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 sporic (diplohaplontic). The gametes are oogamous but the sperm lack flagellae. Gender expression has moved from gametophyte to sporophyte.
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 bottom up A flower is a short shoot (stem with leaves) The stem is represented by the receptacle with very short internodes The leaves appear in four whorls
Microsporogenesis: Prophase I of Meiosis
Microsporogenesis: Late Prophase I of Meiosis
Microsporogenesis: Metaphase I of Meiosis
Microsporogenesis: Anaphase I of Meiosis
Microsporogenesis: Telophase I of Meiosis
Microsporogenesis: Metaphase II and Anaphase II of Meiosis
Microsporogenesis: Telophase II of Meiosis
Microsporogenesis: Meiosis complete (but prophase of mitosis)
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?)
Pollen Tube Growth The tube cell germinates through the pollen wall. The cell grows chemotropically toward the egg. The pollen tube must find the ovules micropyle. The generative cell slides along this tube. It divides by mitosis to form two sperm cells.
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
30/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-gro, no compost!