西瓜不同发育时期的助细胞超微结构的变化

被子植物胚囊的“雌性生殖单位”,已在多种植物上进行了超微结构的观察,但大多都以卵细胞受精前后的结构变化为主要研究内容。对于“雌性生殖单位”中的另一重要成员——助细胞,在不同发育状态下其结构变化的详细资料不多,尤其是助细胞退化后的物质去向,少见报道。本研究主要观察了西瓜不同发育时期(受精前后)、不同发育状态(柱头授粉和未授粉)的助细胞超微结构,以期为研究助细胞在双受精中所起作用提供新的资     

FERTILIZATION IN PLUMBAGO ZEYLANICA: GAMETIC FUSION AND FATE OF THE MALE CYTOPLASM

Developmental phases surrounding the processes of gametic delivery and fusion were examined ultrastructurally in the reduced megagametophyte of Plumbago zeylanica, which lacks synergids. Gametic delivery occurs at the end of pollen tube growth and results in deposition of two male gametes, a vegetative nucleus, and a limited amount of pollen cytoplasm between the egg and central cell. Discharge of these materials from the tube is accompanied by loss of inner and outer pollen tube plasma membranes, loss of sperm-associated cell wall components, and disruption of the formerly continuous cell wall between the egg and central cell. The dispersion of egg cell wall components directly exposes female reproductive cell membranes to the unfused male gametes and pollen tube without disrupting gametic cell plasma membranes. Presence of unfused sperms within the female gametophyte appears to be a transitory phenomenon, lasting less than 5 min at the end of over 8½ hr of pollen tube growth. At the time of gametic deposition, plasma membranes of unfused sperm cells become directly appressed to plasma membranes of both the egg and central cell. Gametic fusion is initiated by a single fusion event between membranes of participating male and female cells, which is rapidly followed by subsequent, secondary fusion events between the same two cells at different locations along their surface. Gametic fusion results in the transmission of male gamete nuclei with co-transmission of nearly the entire sperm cytoplasmic volume and organellar complement, and it is possible to identify heritable male cytoplasmic organelles within both the incipient zygote and endosperm. Paternally originating plastids may be distinguished from maternal plastids by differences in morphology and staining characteristics, whereas paternal mitochondria may be distinguished from maternal mitochondria by populational differences in mitochondrial size which are statistically significant. Such observations further indicate that transmitted paternal mitochondria seem to remain viable, as judged by their ultrastructural appearance, and are transmitted exclusively by sperm cytoplasm rather than discharged pollen cytoplasm. The presence of anucleate, membrane-bounded cytoplasmic bodies between the egg and central cell are identifiable on the basis of their enclosed organelles and indicate that fragmentation of a small amount of the sperm cytoplasm associated with the vegetative nucleus commonly occurs. The presence and identification of sperm cytoplasmic organelles and associated membranes within female reproductive cells following gametic transmission represents strong evidence in support of the cellular basis of nuclear and cytoplasmic transmission during sexual reproduction in Plumbago.     

經離心作用後,魚類卵子分割的研究

硬骨魚類的卵子因卵黄多,細胞質的黏性低,所以進行各種實驗比較困難,尤其是發育的初期,工作更不容易進行。因此我們對於魚類卵子的構造,比兩棲類和鳥類等卵子知道的少得多。當卵子初產生出來的時候,細胞質主要是分佈在卵黄的外面。卵子一接觸水     

INDUCTION OF THE ACROSOME REACTION ON THE EGG SURFACE OF DE-JELLIED SEA URCHIN EGGS BEFORE AND AFTER FERTILIZATION*

The capacity of the surface of sea urchin eggs to induce the acrosome reaction was assayed by estimating the rate of acrosome reaction of supernumerary spermatozoa in the presence of variously treated eggs before and after fertilization. DTT-disruption of the vitelline coat did not eliminate the acrosome reaction-inducing capacity. This capacity was retained after fertilization in eggs of both H. pulcherrimus and A. crassispina. The acrosome reaction-inducing capacity of the eggs was markedly decreased by treatment with trypsin. The low capacity of the trypsin-treated eggs was maintained after fertilization in H. pulcherrimus, but in A. crassispina the capacity returned to the pre-trypsin treatment level after fertilization. Fertilized eggs from which the fertilization membrane was mechanically removed retained the inducing capacity to a considerable extent, independent of the presence or absence of the hyaline layer, but the capacity diminished rapidly as cleavage proceeded. It was concluded from these data that the acrosome reaction of spermatozoa actually occurred at the surface of de-jellied eggs and that the inducing substance resides in the plasma membrane in addition to the fertilization membrane. A chemical difference between the inducing substance of egg surface and jelly substance is discussed.     

