Calcium distribution in fertilized and unfertilized ovules and embryo sacs of Nicotiana tabacum L.

Abstract

Potassium antimonate was used to localize Ca 2+ in tobacco ovules from 0 to 7 d after anthesis in pollinated and emasculated flowers. Antimonate binds ''loosely bound'' Ca 2+ into calcium antimonate; lesssoluble forms are unavailable and free calcium usually escapes. Ovules are immature at anthesis. Abundant calcium precipitates in nucellar cells surrounding the micropylar canal. A difference between calcium in the two synergids emerges at 1 d, which is enhanced in pollinated flowers. The future receptive synergid accumulates more precipitates in the nucleus, cytoplasm and cell walls. After fertilization, micropyle precipitates diminish, and the ovule is unreceptive to further tube entry. In emasculated flowers 6 d after anthesis, ovular precipitates essentially disappear; however, flowers pollinated at 4-5 d and collected 2 d later largely restore their prior concentration of precipitates. Ovular precipitates occur initially in the nucellus, then the embryo sac, and finally the synergid and micropylar filiform apparatus. Possibility, calcium is released from the embryo sac, although no structural evidence of exudate formation was observed. Calcium precipitates in the ovule correlate with the ability of the ovule to be fertilized, suggesting that successful pollen tube entry and later development may require calcium of the class precipitated by antimonate.Abbreviations: EDXA = energy-dispersive X-ray analysis; ES = embryo Sac; ppt = precipitate Correspondence

Species Preferentiality of the Pollen Tube Attractant Derived from the Synergid Cell ofTorenia fournieri

“…7). Although calcium has been detected in the synergid cell and the neighboring extracellular matrix, as described above (Jensen, 1965;Chaubal and Reger, 1990, 1992a, 1992bHuang and Russell, 1992;Tirlapur et al, 1993;Tian and Russell, 1997;Kristó f et al, 1999), Ca 21 may play a primary role in pollen tube discharge, gamete fusion, or both, but not in species-related pollen tube attraction. In an Arabidopsis mutant in which a plasma membrane Ca 21 pump of the pollen tube, ACA9, is disrupted, the pollen tube arrives at the embryo sac but cannot discharge its contents to the receptive synergid cell and shows overgrowth in the embryo sac (Schiøtt et al, 2004).…”

“…In vitro test results suggest that calcium is an attractant derived from the pistil, in particular the ovule Machlis, 1962, 1964;Reger et al, 1992). Using various histochemical methods including calcium antimonate precipitation, proton-induced x-ray emission, and fluorescent calcium probes, high concentrations of calcium have been observed in synergid cells and the neighboring extracellular matrices in various species (Jensen, 1965;Chaubal and Reger, 1990, 1992a, 1992bHuang and Russell, 1992;Tirlapur et al, 1993;Tian and Russell, 1997), including T. fournieri (Kristó f et al, 1999). The second potential attractant is ZmEA1 (Márton et al, 2005).…”

Plant Somatic Embryogenesis: Some Useful Considerations

“…In the sexual reproduction of angiosperms, the pollen grain is transferred from the anther to the stigma where it germinates and forms the pollen tube (Yadegari & Drews, 2004) which travels long distances directed first by sporophytic signals and then by the female gametophyte (Wetering & Russell, 2004). Afterwards, the pollen tube reaches the micropyle where it is guided by signals generated by the synergid cells through high calcium concentrations (Tian & Russell, 1997). Then the spermatic cells are discharged into one of the synergids through the filiform apparatus (Yadegari & Drews, 2004).…”

Female Gametophyte Development

“…Calcium has been proposed to be a guidance signal because it can attract pollen tubes in vitro in some species Machlis, 1962, 1964;Reger et al, 1992), is present in high concentrations in synergid cells (Jensen, 1965;Chaubal and Reger, 1990, 1992a, 1992bTian and Russell, 1997), and is necessary for pollen tube growth (Pierson et al, 1994(Pierson et al, , 1996Holdaway-Clarke et al, 1997;Li et al, 1999). However, the addition of calcium to the medium in the in vitro T. fournieri system does not affect pollen tube attraction, indicating that calcium is not a universal attractant (Higashiyama, 2002;Higashiyama et al, 2003).…”