Embryo Sac Development in Almond [Prunus dulcis (Mill.) D. A. Webb] as Affected by Cross-, Self- and Non-pollination

Embryo sac development in ‘Nonpareil’ almond wasstudied following cross-, self- and non-pollination under fieldand greenhouse conditions. The embryo sac, which develops accordingto the Polygonum type, does not begin to differentiate untilanthesis in contrast to other Prunus spp. where a well-developedembryo sac is present at the time of flower opening. The developingmegagametophyte appears to be isolated from surrounding nucellartissue by the deposition of a ring of callose, which, as indicatedby aniline blue-induced fluorescence in the walls of nucellarcells, encloses the embryo sac during its elongation. Developmentand growth of the embryo sac following the different pollinationtreatments indicated that embryo sac development was stimulatedby the presence of compatible pollen tubes in the style andfinal elongation growth of the embryo sac was promoted by cross-pollination.Irregularities in megagametophyte development, including delayeddifferentiation of the megaspore mother cell, embryo sac abortionand lack of polar nuclei fusion and embryo sac elongation, werefrequently noted in ovules of self- and non-pollinated flowers. Almond, callose, embryo sac, megagametophyte, pollination, Prunus dulcis (Mill.) D. A. Webb.     

Endosperm Development in Solanum nigrum L. Formation of the Zone of Separation and Secretion

Endosperm development in Solanum nigrum was ab initio cellular.During early seed development, a Zone of Separation and Secretion(ZSS) differentiated within the endosperm. There were threephases in the formation of the ZSS. Phase I—stainabilityof the cell walls and middle lamella increased followed by numeroussmall plasmalemma invaginations (blebs) which became filledwith a fibrillar material. Phase II—the plasmalemma withdrewfrom the cell wall as a fibrillar lipo-carbohydrate matrix accumulatedoutside the plasmalemma. The middle lamella was gradually removedfrom between the cells forming the central axis of the cone.Phase III—the lipo-carbohydrate matrix continued to accumulateoutside the plasmalemma and also within the developing intercellularspaces. Some axial cells were completely separated from theremaining ZSS cells and became embedded in the matrix. The formationof the ZSS did not entail the destruction of the endosperm cellsand cell divisions were frequent. The ZSS was initially cone-shaped,capping the globular embryo. As the embryo sac enlarged, theZSS continued to differentiate. This resulted in a narrow curvedcorridor through the peripheral region of the endosperm whichterminated above the vascular trace. The embryo grew throughthe centre of the ZSS and pushed aside the separated axial cells.The ZSS facilitated the growth of the embryo through the restof the endosperm.Copyright 1993, 1999 Academic Press Lipo-carbohydrate matrix, extracellular matrix, endosperm development, Solanum nigrum, Zone of Separation and Secretion     

Comparative ovule and megagametophyte development in Hydatellaceae and water lilies reveal a mosaic of features among the earliest angiosperms

Background and Aims: The embryo sac, nucellus and integuments of the early-divergentangiosperms Hydatellaceae and other Nymphaeales are comparedwith those of other seed plants, in order to evaluate the evolutionaryorigin of these characters in the angiosperms. Methods: Using light microscopy, ovule and embryo sac development aredescribed in five (of 12) species of Trithuria, the sole genusof Hydatellaceae, and compared with those of Cabombaceae andNymphaeaceae. Key Results: The ovule of Trithuria is bitegmic and tenuinucellate, ratherthan bitegmic and crassinucellate as in most other Nymphaeales.The seed is operculate and possesses a perisperm that developsprecociously, which are both key features of Nymphaeales. However,in the Indian species T. konkanensis, perisperm is relativelypoorly developed by the time of fertilization. Perisperm cellsin Trithuria become multinucleate during development, a featureobserved also in other Nymphaeales. The outer integument issemi-annular (‘hood-shaped’), as in Cabombaceaeand some Nymphaeaceae, in contrast to the annular (‘cap-shaped’)outer integument of some other Nymphaeaceae (e.g. Barclaya)and Amborella. The megagametophyte in Trithuria is monosporicand four-nucleate; at the two-nucleate stage both nuclei occurin the micropylar domain. Double megagametophytes were frequentlyobserved, probably developed from different megaspores of thesame tetrad. Indirect, but strong evidence is presented forapomictic embryo development in T. filamentosa. Conclusions: Most features of the ovule and embryo sac of Trithuria are consistentwith a close relationship with other Nymphaeales, especiallyCabombaceae. The frequent occurrence of double megagametophytesin the same ovule indicates a high degree of developmental flexibility,and could provide a clue to the evolutionary origin of the Polygonum-typeof angiosperm embryo sac.     

