Fecundation and Formation of the Primary Endosperm Nucleus in Certain Liliaceae

Apomixis is a common feature of perennial plants, which occurs in ca . 60% of the British flora, but has been largely ignored by reproductive theoreticians. Successful individuals may cover huge areas, and live to great ages, favoured by ‘symmetrical’ selection. Apomixis is favoured by colonizing modes, for instance post–glacially. Despite its theoretical advantages, apomixis usually coexists with sexuality, suggesting ‘hidden’ disadvantages. Agamospermy (apomixis by seed) is relatively uncommon, but gains from the attributes of the seed. It pays agamospermy genes, which discourage recombination, to form co–adapted linkage groups, so that they become targets for disadvantageous recessive mutant accumulation. Consequently, agamospermy genes cannot succeed in diploids and agamosperms are hybrid and highly heterotic. Agamospermous endosperm may suffer from genomic imbalance, so that nutritious ovules, which can support embryos without endosperm, may be preadapted for agamospermy. When primary endosperm nucleus fertilization (‘pseudogamy’) continues as a requirement for many aposporous agamosperms, selfing sex becomes preadaptive and archesporial sex remains an option. Apomictic populations can be quite variable although apomictic families are much less variable than sexuals. Only in some diplosporous species does sex disappear completely, and in those species some release of variability may persist through somatic recombination. The search for an agamospermy gene suitable for genetic modification should target fertile sexuals with a single localized agamospermy ( A ) gene, which therefore lack a genetic load. The A gene should coexist alongside sexuality, so that it would be easy to select seedlings of sexual and asexual origins. Plants with sporophytic agamospermy provide all these attributes.

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EMBRYOLOGY OF INTERSPECIFIC CROSSES IN MELILOTUS

Canadian Journal of Botany ◽

10.1139/b54-041 ◽

1954 ◽

Vol 32 (3) ◽

pp. 447-465 ◽

Cited By ~ 12

Author(s):

John Edward Ross Greenshields

Keyword(s):

Germ Plasm ◽

Female Parent ◽

Early Embryo ◽

Endosperm Nucleus ◽

Interspecific Crosses ◽

Primary Endosperm Nucleus ◽

Embryo Abortion ◽

Advanced Embryo ◽

Essentially Normal ◽

The Cross

Twelve species of Melilotus were intercrossed and the embryology of the hybrids was studied. The species involved in this study are M. alba, M. officinalis, M. suaveolens, M. polonica, M. dentata, M. altissima, M. hirsutus, M. taurica, M. messanensis, M. italica, M. sulcat, and M. speciosa. Among partially compatible crosses, M. officinalis × M. alba produces the most advanced embryo. Growth of the embryo proceeds normally until about eight days, and more slowly thereafter until the 12th or 13th day, when growth is completely inhibited and the embryo aborts. The reciprocal M. alba × M. officinalis embryo does not grow as large or differentiate as much before aborting by the 11th day. Other crosses, including M. officinalis × M. suaveolens and M. alba × M. messanensis form a normal proembryo that grows slowly to about the sixth day. The proembryo then loses polarity, organ development becomes abnormal, and the ovule aborts about the 12th day. Aborted embryos are also produced in the cross, M. alba × M. dentata. Reciprocal crosses of M. suaveolens and M. altissima and M. altissima × M. polonica produce essentially normal embryos up to eight days. These crosses may be sources of economically important germ plasm. Crosses of M. altissima × M. alba and M. italica × M. altissima exhibit early embryo abortion. The suspensor becomes necrotic in four or five days and the proembryo floats into the ovule cavity, which contains abundant noncellular endosperm. In the cross M. officinalis × M. altissima, neither the zygote nor the primary endosperm nucleus divides. When M. altissima is used as the female parent, the zygote does not divide but the endosperm proliferates. In the cross, M. italica × M. officinalis, neither the zygote nor the endosperm divides. Embryos of M. italica × M. sulcata grow for four or five days, but the primary endosperm nucleus does not divide. The hybrid seed of M. alba × M. suaveolens weighs less than seed of either parent. Although developing ovules are smaller than those of M. suaveolens × M. alba, the embryo of the former is much larger and more differentiated, and endosperm is more abundant. This relationship between these two compatible species is of particular theoretical interest. Although many of the crosses do not mature viable seed, some embryos develop normally to a point where they would be worthy subjects for culture on nutrient agar.