CAPSELLA EMBRYOGENESIS: THE SYNERGIDS BEFORE AND AFTER FERTILIZATION

The ultrastructure and composition of the synergids of Capsella bursa-pastoris were studied before and after fertilization. The synergids in the mature embryo sac contain numerous plastids, mitochondria, dictyosomes and masses of ER and associated ribosomes. Each synergid contains a large chalazal vacuole, a nucleus with a single nucleolus and is surrounded by a wall. This wall is thickest at the micropyle end of the cell where it proliferates into the filiform apparatus. At the chalazal end of the cell the wall thins and may be absent for small distances. The pollen tube grows into one of the two synergids through the filiform apparatus and extends one-third the length of the cell before it discharges. Following discharge of the pollen tube, mitochondria and plastids of the tube can be identified in the synergid as can hundreds of 0.5 μ polysaccharide spheres liberated by the tube. The method by which the sperm or sperm nuclei enter the egg or central cell is not known although an apparent rupture was found in the wall of the egg near the tip of the pollen tube. The second synergid changes at the time the pollen tube enters the first synergid. These changes result in the disorganization of the nucleus and loss of the chalazal wall and plasma membrane. Eventually this synergid loses its identity as its cytoplasm merges with that of the central cell.     

CHANGES IN ACTIVITIES OF THYMIDYLATE SYNTHASE AND DIHYDROFOLATE REDUCTASE IN SEA URCHIN EGGS AFTER FERTILIZATION

Thymidylate synthase activity in sea urchin eggs increases just after fertilization and decreases 30 min later. Then, cyclic variation in the activity occurs in association with the cleavage cycle. Dihydrofolate reductase activity in fertilized eggs is almost the same as in unfertilized eggs and shows no marked change within 3 hr after fertilization. Aminopterin, an analogue of dihydrofolate, inhibits dihydrofolate reductase, and arrests cleavage. On incubation in sea water containing aminopterin (20-100μM) from the time of fertilization, the development of Clypeaster and Pseudocentrotus eggs was arrested at the 32–64 cell stage, and that of Anthocidaris eggs was arrested at the morula stage. Dihydrofolate (100μM) counteracts the inhibitory effect of aminopterin on egg cleavage. Thymidine at concentrations above 10μM also prevents inhibition by aminopterin. Other deoxyribonucleosides at concentrations of 10μM to 100μM do not affect inhibition of egg cleavage by aminopterin. Deoxyadenosine at concentrations above 5 mM inhibits egg cleavage, but other deoxyribonucleosides have no effect.     

牵牛花受精前后卵细胞质体和线粒体及其细胞质DNA的变化

应用透射电镜研究了圆叶牵牛（Ｐｈａｒｂｉｔｉｓｐｕｒｐｕｒｅａ （Ｌ．） Ｖｏｙｇｈｔ）和大花牵牛（Ｐ． ｌｉｍ ｂａｔａ Ｌｉｎｄｌ．）卵细胞在受精前和受精后质体和线粒体的变化。观察到卵细胞在受精前高度液泡化,在核周及卵细胞周围的薄层细胞质中有质体和线粒体。质体含１～２ 个较大淀粉粒。线粒体多呈环形或杯状。卵细胞受精后,细胞质增多,质体的数量也明显增加。质体基质变得更加浓厚,并且普遍含有嗜锇的球体。合子中线粒体丰富,但缺乏卵细胞中那种环形或杯状线粒体,多呈圆形。细胞质ＤＮＡ检测的结果表明,卵细胞质ＤＮＡ荧光有大小和形状不同的两类,它们在细胞中随机分布。一类较大,呈环状,可能是线粒体中的ＤＮＡ显示的荧光;另一类小的点状荧光,可能大多是质体ＤＮＡ荧光,前者比后者多。卵细胞受精后,细胞质类核发生变化,表现在数量上明显地比受精前少。研究揭示了牵牛花合子中细胞质ＤＮＡ 减少的现象,说明了母系质体ＤＮＡ 在受精后可能被降解,提供了母系质体不传递到后代的可能机制。     

大叶杨的受精作用和胚胎发育

用细胞化学方法研究了大叶杨(Populus lasiocarpa Oliv.)的受精作用和胚胎发育。结果表明:柱头在授粉期有蛋白质和多糖性质的分泌物。花粉在授粉后6小时大量萌发。授粉后6天开始出现双受精作用。次生核受精完成较卵核受精完成为早,精卵融合为有丝分裂前型。受精作用消耗大量淀粉粒。核型胚乳于授粉后开始细胞化。胚乳主要成分为蛋白质,游离核形成后不出现淀粉粒。胚乳在胚的发育中被吸收。休眠期的合子经历液泡消失、合子皱缩、液泡再出现、合子伸长等极性化过程。胚胎发生类型为茄型。授粉后44天,胚相继发育成熟。成熟胚直立,具2枚相互包裹的子叶。根冠原中具类根冠柱结构。     

