ONTOGENY, DIFFERENTIATION AND PRECOCIOUS GERMINATION IN ANTHER-DERIVED SOMATIC EMBRYOS OF GRAPEVINE (VITIS-VINIFERA L) - EMBRYONIC ORGANOGENESIS

Somatic embryos of Mis vinifera L. 'Grenache noir' develop abnormally and form viable plantlets at very low frequencies. They grow continuou sly and, after the torpedo stage, they form giant structures which do not undergo further organogenesis. Morphological, histological and cyt ochemical data were used to study development from the globular to the giant-embryo stage. Histological organization of somatic embryos unti l the torpedo stage was similar to that of zygotic embryos. Somatic em bryos formed bipolar axes, which differentiated precociously and simul taneously a root and a shoot meristem. However, they differed from the ir zygotic homologues by forming a cotyledonary crown or multiple coty ledons and by their rapid cellular differentiation. At the end of the torpedo stage and up to the giant-embryo stage, somatic embryos underw ent some characteristic events of germination: the radical grew, tanni ns accumulated, and protodermal cells suberized. However the shoot ape x 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 vitro culture. (C) 1996 Annals of Botany Company