The specialized chalazal endosperm inArabidopsis thaliana andLepidium virginicum (Brassicaceae)

Summary Endosperm of the nuclear type initially develops into a large multinucleate syncytium that lines the central cell. This seemingly simple wall-less cytoplasm can, however, be highly differentiated. In developing seeds of members of the family Brassicaceae the curved postfertilization embryo sac comprises three chambers or developmental domains. The syncytium fills the micropylar chamber around the embryo, spreads as a thin peripheral layer surrounding a large central vacuole in the central chamber, and is organized into individual nodules and a large multinucleate cyst in the chalazal tip. Later in development, after the endosperm has cellularized in the micropylar and central chambers, the chalazal endosperm cyst remains syncytial and shows considerable internal differentiation. The chalazal endosperm cyst consists of a domelike apical region that is separated from the cellularized endosperm by a remnant of the central vacuole and a basal haustorial portion which penetrates the chalazal proliferative tissue atop the vascular supply. In the shallow chalazal depression ofArabidopsis thaliana, the cyst is mushroom-shaped with short tentacle-like processes penetrating the maternal tissues. The long narrow chalazal channel ofLepidium irginicum is filled by an elongate stalklike portion of the cyst. In both, the dome contains a labyrinth of endoplasmic reticulum, dictyosomes with associated vesicles, nuclei, and plastids. The basal portions, which lack the larger organelles, exhibit extensive wall ingrowths and contain parallel arrays of microtubules. The highly specialized ultrastructure of the chalazal endosperm cyst and its intimate association with degrading chalazal proliferative cells suggest an important role in loading of maternal resources into the developing seed.     

Nuclear fusions contribute to polyploidization of the gigantic nuclei in the chalazal endosperm of<Emphasis Type="Italic"> Arabidopsis</Emphasis>

Somatic polyploidization is recognized as a means to increase gene expression levels in highly active metabolic cells. The most common mechanisms are endoreplication, endomitosis and cell fusion. In animals and plants the nuclei of multinucleate cells are usually prevented from fusing. Here, we report that the nuclei from the syncytial cyst of the chalazal endosperm of Arabidopsis thaliana (L.) Heynh. are polyploid with some intermediate ploidy levels that cannot be attributed to endoreplication, suggesting nuclear fusion. Analysis of isolated nuclei, together with fluorescent in situ hybridization (FISH), revealed that nuclei from the chalazal endosperm are two or three times bigger than the nuclei from the peripheral endosperm and have a corresponding increase in ploidy. Together with the consistent observation of adjoined nuclei, we propose that nuclear fusion contributes, at least in part, to the process of polyploidization in the chalazal endosperm. Confocal analysis of intact seeds further suggested that free nuclei from the peripheral endosperm get incorporated into the chalazal cyst and likely participate in nuclear fusions.Abbreviations BAC Bacterial artificial chromosome - CZE Chalazal endosperm - DAPI 4,6-Diamino-2-phenylindole - FISH Fluorescent in situ hybridization - NOR Nucleolar organizing region - NCD Nuclear cytoplasmic domain - PEN Peripheral endosperm     

Development of megagametophyte, embryo, and seed in Senna corymbosa (Lam.) H.S. Irwin & Barneby (Leguminosae – Caesalpinioideae)

The main aspects of seed ontogeny in Senna corymbosa were studied by standard anatomical microtechniques for light microscope observations. The results revealed an ana-campylotropous, bitegmic, and crassinucelate mature ovule. A single archesporocyte developed by an archesporial cell enlargement from the subhypodermal multicellular archesporium. Meiosis originated linear or T-shaped megasporic tetrads. The functional megaspore was the chalazal one. Megagametophytic development conformed to the Polygonum type. Fertilization was porogamic. Endosperm development was free nuclear and conformed to a chalazal haustorium. Cellular endosperm was initiated from the micropylar end during the globular embryo stage. Embryogeny derived from a linear proembryonal tetrad. The mature embryo showed an oblique axis. The testa derived from the outer ovular integument. Nucellar and endosperm remnants, and the micropylar region of the inner ovular integument, persisted at embryo maturity. The absence of a pleurogram would be adaptative to wetland habitats. The taxonomic use of the mature embryo axis in the Cassieae and the phylogenetic employment of megasporic arrangements in Leguminosae needs some reinterpretation.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 169–179.     