Prolongation of Embryo Sac Viability in Pear (Pyrus communis) Following Pollination or Treatment with Gibberellic Acid

Embryo sac development has been investigated in unpollinated,cross pollinated and gibberellic acid (GA₂) treated flowersof Pyrus communis L. While pollination and GA₃ treatments donot alter embryo sac development, they prolong embryo sac viability.In untreated unpollinated flowers, ovules degenerate between12 and 21 d after anthesis, while in cross pollinated and GA₃treated flowers this degeneration is postponed by about 10 d.Thus, in a cross pollinated flower this extends the period overwhich a successful fertilization can take place. This increasedperiod of viability is accompanied by an elongation of the embryosac itself. Elongation takes place two weeks prior to fertilizationin cross pollinated flowers. The extension of life span of embryo sacs following pollinationand treatment with gibberellic acid indicates that a stimulusinduced by ‘pollination’ could be mediated by GA₃Whatever its mechanism of operation, the prolongation of embryosac viability by pollination represents a selective advantage,in that the period at which the ovules are receptive to fertilizationmust be significantly extended. Embryo sac, gibberellic acid, Pyrus communis, pear, pollination     

Fine Structure of Nucellar Cells During Development of the Embryo Sac in Oenothera biennis L.

Developing nucellar cells in Oenothera biennis L. present distinctpatterns of differentiation at the chalaza and around the embryosac. The cytoplasm of nucellar cells surrounding the tetradof megaspores displays cytolysomes, lipid bodies and membranesof smooth ER enveloping different cytoplasmic components. Concomitantto the differentiation of the embryo sac the nucellar cellsconstituting these ‘parietal layers’ undergo cytoplasmicdegeneration with shrinkage and flattening. In addition to theregular nucellar cells the chalaza at this stage presents threeother types: One with pycnotic nuclei, paramural bodies andcytoplasm filled with polymorphic vacuoles containing membranes,granular or flocculent material and multivesicular bodies. Asecond cell type shows swollen perinuclear cisternae aroundtheir pycnotic nuclei and large cytoplasmic vacuoles accumulatingtannins. The third type of cells is characterized by large numbersof starch grains and advanced disorganization of cytoplasmicorganelles; these cells probably become reservoirs after death. Oenothera biennis L., evening primrose, embryo sac, nucellus, cytolysomes, ultrastructure     

Development of the Female Gametophyte in Hydrobryum griffithii (Podostemaceae)

The development of the female gametophyte in Hydrobryum griffithiiis of the Apinagia type. The chalazal megaspore nucleus of thetwo-nucleate embryo sac completely degenerates, and only themicropylar megaspore nucleus contributes to the four nucleipresent in the organized embryo sac. The female gametophyteconsists of two synergids, an egg and a haploid central cell.The latter degenerates before the entry of the pollen tube andthere is only syngamy. The nucellar cells below the embryo sacorganize into a nucellar plasmodium.     

Anatomy of Watermelon Embryo Sacs Following Pollination, Non-pollination or Parthenocarpic Induction of Fruit Development

There is little information on the fate of embryo sacs in plantovules if pollination is prevented. In this study embryo sacsfrom watermelon were observed over a 13 day period followingflowering with (a) normal pollination, (b) non-pollination and(c) induction of parthenocarpic fruit development with naphthaleneacetic acid. Following pollination, and prior to fertilizationapproximately 2 days later, the embryo sacs completed developmentand consisted of two synergids with prominent filiform apparatus,an egg cell, a central cell with two polar nuclei and threeantipodal cells. Sperm nuclei were observed within the embryosac at 2 days and by 4 days the endosperm was proliferating.In the non-pollination treatment the embryo sac was still intactafter 4 days although the antipodal nuclei were becoming hardto distinguish. By 7 days only the two synergids and the eggcell were still well defined, the polar nuclei appeared in somepreparations to be fused, and the antipodals had degenerated.By 10 days the embryo sac was a structure-less watery mass.In parthenocarpic fruit the fate of the embryo sac was similarto that in non-pollinated fruit except that final breakdownwas delayed past 10 days. Maturity of the majority of embryo sacs in an ovary appearedto be contemporaneous with penetration of the pollen tube, andon the basis of the anatomical results it seems possible thatembryo sacs could be fertilized up to 2 days beyond the normaltime. Citrullus lanatus, watermelon, embryo sac, anatomy, pollination, parthenocarpy     

Ultrastructure of the Developing and Fertilized Embryo Sac of Amaranthus hypochondriacus L.

