Histological studies on the developmental stages and differentiation of two different somatic embryogenesis systems of Coffea arabica

Histocytological analysis carried out on leaf explants of Coffea arabica undergoing somatic embryogenesis revealed that, using a culture method involving a single Gelrite-containing semisolid medium, the entire region surrounding the edge of the plant-derived leaf explants showed the differentiation of organized structures with little or no callusing. Histological examination of embryogenesis without callus formation (direct somatic embryogenesis) revealed that at approximately 1 week after the explant had been placed in culture, the development of the embryo began in the form of a small, isodiametric, densely cytoplasmic cell that underwent a series of organized divisions. In embryogenesis from callus (indirect somatic embryogenesis), however, the embryogenic cell was observed within the first week. Our histological observations indicate that both direct and indirect somatic embryos of coffee that form on explanted leaf segments and callus, respectively, have a unicellular origin.