Ovule Primordia Research Articles

Identification of genes expressed during early Arabidopsis carpel development by mRNA differential display: characterisation of ATCEL2, a novel endo-1,4-beta-D-glucanase gene.

The floral homeotic gene AGAMOUS (AG) imparts carpel identity on the fourth whorl of floral organs in wild-type Arabidopsis flowers. Less is known about the genes that regulate carpel patterning and differentiation. To identify cndidate regulators, we screened for genes expressed in developing carpels. Since Arabidopsis carpels are difficult to isolate, we used whole inflorescence apices of two floral homeotic mutants (pi and pi ag) and mRNA differential display, to identify carpel transcripts. Two of the resulting cDNA clones were shown to be expressed predominantly in flowers. They encoded AGL11, a MADS box transcription factor known to be expressed in the carpel and ovules, and a novel Arabidopsis endo-1,4-beta-D-glucanase (ATCEL2). In situ hybridisation localised the ATCEL2 transcript to the developing septum and ovule primordia of young carpels.

Pattern formation and growth during floral organogenesis: HUELLENLOS and AINTEGUMENTA are required for the formation of the proximal region of the ovule primordium in Arabidopsis thaliana.

Our understanding of the molecular mechanisms that regulate and integrate the temporal and spatial control of cell proliferation during organ ontogenesis, particularly of floral organs, continues to be primitive. The ovule, the progenitor of the seed, of Arabidopsis thaliana has been used to develop an effective model system for the analysis of plant organogenesis. A typical feature of a generalized ovule is the linear arrangement of at least three distinct elements, the funiculus, chalaza and nucellus, along a proximal-distal axis. This pattern is supposed to be established during the early proliferative phase of ovule development. We provide genetic evidence that the young ovule primordium indeed is a composite structure. Two genes, HUELLENLOS and AINTEGUMENTA have overlapping functions in the ovule and differentially control the formation of the central and proximal elements of the primordium. The results indicate that proximal-distal pattern formation in the Arabidopsis ovule takes place in a sequential fashion, starting from the distal end. Furthermore, we show that HUELLENLOS also regulates the initiation and/or maintenance of integument and embryo sac ontogenesis and interestingly prevents inappropriate cell death in the young ovule.

Suppressive effect of perinatal testes on the differentiation of fetal ovaries transplanted into adult males in the rat.

A 14 d ovarian primordium was transplanted with a fetal testis (13-18 d and 21 d of gestation) or a neonatal testis (15, 20, 30 and 45 d after birth) into the renal subcapsular position of an adult male rat. Two weeks after transplantation, transplants were examined as to the degree of ovarian and testicular differentiation. In the combination of a 14 d ovary and a 13 d testis, there were 3 types of result: either the ovary or the testis alone developed or both gonads developed well. Ovaries transplanted in union with 15-18 d testes did not develop, although the testes developed normally. Some ovaries in union with 21 d testes developed normally. In combination with infantile testes, the incidence of developed ovaries increased as the age of testes advanced. These results suggest that the 13 d fetal testes begin to suppress the development of cotransplanted 14 d ovaries, that 14-18 d fetal testes maintain such suppressive effects and that this effect gradually diminishes in infantile testes as they progress toward 45 d after birth.

A floral ontogenetic investigation of the Hydrangeaceae

As a first step towards a broader floral ontogenetic study on Cornales, the flowers of four species of Hydrangeaceae (Deutzia corymbosa, Kirengeshoma palmata, Philadelphus purpurascens and Hydrangea petiolaris) were studied. In Deutzia and Kirengeshoma five sepal primordia are generally initiated, in Philadelphus only four. Sepal initiation in Kirengeshoma shows a tendency to tetramony. Deutzia has a variable sepal initiation. Petal growth was never retarded in the studied species. Initiation of the androecium in Kirengeshoma, Philadelphus and Hydrangea starts with antesepalous primary primordia, on which secondary primordia are soon formed, leading ultimately to the formation of polystaminate androecia. In Deutzia a diplostemonous androecium is formed, starting with the initiation of the antesepalous stamen primordia. Gynoecium development is similar in all species studied: on a concave floral apex, a ring meristem is initiated; it develops into a variable number of continuous carpel primordia, while the centripetally growing common margins form the septa. Initiation of the ovule primordia starts halfway up each placenta and extends in an apical, basal and lateral direction. A number of morphological problems are discussed, such as the derivation of tetramery, and evolutionary and developmental trends in the androecium and gynoecium. Kirengeshoma is well settled in Hydrangeaceae, although its exact position within the family remains uncertain. A sistergroup relationship of Hydrangeaceae with Loasaceae is supported. However, Hydrangeaceae also share features with Saxifragaceae (e.g. similar gynoecium development).