Amaranthus hypochondriacus embryo sac development was investigatedbefore and after fertilization. During the early stages of development,the young embryo sac displays three antipodal cells at the chalazalpole that degenerate very early in the maturation process, beforethe synergids and egg cell are completely differentiated. Themature embryo sac is composed only of the female germ unit.The synergid cells organize a filiform apparatus accompaniedby the presence of mitochondria and dictyosomes with numerousvesicles. The involvement of the synergids in transport andsecretory functions related to pollen tube attraction and guidance,are discussed. The egg cell is located at the micropylar polenear the synergids and displays exposed plasma membranes atthe chalazal pole. The fertilized egg cell does not exhibitmarked changes after fertilization except for the closure ofthe cell wall. The central cell is the largest cell of thisvery long embryo sac. The fused nucleus is close to the eggapparatus before fertilization and displays a remarkable chalazalmigration after gamete delivery. The ultrastructure of the centralcell cytoplasm and the numerous wall ingrowths around this cellsuggest an important role in nutrient transportation. Aftergamete delivery, the embryo sac displays electron dense bodiesthat aggregate within the intercellular space between the synergids,egg cell and central cell. These bodies, that appear in theembryo sac of several plants, are probably involved in gametedelivery for double fertilization. The possibility of biparentalinheritance of mitochondria in this plant is also discussed.Copyright 1999 Annals of Botany Company Amaranthus hypochondriacus, grain amaranth, embryo sac, fertilization.     

Effects of Phytophthora palmivora on Zygotic Embryos of Papaya In Vitro

Zygotic embryos of Carica papaya were successfully germinatedin vitro on Murashige and Skoog's medium supplemented with 2%activated charcoal. The effects of light, temperature, sucroseand nutrient concentrations in the medium, on growth and developmentof embryos were examined. Strength of the nutrients in the mediumhad no effect on the growth and development of embryos. Thegerminated embryos of different varieties of papaya were inoculatedusing a sporangial suspension of different isolates of Phytophthorapalmivora. In the analysis of variance, varieties, isolatesand variety—isolate interactions differed significantly.The results were compared with the inoculation of glasshouse-grownseedlings; it is suggested that embryo inoculation could bea useful method of detecting resistance at an early stage ofplant development. Papaya, Carica papaya L., embryo culture, Phytophthora palmivora, resistance, in vitro screening     

The Nucellus, Embryo Sac, Endosperm, and Embryo of Aesculus and their Interdependence during Growth

Immature fruits of Aesculus yield powerful stimuli to growthand cell division. Therefore, the developing fruit of Aesculuswoerlitzensis Koehne has been investigated from pollinationto maturity. The fluid, or liquid endosperm, which containsthe growth-promoting substances is produced in a large vesiclewhich forms at the chalazal tip of the embryo sac. As the vesiclegrows, it encroaches upon the nucellus and, when the embryodevelops, one of its cotyledons penetrates into the vesicleof the embryo sac where it grows and absorbs the contents. Theembryo, which has only a vestigial suspensor, reaches the vesicleby growing along the neck of the long curved embryo sac. Thecotyledon which first penetrates the vesicle grows into a massivestructure; the other remains small. The tip of the cotyledonseems to function as an absorbing surface, for the endospermwith which it comes into contact disorganizes. Fertilizationand the presence of a viable embryo at the micropylar end ofthe embryo sac therefore sets in train a number of other events.These are the extensive development of the nucellus at the chalazalend of the embryo sac, the swelling of the vesicle and the formationof a free nuclear and some cellular endosperm, and the disorganizationof the nucellus as it is encroached upon by the vesiculate embryosac. Attention is directed to the organization of the nucellusin the vicinity of the embryo sac. Files or richly protoplasmicnucellar cells(hypostase) which converge upon the chalazal tipof the embryo sac suggest a principal route by which the vesiclemay be nourished. Special attention is drawn to the very differentsizes of cells, their nuclei and nucleoli, in the differentparts of the nucellus. The growth and development of the embryohas also been traced from the zygote to the mature seed. Thenutritive role of the veaiculate embryo sac, and the supplyof growthstimulating substances, through the function of a cotyledonas an absorbing organ, are now seen as important features ofthe development of the Aesulus embryo in the ovule. Many outstandingproblems still remain. The sequential events that follow fertilizationin the different interdependent regions (nucellus, embryo sac,cotyledon, &c.) are here described, but not casually explained.     

