In vitro double fertilization in Nicotiana tabacum (L.): the role of cell volume in cell fusion

Abstract

The role of cell volume in regulating cell fusion was investigated by in vitro fertilization to elucidate mechanisms involved in double fertilization. The results revealed that in our model gamete fusion was more efficient than the fusion of somatic cells under the same conditions. The fusion of selected mesophyll protoplasts of different sizes and their fusion with chloroplasts demonstrated that cell volume ratio played a role in this process: as the ratio increased, fusion was more efficient and faster. When one of the cells was as small as a sperm, the formation of a round fusion product was faster. This might explain why gamete fusion was highly efficient in all in vitro germ cell fusion systems. This finding may also explain why sperm evolved as small cells. The results reported here will be useful for interpreting and evaluating data of in vitro fertilization experiments and for distinguishing gamete-specific characters.

Sperm movement during double fertilization of a flowering plant, Phaius tankervilliae

“…This consistency suggests that positionally pre-determined regions are present on the surface of the egg cell and the central cell, and these regions are responsible for ''receiving'' the sperm cells. Recent studies using in vitro methods (Kranz 2001;Sun et al 2001) to study plant fertilization should further our understanding of the mechanism of gamete fusion in flowering plants.…”

The Mechanisms of Pollination and Fertilization in Plants

“…The greater apparent efficiency of gamete-to-gamete fusion has also been challenged. Recently, Sun et al (2001), fusing somatic cells (and even chloroplasts) with cells of various sizes, found that efficiency of fusion in each size class did not appear to differ with that found in male gamete lineage cells of similar size. Disparities in volume could also be a mechanism for preferentiality during fertilization when sperm cells differ in volume (Tian et al 2001).…”

“…Attempts to combine dicot gametes have met with some success in Nicotiana tabacum. (Sun et al 1995(Sun et al , 2000(Sun et al , 2001Tian & Russell 1997b). In each of these cases, fusion has been stimulated using chemical means with polyethylene glycol (PEG).…”

In vitro fertilization: analysis of early post-fertilization development using cytological and molecular techniques

“…Individual isolated gametes have been fused electrically (e.g., Kranz et al 1991Kranz et al , 1998Kovács et al 1995;Uchiumi et al 2007b) and chemically, by calcium Faure et al 1994;Digonnet et al 1997;Kranz et al 1998;Antoine et al 2000;2001b;Khalequzzaman and Haq 2005) or by polyethyleneglycol (e.g., Sun et al 1995Sun et al , 2000Sun et al , 2001Tian and Russell 1997). The fusion method which uses electrical pulses is well established and efficiently Fig.…”