Embryology of a Lady’s Slipper Orchid, Paphiopedilum spicerianum and Cytokinin Requirements for Seed Germination and Protocorm Development

Abstract

In this study, we document the primary structural changes that occur during the seed development of Paphiopedilum spicerianum (Rchb.f.) Pfitzer, an endangered species with high horticultural value. Within a defined timeline, our results offer insights into the connection between these structural changes in seeds and their germination percentage. The optimum germination was recorded for immature seeds collected at 180 to 210 days after pollination (DAP), during which the embryos are in the late globular stage and the suspensor begins to degenerate. As seeds continued to mature by 240 DAP, there was a gradual decline in germination. Histochemical staining of mature seeds reveals that only the inner seedcoat and the surface of the embryo exhibit positive reactions to the Nile red stain, suggesting a relatively weak coat-imposed dormancy. This weaker dormancy may contribute to the higher germination observed in mature seeds of P. spicerianum compared with other challenging-to-germinate species. Of the cytokinins examined, 6-(γ,γ-dimethylallylamino)purine (2iP), kinetin (KN), and 6-benzylaminopurine (BA) exhibited a stimulating effect on germination, concurrently enhancing the formation of amorphous protocorms.