During
in vitro fertilization of wheat (
Triticum aestivum, L.) in egg cells isolated at various developmental stages, changes in cytosolic free calcium ([Ca
2+]
cyt) were observed. The dynamics of [Ca
2+]
cyt elevation varied, reflecting the difference
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During
in vitro fertilization of wheat (
Triticum aestivum, L.) in egg cells isolated at various developmental stages, changes in cytosolic free calcium ([Ca
2+]
cyt) were observed. The dynamics of [Ca
2+]
cyt elevation varied, reflecting the difference in the developmental stage of the eggs used. [Ca
2+]
cyt oscillation was exclusively observed in fertile, mature egg cells fused with the sperm cell. To determine how [Ca
2+]
cyt oscillation in mature egg cells is generated, egg cells were incubated in thapsigargin, which proved to be a specific inhibitor of the endoplasmic reticulum (ER) Ca
2+-ATPase in wheat egg cells. In unfertilized egg cells, the addition of thapsigargin caused an abrupt transient increase in [Ca
2+]
cyt in the absence of extracellular Ca
2+, suggesting that an influx pathway for Ca
2+ is activated by thapsigargin. The [Ca
2+]
cyt oscillation seemed to require the filling of an intracellular calcium store for the onset of which, calcium influx through the plasma membrane appeared essential. This was demonstrated by omitting extracellular calcium from (or adding GdCl
3 to) the fusion medium, which prevented [Ca
2+]
cyt oscillation in mature egg cells fused with the sperm. Combined, these data permit the hypothesis that the first sperm-induced transient increase in [Ca
2+]
cyt depletes an intracellular Ca
2+ store, triggering an increase in plasma membrane Ca
2+ permeability, and this enhanced Ca
2+ influx results in [Ca
2+]
cyt oscillation.
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