Development of endosperm inScrophularia himalensis with a discussion on the variation in the endosperm of the tribeScrophularieae (Scrophulariaceae)

Scrophularia himalensis has anab initio cellular endosperm. A transverse division separates a micropylar chamber from a chalazal chamber. The second division is vertical in both, the third is also vertical but at right angles to the second and restricted to the micropylar chamber just as the fourth transverse division. The four-celled micropylar haustorium is branched, highly aggressive, and persists for a long time during seed development. The bicelled chalazal haustorium is non-aggressive and is relatively short-lived. The endosperm proper is ruminate. Variation in the early ontogeny of the endosperm and the structure of endosperm haustoria in the tribeScrophularieae are evaluated.     

A preliminary study of the seed anatomy of Zingiberaceae

Seeds in Zingiberaceae comprise an aril, seed coat, perispenn, endosperm, embryo, and micropylar and chalazal region. The seed coat is derived from the outer integument, and can be divided into cxotesta, mcsotesta and endotesta; the mesotesta is further subdivided into hypodcrmis, translucent cell layer and pigmented cell layer. The micropylar region includes a micropylar collar and operculum; in some taxa it also includes a caruncle-like structure or a stalk-like structure. A chalazal pigmented cell group (CPG), endotcstal gap, diaphragm and the course of raphe bundle in the chalazal region may be of systematic significance in some species. There are two types of endotesta in the family: parenchymatous (in tribes Hedychieae, Zingibereae and Globbeae) and sclerenchymatous (in Alpineae). The exception is Pommereschea lacknen , which is placed in Alpineae but has the parenchymatous type of endotesta. For this and other reasons this taxon should be transferred to another tribe. On the basis of seed characters, Hedychieae, Zingibereae and Globbeae are apparently closely related, although Hedychieae and Zingibereae differ from Globbeae which has a multiple-layered exotestal epidermis. Seeds of most Zingibereae have a peculiar carunclelike structure at the base of the seed which forms the expanding part beyond the micropylar collar. Zingiberaceae and Costaceae are connected through tribe Alpineae with a sclerenchymatous type of endotesta.     

Embryo sac, endosperm, and seed of Nemophila (Boraginaceae) relative to taxonomy, with a remark on embryogeny in Pholistoma

Studies on embryology and seed morphology are complementary to molecular phylogenetics and of special value at the genus level. This paper discusses the delimitation and evolutionary relationships of genera within the tribe Hydrophylleae of the Boraginaceae. The seven Nemophila species characterized by a conspicuous seed appendage are similar in embryology and seed structure. The ovule is tenuinucellate and unitegmic with a meristematic tapetum. The embryo sac penetrating the nucellar apex is of the Polygonum type, has short-lived antipodal cells, and an embryo sac haustorium. The endosperm is cellular, producing two terminal endosperm haustoria, of which the chalazal has a lateral branch. Embryogeny is of the Chenopodiad type (as in Pholistoma). The seed coat is formed from the small-celled inner epidermis of the integument. The large-celled outer epidermis of the integument disintegrates into scattered cells. Seed pits evolve from irregularly placed inner epidermal cells of the integument. The chalazal part of the ovule produces a cucullus, that functions as an ant-attracting elaiosome. Those species of Nemophila with a conspicuous cucullus form a natural genus. Nemophila is most closely related to Pholistoma. The integumentary seed pits of Nemophila might have evolved from ovular seed pits similar to those in Pholistoma.     

