Changes of calcium distribution in egg cells, zygotes and two-celled proembryos of rice (Oryza sativa L.)

Changes in loosely bound calcium of rice egg cells (pre- and post-pollination) and two-celled proembryos were localized using potassium pyroantimonate precipitation. Egg cells and zygotes (6 h after pollination) have few calcium precipitates (ppts); however within 3 h, (9 –12 h after pollination), ppts become locally abundant in all regions. Statistical analysis indicates that ppts in cytoplasm and nucleoplasm increase by 4.4 and 10.5-fold in zygotes at 9 h and 12 h after pollination, respectively. The ppts labeling the nucleolus 9 h after pollination show a 52-fold increase. In two-celled proembryos, ppts declined to a level similar to that of zygotes 6 h after pollination, except in the nucleolus and cell wall. Following pollination, abundant calcium was detected in the apoplast of the embryo sac.