竹节参雌配子体发育的研究

本文报道了竹节参(Panax japonicus C.A.Mey)雌配子体(胚囊)的发育过程。竹节参大孢子母细胞减数分裂产生线形排列的大孢子四分体。胚囊发育属蓼型,由合点端大孢子发育而成。游离核胚囊时期,胚囊珠孔端的细胞器种类和数量都较胚囊合点端多;胚囊合点端相邻的珠被细胞中有含淀粉粒的小质体,与胚囊珠孔端相邻的退化中的非功能大孢子中则有含淀粉粒的大质体和大类脂体。成熟胚囊中,反足细胞较早退化;极核融合成次生核;卵细胞高度液泡化,细胞器数量较少;助细胞则有丰富的细胞器和发达的丝状器。PAS反应表明,受精前的成熟胚囊中积累淀粉粒。次生核受精后,很快分裂产生胚乳游离核,到几十至数百个核时形成胚乳细胞。卵细胞受精后则要经过较长的休眠期。     

五唇兰大孢子发生的超微结构观察

五唇兰(Doritis pulcherrima Lind l．)大孢子母细胞在减数分裂前呈长圆形,细胞核偏向珠孔端,细胞呈现极性分化。大孢子母细胞第一次减数分裂形成二分体。随后,二分体珠孔端的一个细胞退化,合点端的一个细胞体积增大成为功能大孢子。功能大孢子进行第二次减数分裂,形成二核胚囊。这一过程属于双孢子葱型胚囊的大孢子发生类型。珠孔端的二分体细胞(大孢子)在退化过程中质膜保持完好,液泡数量增多,染色质高度凝集,具有细胞程序死亡的部分特征。功能大孢子的细胞器和染色质分布均匀。功能大孢子合点端的细胞壁上有发达的胞间连丝,二核胚囊期胞间连丝消失。在功能大孢子靠近合点端一侧有吞噬结构,其内含有结构模糊的细胞器     

荔枝雌蕊发育过程中钙分布变化与细胞程序性死亡

应用焦锑酸钾沉淀法研究了荔枝雌花和雄花雌蕊发育过程中钙的分布变化。在大孢子母细胞阶段,雌花近珠孔内珠被细胞和花柱细胞的钙沉淀颗粒主要分布在细胞壁和细胞间隙,少部分在液泡;雌花花柱维管细胞中含有很多的钙沉淀颗粒;在雄花的近珠孔内珠被细胞钙沉淀颗粒大多在液泡中;雄花花柱细胞和维管细胞中钙沉淀颗粒很少。大孢子母细胞减数分裂后,雌花雌蕊继续发育,雄花雌蕊败育。雌花维管中的钙沉淀颗粒数量减少,可能被转运到将要发生花粉萌发和受精的部位。雌花近珠孔内珠被细胞壁的钙沉淀颗粒分布增加,花柱细胞从上（近柱头）到下（近子房）钙沉淀颗粒量递增。雄花近珠孔内珠被细胞发生程序性死亡：液泡中的钙进入细胞核启动细胞程序性死亡,核周隙与质膜腔形成连续的通道,钙在核与细胞质之间的流动不受限制;在特定的时间段,钙沉淀颗粒出现在线粒体、过氧化物体和线型内质网的外膜上。钙在细胞中重新分布可能触发和调节细胞程序性死亡的进程。缺乏钙沉淀颗粒的雄花花柱细胞迅速解体。     

东北地区白桦雌配子体的形成与胚胎发育研究

以20年生白桦(Betula platyphylla)的雌花序为材料,研究了白桦的大孢子发生、雌配子体形成和胚胎发育过程.结果表明:1)大孢子母细胞经过减数分裂形成直线排列的4个大孢子,其中珠孔端的3个大孢子退化,合点端的大孢子进行3次有丝分裂,形成八核胚囊,8个核迅速细胞化,最终发育为成熟胚囊.胚囊发育类型为单孢子蓼型胚囊;2)胚的发育经过原胚、球形胚、心形胚和鱼雷胚等阶段发育为成熟胚;胚柄在球形胚时期最发达,但胚柄短小,只由3个扁平细胞组成,之后逐渐退化.本文同时对雌花的结构和发育特点在桦木科各属中的异同、白桦胚胎发生类型及胚胎发育进程的同步性进行了讨论.     

