Outer Integument Research Articles

Spatiotemporal Secretion of PEROXIDASE36 Is Required for Seed Coat Mucilage Extrusion in Arabidopsis

The epidermal cells of the Arabidopsis thaliana seed coat, which correspond to the second layer of the outer integument (oi2), contain large quantities of a pectic polysaccharide called mucilage within the apoplastic space beneath the outer periclinal cell wall. Immediately after seed imbibition, the mucilage is extruded and completely envelops the seed in a gel-like capsule. We found that a class III peroxidase family protein, PEROXIDASE36 (PER36), functions as a mucilage extrusion factor. Expression of PER36 occurred only in oi2 cells for a few days around the torpedo stage. A PER36-green fluorescent protein fusion was secreted into the outer cell wall in a polarized manner. per36 mutants were defective in mucilage extrusion after seed imbibition due to the failure of outer cell wall rupture, although the mutants exhibited normal monosaccharide composition of the mucilage. This abnormal phenotype of per36 was rescued by pectin solubilization, which promoted cell wall loosening. These results suggest that PER36 regulates the degradation of the outer cell wall. Taken together, this work indicates that polarized secretion of PER36 in a developmental stage-dependent manner plays a role in cell wall modification of oi2 cells.

The genesis of ovule and female gametophyte in Hemerocallis ×hybrida Hort. ex Bergmans (Hemerocallidaceae)

The results of the study on formation and morphology of ovules’ structures in Hemerocallis ×hybrida Hort. ex Bergmans (Hemerocallidaceae) are represented. It has been determined that ovules are anatropous, of medionucellate type. The sequences of initiation and development of inner and outer integuments, as well as morphological features of nucellus and ovule organization (presence of postamento-podium; coalescence of inner integument and nucellus; lysis of nucellar epidermis; well developed vascular bundle attaining the outer integument; hypostasa which is poor morphologically expressed; raphe; differentiated cells of the outer epidermis of inner integument) have been described. The inner integument is of dermal origin, and outer integument is both of dermal and subdermal origin. Embryo sac in H. ×hybrida develops from a chalazal megaspore according to Polygonum-type. Antipods are binuclear. The two polar nuclei and antipods’ nuclei fuse before fertilization. Degeneration of sporogenous cells and embryo sacs, anomalies of their structures differentiation lead to the ovules sterility. Sterile ovules in the cultivar ‘Pandora’s Box’ are about 90%. The ovules with morphologically normal embryo sac prevail in the cultivar ‘Wally Nance’.

Mapping Grape Berry Photosynthesis by Chlorophyll Fluorescence Imaging: The Effect of Saturating Pulse Intensity in Different Tissues

Grape berry development and ripening depends mainly on imported photosynthates from leaves, however, fruit photosynthesis may also contribute to the carbon economy of the fruit. In this study pulse amplitude modulated chlorophyll fluorescence imaging (imaging-PAM) was used to assess photosynthetic properties of tissues of green grape berries. In particular, the effect of the saturation pulse (SP) intensity was investigated. A clear tissue-specific distribution pattern of photosynthetic competence was observed. The exocarp revealed the highest photosynthetic capacity and the lowest susceptibility to photoinhibition, and the mesocarp exhibited very low fluorescence signals and photochemical competence. Remarkably, the seed outer integument revealed a photosynthetic ability similar to that of the exocarp. At a SP intensity of 5000 μmol m(-2) s(-1) several photochemical parameters were decreased, including maximum fluorescence in dark-adapted (F(m)) and light-adapted (F'(m)) samples and effective quantum yield of PSII (Φ(II)), but the inner tissues were susceptible to a SP intensity as low as 3200 μmol m(-2) s(-1) under light-adapted conditions, indicating a photoinhibitory interaction between SP and actinic light intensities and repetitive exposure to SP. These results open the way to further studies concerning the involvement of tissue-specific photosynthesis in the highly compartmentalized production and accumulation of organic compounds during grape berry development.

