Abscisic Acid and the Maturation of Cacao Embryos in Vitro

Abstract

Abscisic acid (ABA) was tested for its ability to affect development of immature zygotic embryos of cacao (Theobroma cacao) in vitro, by adding exogenous ABA, fluridone, or mefluidide to cultured embryos. Endogenous ABA levels, measured by enzyme-linked immunosorbent assay, were increased by exogenous ABA or by culture on sucrose increasing to 21%, and were decreased by fluridone and, to a lesser extent, by mefluidide. The effects of these on maturation were measured as effects on anthocyanins, lipids, and fatty acid saturation, all of which increase with maturation of the cacao embryo. Maturation was stimulated by increasing sucrose and, to a lesser degree, the addition of ABA, but decreasing endogenous ABA by treating with flundone significantly inhibited all maturation parameters. Although desiccation tolerance does not develop in cacao embryos, these results suggest that ABA and sucrose are both needed for the initiation of events associated with maturation in vitro.Many species from moist tropical habitats, including the commercially important tree, cacao, produce seeds that lack dormancy and are recalcitrant (desiccation sensitive). Such seeds are thus unsuitable for long-term storage using conventional seed storage techniques (8). With species of economic interest like cacao, this characteristic also poses problems for the transport of seeds during germplasm collection from wild species.Studies with orthodox (desiccation tolerant) seeds have suggested the involvement of the growth regulator ABA in the development ofdesiccation tolerance. Mutants and chemically treated plants with reduced levels of ABA or reduced sensitivity to ABA produce seeds exhibiting vivipary, reduced dormancy, or reduced tolerance to desiccation (5,9,22). ABA added to immature somatic embryos has been shown to promote the development of desiccation tolerance in several orthodox species (6, 25). In addition, several studies of orthodox species have shown that the highest endogenous levels of ABA in zygotic embryos occur midway through embryonic development (21), shortly preceding the onset of desiccation tolerance. Developing embryos of cacao, however, also undergo a similar increase in ABA before maturation, but do not develop desiccation tolerance (18).' These studies were supported in part by a grant from the Hershey Foods Corporation.In orthodox species, this increase in ABA has been shown to stimulate other embryo or seed maturation events, including the synthesis of anthocyanins (26) and storage lipids (3, 7). In light of this, developing embryos of cacao were examined for their sensitivity to exogenously applied ABA in vitro. The effects on the maturation of immature cacao embryos were determined using the accumulation of cotyledonary anthocyanins, lipids, and increases in lipid saturation as indicators of maturation (10). Endogenous ABA levels were also measured in both cotyledons and axes. For comparison, embryos were also cultured on media containing an increasing concentration of sucrose, which has been shown to tr...

Developmental Changes in Endogenous Abscisic Acid Concentrations and Asymbiotic Seed Germination of a Terrestrial Orchid, Calanthe tricarinata Lindl.

“…Coincidently, the ABA concentration was relatively low. ABA is an effective inhibitor of germination in immature wheat (Triticum aestivum L.) grain (Walker-Simmons, 1987), cacao (Theobroma cacao L.) embryos (Pence, 1992), and rape (Brassica rapa L.) seed (Finkelstein and Crouch, 1986). In orchids, it has been suggested that high concentrations of ABA occur in seeds that are difficult to germinate such as E. helleborine (Van der Kinderen, 1987).…”

Effect of abscisic acid, osmolarity and temperature onin vitro development of recalcitrant mango nucellar embryos

“…Etienne et al (1993) observed that germination of recalcitrant somatic embryos of Hevea brasiliensis (rubber) was promoted by high concentrations of sucrose and ABA (100-1000 #M) in the plant growth medium, and that these somatic embryos acquired a degree of desiccation tolerance similar to that reported with orthodox embryos (Carman, 1988;Welbaum et al, 1990). Pence (1992) demonstrated that endogenous ABA levels in maturing cacao embryos corresponded with increased production of lipids and fatty acid saturation. She also noted that moisture levels drop from 90% in prematuration embryos to 30% in mature cacao embryos, but that the embryos lack desiccation tolerance.…”

Abscisic acid and sucrose increase the protein content in date palm somatic embryos, causing changes in 2-DE profile

“…ABA has also been shown to regulate the amount of storage lipids in zygotic (Finkelstein and Somerville, 1989) as well as somatic (Kim and Janick, 1991) embryos. In cacao ZE, the effects of ABA and high sucrose are qualitatively similar, both increasing the amount of storage lipids (Pence, 1992). Both ABA and osmoticum are known to promote synthesis of a number of proteins in developing embryos (Skriver and Mundy, 1990), including storage protein.…”