Chapter 38. Plant Reproduction 1
Animal vs. Plant life cycle Animal multicellular 2n Plant multicellular sporophyte 2n gametes 1n spores 1n unicellular gametes 1n multicellular gametophyte 1n 2
Alternation of generations diploid haploid 3
Angiosperm life cycle male gametophyte (pollen) female gametophyte (embryo sac in ovary) new sporophyte in seed 4
Flowers 5
Idealized flower Modified shoot with 4 rings of modified leaves u sepals u petals u stamens male u carpels female pistil carpel 6
Flower model these structures evolved from modified leaves sepals petals stamens carpels eggs pollen 7
Male & female parts of flower pollen = male gametophyte (1n) pollen nuclei are sperm embryo sac = female gametophyte (1n) 8
Male & female parts of flower 9
Parts of flower Male u stamens = male reproductive organs u stamens have stalks (filament) & terminal anthers which carry pollen sacs u pollen sacs produce pollen u pollen grain male gametophyte sperm-producing structure u sperm 10
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Pollen male gametophyte u how is this similar to or different from a spore? u what is the adaptive advantage of pollen? 12
Parts of flower Female u carpels = female reproductive organs u tip = stigma u slender neck = style u base = ovary u in ovary = 1 or more ovules u in ovules = embryo sacs u embryo sac female gametophyte egg-producing structure u eggs 13
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male female 15
Fertilization Pollination u pollen released from anthers carried by wind/animals to stigma u pollen grain produces pollen tube pollen tube grows down style into ovary discharges 2 sperm into embryo sac u double fertilization 1 sperm fertilizes egg = 2n zygote zygote develops into embryo (new plant) 1 sperm fertilizes polar nuclei = 3n endosperm u ovule develops into seed u ovary develops into fruit containing 1 or more seeds 16
Double fertilization in flowering plants 2 sperm from pollen u 1 sperm fertilizes egg = 2n zygote u 1 sperm fuses with 2 polar nuclei = 3n endosperm u endosperm = food tissue in seed coconut milk grains What is adaptive advantage of double fertilization? 17
Pollen tube growth grow down style to ovule path for sperm nuclei 1. pollen grain 2. pollen nucleus 3. pollen tube 4. pollen nucleus 18
Preventing self-pollination Various mechanisms stamens & carpels may mature at different times arranged so that animal pollinator won t transfer pollen from anthers to stigma of same flower biochemical self-incompatibility = block pollen tube growth 19
Preventing self-fertilization This model involves the S allele u pollen (male) with same allele cannot germinate on stigma (female) matching alleles interact & inhibit RNA production 20
Biochemical mechanism Preventing self-fertilization u pollen produces signal Æ receptor Æ kinase Æ signal transduction path Æ effector protein produced Æ block pollen tube growth 21
Fertilization in flowering plants Development of the new sporophyte u zygote Æ embryo Æ new seedling 22
Plant embryo seed coat endosperm cotyledons ovary wall embryo What supplies nutrients for embryo & new seedling growth? 23
Seed anatomy Sporophyte in seed u sets stage for structure of plant roots shoots leaves How does the dicot differ from the monocot? 24
Germination How does the dicot differ from the monocot? Dicot Monocot 25
Mobilization of nutrients Seed germination 1. seed imbibes water 2. gibberellin release signals aleurone layer 3. amylase is released which hydrolyzes starch 4. sugar is absorbed by embryo 26
Fruit Fruit is a mature ovary u seeds develop from ovules u wall of ovary thickens to form fruit u fruits protect dormant seeds & aid in their dispersal 27
Fruit Development pea (legume) 28
Fruit development peach (stone fruit or drupe) u 1 flower : 1 carpel : 1 ovary : 1 seed 29
Fruit development apple (pome fruit) u 1 flower : 5 carpels : many ovaries : many seeds 30
Fruit development Citrus fruit (berry!) u 1 flower : many carpels : many ovaries : many seeds 31
Fruit development Raspberry (aggregate fruit) u 1 flower : many ovaries : many seeds 32
Other fruits 33
Seed dispersal Plants produce enormous numbers of seeds to compensate for low survival rate u a lot of genetic variation for natural selection to screen 34