Accumulation of Metabolites during Seed Development in Trifolium repens L.

Metabolite deposition during seed development was examined histochemicallyin Trifolium repens by light- and fluorescence microscopy. Allendosperm haustorium at the chalazal pole of the embryo sacand wall protrusions in cell walls of the suspensor and theembryo sac suggest that transfer of metabolites from maternalto offspring tissue takes place primarily at these sites. Thisis further supported by prominent cutinization of the interpolarregion of the embryo sac wall, accumulation of starch in integumentaltissue at the embryo sac poles, and breakdown of interpolarendothelial cells. Decomposition of osteosclereid starch isfollowed by accumulation in the cellular endosperm and subsequentlyin the embryo parallel to endosperm degradation. The starchaccumulates gradually inward from the subepidermal cells ofthe embryo to the stele. Protein bodies are formed in the vacuolesalong the tonoplast, later to be cut off in vesicles releasedinto the cytoplasm. At maturity the embryo is packed with proteinand starch, but without lipid reserves. Phytin is observed inthe protein bodies. The mature embryo is surrounded by a proteinand starch containing aleurone layer which originates from theendosperm.Copyright 1994, 1999 Academic Press White clover, protein, starch, cuticle, embryo sac wall     

Glycosylation sites identified by solid-phase Edman degradation: O-linked glycosylation motifs on human glycophorin A

The human red blood cell sialoglycoprotein, glycophorin A (GpA),contains a ‘mucin-like’ extensively O-glycosylatedextracellular domain which carries the MN blood group antigens.We have revised the sites of O-glyccsylation in the extracellulardomain of GpA by automated solid-phase Edman degradation, whichallowed positive identification and quantitation of O-glycosylatedSer and Thr residues, as well as the single N-glycosylationsite. One N-linked and 16 O-linked sites were identified. Carbohydratewas absent on Ser 1, Ser14, Ser15, Ser23, Thr28 and Thr58 inGpA. We propose that the glycosyltransferases present in erythrocytesrecognize specific flanking sequences around potential O-glycosylationsites. All 16 O-glycosylation sites are explained on the basisof four motifs. Three motifs are associated with Thr-glycosylation:Xaa—Pro—Xaa—Xaa where at least one Xaa = Thr;Thr—Xaa—Xaa—Xaa where at least one Xaa = Thr;Xaa—Xaa—Thr—Xaa where at least one X = Argor Lys. The fourth motif is associated with Ser-glycosylation:Ser—Xaa—Xaa—Xaa where at least one Xaa = Ser.These simple rules explain the glycosylation (or lack of it)on 21 of 22 Ser/Thr in the extracellular domain of GpA. glycophorin A O-glycosylation motif solid-phase Edman degradation     

Inverse Correlation between ABA Content and Germinability throughout the Maturation and the In Vitro Culture of the Embryo of Phaseolus vulgaris

Prevost, I. and Le Page-Degivry, M. Th. 1985. Inverse correlationbetween ABA content and germinability throughout the maturationand the in vitro culture of the embryo of Phaseolus vulgaris.—J.exp. Bot. 36: 1457–1464. Changes in embryo abscisic acid (ABA) content during the maturationof the seed of Phaseolus vulgaris cv. Contender were followed,using a radio-immunoassay. The pattern of change is similarto that already described in several species: a rapid increase(from the 18th to 29th day after anthesis), was followed bya decrease, the ABA level being ten times lower on the 48thday than on the 29th. Embryos isolated from the 18th to the48th day after anthesis were able to ‘germinate’when cultivated on a mineral medium supplemented with sucroseand agar. The development pattern varied throughout the embryogenesisand could be correlated with the differentiation of the embryoat the time of isolation. Before germination could take place,we observed a lag phase, the duration of which could be correlatedwith embryo ABA content. As ABA content increased in the youngestembryos the duration of the lag phase increased. In the sameway, the number of days to germination was shown to diminishas ABA content decreased. Inverse correlation between ABA contentand germinability was thus demonstrated throughout the developmentof the embryo. During in vitro culture, free ABA content decreased in the embryoand reached low values a few days before germination occurred.So the beginning of root elongation in culture was again wellcorrelated with the disappearance of free endogenous ABA. Atransfer experiment inducing an earlier germination associatedwith a more limited development suggests that the lag phaseis associated with an active continuation of embryonic development Key words: Embryo maturation, abscisic acid, germinability     

