CHAPTER 38 PLANT REPRODUCTION Sexual Reproduction & Biotechnology.
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Transcript of CHAPTER 38 PLANT REPRODUCTION Sexual Reproduction & Biotechnology.
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CHAPTER 38 PLANT REPRODUCTION
Sexual Reproduction & Biotechnology
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Floral Organs
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• Sepals and petals are nonreproductive organs.
• Sepals: enclose and protect the floral bud before it opens; usually green and more leaf-like in appearance.
• In many angiosperms, the petals are brightly colored to attract pollinators.
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Stamens: male reproductive organs
• Stalk: the filament
• Anther: pollen sacs.
- The pollen sacs produce pollen.
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Carpels: female reproductive organs• Ovary- base of the carpel
- Ovules
- Egg cell - Embryo Sac (female
gametophyte), i.e., seed
• Stigma- platform for pollen grain
• Style- slender neck, connects ovary and stigma
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• The stamens and carpels of flowers contain sporangia, within which the spores and then gametophytes develop.
• The male gametophytes are sperm-producing structures called pollen grains, which form within the pollen sacs of anthers.
• The female gametophytes are egg-producing structures called embryo sacs, which form within the ovules in ovaries.
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• Pollination begins the process by which the male and female gametophytes are brought together so that their gametes can unite.
• Pollination- when pollen released from anthers lands on a stigma.
• Each pollen grain produces a pollen tube, which grows down into the ovary via the style and discharges sperm into the embryo sac, fertilizing the egg.
• The zygote gives rise to an embryo.
• The ovule develops into a seed and the entire ovary develops into a fruit containing one or more seeds.
• Fruits disperse seeds away from the source plant where the seed germinates.
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Function of Flowers
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Classification of Flowers
• Complete Versus Incomplete Flowers
• Complete: possess sepals, petals, stamens, and carpels
• Incomplete: lack one or more of these components
• Perfect Versus Imperfect Flowers
• Perfect: possess both stamens and carpels
• Imperfect: possess either stamens (staminate) or carpels (carpelate), but not both
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Complete Flower
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Monoecious Versus Dioecious
• Monoecious: both staminate and carpellate flowers are found together on the same plant (e.g., corn).
• Dioecious: staminate flowers occur on separate plants from those that carry carpellate flowers (e.g., date palms).
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Monoecious
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Dioecious
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Angiosperm Life Cycle
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Important Things to Note About Angiosperm Life Cycles
• Mature pollen grains are entire haploid male gametophyte plants.
• Microsporangia in anthers produce microsporocytes that undergo meiosis and become haploid microspores.
• Each microspore undergoes mitosis to produce two-celled male gametophyte plants (pollen grains).
• One cell is the generative cell while the other is the tube cell.
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Important Things to Note About Angiosperm Life Cycles
• Entire mature female gametophyte plants spend their entire lives supported by the parent sporophyte.
• Megasporangia in ovules produce megasporocytes that each undergo meiosis and become four haploid megaspores.
• Only one of these four cells become functional megaspores, the remaining three degenerating.
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Important Things to Note About Angiosperm Life Cycles
• The haploid nucleus of the megaspore undergoes three mitotic divisions to produce a multinucleate cell with eight haploid nuclei.
• Cytokinesis divides these nuclei into seven cells: three antipodal cells, two synergids, one egg cell, and one binucleate central cell.
• Together these cells form the mature female gametophyte or embryo sac.
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Important Things to Note About Angiosperm Life Cycles
• Fertilization involves a double fertilization event.
• After attachment to the stigma, the haploid generative cell of a pollen grain undergoes mitosis to produce two sperm nuclei.
• The two sperm nuclei migrate down the pollen tube as it elongates through the style to the ovary containing the ovules.
• One sperm nucleus enters the egg cell; the other enters the binucleate central cell of the female gametophyte.
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Important Things to Note About Angiosperm Life Cycles
• The central cell is trinucleate for a while.
• Fusion of all three haploid nucleus yield one triploid nucleus.
• Mitosis of the triploid central cell produces the multinucleate triploid endosperm tissue.
• This endosperm tissue represents a source of stored organic energy to be used by the developing sporophyte embryo (derived from the zygote) and to be used during seed germination.
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• The development of angiosperm gametophytes involves meiosis and mitosis.
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• The male gametophyte begins its development within the sporangia (pollen sacs) of the anther.
• Within the sporangia are microsporocytes, each of which will from four haploid microspores through meiosis.
• Each microspore can eventually give rise to a haploid male gametophyte.
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• A microspore divides once by mitosis and produces a generative cell and a tube cell.
• The generative cell forms sperm.
• The tube cell, enclosing the generative cell, produces the pollen tube, which delivers sperm to the egg.
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Pollen Tubes
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Pollen Grains• This is a pollen grain, an immature male gametophyte.
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Barriers to Self-Fertilization• Stamens and carpels may mature at different times.
