Abstract: Potassium pyroantimonate precipitation method was used for ultracytochemical localization of calcium in rice ( Oryza sativa L. ) stigma, style, ovary and embryo sac before and after fertilization. To identify the nature of the pyroantimonate deposits, the energy-dispersive X-ray microanalysis (EDXA) was employed and the deposits observed were proved as calcium pyroantimonate. Transmission electron microscopic observations revealed that abundant deposits were present at the surface of stigma papillae and parenchymatous cells of style. One day before anthesis, when the embryo sac was immature and contained a few deposits, calcium distribution showed no difference between two synergids. By the time just prior to anthesis, one of the synergids that had degenerated accumulated more calcium than before, and than the other synergid. Six hours after anthesis at time when double fertilization had finished, the calcium deposits in the degenerated synergid increased. Before fertilization, the deposits in the egg cell were mainly localized in the vacuoles, whereas few deposits could be observed in the nucleus and cytoplasm. After fertilization, the amount of calcium increased dramatically in the zygote, especially in its nucleus. The results are discussed in relation to the role of calcium in mediating synergid degeneration and egg activation.

Key words: Rice, Calcium, Ultracytochemistry, Gynoecium, Synergid, Egg cell