Taxonomic significance of pericarp and seed structure in Heeria argentea (Thunb.) Meisn. (Anacardiaceae) including reference to pachychalazy and recalcitrance

Heeria argentea (tribe Rhoeae), a monotypic, dioecious tree, is endemic to the core area of the Cape Floristic Region. The mature exocarp consists of a uniseriate layer of palisade-like epidermal cells, interspersed with modified stomata. The mature endocarp sensu stricto develops solely from the inner epidermis. It is essentially two-layered and resembles the state in Protorhus longifolia. This endocarp is here proposed as a distinct fourth endocarpal subtype under the so-called Anacardium -type. The large, pachychalazal, recalcitrant seed develops from the single, anatropous, bitegmic, crassinucellate ovule. This ovule is characterized by an extensive chalaza, vascularization and Anacardiaceae-type hypostase. The pachychalazal seed coat contains abundant vascular bundles and a tanniniferous hypostase. The inner epidermis of the inner integument differentiates into an endotegmen. The contribution of the integuments towards seed coat development is negligible. Concerning characters of the disc in the female flower, the meso- and endocarp, as well as seed size, degree of pachychalazy, nutrient reserves (starch) in the chlorophyllous cotyledons and hypogeal germination, Heeria shows a very close phylogenetic relationship to Protorhus longifolia. However, fruit and seed structure clearly supports the taxonomic separation of Heeria from Ozoroa. Data also support the view that Heeria is a tropical relict, and the hypothesis that pachychalazy, greater seed size, as well as recalcitrant seed viability behaviour constitute ancestral seed character states. Pachychalazy is regarded as a functional adaptation for more efficient transfer of nutrients.     

Ontogeny of the seed-coat of Rhus lancea L. fil., and pachychalazy in the Anacardiaceae

VON TEICHMAN, I., 1991. Ontogeny of the seed-coat of Rhus lancea L. fil., and pachychalazy in the Anacardiaceae. The bitegmic, anatropous ovule develops into an exalbuminous, partially pachychalazal and endotegmic seed. In the mature seed-coat the extensive chalaza with associated tanniniferous hypostase sensu lato manifests externally as a characteristic brown patch. The walls of the cells of the hypostase are impregnated with callose and lipidic substances, which most probably represent cutin. Ultimately the outer integument and outer parts of the inner integument are more or less squashed. However, the cell walls of the inner epidermis of the inner integument show distinct secondary thickening and lignification. The pachychalazal seed with undifferentiated seed-coat characterizes not only a number of the genera of the tribe Anacardieae, but also occurs in Heeria of the tribe Rhoeae. A number of genera of the tribe Spondiadeae have a partially pachychalazal seed. The seed-coat of the latter shows varying degrees of traces of an exo-, meso- and/or endotestal lignification. The seed of certain genera of the Rhoeae, is partially pachychalazal and endotegmic, or probably only endotegmic.     

The generic position of Lithraea brasiliensis Marchand (Anacardiaceae): evidence from fruit and seed structure

In Lithraea brasiliensis Marchand the exocarp is characterized by brachysclereids and the parenchymatous mesocarp by large secretory ducts; inner sclerenchymatous ridges are absent in die mesocarp. The stratified endocarp s. s. comprises a crystal layer, palisade-like brachysclereids, osteosclereids and macrosclereids. The osteosclereids are characterized by a distinct light line or linea lucida , which has hitherto also been recorded in a species of Rhus. In the partially pachychalazal seed, a typical Anacardiaceae-like hypostase typifies the chalazal part of the seed coat, while the integumentary seed coat reveals a well preserved outer epidermis, a compressed endotegmen and well developed inner cuticular layer. Our comparison of die characters of the ovule, fruit and seed of L. brasiliensis with those of various species of Rhus and other genera of the tribe Rhoeae (some closely related) presents evidence that L. brasiliensis could be most closely associated with the genus Rhus.     

Origin of the Coleorhiza in Cycad Seedlings and its Structural Homology with That of the Poaceae

In the literature there is disagreement about the existence of a coleorhiza in cycad embryos. In this paper the terminology of the cycad ovule, seed and embryo is revised. It was confirmed that the cycad ovule and seed are pachychalazal and that the seed coat is exclusively formed by the pachychalaza. The term ‘pleurotesta’ as a substitute for the so-called ‘endotesta’ is suggested to describe the inner, membranous part of the seed coat. The anatomy of the cycad embryo was studied in comparison with the grass embryo and it was found that a coleorhiza does exist in cycad embryos and derives from the distal part of the suspensor. It is postulated that the coleorhiza in grasses also derives from the distal part of the suspensor and that the two structures are therefore structurally homologous.     

