Ovule morphogenesis in Ranunculaceae and its systematic significance

BACKGROUND AND AIMS: Ranunculaceae has a prominent phylogenetic position in Ranunculales which appears at the base of eudicots. The aims of the present paper are to reveal the features of ovule morphogenesis in different taxa and gain a better understanding of the systematics of Ranunculaceae. METHODS: Flowers of 17 species from three subfamilies, nine tribes and 16 genera of Ranunculaceae, at successive developmental stages, were collected in the wild and studied with a scanning electron microscope. KEY RESULTS: The integuments in the unitegmic ovules in Helleborus, Ranunculus and Oxygraphis, as well as the inner integuments in the bitegmic genera, initiate annularly and eventually become cup-shaped. However, the integuments in the unitegmic ovules in Anemone and Clematis, as well as the outer integuments in the bitegmic genera, arise semi-annularly and eventually become hood-shaped. Different kinds of appendages appear on the ovules during development. In Coptis of subfamily Coptidoideae, a wrap-shaped appendage arises outside the ovule and envelopes the ovule entirely. In the genera of subfamily Thalictroideae and tribe Anemoneae of subfamily Ranunculoideae, appendages appear on the placenta, the funicle or both. In tribe Helleboreae of subfamily Ranunculoideae, an alary appendage is initiated where the integument and the funicle join and becomes hood-shaped. CONCLUSIONS: Ovule morphogenesis characteristics are significant in classification at the levels of subfamilies and tribes. The initiation patterns of the integuments and the development of appendages show diversity in Ranunculaceae. The present observations suggest that the bitegmic, hood-shaped outer integument and endostomic micropyle are primitive while the unitegmic, cupular-shaped outer integument and bistomic micropyle are derivative.     

甘蔗雌雄蕊的解剖学研究

甘蔗雄蕊花药的壁由四层细胞构成,药室内壁在花药成熟时才发育。花粉母细胞减数分裂属连续型,四分体正常发育为小孢子,但当开花时,只有少数进一步发育为成熟的花粉粒。甘蔗雌蕊柱头是分枝的,每一柱头毛是由数个细胞质浓密的细胞,呈不规则的纵列而组成。倒生胚珠一个,着生于子房室的内侧;内、外珠被均由两层细胞构成,外珠被上侧未能生长到珠孔,内珠被的内层细胞在胚珠发育中不断增大体积。石蜡制片是以樟油为透明剂的。     

The outer integument and funicular outgrowth complex in the ovule of<Emphasis Type="Italic"> Magnolia grandiflora</Emphasis> (Magnoliaceae)

The development of the outer integument and funicular outgrowth in the ovule of Magnolia grandiflora was examined by microtomy and scanning electron microscopy to reveal the morphology and evolution of the outer integument, a novel angiosperm structure. Early in development the outer integument is semiannular, decurrent to the lateral sides of the funiculus, and extends downwards beyond the funicular outgrowth that forms in the gap of the outer integument, and is transverse to the funiculus. The outer integument then overgrows the funicular outgrowth perpendicularly to the funiculus to form a micropyle together. The hood-shaped outer integument and the funicular outgrowth compose an envelope complex, and the interpretation of a single cupular outer integument is not supported. This envelope complex may differ from the cupular outer integument of other angiosperms, e.g., Nymphaeaceae, suggesting independent origin of apparently cupular outer integuments and hood-shaped outer integuments. Anatropous curving is due mainly to differential growth of the chalaza. The bistomic micropyle of Magnoliaceae seems to represent a derived character state, compared to an endostomic micropyle. T. Yamada is a research fellow of the Japan Society for the Promotion of Science.     