THE DEVELOPMENT OF THE SEED IN ANDROGRAPHIS SERPYLLIFOLIA

Mohan Ram , H. Y. (U. Delhi, India.) The development of the seed in Andrographis serpyllifolia. Amer. Jour. Bot. 47(3) : 215—219. Illus. 1960.–Andrographis serpyllifolia, a member of the Acanthaceae, has an embryo sac with a bifurcated chalazal part. At the time of fertilization both synergids and antipodal cells disintegrate. Early in its development the endosperm is composed of 3 distinct parts: (1) a binucleate densely cytoplasmic chalazal haustorium; (2) a large binucleate micropylar haustorium; and (3) a central chamber which develops into the endosperm proper. The divisions in the central endosperm chamber are ab initio cellular. A few of the endosperm cells elongate enormously, ramify into the integument and destroy the surrounding cells. These cells have been termed secondary haustoria. Due to the unequal destruction of the integument, the endosperm assumes a ruminate condition. The mature seed is nearly naked because the seed coat is almost completely digested. The embryo has a long suspensor. The micropylar cells of the suspensor are hypertrophied and multinucleate. Contrary to Mauritzon's (1934) belief, the course of endosperm development is markedly different from that observed in Thunbergia. So far, albuminous seeds have been reported only in the subfamily Nelsonioideae. The present investigation provides a case of its occurrence in the Acanthoideae also.     

姜目芭蕉群植物种子解剖学研究及其系统学意义

研究了姜目芭蕉群代表植物象腿蕉属象腿蕉(Ensete glaucum)、旅人蕉属旅人蕉(Ravenala madagascariensis)与蝎尾蕉属Heliconia faranmansis?D6肿咏馄侍卣鳌＝峁砻鳎笸冉段藜僦制ぃ制し只霰砥ぁ⒑癖谧橹赴褪赴悖赴瞿谇邢虮谟刖断虮谠龊瘢缓系闱哂泻系闶矣牒系愣眩谥制ち恢榭浊兄榭琢旌涂赘堑姆只榭琢煳涡停赘侵挥赡谥制は赴钩桑褐榭浊制ぱ由煨纬芍制昵唬和馀呷?层细胞：内胚乳细胞径向延长,细胞内充满淀粉粒。旅人蕉具假种皮,种皮分化出外种皮、中种皮和内种皮,外种皮细胞纵向延长,中种皮为7-9层切向延长的薄壁细胞,内种皮为石细胞型：合点区无合点室,内种皮在此出现缺口,缺口为整体轮廓呈喇叭形的近等径薄壁细胞群填充;珠孔区无珠孔领与孔盖的分化：外胚乳缺,内胚乳发达。蝎尾蕉属的Heliconia faranmansis?D6肿游藜僦制ぃ制の薹只墒闾寤闲∏揖断蜓映げ⑴帕形だ缸吹谋”谙赴钩桑褐榭锥酥制は蛲庋由欤纬衫嗨平浦肿拥闹指纷唇峁梗何蘅赘怯胫榭琢斓哂杏晒ば纬傻挠不牵缓系闱肼萌私断嗨疲煌馀呷樵?-4层细胞,细胞壁波浪形弯曲,内胚乳发达。综合作者对兰花蕉(Orchidanha chinensis)和前人对芭蕉群的种子解剖学研究结果,初步总结了芭蕉群种子解剖学特征及其进化式样,讨论了姜目芭蕉群四科种子解剖学特征的系统分类学意义。     

Seed fertilization, development, and germination in Hydatellaceae (Nymphaeales): Implications for endosperm evolution in early angiosperms

New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies. The endosperm condition in Trithuria and waterlilies resembles the helobial condition that characterizes some monocots, but contrasts with Amborella and Illicium, in which most of the mature endosperm is formed from the chalazal domain. The precise location of the primary endosperm nucleus governs the relative sizes of the chalazal and micropylar domains, but not their subsequent developmental trajectories. The unusual tissue layer surrounding the bilobed cotyledonary sheath in seedlings of some species of Trithuria is a belt of persistent endosperm, comparable with that of some other early-divergent angiosperms with a well-developed perisperm, such as Saururaceae and Piperaceae. The endosperm of Trithuria is limited in size and storage capacity but relatively persistent.     