刺五加大、小孢子发生和雌、雄配子体发育的观察

刺五加Eleutherococcus senticosus(Rupr．et Maxim．)Maxim．雄株的小孢子发生和雄配子体发育过 程正常,大孢子发生和雌配子体发育过程多不正常。雄花具5个花药,花药4室,药壁发育属双子叶型, 腺质绒毡层,绒毡层细胞多具2核。小孢子母细胞经减数分裂形成四面体形四分体,其胞质分裂为同时 型。成熟花粉为3细胞型。子房下位,5室;每室有上胚珠和下胚珠,上胚珠退化,下胚珠倒生、具单珠 被、厚珠心;大孢子母细胞经减数分裂形成线形或“T”形四分体,偶尔有2个并列或串联的四分体或在 四分体之上又出现孢原细胞。其功能大孢子位置不确定。雌配子体发育中异常现象较多。开花时,雌 配子体主要为反足细胞退化后的四细胞胚囊。刺五加雌株的小孢子母细胞不能进行减数分裂或减数分 裂不正常,不能形成四分体。开花时,药室空瘪,无花粉形成。其大孢子发生和雌配子体发育过程正常, 大孢子母细胞减数分裂形成线形或“T”形四分体,合点端大孢子为功能大孢子,胚囊发育属蓼型。开花 时,雌配子体主要为七细胞八核或七细胞七核胚囊,其卵器尚未发育成熟。刺五加两性株的小孢子发生 过程无异常,但雄配子体发育过程有部分异常;开花时,药室内有或多或少的空花粉,且花粉粒大小悬 殊,大的直径达35μm,小的仅15～18 μm。两性株的雌蕊发育大部分正常,也有一些异常胚囊形成。开 花时,雌配子体主要是七细胞八核胚囊、七细胞七核胚囊和反足细胞退化后的四细胞胚囊,其卵器也未发育成熟。     

华山新麦草大孢子发生和雌配子体的形成

华山新麦草大孢子发生始于孢原细胞。大孢子母细胞减数分裂形成直线型四分体。功能大孢子位于合点端,大孢子发育为蓼型胚囊。成熟胚囊为八核七细胞,卵细胞极性明显,助细胞在极核融合前已退化一个,另一个宿存,宿存助细胞丝状器明显,并保留退化助细胞的痕迹。极核排列方向不定,反足细胞在胚囊发育早期增殖,并液泡化。此外,在华山新麦草中发现有双孢原细胞及双胚囊的现象。     

银杏大孢子形成的超微结构研究

银杏 (GinkgobilobaL .)的大孢子母细胞在减数分裂前变成近长圆形 ,细胞核移向珠孔端 ,造粉质体围绕细胞核分布。线粒体主要分布在细胞的偏向合点端。细胞的偏向珠孔端存在大量的粗面内质网 ,而线粒体和质体较少。到了减数分裂前期Ⅰ时 ,细胞中液泡增加 ,向珠孔端的内质网减少。减数分裂的第一次分裂形成二分体细胞后 ,更表现出明显的极性分化。偏向珠孔端的细胞 (A)相对较小 ,细胞中除环状内质网和少量线粒体外 ,几乎看不到质体 ,而偏向合点端的细胞 (B)体积增大 ,各种细胞器的含量也较丰富。减数分裂第二次分裂时 ,这两个二分体细胞 (A和B细胞 )的分裂时间也不相同。形成直立四分体大孢子细胞时 ,最向合点端的细胞 (B2 )最大 ,成为具功能大孢子。其余 3个大孢子细胞陆续退化 ,但是细胞间差别很大。偏向珠孔端的两个细胞 (A1和A2 )首先退化。后来B1和B2 细胞之间形成了厚壁。由于减数分裂时极性的变化也可能形成T字型四分体大孢子细胞或只产生 3个大孢子细胞 ,最后只有最下面的一个细胞 (B2 )成为具功能大孢子。     