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Fertilisation of polar nuclei and formation of early endosperms in Dendrobium catenatum: evidence for the second fertilisation in Orchidaceae

Australian Journal of Botany ◽

10.1071/bt17211 ◽

2018 ◽

Vol 66 (4) ◽

pp. 354 ◽

Cited By ~ 1

Author(s):

Yong Chen ◽

Chu Zhang ◽

Xiao-feng Wang ◽

Cheng-qi Ao

Keyword(s):

Embryo Development ◽

Endosperm Development ◽

Endosperm Nucleus ◽

Primary Endosperm Nucleus ◽

Section Technique ◽

Embryo Stage ◽

New Evidence

Whether the second fertilisation, i.e. fertilisation of polar nuclei, or fusion of the second sperm with polar nuclei occurs in Orchidaceae has long been controversial because of lack of evidence. In the present study, we observed fusion and fertilisation of polar nuclei and formation of early endosperms in the orchid Dendrobium catenatum Lindl., by using a resin-embedded section technique. As the product of the second fertilisation, the primary endosperm nucleus (fertilised polar nuclei) can last until the global embryo stage, indicating that initiation of endosperm development and that of embryo development were fully asynchronous. The present study demonstrated the occurrence of the second fertilisation in D. catenatum by providing lines of new evidence.

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Capsella Embryogenesis: The Central Cell

Journal of Cell Science ◽

10.1242/jcs.12.3.741 ◽

1973 ◽

Vol 12 (3) ◽

pp. 741-763

Author(s):

PATRICIA SCHULZ ◽

W. A. JENSEN

Keyword(s):

Central Cell ◽

Endosperm Nucleus ◽

Binucleate Cell ◽

Cell Cytoplasm ◽

Primary Endosperm Nucleus ◽

Structural Reorganization ◽

Nucleolar Material ◽

And Function ◽

Relationship Of ◽

The Relationship

The central cell is the binucleate cell of the angiosperm megagametophyte which contains the polar nuclei and participates in double fertilization. The structure of the mature central cell, the fusion of the polar nuclei and the primary endosperm nucleus were studied with the electron microscope. The central cell cytoplasm appears very active and has an extensive ER, many mitochondria, dictyosomes, microbodies, polysomes, chloroplasts with well developed grana and starch and lipid reserves. A single, giant mitochondrion appears in the cytoplasm near the polar nuclei at the time of fertilization, but its origin, fate and function are not known. Cytoplasmic aggregates of dense, granular material are associated with the primary endosperm nucleus and structurally resemble the nucleolus and similar aggregates in the nucleoplasm. It is suggested that these cytoplasmic perinuclear bodies may represent extruded nucleolar material. The central cell cytoplasm does not undergo any notable structural reorganization as a result of fertilization. The relationship of the central cell to the other cells of the mature megagametophyte and its possible role in embryogenesis is discussed.

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Reproductive development in two species of Darwinia Rudge (Myrtaceae)

Australian Journal of Botany ◽

10.1071/bt9690215 ◽

1969 ◽

Vol 17 (2) ◽

pp. 215 ◽

Cited By ~ 8

Author(s):

N Prakash

Keyword(s):

