Early cytological events after induction of cell division in egg cells and zygote development following in vitro fertilization with angiosperm gametes

Abstract

Early events, such as formation of the cell wall, first nuclear division and first unequal division of the zygote, were examined following in vitro fusion of single egg and sperm protoplasts of maize (Zea mays L.). The time course of these events was determined. The formation of cell wall components was observed 30 sec following egg—sperm fusion and proceeded continuously thereafter. Within 15 h after fusion most of the organelles became more densely grouped around the nucleus of the zygote. In the in vitro produced zygote the location of the cell organelles and of the dividing nucleus showed polarity. Two nucleoli were first observed 18 h after gamete fusion. The zygotic nucleus remained undivided for about 40 h. The first cell division was observed 40–60 h, generally 42–46 h, after egg—sperm fusion. The non‐fused egg cell could be triggered to sporophytic development in vitro by pulses of high amounts of 2,4‐D. Without such a treatment, cultured egg cells of different maize lines did not divide. Although nuclear fusion seemed to occur, fusion products of two egg cells also did not divide. Cell wall formation was incomplete and non‐uniform, showing a polarity of cultured egg cells and fusion products of two egg protoplasts. Cell division was also induced after fusion of maize egg with sperms of genetically remote species, such as Coix, Sorghum, Hordeum or Triticum. These gametic heterologous fusion products developed to microcalli. Moreover, cell division occurred in fusion products of an egg and a diploid somatic cell‐suspension protoplast from maize.

Isolation of gametes from <i>Brachypodium distachyon</i>

“…Kranz and Lörz (1993) first developed a complete IVF system using maize gametes and electrical fusion, and, to take advantage of the abundant resources stemming from rice research, a rice IVF system was also established by Uchiumi et al (2007). By the use of these IVF systems, post-fertilization events, such as karyogamy (Faure et al 1993;Ohnishi et al 2014), egg activation and zygotic development (Kranz et al 1995;Nakajima et al 2010;Sato et al 2010), paternal chromatin decondensation in zygote nucleus (Scholten et al 2002), the microtubular architecture in egg cells and zygotes (Hoshino et al 2004), fertilizationinduced/suppressed gene expression (Okamoto et al 2005), epigenetic resetting in early embryos (Jahnke and Scholten 2009), have been successfully observed and investigated.…”

The Role of Auxin, pH, and Stress in the Activation of Embryogenic Cell Division in Leaf Protoplast-Derived Cells of Alfalfa

“…A high concentration of exogenous auxin is needed to maintain the embryogenic nature of most embryogenic monocot cultures (KrishnaRaj and Vasil, 1995). Moreover, 2,4-D treatment could induce zygote development in unfertilized maize (Zea mays) egg cells, emphasizing its role as a general inducer of the embryogenic response (Kranz et al, 1995). However, it is not known how and why 2,4-D is so effective in the induction of embryogenic competence.…”

Endosperm Development after Fusion of Isolated, Single Maize Sperm and Central Cells in Vitro

“…Spermcentral cell fusion occurred rapidly and efficiently. Using spindle-shaped sperm cells was most effective, as had been observed in sperm-egg fusions (Kranz et al, 1995). Spindleshaped sperm cells had been observed during fertilization as early as 1898 (Nawaschin, 1899).…”