水蔗草胚珠附器的研究

本文对水蔗草的胚珠附器进行研究,结果表明：在功能大孢子时期,珠孔端的1—3个珠心细胞开始特化,发育成胚珠附器;胚珠附器发生时,有些胚珠同时出现无孢子生殖原始细胞;有性生殖和无孢子生殖的胚囊中均有胚珠附器存在;但在无孢子生殖的胚囊中,胚珠附器一般很大,长约是宽的1—3倍;而有性生殖胚囊的胚珠附器的长约是宽的1—2倍;和有性生殖胚囊相比,无孢子生殖胚囊的胚珠附器更加发达;存在发达的胚珠附器是水蔗草无孢子生殖胚囊的特点之一。     

四倍体双穗雀稗兼性无孢子生殖的研究

研究了四倍体双穗雀稗(Paspalum distichum L)无孢子生殖胚囊、胚胎发育以及假受精特点。当其大孢子母细胞发育至四分体阶段时,大多数情况下会发生四分体退化,同时有多个特化珠心细胞发育为1—3个无孢子生殖胚囊的现象。成熟无孢子生殖胚囊一般3核,包括1个卵细胞和2个极核。卵细胞在抽穗前就能自发分裂形成原胚团,而极核则在抽穗和传粉后参与假受精形成胚乳。当胚珠内存在多个无孢子生殖胚囊时,只是靠近珠孔端的1个无孢子生殖胚囊内的极核与精核结合,而其它的并不参与。种子成熟后出现很低频率的二胚苗。此外,还能观察到少量的有性生殖胚囊的发育以及有性生殖胚囊和无孢子生殖胚囊在同一胚珠中的发育现象,因此判断该类群为兼性无孢子生殖体。     

水蔗草兼性无融合生殖胚胎学研究

对水蔗草 (ApludamuticaL .)的生殖方式进行研究 ,结果表明水蔗草进行兼性无融合生殖。胚囊发育分为两种类型 ,即有性生殖的蓼型和无孢子生殖的大黍型。无融合生殖胚囊频率为 6 0 .74%。在大孢子母细胞发育至四分体后 ,珠孔端的 3个大孢子解体。合点端的大孢子未解体时 ,邻近大孢子的 1个珠心细胞开始特化 ,形成无融合生殖的原始细胞 ,由该原始细胞发育形成有 1个卵细胞、1个助细胞和 2个极核的四核胚囊。     

水蔗草兼性无融合生殖胚胎学研究

对水蔗草(Apluda mutica L.)的生殖方式进行研究,结果表明水蔗草进行兼性无融合生殖.胚囊发育分为两种类型,即有性生殖的蓼型和无孢子生殖的大黍型.无融合生殖胚囊频率为60.74%.在大孢子母细胞发育至四分体后,珠孔端的3个大孢子解体.合点端的大孢子未解体时,邻近大孢子的1个珠心细胞开始特化,形成无融合生殖的原始细胞,由该原始细胞发育形成有1个卵细胞、1个助细胞和2个极核的四核胚囊.     

水蔗草兼性无融合生殖的季节变化

对广州地区水蔗草在不同季节的无融合生殖胚囊和有性生殖胚囊频率进行了研究。结果表明:无融合生殖胚囊和有性生殖胚囊的频率在不同季节差异十分显著。两年中,无融合生殖胚囊出现的频率分别在冬季和夏季最高。     

土壤水分亏缺对水蔗草兼性无融合生殖的影响

无融合生殖是植物界中普遍存在的一种不经过精卵结合而产生种子的特殊生殖方式.水蔗草是禾本科水蔗草属的一种多年生草本植物,我国西南、华南等地均有分布,是广东、云南、海南等稀树草原常见的伴生植物.常生于海拔2 000 m以下的田边、水旁湿地及山坡草丛中.营养期草质柔嫩,可作饲料;根可治疗毒蛇咬伤.我们曾报道过水蔗草进行兼性无融合生殖,胚囊发育分为有性生殖的蓼型和无孢子生殖的大黍型两种类型     