Spectrochemical study of coalified Trigonocarpus grandis (Pennsylvanian tree-fern ovule, Canada): Implications for fossil–organ linkage

Five coalified ovules of the type Trigonocarpus grandis are investigated four of which co-occur with tree-fern foliage Alethopteris pseudograndinioides in the medullosalean forest (basal Cantabrian), and the fifth occurs in top Asturian D (Sydney Coalfield, Canada). Addressed are questions of variability (what is a coalified ovule?), comparison with petrified ovules, pyrolysates and the original make-up of the grandis seeds, and can similar chemistry proxy for organic connection between ovule and foliage?The results demonstrate variable preservation quality despite similar thermal-maturity levels in the geological interval in which the ovules were collected. Nevertheless, the proposed T. grandis model is based on evidence from epidermises associated with inner and outer integuments, and a two-layered nucellus with granulose exine that is covered by a diaphanous layer (tectum?) and nucellar cuticle. The latter separates the inner cuticle of the inner integumentary surface from the megaspore membrane. Parenchymatous and sclerenchymatous cell structures are rare, whereas evidence for integuments, vasculature, and sclerotesta is equivocal. Overall, these features compare with petrified seeds.13C nuclear-magnetic resonance analysis suggests that the A. pseudograndinioides tree fern bore T. grandis seeds. Pyrolysates from low and high molecular weights can almost exclusively be grouped with alkenes and aromatics; phenolics, furan and branched alkenes; and with n-alkene/n-alkane homologous series (~3 to 1) for cuticles from the inner integumentary surface which suggests a cutin-based, aliphatic-rich biomacromolecule. More generally, preservation is presumed correlative with aliphatic content, but not exclusively, and organ–organ linkage by spectrochemical means certainly has potential as a new research vector in palaeobotany.

Semi-permeable layer formation during seed development in Elymus nutans and Elymus sibiricus

<p>The semi-permeable layer is a layer in the seeds of certain plants that restricts or impedes the exchange of the solute while allowing the permeability of internal and external water and gas, which is valuable protection to sustain the health and secure the growth, development and germination. In this study, the formation time and location of the semi-permeable layer in seed coats of <em>Elymus nutants</em> (Griseb.) and <em>Elymus sibiricus</em> (L.) were investigated. The experimental seed materials were gathered in the field from the flowering to seed maturation. The light microscopy and transmission electron microscopy for lanthanum nitrate identification were used to examine the characteristics of pericarp, seed coat and nucellus. The results showed that the semi-permeable layer was identified as the position, which can inhibit the penetration of the lanthanum, and it was checked as an amorphous membrane located at the outermost layer of the seed coat that is firmly attached to the seed coat. With seed development, the cells had differentiated and some parts of the ovary and the outer integument had disappeared. The semi-permeable layer originated from the outer layer of the inner integument, which was the original form of the seed coat. It can be stained by the Sudan III and clearly distinguished from other parts of the seed. The formation time of the semi-permeable layer in both species was nearly at 10 to 12 days post-anthesis (dpa), whereas seed physiological maturity was 24 to 26 dpa.</p>

Positive- and negative-acting regulatory elements contribute to the tissue-specific expression of INNER NO OUTER, a YABBY-type transcription factor gene in Arabidopsis.

BackgroundThe INNER NO OUTER (INO) gene, which encodes a YABBY-type transcription factor, specifies and promotes the growth of the outer integument of the ovule in Arabidopsis. INO expression is limited to the abaxial cell layer of the developing outer integument of the ovule and is regulated by multiple regions of the INO promoter, including POS9, a positive element that when present in quadruplicate can produce low-level expression in the normal INO pattern.ResultsSignificant redundancy in activity between different regions of the INO promoter is demonstrated. For specific regulatory elements, multimerization or the addition of the cauliflower mosaic virus 35S general enhancer was able to activate expression of reporter gene constructs that were otherwise incapable of expression on their own. A new promoter element, POS6, is defined and is shown to include sufficient positive regulatory information to reproduce the endogenous pattern of expression in ovules, but other promoter regions are necessary to fully suppress expression outside of ovules. The full-length INO promoter, but not any of the INO promoter deletions tested, is able to act as an enhancer-blocking insulator to prevent the ectopic activation of expression by the 35S enhancer. Sequence conservation between the promoter regions of Arabidopsis thaliana, Brassica oleracea and Brassica rapa aligns closely with the functional definition of the POS6 and POS9 regions, and with a defined INO minimal promoter. The B. oleracea INO promoter is sufficient to promote a similar pattern and level of reporter gene expression in Arabidopsis to that observed for the Arabidopsis promoter.ConclusionsAt least two independent regions of the INO promoter contain sufficient regulatory information to direct the specific pattern but not the level of INO gene expression. These regulatory regions act in a partially redundant manner to promote the expression in a specific pattern in the ovule and suppress expression outside of ovules. Establishment of this pattern requires cooperation and competition between multiple positive and negative regulatory elements.