Investigations into seed dormancy in Grevillea linearifolia, G. buxifolia and G. sericea: anatomy and histochemistry of the seed coat

BACKGROUND AND AIMS: Seeds of east Australian Grevillea species generally recruit post-fire; previous work showed that the seed coat was the controller of dormancy in Grevillea linearifolia. Former studies on seed development in Grevillea have concentrated on embryology, with little information that would allow testing of hypotheses about the breaking of dormancy by fire-related cues. Our aim was to investigate structural and chemical characteristics of the seed coat that may be related to dormancy for three Grevillea species. METHODS: Seeds of Grevillea linearifolia, Grevillea buxifolia and Grevillea sericea were investigated using gross dissection, thin sectioning and histochemical staining. Water movement across the seed coat was tested for by determining the water content of embryos from imbibed and dry seeds of G. sericea. Penetration of intact seeds by Lucifer Yellow was used to test for internal barriers to diffusion of high-molecular-weight compounds. KEY RESULTS: Two integuments were present in the seed coat: an outer testa, with exo-, meso- and endotestal (palisade) layers, and an inner tegmen of unlignified sclerenchyma. A hypostase at the chalazal end was a region of structural difference in the seed coat, and differed slightly among the three species. An internal cuticle was found on each side of the sclerenchyma layer. The embryos of imbibed seeds had a water content six times that of dry seeds. Barriers to diffusion of Lucifer Yellow existed at the exotestal and the endotestal/hypostase layers. CONCLUSIONS: Several potential mechanisms of seed coat dormancy were identified. The embryo appeared to be completely surrounded by outer and inner barriers to diffusion of high-molecular-weight compounds. Phenolic compounds present in the exotesta could interfere with gas exchange. The sclerenchyma layer, together with strengthening in the endotestal and exotestal cells, could act as a mechanical constraint.     

The Morphology and Anatomy of Ovule and Fruit Development in Arachis hypogaea L

The vascular system of the monocarpellary gynoecium with tenwell differentiated traces and a few cross links probably representsa precocious development of the post-fertilization vasculatureof the fruit wall. The restriction of the two integuments ofthe ovule to the micropylar half, and the endothecial natureof the chalazal cells adjoining the embryo sac appear to indicatea pathway of derivation of the unitegmic tenumucellate ovulefrom the bitegmic crassinucellate one. During double fertilization,a dark staining refractive body appears in the nucleolus ofthe egg as well as the fusion product of the polar nuclei. The peg that carries the ovary into the soil after fertilizationgrows by the activity of a rib meristem at the basal solid partof the gynoecium. During sub-soil fruit development, the ovarywall develops a prominent spongy inner zone which finally disappears,and a peripheral zone that forms the mature fruit wall. Theabinitio nuclear endosperm is much reduced and degenerates afterproducing a few cell layers in the chalazal half alone. Seeddevelopment is pachychalazal. The main vascular supply of theseed branches at the chalaza into eight to ten strands in theseed coat. All seeds that have a vascular ramification in theseed coat are probably pachychalazal. In the variety Valencia, diminutive fruits with viable seedmay develop aerially from pegs that fail to grow long enoughto reach the soil from the higher nodes. Arachis hypogaea L., groundnut, fruit development, seed development, carpel vasculature, seed vasculature, pachychalaza     

Ovule,fruit and seed development in Abolboda (Xyridaceae,Poales): implications for taxonomy and phylogeny

Xyridaceae belongs to the xyrid clade of Poales, but the phylogenetic position of the xyrid families is only weakly supported. Xyridaceae is divided into two subfamilies and five genera, the relationships of which remain unclear. The development of the ovule, fruit and seed of Abolboda spp. was studied to identify characteristics of taxonomic and phylogenetic value. All of the studied species share anatropous, tenuinucellate and bitegmic ovules with a micropyle formed by the inner and outer integuments, megagametophyte development of the Polygonum type, seeds with a tanniferous hypostase, a helobial and starchy endosperm and an undifferentiated embryo, seed coat derived from both integuments with a tanniferous tegmen and a micropylar operculum, and fruits with a parenchymatous endocarp and mesocarp and a sclerenchymatous exocarp. Most of the ovule and seed characteristics described for Abolboda are also present in Xyris and may represent a pattern for the family. Abolboda is distinguished by the ovule type, endosperm formation and the number of layers in the seed coat, in agreement with its classification in Abolbodoideae. The following characteristics link Xyridaceae to Eriocaulaceae and Mayacaceae, supporting the xyrid clade: tenuinucellate, bitegmic ovules; seeds with a tanniferous hypostase, a starchy endosperm and an undifferentiated embryo; and a seed coat with a tanniferous tegmen. A micropylar operculum in the seeds of Abolboda is described for the first time here and may represent a synapomorphy for the xyrids. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 144–154.     

Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance

VON TEICHMAN, I. & VAN WYK, A. E., 1991. Trends in the evolution of dicotyledonous seeds based on character associations, with special reference to pachychalazy and recalcitrance. The possible evolutionary status of the endothelium, hypostase, pachychalaza and the recalcitrant viability behaviour of seeds is considered in relation to bitegmy/unitegmy, crassinucellate/tenuinucellate ovules, nuclear/cellular endosperm development, large/small seed size, woody/herbaceous habit and tropical/temperate habitat. The presence of the endothelium, hypostase, pachychalaza and recalcitrance in dicotyledonous families is plotted against Dahlgren's system of classification. Results are compared with Sporne's advancement index for the various families. An endothelium is considered derived since it occurs more often in highly evolved superorders and is significantly associated with derived ovule and endosperm character states as well as with smaller seed size. A hypostase appears to be relatively ancestral and is significantly associated with pachychalazy and recalcitrance. The endothelium and hypostase have developed independently in many taxa and could be interpreted as being structurally and functionally analogous. Pachychalazy and recalcitrance are significantly associated with ancestral ovule character states and, at the species level, with large seed size (overgrown seed), woody habit and tropical habitat. The presence of pachychalazy, recalcitrance and associated large seed size are therefore regarded as ancestral character states of the dicotyledons. Consideration of currently accepted dicta on seed character state polarity, suggests a reversal in the evolutionary status of pachychalazy and large seed size.     

Embryological features of Alhagi persarum (Fabaceae): Adapt to environmental constraints

Reproductive organs, in flowering plants, are sensitive to stressful environments. Alhagi persarum Boiss. & Buhse copes with the stresses and produce reproductive organs under difficult climatic conditions. Embryological characters of this plant were investigated for the first time using different microscopy and staining techniques. The results of this study showed unique reproductive characters and strategies in A. persarum that we named reproductive adaptation. These characters have roles in protection and nutrition of reproductive organs, some of which were visible in ovule: accumulation of phenolic compounds, presence of ovular endothelium with its cuticle coat, hypostase, postament, endosperm haustorium, presence of operculum, curvature of the embryonic axis. The other characters in the seed are macrosclereid cells with cuticle coat, double palisade layer and lignified tracheids in hilar groove. Thickness increasing of endothecium and exine are the adaptive characters in anther. Unlike many of the stress-sensitive plants, all developmental stages of the embryo sac, anther, pollen and pollen tube are without any defects in these stress-tolerant plants. Seed germination rate is low in this species that is due to the hardness of seed coat which causes seed deep exogenous dormancy. This dormancy is also a developmental program for stress tolerance to keep seed viability for a long time in difficult conditions.     

从胚胎学特征探讨四合木的系统位置

本文从胚胎学特征探讨了四合木的系统位置。胚胎学研究表明,四合木与蒺藜利具较近亲缘关系,但又有明显区别。表现为。四合木花药壁发育为基本型,绒毡层细胞多数具单核,心皮合生但深裂至近基部,胚株直生,具较长珠柄,无承珠盘,无珠被绒毡层,只具一列线形大孢子四分体,成熟胚囊为四细胞(四核),珠被在胚胎发育过程逐渐退化,因此,成熟种子中只具外珠被内层残迹;胚乳大部分细胞解体,而外缘胚乳细胞特化,在成熟种子中代替种皮起保护功能。因此,四合木是否应从蒺藜科分出而另列一种,值得进一步研究。     

Ovules and seeds in Acalyphoideae (Euphorbiaceae): structure and systematic implications