草地早熟禾胚胎学研究 Ⅲ．多胚囊及多胚现象

报道了草地早熟禾中多胚囊的起源、发育和结构。在１个胚珠中,大孢子母细胞周围可以有一到多个起源于珠心细胞的胚囊原始细胞,并可以发育成为多胚囊,其中具有两个胚囊的可以发育成为成熟胚囊。起源于珠心的体细胞无孢子生殖胚囊的发育属于山柳菊型。两个成熟胚囊中,都可以形成胚和胚乳,因而形成了具假多胚的种子。位于中部的胚来源于珠心还囊,属于无融合生殖形成的胚。两个以上的多胚囊不能形成成熟胚囊。     

龙须草无融合生殖的胚胎学证据

采用石蜡切片技术对龙须草(Eulaliopsis binata(Rotz)C.E.Hubb)进行了系统的胚胎学研究,证明龙须草为禾本科植物中一种新的无融合生殖材料.龙须草无融合生殖方式为无孢子生殖,在胚珠发育早期,多个珠心细胞特化为无孢子生殖原始细胞,由原始细胞发育为单核胚囊,经两次有丝分裂形成4核胚囊,进一步分化形成两种类型的成熟胚囊:(1)具1个卵细胞,1个助细胞和2个极核,占观察总数的67.6%;(2)具1个卵细胞,2个助细胞和1个极核,占观察总数的32.4%.胚囊发育属大黍型.多个无孢子生殖原始细胞可以同时发育,最后形成2个或多个胚囊,其比例为17.7%.胚珠内没有有性胚囊的发育.胚的发生有两种类型:(1)早发生胚(74%),开花前1～2 d,极核未分裂前卵细胞分裂形成胚;(2)迟发生胚(26%),开花后2～3 d,极核分裂形成多个胚乳游离核后,卵细胞启动分裂形成胚.存在多胚现象,多胚来自不同胚囊内卵细胞的孤雌生殖,多胚发生率为13%.胚乳由极核不经受精自发分裂产生.     

有花植物的有性生殖

花是有花植物（被子植物）的有性生殖器官。在雄蕊的花药中产生雄配子体,通常称花粉;在雌蕊子房内的胚珠中发育雌配子体,通常称胚囊。在花粉或花粉管中形成的一对精细胞分别与胚囊中的卵和中央细胞受精,由此产生胚和胚乳。随着胚和胚乳的发育,整个胚珠发育为种子。这是被子植物有性生殖的一般过程。     

有花植物的有性生殖

花是有花植物（被子植物）的有性生殖器官。在雄蕊的花药中产生雄配子体,通常称花粉;在雌蕊子房内的胚珠中发育雌配子体,通常称胚囊。在花粉或花粉管中形成的一对精细胞分别与胚囊中的卵和中央细胞受精,由此产生胚和胚乳。随着胚和胚乳的发育,整个胚珠发育为种子。这是被子植物有性生殖的一般过程。     

Ultrastructural characterization of apospory in Panicum maximum

The nucellar ultrastructure of apomictic Panicum maximum was analyzed during the meiocytic stage and during aposporous embryo sac formation. At pachytene the megameiocyte shows a random cell organelle distribution and sometimes only an incomplete micropylar callose wall. The chalazal nucellar cells are meristematic until the tetrad stage. They can turn into initial cells of aposporous embryo sacs. The aposporous initials can be recognized by their increased cell size, large nucleus, and the presence of many vesicles. The cell wall is thin with few plasmodesmata. If only a sexual embryo sac is formed, the nucellar cells retain their meristematic character. The aposporous initial cell is somewhat comparable to a vacuolated functional megaspore. It shows large vacuoles around the central nucleus and is surrounded by a thick cell wall without plasmodesmata. In the mature aposporous embryo sac the structure of the cells of the egg apparatus is similar to each other. In the chalazal part of the egg apparatus the cell walls are thin and do not hamper the transfer of sperm cells. Structural and functional aspects of nucellar cell differentiation and aposporous and sexual embryo sac development are discussed.     