Embryology of the dioecious Woonyoungia septentrionalis (Magnoliaceae)

The embryological characteristics and ovular integument development of the dioecious species Woonyoungia septentrionalis (Dandy) Law (Magnoliaceae), which are poorly understood, were investigated under laser scanning confocal microscope (LSCM) and light microscope (LM). The embryological characteristics conform to most of the previously studied species in Magnoliaceae. The anther has 4 microsporangia, and the anther wall develops according to the dicotyledonous type. Cytokinesis at meiosis of the microspore mother cells follows a modified simultaneous type, giving rise to isobilateral or decussate tetrads, and a cell plate is absent, but a membrane was observed. Mature pollen grains are 2‐cellular and have high germination rates. The ovule is anatropous, crassinucellate and bitegmic, and meiotic result in linear tetrads of megaspores, the one at the chalazal end functions directly as an embryo‐sac cell. The development of the embryo sac is of the Polygonum‐type and endosperm formation is of the nuclear type. The outer integument of the ovule differentiates into an outer fleshy and an inner stony layer while the inner integument is reduced to a tanniniferous layer. The normal embryological development, high germination rates of pollen and high seed set indicate that the primary reason for the decline of the species is not to be found in these developmental processes.

DEVELOPMENT OF THE INTEGUMENT IN TRIFOLIUM PRATENSE L. (ELÇİ ÇAYIRÜÇGÜLÜ-FABACEAE)

This study aims to reveal the histological and cytological changes undergone by integument cells in natural tetraploid Trifolium pratense L. (Elci Cayirucgulu) in the stages of proembryo, zygote, mature embryo sac and throughout ovule development. Female organs of flowers buds and flowers sampled from those at different developmental stages were embedded both in paraffin and epon 812. The structure of integument cells was examined in the stage of mature embryo sac and throughout ovule development by a light and a transmission electron microscopy. The ovules in natural tetraploid Trifolium pratense L. (Elci Cayirucgulu) have two integuments, namely inner and outer integuments. The primordia of both integuments start to appear from the medial part, chalaza. While the megaspore mother cell is in earlier stage of Prophase I, integuments start to develop. In the stage of mature embryo sac, the inner integument is two-cells thick and it fully covers the nucellus. The outer integument becomes thicker and thicker, and one of the cells grown faster covers the junction of inner integuments and joins with the other outer integument. It was concluded that necessary nutrients were sufficiently stored and transmitted in integument cells during the stages of ovule, embryo sac, zygote and proembryo development in natural tetraploid Trifolium pratense L. (Elci Cayirucgulu).

Epoxycarotenoid cleavage by NCED5 fine‐tunes ABA accumulation and affects seed dormancy and drought tolerance with other NCED family members

Carotenoid cleavage, catalyzed by the 9-cis-epoxycarotenoid dioxygenase (NCED) constitutes a key step in the regulation of ABA biosynthesis. In Arabidopsis, this enzyme is encoded by five genes. NCED3 has been shown to play a major role in the regulation of ABA synthesis in response to water deficit, whereas NCED6 and NCED9 have been shown to be essential for the ABA production in the embryo and endosperm that imposes dormancy. Reporter gene analysis was carried out to determine the spatiotemporal pattern of NCED5 and NCED9 gene expression. GUS activity from the NCED5 promoter was detected in both the embryo and endosperm of developing seeds with maximal staining after mid-development. NCED9 expression was found at early stages in the testa outer integument layer 1, and after mid-development in epidermal cells of the embryo, but not in the endosperm. In accordance with its temporal- and tissue-specific expression, the phenotypic analysis of nced5 nced6 nced9 triple mutant showed the involvement of the NCED5 gene, together with NCED6 and NCED9, in the induction of seed dormancy. In contrast to nced6 and nced9, however, nced5 mutation did not affect the gibberellin required for germination. In vegetative tissues, combining nced5 and nced3 mutations reduced vegetative growth, increased water loss upon dehydration, and decreased ABA levels under both normal and stressed conditions, as compared with nced3. NCED5 thus contributes, together with NCED3, to ABA production affecting plant growth and water stress tolerance.