Acalyphoideae, the largest subfamily of Euphorbiaceae, are investigated with respect to ovule and seed structure on the basis of 172 species of 80 genera in all 20 tribes of Acalyphoideae sensu Webster. All species of Acalyphoideae examined have bitegmic ovules with a non-vascularized inner integument. However, noticeable differences exist among and sometimes within the genera in the thickness of the inner and outer integument, the presence or absence of vascular bundles in the outer integument, whether ovules are pachychalazal or not, the presence or absence of an aril, seed coat structure (in terms of the best-developed mechanical cell-layer), and the shape of cells constituting the exotegmen. For the latter two characters, two different types of seed coat (i.e., "exotegmic" and "exotestal") and three different types of exotegmic cell (i.e., palisadal, tracheoidal and ribbon-like) were distinguished. Comparisons showed that three tribes Clutieae, Chaetocarpeae and Pereae are distinct from the other Acalyphoideae as well as from the other Euphorbiaceae in having an exotestal seed coat with a tracheoidal exotegmen. The tribe Dicoelieae is also distinct from the other Acalyphoideae in having an exotegmic seed that is composed of ribbon-like cells of exotegmen (i.e., cells both longitudinally and radially elongated, sclerotic and pitted). The tribe Galearieae, which should be treated as a distinct family Pandaceae, is also distinct from the other Acalyphoideae in having an exotegmic seed with a tracheoidal exotegmen (i.e., cells longitudinally elongated, sclerotic and pitted). The remaining genera of Acalyphoideae always have an exotegmic seed with a palisadal exotegmen (i.e., cells radially elongated, sclerotic and pitted). The shared palisadal exotegmen supports the close affinity of Acalyphoideae (excluding five tribes) with Crotonoideae and Euphorbioideae. Within the remaining genera of Acalyphoideae, a significant diversity is found in ovule and seed morphology with respect to the thickness of the inner and outer integument, the size of chalaza, vascularization of an outer integument and an aril.     

Embryology of Abeliophyllum (Oleaceae) and its phylogenetic relationships

Abeliophyllum, a monotypic endemic genus of Oleaceae, resembles Forsythia in various morphological characters, but its phylogenetic position is disputed and no embryological study of the genus has been carried out. We investigated more than 40 embryological characters of Abeliophyllum, compared them with previous information on Oleaceae, and discusses its phylogenetic relationships. Abeliophyllum is similar to other genera of Oleaceae in many embryological features, having some distinct features such as the mode of anther wall formation, formation of a nucellar cap, and formation of obturator and hypostase. The basic type of anther wall development and formation of a nucellar cap have not previously been reported in Oleaceae. In addition, differentiation of the obturator and formation of hypostase are not reported in the previously investigated genera of the family. Compared with close relatives, the seed coat structure of Abeliophyllum resembles Forsythia more than Fontanesia and supports existing molecular data which place Abeliophyllum as the sister group of Forsythia.     

Notes on the ontogeny and structure of the seed-coat of Sclerocarya birrea (Richard) Hochst. subsp. caffra (Sonder) Kokwaro (Anacardiaceae)

The pendulous, bitegmic, anatropous ovulr with dorsal raphe is suspended at the tip of a massive funicle. A group of nurellar cells with intensively staining cell walls, the hypostase sensu stricto , is present. The initially plate-like tanniniferous chalazal-nucellar tissue, with suberin and lignin impregnated cell walls represents a hypostase sensu lato . The mature seed-coat is formed by the raphe, extensive chalaza, adjacent, well-developed, cup-like hypostase sensu lato , remnants of the two integuments and a cuticular layer. The exalbuminous seed of Sclerocarya birrea suhsp. caffra (the Marula), is regarded to he a derived and phylogenetically advanced type. The undifferentiated seed-roat is very similar to that found in Lannea discolor which, like the marula, belongs to the tribe Spondieae. The similarities in the structure of the seed-coat and seed of the marula and L. discolor confirm their proposed close phylogenetir relationship.     

Structure and development of the ovule and seed in Aristolochiaceae, with particular reference to Saruma

All members of Aristolochiaceae have anatropous, bitegmic, crassinucellate ovules, which are endostomic except in Saruma and Asarum arifolium where ovules are amphistomic. The outer integument is two cell-layered and the inner integument is three cell-layered. The chalazal megaspore is the functional one. All these conditions appear to be plesiomorphic for the order Piperales, which consists of five families, Aristolochiaceae, Hydnoraceae, Lactoridaceae, Piperaceae and Saururaceae. The embryo sac in Aristolochiaceae is eight-nucleate and corresponds to the Polygonum type; a hypostase is frequently present in this family. The seed coat of Aristolochia s.l., Asarum, Saruma and some Thottea species consists primarily of a two cell-layered testa, and a three cell-layered tegmen. In some species the cells of the outer epidermis become radially elongated, forming reticulate wall thickenings. Cells of the inner layer of the testa have crystals and thickened inner walls. The three layers of the tegmen are tangentially elongated, and become cross fibres at maturity, as fibres of the outer and inner layers are parallel to the seed axis, whereas those of the middle layer are perpendicular to it. This type of seed coat anatomy is synapomorphic for Aristolochiaceae. In addition, the gross morphology of the seed and elaiosome histology are remarkably similar in Asarum and Saruma, thus supporting a sister-group relationship between them. Embryological and seed characters do not supply any synapomorphy that support a close relationship between Aristolochiaceae, Hydnoraceae and Lactoridaceae. Instead, some seed features such as the absence of seed appendages and the collapsed cells of endotesta may indicate a close relationship of Lactoris with Piperaceae plus Saururaceae, although this is the subject of further analysis.     

