[Calcium distribution in the central cell of lettuce (Lactuca sativa L.) before and after pollination]

Potassium antimonite precipitation was used to locate calcium in the central cell of lettuce (Lactuca sativa L.) before and after pollination. At 3d before anthesis, two polar nuclei of central cell separately located at two polarity of the cell, and few calcium precipitates (ppts) appeared in the polar nuclei and cytoplasm, but some ppts in its small vacuoles. At 2d before anthesis, two polar nuclei moved toward the middle of the cell and fused to form a secondary nucleus, and the ppts evidently increased in the nucleus and cytoplasm. At 1d before anthesis, secondary nucleus again moved toward micropylar end and located near the egg to prepare for fertilization. Calcium precipitates were mainly accumulated in the secondary nucleus. After pollination and before fertilization, the distribution of calcium ppts was similar to that before pollination. At 4h after pollination, the central cell was fertilized, and calcium ppts evidently increased in the cell and numerous were accumulated in its nucleus and cytoplasm. At 6h after pollination, the primary endosperm nucleus completed its first division and formed two dissociate endosperm nuclei, and still many calcium precipitates appeared in the nucleus and cytoplasm. With endosperm development, calcium ppts decreased in the endosperm cell. At 1d after emasculated and without pollination, the secondary nucleus of the cell still bordered on the egg and some calcium ppts appeared in the secondary nucleus. The results indicated that the temporal and spatial changes of calcium in the central cell may play an important physiological role during the development of the central cell and endosperm.