Embryonic development and seed coat ultrasculpture of orchids Crepidium acuminatum, Crepidium taurinum, and Dienia ophrydis from the subtribe Malaxidinae (Orchidaceae)
摘要
A comparative analysis of the embryonic development and the ultrasculpture of the seed coat of orchids Crepidium acuminatum, C. taurinum, and Dienia ophrydis from the subtribe Malaxidinae (Orchidaceae) was carried out. Ovules and mature seeds from greenhouse-grown plants were examined using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The ovules were found to be tenuinucellate, while the embryo sacs had four to six nuclei and developed according to a modified Polygonum-type pattern. The embryos of the studied species differ in the shape of the suspensor and the transmission structure between the suspensor and the embryo proper. In D. ophrydis, the suspensor is rounded with a neck, and the transmission structure is unicellular, elongated, and truncate-conical. In C. acuminatum, the suspensor is rounded with a neck, and the transmission structure is 2-celled, with a total length practically equal to that of the unicellular transmission structure of D. ophrydis. In C. taurinum, the suspensor is branched, and the transmission structure is unicellular and truncate-conical. The seeds of D. ophrydis and C. acuminatum belong to one morphological variant of the Eulophia-type, characterized by a spindle shape with a narrow chalazal end and transverse secondary thickenings. The seeds of C. taurinum belong to a different morphological variant of the Eulophia-type, exhibiting a club-shaped morphology with a rounded end and concentric or grooved secondary thickenings. Thus, the distinctive features of the seed coat and embryo development in C. acuminatum, D. ophrydis, and C. taurinum have been revealed. These morphological features can be used for taxonomic purposes, supporting the molecular phylogenetic data on the division of the studied representatives of the Malaxidinae subtribe into distinct subclades.