东北地区白桦雌配子体的形成与胚胎发育研究

以20年生白桦(Betula platyphylla)的雌花序为材料, 研究了白桦的大孢子发生、雌配子体形成和胚胎发育过程。结果表明：1)大孢子母细胞经过减数分裂形成直线排列的4个大孢子, 其中珠孔端的3个大孢子退化, 合点端的大孢子进行3次有丝分裂, 形成八核胚囊, 8个核迅速细胞化, 最终发育为成熟胚囊。胚囊发育类型为单孢子蓼型胚囊; 2)胚的发育经过原胚、球形胚、心形胚和鱼雷胚等阶段发育为成熟胚; 胚柄在球形胚时期最发达, 但胚柄短小, 只由3个扁平细胞组成, 之后逐渐退化。本文同时对雌花的结构和发育特点在桦木科各属中的异同、白桦胚胎发生类型及胚胎发育进程的同步性进行了讨论。     

防风大、小孢子发生与雌、雄配子体发育的研究

利用常规石蜡制片法研究了防风大、小孢子发生及其雌、雄配子体的发育过程。主要结果是：(1)小孢子母细胞减数分裂过程中的胞质分裂为同时型,小孢子四分体为四面体形;(2)成熟的花粉粒为三细胞型,具3个孔沟;(3)花药壁发育类型为双子叶型。花药壁由4层结构组成：最外层为表皮,其内分别为药室内壁、1层中层、绒毡层,绒毡层为分泌型;(4)防风的子房为2室,每室1胚珠,单珠被,薄珠心,倒生型胚珠。大孢子母细胞经减数分裂形成线形排列的4个大孢子,合点端大孢子具功能;(5)大孢子发生过程中,具有多个孢原细胞及多个大孢子母细胞的现象,但通常只有一个大孢子母细胞能继续发育;(6)胚囊发育属于蓼型;(7)防风的花为极端的雌雄蕊异熟,雄蕊的发育早于雌蕊的发育。     

车桑子大孢子发生与雌配子体发育

采用常规石蜡切片法,对车桑子大孢子的发生和雌配子体的发育进行观察,探讨车桑子自然结籽率低的原因和明确其胚胎发育特征。结果表明:(1)车桑子花柱有花柱道,子房3室,中轴胎座,横生胚珠,每心室两枚胚珠,双珠被,厚珠心,无承珠盘。(2)位于珠心表皮细胞下的孢原细胞经平周分裂产生造孢细胞,造孢细胞发育为大孢子母细胞,大孢子母细胞经减数分裂形成线性四分体,靠近珠孔端3个大孢子退化消失,靠合点端大孢子发育为功能大孢子,大孢子发生类型为单孢子发生型。(3)单核胚囊经3次有丝分裂形成7细胞8核的成熟胚囊,胚囊发育类型为蓼型。(4)花器官形态的变化和大孢子发育过程有一定联系,可根据雌花形态特征大致判断大孢子发育时期。研究认为,车桑子雌配子体发育过程中出现的胚囊不中空、游离核不进一步细胞化等异常现象,可能是导致车桑子自然结籽率低的原因之一。     

Calcium changes during megasporogenesis and megaspore degeneration in lettuce (<Emphasis Type="Italic">Lactuca sativa</Emphasis> L.)

