Ontogenesis, Differentiation and Precocious Germination in Anther-derived Somatic Embryos of Grapevine ( Vitis viniferaL.): Embryonic Organogenesis

Abstract

Somatic embryos of Vitis viniferaL. ‘Grenache noir’ develop abnormally and form viable plantlets at very low frequencies. They grow continuously and, after the torpedo stage, they form giant structures which do not undergo further organogenesis. Morphological, histological and cytochemical data were used to study development from the globular to the giant-embryo stage. Histological organization of somatic embryos until the torpedo stage was similar to that of zygotic embryos. Somatic embryos formed bipolar axes, which differentiated precociously and simultaneously a root and a shoot meristem. However, they differed from their zygotic homologues by forming a cotyledonary crown or multiple cotyledons and by their rapid cellular differentiation. At the end of the torpedo stage and up to the giant-embryo stage, somatic embryos underwent some characteristic events of germination: the radical grew, tannins accumulated, and protodermal cells suberized. However the shoot apex was rapidly disorganized and disappeared. This peculiar behaviour is discussed in comparison with the phenomenon of precocious germination often observed for immature zygotic embryos in in vitroculture.