Megasporogenesis: taking place inside the ovule inside the ovary. megasporocyte 4 megaspores meiosis I meiosis II 3 disintegrate functional megaspore mitotic divisions without cytokinesis megagametophyte 3 antipodals central cell egg cytokinesis 2 synergids Compare Fig. 41.7 Pg. 828 and Fig. 41.11 Pg. 832

Life Cycle of Flowering Plants http://www.bakerlite.co.uk/pics/Wales/South%20Wales/Vale/Trees/Tree-8.jpg central cell egg SYNGAMY zygote Sporophyte Gametophyte sporangium sporocyte spores gametangia gametes germination mitosis differentiation 1N 2N MEIOSIS embryo sac ovule antipodals synergids megasporocyte 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.

karyogamy! In Flowering Plants, syngamy is a double event: syngamy#2: Compare Fig. 41.11 Pg. 832 In Flowering Plants, syngamy is a double event: syngamy#2: 2 x 1N polar nuclei + 1N sperm = 3N primary endosperm cell sperm nuclei no miracle-grow, no compost! 1N egg + 1N sperm = 2N zygote syngamy#1: synergids disintegrating In this slide, plasmogamy has already occurred…but what part of syngamy has not occurred yet? karyogamy! http://botit.botany.wisc.edu/courses/img/Botany_130/Diversity/Angiosperms/Fertilization.jpg

How about Dicots? seed coat cells Cells to become storage tissue Polar Nuclei Sperm Nucleus Syngamy => Endosperm 3N Egg Cell Sperm Nucleus Egg Nucleus Syngamy => Zygote 2N

These are globular embryos with suspensors. suspensor cells In Dicots (Capsella), the development lacks competition, but the sequence is similar. These are globular embryos with suspensors. Compare Fig. 41.12 Pg. 833 Compare Fig. 23.5 Pg. 471

Heart-shaped embryo with suspensor Protoderm Ground   meristem Undeveloped? Provascular Heart-shaped embryo with suspensor Compare Fig. 41.12 Pg. 833

Maturing embryo “torpedo” Mature      embryo Maturing embryo “torpedo” Compare Fig. 41.12 Pg. 833

Capsella Seed: Embryo Seed Coat Shoot Apex Endosperm Cotyledons - eudicot Hypocotyl Radicle Root Apex Micropyle

radicle penetrates seed coat Lettuce Seed Germination radicle penetrates seed coat starch hydrolysis Seed Coat shoot apex sugar -amylase cotyledons dicot translation Compare Fig. 40.1 Pg. 801 RNA growth red and white light stimulate germination transcription Embryo DNA radicle apex phytochrome photoreversibility 660 nm Pfr Pr water photoactivation 730 nm imbibition dark