Fruit maturation and in vitro germination of macaw palm embryos

Acrocomia aculeata (macaw palm) is oil producing palm tree with significant agro-industrial potential. Seed dormancy in palm species may be due to embryo immaturity, which could result from delayed embryogenesis. We evaluated the correspondence between the visual characteristics of maturing fruits and their physiological aspects and the in vitro germination capacity of the embryos. 11 fruit bunches in different stages of maturity were collected and classified in terms of the degree of maturation of the endosperm, the color of the exocarp, and the occurrence of abscission. The water and oil contents of the mesocarp and seed were determined, and lipids and proteins were identified through histochemical analyses of the mesocarp, endosperm, and embryo. The embryos from each fruit bunch were cultivated in vitro in 75% Murashige and Skoog (1962) media with added organic compounds. The water contents of the seeds varied from 71.2 to 21.1% among the different stages of fruit ripening and were related to the visual markers of fruit maturation (exocarp color ranging from dark green to brown). Lipid accumulation in the mesocarp occurred later than in the endosperm, and only occurred in fruits from bunches showing signs of abscission. Embryos from bunches in different stages of maturation showed similar germinative capacities, as well as similar patterns of lipid and protein storage. Embryogenesis in A. aculeata is precocious, and the embryos of immature fruits can be utilized for in vitro cultivation.Keywords: Acrocomia aculeata, embryo culture, embryogenesis, water content, oil contentAfrican Journal of Biotechnology Vol. 12(5), pp. 446-45

Pericarp development in the macaw palm Acrocomia aculeata (Arecaceae)

The anatomy of the pericarp of the macaw palm (Acrocomia aculeata) was followed during development. Ovaries of flowers collected at anthesis of the bracts as well as pericarps were evaluated at different development phases using traditional plant anatomy techniques. The ovary wall has two meristematic regions, one adjacent to the external epidermis and the other surrounding the seminal cavity. The external meristematic region gives rise to the woody exocarp, and the internal meristematic region is responsible for thickening of the oily/fibrous mesocarp as well as the hard endocarp. Sclerification of the exocarp and endocarp occurs approximately 70 days after anthesis and defines the final fruit volume. Lignification of the exocarp cell layers is incomplete, lending porosity to the structure. Numerous canals develop in the mesocarp that are formed by the fusion of raphide-containing idioblasts. Lignification of the sclereids and their generally random arrangement confers impermeability and rigidity to the endocarp. In mature fruits, lipidic reserves are observed in parenchymatic cells of the mesocarp, and the germination pore in the endocarp is composed of parenchymatic cells

Histological study of micrografting in passionfruit

Micrografting, used to eliminate viruses, involves the utilization of very small grafts, and detailed structural analyses of the micrografting region in different phases are presented here. Shoot tips with 2–3 leaf primordia, and 600–800 µm in length, were grafted to the hypocotyl of 21–28 day-old rootstock seedlings, and their development was followed for 30 days using scanning electron and visible light microscopy. The success of micrografting was found to depend on the preservation of the vascular tissue of the rootstock and the placement of the scion adjacent to the rootstock phloem. Callus formation, which initiates approximately 3 days after micrografting (DAM) through the proliferation of parenchymatous cells of the rootstock cortex, fills the space left by the incision and guarantees adherence and nutrition for the scion during the initial phases of development. At seven DAM, connective cells that develop at the base of the scion produce a junction with the callus. At 10 DAM, differentiation of procambial strands and parenchymatous cells initiates in the callus. At 15 DAM, parenchymatous cells derived from the callus give rise to procambial strands and initiate the differentiation of tracheal elements and the epidermis in the junction region. Vascular connections are established at 20 DAM, promoting the accelerated development of the scion, which, at 30 DAM, shows shoot development. The developmental phases of micrografting in passionfruit plants therefore include: placement of the scion; callus formation by the rootstock; cellular connections; differentiation of the callus; vascular connection; and shoot development