Женские репродуктивные структуры Ginkgo gomolitzkyana N. Nosova, sp. nov. из среднеюрских отложений Ангрена (Узбекистан)

Ovules (seeds) of Ginkgo gomolitzkyana N. Nosova, sp. nov. are described from the Angrenian Formation of the Middle Jurassic in Angren, Uzbekistan. Ovules are attached to pedicels with a collar at bases. Collar diameter of G. gomolitzkyana is similar to that of G. ginkgoidea from the Middle Jurassic of Sweden and G. apodes from the Lower Cretaceous of China. Unfortunately the epidermal structures of the two last species are not described. Epidermal patterns of the outer surface of the collar of G. gomolitzkyana are similar to those of G. yimaensis. Lack of data on the structures of the collar inner surface of G. gomolitzkyana does not allow any detailed comparison. G. yimaensis differs from G. gomolitzkyana by 1.5โ€”2 times larger collar diameter. The ovules (seeds) of G. gomolitzkyana are similar to the ovules (seeds) of G. ginkgoidea, G. yimaensis, G. apodes, G. cranei and Ginkgo sp. (Deng et al., 2004), but they are smaller. The cuticle of the integument and the nucellus cuticle of G. apodes and Ginkgo sp. are not described, what does not allow a comparison with them. G. cranei, unlike G. gomolitzkyana, has thicker outer cuticle of integument and lacking papillae on the subsidiary cells of the stomata. The structures of megaspore membrane are studied only for G. ginkgoidea and G. yimaensis. They are similar to the structures of G. biloba and G. gomolitzkyana. Megaspore membrane of G. ginkgoidea is thicker, than that of G. gomolitzkyana. The dimensions of lacuna and bacula of G. ginkgoidea are not specified. The bacula of the megaspore membrane of G. yimaensis are smaller, than those of G. gomolitzkyana. In addition, G. yimaensis differs from the new species by the curved anticlinal cell walls of the outer integument epidermis. Unlike G. gomolitzkyana anticlinal cell walls of the nucellus of G. ginkgoidea are sometimes sinuous and mostly puncticulate. The seeds of G. biloba are five times larger than seeds of G. gomolitzkyana. The thickness of the outer integument cuticle of the living species is larger and the bacula of the megaspore membrane are thicker. This is the first record of the female reproductive structure of Ginkgo from the Jurassic in the Middle Asia.

Aril development in Celastraceae

AbstractTo learn more about the evolution of secondarily intercalated seed envelopes, a series of developmental studies of arillate seeds in gymnosperms and angiosperms was undertaken. The goal was to test whether the second (outer) integument could be derived from an aril of gymnospermous ancestors. In our developmental studies of three species of Celastraceae, however, it turned out that the structure termed aril in this family does not originate from the funiculus or the hilum but from the exostomatic micropyle. As a consequence, the micropyle is not inside the aril but at the base of the fleshy structure which is thus better referred to as a caruncula. The fleshy part in seeds of Celastraceae differs thus markedly from those seed appendages usually referred to as an aril. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Morphology and development of anthers and ovules in Croton and Astraea (Euphorbiaceae)

We examined the embryological development of anthers and ovules from Astraea (A. lobata and A. praetervisa) and Croton (C. floribundus, C. fuscescens, C. glandulosus, C. lundianus, C. piptocalyx, C. urucurana and C. triqueter) focusing on features with systematic significance for the group. Some of these features are common in Euphorbiaceae including: a dicotyledonous type of anther wall formation, a secretory tapetum, a mixed origin of the outer ovule integument, an epidermal origin of the inner ovule integument, the occurrence of many archesporial cells inside the ovules and a megagametophyte of the Polygonum‐type. Other features, such as the presence of styloid crystals in the tapetum, an idioblast with a druse in the endothecium, simultaneous and successive microsporogenesis, and a functional micropylar megaspore, have not previously been reported in the family. These characters appear to distinguish Croton and Astraea from other Euphorbiaceae and possibly represents autapomorphies for the tribe Crotoneae.

Subfunctionalization of Cellulose Synthases in Seed Coat Epidermal Cells Mediates Secondary Radial Wall Synthesis and Mucilage Attachment

Arabidopsis (Arabidopsis thaliana) epidermal seed coat cells follow a complex developmental program where, following fertilization, cells of the ovule outer integument differentiate into a unique cell type. Two hallmarks of these cells are the production of a doughnut-shaped apoplastic pocket filled with pectinaceous mucilage and the columella, a thick secondary cell wall. Cellulose is thought to be a key component of both these secondary cell wall processes. Here, we investigated the role of cellulose synthase (CESA) subunits CESA2, CESA5, and CESA9 in the seed coat epidermis. We characterized the roles of these CESA proteins in the seed coat by analyzing cell wall composition and morphology in cesa mutant lines. Mutations in any one of these three genes resulted in lower cellulose content, a loss of cell shape uniformity, and reduced radial wall integrity. In addition, we found that attachment of the mucilage halo to the parent seed following extrusion is maintained by cellulose-based connections requiring CESA5. Hence, we show that cellulose fulfills an adhesion role between the extracellular mucilage matrix and the parent cell in seed coat epidermal cells. We propose that mucilage remains attached to the seed coat through interactions between components in the seed mucilage and cellulose. Our data suggest that CESA2 and CESA9 serve in radial wall reinforcement, as does CESA5, but CESA5 also functions in mucilage biosynthesis. These data suggest unique roles for different CESA subunits in one cell type and illustrate a complex role for cellulose biosynthesis in plant developmental biology.

