Outer Integument Research Articles

The Arabidopsis SUPERMAN Gene Mediates Asymmetric Growth of the Outer Integument of Ovules.

Arabidopsis superman (sup, also referred to as floral mutant10) mutants have previously been shown to have flowers with supernumerary stamens and reduced carpels as a result of ectopic expression of the floral homeotic gene APETALA3 (AP3). Here, we report that sup mutations also cause specific alterations in ovule development. Growth of the outer integument of wild-type ovules occurs almost exclusively on the abaxial side of the ovule, resulting in a bilaterally symmetrical hoodlike structure. In contrast, the outer integument of sup mutant ovules grows equally on all sides of the ovule, resulting in a nearly radially symmetrical tubular shape. Thus, one role of SUP is to suppress growth of the outer integument on the adaxial side of the ovule. Genetic analyses showed that the effects of sup mutations on ovule development are independent of the presence or absence of AP3 activity. Thus, SUP acts through different mechanisms in its early role in ensuring proper determination of carpel identity and in its later role in asymmetric suppression of outer integument growth.

Histochemical study of the development of the phytomelan layer in the seed coat ofGasteria verrucosa (Mill.) H. Duval

In this study we document the development of the phytomelan layer in the outer epidermis of the outer integument ofGasteria verrucosa. Phytomelan has been described as a black, melanin-like substance which is chemically very inert. Using histochemical techniques we show that phytomelan development in the cell wall can be divided into three stages. The first stage is deposition of a callosic layer against the tangential wall, with simultaneous thickening of the adjacent parts of the radial walls. The second stage is the conversion of this callosic wall, which we call a tertiary wall, into a noncallosic inner and outer layer. The inner layer stains predominantly for cellulose and a little for pectin. The outer layer is of unknown composition, since it did not react with the stains that were used. In the third stage the outer tertiary layer becomes black, the phytomelan. The callosic wall deposited in the first developmental stage seems to function as a carbohydrate source and as a mould for the tertiary cell wall. The conversion of the callose in the second stage might be the result of penetration of substances which react with callose. All the components for phytomelan seem to be present in the outer layer before the conversion. Phenolics might be involved in this second conversion.

Seed ontogeny in Adesmia securigerifolia (Fabaceae‐Adesmieae)

A study of the reproductive processes of Adesmia securigerifolia from bud to mature seed was carried out by means of field observations and the paraffin technique. Observations revealed the following new contributions to the study of legume embryology: 1) after fertilization, a small nucellar haustorium, or micropylar nucellar beak, was observed for the first time, originating from two obliterating nucellar cells that extended outwards. Their globose distal end comes in contact with the internal carpel wall, while the wedge shaped base stretches into the micropyle; a suspensor consisting of five or more cells ‐ the two basal cells are large and falcate and fit into the micropylar pore ‐ coexists with the undivided polar nuclei thus showing that endosperm formation begins after zygote division; 2) at the young embryo stage, a sac‐ shaped nuclear haustorium, formed by the endosperm, adjoins the outer integument and is not connected to the chalaza, or any vascular element; at the hilar level, a nucellar projection is formed in connection with the haustorial coenocytic endosperm. This projection persists up to the mature seed stage when it starts to degenerate, after performing another linking with the embryo nutrition system; 3) at the mature seed stage, the seed coat evolving from the outer integument has a single macrosclereid layer, though inclusions in the cell vacuoles simulate the presence of more layers and/or transverse walls. The lens, a hypodermal layer of osteosclereids (hour‐glass cells), and the astrosclereids are also described.

Embryology of Plagiopteron suaveolens Griffith (Plagiopteraceae) and its systematic implications

A study of the embryology of Plagiopteron suaveolens Griffith is presented in order to evaluate the affinities of the genus. Anther wall formation is of the dicotyledonous type. The anther tapetum is glandular and its cells become two to four nucleate. Cytokineses in the microspore mother cell is simultaneous and the resultant tetrad is tetrahedral. The mature pollen grains are two-celled. The anther has 4-locules at anthesis. The ovule is anatropous, bitegmic and weakly crassinucellate with only one cell-layered parietal tissue. The micropyle is zig-zag in section and formed by both inner and outer integuments which are three and three to four cell layers thick respectively. The megaspore archesporium is one-celled and the embryo sac development is of the Polygonum type. An endothelium is formed with early disintegration of nucellar tissue. The antipodals multiply to 15 to 20 cells. Embryological evidence supports the placement of Plagiopteron in its own family, Plagiopteraceae, with closest relationship with Celastraceae and close relationship with Elacocarpaceae, Rhizophoraceae and some families of the Geraniales.

