Cell Determination During Embryogenesis in Citrus jambhiri. I. Ontogeny of the Epidermis

Epidermal features are present in the embryo of the rough lemon, Citrus jambhiri, from the zygotic stage. The zygote, or nucellar progenitor in adventive embryos, is cuticularized. As derivatives are cut off to the inside of the periphery, they gradually diverge ultrastructurally in plastid structure and wall characteristics from the protodermal cells. Periclinal divisions continue in the surface cells of the root-hypocotyl axis until the heart-shaped stage, at which point cell divisions become confined to the anticlinal plane. We propose that the zygote and all subsequent surface derivatives are epidermal in nature, while internal derivatives diverge from epidermal to form the ground and vascular systems. The presence of cuticle and restriction of cell division to the anticlinal plane in the outer tunica of the shoot apical meristem support the conclusion that this layer is a previously formed epidermis.