Histology of in vitro organogenesis and somatic embryogenesis in callus cultures of Rosa

Histological studies of callus proliferation, organogenesis and somatic embryogenesis in leaf-and stem-derived calluses of Rosa hybrida cv. Landora were made by light microscope. During organogenesis, rapid periclinal divisions of superficial cells formed nodules, many of which developed vascular strands, promeristems and adventitious leaves. Additional promeristems with small, densely staining cells and a distinct tunica layer also originated in the organogenic region by cell division in the epidermal and subepidermal cell layers. During embryogenesis, some cells on the periphery of the callus underwent internal segmenting divisions and either directly formed somatic embryos or continued to proliferate and produce an, embryogenic callus. The vascular system of the somatic embryos was separated without connection to the callus. Secondary embryos occasionally formed at the base of primary embryos. The details of the histological development during organogenesis and somatic embryogenesis of rose plants may help to identify the cause of developmental failures in recalcitrant genotypes.