Embryology of Plagiopteron suaveolens Griffith (Plagiopteraceae) and its systematic implications

A study of the embryology of Plagiopteron suaveolens Griffith is presented in order to evaluate the affinities of the genus. Anther wall formation is of the dicotyledonous type. The anther tapetum is glandular and its cells become two to four nucleate. Cytokineses in the microspore mother cell is simultaneous and the resultant tetrad is tetrahedral. The mature pollen grains are two-celled. The anther has 4-locules at anthesis. The ovule is anatropous, bitegmic and weakly crassinucellate with only one cell-layered parietal tissue. The micropyle is zig-zag in section and formed by both inner and outer integuments which are three and three to four cell layers thick respectively. The megaspore archesporium is one-celled and the embryo sac development is of the Polygonum type. An endothelium is formed with early disintegration of nucellar tissue. The antipodals multiply to 15 to 20 cells. Embryological evidence supports the placement of Plagiopteron in its own family, Plagiopteraceae, with closest relationship with Celastraceae and close relationship with Elacocarpaceae, Rhizophoraceae and some families of the Geraniales.

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.): Ultrastructural Seed Development and Nutrient Pathways

Ovules of broad bean (Vicia faba L.) were studied to disclose ultrastructural features, which can facilitate nutrient transport to the embryo sac from 10 d after pollination (DAP) to the mature seed. Fertilization occurs during the first 24 h after pollination. The endosperm is a coenocyte, which is eventually consumed by the embryo. By 10 DAP the inner integument is degraded and the outer integument adjoins the embryo sac boundary. The heart-shaped embryo approaches the embryo sac boundary at two sites, which here are named contact zones. Small integument cells in the neighbourhood of the first formed contact zones become separated by prominent intercellular spaces. A heterogenous scattering material, probably representing secretion products accumulates in these spaces. By 14-16 DAP the integument exudate disappears, and the suspensor degenerates. As the contact zones increase in size, wall ingrowths form a bridging network in the narrow space between the embryo sac boundary and the extra-embryonic part of the endosperm wall. The epidermal cells of the embryo separate adjacent to these zones, and develop conspicuous wall ingrowths. At 20 DAP vacuoles showing various stages in formation of protein bodies appear in the cells of the embryo.

Anatomía de la semilla de Chenopodium berlandieri ssp. nuttalliae (Chenopodiaceae) "huauzontle"

La semilla del huauzontle (Chenopodium berlandieri ssp . nuttalliae) se estudió con microscopía fotónica y con microscopía electrónica de barrido. Se encontró que cuando el tegumento externo se eleva alrededor del óvulo joven, en lugar de cubrir al tegumento interno y la nucela, crece en sentido inverso y rodea parcialmente al funículo. Cuando el pericarpo se retira, el color de la semilla es pajizo, ya que solamente el tegmen cubre la semilla madura. La cálaza aquí tiene forma semejante a un cono truncado, con una base elíptica hacia la nucela; en esta zona de contacto entre la cálaza y la nucela, se deposita una cutícula que rodea algunas células en forma de red tridimensional. Esta red cuticular-calazal está en contacto con una cutícula nucelar lisa que forman parte de la cubierta seminal. La inversión del tegumento interno podría representar una mutación seleccionada durante la domesticación.

Ovular Development and Morphology of the Outer Integument of Magnolia grandiflora (Magnoliaceae)

Ovular development of Magnolia grandiflora was examined to determine the morphology of the outer integument. At the time the ovular primordium begins incurving, the outer integument is initiated subdermally, and later the inner integument arises from the dermal layer. Whereas the inner integument is annular, the outer integument is formed as a semiannular rim interrupted on the concave side of the funiculus. Later the outer integument becomes a hood-shaped envelope. The obturator is formed as a transversely elongate outgrowth on the concave side of the funiculus and intervenes in the gap of the outer integument. During further development the inner integument produces several distal lobes, and the outer integument becomes bilobed. The exostome is a transverse slit with a middle notch, formed by the outer integument and the obturator. Presumed wide occurrence of the hood-shaped outer integument in primitive families suggests that it is a primitive state. The outer integument is compared with the ovuliferous sporophylls of the glossopterid and caytonialean seed ferns.

Ovular development and morphology of the outer integument of Magnolia grandiflora (Magnoliaceae)

Ovular development of Magnolia grandiflora was examined to determine the morphology of the outer integument. At the time the ovular primordium begins incurving, the outer integument is initiated subdermally, and later the inner integument arises from the dermal layer. Whereas the inner integument is annular, the outer integument is formed as a semiannular rim interrupted on the concave side of the funiculus. Later the outer integument becomes a hood‐shaped envelope. The obturator is formed as a transversely elongate outgrowth on the concave side of the funiculus and intervenes in the gap of the outer integument. During further development the inner integument produces several distal lobes, and the outer integument becomes bilobed. The exostome is a transverse slit with a middle notch, formed by the outer integument and the obturator. Presumed wide occurrence of the hood‐shaped outer integument in primitive families suggests that it is a primitive state. The outer integument is compared with the ovuliferous sporophylls of the glossopterid and caytonialean seed ferns.

