Relatively high calcium is localized in synergid cells of wheat ovaries

Summary Using energy-dispersive X-ray microanalysis of mature, unpollinated wheat ovaries fixed by freeze-substitution, we show here that the synergid cells store a relatively high concentration of calcium. Based on our results and other indirect evidence, we suggest that supraoptimal levels of calcium in synergids may regulate: (1) correct orientation of the pollen tube, by forming a calcium gradient in the vicinity of the synergids, and (2) arrest and rupture of the pollen tube to release the sperm near the egg.