Angiosperm ovules: diversity, development, evolution

Ovules as developmental precursors of seeds are organs of central importance in angiosperm flowers and can be traced back in evolution to the earliest seed plants. Angiosperm ovules are diverse in their position in the ovary, nucellus thickness, number and thickness of integuments, degree and direction of curvature, and histological differentiations. There is a large body of literature on this diversity, and various views on its evolution have been proposed over the course of time. Most recently evo-devo studies have been concentrated on molecular developmental genetics in ovules of model plants. The present review provides a synthetic treatment of several aspects of the sporophytic part of ovule diversity, development and evolution, based on extensive research on the vast original literature and on experience from my own comparative studies in a broad range of angiosperm clades. In angiosperms the presence of an outer integument appears to be instrumental for ovule curvature, as indicated from studies on ovule diversity through the major clades of angiosperms, molecular developmental genetics in model species, abnormal ovules in a broad range of angiosperms, and comparison with gymnosperms with curved ovules. Lobation of integuments is not an atavism indicating evolution from telomes, but simply a morphogenetic constraint from the necessity of closure of the micropyle. Ovule shape is partly dependent on locule architecture, which is especially indicated by the occurrence of orthotropous ovules. Some ovule features are even more conservative than earlier assumed and thus of special interest in angiosperm macrosystematics.

Ancestral expression patterns and evolutionary diversification of YABBY genes in angiosperms

Lateral organ growth in seed plants is controlled in part by members of the YABBY (YAB) and class III homeodomain/leucine zipper (HD-ZIPIII) families of transcription factors. HD-ZIPIII genes appear to play a conserved role in such organs, but YAB genes have diversified, with some members of the family having specialized functions in leaves, carpels or ovule integuments. The ancestral expression patterns and timing of divergence of the various classes of YAB genes remain to be established. We isolated and evaluated the expression of one HD-ZIPIII and five YAB genes representing the five major YAB gene classes from Cabomba caroliniana, a member of the earliest-diverging angiosperms. Consistent with observations in eudicots, the FILAMENTOUS FLOWER (FIL) and YABBY5 (YAB5) genes of C.caroliniana were expressed in the abaxial regions of the leaf where new laminar segments arise, and the patterns of expression were mutually exclusive to those of HD-ZIPIII, indicating that these expression patterns are ancestral. Expression of CRABS CLAW (CRC) in the abaxial carpel wall, and of INNER NO OUTER (INO) in the abaxial outer integument of ovules was also conserved between eudicots and C.caroliniana, indicating that these patterns are primitive. However, the CRC gene was also expressed in other floral organs in C.caroliniana, and expression in stamens was also observed in another early-diverging species, Amborella trichopoda, indicating that carpel-specific expression was acquired after divergence of the Nymphaeales. The expression data and phylogeny for YAB genes suggest that the ancestral YAB gene was expressed in proliferating tissues of lateral organs.

Investigation of lignan accumulation in developing Linum usitatissimum seeds by immunolocalization and HPLC

Lignans are widely distributed plant metabolites associated with a large range of biological activities. An immunological probe was previously developed to immunolocalize lignans in mature flaxseed ( Linum usitatissimum) and allowed to show that they are mainly localized in the secondary wall of the sclerite cells layer of the outer integument of the seed. In order to precise the temporal regulation of these secondary metabolites, L. usitatissimum plants were cultivated and their developing seeds were investigated according to their SDG (secoisolariciresinol diglucoside) content (main lignan in seeds) by immunolocalization and HPLC techniques. The HPLC results showed that SDG content increased as a function of the developmental stage to reach a maximum of about 9 mg/g at the end of seed maturation. In addition, the seed dissection during seed maturation allowed to observe a similar pattern of evolution of SDG content in the outer integument whereas this content decreased in the inner integument and the endosperm. These results were confirmed by immunolocalization experiments.

