Biochemical events during somatic embryogenesis in Coffea arabica L.

Several biochemical components associated with different stages of somatic embryogenesis in coffee (Coffea arabica L.) are investigated using foliar explants. Soluble sugar, starch, free amino acids and total proteins were extracted and quantified at different stages of somatic embryogenesis, such as foliar segments (initial explants), primary calluses, embryogenic calluses, globular embryos, torpedoes, cotyledonary embryos and mature fruit zygotic embryos. Total soluble sugar levels increased sixfold at the initial stages of somatic embryogenesis induction. During this period, total soluble sugar in the cultures contained approximately 99.3% glucose and fructose. At 67.4 μg/mg MS, no significant changes were observed in total sugar content during the embryo's somatic maturation and regeneration. During this stage, total soluble sugar was composed of 60% sucrose. After primary callus formation, starch contents increased gradually until the culture's conclusion. Total free amino acids, particularly arginine, lysine, methionine, asparagine, glutamine and histidine, revealed a higher synthesis until the formation of the primary callus, after which they remain statistically constant up to the end of the process. During the induction of calluses, a gradual increase of total proteins occurred, which, in the differentiating and maturing of somatic embryos, did not differ statistically till the formation of a cotyledonary embryo, when rates decreased 21.8%.