Dissection of sexual organ ontogenesis: a genetic analysis of ovule development in Arabidopsis thaliana.

Understanding organogenesis remains a major challenge in biology. Specification, initiation, pattern formation and cellular morphogenesis, have to be integrated to generate the final three-dimensional architecture of a multicellular organ. To tackle this problem we have chosen the ovules of the flowering plant Arabidopsis thaliana as a model system. In a first step towards a functional analysis of ovule development, we performed a large-scale genetic screen and isolated a number of sterile mutants with aberrant ovule development, We provide indirect genetic evidence for the existence of proximal-distal pattern formation in the Arabidopsis ovule primordium. The analysis of the mutants has identified genes that act at an intermediate regulatory level and control initiation of morphogenesis in response to proximal-distal patterning. A second group of genes functions at a subordinate control level and regulates general cellular processes of morphogenesis. A large group of male and female sterile mutants shows defects restricted to early or late gametogenesis. In addition, we propose that the mature ovule obtains its overall curved shape by at least three different processes that act in only one domain of the ovule.

Ultrastructure of Megasporogenesis and Early Megagametogenesis in Arundo formosana Hack. (Poaceae)

The ovule of Arundo formosana Hack. is tenuinucellate, the megasporocyte originating from a hypodermal cell of the ovule primordium. Embryo sac development is of the Polygonum type. At its inception, the megasporocyte appears to be identical to the surrounding nucellar cells except for its larger size and dominant nucleus. The onset of megasporogenesis is indicated by the expansion of the megasporocyte, which is accompanied by a decrease in cytoplasmic density. Callose deposition in the expanded megasporocyte originates from the micropylar end and extends laterally. During megasporocyte expansion, the nucleus retains the micropylar location. Meiosis results in the formation of a linear, T-shaped, or intermediate tetrad: the chalazal megaspore is functional; all others will degenerate. The functional megaspore appears least dense among the cells of the tetrad and seldom contains vacuoles. As the megaspore enlarges, the organelles and the cytoplasmic density increase, the callose wall is gradually digested, and a electron-dense wall appears. The vacuoles are randomly distributed and then gradually migrate to both poles of the megaspore. A well-developed megaspore shows organelle polarity such that most plastids and dictyosomes are distributed in the micropylar region. The polarized dictyosome and plastid distributions persist through the two- and four-nucleate stage of the embryo sac, respectively. The two- and four-nucleate embryo sac is characterized by the presence of large central and chalazal vacuoles. Plasmodesmata persist in the chalazal wall during megasporogenesis and megagametogenesis to the four-nucleate stage.

Ovule and gametophyte development in Nicotiana glauca Graham (Solanaceae)

Abstract The development of ovule and megagametophyte is examined in Nicotiana glauca, using light microscopy. The ovules proved unitegmic, tenuinucellate and endothelial as in all the Solanaceae so far studied. The ovule primordia are of the three-zonate type. The integument, which is of dermal origin, is at first two-layered but later produces additional intermediate cells whose origin is not constant. The nucellus, whose initial curvature bears no relation to the origin of the integument, has, like other Solanaceae, a one or two-celled archesporium from which a single meiocyte develops. The gametophyte is confirmed to be bisporic in origin and its development follows the Allium type. Furthermore, the hypostase, which is rare in the family, is observed below the antipodal cells.

The BELL1 gene encodes a homeodomain protein involved in pattern formation in the Arabidopsis ovule primordium

Ovule development in Arabidopsis involves the formation of three morphologically defined proximal-distal pattern elements. Integuments arise from the central pattern element. Analysis of Bell1 (Bell) mutant ovules indicated that BEL1 was required for integument development. Cloning of the BEL1 locus reveals that it encodes a homeodomain transcription factor. Prior to integument initiation, BEL1 RNA localizes to the central domain, providing molecular evidence for a central pattern element. Therefore, proximal-distal patterning of the ovule involves the regulated expression of the BEL1 gene that controls integument morphogenesis. A model for BEL1 function is evaluated with regard to new data showing the expression pattern of the floral homeotic gene AGAMOUS (AG) early in wild-type and Bell ovule development.

The petunia MADS box gene FBP11 determines ovule identity.

