Embryological features of early development of zygotic embryo and endosperm in Senecio scandens (Compositae)

Senecio scandens Buch. -Ham.ex D.Don (Compositae) plays a crucial antibacterial role in Chinese traditional medicines. Here, we characterized the development of the zygotic embryo and endosperm of this species to obtain basic knowledge regarding its cytological mechanism and practical breeding application. Based on chronological description of the embryogenesis events, the oblique first division in the zygote indicated that the origin of the apico-basal polarity of zygotic embryo development was established by the polar ovule. We deduced, therefore, that cell differentiation was attributable to an unevenly spaced distribution of cytoplasm in the zygotic embryo, where the ovule polarity impinged on the polar orientation of the embryo sac, egg cell, and thereby zygotic embryo. The recognizable developmental structure appeared at the torpedo stage, suggesting that tissue differentiation could be related to the signal substance throughout the outer and inner cells. Moreover, endosperm development followed the nuclear type model, resulting from the initial endosperm nuclei repeatedly dividing without cell wall formation. These representative morphological features of embryo development will be useful for further studies on functional genes, in vitro fertilization, and haploid plant production in this species.