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101.
Mature pollen grains ofNymphaea mexicana have a verrucate proximal surface, a psilate distal surface and an anazonasulculus (encircling-sulcate aperture). The developmental events of microspores and tapetal cells were observed with TEM and SEM. Radially oriented substructural elements are seen in the microspore surface coating ofNymphaea mexicana from the early tetrad stage through the whole exine development. These elements, being the structural units of the microspore surface matrix (glycocalyx), are associated with sporopollenin precursor accumulation. In young free microspores, radially oriented elements are observed at both proximal and distal poles as a palisade between the endexine and plasmalemma.—Several points are discussed: (1) the initial and mature forms of exine substructure elements; (2) the significance of exine substructure for realisation of morphogenetic processes; (3) the ways by which verrucate and psilate sculpture patterns are developed. 相似文献
102.
Michael Hesse 《Plant Systematics and Evolution》1979,132(1-2):107-139
Different members of the Angiosperm familiesOleaceae, Scrophulariaceae, Plantaginaceae andAsteraceae with variable modes of pollination were studied in relation to ultrastructure of pollenkitt and exine. In entomophilous representatives the mostly electron-dense and homogeneous pollenkitt is located on the outside layer of the exine, making the pollen sticky. In related anemophilous taxa the pollenkitt mostly is electrontransparent and inhomogeneous; it becomes inactive by remaining in the loculus or sinking to the bottom of the exine caves; this makes the pollen powdery. According to such criteria,Fraxinus ornus andRhinanthus serotinus are entomophilous, whileFraxinus excelsior is anemophilous. The pollen ofLathraea squamaria eventually becomes powdery and suited for wind dispersal. The broad transition field between entomo- and anemophily is demonstrated byPlantago andArtemisia. Plantago lanceolata is anemophilous, whilePl. serpentina andPl. media are amphiphilous.Artemisia nitida andA. mutellina are entomophilous,A. absinthium, A. pedemontana andA. gabriellae are amphiphilous, but tend towards entomo- (A. absinthium) or anemophily (A. gabriellae), whileA. chamaemelifolia and especiallyA. vulgaris are anemophilous. 相似文献
103.
Radial sculptural elements (e.g. ribs, lirae), formed by imbrication of two succeeding shell lamellae are found in members of both the Nautiloidea (Cymatoceras) and Ammonoidea (Phylloceratinae and Aspidoceratinae). Their formation involves periodic cessation of shell growth due to weak to moderate withdrawal of the shell secreting mantle. The radial lirae (0.5–1.5 mm in width) of Phylloceratinae and Aspidoceratinae (Aspidoceras and Pseudowaagenia) are created by the succession of sigmoid lamellae of the organic periostracum or of the outer prismatic layer, respectively. Each lira has a characteristic adorally‐projecting, scythe‐like appendage, arising from its crest. The prismatic lirae of Aspidoceras and Pseudowaagenia are analogous to the larger scaled pseudoribs of Cymatoceras. Garland‐like lamellae of the outer prismatic layer form the radial lirae of Mirosphinctes and Epaspidoceras (Aspidoceratinae), but these lack a conspicuous, projecting scythe‐like appendage. Additional prismatic cement is formed within adoral, oval hollow spaces of scythe‐appendage‐bearing lirae, either through diagenetic crystal growth, remote biomineralization or as a component of the dorsal shell. In Aspidoceratinae these prismatic infillings are replaced by a continuous herringbone layer, accompanied by a reduction of the lirae. 相似文献
104.
Most biological construction systems operate within the colloidal dimension. In view of this, it seems reasonable to reassess
what is known of the early stages of exine development in the light of a brief excursion into colloid and micelle behaviour.
The results of this analysis show remarkable similarity of structures and suggest that almost all of the features seen during
early pollen wall development can be easily interpreted using simple, established colloidal principles. This study of exine
framework and endexine development offers the possibility that growth of the early exine progresses by successive transitory
mesophases of a constrained micellar system. The self-assembling micelle mesophases will all be clearly recognized as constituents
of the developing exine. They include spherical, cylindrical, continuous layers of hexagonally-packed cylindrical units and
lamellar mesophases which most probably correspond to future granules, columellae, complex columellar (and alveolar) microarchitecture
and ``white-line-centred' lamellae. Furthermore, the various types of micelle involved have the potential to perform the
functions previously loosely assigned to the exine. 相似文献
105.
To better understand the relationships within the Asteroideae and Inuleae, the structure of the pollen exine was investigated
in seven genera and nine species of the subtribe Inulinae using LM, TEM and SEM. All taxa have a senecioid pattern of exine.
The tectal complex consists of three main layers that differ in thickness and morphology: a tectum, a columellar layer, and
a layer consisting of the basal region of the columellae. The absence or the vestigial condition of the foramina is considered
as a plesiomorphy within the Asteroideae. All taxa have a complex apertural system that consists of an ecto-, a meso-, and
an endoaperture. These apertures intersect respectively the tectal complex, the foot layer and the upper part of the endexine,
and the inner layer of the endexine. A continuous transition among the different species of Inulinae was found for all the
quantitative characters examined. This relative homogeneity of the pollen morphological characters enhances the naturality
of the subtribe Inulinae. 相似文献
106.
