Inhibitory factor(s) of somatic embryogenesis regulated suspensor differentiation in suspension culture of Japanese larch (Larix leptolepis GORDON)

Abstract

Using somatic embryogenesis system of Japanese larch that develops embryos composed of embryo - proper and suspensor, the effects of high - cell - density culture and conditioned medium on the somatic embryogenesis were investigated. High - cell - density culture strongly inhibited the somatic embryogenesis. Furthermore, the conditioned medium derived from high - cell - density culture also strongly inhibited the somatic embryogenesis, especially differentiation of the suspensor. The inhibitory effect of the conditioned medium was not attributable to the depletion of nutrients, but to the accumulation of inhibitory factor(s) in the medium. The addition of activated charcoal to high - cell - density culture resulted in the formation of numerous somatic embryos with longer suspensors than in the untreated one. This treatment also resulted in the formation of numerous vacuolated cells-like suspensor on the surface surrounding the embryo-proper. These results indicate that some inhibitory factor(s) that regulates suspensor differentiation are released into the medium of high cell density.