Ovule and seed characters ofBalanites aegyptiacaand the classification of the Linales-Geraniales-Polygalales assembly

Balanites aegyptiaca (L) Del. has a trizonate ovule primordium and an elongated bitegmic, crassinucellate and anatropous ovule. The dermal inner and outer integument are about 45-layered and the inner layer of the inner integument becomes slightly endothelial. After fertilization the nucellus and subsequently the inner integument are resorbed. The outer integument ultimately becomes about 30-layered. The cells of the inner layer of the outer integument divide once periclinally. The vascularized seed-coat consists of parenchyma cells with scattered, lignified sclerenchyma elements. Ovule and seed characters support the recognition of a separate family Balanitaceae and a relationship with an enlarged order Linales

Homeotic Transformation of Ovules into Carpel-like Structures in Arabidopsis.

Ovules are specialized reproductive organs that develop within the carpels of higher plants. In Arabidopsis, mutations in two genes, BELL1 (BEL1) and APETALA2 (AP2), disrupt ovule development. In Bel1 ovules, the inner integument fails to form, the outer integument develops abnormally, and the embryo sac arrests at a late stage of megagametogenesis. During later stages of ovule development, cells of the outer integument of a Bel1 ovule sometimes develop into a carpel-like structure with stigmatic papillae and second-order ovules. The frequency of carpel-like structures was highest when plants were grown under conditions that normally induced flowering and was correlated with ectopic expression in the ovule of AGAMOUS (AG), an organ-identity gene required for carpel formation. Together, these results suggested that BEL1 negatively regulates AG late in ovule development. Likewise, mutants homozygous for the strong AP2 allele ap2-6 sometimes displayed structures with carpel-like features in place of ovules. However, such abnormal Ap2 ovules are much less ovulelike in morphology and form earlier than the Bel1 carpel-like structures. Because one role of the AP2 gene is to negatively regulate AG expression early in flower development, it is possible that AP2 works in a similar manner in the ovule. A novel ovule phenotype observed in Bel1/Ap2-6 double mutants suggested that BEL1 and AP2 genes function independently during ovule development.

Comparative structure of ovules and seeds inRafflesiaceae

The genera of theRafflesiaceae show a marked diversity in the structure of their ovules and seeds. Evolutionary trends are recognizable in ovule orientation and number of integuments. A change from anatropous ovules inApodantheae andMitrastemoideae towards incomplete anatropy inRafflesieae and orthotropy inCytineae occurs, next to a change from bitegmic ovules inApodantheae towards unitegmy with rudimentary outer integuments inRafflesieae andCytineae and full unitegmy inMitrastemoideae.—The differences in ovule structure are clearly reflected in the seeds. The seeds are essentially exotegmic, have very small embryos and an oily endosperm.—Seed structure strongly confirms the existing subfamilial classification and supports additional arguments for the generic status ofApodanthes. It does not support a separate status of the genusBerlinianche. InRafflesiaceae, seed micromorphology is only of limited use at the species level. As far as known seed dispersal is endo- or exozoochorous in all genera.

Anatomía del desarrollo de la semilla de Hippocratea celastroides

El estudio embriológico de Hippocratea se restringe a pocas especies, e indica similitudes entre Hippocratea y las celastráceas. Sin embargo, diferencias basadas en H. grahamii han originado controversia sobre la posición taxonómica del género. Se estudió el desarrollo de semillas de H. celastroides H.B.K, mediante microscopía fotónica. Esta especie presenta óvulos anátropos y bitégrnicos. En antesis, el micrópilo se forma sólo por el tegumento interno. Hay depósito de taninos en el endotegmen y exotesta desde estados tempranos. Después de la fertilización, el tegumento externo crece abundantemente; él solo forma el ala. El desarrollo del endospermo es de tipo nuclear. El cigoto presenta un periodo de reposo de tres meses después de la singamia. La mesotesta desarrolla aerénquima que se diferencia gradualmente en células traqueoidales. Un estrato de endospermo permanece hasta la madurez. Los cotiledones son connados y dan un giro de 90°. Con base en estos resultados, aquí se considera a Hippocratea dentro de la familia Celastraceae.

Ovular development and morphology in some magnoliaceae species

Floral phenology and ovular development ofLiriodendron tulipifera are described. The ovule primordia are initiated in December, followed by prominent development in March, and the ovules are mature in May. The inner integument is formed as an annular rim on the incurving ovule primordia, but the outer integument develops as a semi-annular rim interrupted on the concave side of the funicle. Later, an outgrowth, which is interpreted here as an obturator, arises on the concave side of the funicle. The funicular outgrowth arises far from the inner integument, while the outer integument is close to the inner. The outer integument and the funicular outgrowth together form an envelope complex. Later the outer integument produces two distal lobes, which disappear at maturity. Mature ovules of the threeMagnolia species examined have similar lobes. It is suggested that the hood-shaped outer integument is primitive in angiosperms.