Functional Anatomy of the Ovule in Broad Bean (Vicia faba L.): Ultrastructural Seed Development and Nutrient Pathways

Ovules of broad bean (Vicia faba L.) were studied to discloseultrastructural features, which can facilitate nutrient transportto the embryo sac from 10 d after pollination (DAP) to the matureseed. Fertilization occurs during the first 24 h after pollination.The endosperm is a coenocyte, which is eventually consumed bythe embryo. By 10 DAP the inner integument is degraded and theouter integument adjoins the embryo sac boundary. The heart-shapedembryo approaches the embryo sac boundary at two sites, whichhere are named contact zones. Small integument cells in theneighbourhood of the first formed contact zones become separatedby prominent intercellular spaces. A heterogenous scatteringmaterial, probably representing secretion products accumulatesin these spaces. By 14-16 DAP the integument exudate disappears,and the suspensor degenerates. As the contact zones increasein size, wall ingrowths form a bridging network in the narrowspace between the embryo sac boundary and the extra-embryonicpart of the endosperm wall. The epidermal cells of the embryoseparate adjacent to these zones, and develop conspicuous wallingrowths. At 20 DAP vacuoles showing various stages in formationof protein bodies appear in the cells of the embryo.Copyright1994, 1999 Academic Press Vicia faba, broad beans, ovule, seed, nutrient transport     

Development of the Embryo Sac in Amitostigma kinoshitae (Makino) Schltr. (Orchidaceae)

The embryo sac of Amitostigma kinoshitae was studied. The ovuleis anatropous, bitegmic, and tenuinucellate. The inner integumentalone forms a micropyle. The megaspore of a tetrad nearest tothe chalaza develops into an eight-nucleate embryo sac of thetypical Polygonum-type. Double fertilization takes place normally.     

The Red-Eared Slider Turtle: An Animal Model for the Study of Low Doses and Mixtures

Current risk assessment techniques for almost all chemicalsinvolve establishing a threshold dose, or the dose below whichno adverse effects are seen. But threshold doses may not applyin situations where the chemical mimics the actions of an endogenouscompound—such as a steroid hormone—that is importantto development. In such cases, any exposure may exceed the threshold.Recent studies with the red-eared slider turtle have shown thatexogenous estradiol—even when applied to eggshell in dosesas low 0.4 ng—will affect sex development during embryogenesis.Considering that only 0.2% of the estradiol applied to the eggshellends up in the embryo, it becomes apparent that even very lowdosages of steroid hormones or their mimics can have profoundbiological effects. We tested this idea using eight compoundsidentified in the yolk of alligator eggs from Lake Apopka, Fla.Five of the compounds—the PCB mixture Aroclor 1242,trans-Nonachlor,cis-Nonachlor,p,p'-DDE, and chlordane—altered sex ratio outcomes whenapplied to eggshells during development. Aroclor 1242 producedthe most powerful effects, shifting the ratio of females almosttwofold, while chlordane had the greatest effect when combinedwith estradiol. Administration of all eight compounds togetheralso increased the ratio of females to males. However, comparingthe single-compound exposures at the same dosages indicate thatthese compounds behave differently in combination than theydo singly, emphasizing the need for further studies using chemicalmixtures reflecting proportions found in nature. The effectof chlordane and Aroclor 1242 on aromatase activity levels duringembryogenesis in the brain and adrenal-kidney-gonad (AKG) complexwas also examined. Chlordane, a suspected anti-androgen in thisspecies, did not affect aromatase activity in either the brainor the AKG. However, Aroclor 1242 significantly altered aromataseactivity levels in the red-eared slider turtle brain—butnot in the AKG—during a crucial developmental period.After this crucial period, Aroclor 1242 caused an increase inaromatase activity in the AKG of embryos just prior to hatch.Additionally, hatchling males treated during embryogenesis withAroclor 1242 and chlordane exhibited significantly lower testosteronelevels than controls in response to follicle-stimulating hormoneadministration, while chlordane-treated females had significantlylower progesterone, testosterone, and 5-dihydrotestosteronelevels relative to controls. These results are similar to thosefound in juvenile alligators from Lake Apopka. Males treatedwith Aroclor 1242 and trans-Nonachlor displayed an elevatedestradiol response to FSH administration vs. control males.Taken together, these results suggest that EDCs exert effectsduring embryonic development that extend beyond birth. Theyalso suggest that the alterations in sex steroid hormone levelsobserved in animals from contaminated areas may result fromEDC-induced alterations in the neuroendocrine axis controllinggonadal sex steroid hormone production.     