Development and structure of the seed-coat of Lannea discolor (Sonder) Engl. (Anacardiaceae)

VON TEICHMAN, I., 1988. The development and structure of the seed-coat of Lannea discolor (Sonder) Engl. (Anacardiaceae). The bitegmic, anatropous ovule contains a group of nucellar cells with slightly thickened and intensively staining cell walls. Besides this hypostase sensu stricto, the nucellus cells in the chalaza become tanniniferous. This tanniniferous chalazal-nucellar tissue is intially plate-like. It is referred to as the hypostase sensu lato. The latter and the chalaza enlarge significantly. The raphe, extensive chalaza and well-developed cup-like hypostase sensu lato play an important role in the development of the seed-coat. The inner, tanniniferous epidermis of the inner integument persists in parts of the mature seed-coat. The outer, distinctly tanniniferous epidermis of the outer integument shows in the mature seed-coat a degree of secondary wall thickening. This undifferentiated type of seed-coat of L. discolor (tribe Spondieae) is remarkably similar to that of Camnosperma minor (tribe Rhoideae), both also showing tendency towards the exotestal type. In the Rhoideae the endotestal, i.e. differentiated type, of seed-coat is also present. The exalbuminous seed of L. discolor represents a derived and advanced type.     

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

Abstract

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.     

Genetics of rough seed coat texture in cowpea

Seed coat texture is an important trait in determining the acceptability of cowpea varieties in different regions. A rough seed coat is preferred in western and central Africa, since it permits easy removal of the seed coat which is essential for indigenous food preparations. On the other hand, a smooth seed coat is preferred in eastern and southern Africa as well as in parts of South America where cowpea is consumed as boiled beans without removing the seed coats. This study was undertaken to elucidate the inheritance of seed coat texture so that cowpea breeders may adopt appropriate breeding strategy to develop cowpea varieties with preferred seed types for different regions. The F1 plants between smooth- and rough-seeded parents as well as between rough- and rough-seeded parents produced smooth seeds, indicating a complementary gene action and dominance for smooth seed coat. The F2 plants from the smooth x rough cross segregated into a 3 smooth:1 rough seed coat ratio, but the F2 plants from rough x rough crosses segregated into a 9 smooth:7 rough seed coat ratio. The F1 plants from backcross to the smooth parent were all smooth, while the F1 plants from backcross to rough parent segregated in a 1 smooth:1 rough seed coat ratio. However, both the backcross populations in rough x rough crosses segregated into 1 smooth:1 rough seed coat ratio. These results indicate that two pairs of independent recessive genes confer rough seed coat texture in cowpea and the presence of at least one dominant gene at each of the two loci results into smooth seed coat. The gene symbols rt1rt1 and rt2rt2 are being assigned for rough seed coat texture in cowpea.     

Seed coats: Structure,development, composition,and biotechnology

Summary Although seeds have been the subject of extensive studies for many years, their seed coats are just beginning to be examined from the perspective of molecular genetics and control of development. The seed coat, plays a vital role in the life cycle of plants by controlling the development of the embryo and determining seed dormancy and germination. Within the seed coat are a number of unique tissues that undergo differentiation to serve specific functions in the seed. A large number of genes are known to be specifically expressed within the seed coat tissues; however, very few of them are understood functionally. The seed coat synthesizes a wide range of novel compounds that may serve the plant in diverse ways, including defense and control of development. Many of the compounds are sources of industrial products and are components of food and feeds. The use of seed coat biotechnology to enhance seed quality and yield, or to generate novel components has not been exploited, largely because of lack of knowledge of the genetic systems that govern seed coat development and composition. In this review, we will examine the recent advances in seed coat, biology from the perspective of structure, composition and molecular genetics. We will consider the diverse avenues that are possible for seed coat biotechnology in the future. This review will focus principally on the seed coats of the Brassicaceae and Fabaceae as they allow us to merge the areas of molecular biology, physiology and structure to gain a perspective on the possibilities for seed coat modifications in the future. The authors have contributed equally and are considered first authors.     

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.