Translocation of Uranin within the Living Ovules of Vanilla

In the ovules of Vanilla (Vanilla planifolia Andr.) before fertilization, outer integument surrounded the lower part of ovule. Uranin got into ovule through funiculus, forming, the first center of fluorescence at the chalaza zone of ovule. Then uranin was transported to micropyle end along inner integument, forming the second center of fluorescence at micropyle end of inner integument. Soon, fluorescence appeared in the egg apparatua. After fertilization, the outer integument ovule extended upward, forming micropyle ogerber with inner integument. After getting into ovule through funiculus, uranin spreads to- ward several directions: l. transported to outer integument at the entrance of micropyle; 2. transported downward to chalaza zone along outer integument at the side of funiculus; 3. extended from chalaza zone to the inside and to the outer integument at the side far from funiculus The ovules of Vanilla had no vascular bundles. On transporting in inner integument, however, the cells in inner layer next to the embryo sac appeared to be the major passage. In mature embryo sac, there was cuticle between inner integument and embryo sac at the half of micropyle end. But between embryo sac at the half of chalaza end and nucellus, cuticle was absent. Nutrient could get into embryo sac from chalaza end undoubtedly. As egg apparatus showed the fluorescence after formation of fluorescence center of inner integument at micropylar end, the possibility that nutrient got into embryo sac from micropyle could not be excluded.     

非洲狼尾草胚珠(着重胚珠附器)发育的特点

用光学显微镜对非洲狼尾草胚珠发育做了进一步观察。结果表明有如下几个特点：（１）珠孔区域的珠心细胞发生特化,膨大１伸长并进入珠孔,形成胚珠附器。（２）珠心表皮平周分裂产生周缘珠心组织。（３）珠孔由内珠被和腹侧外珠被构成。     

Integument initiation and testa development in some Cruciferae

This study has shown for the first time that the middle layer (or layers) of the outer integument is (are) of subdermal derivation in at least some taxa of the Cruciferae. The outer integument is initiated in the Cruciferae in three different ways, viz. subdermally (Brassica, Sinapis) , partly subdermally and partly dermally (Lunaria) , or completely dermally (Capsella). These differences in initiation are reflected in the structure of the mature testa. The inner integument is completely of dermal derivation and originally two cell-layers thick, but may become more than two-layered during the ovule and seed maturation by periclinal divisions of the inner cell layer. The consequences of the ontogeny of the integuments for the terminology and interpretation of the mature testa is discussed.     

Embryogenesis and seed development in Sinomanglietia glauca (Magnoliaceae)

The development of the floral bud, especially the ovule and seed coat, of Sinomanglietia glauca was observed. Floral buds were covered by eight to nine hypsophyll pieces. The hypsophyll nearest the tepal was closed completely and characterized by two arrays of densely stained cells with dense cytoplasm, which split longitudinally at flowering. The perianth consisted of 16 tepals arranged in three whorls. The gynoecium was composed of numerous apocarpous carpels; the ovule was anatropous with two integuments. Embryogenesis was of the Polygonum type, and the endosperm was nuclear. The inner integument degenerated during seed development. The seed of S. glauca had an endotestal seed coat comprised of a sclerotic layer derived from the inner adaxial epidermis of the outer integument and a sarcotesta derived mainly from the middle cells between the inner and outer epidermis of the outer integument. The embryo developed normally, so embryogenesis is not the cause of difficult regeneration.     

Ovule morphogenesis and structure in Menispermaceae,focusing on the development of the single fertile ovule and its systematic significance

Menispermaceae is one of the core groups of Ranunculales. The single fertile ovule in each ovary in Menispermaceae varies greatly in integument number, micropyle formation, and integument lobe. However, data regarding ovule morphogenesis in the family are very limited. In this study, we document ovule development of selected species in the Menispermaceae using scanning electron microscopy and light microscopy. Ovule development in Menispermaceae shows the following characteristics. Two ovules are initiated in a young carpel, one of them degenerates gradually and the other develops into a fertile ovule in subsequent stages. Bitegmic in Sinomenium Diels. and Cocculus DC. and unitegmic in Stephania Lour. The formation of unitegmy is probably due to integumentary shifting. The annularly initiated inner integument is of dermal origin and has 2–3 cell layers in the family, but the semi-annularly initiated outer integument is of both dermal and subdermal origin. Both inner and outer integument are cup-shaped at maturity. The cup-shaped outer integument is formed due to the outer integument's extension to the concave (adaxial) side of the funiculus. The obturator is well developed and consists of 2–3 cell layers in Cocculus or 9–11 cell layers in Stephania. Ovule development of Menispermaceae suggests some common characteristics between Cocculus and Sinomenium, and derived unitegmy supports molecular data that indicate Stephania is one of the late-diverging lineages in the family. Integument lobations are present. The sterile ovule shows variations in the degeneration process. These results will provide evidence for exploring the evolution of ovules in Ranunculales.     