An Analysis of Seed Development in Pisum sativum L.

Growth analysis has been performed on developing seeds and seedcomponents of six contrasting genotypes of Pisum sativum. Seeddevelopment has been divided into three phases of high growthrate separated by two ‘lag’ phases, or phases oflow growth rate. It is suggested that the timing of these growthphases may not be determined by the developing seed, since thereappeared to be no consistent correlation with particular physiologicalstages of seed development. The relationship between the absolutegrowth rate of the embryo sac and of the embryo as determinedfrom changes in volume is reflected in the accumulation andabsorption of the endosperm. The relative growth rate of theembryo volume was invariably higher than that of the embryosac although the difference between these two relative ratesvaried with genotype and may account in part for the differencein seed phenotype. It is suggested that the testa and embryo are sinks which bothcompete for the endosperm which may act as a common source,and that this relationship accounts for variation in endospermvolume. It is concluded that seed development is dependent on threelevels of plant organization, the maternal parent, interactionsbetween the components of the seed and the genetic constitutionof the embryo. Pisum sativum L., garden pea, seed development, growth analysis     

Plant Growth-promoting Rhizobacteria and Soybean [ Glycine max (L.) Merr.] Growth and Physiology at Suboptimal Root Zone Temperatures

Application of plant growth-promoting rhizobacteria (PGPR) hasbeen shown to increase legume growth and development under optimaltemperature conditions, and specifically to increase nodulationand nitrogen fixation of soybean [Glycine max (L.) Merr.] overa range of root zone temperatures (RZTs). Nine rhizobacteriaapplied into soybean rooting media were tested for their abilityto reduce the negative effects of low RZT on soybean growthand development by improving the physiological status of theplant. Three RZTs were tested: 25, 17.5, and 15 °C. At eachtemperature some PGPR strains increased plant growth and development,but the stimulatory strains varied with temperature. The strainsthat were most stimulatory at each temperatures were as follows:15 °C—Serratia proteamaculans 1–102; 17.5 °C—Aeromonashydrophila P73, and 25 °C—Serratia liquefaciens 2–68.Because enhancement of plant physiological activities were detectedbefore the onset of nitrogen fixation, these stimulatory effectscan be attributed to direct stimulation of the plant by thePGPR rather than stimulation of plant growth via improvementof the nitrogen fixation symbiosis. Legume; nitrogen fixation; nodulation; root zone temperature; PGPR     

Early Events in the Penetration of the Embryo Sac in Torenia fournieri(Lind.)

At maturity, Torenia fournieri(Lind.) has an embryo sac whichprotrudes through the micropyle placing the synergids, egg celland part of the central cell within the ovary locule adjacentto the placenta. The present study utilized this unique attributein combination with confocal and light microscopy to characterizethe timing and associated structural changes during pollinationevents leading to double fertilization. The observation of spermnuclei in living gametophyte tissue is an important advancein the identification, in real time, of stages leading to fertilizationin angiosperms. A continuum of fertilization occurred between12 and 16 h after pollination (hap), with peak frequency ofegg and sperm fusion at 14 hap (43%). Movement of the spermcells through the degenerated synergid took several hours andfusion between sperm and their respective female nuclei occurredsimultaneously. Changes in embryo sac structure were also documented.Cell walls in the region between the synergids and egg cellwere poorly developed prior to pollen tube penetration. Thickenedcell walls were observed around the periphery of the synergidsand egg cell following pollination, and in the central cellwhere it lay within the body of the ovule. Starch was observedin the cells of the embryo sac, although the number and distributionof granules varied before and after pollination. These temporaland spatial observations of the embryo sac inTorenia fournieriprovide a basis for further research to determine control mechanismsoperating during specific double fertilization events in angiosperms.Copyright 2000 Annals of Botany Company Double fertilization, embryo sac, sperm nuclei, Hoechst, Torenia fournieri     

Ovule and Embryo Sac Development in Malus pumila L. cv. Cox's Orange Pippin, from Dormancy to Blossom

Ovule and embryo sac development in the flowers of Cox's OrangePippin apple (Malus pumila L.) were studied from dormancy topetal fall using both scanning electron and light microscopy.The relative timing was established between these developmentsand the external development of the flower bud and flower. Malus pumila L. cv. Cox's Orange Pippin, apple, Cox, SEM, ovule development, anatomy, histology