几种植物生活胚囊的分离与鉴定

向日葵、金鱼草和烟草的成熟胚囊以及前两种植物受精后具原胚和胚乳的胚囊均已从新鲜胚珠中分离出来。干涉差显微观察与 H33258荧光显微技术表明它们确系保持了细胞结构和含有丰富内含物的完整胚囊。荧光素二醋酸酯的显微鉴定进一步证明它们是有生活力的。     

ULTRASTRUCTURE AND BIREFRINGENCE OF THE ISOLATED MITOTIC APPARATUS OF MARINE EGGS

Isolated mitotic apparatuses (MA) of clam and sea urchin eggs were investigated by polarizing and electron microscopy. Examination of fixed MA in oils of different refractive index revealed that at least 90% of the retardation of isolated MA is due to positive, form birefringence, the remaining retardation deriving from positive, intrinsic birefringence. Electron micrographs reveal the isolated MA to be composed of microtubules, ribosome-like particles, and a variety of vesicles. In the clam MA the number of vesicles and ribosome-like particles relative to the number of microtubules is much lower than in the sea urchin MA. In clam MA this allows form and intrinsic birefringence to be related directly to microtubules. The relation of birefringence to microtubules in isolated sea urchin MA is more complex since ribosome-like particles adhere to microtubules, are oriented by them, and are likely to contribute to the form birefringence of the isolated MA. However, comparison of values of retardation for clam and sea urchin MA, indicates that the major part of the birefringence in sea urchin MA is also due to microtubules. The interpretation of the structures giving rise to birefringence in the MA of the living cells is likely to be even more complex since masking substances, compression, or tension on the living MA may alter the magnitude or sign of the birefringence.     

烟草受精后胚囊和合子的分离及合子的离体分裂

以酶解－振荡、酶解－解剖及酶解－研磨３ 种方法分离出烟草（Ｎｉｃｏｔｉａｎａ ｔａｂａｃｕｍ ）受精后生活胚囊。其中以第三种方法效果最好。将分离的胚囊经再次酶解并结合显微解剖,进一步分离出合子、胚乳细胞及其原生质体。以微室饲养法培养离体合子,启动了第一次分裂。     

甜叶菊的受精作用及胚和胚乳的早期发育

成熟胚囊被珠被绒毡县包围,由卵器、具次生核的中央细胞以及数目为1至6个反足细胞组成。传粉后6小时左右,雌、雄性核融合。配子融合同精核与次生核的融合几乎同时发生;精核与次生核融合速度快于配子融合。甜叶菊受精作用属于有丝分裂前类型。传粉后8小时左右,初生胚乳核分裂,其分裂方向可与胚囊长轴平行或垂直,从而形成最初的两个胚乳细胞。胚乳细胞前5次分裂是同步的。心形胚阶段,胚乳细胞呈现被消化吸收的迹象。胚乳发育属细胞型。传粉后10小时左右,合子第一次分裂,为横分裂。胚胎发育属紫菀型。     

EMBRYO SAC DEVELOPMENT IN SOYBEAN: THE CENTRAL CELL AND ASPECTS OF FERTILIZATION

Development of the soybean central cell and events associated with fertilization are described. Central cell development involves the simultaneous formation of numerous multigrain amyloplasts, development of wall ingrowths, reduction of the cell's major vacuole, and nuclear migration. As these processes reach completion, a phase of lytic activity begins. This activity ultimately results in both the breakdown of most multigrain amyloplasts in the central cell and the reestablishment of the cell's large vacuole. While these processes occur, the egg and synergid cells continue development. Examination of the egg apparatus after plasmogamy but prior to karyogamy reveals several changes. Whereas the synergid containing the pollen tube is degenerate and the distribution of organelles in the persistent synergid has changed, the egg cell with a free sperm nucleus exhibits higher levels of metabolite storage and changes in its wall structure. The walls of the newly formed sporophyte are similar to those of egg apparatus cells (Folsom and Cass, Canadian Journal of Botany 68: 2135–2147 [1990]) in that they seem to lack a middle lamella. This layer becomes apparent only in the two-celled proembryo. While these changes occur in the egg, zygote, and proembryo, synergids undergo different degradative pathways.