1 / 47

Chapter7 Apomixis and Polyembryony

Chapter7 Apomixis and Polyembryony. Apomixis ： The embryos develop without the contribution of a male gamete.

szimmerman
Download Presentation

Chapter7 Apomixis and Polyembryony

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter7 Apomixis and Polyembryony

  2. Apomixis ： The embryos develop without the contribution of a male gamete. The result is that apomictically produced seeds inherit their genes exclusively from the mother, and so the plants that grow from these seeds are identical to the mother plant.

  3. The two types： One，the reduction in chromosome number 1．Haploid parthenogenesis 2．Haploid androgenesis 3．Apogamy

  4. Two， the unreduction in chromosome number： 1．Diplospory 2．Somatic apospory

  5. The sexual developmental pathway is short-circuited during apomictic reproduction

  6. 1.The reduction in chromosome number 1.1 Haploid parthenogenesis The unreduced egg cell develops into an embryo without fertilization.

  7. 图13—2 宽叶火烧兰的单倍体孤雌生殖 A、B. 胚囊中单倍体的卵在分裂，花粉管未开裂；C．胚囊未接受花粉管，但卵和次生核已经分裂；D、E. 单倍体的卵第一次分裂的中期，示20个染色体

  8. 1.2 Haploid androgenesis The sperm develops into an embryo solely.

  9. 1.3 Apogamy The other cells in embryo sac develops into an embryo without fertilization.

  10. 2. The unreduction in chromosome number

  11. 2.1 Diplospory The magasporocyte doesn’t enter into meiosis and proceeds directly to the first mitosis. The female meiosis is omitted. 2.1.1 The magasporocyte proceeds directly to embryo sac.

  12. 齿叶苦荬菜未减数胚囊的发育 A．大孢子母细胞第一次分裂的前期；B．后一时期，示21个单价染色体；C．再组核；D．中期；E．末期；F—G．二核胚囊；H．四核胚囊；L成熟胚囊；J．后一时期，示二细胞原胚

  13. 2.1.2 The magasporocyte enters into mitosis and proceeds dyad, one of the dyad undergoing three mitoses leading to an eight-nucleate embryo sac .

  14. 白花蒲公英未减数胚囊的发育 A、B，大孢子母细胞的连续切片，示再组核；C．大孢子母细胞在分裂；D．二分体细胞形成，下方的二分体细胞起作用，产生胚囊；E．二核胚囊；F．成熟胚囊，示胚乳的形成

  15. 2.1.3 The magasporocyte proceeds to embryo sac by mitosis which is similar with somatic.

  16. 2. 2．Somatic apospory The type of embryo sac is origin from nucellus。

  17. A．大孢子母细胞及在珠心中一个无孢子生殖胚囊的原始细胞； A．大孢子母细胞及在珠心中一个无孢子生殖胚囊的原始细胞； B．在大孢子母细胞之下的一个发育的原始细胞；C．大孢子母细 胞在分裂，6个原始细胞；D．大孢子母细胞退化，6个原始细胞

  18. Semigamy 图13—9 齿叶金光菊的半受精 A．卵内含有一雄核，胚乳核在分裂；B．卵内雄核和雌核在分裂；C．二细胞原胚，基细胞内的2个小核是由精子核分裂而来的；D．更后时期的胚，由精核衍生的核是小的

  19. 3. Polyembryony

  20. Polyembryony: Production of two or more embryos within an ovule.

  21. Two types： Simple polyembryony：are produced from one embryo sacs. Multiple polyembryony ：are produced from two or more embryo sacs in the same ovule. Cause: Fusion or division of two or more nucelli; The formation of several embryo sacs.

  22. Polyembryony Multiple Simple Sexual Asexual Gametophytic Sporophytic (adventive) Zygotic 2n Synergid n or 2n Diploid 2n Egg, synergid (unreduced gametophyte) Haploid n Egg, synergid (reduced gametophyte) Nucellar 2n (with or without interpolation of aposporous gametophyte phase) Integumentary

  23. 3.1 Zygotic and Suspensor Polyembryony The development of supernumerary embryos results from the cleavage of the apical cells of the embryogenic mass of cells produced by the zygote.

  24. The twn2 mutant of Arabidopsis exhibits a defect in early embryogenesis where, following one or two divisions of the zygote, the decendents of the apical cell arrest. The basal cells that normally give rise to the suspensor proliferate abnormally, giving rise to multiple embryos cell and its decendents during early embryo development.

  25. Wild-type embryo development. (A) Two cell stage. (B) Octant-dermatogen stage. (C) Early globular stage. (D) Mid-heart stage. (E) Early torpedo stage. (F) Late torpedo stage. ac, Apical cell; bc, basal cell; ec, embryonic cells; bd, derivatives of basal cell; ep, embryo proper; s, suspensor; co, cotyledon primordia or cotyledon; dh, derivatives of hypophysis; hy, hypocotyl.

  26. twn2 embryo development. (A) Two cell stage. (B) The apical cell appears to have arrested and the proximal basal cells have begun to swell. (C) Apical cells are arrested at the two to four cell stage and basal cells have begun to proliferate with out-of-file divisions. (D) Apical cell arrested and three putative embryonic cell masses have formed from proliferation of basal cells. (E) Late torpedo stage embryo showing persistence of arrested apical cells. (F) Malformed early torpedo stage duplicated embryos. ac*, Arrested apical cell; e*, ectopic embryos.

  27. Wild-type and twn2 shoot apical meristems. (A) Wild type. (B) twn2. sm, Shoot apical meristem; acd, arrested apical cell derivatives.

  28. A high proportion of the seeds fail to develop viable embryos, and those that do, contain a high proportion of partially or completely duplicated embryos. The adult plants are smaller and less vigorous than the wild type and have a severely stunted root.

  29. Wild-type and twn2 seeds, seedlings, and adult plants. (A) Wild-type and twn2 seeds. (B-D) twn2 seedlings. (E) Wild-type and twn2 adult plants.

  30. The twn2-1 mutation, which is the only known allele, was caused by a T-DNA insertion in the 5 untranslated region of a putative valyl-tRNA synthetase gene, valRS. The insertion causes reduced transcription of the valRS gene in reproductive tissues and developing seeds but increased expression in leaves.

  31. (A) Schematic drawing of the region surrounding the T-DNA insert in the twn2 mutant and some of the clones described herein. The T-DNA insert is not shown to scale. Exons are represented by boxes. The nontranslated 5 region of the valRS gene is shown in black. The nontranslated 3 region of the decoy gene is crosshatched. The coding region of the -glucuronidase gene in constructs pGUS1 and pGUS2 are hatched. cDNA1 and cDNA2 represent two of the 5 nucleotide sequences obtained by 5 RACE of wild-type mRNA. cDNA3 an cDNA4 were obtained by 5 RACE of mRNA from leaves of the twn2 mutant. Bold sequences represent sequences that correspond to T-DNA. (B) -Glucuronidase constructs used in this study.

  32. TWN2 expression in wild-type and the twn2 mutant. (A) RNA blot probed with the 3.6 ApaI-SacI fragment from pVRS19. (B) Ethidium bromide-stained RNA gel. r, Root; l, leaf; f/e, flower and embryos.

  33. 3.2 Synergid Polyembryony When the synergid and egg cell are fertilized by two sperm cells of the same pollen tube, there is no possibility for the secondary nucleus to be fertilized. The embryos collapse in the absence of endosperm. Or the egg cell or one of the synergid are fertilized solely.

  34. 3.3 The Antipodal Cell Polyembryon

  35. 3.4 Nucellar and Integumentary Polyembryony– adventive embryony

More Related