Female gametophyte development and double fertilization in Balsas teosinte, Zea mays subsp. parviglumis (Poaceae)

Abstract

Over the course of maize evolution, domestication played a major role in the structural transition of the vegetative and reproductive characteristics that distinguish it from its closest wild relative, Zea mays subsp. parviglumis (Balsas teosinte). Little is known, however, about impacts of the domestication process on the cellular features of the female gametophyte and the subsequent reproductive events after fertilization, even though they are essential components of plant sexual reproduction. In this study, we investigated the developmental and cellular features of the Balsas teosinte female gametophyte and early developing seed in order to unravel the key structural and evolutionary transitions of the reproductive process associated with the domestication of the ancestor of maize. Our results show that the female gametophyte of Balsas teosinte is a variation of the Polygonum type with proliferative antipodal cells and is similar to that of maize. The fertilization process of Balsas teosinte also is basically similar to domesticated maize. In contrast to maize, many events associated with the development of the embryo and endosperm appear to be initiated earlier in Balsas teosinte. Our study suggests that the pattern of female gametophyte development with antipodal proliferation is common among species and subspecies of Zea and evolved before maize domestication. In addition, we propose that the relatively longer duration of the free nuclear endosperm phase in maize is correlated with the development of a larger fruit (kernel or caryopsis) and with a bigger endosperm compared with Balsas teosinte.

Flowering Plants. Monocots

“…At Meiosis II, the chalazal cell divides in a plane crosswise to the long axis of the developing megagametophyte, whereas the micropylar cell may divide either crosswise or longitudinally. These divisions result in a linear (Bhanwra et al 1991;Wu et al 2011) or T-shaped tetrad of megaspores Stover 1937), respectively. Variation in tetrad pattern is reported within a single species (Aulbach-Smith and Herr, Jr. 1984), suggesting that the pattern is not of phylogenetic significance and may in fact be random.…”

“…The megagametophyte is monosporic and develops from the chalazal megaspore ( Evans and Grossniklaus 2009;Stover 1937;Wu et al 2011). In most species, the megagametophyte is of the Polygonum-type, with three mitoses followed by cellularization leading to seven cells; the central cell contains two nuclei.…”

“…In most species, the megagametophyte is of the Polygonum-type, with three mitoses followed by cellularization leading to seven cells; the central cell contains two nuclei. In most grasses, the antipodal cells continue to divide after cellularization, although the number of extra divisions varies (Anton and Cocucci 1984;Evans and Grossniklaus 2009;Shadowsky 1926;Stover 1937;Wu et al 2011);Yamaura (1933) reports as many as 300 antipodals in Sasa paniculata, although only 16 are shown in the figure. Proliferation of the antipodals is not unique to Poaceae.…”

Analysis of proliferation and survival of agrobacteria after inoculation of maize pistil filaments

“…Depending on the sort and line, the growth rate of a maize pollen tube in vivo may reach 6 to 12.5 mm/h (Wu et al, 2011;Williams, 2008). Sperm cells in the pollen tube are capable of proper motion, which under in vitro conditions was estimated as 2.5 mm/h (Kliwer and Dresselhaus, 2010).…”

“…Sperm cells in the pollen tube are capable of proper motion, which under in vitro conditions was estimated as 2.5 mm/h (Kliwer and Dresselhaus, 2010). Assuming the minimal rate of pollen tube movement in maize pistil filaments of 6.0-6.5 mm/h (Wu et al, 2011;Williams, 2008), pistil filaments/agrobacteria can theoretically arrive to zone B after 1.5-21 h and to zone C after 21-32 h.…”