莴苣大孢子发生过程中钙的分布动态

The Dynamic of Calcium Distribution During Megasporegenesis of Lettuce (Lactuca sativa L.)

莴苣胚囊发育为蓼型,减数分裂形成的4个大孢子中只有合点端的一个大孢子可继续发育,其余3个大孢子从珠孔端依次退化。大孢子母细胞中的钙沉淀颗粒很少,减数分裂后的四分体中的钙沉淀颗粒稍有增加。以后,4个大孢子中的钙沉淀颗粒在数量上有明显差异:即将退化的大孢子中钙明显减少,而未退化大孢子细胞质中则保持有较多的细小钙沉淀颗粒。大孢子的退化是一种细胞程序死亡现象,细胞中的钙浓度降低时可能启动了大孢子细胞的程序性死亡过程,而细胞中的钙浓度高时则保持大孢子细胞的继续发育。文章首次揭示了大孢子发生过程中钙的分布特征。

Potassium antimonite was used to deposit calcium in the young ovule of lettuce （Lactuca sativa L.） at megasporogenesis stage to study the relationship between calcium and megaspore degeneration. At the megaspore mother cell stage, few calcium granules were formed in the cell （Plate I-1, 2）. After meiosis of megaspore mother cell and forming an arrayed tetrad in a line （Plate I-3）, three megaspores degenerated one by one from the micropyle end.In the process of degeneration, the numbers of calcium granules decreased in the three megaspores. After the first megaspore degenerated, the number of calcium granules decreased in the second megaspore, which began to degenerate （Plate Ⅱ-7, 8）. The third megaspore also had its number of calcium granules diminishing before it degenerated （Plate Ⅲ-13,14）. The fourth megaspore always accumulated many calcium granules in the cytoplasm during its development （Plate Ⅳ-17, 18） and finally becomes functional one that will develop into an embryo sac （Plate Ⅳ-20）. Megaspore degeneration is a process of programmed cell death which may be closely related with change in calcium content： when a megaspore of tetrad decreases calcium content the cell begins to degenerate, and when calcium increases in the cell, it will continue to develop into a functional megaspore. This is the In＇st report about calcium distribution in megaspores of a tetrad during megasporogenesis in higher plants and will open a door to study the physiological function of calcium in megasporogensis.