Embryological Studies on Sagittaria guayanensis H. B. K. Subsp. lappula (D. Don) Bojin (Alismataceae)

This paper deals with the embryological characteristics of Sagittaria guayanensis H. B.K. subsp. lappula (D. Don) Bojin. The anther wall development follows the Monocotyledonous type. The cytokinesis of microspore mother cell in meiosis is of the Successive type. The tetrads of microspores show an isobilateral arrangement, and the mature pollen grains are 3-celled. The ovule is bitegminous, pseudo-crassinucellate and anatropous. The megaspore mother cell originates directly from a single archesporial cell. The mature embryo sac consists of 7 cells including 8 nuclei and conforms to the Allium type. The two polar nuclei do not fuse into a secondary nucleus before fertilization. Instead, one sperm fuses with the micropylar end polar nucleus first , and the fertilized polar nucleus then migrates to the chalazal end, where it fuses with the second polar nucleus, forming the primary endosperm nucleus. The embryo development conforms to the Caryophyllad type. The mature embryo is U-shaped and forms the embryonic shoot apex accompanied by two leaves. The endosperm development corresponds to the Helobial type. The primary endosperm nucleus (invariably lying in the chalazal part of the embryo sac) divides and forms two chambers:large micropylar one and small chalazal one. The chalazal endosperm chamber remains binucleate, while, in the micropylar chamber free nuclear divisions occur and then cellnlarization takes place. During the embryo formation the endosperm gradually degrades and can not be found in the mature seed. The subgenus Lophotocarpus is different from the subgenus Sagittaria in some embryological aspects, especially in the structure of mature embryo sac and the double fertilization process.     

冠果草的胚胎学研究

冠果草花药壁的发育为单子口十型,绒毡层为周原质团型。小孢子母细胞减数分裂为连续型,四分体呈左右对称式排列,成熟花粉为三细胞型。双珠被,假厚珠心,倒生胚珠。胚囊发育为葱型,成熟胚囊的特点是两个极核分别位于中央细胞两端,不融合成次生核。受精过程中,一个精于与卵核融合形成合子,另一精子先与珠孔端极核融合,之后受精极核再移动到合点端与另一极核融合,形成初生胚乳核。胚的发育为石竹型。成熟胚呈马蹄形,具有2片真叶。胚乳发育为沼生目型。随着胚的发育,胚乳细胞逐渐解体,成熟种子中无胚乳。     

Arabidopsis haiku mutants reveal new controls of seed size by endosperm

In flowering plants, maternal seed integument encloses the embryo and the endosperm, which are both derived from double fertilization. Although the development of these three components must be coordinated, we have limited knowledge of mechanisms involved in such coordination. The endosperm may play a central role in these mechanisms as epigenetic modifications of endosperm development, via imbalance of dosage between maternal and paternal genomes, affecting both the embryo and the integument. To identify targets of such epigenetic controls, we designed a genetic screen in Arabidopsis for mutants that phenocopy the effects of dosage imbalance in the endosperm. The two mutants haiku 1 and haiku 2 produce seed of reduced size that resemble seed with maternal excess in the maternal/paternal dosage. Homozygous haiku seed develop into plants indistinguishable from wild type. Each mutation is sporophytic recessive, and double-mutant analysis suggests that both mutations affect the same genetic pathway. The endosperm of haiku mutants shows a premature arrest of increase in size that causes precocious cellularization of the syncytial endosperm. Reduction of seed size in haiku results from coordinated reduction of endosperm size, embryo proliferation, and cell elongation of the maternally derived integument. We present further evidence for a control of integument development mediated by endosperm-derived signals.     