Potassium pyroantimonate was used to localize loosely-bound calcium in young ovules of lettuce (Lactuca sativa L.) during megasporogenesis to investigate the relationship between ionically available calcium and megaspore degeneration. At the megasporocyte (megaspore mother cell) stage, few calcium precipitates were located in the ovule. Following meiosis in the megasporocyte, a linear tetrad of four megaspores is formed, with three of the four megaspores degenerating from the micropylar end inward. Only the chalazal-most megaspore continues to develop, becoming the functional megaspore. A decrease in amount of calcium precipitates in the megaspore, particularly in the nucleus, precedes the breakdown of the micropylar megaspores, which subsequently undergo structural disintegration and loss of recognizable cellular features. A partial recovery of calcium precipitates occurs during later degeneration. The functional megaspore retains a consistently higher concentration of calcium precipitates during development, which is retained in the developing embryo sac. This, to our knowledge, is the first report related to calcium dynamics during megaspore degeneration, and may facilitate future research aimed at elucidating the mechanisms of megasporogenesis.     

白菜核雄性不育系可育和不育花药中Ca2+的分布

研究了白菜(Brassica campestris L. ssp.chinensis Makino)细胞核雄性不育系花药中Ca2 的分布特征.在可育花药发育过程中,减数分裂后花药壁细胞中钙颗粒明显增加.早期小孢子开始积累钙颗粒并特异性地附在小液泡膜上.小孢子分裂后,大液泡消失过程中又伴随着许多钙颗粒附在小液泡膜上,显示出Ca2 与花粉中液泡的形成和分解有关.在不育花药中,最早出现的钙颗粒异常分布是在小孢子母细胞的胼胝质壁中积累了较多的钙颗粒.然而,在小孢子细胞质中钙颗粒一直很少,也不形成大液泡,最后通过细胞质收缩的方式败育.这是首次发现Ca2 参与调控花药发育过程,其异常分布与花粉败育密切相关.     

Megasporogenesis and programmed cell death in <Emphasis Type="Italic">Tillandsia</Emphasis> (Bromeliaceae)

The degeneration of three of four meiotic products is a very common process in the female gender of oogamous eukaryotes. In Tillandsia (and many other angiosperms), the surviving megaspore has a callose-free wall in chalazal position while the other three megaspores are completely embedded in callose. Therefore, nutrients and signals can reach more easily the functional megaspore from the nucellus through the chalazal pole with respect to the other megaspores. The abortion of three of four megaspores was already recognized as the result of a programmed cell death (PCD) process. We investigated the process to understand the modality of this specific type of PCD and its relationship to the asymmetric callose deposition around the tetrad. The decision on which of the four megaspores will be the supernumerary megaspores in angiosperms, and hence destined to undergo programmed cell death, appears to be linked to the callose layer deposition around the tetrad. During supernumerary megaspores degeneration, events leading to the deletion of the cells do not appear to belong to a single type of cell death. The first morphological signs are typical of autophagy, including the formation of autophagosomes. The TUNEL positivity and a change in morphology of mitochondria and chloroplasts indicate the passage to an apoptotic-like PCD phase, while the cellular remnants undergo a final process resembling at least partially (ER swelling) necrotic morphological syndromes, eventually leading to a mainly lipidic cell corpse still separated from the functional megaspore by a callose layer.     

DEVELOPMENT OF THE OVULE AND MEGAGAMETOPHYTE IN SAXIFRAGA HIERACIFOLIA

Wiggins , Ira L. (Stanford U., Stanford, Calif.) Development of the ovule and megagametophyte in Saxifraga hieracifolia. Amer. Jour. Bot. 46(10): 692–697. Illus. 1059.—Buds of Saxifraga hieracifolia collected in the vicinity of Point Barrow, Alaska, fixed, sectioned, and stained by standard methods, revealed that the archesporial cell in the ovule of this species is hypodermal and gives rise to the megaspore mother cell and a small number of parietal cells. Occasionally 2 megaspore mother cells occur within an ovule. Meiosis in the megaspore mother cell produces a linear tetrad of megaspores, the chalazal one of which normally gives rise to a monosporic, Polygonum-type megagametophyte. The polar nuclei fuse near the chalazal end of the megagametophyte and the antipodal cells disintegrate prior to fertilization. A distinct filiform apparatus and a marked lateral “spur” develop on each synergid. Vacuolation in the egg cell and in the synergids follows the usual pattern. Only a single integument surrounds the nucellus.     

