马蹄香大小孢子发生及雌雄配子体形成

马蹄香（Ｓａｒｕｍａｈｅｎｒｙｉ,Ｏｌｉｖ．）花药壁的发育属双子叶型。花粉母细胞减数分裂为同时型,四分体主要为四面体形,少数为左右对称式排列。腺质绒毡层,其细胞可排列为不规则的两层,双核或多核。到单细胞花粉阶段,绒毡层细胞内切向壁上出现许多乌氏体。成熟花粉为２细胞型,圆球状,具单萌发沟。雌蕊６心皮,上部彼此分离、下部联合。倒生胚珠,双珠被,厚球心。胚囊发育蓼型。成熟胚囊为七细胞结构,但两个助细胞退化较早。     

Polarity and competition between megaspores in the ovule ofOenothera hybrids

New data on the development of polarity in the ovules during megasporogenesis and early stages of embryo sac development inOenothera-hybrids are presented. It is confirmed that allOe. hookeri-hybrids show a strong tendency to form heteropolar tetrads, with the micropylar megaspore developing into an embryo sac. This preference is seen in the delay of the second meiotic division on the chalazal side, the absence of callose in the lateral wall of the micropylar megaspore, and the accumulation of starch in this megaspore. However, homopolar tetrads, chalazal preference, and ovules with two developing embryo sacs are also observed with considerable frequency. Quantitative data on the frequency of the different developmental types are compared with earlier genetic results about competition in the haplophase. There is sufficiently good agreement to support the hypothesis ofRenner that there is a correlation between the developmental processes in the megaspore tetrad and the genetic phenomena of competition in the haplophase.     

An unusual megaspore of uncertain systematic affinity from Lower Cretaceous deposits in south-east England and its biostratigraphic and palaeoenvironmental significance

An unusual megaspore has been recorded from beds within the Weald Clay Group of south-east England. Described as Clockhousea capelensis gen. et sp. nov., it is characterised by having a thick outer layer of exine consisting of closely packed columnar to clavate elements with constricted bases attached to a perforated inner layer and a sculpture that ranges from having the appearance of a negative reticulum through closely spaced verrucae to a mixture of verrucate and essentially baculate elements, all of which are surface manifestations and extensions of the underlying structure. These characters do not readily indicate a systematic relationship with any known heterosporous plant genus or family. The localised occurrence and relative abundance of the spores in a few beds suggest that some of the parent plants grew close to water bodies where they were deposited and preserved. Their recovery from sediments of late Hauterivian–early Barremian age indicates that the species has potential as a biostratigraphic marker in the upper Wealden succession of southern England and perhaps elsewhere.     

Cytokinin‐dependent specification of the functional megaspore in the Arabidopsis female gametophyte

The life cycle of higher plants alternates between the diploid sporophytic and the haploid gametophytic phases. In angiosperms, male and female gametophytes develop within the sporophyte. During female gametophyte (FG) development, a single archesporial cell enlarges and differentiates into a megaspore mother cell, which then undergoes meiosis to give rise to four megaspores. In most species of higher plants, including Arabidopsis thaliana, the megaspore closest to the chalaza develops into the functional megaspore (FM), and the remaining three megaspores degenerate. Here, we examined the role of cytokinin signaling in FG development. We characterized the FG phenotype in three triple mutants harboring non‐overlapping T–DNA insertions in cytokinin AHK receptors. We demonstrate that even the strongest mutant is not a complete null for the cytokinin receptors. Only the strongest mutant displayed a near fully penetrant disruption of FG development, and the weakest triple ahk mutant had only a modest FG phenotype. This suggests that cytokinin signaling is essential for FG development, but that only a low threshold of signaling activity is required for this function. Furthermore, we demonstrate that there is elevated cytokinin signaling localized in the chalaza of the ovule, which is enhanced by the asymmetric localization of cytokinin biosynthetic machinery and receptors. We show that an FM‐specific marker is absent in the multiple ahk ovules, suggesting that disruption of cytokinin signaling elements in Arabidopsis blocks the FM specification. Together, this study reveals a chalazal‐localized sporophytic cytokinin signal that plays an important role in FM specification in FG development.     