Fatemeh‐Zahra Amirmohammadi Majid Azizi Seyyed Hossein Neamati Farshid Memariani Ryan Murphy 《Nordic Journal of Botany》2019,37(8)
To evaluate nutlets characteristics for systematic relationships, a comprehensive morphological and micro‐morphological study of the nutlets of 16 Iranian taxa of Nepeta (Lamiaceae) was conducted using scanning electron microscopy (SEM). Differences in surface ornamentation, size, shape and color were observed between the species. The studied taxa were categorized in two basic types based on surface ornamentation: non‐sculptured (smooth‐type) and sculptured nutlets. The non‐sculptured nutlets type could be further divided into four sub‐types, including smooth, granulate, undulate‐cellular and reticulate. In the sculptured nutlets, three subtypes of tuberculate, tuberculate‐cellular and verrucate were recognized. The shape of nutlets were described as oblong, ovoid‐oblong, oblong‐linear, to elliptic‐oblong and their size range are 1.2–2.0 mm in length and 0.5–2.0 mm in width. Based on micrographs, the areole form and location were defined as bi‐lobed, straight, basal, sub‐basal or lateral. Nutlet micromorphological characteristics such as surface ornamentation can be useful for classification and identification of e.g. medicinal species of Nepeta in Iran. 相似文献
107.
NataliaE.ZAVIALOVA 《古生物学报》2003,42(1):1-7
通过对西西伯利亚西南部某钻孔中侏罗统上部(Callovian,Tyumen组)所获得的一个Classopollis的四孢体光学显微镜和切片的透射电镜观察研究后认识到,Classopollis的外壁超微结构与它复杂的外部形态一致。外壁由几层组成:上部均质层,具不平的外、内表面,中间均质层,穴状层和下部均质层。在它们之间的柱状体和穴在赤道区更明显。这种结构与光学显微镜下所见的条纹圈相当。环沟(亚赤道沟)是由柱状区和远极面之间的外壁突然变薄形成的。近极区的穴较之赤道区的要小且形状较不规则。外壁远极面较近极面为簿。远极面隐孔区无穴。比较表明此种花粉与掌鳞杉科花粉形态相似。 相似文献
108.
Rice CYP703A3, a cytochrome P450 hydroxylase,is essential for development of anther cuticle and pollen exine 总被引:2,自引:0,他引:2
Xijia Yang Di Wu Jianxin Shi Yi He Franck Pinot Bernard Grausem Changsong Yin Lu Zhu Mingjiao Chen Zhijing Luo Wanqi Liang Dabing Zhang 《植物学报(英文版)》2014,56(10):979-994
Anther cuticle and pollen exine act as protective envelopes for the male gametophyte or pollen grain, but the mechanism underlying the synthesis of these lipidic polymers remains unclear. Previously, a tapetum-expressed CYP703A3, a putative cytochrome P450 fatty acid hydroxylase, was shown to be essential for male fertility in rice (Oryza sativa L.). However, the biochemical and biological roles of CYP703A3 has not been characterized. Here, we observed that cyp703a3-2 caused by one base insertion in CYP703A3 displays defective pollen exine and anther epicuticular layer, which differs from Arabidopsis cyp703a2 in which only defective pollen exine occurs. Consistently, chemical composition assay showed that levels of cutin monomers and wax components were dramatically reduced in cyp703a3-2 anthers. Unlike the wide range of substrates of Arabidopsis CYP703A2, CYP703A3 functions as an in-chain hydroxylase only for a specific substrate, lauric acid, preferably generating 7-hydroxylated lauric acid. Moreover, chromatin immunoprecipitation and expression analyses revealed that the expression of CYP703A3 is directly regulated by Tapetum Degeneration Retardation, a known regulator of tapetum PCD and pollen exine formation. Collectively, our results suggest that CYP703A3 represents a conserved and diversified biochemical pathway for in-chain hydroxylation of lauric acid required for the development of male organ in higher plants. 相似文献
109.
莼菜(Brasenia schreberi Gmel)的绒毡层属腺质绒毡层。四分体时期是绒毡层细胞发育的高峰期,大量膨胀的内质网互相连接,在切面网格构布满细胞,用三维空间结构分析,内质网从多的小室,每个小室中充满核糖体。四分体发育后期,内质网小室中的核糖体开始解体,形成高电子密度的球形体,内质网消失后,从金钱求证菜体游离于细胞基质中。花粉单核期,球形体通过质膜进入花粉囊。在花粉外壁形成 ,球形体不 相似文献
110.
The genus Nothofagus is mainly distributed in South America and New Zealand.
The present paper describes its pollen exine ultrastructure and compares the exine ultrastructure with that of the other genera of Fagaceae. The pollen grains were examined using ultrathin sectioning technique under transmission electron microscope. The study shows that the
pollen exine ultrastructure of Nothofagus differs from that of the other genera of Fagaceae by
its exine structure and thickness, type of aperture, and ornamentation. The pollen exine of
Nothofagus is thin and possesses granular bacules, regular foot layer and tectum, spinulate
ornamentation, and the endexine is usually visible at poral area, and 5~8 colpate. The pollen
exine of the other genera of Fagaceae possesses entire bacules, irregular foot layer and tectum, granulate and tuberculate ornamentation, thicker endexine, and is 3-colporate ( 3-colpate
or 3-colporoidate). The pollen exine ultrastructure of Nothofagus may belong to primitive
type. The pollen exine ultrastructure data support Kuprianova’s opinion that Nothofagus
should be separated from Fagaceae and established as a monogenetic family, i.e. Nothofa-gaceae. 相似文献