In contrast to the wealth of information relating to genes regulating floral meristem and floral organ identity, only limited data are available concerning genes that are involved in determining and regulating the identity and development of an ovule. We have recently isolated the floral binding protein 11 (FBP11) MADS box gene from petunia and found that it is expressed exclusively in ovule primordia and subsequently in the ovules, suggesting a role for this gene in ovule formation. To test this hypothesis, we constructed a recombinant gene in which the full-size FBP11 cDNA was placed under the control of a strong cauliflower mosaic virus 35S promoter. Transgenic petunia plants expressing this chimeric gene have ovulelike structures on the adaxial side of the sepals and the abaxial side of the petals. Detailed morphological studies showed that these ovulelike structures are true ovules. RNA gel blot analysis was performed to investigate ectopic FBP11 expression in relation to the expression of the closely related FBP7 gene and the putative petunia class C-type homeotic genes FBP6 and pMADS3. Our results indicate that FBP11 represents an ovule identity gene. A new model describing the mode of action of FBP11 as an additional class D MADS box gene is presented.

A novel class of MADS box genes is involved in ovule development in petunia.

We isolated and characterized two ovule-specific MADS box cDNAs from petunia, designated floral binding protein (fbp) genes 7 and 11. The putative protein products of these genes have approximately 90% of their overall amino acid sequence in common. In situ RNA hybridization experiments revealed that both genes are expressed in the center of the developing gynoecium before ovule primordia are visible. At later developmental stages, hybridization signals were observed only in the ovules, suggesting that these genes are involved in ovule formation. To test this hypothesis, we raised transgenic petunia plants in which both fbp7 and fbp11 expression was inhibited by cosuppression. In the ovary of these transformants, spaghetti-shaped structures developed in positions normally occupied by ovules. These abnormal structures morphologically and functionally resemble style and stigma tissues. Our results show that these MADS box genes belong to a new class of MADS box genes involved in proper ovule development in petunia.

Petunia hybrida homologues of shaggy/zeste‐white 3 expressed in female and male reproductive organs

Petunia hybrida ovule-specific cDNA libraries were screened for genes encoding homologues of protein kinases known to be involved in developmental processes. Two cDNAs, PSK4 and PSK6 (Petunia hybrida shaggy related protein kinase), homologous to GSK-3 from rat, MDS1 from yeast and to the segment polarity gene shaggy/zeste-white 3 (sgg/zw3) from Drosophila were characterized in detail. Southern blot analysis showed that the PSK4 and PSK6 genes belong to a small multigene family in P. hybrida. The PSK4 and PSK6 proteins, which are 70% identical to sgg/zw3 and its functional homologue GSK-3 over the protein kinase catalytic domain and 55% identical to MDS1, represent two different subgroups of protein kinases. RNA gel blot and RT-PCR analyses revealed that the PSK4 gene is expressed during the vegetative phase and the female reproductive phase of development and the PSK6 gene predominantly during the male and female reproductive phases. In situ hybridization on developing flower buds confirmed that PSK4 is expressed throughout the different developmental stages from ovule primordium formation until embryo sac maturation, while PSK6 showed expression during anther cell differentiation and at pollen maturity, and an expression pattern similar to PSK4 in the female reproductive organs. The results also revealed transcripts of a PSK gene in embryos at the globular stage.

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

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.

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...

Alternative pathways of tobacco placental development: Time of commitment and analysis of a mutant

Previous work from our lab identified mutants, Mgr3 and Mgr9, of tobacco (Nicotiana tabacum) that produced unusual elongated green outgrowths from placentae in vivo. Similarly appearing stigmatoid growths were described developing from some in vitro cultures of excised placentae of tobacco (Hicks and McHughen, 1974, 1977). Here we report a developmental analysis and comparison of the unusual stigmatoid outgrowths seen in in vitro cultures of wild-type and mutant placentae, as well as the green outgrowths seen in vivo in the mutants. The growths produced by wild-type and mutant placental cultures in vitro, and the growths produced by the mutants in vivo, are identified as abnormal stigmas and styles. Wild-type in vitro placental cultures also produce outgrowths identified as homologs of whole carpels. Carpel fusion is not required for differentiation of stigma, style, transmitting tract, vascular traces, ovary, and ovules in these structures. The type and extent of stigmatoid growth production depends upon the age of the explant at excision and culture initiation. Before ovule primordium initiation, few growths are seen in culture; for a short window of time afterward, the primordia are competent to give rise to stigmatoid and carpelloid growths when cultured. After commitment to ovule development occurs, the primordia produce only ovules when cultured. The behavior of the mutant placental cultures is dimorphic. Explants from early stages behave similarly to wild-type when cultured, but differences between wild-type and the mutant behaviors in culture arise at the time when the stigmatoid growths begin to appear in vivo in the mutants. These results imply that ovule primordia pass through stages of distinct sequential restrictions of fate, first to growth as gynoecia, and then second to growth as ovules. The mutant strains described here perturb the commitment to differentiation as ovules.