Embryo Sac ◽

Pollen Grains ◽

Reproductive Development ◽

Outer Zone ◽

Mature Embryo ◽

Globular Embryo ◽

Primary Endosperm Nucleus ◽

Oil Glands ◽

Polygonum Type ◽

History Of

In Darwinia the floral parts are differentiated in a "calyx-orolla-gynoeciumandroecium" sequence. In individual buds stages of microsporogenesis markedly precede corresponding stages of megasporogenesis. The anther is tetrasporangiate with all sporangia lying in one plane. The secretory tapetum is one- to three-layered within the same microsporangium and a large number of Ubisch bodies are formed. The anthers dehisce by minute lateral pores and an ingenious mechanism helps disperse the twocelled pollen grains. A basal placenta in the single loculus of the ovary bears four ovules in D. micropetala and two in D. fascicularis. In both species, however, only one ovule is functional after fertilization. The fully grown ovules are anatropous, crassinucellar, and bitegmic; the inner integument forms the micropyle. The parietal tissue is most massive at the completion of megasporogenesis but is progressively destroyed later. The embryo sac follows the Polygonum type of developnlent and when mature is five-nucleate, the three antipodals being ephemeral. Following fertilization, the primary endosperm nucleus divides before the zygote. Subsequent nuclear divisions in the endosperm mother cell are synchronous and lead to a free-nuclear endosperm which becomes secondarily cellular, starting from the micropylar end at the time the globular embryo assumes an elongated shape. Embryogeny is irregular and the mature embryo is straight with a massive radicle and a hypocotyl which terminates in two barely recognizable cotyledons. Sometimes the minute cotyledons are borne on a narrow neck-like extension of the hypocotyl. A suspensor is absent. Both integuments are represented in the seed coat and only the outer layer of the outer and the inner layer of the inner integuments, with their thick-walled tanniniferous cells, remain in the fully grown seed. The ovary wall is demarcated into an outer zone containing oil glands surrounded by cells containing a tannin-like substance and an inner zone of spongy parenchyma. In the fruit this spongy zone breaks down completely but the outer zone is retained. The two species of Darwinia, while closely resembling each other in their embryology, differ significantly from other Myrtaceae. However, no taxonomic conclusions are drawn at this stage, pending enquiry into the life history of other members of the tribe Chamaelaucieae.

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Early events in the embryo sac after intraspecific and interspecific pollinations in Rhododendron kawakamii and R. retusum

Canadian Journal of Botany ◽

10.1139/b86-042 ◽

1986 ◽

Vol 64 (2) ◽

pp. 282-291 ◽

Cited By ~ 11

Author(s):

V. Kaul ◽

J. L. Rouse ◽

E. G. Williams

Keyword(s):

Seed Set ◽

Embryo Sac ◽

Pollen Tubes ◽

Interspecific Crosses ◽

Primary Endosperm Nucleus ◽

Kalmia Latifolia ◽

Taxonomic Grouping ◽

Similarities And Differences ◽

Normal Fertilization

Early events in the embryo sac of Rhododendron kawakamii and R. retusum have been studied after compatible self-pollinations and eight interspecific crosses, using sectioned ovaries, pistil squashes, and seed-set data. Ovules of Rhododendron kawakamii and R. retusum are anatropous, unitegmic, and tenuinucellate, with a typical eight-nucleate, seven-celled embryo sac. Fertilization normally occurs 4–5 days after pollination. The zygote lays down a callose wall but remains undivided during the first 13–15 days after pollination. The primary endosperm nucleus divides soon after fertilization, and development is cellular ab initio. Crosses of R. kawakamii (♂) with R. santapaui and R. retusum and crosses of R. retusum (♂) with R. kawakamii, R. santapaui, R. ovatum, and R. tashiroi showed apparently normal fertilization in a majority of ovules entered by pollen tubes. In crosses of R. kawakamii (♂) with R. quadrasianum and Kalmia latifolia entry of pollen tubes into ovules was delayed and frequently abnormal. Apart from compatible self-pollinations of R. kawakamii an R. retusum, only the cross of R. kawakamii (♂) with R. santapaui produced healthy seedlings. Of the remaining seven interspecific crosses only three showed significant embryo development in control pistils left to mature in situ. Similarities and differences in the breeding behaviour of R. kawakamii and R. retusum are discussed with reference to their taxonomic grouping within subsection Pseudovireya.

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Corrigendum - Cell Development in the Young Seed of Two Inbred Lines of Pearl Millet, Pennisetum Americanum.