大车前胚乳发育的超微结构研究

采用透射电镜技术对大车前(Plantago major L.)胚乳发育的超微结构进行了研究。结果表明:(1)大车前为细胞型胚乳;初生胚乳核经一次横分裂产生1个珠孔室细胞和1个合点室细胞;珠孔室两次纵向分裂一次横向分裂形成2层8个细胞,位于上层的4个细胞发育为4个珠孔吸器,位于下层的4个细胞发育为胚乳本体;合点室细胞进行一次核分裂,发育为两核的合点吸器。(2)珠孔吸器呈管状插入珠被组织,珠孔端细胞壁加厚呈现少量分支并具有壁内突,壁内突周围细胞质里分布着大量线粒体、粗面内质网、高尔基体、质体等,细胞核与核仁明显,细胞质浓厚,代谢活动旺盛;球胚期,珠孔吸器的体积呈现最大值,珠孔吸器周围的珠被组织均被水解,形成明显的空腔。珠孔吸器从珠被组织吸收并转运营养物质至胚乳本体,参与胚乳的构建与营养物质的贮藏。球胚后期,珠孔吸器逐渐退化。(3)4个胚乳本体原始细胞具旺盛的分生能力,经不断的平周与垂周分裂增加胚乳细胞数目,使胚乳本体呈现圆球体状,并将胚包围其中;珠孔吸器、合点吸器以及珠被绒毡层吸收转运的营养物质贮存在胚乳本体;球胚后期,随着胚柄的退化,胚体周围的胚乳细胞被水解,为发育的胚所利用。(4)合点吸器的2个细胞核与核仁巨大,线粒体、质体、高尔基体、内质网主要绕核分布,液泡化明显;胚体与胚乳本体的体积增大,逐渐将合点吸器向胚珠合点部位挤压,合点吸器周围的合点组织逐渐被水解,形成巨大空腔。合点吸器自珠心组织吸收并转运营养物质至胚乳本体,参与胚乳的结构构建与营养物质的贮藏。球胚后期,合点吸器逐渐失去功能,呈现退化状态。     

maternally expressed gene1 Is a novel maize endosperm transfer cell-specific gene with a maternal parent-of-origin pattern of expression

Growth of the maize (Zea mays) endosperm is tightly regulated by maternal zygotic and sporophytic genes, some of which are subject to a parent-of-origin effect. We report here a novel gene, maternally expressed gene1 (meg1), which shows a maternal parent-of-origin expression pattern during early stages of endosperm development but biallelic expression at later stages. Interestingly, a stable reporter fusion containing the meg1 promoter exhibits a similar pattern of expression. meg1 is exclusively expressed in the basal transfer region of the endosperm. Further, we show that the putatively processed MEG1 protein is glycosylated and subsequently localized to the labyrinthine ingrowths of the transfer cell walls. Hence, the discovery of a parent-of-origin gene expressed solely in the basal transfer region opens the door to epigenetic mechanisms operating in the endosperm to regulate certain aspects of nutrient trafficking from the maternal tissue into the developing seed.     

DEVELOPMENT OF THE SEED AND FRUIT IN RHINANTHUS MAJOR AND R. SEROTINUS

There are seven sessile, campylotropous, discoid ovules in each loculus of the anteroposteriorly flattened bilocular ovary. They are arranged alternately in two rows in each chamber on the axile placenta which is nodular where the ovules are borne. Nucellus degenerates early except at the chalazal end of the curved embryo sac, and the inntermost layer of the integument functions as endothelium. The aggressive, multinucleate micropylar haustorium grows as a tubular body through the micropylar canal and ramifies in the placenta while the two-nucleate chalazal haustorium creates a large space by digesting a good deal of the chalazal tissue. Endosperm is differentiated into three regions: the middle storage, the haustorial micropylar, and the chalazal. Thickness of the integument is considerably added to by the endothelium and by its surrounding meristematic zone of the integument. There are two prominent wings on the dorsal and smaller ones on the lateral faces of the cochlidiospermous seed, its ventral face being occupied by a prominent basal body. A heavily cutinized envelope, formed by the endothelium, surrounds the ovoid storage endosperm. Testa of the seed is mainly composed of the thickened epidermis and the endothelium. The micropylar and the chalazal parts of the endosperm become tanniferous and serve to plug the two ends of the seed. Embryo is straight, and it bears two cotyledons and two plumular leaves.     

Abortive seed development in Ulmus minor (Ulmaceae)

Three genotypes of field elm ( Ulmus minor ) were studied to determine the structural basis of seed abortion in this species. In the non-abortive control, P-VV1, the pattern of seed development is similar to many flowering plants. The embryo progresses through defined morphological stages leading to developmental arrest as the seed matures. Storage products are abundant within embryo cells. Endosperm development is similar to the nuclear type; however, a more extensive cellularization of the endosperm occurs prior to it being crushed by the expanding embryo. For the abortive genotypes, M-SF1 and V-JR1, abnormalities in endosperm development are found. This is judged by the early cellularization and the massive synthesis of the PAS-positive material in the cellular endosperm. In these abortive genotypes, embryo development is delayed and storage products failed to accumulate within embryo cells. After seed desiccation, no living embryo tissue remains within the seed coat in the abortive genotypes.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 455–467.     