The carrot secreted glycoprotein gene EP1 is expressed in the epidermis and has sequence homology to Brassica S‐locus glycoproteins

Non-embryogenic carrot suspension cells secrete the EP1 glycoprotein. A cDNA clone encoding EP1 was isolated and sequenced. The EP1 sequence revealed a region of homology with Brassica S-locus glycoprotein genes, an Arabidopsis S-like gene and putative S-like receptor protein kinases from maize and Arabidopsis. EP1 gene expression, analysed by in situ mRNA localization, was detected in cells located at the surface of the seedling: in the epidermis of the root, the hypocotyl and the cotyledons, in the root cap, and in a crescent of cells in the apical dome of the shoot. In developing seeds, expression was most pronounced in both the inner and outer integument epidermis.

EMBRYOLOGY AND KARYOMORPHOLOGY OF LACTORIDACEAE

The embryology and karyomorphology of Lactoris fernandeziana, representing the monotypic family Lactoridaceae, were studied in an attempt to clarify its relationships. Embryologically, Lactoris is characterized by a combination of many generalized, plesiomorphic features, which are mostly shared with Magnoliales and partly shared with Laurales and Piperales, and some specialized, apomorphic features including a tenuinucellate ovule, a small nucellus with early disintegrating nucellar tissue, a nonmultiplicative outer integument, an endothelium, and haustorial endosperm. Karyomorphologically Lactoris is confirmed to have 2n = 40 at metaphase, probably as a tetraploid of x = 10, and more or less distinctive features at inter‐ and prophase. Comparisons based on its embryological and karyomorphological features suggest that Lactoris is not closely related to any other family. Based on evidence from various sources, we hypothesize that an evolutionary line was derived from a common ancestor with Magnoliales, and then diverged into Lactoris, which retains many primitive magnolialean features, and Piperales (and possibly other groups) with more specialized characteristics. Lactoris seems best placed in its own order, Lactoridales, near Piperales.

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.

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

Abstract 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.

An anatomical study of ovary-to-cuke development in consistently low-producing trees of the ?Fuerte? avocado (Persea americana Mill.) with special reference to seed abortion

Cukes develop from female-sterile, cryptically male flowers on consistently low-producing ‘Fuerte’ trees. A hypostase that has, as yet, not been reported for the avocado, is present in the chalazal tissue of the mature ovule and aborting seed. This layer seems to play a role in the degeneration of the peripheral nucellar tissue and the non-development of the intercalary meristem of the pachychalaza. The ultimate cause of cuke formation, however, seemingly lies in the disturbance of the polarity of the primordial nucellar tissue. Additional megagametophytes and non-functional megaspores that develop in the nucellus effect the collapse of the chalazal region of the embryo sac. Degeneration of these gametophytes and megaspores causes the formation of nucellar cavities that isolate the embryo sac from the nutritive tissues and chalazal flow of nutrients. The micropylar region of the embryo sac contains a well-developed egg cell, synergids and central cell nucleus. An embryo and a limited amount of endosperm tissue are formed. Because the endosperm is starved of nutrients, the formation of this tissue is curtailed at an early stage, and embryo development ceases. A meristematic zone that initiates from the inner layers of the outer integument, directly opposite the place where the vascular supply to the chalaza terminates, causes abnormal growth in the outer integument. It is suggested that, due to the absence of meristematic activity in the chalazal region of the embryo sac and the non-developing pachychalaza, resources are redistributed towards the stronger sink, i.e. the outer integument. Consequently, this part of the seed coat proliferates, while the embryo sac and pachychalaza degenerate. In spite of the abortion of the seed, the pericarp of the cuke continues to develop, possibly because the pericarp of the avocado contains phytohormones.

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.). I. Histogenesis Prior to and after Pollination

Structural adaptations promoting apoplastic transport to the embryo sac were studied in broad beans (Vicia faba) during histogenesis from ovule primordia to seed. Nucellus and the inner integument disappear at an early stage. The outer integument then adjoins the embryo sac boundary. In the thin part distal to the funiculus the cells of the persisting integument are smaller than in other parts and develop PAS-positive wall ingrowths opposite the embryo. At the late globular stage, the embryo establishes contact with the embryo sac boundary. In the contact zone, embryo cells develop wall ingrowths. Wall ingrowths are further formed on both sides of that part of the endosperm that is inserted between the outside of the cotyledons and the embryo sac boundary. The wall proliferations characterize all these cells as transfer cells. We conclude that the embryo sac is supported with nutrients from digested maternal tissues (nucellus, chalaza, inner integument, and part of the outer integument). These tissues are...