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.     

The pachychalaza in dicotyledons: primitive or advanced?

CORNER, E. J. H., 1992. The pachychalaza in dictoyledons: primitive or advanced? Reasons for regarding pachychalazy as an advanced seed character are restated and found to disagree with the recent postulate of von Teichman & van Wyk that pachychalazy is primitive for the dicotyledonous seed.     

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.     

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。     

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.     

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

Summary 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.     

Development and structure of the seed of Ozoroa paniculosa (Anacardiaceae) and taxonomic notes

The anatropous, bitegmic and crassinucellar ovule has a nuclear endosperm development. It is further characterized by a hypostase sensu lato. This hypostase being an integral part of the chalaza undergoes a secondary extension with it. At maturity the exalbuminous seed is partially pachychalazal and therefore two anatomically distinct larger parts can be distinguished in the mature seed coat. An endotegmen typifies the integumentary seed coat, while a saddle-shaped hypostase characterizes the chalazal seed coat. This seed coat shows several characteristics of the typical anacardiaceous pachychalazal seed. The cotyledons store lipids and protein as nutrient reserveS. A well-developed cuticle, cuticular layer, cutin and callose in the hypostase cell walls, as well as tannin-like deposits in the seed coat, protect the physiologically ripe seed against dehydration.     

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.     

Embryology of Early Abortion Due to Limited Maternal Resources in Pisum sativum L.

In most flowering plants, many embryos are aborted early intheir development due to limited maternal resources. The kin-conflictinterpretation of plant embryology predicts these abortionsshould be under maternal control. In a study of the abortionprocess in Pisum sativum, we found the first visible indicationof abortion was formation of a weak hypostase. Callose was locallydeposited around the chalazal endosperm haustorium, and ligninalong the outer cell walls of the remnant nucellar tissue. Thenucellus was compressed by proliferating adjacent inner integumentalcells. The endosperm haustorium's cytoplasm was forced backinto the embryo sac cavity. With suppression of haustorial activitythe endosperm nuclei gradually enlarged followed by enlargementof the embryo and suspensor nuclei. Finally, nuclei and cytoplasm throughout the endosperm and embryolost stainability and broke down. Four successive stages wererecognized in seed abortion. In seeds developing to maturity,no hypostase was developed and the haustorium continued to digestboth the remnant nucellus and the proliferated inner integumentalcells. These observations are consistent with the kin-conflicthypothesis. Pisum sativum, garden pea, ovule abortion, histology, hypostase, kin-conflict hypothesis     

Development of ovule, megagametophyte and early endosperm in representative species of Rhododendron L. (Ericaceae)

PALSER, B. F., PHILIPSON, W. R. & PHILIPSON, M. N., 1989. Development of ovule, megagametophyte and early endosperm in Rhododendron L. (Ericaceae). Complete development of ovule, megagametophyte and early endosperm is compared for 15 species (almost complete for four additional species) representing all subgenera and most sections of Rhododendron. In all the ovule is anatropous, unitegmic, tenuinucellate with the lateral and micropylar nucellus disintegrating completely. The integument has a tanniniferous epidermis, starch around egg apparatus and micropyle, an endothelium and hypostase. Differences occur in time of closure of the micropyle and its final length, total proportion of ovule occupied by gametophyte and by formation of ovule tails only in section Vireya. Megagametophyte development follows the Polygonum pattern in all species. A single archesporial cell becomes the megaspore mother cell directly, and the chalazal spore of a linear tetrad functions. Between the eight-nucleate stage and maturity the micropylar end of the gametophyte elongates into the micropyle. Starch is characteristically present in the mature central cell. The pollen tube penetrates porogamously and double fertilization is rapid. Endosperm development starts promptly and is cellular, first forming a linear row of four cells. The zygote elongates slightly but does not divide during the stages followed. Differences may occur in time of enlargement, orientation of some mitoses, some cellular characteristics, amount of starch present and final size of megagametophyte. Rare abnormalities occur.     

藏药椭圆叶花锚的胚胎学

本文首次报道了藏药椭圆叶花锚的胚胎学特征。花药四室,药壁发育为双子叶型;绒毡层异型起源,腺质型绒毡层。小孢子母细胞减数分裂为同时型,四分体的排列方式为四面体型;成熟花粉为３－细胞。子房２心皮,而二心皮连接处强烈膨大、内凸,４列胚珠。薄珠心,单珠被,直生胚珠。胚囊发育为蓼型。胚乳发育为核型。胚胎发育为茄型酸浆Ｉ变型。反足细胞在胚囊成熟时期宿存。承珠盘发达。果实成熟时,种子只发育至球型胚阶段。比较了该种与龙胆族其它属、种的胚胎学特征,发现它们大部分特征是相似的,但在如下３个特征上存在区别：子房二心皮连接处强烈膨大、内凸;直生胚珠;具有发达的承珠盘。其胚胎学特征的系统学和分类学意义有待进一步比较与评价     

The female gametophyte and the endosperm control cell proliferation and differentiation of the seed coat in Arabidopsis

Double fertilization of the female gametophyte produces the endosperm and the embryo enclosed in the maternal seed coat. Proper seed communication necessitates exchanges of signals between the zygotic and maternal components of the seed. However, the nature of these interactions remains largely unknown. We show that double fertilization of the Arabidopsis thaliana female gametophyte rapidly triggers sustained cell proliferation in the seed coat. Cell proliferation and differentiation of the seed coat occur in autonomous seeds produced in the absence of fertilization of the multicopy suppressor of ira1 (msi1) mutant. As msi1 autonomous seeds mostly contain autonomous endosperm, our results indicate that the developing endosperm is sufficient to enhance cell proliferation and differentiation in the seed coat. We analyze the effect of autonomous proliferation in the retinoblastoma-related1 (rbr1) female gametophyte on seed coat development. In contrast with msi1, supernumerary nuclei in rbr1 female gametophytes originate mainly from the endosperm precursor lineage but do not express an endosperm fate marker. In addition, defects of the rbr1 female gametophyte also reduce cell proliferation in the ovule integuments before fertilization and prevent further differentiation of the seed coat. Our data suggest that coordinated development of the seed components relies on interactions before fertilization between the female gametophyte and the surrounding maternal ovule integuments and after fertilization between the endosperm and the seed coat.     