Australian Journal of Botany ◽

10.1071/bt9810617c ◽

1981 ◽

Vol 29 (5) ◽

pp. 617

Author(s):

MK Rao ◽

KA Kumari

Keyword(s):

Pearl Millet ◽

Mitotic Cycle ◽

Inbred Lines ◽

Cell Development ◽

Field Conditions ◽

Endosperm Nucleus ◽

Pennisetum Americanum ◽

Young Seed

Rate of cell development in embryo and endosperm during the 1st 4 days after pollination was similar in 2 lines of P. americanum under field conditions. 1st division of the endosperm nucleus was complete within 6 h after pollination. Synchronous mitoses, the mitotic cycle, divisions within the embryo and the endosperm and embryo volume increases are described.

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The development of the embryo sac of sunflower Helianthus annuus after fertilization

Canadian Journal of Botany ◽

10.1139/b73-110 ◽

1973 ◽

Vol 51 (5) ◽

pp. 879-890 ◽

Cited By ~ 72

Author(s):

William Newcomb

Keyword(s):

Helianthus Annuus ◽

Mitotic Spindle ◽

Embryo Sac ◽

Endosperm Development ◽

Primary Endosperm Nucleus ◽

Single Row ◽

Wall Formation ◽

Globular Stage ◽

Spindle Apparatus ◽

Single Fertilization

The degeneration of one synergid denotes the initiation of embryo and endosperm development in the embryo sac of sunflower Helianthus annuus L. The other synergid, the persistent synergid, is present until the late globular stage of embryogenesis. The primary endosperm nucleus divides before the zygote nucleus forming a coenocytic nuclear endosperm. When about eight endosperm nuclei are present during the early globular stage of embryogenesis, endosperm wall formation starts at the micropylar end of the embryo sac. The walls continue to grow toward the chalazal end of the embryo sac apparently as a result of the activity of Golgi located at the tips of the growing walls. Most endosperm wall formation is not associated with a mitotic spindle apparatus in sunflower. The suspensor of the embryo consists of a large basal cell during the proembryo stages, a single row of cells during the early globular stages, and at the late globular stage a double tier of cells near the radicle end of the embryo and a single row at the micropylar end of the embryo sac. Occasionally embryo development occurs in the absence of endosperm when only single fertilization has taken place. The development and nutritional implications of post-fertilization events in the sunflower embryo sac are discussed.

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Endosperm mitotic activity and endoreduplication in maize affected by defective kernel mutations

Genome ◽

10.1139/g92-012 ◽

1992 ◽

Vol 35 (1) ◽

pp. 68-77 ◽

Cited By ~ 23

Author(s):

R. V. Kowles ◽

M. D. McMullen ◽

G. Yerk ◽

R. L. Phillips ◽

S. Kraemer ◽

...

Keyword(s):

Mitotic Activity ◽

Dna Content ◽

Endosperm Development ◽

Kernel Weight ◽

Endosperm Nucleus ◽

Endosperm Cell ◽

Cell Numbers

A group of 35 defective kernel (dek) mutants in maize has been studied with regard to their effect on endosperm development. Information is reported on kernel weight, kernel viability, mutant transmission, DNA content per endosperm nucleus, endosperm cell numbers during development, and DNA endoreduplication patterns. All of the dek mutations reduced mitotic activity and resulted in greatly reduced cell numbers. All except one mutation decreased DNA endoreduplication. The exception indicates that the processes of mitotic activity and endoreduplication can be uncoupled. Notable differences in DNA endoreduplication patterns were observed among the dek strains. Defective kernels with homozygous defective embryos did not germinate in any of these strains, although some morphologically defective kernels did germinate and were shown to have normal embryos of +/+ or +/dek genotype. Dek mutants that had a defective endosperm and an embryo that developed normally were not identified. The mutations investigated are recessive, but F2 segregation for many of the mutants revealed significant deviations from expected 3:1 ratios.Key words: defective kernels, endosperm, endoreduplication.

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