Search

The objective of this study was to characterize the histodifferentiation of somatic embryogenesis obtained from leaf explants of C. arabica. Therefore, we histologically analyzed the respective stages of the process: leaf segments at 0, 4, 7, 15 and 30 days of cultivation, Type 1 primary calli (primary calli with embryogenic competence) and 2 (primary calli with no embryogenic competence), embryogenic calli, globular, torpedo and cotyledonary embryos, and mature zygotic embryos. Callus formation occurred after seven days of culture, with successive divisions of procambium cell. In this cultivation phase, it was found that Type 1 primary calli are basically formed by parenchymal cells with reduced intercellular spacing, whereas Type 2 primary calli are predominantly composed of parenchymal cells with ample intercellular spaces and embryogenic calli composed entirely of meristematic cells. After 330 days, it was evident from the differentiation of somatic embryogenesis that there was formation of globular somatic embryos, consisting of a characteristic protoderm surrounding the fundamental meristem. With the maturation of these propagules after 360 days, torpedo-stage somatic embryos arose, in which tissue polarization and early differentiation of procambial strands were verified. After 390 days, cotyledonary somatic embryos were obtained, where the onset of vessel elements differentiation was verified, a characteristic also observed in mature zygotic embryos. We concluded that somatic embryogenesis obtained from C. arabica leaves initiates from procambium cell divisions that, in the course of cultivation, produce mature somatic embryos suitable for regenerating whole plants. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]