Developmental switch during embryo sac formation from a bisporic mode to the tetrasporic Fritillaria type in Hyacinthoides vincentina (Hoffmannsegg & Link) Rothm. (Hyacinthaceae)

摘要

Developmental transitions between the major types of embryo sac formation, in which development starts according to one type and continues according to another type, have been reported seldom in the embryological literature. Here we describe in a sample of the rare taxon Hyacinthoides vincentina (a species of the Hyacinthaceae related to H. italica, sometimes considered conspecific with H. inauritanica) a bisporic start of embryo sac development and its tetrasporic continuation according to the Fritillaria type. The decisive events are the postmeiotic dissolution of the cell wall, which had been formed after the first meiotic division, the assumption of a 1+3 position of the spore nuclei in the germinating coenomegaspore, and the formation of a triploid chalazal spindle during the first embryo sac mitosis (Carano-Bambacioni phenomenon). The endosperm is pentaploid. While the bisporic Hyacinthoides type is considered characteristic for the genus Hyacinthoides, the Fritillaria type has not been found in the family hitherto. These observations add one further and particular example to the remarkable diversity of embryo sac types in the family Hyacinthaceae, in which the Polygonum, Allium, and Drusa-I types have been described, in addition to the Hyaeinthoides type.