Floral morphology of the family compositae

Vernonia anthelmintica (Linn.) Willd., tribe Vernonieae, family Compositae has been studied. The cypsela has dimorphic pappus, 20 longitudinal ribs (10 primary and 10 secondary), and two types of hairs developing from single epidermal cells on surface. Certain features of vasculature of floret observed in this taxon have been considered as intermediate between relatively primitive and highly advanced conditions known in the family. Others elucidate further that the ovary is bilocular with axile placentation at base in which region the ovule is attached, and unilocular with parietal placentation in the remaining portion, and also that the ovule possibly belongs to one of the two carpels, which alone is fertile, and is an organ morphologically double in nature. The pappus has been regarded as a longitudinally dismembered calyx tube. The tissue of the ovule outside nucellus differentiates into an endothelium, a periendothelial zone, and an outer zone. In the mature seed the thickned outer epidermis and remmants of a few subjacent layers form the outer zone, and endothelium redued to a pellicle, the inner zone of the seed coat. The jacket layer of the endosperm persists between the seed coat and the dicotyledonous, orthorrhizal embryo. The pericarp development resembles that of most other Compositae in an early differentiation of the ovary wall into two zones, and later breakdown of a major part of the inner zone. But it is quite characteristic in other respects, especially, the peripheral chin of firovascular bundles which forms its main mechanical zone.     

Embryology and taxonomical position of Retzia capensis (Retziaceae)

The ovules of Retzia capensis are anatropous, unitegmic and tenuinucellate. A well-developed hypostase of concentric layers of cells is present. Embryo sac formation follows Polygonum type. The central part of the mature embryo sac contains rich amounts of starch grains, which disappear at the beginning of the endosperm development. The endosperm formation results in a chalazal haustorium of a great number of long, narrow, densely plasmatic cells, a micropylar haustorium of loosely plasmatic cells, and a middle region which in the beginning is only partly cellular, but later the whole endosperm consists of long, narrow cells. The hypostase prevents the chalazal endosperm haustorium from penetrating to the lower part of the ovule, while the micropylar haustorium is able to grow upwards into the long micropyle. The cellular endosperm formation, the formation of endosperm haustoria, of which the micropylar is most distinctive, and formation of a well-developed hypostase all indicate a close relationship to Buddleiaceae and part of Scrophulariaceae. Therefore, both Retziaceae and Buddleiaceae should be placed in the order Scrophulariales.     

The ontogeny and structure of the pericarp and seed-coat of Harpephyllum caffrum Bernh. ex Krauss (Anacardiaceae)

The exocarp sensu lato , which develops from the outer epidermis and adjacent parenchyma of the ovary wall, consists of collenchyma cells with a stomatous epidermis. The fleshy, parenchymatous mesocarp or sarcocarp develops after endocarp differentiation. The endocarp is partly spongy and partly woody. The spongy endocarp contains most of the vascular tissue and fills the cavities and grooves of the intricately sculptured outer woody endocarp. The inner woody endocarp and adjacent woody, endocarpal operculum develop from the inner epidermis and subepidermal parenchyma of the ovary wall. The bitegmic, anatropous ovule develops into a derived, exalbuminous seed with an undifferentiated seed-coat. An extensive chalaza, extensive hypostase sensu lato and the raphe are important in the development of the seed-coat. The pericarp and seed-coat of H. caffrum is compared with those of Sclerocarya birrea subsp. caffra and Lannea discolor . The close phylogenetic relationship of these three species of the Spondieae is reaffirmed. The marked similarities in pericarp and seed structure between H. caffrum and species of the genus Spondias are noted.     

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.     

漆树胚,胚乳发育及花果生长的相关性研究

漆树为倒生胚珠,双珠被,厚珠心,具承珠盘及拟珠孔塞,胚囊发育为蓼型,核型胚乳,胚发育为柳叶菜型,后历经棒状形胚、心形胚、鱼雷形胚和成熟胚各期。花和果实生长与胚及胚乳发育有密切的相关性,胚内具原始的乳汁道系统为重要特征。一些胚珠内无胚或胚乳早期退化引起胚败育是造成种子空籽原因之一。     

Seed size, seedling morphology, and response to deep shade and damage in neotropical rain forest trees

To investigate the existence of coordinated sets of seedling traits adapted to contrasting establishment conditions, we examined evolutionary convergence in seedling traits for 299 French Guianan woody plant species and the stress response in a shadehouse of species representing seed size gradients within five major cotyledon morphology types. The French Guianan woody plant community has larger seeds than other tropical forest communities and the largest proportion of hypogeal cotyledon type (59.2%) reported for tropical forests. Yet the community includes many species with intermediate size seeds that produce seedlings with different cotyledonal morphologies. A split-plot factorial design with two light levels (0.8% and 16.1% PAR) and four damage treatments (control, seed damage, leaf damage, stem damage) was used in the shadehouse experiment. Although larger-seeded species had higher survival and slower growth, these patterns were better explained by cotyledon type than by seed mass. Even larger-seeded species with foliar cotyledons grew faster than species with reserve-type cotyledons, and survival after stem grazing was five times higher in seedlings with hypogeal cotyledons than with epigeal cotyledons. Thus, to predict seedling performance using seed size, seedling morphology must also be considered.