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SYNGAMY zygote SporophyteGametophyte sporangium sporocyte spores gametangia gametes germination mitosis differentiation mitosis germination mitosis 1N 2N differentiation MEIOSIS Life Cycle of Flowering Plants The flowering plant is a multicellular diploid sporophyte. The sporophyte encloses the multicellular haploid gametophyte. The life history is thus diplohaplontic. The gametes are oogamous but the sperm lack flagellae. Gender expression has moved from gametophyte to sporophyte. Compare Fig Pg. 824

androecium petal corolla calyx gynoecium stigma style ovary ovule locule filament anther sepal pedicel receptacle carpel stamen complete perianth flower perfect superior flower hypogynous pollen Flower Organization- building a flower from the bottom up! A flower is a short shoot (stem with leaves) The stem is the receptacle with very short internodes The leaves appear in four whorls Compare Fig. 41.4a Pg. 826

Microsporogenesis: Prophase I of Meiosis

Microsporogenesis: Late Prophase I of Meiosis Synapsis: homologs join Recombination: crossing over

Microsporogenesis: Metaphase I of Meiosis

Microsporogenesis: Anaphase I of Meiosis Centromeres do not breakdown Homologs are separated: not sister chromatids

Microsporogenesis: Telophase I of Meiosis Already haploid but sister chromatids still joined

Microsporogenesis: Metaphase II and Anaphase II of Meiosis

Microsporogenesis: Telophase II of Meiosis

Microsporogenesis: Meiosis complete (but prophase of mitosis)

Microsporogenesis: Completed, Separated Microspores (note prophase)

Pollen Grain: Mitosis Makes Endosporic Microgametophyte Tube Cell Nucleus Cytoplasm Generative Cell Nucleus Cytoplasm The tube cell digests a path from the stigma to the egg. The generative cell follows the path to the egg, and divides to make two sperm cells. Both participate in syngamy. Pollination: vector- assisted movement of the pollen grain from the anther to the stigma. Pollen Wall: Microspore Wall (allergenic?) Compare Fig Pg. 829

Pollen Tube Growth The tube cell germinates through the pollen wall. The cell grows chemotropically toward the egg. The pollen tube must find the ovule’s micropyle. The generative cell slides along this tube. It divides by mitosis to form two sperm cells.

SYNGAMY zygote SporophyteGametophyte sporangium sporocyte spores gametangia gametes germination mitosis differentiation mitosis germination mitosis 1N 2N differentiation MEIOSIS Life Cycle of Flowering Plants The large plant is a sporophyte. Its flower produces the sporangia; on the male side, the anther of the stamen The anther contains sporocytes that divide by meiosis to make spores The spore cell divides to make an endosporic microgametophyte… a pollen grain The tube cell digests a path to the egg The generative cell divides into two sperm cells that participate in syngamy anther microspore pollen grain sperm cells tube cell generative cell

androecium filament anther stamen flower perfect flower hypogynous pollen petal corolla calyx sepal pedicel receptacle complete perianth gynoecium stigma style ovary ovule locule carpel superior Flower Organization Compare Fig. 41.4a Pg. 826 Now we focus on what is happening on the female side… We will examine what is going on inside the ovule of the carpel.

Alstroemeria: What is different two weeks later? protandrous: first-male protogynous: first-female (antonym) Bisexual …but functionally unisexual …by being trans-sexual

Megasporogenesis: taking place inside the ovule inside the ovary. megasporocyte meiosis I meiosis II 4 megaspores 3 disintegrate functional megaspore mitotic divisions without cytokinesis cytokinesis megagametophyte egg central cell 3 antipodals 2 synergids Compare Fig Pg. 828 and Fig Pg. 832

SYNGAMY zygote SporophyteGametophyte sporangium sporocyte spores gametangia gametes germination mitosis differentiation mitosis germination mitosis 1N 2N differentiation MEIOSIS Life Cycle of Flowering Plants The large plant is a sporophyte. Its flower produces the sporangia; on the female side, the ovule of the carpel The ovule contains a megasporocyte that divides by meiosis to make four megaspores Three megaspores disintegrate. The remaining megaspore cell divides by mitosis to make 8 nuclei. Cytokinesis divides the 8 nuclei into seven cells of the megagametophyte (embryo sac) The egg cell and the central cell are gametes that fuse with two sperm cells in syngamy The ovule, with zygotic embryo and triploid endosperm, becomes a seed. embryo sac ovule megasporocyte antipodals synergids central cell egg

130/Diversity/Angiosperms/Fertilization.jpg 1N egg + 1N sperm = 2N zygote syngamy#1: syngamy#2: 2 x 1N polar nuclei + 1N sperm = 3N primary endosperm cell In Flowering Plants, syngamy is a double event: sperm nuclei synergids disintegrating In this slide, plasmogamy has already occurred…but what part of syngamy has not occurred yet? karyogamy! no miracle-grow, no compost! Compare Fig Pg. 832