Synergids and filiform apparatus in the sexual and apomictic dandelions from section Palustria (Taraxacum, Asteraceae)

Abstract

An evolutionary trend to reduce “unnecessary costs” associated with the sexual reproduction of their amphimictic ancestors, which may result in greater reproductive success, has been observed among the obligatory apomicts. However, in the case of the female gametophyte, knowledge about this trend in apomicts is not sufficient because most of the ultrastructural studies of the female gametophyte have dealt with amphimictic angiosperms. In this paper, we tested the hypothesis that, in contrast to amphimictic plants, synergids in apomictic embryo sacs do not form a filiform apparatus. We compared the synergid structure in two dandelions from sect. Palustria: the amphimictic diploid Taraxacum tenuifolium and the apomictic tetraploid, male-sterile Taraxacum brandenburgicum. Synergids in both species possessed a filiform apparatus. In T. brandenburgicum, both synergids persisted for a long time without any degeneration, in spite of the presence of an embryo and endosperm. We propose that the persistent synergids in apomicts may play a role in the transport of nutrients to the embryo.

Immunodetection of some pectic, arabinogalactan proteins and hemicellulose epitopes in the micropylar transmitting tissue of apomictic dandelions (Taraxacum, Asteraceae, Lactuceae)

“…1a, b), whereas the flowers harvested during anthesis already contained an embryo and endosperm (Fig. 1c, d) as it was previously observed (Płachno et al 2014; Płachno et al 2015a, b).

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“…AGP epitopes were not detected in open but unpollinated flowers of Galanthus ovules (Chudzik et al 2005a, b). In Taraxacum (Płachno et al 2014) as in other Asteraceae (e.g. Helianthus , Newcomb 1973; Yan et al 1991), the thickened adjacent walls of both synergids build the filiform apparatus.…”

“…Preparation of the samples for transmission electron microscopy (TEM) followed the procedure used by Płachno et al (2014). The sections were examined using a Hitachi H500 electron microscope at 75 kV in the Faculty of Biology and Environmental Protection, University of Silesia in Katowice.…”

Deposition of callose in young ovules of two Taraxacum species varying in the mode of reproduction

“…Individual flowers were then isolated and dehydrated for 30 min in 80 %, 90 % (one change), and 100 % ethanol (two changes). After dehydration, flowers were cleared in methyl salicylate using a modified procedure earlier described by Musiał et al ( 2013 ) and Płachno et al ( 2014 ). Samples were incubated in absolute ethanol/methyl salicylate solutions (3:1, 1:1 and 1:3, v/v) and in two changes of pure methyl salicylate (1 h per step).…”

Comparative Anatomy of Ovules in Galinsoga, Solidago and Ratibida (Asteraceae)

“…Special modifications of the ovule tissue (e.g., the occurrence of nutritive tissue) have been recorded in several Asteraceae genera: Helianthus (Newcomb, 1973a), Bellis (Engell and Petersen, 1977), Hieracium (Koltunow et al, 1998), Cynara (Figueiredo et al, 2006), Taraxacum (Cooper and Brink, 1949;Musiał et al, 2013a;Płachno et al, 2014), Chondrilla (Kościńska-Pająk, 2006;Musiał et al, 2013a). It has even been suggested that in Hieracium (Koltunow et al, 1998), Taraxacum (van Baarlen et al, 1999;Musiał et al, 2013a) and Chondrilla (Musiał et al, 2013a;Musiał and Kościńska-Pająk, 2013) modifications of the ovule tissue may have facilitated the evolution of apomixis in these genera.…”