Morphogenic events during indirect somatic embryogenesis in coffee “Catimor”

Summary

The main goal of this research was to identify and describe the morphological and histological events during coffee somatic embryogenesis. Leaf sections of coffee “Catimor” (Coffea arabica CV. Red Caturra X hybrid of Timor) were cultivated in vitro on solid medium containing 2,4-dichlorophenoxyacetic acid and benzyladenine. After 4 months, the calli produced were transferred to a medium containing naphthalene acetic acid. During the process of somatic embryogenesis, calli were sampled for histological observation. After four days of culture, the expiant produced a callus in the cut edges, where cell division occurred in the spongy parenchyma and in the perivascular parenchyma. After two months of culture, the first sign of organization within the growing callus was evidenced by the formation of densely stained cell groups appearing physically isolated, surrounded by thick cell walls. Two months later, proembryogenic clumps were formed by groups of dividing cells, unconnected to the callus. These cells were small, relatively isodiametric, with a dense cytoplasm, large nucleus, prominent nucleoli and thick cell walls. Afterwards, embryogenic calli formed somatic embryos going through the typical stages of development: globular, heart, and torpedo shapes. Histological observations revealed that the somatic embryos originated from a single cell, with dense cytoplasm, prominent nucleus and with signs of isolation evidenced by the presence of a thick cell wall.