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Angiosperm Reproduction and
BiotechnologyCh. 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
Flowers, Double Fertilization, Flowers, Double Fertilization, and Fruits…Unique to and Fruits…Unique to Angiosperm Life CycleAngiosperm 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
Angiosperm - Alternation of Angiosperm - Alternation of GenerationsGenerations
Sporophyte• produces haploid spores by meiosis in sporangiaSpores undergo mitosis• develop into a multicellular male or female
gametophyteGametophytes produce gametes• by mitosis• pollen or eggs
Gametes fuse• zygote forms and develops into a multicellular
sporophyteSporophyte is dominant in the life cycle of the
angiosperm
Flower Structure and FunctionSepals
• bottom whorl; protects developing petals
• Calyx – collection of sepalsPetals• top whorl; important in
pollination• Corolla – collection of
petalsStamens• anther + filamentCarpels• stigma + style + ovary• Ovules within ovaries; #
dependent on species
Variations of Basic Flower Structure
Complete flower• sepals, petals,
stamens, carpelsIncomplete flower• missing 1 or more
complete flower parts
Inflorescences• Showy clusters of
flowers
Variations of Basic Flower Structure
Perfect flower• both stamens and carpels
present• may also be incomplete if
missing petals or sepalsImperfect 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
Development of Male Gametophytes in Pollen GrainsAnther
• 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 cellTube 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
Development of Female Gametophytes Embryo Sacs
Megasporangium• Site of female gametophyte
development• Is surrounded by integuments except
at the micropyleMegasporocyte• Enlarges and undergoes meiosis
producing 4 haploid megaspores• One megaspore survives; others dieMegaspore• Divides 3 times by mitosis to form
the embryo sacEmbryo sac• 3 antipodal cells, 2 polar nuclei, 1
egg, 2 synergids
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
Pollination
Double fertilization• union of 2 sperm cells with 2 cells within the
embryo sac• gives rise to endosperm (sperm + 2 polar
nuclei)
Pollination1. Pollen grain germinates and pollen tube grows
down the style2. Tube discharges two sperm into the embryo sac3. One sperm fertilizes the egg zygote; other sperm
combines with 2 polar nuclei triploid endosperm
Coevolution of Flower and Pollinator
Coevolution
• Joint evolution of two interacting species in response to selection imposed by the other
Seed Development, Form, and FunctionEndosperm Development
• Develops prior to embryo• Multinucleate “supercell” with a
milky consistency• Stores nutrients that can be used
by the seedling after germinationEmbryo Development• First mitotic division forms the
basal cell and terminal cell• Terminal cell suspensor• Basal cell proembryo• Cotyledons begin to appear
Structure of a Mature Eudicot Seed
Embryo is quiescent until germination• dehydrates; embryo surrounded by endosperm; seed coat formed• Enters dormancyHypocotyl• embryonic axis below the cotyledon(s)Radicle• end of the hypocotyl• embryonic rootEpicotyl• embryonic axis above the cotyledon(s)Plumule• end of the epicotyl• shoot tip with a tiny pair of leaves
Structure of a Mature Monocot Seed
Scutellum• Specialized cotyledon in
maize and wheat• Large SA and pressed
against the endospermColeoptile• Encloses the young shoot in
a grass seed• Aid in soil penetrationColeorhiza• Encloses the young root in a
grass seed• Aid in soil penetration
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
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
Fruit Form and FunctionFertilization necessary for fruit to form
True fruit = ripened ovary• fruit develops from the ovary• ovary wall becomes the pericarp• seed develops from the ovuleDry fruits• fruit ages and pods open to release seedsFleshy fruits• Ripens through hormonal changes• Fruit becomes sweeter and color change
Types of FruitsAggregate fruits• from a single flower
w/ separate carpels• Strawberries,
raspberry, blackberry
Types of Fruits
Multiple fruits• from separate
tightly clustered flowers
• PineappleAccessory fruit• Other floral parts
contribute to the fruit
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
Mechanisms of Asexual Reproduction
Fragmentation• Separation of parent plant into
parts that reform new whole plants• Kelanchoe, aspen treeApomixis• Production of seeds without
meiosis and fertilization• Diploid cell in the ovule gives rise
to the embryo• Dandelions
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
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 timesStructural arrangement• anthers are below the
stigma
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
Vegetative Propagation and Agriculture
Test tube cloning• Transgenic
genetically modified organisms
Protoplast fusion• Protoplasts lack cell
walls
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
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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