The phenotype of Arabidopsis ovule mutants mimics the morphology of primitive seed plants

In seed plants, the ovule is the female reproductive structure, which surrounds and nourishes the gametophyte and embryo. This investigation describes the PRETTY FEW SEEDS2 (PFS2) locus, which regulates ovule patterning. The pfs2 mutant exhibited developmental defects in the maternal integuments and gametophyte. This mutation was inherited as a maternal trait, indicating that gametophyte defects resulted from ovule patterning aberrations. Specifically, the boundary between the chalaza and the nucellus, two regions of the ovule primordia, shifted towards the distal end of pfs2 ovule primordia. Results indicated that the PFS2 locus could: (i) be involved in the development of either the nucellus or the chalaza; or (ii) establish a boundary between these two regions. Examination of genetic interactions of the pfs2 mutation with other well-characterized ovule loci indicates that this locus affects integument morphogenesis. Interestingly, the pfs2 inner no outer and pfs2 strubbelig double mutants had inner integuments that appeared similar to their ancestral precursor. The fossil record indicates that the inner integument evolved by fusion of sterilized sporangia or branches around a central megasporangium. The question of whether the structures observed in these double mutants are homologous or merely analogous to the ancestral precursors of the inner integument is discussed.     

FURTHER CYTOLOGICAL STUDIES OF A PERIODIC ACID-SCHIFF'S SUBSTANCE IN THE OVULES OF PASPALUM ORBICULARE AND P. LONGIFOLIUM

A periodic acid-Schiff's substance present in the micropylar end of the ovules of Paspalum orbiculare and P. longifolium was further studied by light and electron microscopy of glutaraldehyde-osmium-fixed and freeze-substituted, osmium-fixed tissues. The PAS substance is water soluble and is found in intercellular spaces between the nucellus and inner integument, the inner and outer integuments, the outer integument and ovary wall, and in the micropyle. Structurally the substance consists of fibrils embedded in a dense, amorphous matrix and may be associated with membranous structures in special layers between the plasmalemma and the cell wall in nucellar and integumentary cells. Part of the water soluble substance is believed to be secreted from the nucellar and integumentary cells. A large amount of this substance may be formed as a result of the dissolution of about one third of the distal micopylar portion of the outer integument prior to anthesis. Many of the electron-dense fibrils seem to be fibrillar intercellular substances and others appear to originate from the cell walls, including the cuticle. Both the matrix and the fibrils may be chemically heterogeneous and together form a mucilagenous substance which may facilitate the final growth of pollen tubes in these two species.     

Interactions among Genes Regulating Ovule Development in Arabidopsis Thaliana

The INNER NO OUTER (INO) and AINTEGUMENTA (ANT) genes are essential for ovule integument development in Arabidopsis thaliana. Ovules of ino mutants initiate two integument primordia, but the outer integument primordium forms on the opposite side of the ovule from the normal location and undergoes no further development. The inner integument appears to develop normally, resulting in erect, unitegmic ovules that resemble those of gymnosperms. ino plants are partially fertile and produce seeds with altered surface topography, demonstrating a lineage dependence in development of the testa. ant mutations affect initiation of both integuments. The strongest of five new ant alleles we have isolated produces ovules that lack integuments and fail to complete megasporogenesis. ant mutations also affect flower development, resulting in narrow petals and the absence of one or both lateral stamens. Characterization of double mutants between ant, ino and other mutations affecting ovule development has enabled the construction of a model for genetic control of ovule development. This model proposes parallel independent regulatory pathways for a number of aspects of this process, a dependence on the presence of an inner integument for development of the embryo sac, and the existence of additional genes regulating ovule development.     

