The ultrastructure of somatic embryo development in pearl millet (Pennisetum glaucum; Poaceae)

Abstract

The ultrastructure, morphology, and histology of somatic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and electron microscopic techniques. Somatic embryogenesis was initiated from zygotic embryo explants cultured =8 d after pollination. Formation of a ridge of tissue began 3--4 d after culture (DAC) by divisions in the epidermal and subepidermal cells of the scutellum. Ridge formation was accompanied by a decrease in vacuoles, lipid bodies, and cell size, and an increase in endoplasmic reticulum (ER). Proembryonic cell masses (proembryoids) formed from the scutellar ridge by 10 DAC. Proembryoid cells had abundant Golgi bodies and ER while the amounts of lipids and starch varied. Somatic embryos developed from the proembryonic masses 13 DAC and by 21 DAC had all the parts of mature zygotic embryos. Although shoot and root primordia of somatic embryos were always less differentiated than those of zygotic embryos, scutellar cells of somatic and zygotic embryos had similar amounts of lipids, vacuoles, and starch. Somatic scutellar epidermal cells were more vacuolated than their zygotic counterparts. In contrast, somatic scutellar nodal cells were smaller and not as vacuolated as in zygotic embryos. Somatic embryogenesis was characterized by three phases of cell development: first, scutellar cell dedifferentiation with a reduction in lipids and cell and vacuole size; second, proembryoid formation with high levels of ER; and third, the development of somatic embryos that were functionally and morphologically similar to zygotic embryos.

Explant type and stress treatment determine the uni- and multicellular origin of somatic embryos in the tree fern Cyathea delgadii Sternb.

“…Its cells require minor gene reprogramming and hence, direct SE can be readily induced from these (Merkle et al 1995;Karami et al 2009). The initiation of SE can occur simultaneously along unicellular and multicellular pathways on the same explant, as it was demonstrated for zygotic embryo cultures of white clover (Maheswaran and Williams 1985), pearl millet (Taylor and Vasil 1996) and pineapple guava . Alternatively, both pathways of SE can be induced independently of each other by using various types of initial explants (Choi et al 1998;Maximova et al 2002) or plant growth regulators (PGRs) (Lee et al 1990;Choi and Soh 1995;de Almeida et al 2012).…”

“…In this process, somatic embryos may develop directly from cells of explant, or indirectly with an intermediate callus phase (Williams and Maheswaran 1986). In direct SE, depending on the relationship between neighbouring cells within the explant, the embryos are able to initiate from a single cell (Choi et al 1998;Mikuła et al 2015b) or groups of competent cells (Choi and Soh 1995;Taylor and Vasil 1996;Choi et al 1998;Puigderrajols et al 2001;Corredoira et al 2006). Although SE has been successfully achieved in numerous species of seed plants, only a few published reports describe this phenomenon in monilophytes, and all these studies were performed on the tree fern Cyathea delgadii Sternb.…”

EMBRIOGENESIS SOMATIK ANGGREK BULAN Phalaenopsis amabilis (L.) Bl: STRUKTUR DAN POLA PERKEMBANGAN

“…), dan adanya butir-bitir tepung (panah) (Gambar 2.B. ), di mana ciri-ciri sel demikian ini dimiliki oleh sel-sel embriogenik atau meristematik (Taylor dan Vasil, 1996) serta memiliki regenerasi yang tinggi. Pola perkembangan seperti ini dilaporkan juga terjadi pada Saccharum officinarum (Ho dan Vasil, 1983dalam Toonen dan de Vries, 1996.…”