about 30–50% in large embryos induced by the treatment with sucrose, cadmium or sodium hypochlorite, and about 15% in 2,4-D induced embryos. When 2,4-D induced embryos were encapsulated and sown, numerous secondary and tertiary embryos were formed but they did not develop into normal seedlings.