透射电子显微镜(TEM)技术在大孢子化石 超微结构研究中的应用

透射电子显微镜(TEM)具有优异的纳米尺度显微成像性能,因此被广泛应用于材料科学、物理学和生物学等学科的超微结构研究领域。文中根据应用TEM技术研究大孢子化石壁超微结构的实践体会,系统归纳和总结了大孢子化石TEM样品制备的前处理过程,主要步骤包括:材料选取、梯度脱水、包埋剂配比、梯度渗透、包埋、聚合、超薄切片和染色。运用上述TEM实验技术,文中以云南省曲靖市沾益区龙华山剖面中泥盆统吉维特阶上双河组分散拟网龙华山大孢(Longhuashanispora reticuloides Lu and Ouyang, 1978)的壁层超微结构为研究案例,揭示了这类孢子壁主要由三层薄壁组成,包括内部基底层、中部疏松层和外部致密层,其射线唇基底层下部具有近平行排列的多细纹带结构。此类大孢子的多细纹带结构与从加拿大新不伦瑞克省下泥盆统埃姆斯阶Campbellton组同孢植物化石Leclercqia complexa Banks et al., 1972中发现的原位小孢子射线唇基底层下部的多细纹带结构特征非常相似。此外,两者都具有相似的完全弓形脊和远极表面刺瘤状二型纹饰。因此综合外壁超微结构和纹饰形态特征,文中认为Longhuashanispora reticuloides的母体植物可能属于同孢植物向异孢植物演化过程中的过渡类型植物,并与Leclercqia complexa具有较近的亲缘关系。当前研究表明TEM技术在孢粉化石壁超微结构研究领域中具有独特优势,可为深入研究大孢子形态分类和揭示其与母体植物的亲缘关系提供新的线索,也可以被推广和应用到其他微体有机壁类化石的超微结构研究。     

化石大孢子Tricristatispora tricristata(Li,1974)comb.nov.

三冠大孢属Ｔｒｉｃｒｉｓｔａｔｉｓｐｏｒａ是我国西部地区上三叠统特征的常见化石。此前分别命名为Ｃａｌａｍｏｓｐｏｒａ ｔｒｉｃｒｉｓｔａｔａ Ｌｉ,１９７４,Ｔｒｉｃｒｉｓｔａｔｉｓｐｏｒａ ａｐｈｅｌａ Ｌｉｕ,１９８１和Ｖｉｂｕｒａｍｅｇａｓｐｏｒａ ｏｒｉｅｎｔａｌｉｓ Ｚｈａｎｇ,１９８４的几个种实属具相同特征的同种化石,后２个种名为前１种的晚出同义名,应予废弃。这里将种名ｔｒｉｃｒｉｓｔ     

藠头大小孢子的发生及雌雄配子体败育的细胞学研究

对栽培Ｊｉａｏ头４个品种大小孢子发生和雌雄配子体发育的细胞学观察表明,Ｊｉａｏ头小孢子细胞减数分裂过程基本正常,四分体左右对称或四面体体型,部分单核小孢子解体。散粉时,多数花粉粒空瘪,无萌发沟;部分花粉粒人单核或二核;极少数花粉粒具有生殖核和营养核。共 粒生活力低或无,无花粉管萌发。囊发育属葱型,部分能发育形成四核胚囊,大部分发育异常,出现二 核至五核胚囊,未观察到正常七细胞八核胚囊的形成。结果表     

鹤顶兰胚囊发育的超微结构观察

运用电子显微镜技术对鹤顶兰(Phaius tankervilliae(Aiton)BI.)胚囊发育过程中功能大孢子、二核胚囊、四核胚囊、成熟胚囊的超微结构进行观察,捕捉到了功能大孢子的三个阶段、成熟胚囊的两个阶段,进一步积累了鹤顶兰生殖生物学研究的基础资料.在功能大孢子、四核胚囊时期的合点端壁上可观察到胞间连丝,与体细胞间有物质及信息的交换,胚囊发育并非处于完全“隔离”状态.功能大孢子早期可见明显大液泡,随后进入第一次有丝分裂时大液泡消失,移向两极的染色体之间可见大量体积较小的液泡,成熟胚囊前期助细胞及卵细胞内也可见明显液泡,但当助细胞解体时,卵细胞内的大液泡也消失,液泡形态的变化可能是细胞生理状态发生改变的结果.