• Self-incompatibility- plant rejects its own pollen
• Plant design prevents an animal pollinator from transferring pollen from the anthers to the stigma of the same flower.
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The Genetic Basis for the Inhibition of Self-Fertilization
S-genes: self-incompatibility gene
• If a pollen grain and the carpel’s stigma have matching alleles at the S-locus, then the pollen grain fails to initiate or complete the formation of a pollen tube.
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Pollen Tube Formation and Double Fertilization
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Seed Development
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Release of Sugars from the Endosperm During Germination
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Fate of the Endosperm• Typical Monocot (e.g., corn)
• endosperm present in substantial quantities in mature seed.
• cotyledon absorbs nutrients from endosperm during seed germination.
• Typical Dicot (e.g, garden bean)
• endosperm completely absorbed into cotyledons during seed maturation.
• Other Dicots (e.g., castor bean)
• endosperm only partially absorbed by cotyledons during seed maturation.
• remainder of endosperm absorbed by cotyledons during germination.
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Seed Structure
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Relationship of the Flower to the Fruit
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• As the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and aids in their dispersal by wind or animals.
• Pollination triggers hormonal changes that cause the ovary to begin its transformation into a fruit.
• If a flower has not been pollinated, fruit usually does not develop, and the entire flower withers and falls away.
The ovary develops into a fruit adapted for seed dispersal
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Fruit Formation
• The ovary wall becomes the pericarp, the thickened wall of the fruit
• Other flower parts wither and are shed.
• However, in some angiosperms, other floral parts contribute to what we call a fruit.
Development of a pea fruit (pod)
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Functions of the Fruit
• Protection of the enclosed seed (e.g., pea pods).
• Facilitating dispersal.
• wings for wind dispersal (e.g., maple).
• hocks and barbs for attachment to animal fur or avian feathers (e.g., cocklebur).
• sweet, fleshy fruit encouraging ingestion and dispersal of seeds by animals (e.g., cherry).
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Fruits
QuickTime™ and a Cinepak decompressor are needed to see this picture.
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Types of Fruits
Simple Fruits
Aggregate Fruits
Multiple Fruits
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Seed Dormancy
• Function: allows seeds to germinate at the most optimal time.
• Length of dormancy
• Signals triggering the end of dormancy.
• occurrence of water
• period of cold temperature
• fire
• light
• scarification
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Germination of Bean
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Germination of a Pea
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Germination of Corn
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Genet Concept
Asexual and Sexual Reproduction in the Life
Histories of Plants
Asexual and Sexual Reproduction in the Life
Histories of Plants
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Types of Asexual Reproduction in Plants
• Vegetative Reproduction
• consequence of the existence of meristematic tissues and indeterminate growth in plants
• typically involves fragmentation
• Apomixis
• =production of seeds without fertilization
• diploid cell in ovule develops into embryo
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Asexual Propagation
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Asexual Propagation of Plants in Agriculture
• Shoot or stem cuttings generate roots.
• Cloning from single leaves.
• Potato eyes used to generate whole potato plants.
• Grafting.
• Plant tissue culture.
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Plant Tissue Culture: Cloning from Individual Cells
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Plant Tissue Culture: Plant biotechnologists have
adopted in vitro methods to create and clone novel plants varieties.
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Genetic Engineering Applications of Plant Tissue Culture
• Injecting foreign DNA into host cells
• Protoplast fusion
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A DNA Gun
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Protoplasts
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MonocultureRisks and Benefits
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Humans as Genetic Engineers
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Some Definitions Related to Plant Development
development
• the sum of all of the changes that progressively elaborate an organism’s body; involves growth, morphogenesis, and cellular differentiation
growth
• an irreversible increase in size resulting from increases in cell number and size
morphogenesis
• the development of form
cellular differentiation
• the specialization of cells into different types with different functions
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Plant and Animal Development
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Lifelong Morphogenesis
• Indeterminant growth in plants means that morphogenesis is a continuous, never-ending process.
• Plant morphogenesis involves oriented cell division and growth but not the migration of cells to different parts of the plant body.
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Role of the Cytoskeleton in the Orientation of Cell Division
• Ring of microtubles (preprophase band) in the cortex of the cell determines the division plane.
• Preprophase band of microtubules disappears, leaving an imprint of actin microfilaments.
• hold nucleus in place until spindle apparatus forms.
• directs the movements of cell plate vesicles.
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Orientation of Mitosis
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Cell Growth Depends upon the Orientation of Cellulose Microfibrils in the Cell Wall
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Hypothetical Mechanism for the Orientation of Cellulose Microfibrils
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Cellular Differentiation in Plants
• Involves changes in gene expression, not in the genomic information of the cells.
• Pattern Formation.
• development of specific structures in specific locations
• depends upon positional information of the cells
• also related to positional consequences of cell division and elongation
• Clonal analysis.
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Genetic Basis for Pattern Formation in Flower Development
Genetic Basis for Pattern
Formation in Flower
Development
Genetic Basis for Pattern
Formation in Flower
Development