Embryological Studies on Apomixis in Pennisetum squamulatum

Studies on the formation and development of the embryo sac of the apomictic material of Pennisetum squamulatum Fresen indicated that normal archesporial cell did form with consequent development of a megaspore mother cell and later meiotic division to give rise to a triad. But invariably the megaspore mother cell and the triad underwent degeneration after formation. During the period of formation or degeneration of the megaspore or the triad a number of nucellar cells around the degenerated sexual cell became much enlarged. Frequently, one of the enlarging nucellar cells near the micropylar end became vacuolated and then developed into an aposporous uninucleate embryo sac, which underwent two further mitotic divisions to form an aposporous four-nucleate embryo sac, where the four nuclei remained in the micropylar end. Thus in the mature aposporous embryo sac there were one egg cell, one synergid and one central cell (containing two polar nuclei). Antipodal cells were completely lacking. The pattern of development of the aposporous embryo sac resembles the panicum type. There were two types of embryo formed during apomictic development namely ( 1 ) The pre-genesis embryo--embryo formed without fertilization, 1 to 2 days before anthesis, and (2) The late-genesis embryo--derived from the unfertilized egg cells, 3 to 4 days after anthesis. In the late-genesis embryo type, the egg cell divided after the secondary nucleus has undergone division to form the endosperm nuclei. All egg cells developed vacuoles before they differentiated into embryos. The development of the aposporous embryo followed the sequence of the formation of globular, pearshaped embryo and full stages of differentiation. The unfertilized secondary nucleus divides to form free endosperm nuclei after being stimulated by pollination. The development of the endosperm belongs to the nuclear-type.     

龙须草无融合生殖的胚胎学证据

采用石蜡切片技术对龙须草(Eulaliopsisbinata(Rotz)C.E.Hubb)进行了系统的胚胎学研究,证明龙须草为禾本科植物中一种新的无融合生殖材料。龙须草无融合生殖方式为无孢子生殖,在胚珠发育早期,多个珠心细胞特化为无孢子生殖原始细胞,由原始细胞发育为单核胚囊,经两次有丝分裂形成4核胚囊,进一步分化形成两种类型的成熟胚囊:(1)具1个卵细胞,1个助细胞和2个极核,占观察总数的67.6%;(2)具1个卵细胞,2个助细胞和1个极核,占观察总数的32.4%。胚囊发育属大黍型。多个无孢子生殖原始细胞可以同时发育,最后形成2个或多个胚囊,其比例为17.7%。胚珠内没有有性胚囊的发育。胚的发生有两种类型:(1)早发生胚(74%),开花前1~2d,极核未分裂前卵细胞分裂形成胚;(2)迟发生胚(26%),开花后2~3d,极核分裂形成多个胚乳游离核后,卵细胞启动分裂形成胚。存在多胚现象,多胚来自不同胚囊内卵细胞的孤雌生殖,多胚发生率为13%。胚乳由极核不经受精自发分裂产生。     

Sexual reproduction development in apomictic Eulaliopsis binata (Poaceae)

Apomixis is a particular mode of reproduction that allows progeny formation without meiosis and fertilization. Eulaliopsis binata, a tetraploid apomictic species, is widely used for making paper, rope and mats. There is great potential for fixation of heterosis in E. binata due to autonomous endosperm formation in this species. Although most of its embryo sac originates from nucellus cells, termed apospory, we observed sexual reproduction initiation in 86.8 to 96.8% of the ovules, evidenced by callose deposition on the walls of cells undergoing megasporogenesis. However, only 2-3% mature polygonum-type sexual embryo sacs were confirmed by embryological investigation. Callose was not detected on aposporous initial cell walls. The aposporous initial cells differentiated during pre- and post-meiosis of the megaspore mother cell, while the sexual embryo sac degenerated at the megaspore stage. DNA content ratio of embryo and endosperm in some individuals was 2C:3C, based on flow cytometry screening of seed, similar to that of normal sexual seed. These results confirm that apomictic E. binata has conserved sexual reproduction to a certain degree, which may contribute to maintaining genetic diversity. The finding of sexual reproduction in apomictic E. binata could be useful for research on genetic mechanism of apomixis in E. binata.