Epidermal Cell Wall Biogenesis with Emphasis on Cuticular Layer Formation during Direct Somatic Embryogenesis in Rice

Abstract

Epidermal cell wall biogenesis with emphasis on cuticular layer formation during direct somatic embryogenesis in rice was examined by transmission electron microscopy. The first phenomenon noticed in the early globular stage of somatic embryos was a high activity of cell wall formation. In this stage, many endoplasmic reticula, Golgi bodies and their vesicles were present and epidermal cells were covered by fibrillar material. Cutin was initially deposited on the epidermal cell wall of late globular or early elongate stage embryos. In the late elongate stage, a lamellated cuticular layer formed, and in the late scutellar stage, a more homogenous continuous cuticular layer formed. The cuticular layer disappeared gradually from the scutellum cell wall as the somatic embryo germinated. The disappearance of the cuticular layer was similar to that of the zygotic embryo. There is no cuticular layer on the scutellar epithelial cell wall of the immature zygotic embryo 5 days after germination. Our observations lead to the conclusion that one of the structural and physiological markers of direct somatic embryogenesis is the transformation of fibrillar material into the cuticular layer.