Anatomical Sequence and Morphometric Analysis during Somatic Embryogenesis on Cultured Cotyledon Explants of Camellia japonica L.

This article describes the origin and anatomical development of somatic embryos differentiated on Camellia japonica L. cotyledons cultured on Murashige and Skoog's medium containing 1 mg l-1 of 6-benzylaminopurine. Only the abaxial surface of the cotyledon explants was morphogenetically competent. Embryos developed in abaxial parenchymatic protuberances or nodules arising by dedifferentiation and active cell division in the epidermis and subepidermis. After 12-15 d in culture, successive divisions at the surface of the nodules led to the formation of embryogenic precursor cells which dedifferentiated into embryogenic cells; most somatic embryos apparently had a multicellular origin from multicellular proembryonal complexes, though a number of few-celled proembryos within a thick common wall seemed to have originated unicellularly. Between days 24 and 27, somatic embryos at the heart-shaped, torpedo-shaped and cotyledonary stages were apparent. Computer-aided image analysis of the histological events showed a progressive increase in the nucleus-to-cell area ratio. During the first 7 d culture the explants exhibited a rapid decline in protein body content, which was high in the initial cotyledon, and an increase in starch content. Developing nodules strongly PAS-positive, but starch content subsequently declined in the tissues underlaying embryogenic areas and reached a minimum when somatic embryos developed.Peer reviewe