Female gametophyte development in Eleocharis sellowiana (CYPERACEAE): a species with atypical nuclear staining and polarity of the megaspore mother cell

Abstract

Megasporogenesis begins when one cell arising from the hypodermis of the nucellus differentiates into a megaspore mother cell. This cell undergoes meiosis, giving rise to a tetrad of megaspores, whose functional megaspore originates the megagametophyte. Representatives of the family Cyperaceae draw attention because both micro-and megasporogenesis culminate in the selection of a functional cell and the loss of the other three by programmed cell death after meiosis. We investigated in a more detailed manner the megasporogenesis and megagametogenesis in Eleocharis sellowiana Kunth using structural and ultrastructural tools. Although the megagametophyte of E. sellowiana is of the Polygonum type, we found some new features related to the megaspore mother cell, such as (1) absence of nuclear staining when exposed to toluidine blue and (2) presence of plastids and nucleus located at the micropilar pole, instead of the central region to the chalazal pole, as found in the literature for the Polygonum type. This opposite polarity could indicate that the cytoplasmic orientation in the megasporocyte is not a decisive event in the selection of the functional meiotic product for Polygonum type development.

Ultrastructural and cytochemical aspects of female gametophyte development in Sedum hispanicum L. (Crassulaceae)

“…Furthermore, these observations also point to the possibility that asymmetric distribution of organelles is not maintained during the first meiotic division in S. hispanicum . The megaspore mother cell is characterized by a polar distribution of organelles (Tung et al 1999 ; Bajon et al 1999 ; Rocha et al 2015 ), which is not contradicted by observations made during this study. However, it is not confirmed whether polarity is mentioned during the first and the second meiotic divisions (Yang 2006 ).…”

“…However, the megasporocyte stands out against the neighboring cells with a dense cytoplasm, in which small vacuoles and an elongated nucleus are present. At this stage, in other species of angiosperms, the following have been observed in various studies: bean-shaped nucleus, which after treatment with toluidine blue does not stain in Eleocharis sellowiana (Rocha et al 2015 ); nucleus, which changes its position during maturation of megasporocyte in Glycine max (Kennell and Horner 1985 ); and Cymbidium sinense (Tung et al 1999 ). The nucleus of the megaspore mother cell is always very conspicuous (Bajon et al 1999 ; Papini et al 2011 ; Mendes et al 2014 ).…”

“…Polarization, where organelles are mostly positioned at the chalazal end of the megaspore mother cell, contribute to the fact that the chalazal functional megaspore received a significant part of the organelles (Stewart and Gifford 1967 ; Webb and Gunning 1990 ; Reiser and Fischer 1993 ). However, in Eleocharis sellowiana , the opposite polarity of the megaspore mother cell in comparison with the most common pattern described for the Polygonum -type is not an obstacle for the choice of the functional meiotic product (Rocha et al 2015 ). The mechanisms involved in the determination of the functional megaspore have not been fully understood (Russell 2001 ; Qiu et al 2008 ; Drews and Koltunow 2011 ).…”

“…However, ephemeral antipodes are also present in many other angiosperms, such as Amaranthus hypochondriacus (Coimbra and Salema 1999 ), P. caerulea (Garcia et al 2003), Cytisus multiflorus , and Cytisus striatus (Rodríguez-Riaño et al 2006 ). By-products of its degeneration can be used by the gametophyte (Yang 2006 ; Rocha et al 2015 ). Degeneration of the S. hispanicum antipodes takes place quickly, which is similar to what has been observed in A. hypochondriacus .…”

Are unusual ultrastructural features occurring in the pollen endomembrane system of Cyperaceae and other angiosperms?

“…Commonly, the ER is present near the nucleus because this organelle organizes the nuclear envelope. However, in Cyperaceae vegetative pollen cells, the ER presents some unusual configurations, such as the concentric ER networks, which are reported during microspore and pseudomonad development, as well as in megaspore mother cells in sedges (Mepham & Lane, 1970; Rocha, Andrade, & Vanzela, 2015; San Martin et al, 2013). The appearance of this structure can represent many processes, one of each is the cytoplasm turnover from sporophytic to gametophytic generations (Bhandari, 1984; Knox, 1984).…”