Occurrence of Endosperm Haustorium in Cannabis sativa L.: With thirteen Figures in the Text

The development and structure of the chalazal endosperm haustoriumin Cannabis sativa are described. The endosperm is nuclear anda haustorium is formed at the chalazal end. The latter remainsfree nuclear throughout. Enucleate vesicles appear in the upperpart of the endosperm but finally they merge with the cytoplasmof the haustorium. As the embryo reaches maturity it occupiesthe whole seed cavity, the haustorium collapses and the endospermpersists only as a thin layer.     

EMBRYOLOGICAL DEVELOPMENT OF LACHNANTHES CAROLINIANA (HAEMODORACEAE)

Embryological development of Lachnanthes caroliniana was studied utilizing standard anatomical techniques and SEM. Lachnanthes has a monocotyledonous anther wall development (endothecial cells with spiral secondary wall thickenings), successive microsporogenesis, and amoeboid (periplasmodial) tapetal development. Mature pollen grains are 2-nucleate with a proximal, fusiform generative cell. Ovules are initiated as 5–7 cylindrical primordia from a common placental base. Basal ovular swellings collectively contribute to the enlarged, peltate placenta. Mature ovules are pleurotropous, anatropous, bitegmic, and crassinucellate; the nucellus consists of a chalazal hypostase, radially elongate lateral cells, and a prominent micropylar nucellar cap. Megasporogenesis is successive, forming a linear tetrad of megaspores. Megagametogenesis is monosporic; the female gametophyte is of the Polygonum-type with relatively large, pyriform antipodals. Endosperm formation is helobial, resulting in the establishment of a ring of four thick-walled basal endosperm cells (the chalazal chamber) and numerous free nuclei (in the micropylar chamber). The mature cellular endosperm is filled with starch grains and has a chalazal cavity and a thick-walled peripheral layer. The discoid, peltately attached seeds have marginal wings derived by anticlinal divisions and buckling of the outer integument alone. Inner and middle cuticular layers are present in the seed coat. Lachnanthes is similar to all other investigated members of the Haemodoraceae in major embryological features. The significance of embryological evidence with regard to interfamilial classification is discussed. Future studies of ovule and seed development may prove valuable in phylogenetic studies in assessing the homology of placental, ovule, and seed morphology and anatomy.     

The globby1-1 (glo1-1) mutation disrupts nuclear and cell division in the developing maize seed causing alterations in endosperm cell fate and tissue differentiation

Cereal endosperm tissues account for most of the world's calorific intake, yet the regulation of monocot seed development remains poorly understood. The maize endosperm originates with a series of free-nuclear divisions, followed by cellularisation and subsequent formation of a range of functional cellular domains. We describe the isolation and characterisation of a mutation that induces aberrant globular embryo and endosperm morphology, globby1-1 (glo1-1). Our data indicate that glo1-1 plays a role in nuclear division and cytokinesis in the developing seed. Pattern formation in the embryo is severely impaired with development arresting at premature stages, while in the endosperm, the effects of the glo1-1 mutation are manifest at the free-nuclear or syncytial stage. During cellularisation, and at later stages of development, aberrant cell division and localised domains of cell proliferation are apparent in glo1-1 endosperms. As a consequence, cell fate acquisition and subsequent differentiation of endosperm tissues are affected to varying degrees of severity. To date, it has been hypothesised that BETL cell fate is specified in the syncytium and that cell files subsequently develop in response to a gradient of signal(s) derived from the maternal pedicel region. Based on our findings, however, we propose that specification of BETL cells is an irreversible event that occurs within a narrow window of syncytial development, and that BETL cell identity is subsequently inherited in a lineage-dependent manner. Additionally, our data suggest that acquisition of aleurone cell fate does not solely rely upon signalling from the maternal surrounding tissue to the periphery of the endosperm, as previously thought, but that other factor(s) present within the endosperm are involved.