长豇豆种皮和种脐的发育

长豇豆的胚珠具内外两层珠被,内珠被在种子发育早期退化消失,种皮仅由外珠被发育而成。外珠被的外表皮细胞径向伸长,外壁和经向壁增厚,形成约占成熟种皮厚度一半的栅栏层;亚表皮细胞发育为骨状石细胞层。第三层细胞类似于亚表皮层但细胞壁增厚不明显,其内方的多层薄壁细胞形成海绵组织。种脐具两层栅栏细胞,外栅栏层及其以外部分由珠柄组织发育而成管胞群。本文还对脐缝和管胞群的作用以及豆科种子的吸水机制进行了讨论。     

Embryology and Seed Development of Paepalanthus sect. Actinocephalus (Koern.) Ruhland (Eriocaulaceae)

Abstract: The embryology and seed structure of Paepalanthus sect. Actinocephalus species were studied. The embryological and structural seed characters fit well with those of the other commelinaceous families. Within the Commelinales sensu Dahlgren, Eriocaulaceae and Xyridaceae represent two embryologically close families. In Paepalanthus sect. Actinocephalus the ovule is orthotropus, bitegmic, and tenuicellate with a micropyle formed by the inner integument. The seeds are endotestal. The outer cell layer of the testa and the outer periclinal wall of the endotesta disintegrate during development. The endotegmen is tanniniferous. The outer layer of the tegmen becomes compressed and is no longer recognizable in the mature seed. The seeds are operculate.     

Gynoecium diversity and systematics of the Laurales

Carpel and ovule structure was comparatively studied in representatives of all eight families of the Laurales: Amborellaceae, Calycanthaceae, Chloranthaceae, Gomortegaceae, Hernandiaceae, Lauraceae, Monimiaceae, and Trimeniaceae. In all representatives the carpels are closed at anthesis. As in Magnoliales/winteroids, closure takes place in three different modes: (1) by postgenital fusion of the stylar (and ovarial) ventral slit (Calycanthaceae, Gomortegaceae, Lauraceae, Hernandiaceae); (2) by occlusion of the inner space by secretion (Amborellaceae, Chloranthaceae, Trimeniaceae, Mollinedioideae of Monimiaceae), all having extremely ascidiate carpels; (3) by a combination of (1) and (2), whereby the ventral slit in the style is postgenitally fused but a central canal remains open, which is filled by secretion (Monimiaceae except Mollinedioideae). The carpels have a single ovule in ventral median placentation; only Calycanthaceae have two lateral ovules, although the upper ovule degenerates. In contrast to Magnoliales/winteroids, several representatives have orthotropous or almost orthotropous ovules (Amborellaceae, Chloranthaceae, Gomortegaceae). Mature ovules vary in length between 425 μm (some Monimiaceae) and 1500 urn (some Calycanthaceae, Trimeniaceae). Although all ovules are crassinucellar, nucellus breadth varies between 60 μm (Chimonanthus, Calycanthaceae) and 500 μm (Hemandia, Hernandiaceae). In almost all representatives the single ovule (two in Calycanthaceae) tightly fills out the ovarial cavity. The micropyle is mostly formed by the inner integument. In a few cases there is no micropyle and the nucellar apex makes direct contact with the inner ovary surface or the funicle (Lauraceae p.p., Calycanthaceae p.p., Hernandiaceae p.p., Monimiaceae p.p.). The ovule is pachychalazal (or perichalazal) in Lauraceae, some Hernandiaceae, and Gomortegaceae. Both integuments are variously lobed or unlobed. The outer integument is semiannular or annular, and this may vary within a family (Calycanthaceae, Hernandiaceae, Monimiaceae); it is also exceedingly diverse in thickness (2–23 cell layers). Gynoecial traits support the association of Chloranthaceae, Trimeniaceae, and Amborellaceae, and also separately Gomortegaceae, Hernandiaceae, and Lauraceae. In addition, affinities of the first group with Schisandraceae, Illiciaceae and Austrobaileyaceae may also be supported.     

