‘Dust seeds’ with undifferentiated embryos and their germination in mycoheterotrophic Monotropoideae (Ericaceae)

Abstract

‘Dust seeds’ with an undifferentiated (organless) embryo are known to be produced by mycoheterotrophic species (MH) in nine families of angiosperms. However, aside from the numerous studies on seed germination of orchids, relatively little is known about germination in MH families. In the Ericaceae, some degree of mycoheterotrophy (full, partial or initial) and dust seeds with an undifferentiated embryo occur in all species in the three tribes of Monotropoideae, the only subfamily of Ericaceae with this combination of characters. In most species, the seed is <0.90 mm in the greatest dimension, the endosperm is absent (Pityopus) or consists of few to many (30–40) cells, and the embryo is minute, consisting of as few as two cells in Monotropa. Germination in Monotropoideae is monopolar, with only the radicular pole of the embryo participating in germination. Thus, germination polarity differs from that of the dust seeds of orchids in which only the plumular pole of the embryo (protocorm) participates in germination. The dust seeds in Monotropoideae require the presence of fungi, either direct contact with a fungus or the presence of a diffusible substance therefrom, to germinate (symbiotic germination). Recently, representatives of the four genera of tribe Pyroleae have been successfully germinated asymbiotically in vitro. We present a broad overview of dust-size seeds in angiosperms and conclude that they should be subdivided into at least two major categories.

Symbiotic germination and development of fully mycoheterotrophic plants convergently targeting similar Glomeraceae taxa

“…Little is known about germination in AM mycoheterotrophic plants (Baskin and Baskin, 2020), although decades ago, Leake (1994) stated that further research is required to determine the role of fungi and environmental conditions that are necessary for seed germination of mycoheterotrophic species. To the best of our knowledge, this is the first study to identify fungal identities at the seedling stage in AM fully mycoheterotrophic plants.…”

“…Plants have developed various strategies to ensure seed germination and seedling survival (Hoyle et al ., 2015); dust seed production is arguably one of the most intriguing of these strategies (Eriksson and Kainulainen, 2011; Hynson et al ., 2013a). Owing to their limited carbohydrate reserves, dust seeds with a minute undifferentiated embryo depend on external carbon sources to support their germination (Baskin and Baskin, 2020).…”

Effects of fungicide treatments on mycorrhizal communities and carbon acquisition in mixotrophic plants, Pyrola japonica (Ericaceae)

“…However, Py. japonica produces minute-sized dust seeds with a limited endosperm (Takahashi 1993) as with, similar to other pyroloids (Johansson et al 2014;Baskin and Baskin 2021) and we used only seed fractions devoid of capsules. During the fruiting season, mycorrhizal formation of Py.…”