The dynamics of calcium distribution in the synergid cells of wheat after pollination.

Sister synergids of wheat were examined for post-pollination calcium distribution using freeze-substitution fixation, scanning electron microscopy, and energy-dispersive X-ray microanalysis. At 15-30 min postpollination (before pollen-tube penetration and discharge), the sister synergids were similar in size and in elemental concentrations. Both synergids measured about the same as the egg and contained relatively high concentrations of calcium, potassium, and magnesium. The sister synergids remained identical even in an aberrant case where a pollen tube had penetrated, but not discharged into a synergid. After 30 min post-pollination (after pollen-tube discharge), typically one of the sister synergids was reduced in size and devoid of high concentrations of elements. The other synergid initially remained unaltered and only later underwent slight size reduction; however, it retained high concentrations of elements. The results indicate that high concentrations of calcium, potassium, and magnesium are rapidly lost from a synergid following pollen-tube discharge. A hypothesis is proposed to explain the regulation of entry by only a single pollen tube into an embryo sac. [ABSTRACT FROM AUTHOR]