2 Life Cycle of Flowering Plants SYNGAMYzygoteSporophyteGametophytesporangiumsporocytesporesgametangiagametesgerminationmitosisdifferentiation1N2NMEIOSISThe 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.
3 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 internodesThe leaves appear in four whorlsstigma™carpelgynoeciumflowerperfectstyleloculeovaryanthersuperiorstamenpollenovulefilamentandroeciumflower hypogynouspetalcorollareceptaclesepalcompleteperianthcalyxpedicel
13 Pollen Grain: Mitosis Makes Endosporic Microgametophyte Pollen Wall: Microspore Wall (allergenic?)Tube CellNucleusCytoplasmGenerative CellNucleusCytoplasmThe 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.
14 The tube cell germinates through the pollen wall. Pollen Tube GrowthThe 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.
15 Megasporogenesis: taking place inside the ovule inside the ovary. megasporocyte4 megasporesmeiosis Imeiosis II3 disintegratefunctionalmegasporemitotic divisions without cytokinesis3 antipodalsmegagametophytecentral celleggcytokinesis2 synergids
16 karyogamy! In Flowering Plants, syngamy is a double event: syngamy#2: 2 x 1N polar nuclei + 1N sperm= 3N primary endosperm cellspermnucleino miracle-gro, no compost!1N egg + 1N sperm = 2N zygotesyngamy#1:synergidsdisintegratingIn this slide, plasmogamy has already occurred…but what part of syngamy has not occurred yet?karyogamy!