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

This article describes the origin and anatomical developmentof somatic embryos differentiated on Camellia japonica L. cotyledonscultured on Murashige and Skoog's medium containing 1 mg l^-1of 6-benzylaminopurine. Only the abaxial surface of the cotyledonexplants was morphogenetically competent. Embryos developedin abaxial parenchymatic protuberances or nodules arising bydedifferentiation and active cell division in the epidermisand subepidermis. After 12-15 d in culture, successive divisionsat the surface of the nodules led to the formation of embryogenicprecursor cells which dedifferentiated into embryogenic cells;most somatic embryos apparently had a multicellular origin frommulticellular proembryonal complexes, though a number of few-celledproembryos within a thick common wall seemed to have originatedunicellularly. Between days 24 and 27, somatic embryos at theheart-shaped, torpedo-shaped and cotyledonary stages were apparent.Computer-aided image analysis of the histological events showeda progressive increase in the nucleus-to-cell area ratio. Duringthe first 7 d culture the explants exhibited a rapid declinein protein body content, which was high in the initial cotyledon,and an increase in starch content. Developing nodules stronglyPAS-positive, but starch content subsequently declined in thetissues underlaying embryogenic areas and reached a minimumwhen somatic embryos developed.Copyright 1993, 1999 AcademicPress Camellia japonica, camellia, cellular changes, somatic embryogenesis, histology, image analysis