莴苣大孢子发生过程中钙的分布动态

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.

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

Potassium antimonite was used todeposit calcium in the young ovule of lettuce(Lactuca sativa L.) at megasporogenesis stageto study the relationship between calcium andmegaspore degeneration. At the megasporemother cell stage, few calcium granules wereformed in the cell (Plate I-1, 2). After meiosis ofmegaspore mother cell and forming an arrayedtetrad in a line (Plate I-3), three megaspores de-generated one by one from the micropyle end.In the process of degeneration, the numbers ofcalcium granules decreased in the threemegaspores. After the first megasporedegenerated, the number of calcium granulesdecreased in the second megaspore, which be-gan to degenerate (Plate II-7, 8). The third me-gaspore also had its number of calcium granulesdiminishing before it degenerated (Plate III-13,14). The fourth megaspore always accumulatedmany calcium granules in the cytoplasm duringits development (Plate IV-17, 18) and finally becomes functional one that will develop intoan embryo sac (Plate IV-20). Megaspore degen-eration is a process of programmed cell deathwhich may be closely related with change in cal-cium content: when a megaspore of tetrad de-creases calcium content the cell begins todegenerate, and when calcium increases in thecell, it will continue to develop into a functionalmegaspore. This is the first report about calciumdistribution in megaspores of a tetrad duringmegasporogenesis in higher plants and will opena door to study the physiological function of cal-cium in megasporogensis.