A comparison between Theobroma cacao L. zygotic embryogenesis and somatic embryogenesis from floral explants

Abstract

~UMMARYIn order to improve the late phases of Theobroma cacao L. embryogenesis from tissues of maternal origin, zygotic embryogenesis and somatic embryogenesis were compared, with respect to morphological, histological, and physiological parameters. Zygotic embryogenesis could be divided into three steps: (a) embryogenesis sensu stricto, (b) a growth period in which cotyledonary embryos reached their final dimensionsl and (c) a maturation period in which embryos accumulated protein and starch reserves, dehydrated to a water content equal to 30%, and underwent a modification in soluble sugar composition. Monosaceharides and sucrose contents decreased to the benefit of the oligosaccharides raffinose and stachyose. The formation of somatic embryos by use of basic protocols was studied to define the limiting factors that could lie behind their poor development. Morphological abnormalities of somatic embryos, which represented 80% of the total population, were described. A histological study showed that somatic embryos lacked starch and protein reserves; moreover, their water content was much higher than that of their zygotic counterparts. Introducing a growth period into the culture protocol made for better embryo development. Adding sucrose and abscisic acid to the maturation medium was effective in increasing reserve synthesis and resulted in higher germination, conversion, and acclimatization rates.

Histocytological changes and reserve accumulation during somatic embryogenesis in Eucalyptus globulus

“…Introducing a growth period into the culture protocol improved embryo development. In this species, adding, e.g., abscisic acid to the maturation medium was effective in increasing reserve synthesis and resulted in higher germination, conversion, and acclimatisation rates (Alemano et al 1997). …”

Endogenous Quantification of Abscisic Acid and Indole-3-Acetic Acid in Somatic and Zigotic Embryos of Nothofagus alpina (Poepp. & Endl.) Oerst

“…Alemanno et al (1997) proposed that the immaturity of the SE is based on deficient levels of endogenous ABA and thus, a…”

Characterization of leafy cotyledon1-like during embryogenesis in Theobroma cacao L.

“…For gene expression analyses, zygotic embryos were isolated from pods of clone Sca-6 provided by Cameroonian and Brazilian Institutes, and then separated into two batches: (1) immature, consisting of a mix of stages IIIz, IVz, and Vz respectively 80, 100 and 110 days after pollination as described by Alemanno et al (1997) and (2) mature corresponding to stage VIIIz. Somatic embryos were produced according to a two-step protocol consisting of primary somatic embryogenesis (PSE) induced from staminodes of immature Xower buds, and secondary somatic embryogenesis (SSE) induced from primary somatic embryos.…”

“…Based on this procedure, Weld trials were established to evaluate this new planting material (Figueira and Alemanno 2004). The morphogenetic processes of zygotic and somatic embryogenesis have been described (Alemanno et al 1996(Alemanno et al , 1997Maximova et al 2002). Despite those improvements, the eYciency of the process is not suYcient for a scaling-up step.…”