Relationship between double fertilization and the cell cycle in male and female gametes of tobacco

Abstract

Nuclear DNA content of male and female gametes of tobacco was determined using 4',6-diamindino-2-phenylindole and quantitative microfluorimetry. Pollen grains are released with generative cells containing 2C DNA. Mitotic division occurs in the pollen tube 8-12 h after germination. The resulting sperm cells have 1C DNA content during pollen tube elongation in the style. Sperm cells deposited in the degenerated synergid have a DNA content between 1C and 2C, indicating that sperm are in S-phase in the synergid. Concomitant with pollen tube arrival, the egg cell increases in DNA quantity from 1C to between 1C and 2C at 48 h after pollination. In the absence of pollination, S-phase in the egg cell is delayed by up to 36 h. Newly formed zygotes contain nuclear DNA concentrations of 4C at karyogamy and remain at 4C until zygote division. Tobacco displays cell fusion after the completion of S-phase, apparently during G(2). Failure to achieve an optimized system for in vitro fertilization in Nicotiana may reflect the challenges of achieving cell cycle synchrony in gametes isolated from pollen tubes. Receptive gametes are presumably those that pass through the protracted S-phase, reaching G(2) receptivity and cell cycle congruity before fusion

Florogenesis and Female Gametophyte Development in <i>Allium cepa</i> L. cv. Krishnapuram

“…In addition to that, the close contact of the egg apparatus with the micropyle is highly similar to what was observed in the ovular apparatus of Ornithogalum caudatum [33]. Moreover, as observed in many other angiosperms, the egg cell possesses a highly dense nucleus placed towards the chalazal extreme of the embryo sac [34].…”

Endosperm: an integrator of seed growth and development

“…The simplest assumption derived from the cell cycle phase of the male gamete is that female gametes also reach the G 2 phase, matching the cell cycle stage of sperm cells. This assumption was recently supported by measurements of DNA content in tobacco gametes [8].…”

“…In Arabidopsis, direct measurements of DNA content suggest that sperm cells enter a new S-phase after PMII, which is presumably completed either before or during pollen tube growth [6,7]. Thus, when delivered to the embryo sac, sperm cells are likely to be in G 2 phase [8]. Further evidence of a fusion at G 2 phase comes from a mutant in the Arabidopsis cyclindependent kinase gene CDKA;1, which encodes a homolog of the yeast cdc2a kinase.…”

Relationship between Nuclear DNA-Content of Sperm Cells and the Timing of Events in the Cell Cycle of Brassica campestris L. (Brassicaceae)

“…Friedman 4 later examined the nuclear DNAcontent of sperm cells in Arabidopsis thaliana and determined that two newly formed sperm cells synthesized nuclear DNA-content within pollen grain prior to anthesis and pollen tube germination. Another pattern was reported in tobacco by Tian and colleagues, 11 where the nuclear DNA of male and female gametes initiated nuclear DNA synthesis when the pollen tube entered the embryo sac. All these reports suggest that novel and unconventional processes occur during gamete development.…”

“…Additionally, we note that generally, vegetative cells stay at the differentiation stage, 1 and the fluorescence signal of vegetative cells is weak. 4,11,14,15 However, in this experiment, there was no reliable fluorescence signal from the vegetative cells (their fluorescence was found to be strongly abnormal) hence we disregarded the vegetative cells.…”