Seedless fruits and the disruption of a conserved genetic pathway in angiosperm ovule development.

Although the biological function of fruiting is the production and dissemination of seeds, humans have developed seedless fruits in a number of plant species to facilitate consumption. Here we describe a unique spontaneous seedless mutant (Thai seedless; Ts) of Annona squamosa (sugar apple), a member of the early-divergent magnoliid angiosperm clade. Ovules (seed precursors) of the mutant lack the outer of two normal integuments, a phenocopy of the inner no outer (ino) mutant of Arabidopsis thaliana. Cloning of the INO ortholog from A. squamosa confirmed conservation of the outer integument-specific expression pattern of this gene between the two species. All regions of the gene were detectable in wild-type A. squamosa and in other members of this genus. However, no region of the INO gene could be detected in Ts plants, indicating apparent deletion of the INO locus. These results provide a case of a candidate gene approach revealing the apparent molecular basis of a useful agronomic trait (seedless fruit) in a crop species, and indicate conservation of the role of a critical regulator of ovule development between eudicots and more ancient lineages of angiosperms. The outer integument is one synapomorphy of angiosperms separating them from other extant seed plants, and the results suggest that the evolution of this structure was contemporaneous with the derivation of INO from ancestral YABBY genes. Thus, a unique lateral structure appears to have coevolved with a novel gene family member essential for the structure's formation.

Distribution of tomato chlorotic dwarf viroid in floral organs of tomato

In situ hybridization was used to analyze the distribution pattern of Tomato chlorotic dwarf viroid (TCDVd) in floral organs of tomato plants. Following TCDVd invasion of floral organs, it became localized only in sepals at an early developmental stage, then reached other floral organs at the flower opening stage, with the exception of part of the placenta and ovules. When distribution of TCDVd was compared with that of Potato spindle tuber viroid (PSTVd), TCDVd was not detected in the outer integument around the embryo sac even though PSTVd was able to invade there, suggesting that such specific distribution might reflect the frequent occurrence of viroid disease on crops caused by PSTVd-seed transmission.

Ephemeral and non-ephemeral structures during seed development in two Cytisus species (Papilionoideae, Leguminosae)

Seed formation involves not only the embryo and endosperm development, but also the formation of a series of either ephemeral or non-ephemeral structures. In this article, we study several of those structures in Cytisus multiflorus and Cytisus striatus. The endosperm development is first nuclear and later cellular, except for the chalazal area, whose development is always nuclear. It generates, in the early developmental stages, a sac-like haustorium. As the seed develops, two structures seem to be closely related to nutrient mobilization to the embryo sac: on the one hand, a group of cells and a channel, located in the chalazal area and closely related between them and to the endosperm haustorium, which could be interpreted as a hypostase and on the other hand, an endothelium, derived from the inner integument, which later degenerates leaving no trace in the mature seed. All of these structures would be associated with the directionality of assimilates from ovule tissues to embryo sac. In mature seed and surrounding the embryo appears a unicellular layer of cells rich in proteins (aleurone layer), which is the origin of the outermost layer of the cellular endosperm. The seed coat is made up only of the outer integument.

Comparative study of gametophyte development in the some species of the genus Onobrychis: Systematic significance of gametophyte futures

Male and female gametophytes have special characters that show a great variety in different taxa. In this study, gametophytes of four species belonging to three sections of the genus Onobrychis Mill. were studied with light microscopy. Results showed that the ovular primordium is tetra-zonate and gives rise to an anatropous ovule. The archesporium may consist of one or more archeosporial cells, but only one of them undergoes meiosis, forming a linear or T-shaped tetrad. Normally, only a single megaspore is functional which is located in the chalazal position while the others degenerate very soon. The young ovule is hemi-anatropous but the mature is anatropous, crassinucellar and bitegmic; integuments form a zig-zag micropyle. A 7-celled embryo-sac is formed corresponding to the Polygonum type. Based on our results, the ovular variable characters are the form and condition of ovary, presence or absence of ovary peduncle, the number and condition of ovule in ovary, length and width of ovule, length and width of embryo sac, number of layers in outer integument, condition of megaspore, alignment pattern of the integuments, asymmetrical initiation of the outer integument, shape of tetrad with the presence of one functional megaspore and so on. The separator characters in male gametophyte are including tri-cellular pollen grains and the number of tapetum nuclei. According to our study the female gametophyte characters are more variable than male gametophyte. The present study provides the first report on embryological description in the genus Onobrychis and also in section Heliobrychis.