Embryology of Anoectochilus roxburghii: seed and embryo development

BACKGROUND: Anoectochilus roxburghii is known for its medicinal properties, culinary interests, and ornamental applications in Asian countries. Recent studies focus mainly on its phytochemical properties and little is known about its reproductive biology, especially seed and embryo development. This study documents the major developmental events in seed and embryo development of A. roxburghii upon pollination. RESULTS: Morphological and histological studies revealed that upon pollination embryo and seed development is completed in 40 days. Ovular primordia are at the megaspore mother cell stage at the time of anthesis. Embryo development proceeds after a successful fertilization. A. roxburghii has a single cell suspensor. It elongates but not extended beyond the seed coat. A distinct cell gradient is present within the embryo proper with smaller cells located towards the chalazal end of the seed. Proteins and lipids are the major storage products within the embryo proper cells. At the stage of early globular embryo, the inner seed coat has degenerated and thus a carapace is absent at maturity. A limited deposition of lignin is detected in the mature seed coat. CONCLUSIONS: The seed of A. roxburghii matures rapidly. At maturity, the embryo proper has a well-differentiated apical zone with little constraints impose by the seed coat. These characters indicate adaptations to fast germination that may ensure a successful colonization in the shaded forest understory. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s40529-019-0254-1) contains supplementary material, which is available to authorized users.