Features of the embryonic development of Dienia ophrydis (Orchidaceae)

Abstract

On example of Dienia ophrydis (J. Köenig) Seidenf (Orchidaceae), we have described a new type of embryogenesis of orchids — Dienia-type, which is differs from Liparis-type learned earlier in the tribe Malaxideae. Embryogenesis of Dienia-type is characterized by 1) the development of a single-celled suspensor formed by cb-derivative, 2) linear arrangement of germ cells in the tetrad stage, 3) the special structure of the embryo in the stages of tetrads and octants (l, lR, m, ci, cb), and 4) the absence of ci and cb cell division. The convergent similarity of embryogenesis of Dienia- and Caryophyllaceae-types is proposed. A number of specific for D. ophrydis structures of embryo sac and embryo, including «petassum», «fitting» and «suspensor coat» are described for the first time. Petassum represents remains of the cell walls of pollen tube, and perhaps of filamentous apparatus of synergids, plugging the micropyle side of the fertilized embryo sac. The only cell of suspensor has a specific appendix («fitting»), that connects it with the embryo itself. There is «suspensor coat» which surrounds the only suspensor cell, including «fitting», but does not extend to the basal cells of the embryo itself.