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Angiosperm Reproduction and Biotechnology Ch. 38
Orchid deception… Male wasps attempt to mate with flower b/c of its color and scent that is similar to a female wasp… all to transfer pollen
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Flowers, Double Fertilization, and Fruits…Unique to Angiosperm Life Cycle
Sporophyte and gametophyte generations alternate in the life cycle of plants Multicellular haploid gametophyte generations alternate with diploid sporophyte generation Male and female gametophytes develop within anthers and ovaries, respectively
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Angiosperm - Alternation of Generations
Sporophyte produces haploid spores by meiosis in sporangia Spores undergo mitosis develop into a multicellular male or female gametophyte Gametophytes produce gametes by mitosis pollen or eggs Gametes fuse zygote forms and develops into a multicellular sporophyte Sporophyte is dominant in the life cycle of the angiosperm
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Flower Structure and Function
Sepals bottom whorl; protects developing petals Calyx – collection of sepals Petals top whorl; important in pollination Corolla – collection of petals Stamens anther + filament Carpels stigma + style + ovary Ovules within ovaries; # dependent on species
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Variations of Basic Flower Structure
Complete flower sepals, petals, stamens, carpels Incomplete flower missing 1 or more complete flower parts Inflorescences Showy clusters of flowers
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Variations of Basic Flower Structure
Perfect flower both stamens and carpels present may also be incomplete if missing petals or sepals Imperfect flower staminate or carpellate unisex Monoecious Flowers are either male or female but on the same plant Dioecious Male and female flowers are on separate plants
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Development of Male Gametophytes in Pollen Grains
Anther Contains 4 microsporangia (pollen sacs) Contain microspore mother cells that undergo meiosis producing 4 microspores Each microspore gives rise to a male gametophyte by mitosis Generative cell and tube cell Pollen Grain Spore, generative cell and tube cell Tube cell Produces pollen tube which can grow very quickly to deliver the sperm cells to the female gametophyte Generative cell Divides producing 2 sperm cells
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Development of Female Gametophytes Embryo Sacs
Megasporangium Site of female gametophyte development Is surrounded by integuments except at the micropyle Megasporocyte Enlarges and undergoes meiosis producing 4 haploid megaspores One megaspore survives; others die Megaspore Divides 3 times by mitosis to form the embryo sac Embryo sac 3 antipodal cells, 2 polar nuclei, 1 egg, 2 synergids
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Pollination
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Pollination Placement of pollen from the anther onto the stigma of a carpel Wind, water, animals Bees, moths, butterflies, flies, bats, birds Self or cross pollinate
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Pollination Double fertilization
union of 2 sperm cells with 2 cells within the embryo sac gives rise to endosperm (sperm + 2 polar nuclei)
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Pollination Pollen grain germinates and pollen tube grows down the style Tube discharges two sperm into the embryo sac One sperm fertilizes the egg zygote; other sperm combines with 2 polar nuclei triploid endosperm
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Coevolution of Flower and Pollinator
Joint evolution of two interacting species in response to selection imposed by the other
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Seed Development, Form, and Function
Endosperm Development Develops prior to embryo Multinucleate “supercell” with a milky consistency Stores nutrients that can be used by the seedling after germination Embryo Development First mitotic division forms the basal cell and terminal cell Terminal cell suspensor Basal cell proembryo Cotyledons begin to appear
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Structure of a Mature Eudicot Seed
Embryo is quiescent until germination dehydrates; embryo surrounded by endosperm; seed coat formed Enters dormancy Hypocotyl embryonic axis below the cotyledon(s) Radicle end of the hypocotyl embryonic root Epicotyl embryonic axis above the cotyledon(s) Plumule end of the epicotyl shoot tip with a tiny pair of leaves
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Seed
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Structure of a Mature Monocot Seed
Scutellum Specialized cotyledon in maize and wheat Large SA and pressed against the endosperm Coleoptile Encloses the young shoot in a grass seed Aid in soil penetration Coleorhiza Encloses the young root in a grass seed
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Seed Dormancy: An Adaptation for Hard Times
Prevents germination during unfavorable conditions Increases chance that germination will occur at a time and place most advantageous to the survival of the seedling
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Seed Germination and Seedling Development
Imbibition First step in germination Uptake of water due to low water potential Radicle emerges Shoot tip breaks through soil Hypocotyl straightens Cotyledons and epicotyl raised Epicotyl spreads first leaves Photosynthesis begins Cotyledons shrivel and fall off
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Germination
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Germination
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Germination
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Fruit Form and Function
Fertilization necessary for fruit to form True fruit = ripened ovary fruit develops from the ovary ovary wall becomes the pericarp seed develops from the ovule Dry fruits fruit ages and pods open to release seeds Fleshy fruits Ripens through hormonal changes Fruit becomes sweeter and color change
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Types of Fruits derived from a single ovary cherries, soybeans
Simple fruits derived from a single ovary cherries, soybeans
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Types of Fruits Aggregate fruits
from a single flower w/ separate carpels Strawberries, raspberry, blackberry
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Types of Fruits Multiple fruits
from separate tightly clustered flowers Pineapple Accessory fruit Other floral parts contribute to the fruit
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Fruit and Seed Dispersal
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Mechanisms of Asexual Reproduction
Production of offspring from a single parent Occurs without genetic recombination resulting in a clone Extension of indeterminate growth 2 major natural mechanisms fragmentation apomixis
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Mechanisms of Asexual Reproduction
Fragmentation Separation of parent plant into parts that reform new whole plants Kelanchoe, aspen tree Apomixis Production of seeds without meiosis and fertilization Diploid cell in the ovule gives rise to the embryo Dandelions
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Advantages and Disadvantages of Asexual vs. Sexual Reproduction
Asexual advantages No need for a pollinator Pass on entire genome to it progeny Stronger seedlings Vegetative reproduction offspring arise from mature vegetative fragments Sexual advantages Genetic variation Seeds allow for great dispersal Seed dormancy
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Mechanisms that Prevent Self Pollination
Dioecious plants can’t self pollinate Self-incompatibility rejection of pollen from the same or closely related plant by the stigma (biochemical block) Maturity stamens and carpels mature at different times Structural arrangement anthers are below the stigma
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Vegetative Propagation and Agriculture
Clones from cuttings Callus forms, adventitious roots develop from the callus Grafting Two different species that share each others benefits Use root stock to grow another species Stock plant that provides the roots Scion twig that is grafted onto the stock
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Vegetative Propagation and Agriculture
Test tube cloning Transgenic genetically modified organisms Protoplast fusion Protoplasts lack cell walls
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Humans Modify Crops by Breeding and Genetic Engineering
Plant Breeding Artificial selection Plant Biotechnology Innovations in the use of plants to make products of use to humans Reducing world hunger and malnutrition bt gene Golden Rice Reducing Fossil Fuel Dependency biofuels
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Debate Over Plant Biotechnology
Issues of human health Inadvertent transfer of allergens to food crops Possible effects on nontarget organisms Monarch butterfly caterpillars and pollen from transgenic bt maize Addressing the problem of transgene escape Genes escaping into weeds through crop to weed hybridization
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