EMBRYOLOGY OF CALYPSO BULBOSA. I. OVULE DEVELOPMENT

Calypso bulbosa is a terrestrial orchid that grows in north temperate regions. Like many orchids, the Calypso has ovules that are not fully developed at anthesis. After pollination, the ovule primordia divide several times to produce a nucellar filament which consists of five to six cells. The subterminal cell of the nucellar filament enlarges to become the archesporial cell. Through further enlargement and elongation, the archesporial cell becomes the megasporocyte. An unequal dyad results from the first meiotic division. A triad of one active chalazal megaspore and two inactive micropylar megaspores are the end products of meiotic division. Callose is present in the cell wall of the megaspore destined to degenerate. In the mature embryo sac the number of nuclei is reduced to six when the chalazal nuclei fail to divide after the first mitotic division. The chalazal nuclei join the polar nucleus and the male nucleus near the center of the embryo sac subsequent to fertilization.

Ovule and seed development in Droseraceae

A structural analysis of ovule and seed development in the four genera of the Droseraceae is given. The ovule primordia of the Droseraceae are dizonate. The integuments are dermal in origin. The ovules of Dionaea, Aldrovanda and Drosera are characterized by nucellar elongation and strongly enlarged cells of the nucellar epidermis. This feature is lacking in Drosophyllum. The differences in the seed coat of the four genera are mainly due to variations in the differentiation of the testa. Drosophyllum has an endotestal crystal layer, Dionaea and Aldrovanda are exotestal and exo-/endotestal respectively, whereas Drosera has a less complex testa. Contrary to the testa, the tegmen shows more correspondence. It consists of an endotegmic sclerotized or pigment layer and crushed remaining outer tegmic layers. As a consequence, in spite of the variable testa structure the basic seed coat structure is similar in the four genera. In Drosophyllum, Dionaea and Drosera the sclerotic layers of the seed coat are not lignified. Although the seed dimensions are different, the operculate seeds with starchy endosperm and small embryo have a similar construction. From the point of view of the seed anatomy, the four genera are correctly placed in the Droseraceae.

Development of the Ovary and the Female Reproductive Cells of the Lung Fluke, Paragonimus ohirai (Trematoda: Troglotrematidae)

The ultrastructure of the ovary of Paragonimus ohirai was investigated in different developmental stages of experimental infection in rats, from the metacercarial stage to the adult stage. The female reproductive cells were observed in order to understand the development of the ovary. During its development in the definitive host, the ovarian primordium and the ovary increased in size and cell number and underwent morphological changes. The blind end of the female genitalia was an undifferentiated primordium at the metacercarial stage, but became the bud of an ovary on day 3. Germ cells and supporting cells were observed on day 5. Oogonia were identified in the 15-day-old ovary, followed by the appearance of young oocytes at 17 days. Large oocytes were found on day 19, but the 21-day-old ovary contained degenerated oocytes. Mature ovaries were observed in the 26-day-old worms and egg formation was seen to arise on day 28. The development of the ovary and female reproductive cells was discussed in relation to the physiology of P. ohirai.

OVULES AND SEEDS OF TRIGONIACEAE

Trigonia cipoensis has a trizonate ovule primordium. The mature ovule is anatropous, bitegmic and tenuinucellate. Both integuments are of dermal origin; the inner integument is strongly multiplicative, especially after fertilisation. The mature seed is densely covered by cottony testal hairs. Of the inner integument the outer layer develops into a lignified, fibrous exotegmen, whereas the inner layer is tanniniferous. Endosperm formation is initially nuclear, the tissue later becoming cellular throughout. Ovule and seed structure indicates a relationship with the Linales and not with the Polygalales with which the family Trigoniaceae is ususally associated.

Ovule and seed ontogeny inGnetum gnemon L.

The ovule ofGnetum gnemon has three envelopes around the nucellus. The outer one forms two clear swellings at the lateral sides during the early developmental stages. The middle envelope also shows two swellings in many cases arranged decussately with respect to those of the outer one. All these swellings become obscure or disappear later. The inner envelope arises as an annular primordium and forms several manifest lobes at the stage of pollination. it develops two proliferating structures from its middle portion, viz., a flange and a micropyle-closing tissue. The three envelopes differentiatiate into the fleshy outer, sclerenchymatic middle and compressed inner layers of the seed coat, respectively. The inner one, however, remains restricted to the apical part of the seed owing to endochalazal growth. The outer envelope is derived from both dermal and subdermal cells of the ovule primordium and, therefore, is of dual origin. The middle and inner envelopes are subdermal in origin. The present study has cleared up some conflicting reports in the previous publications.