日本紫花鼠尾草花部發育、小孢子形成和花粉發育之研究

Abstract

本研究使用光學顯微鏡、掃描式電子顯微鏡和穿透式電子顯微鏡觀察日本紫花鼠尾草花部發育、小孢子形成和花粉發育的過程，並配合組織化學染色期望能從中瞭解何時花粉發生不正常的發育，或其內的化學物質產生變化，繼而影響成熟花粉粒的活性。 日本紫花鼠尾草花序為聚繖花序。在四輪的花部器官發育中，近軸面的發育過程為向頂性，然而遠軸面的發育過程則混合了向頂性和向基性。正常雄蕊始原進行雙子葉型的組織分化，其花藥由二個花藥瓣組成，每一花藥瓣僅含一個花粉囊，藥隔組織連接此兩花粉囊。花藥壁由表皮組織、花藥內壁、仲介層及變形蟲型營養層所組成。小孢子母細胞被營養層所圍繞。 在小孢子形成的過成中，小孢子母細胞在減數分裂後，立即進行同時型的細胞質分裂，形成四面形及四面體形的四分體，四分體小孢子的原外壁於此時發育，其細胞質中含有蛋白質及多醣。在胼胝質瓦解後，四個小孢子被釋放至花藥腔中，小孢子的花粉外壁外層、花粉外壁內層和花粉內壁相繼發育，而原本累積在小孢子中的蛋白質及多醣消失。隨後，小孢子漸漸地液胞化。接著小孢子進行細胞不等分裂，形成一個營養細胞和一個生殖細胞。在花藥開裂前，生殖細胞再次分裂成二個精細胞，成為三個細胞的花粉。成熟的花粉粒具6溝，外壁花紋呈網狀。 在成熟花粉粒的細胞質中含有豐富的蛋白質、多醣和脂質。在花藥開裂後，成熟花粉粒細胞內的蛋白質含量下降，脂質形成大小均勻的顆粒，約35％的花粉粒有大的澱粉體，當部份的澱粉體快速變小時，花粉活性亦隨之下降。花粉活性在花藥開裂前後有明顯變化，不具活性的花粉由20％上升至80％。這些不具活性的花粉粒可分為二型：體形非常小及體形稍小二種。前者花粉粒，僅具有4溝，花粉外壁的柱狀體排列緊密，無花粉外壁內層及花粉內壁內層，佔所有不具活性花粉的20％；後者花粉粒體形比正常有活性者稍小，亦具6溝，由外部形態不易與有活性者區分，但無花粉內壁內層發育。由組織化學染色顯示，花粉活性似乎與澱粉體的大小變化有關。花粉的不正常發育是由於花粉本身基因的控制。

The time course of floral development, the microsporogenesis and pollen development in Salvia japonica Thunb. were studied in order to find out the possible reasons of the occurrence of abnormal pollen and the factors related to the viability of mature pollen grains. Histochemical methods related to the viability of mature pollen grains. Histochemical methods and observations under light microscope, scanning and transmission electron microscope were used for this study. The inflorescence type of Salvia japonica is cyme. The development of floral organs on plant was observed. It was found that the development of floral organs in adaxial side was acropetal, whereas the development in abaxial side was a mixture of acropetal and basipetal types. The series of floral development were described. The anther wall formation is typical dicotyledonous type. The anther is composed of two lobes connected by the connective tissue. Each lobe contains only one sporangium. The anther wall is consisted of epidermis, endothecium, middle layer and tapetum. The microspore mother cells are surrounded by the amoeboid tapetum. During microsporogenesis, simultaneous cytokinesis occurred immediately after meiosis. Tetragonal and tetrahedral tetrads are formed. These tetrad microspores had primexine pattern and contained numerous protein and polysaccharide granules in the cytoplasm. After callose has been dissolved, the tetrad microspores were released into anther locule. This was followed by continuous development of the ectexine, endexine, and intine of microspores, associated with a decrease in the contents of protein and polysaccharide granules. Then, the microspore became vacuolized gradually. Soon microspores proceed an asymmetric cell division, a vegetative cell and a generative cell were formed in each pollen grain. Before anthesis, the generative cell divided into two sperm cells. A mature pollen grain is 3-celled pollen with 6-colpi and reticulate exine ornamentation was formed. In mature pollen grains, abundant proteins, polysaccharides, and lipids can be observed in the cytoplasm. During anthesis, the intracellular protein content decreased, along with uniformed lipid particles. About 35% pollen grains still have large starch grain, while the particle size of starch grain in the rest of pollen grains declined rapidly, associated with a loss in pollen viability. There was a dramatic change in pollen viability before and after anthesis, with an remarkable elevation of inviable pollen from 20% to 80%. The inviable pollen can be distinguished into two types: a very small one and another larger. The former one was 4-coplated with bacula very close to each other and did not differentiate into endexine and inner intine. It occupied 20% of total inviable pollen. The latter one was only slightly smaller than normal viable pollen. It was 6-coplated without intine in the pollen wall. Histochemical staining showed that the viability of pollen seemed to be related to the transformation from large to small starch grain. The failure of pollen development was controlled by pollen. To ascertain this, a further study is necessary.