Embryo sac development in Arabidopsis thaliana

Summary Aspects of megasporogenesis in Arabidopsis thaliana have been investigated using a variety of histochemical techniques to visualize general cell organization, DNA and callose in whole ovules and sections by bright field, fluorescence, differential interference contrast and scanning electron microscopy. The microtubular cytoskeleton has been studied using immunofluorescence localization of tubulin in sections and whole cells. The observations deviate from reports of preceding studies in that the megasporocyte was found to undergo both meiotic divisions followed by simultaneous cytokinesis (i.e. without an intermediate dyad stage) to give a multiplanar tetrad of megaspores. This represents a variation of monosporic development not previously described. Polarized distribution of organelles prior to meiosis ensures that the functional megaspore receives the largest share. Aberrant wall formation is common between degenerating megaspores. Localized callose deposition in the tetrad separates these cells from the active megaspore. Their pattern of degeneration and displacement is extremely flexible within the embryo sac space. The microtubular cytoskeleton is extensive and largely cytoplasmic, as distinct from cortical, throughout megasporogenesis. In the megasporocyte, megaspores and one-nucleate embryo sac, randomly oriented microtubules throughout the cells may serve to maintain cytoplasmic integrity and position organelles. Numerous microtubules (MTs) associate closely with the nucleus and some radiate from it, perhaps functioning in nuclear positioning. During meiosis MTs are restricted to the spindle configurations and later to the phragmoplasts which form between daughter nuclei. The lack of interphase cortical arrays suggests that the role of internal influences on cell shape is small.     

Teratisms in living and fossil megaspores of the Lycopsida: tetrad arrangement and exine ontogeny

Abnormal megaspore tetrad configurations from Selaginella laevigata and of Lagenicula crass-iaculeata (Lower Carboniferous) have been studied by SEM. These abnormalities reflect the variation expected in the presumed evolution of the seed-plants from free-sporing het-erosporous ancestors. In addition, they indicate a possible role for the aborted members of a tetrad in the successful development and maturation of the functional spore(s). Aborted members of tetrads also reveal the later stages of the developmental sequence occurring in spore wall construction and highlight the interplay of sporopollenin production, its colloidal flocculation and polymerization, and distortion caused by protoplast expansion. Possible causes of abortion in both living and extinct lycopsid megaspores are discussed.     

Megasporogenesis,Microsporogenesis and Development of Gametophytes in Eleutherococcus senticosus (Araliaceae)

