Embryology of two mycoheterotrophic orchid species, Gastrodia elata and Gastrodia nantoensis: ovule and embryo development

Abstract

Background Gastrodia elata, a famous herbal medicine, has been received great attention on its treatments of headache, vertigo and epilepsy. Gastrodia nantoensis is a newly described species from central Taiwan with potential medicinal value. Gastrodia species are fully mycoheterotrophic orchids, and the courses of their seed development are more rapid as compared to the chlorophyllous orchids. A better understanding of their reproductive biology would provide insights into the propagation and conservation of the mycoheterotrophic orchid species.ResultsBased on the histological and histochemical investigations, we observed some notable features in ovule and embryo development. First, only the archesporial cell and/or megasporocyte are present within their ovaries at the time of anthesis. Second, their suspensors consist of a single cell and their mature embryos consist of a gradient of small to large cells. Nile red staining of a globular embryo reveals the presence of cuticular material in the surface wall of embryo proper and the lateral walls of suspensor cell, indicating that the basal wall of suspensor cell is the major route for nutrient supply from maternal tissues to embryo proper. Third, their seed coats are derived from a single integument, and lignin but not cuticular material is present in the outer most layer of seed coat and persists through seed maturation.ConclusionsThe faster seed development of Gastrodia species is due to the speedy courses of ovule and embryo development. In the mature seeds, the presence of a differentiated apical zone in embryo proper suggests the easy-to-germinate character. This study provides basic knowledge for further molecular studies on embryo development and symbiotic germination of Gastrodia species.

Variation and evolutionary transformation of some characters of the pollinarium and pistil in Epidendroideae (Orchidaceae)

“…In Orchidaceae, non-fertilized flowers have ovules with poorly differentiated tissues (Sagawa and Israel 1964;Zhang and O'Neill 1993;Li et al 2016). This was verified in most of the samples of Epidendroideae studied.…”

First Record of Ategmic Ovules in Orchidaceae Offers New Insights Into Mycoheterotrophic Plants

“…To date, in most species studied, the embryonic sac is bitegmic (Swamy, 1949a; Yeung and Law, 1997; Mayer et al, 2011). However, four unitegmic species, which are all mycoheterotrophic, have been described in previous studies (Abe, 1976; Arekal and Karanth, 1981; Krawczyk et al, 2016; Li et al, 2016).…”

“…Pogoniopsis schenckii is an endemic mycoheterotrophic species found in the Brazilian Atlantic Forest. Prior studies indicate a tendency of reduction in the number of integuments in species of mycoheterotrophic plants, including orchids (Abe, 1976; Arekal and Karanth, 1981; Maas and Ruyters, 1986; Bouman et al, 2002; Endress, 2011; Krawczyk et al, 2016; Li et al, 2016). Thus, our hypothesis is that P. schenckii also exhibits reduction in the number of integuments, leading to a greater exposure of the ovule and simplification of the seed coat involving the embryo, which may facilitate the penetration of fungal hyphae.…”

Gametophyte and embryonic ontogeny: understanding the reproductive calendar of Cypripedium japonicum Thunb. (Cypripedoideae, Orchidaceae), a lady’s slipper orchid endemic to East Asia

“…This failure to form a triploid endosperm is one of the unique features in orchid seed development. In recent years, several studies have been carried out focusing on the embryology of different orchid species [2,[37][38][39][40]. However, little is known about the embryology and reproductive biology of C. japonicum.…”