水稻胚囊超微结构的研究

水稻(Oryza sativa L.)胚囊成熟时,卵细胞的合点端无细胞壁,核居细胞中部,细胞器集中在核周围,液泡分散于细胞周边区域。助细胞珠孔端有丝状器,合点端无壁,核位于细胞中部贴壁处,细胞器主要分布在珠孔端,液泡主要分布在合点端。开花前不久,一个助细胞退化。中央细胞为大液泡所占,两个极核靠近卵器而部分融合,细胞器集中在极核周围和靠近卵器处,与珠心相接的胚囊壁上有发达的内突。反足细胞多个形成群体,其增殖主要依靠无丝分裂与壁的自由生长,反足细胞含丰富活跃的细胞器,与珠心相接的壁上有发达的内突。开花后6小时双受精已完成,合子和两个助细胞合点端均形成完整壁。合子中开始形成多聚核糖体、液泡减小。退化助细胞含花粉管释放的物质,其合点端迴抱合子。极核已分裂成数个胚乳游离核,中央细胞中细胞器呈活化状态。反足细胞仍在继续增殖。讨论了卵细胞的极性、助细胞的退化、卵器与中央细胞间界壁的变化、反足细胞的分裂特点等问题。

AN ULTRASTRUCTURAL STUDY OF EMBRYO SAC IN ORYZA SATIVA L.

Rice embryo sac consists of an egg cell,two synergids,a central cell with two polar nuclei,and a multicellular antipodal mass.The egg cell bears no wall at its chalazal end.Its nucleus is centrally located.The greater part of its cytoplasm surrounds the nucleus,while vacuoles of various sizes are distributed at the peripheral region.The mature egg cell appears to be an inactive cell in the light of its organelle state.The two synergids show no difference with each other one day before anthesis,but by the time just prior to anthesis,one of them has degenerated.The synergids bear no wall at the chalazal end and have a thick wall at the micropylar end,where a filiform apparatus is formed.The nucleus occupies a mid-lateral posi- tion with the majority of organelles distributed at the micropylar part and many vacuoles at the chalazal part.The central cell is occupied by a large vacuole which presses the cytoplasm to a thin peripheral layer.The polar nuclei,partially fused with each other,are located in proximity to the egg apparatus and surrounded by organelles.Long,parallel endoplasmic reticula are seen near the plasma membrane bordering the egg apparatus.A thick,multilayered embryo sac wall which bears numerous finger-like ingrowths seperate the central cell from the nucel- lus.The antipodal cells keep dividing before and even after fertilization,proliferating into a multicellular mass.Amitosis accompanied with freely growing walls is a usual phenomenon in this proliferation process.The cells contain abundant,active organelles and have many ingro- wths at the wall bordering the nucellus.Six hours after fertilization,double fertilization is finished,resuking in a zygote and several endosperm nuclei.The zygote has now formed a new wall at its chalazal end.Its cytoplasm shows no significant changes except that more polysomes are seen and the vacuoles become smaller in size.In contrast,the cytoplasm of endosperm becomes more abundant and active than before.The degenerated synergid elongates and embraces the chalazal part of the zygote.Besides formerly existing electron-dense materials, many starch grains and spherical bodies are seen in the degenerated synergid as a result of pollen tube discharge.After fertilization,both synergids are characterized by newly formed walls at their chalazal part.To our knowledge,the present paper is the first report on ultras- tructure of rice embryo sac.Based on the results obtained by this paper and the reports on other graminaceous species,a discussion is made around the following problems as polarity of the egg cell,degeneration of the synergid,changes of the boundary wall between egg apparatus and central cell,and division of antipodal cells.