Structural evaluations of zygotic embryos and seedlings of the macaw palm (Acrocomia aculeata, Arecaceae) during in vitro germination

Abstract

Acrocomia aculeata is an oil producing tropical palm tree with exceptional potential for producing biofuel.As the propagation of this species is often difficult because of its pronounced seed dormancy, the present work examined the morphology and the anatomy of zygotic embryos and seedlings during in vitro germination. Embryos were put in MS media supplemented with organic compounds and cultivated in the dark at 30°C for 20 days. The dry weights, lengths, and diameters of the cotyledonary petioles, haustoria, roots, ligules, and leaf sheaths of embryos obtained from mature seeds and seedlings removed from culture were measured every 2 days; anatomical and histochemical evaluations were performed on embryos and seedlings removed from culture after 2, 5, 8, 10, 12, and 15 days. Elongation of the embryo axis was observed to initiate after 2 days. Elongation of the cotyledonary petiole was observed starting on the fifth day; this is a morphological indication of germination that is associated with the formation of starch and raphides as well as the differentiation of tracheary elements. The growth of the cotyledon is due to increases in cell volumes as well as the development of a meristematic band peripheral to the haustorium. In spite of the fact that the radicle is less differentiated than the plumule, radicular development is precocious and the root emerges first, indicating the absence of morphological dormancy. Atrophy of the haustorium and the accumulation of phenolic compounds in subepidermal cell layers occur due to culturing conditions.

Embryonic dormancy in seeds of Bactris gasipaes Kunth (peach-palm)

“…In vitro zygotic embryo culture has been used as an alternative for swift propagation, and among other applications, the method has been used to investigate dormancy caused by embryo immaturity or by the presence of germination inhibitors in the endosperm, in order to study the nutritional and physiologic aspects of embryonic development (Anjun, 2014;Medeiros et al, 2015). Thus, palm embryo culture allows for the assessment of seed physiology, development, and germination (Ribeiro et al, 2012).…”

Somatic embryogenesis in Acrocomia aculeata Jacq. (Lodd.) ex Mart using the thin cell layer technique

“…Presently the production of A. aculeata is primarily extractive and its propagation done with seeds, which exhibit dormancy and experience a low germination rate (Lorenzi 2006;Ribeiro et al 2012), although Motoike et al (2007) developed a method that raised the germination rate to 60-80%. For large-scale commercial use of A. aculeata it is necessary to develop a technique for the clonal propagation in order to establish a uniform cultivation system.…”

Tissue‐specific hormonal profiling during dormancy release in macaw palm seeds

“…The family Arecaceae demonstrates morphological dormancy associated with embryo immaturity (Baskin and Baskin , Orozco‐Segovia et al , Perez et al ). Recent work with macaw palm seeds (Ribeiro et al , , ) and other palms species from Cerrado biome (Neves et al , Magalhães et al , Oliveira et al ), has however demonstrated that their dormancy is of the physiological non‐profound type ( sensu Baskin and Baskin ) and is related to the incapacity of the embryo to overcome the resistance of the operculum (a structure formed by the opercular tegument and micropylar endosperm). While physiological dormancy is known to be strongly controlled by alterations in the hormonal profile of seeds (Kucera et al , Nonogaki et al ), studies on this issue in palms have been restricted to a single study in Elaeis guineensis Jacq.…”