This paper describes megasporogenesis, microsporogenesis, and development of female and male gametophytes in Eleutherococcus senticosus. The main results are as follows: Flowers of E. senticosus are epigynous, pentamerous. Anthers are 4 -microsporangiate. An ovary has 5 loculi. Each ovary loculus has 2 ovules: the upper ovule and the lower ovule. The upper one is orthotropous and degenerates after the formation of archesporial cell, while the lower one is anatropous, unitegmic and crassinucellar, and able to continue developing. In male plants, microsporogenesis and development of male gametophytes took place in regular way, but a series of abnormal phenomena were found in megasporogenesis and development of female gametophytes. The microspore mother cells gave rise to tetrahedral tetrads by meiosis. Cytokinesis was of the simultaneous type. The mature pollen was 3-celled and shed singly. The anther wall formation belonged to the dicotyledonous type. At the stage of microspore mother cell, the anther wall consisted of four layers, i.e. epidermis, endothecium, middle layer, and tapetum. The tapetum was of glandular type and its most cells were binucleate. When microspores were at the uninucleate stage, the tapetum began to degenerate in situ. When microspores developed into 3-celled pollen grains, the tapetum had fully degenerates. In the lower ovule of male flower, the megaspore mother cell gave rise to a linear or “T” -shaped tetrad. In some cases, a new archesporial cell over the tetrad or two tetrads parallel or in a series were observed. Furthermore, the position of functional megaspore was variable; any one or two megaspores might be functional, or one megaspore gave rise to a uninucleate embryo sac, but two other megaspores also had a potentiality of developing into the embryo sac. In generally, on the day when flowers opened, female gametophytes contained only 4 cells: a central cell, two irregular synergids and one unusual egg cell. In female plants, microspore mother cells and secondary sporogenous cells were observed. But at the stage of secondary sporogenous cell, the newly differentiated tapetum took the appearance of degeneration. Later, during the whole stage of meiosis, the trace of degenerative tapetum could be seen. At last, the microsporangium degenerated and no tetrad formed. On the blossom day, all anthers shriveled without pollen grains. In female flowers, megasporogenesis and development of female gametophytes were normal: the tetrad of megaspores was linear or “T”-shaped; the chalazal megaspore was usually functional; the development of embryo sac was of the Polygonum type. On the blossom day, most embryo sacs consisted of 7 cells with 8 nuclei or 7 cells with 7 nuclei; but the egg apparatus was not fully developed. In hermaphroditic plants, microsporogenesis was normal but the development of male gametophytes was partially abnormal. When the hermaphroditic flowers blossomed, there were more or less empty pollen grains in the microsporangium and these pollen grains were quite different in size. The development of most gynoecia was normal but numerous abnormal embryo sacs could be seen. On the blossom day, female gametophytes were mainly 7-celled with 8-nuclei or with 7-nuclei or 4-celled with antipodal cells degenerated; the egg apparatus wasnot fully developed either.     

Pteridophytic features in some Lower Carboniferous seed megaspores

Some Lower Carboniferous seed megaspores have triradiate sutures–unequivocal evidence of their being arranged in a tetrahedral configuration. This type of tetrad arrangement is unknown in the ovules of modern gymnospermS. Some of the fossil tetrads consist of one large functional megaspore and three smaller abortive spores attached at the apex of the large one. All four spores have an exinous covering.
Spores arranged in tetrahedral tetrads, and hence with triradiate sutures, are characteristic of many modern and fossil free-sporing pteridophyteS. In possessing this feature the fossil seed megaspores are more similar to the spores of these pteridophytes than to the megaspores of modern gymnosperms.     

Embryology and fruit development in four species of Pistacia L. (Anacardiaceae)

Pistacia atlantica, P. palaestina, P. lentiscus and P. saportae , were found to have great similarity in their embryology and fruit development. The anatropous, pendulous and crassinucellate ovule was initially unitegmic; later, the integument split close to the micropyle, forming a partial second integument. After anthesis there was a development of a hypostase and an obturator. The development of the Polygonum-type embryo sac followed division of a megaspore mother cell, giving a tetrad or triad of megaspores. The functional megaspore was the chalazal one. The ovary developed into a mature pericarp after anthesis, even when pollination was prevented, and before the zygote divided. Therefore, the fruit can be parthenocarpic. The ovule started to grow after initiation of embryo development until it filled the cavity within the pericarp. The zygotes were dormant for 4–18 weeks after pollination. In P. saportae reproduction became arrested during the development of the embryo sac; only very few abnormal embryos were found. No fixed pattern of embryo development could be discerned. The endosperm was initially nuclear, becoming cellular when the embryo started to develop. The seed coat was derived from the integument and the remnants of the nucellus.     

秦艽的胚胎学研究

秦艽具５个雄蕊,花药壁的发育属于双子叶型,为变形绒毡尾,花粉母细胞减粉分裂时的胞质分裂为同时型,四分孢子主要呈四面体型,成熟花粉粒球形,具３－孔沟,多为２细胞。子房一定,中轴胎座,其上着生众多具单珠被,薄珠心的倒生胚珠,大孢子母细胞减数分裂形成线型四分体。合点端大孢子继续发育,少数为合点端第二个大孢子形成功能大孢子,胚囊发育属蓼型,受精作用属于有丝分裂前配子融合类型,胚按茄型发育,胚乳核型,胚乳早