Flower differentiation of Japanese pear with reference to ultrastructural observation of cells of apical meristem.

对日本梨（Pyrus pyrifolia Nakai cv.Shinsui）花分化过程中顶端分生组织的形态学、细胞学和超微结构的变化以及细胞内钙离子的检测进行了研究。在此期间，静止区细胞内淀粉粒开始积累，体细胞活性增强，体细胞和静止区细胞形态发生变化，图尼卡细胞层减少，体细胞层增多。细胞内的网索体和线粒体数量明显增多。内质网（ER）的分布也随核糖体的增加而增加。与此同时，细胞核内染色质增多，染色变浓。核仁也增大。用含焦锑酸盐的固定剂固定的样品中的细胞沉淀出许多黑色颗粒，这些颗粒是Ca^2+-锑酸盐络合物。Ca^<2+>浓度在6月26日达到最高值，此时体细胞非常活跃，随后下降，7月17日达到最低值，细胞核Ca^<2+>浓度在花分化过程中逐渐增加。在细胞核内，Ca^2+主要分布在核液中，部分分布在核仁颗粒区及其释放物中，而不在核仁纤维区、染色体和染色质中。线粒体、胞核和内质网中Ca ^2+含量的变化与细胞质中Ca^2+含量的变化相一致，说明在花分化前，顶端分生组织细胞中DNA、RNA和蛋白质的合成非常活跃，Ca^2+在花分化中起重要作用。

The morphological, cytological and ultrastructural changes in apical meristem of Japanese pear (Pyrus pyrifolia Nakai cv.Shinsui) during flower differentiation were followed as well as the detection of calcium ion in the cell.First sign of morphological flower differentiation became evident on June 26 ; the apical meristem began to enlarge. During these period starch grains started to accumulate in the cells of quiescent zone, the activity of corpus cells was enhanced, shape of the cells of corpus and quiescent zones changed, and the number of tunica cell layrs decreased while that of corpus cell layrs increased. The numbers.of dictiosomes and mitochondria markedly increased. Distribution of endoplasmic reticulum (ER) also increased with the increase in ribosome. At the same time chromatin in the nucleus increased and became densely stained. Nucleoli also increased in size. Cells at samples fixed with pyroantimonte containing fixatives precipitated many black particles which are Ca^<2+>-antimonate complexes. Density of Ca^<2+> increased to a maximum level on June 26 when corpus cells became very active, decreased thereafter, reaching a low value on july 17, Ca^<2+> density in nuclei of cells increased during floral differentition. Within nucleus, Ca^<2+> distributed mainly in nuclear fluid, some in granular region of nucleolus and its releasing materials, but not in the fibrous area of nucleolus, chromosomes or chromatin. Ca^<2+> contents in mitochondria, dictiosomes and ER changed parallel to the changes of Ca^<2+> in cytoplasm.These results suggest that the synthesis of DNA,RNA and protein becomes very active in the cells of apical meristem just before the flower differentiation, and that Ca^<2+> ion plays an important role in flower differentiation.