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 japónica L. cotyledons cultured on Murashige and Skoog’s medium containing 1 mg l“1 of 6-benzylaminopurine. Only the abaxial surface of the cotyledon expiants 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 embryogénie precursor cells which dedifferentiated into embryogénie 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 of culture the expiants exhibited a rapid decline in protein body content, which was high in the initial cotyledon, and an increase in starch content. Developing nodules were strongly PAS-positive, but starch content subsequently declined in the tissues underlaying embryogénie areas and reached a minimum when somatic embryos developed. © 1993 Annals of Botany Company.