Seed coat development in Leucospermum cordifolium (Knight) Fourcade (Proteaceae) and a clarification of the seed covering structures in Proteaceae

MANNING, J. C. & BRITS, G. J., 1993. Seed coat development in Leucospermum cordifolium (Knight) Fourcade (Proteaceae) and a clarification of the seed covering structures in Proteaceae . The development of the seed coat and pericarp is studied in Leucospermum cordifolium from ovule to mature seed. The ovule and seed are characterized by a tegmic pachychalaza. The pericarp is adnate to the integuments from anthesis and remains unthickened to maturity. The outer integument forms the seed coat and the seed is endotestal: the outer epidermis becomes tanniniferous and the inner epidermis develops into a crystalliferous palisade. The inner integument degenerates at an early stage. Examination of the literature reveals that the crystal palisade layer of the outer integument has been erroneously assumed to constitute an endocarp. This finding indicates that a re-interpretation of all published information on the seed coat in indehiscent Proteaceae is necessary before any speculations on the phylogenetic significance of the seed coat can be entertained.     

Embryology of the Theaceae - anther and ovule development of Camellia, Franklinia, and Schima

The anther and ovule development of Camellia, Franklinia, and Schima (Theaceae, Camellioideae) were observed. The three genera share the following embryological traits: anther wall formation of basic type, tapetum of glandular type, walls of endothecial cells with secondary thickening, and production of pseudopollen grains in connective, which are dispersed into pollen sacs at anthesis, ovule bitegmic-tenuinucellate, micropyle formed by inner integument alone, hypostase present, and both integuments generally five-to-seven cell layered. One autapomorphy of the Camellioideae found in the present study is the production of pseudopollen. The three genera surveyed differ with respect to the number of middle layers in the anther, the presence or absence of stomata on connective epidermis, morphology of pseudopollen, type of embryo sac formation, form of ovule, ovular vasculature, and the proliferation of ovular epidermis, etc. Among the three genera, Franklinia and Schima are presumed to be closer embryologically, and Schima possesses more numerous specialized features.     

Development of ovule,fruit and seed of Xyris (Xyridaceae,Poales) and taxonomic considerations

The development of the ovule, fruit and seed of Xyris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick‐walled cells and exotesta with thin‐walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U‐shaped thickened walls. The studied species differ in the embryo sac development, which can be of the Polygonum or Allium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The Allium‐type embryo sac development was observed only in Xyris spp. within Xyridaceae. Xyris also differs from the other genera of Xyridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into Xyridoideae and Abolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 619–628.     

Gone and ovule ontogeny in Phyllocladus (Podocarpaceae)

TOMLINSON, P. B., TAKASO, T. & RATTENBURY, J. A., 1989. Cone and ovule ontogeny in Phyllocladus (Podocarpaceae). Cones are borne directly on phylloclades, usually in the position of basal segments or as segment appendages. Each cone consists of a series of spirally arranged bracts, of which the middle bracts each subtend a single, sessile ovule. There is no ovuliferous scale. Ovules arise as ovoid outgrowths; integument development involves periclinal divisions of hypodermal cells with the integument becoming bilobed and extended laterally. The mature ovule is flask-shaped. The integument includes an extensive middle region bounded by an inner and outer epidermis; the outer hypodermis is differentiated as two contrasted cell layers. An aril differentiates late by periclinal divisions of the outer hypodermal cells at the base of the ovule. The three outermost layers of the integument become differentiated in the mature seed as an epidermis, with thick, cutinized outer tangential walls, an outer hypodermal tanniniferous layer and a sclerotic inner layer. Each ovule is vascularized by two strands that diverge from the axial bundles delimiting the gap left by the departing bract trace.