The Developmental Anatomy and Ultrastructure of Somatic Embryos from Rice (Oryza sativa L.) Scutellum Epithelial Cells

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Abstract
The ontogeny of somatic embryos from tissue cultures of mature caryopses of rice is described. Somatic embryos arose directly from cells of the scutellum epithelium, preferentially in the basal part of the scutellum. The initial event in somatic embryogenesis was a periclinal division in scutellar epithelial cells between 48 h and 60 h of plating. The resultant basal and terminal cells gave rise to the suspensor and embryo, respectively. The terminal cell underwent a series of random divisions and became a globular embryo. The scutellum was initiated and overtopped the shoot apex, which developed in a lateral notch. The coleoptile arose from a rim of tissue surrounding the shoot apex while the root apex differentiated internal to the coleorhiza. At maturity, a rice somatic embryo closely resembles a zygotic embryo, complete with a scutellum epithelium, which is a source of secondary somatic embryos on further subculturing.