CHAPTER 38 PLANT REPRODUCTION. Sexual Reproduction & Biotechnology. Floral Organs. Sepals and petals are nonreproductive organs. Sepals : enclose and protect the floral bud before it opens; usually green and more leaf-like in appearance.
Sexual Reproduction & Biotechnology
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.
Ovary- base of the carpel
Embryo Sac (female gametophyte), i.e., seed
Stigma- platform for pollen grain
Style- slender neck, connects ovary and stigma
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.
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.
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 bothClassification of Flowers
Dioecious: staminate flowers occur on separate plants from those that carry carpellate flowers (e.g., date palms).Monoecious Versus Dioecious
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.Important Things to Note About Angiosperm Life Cycles
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.Important Things to Note About Angiosperm Life Cycles
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.Important Things to Note About Angiosperm Life Cycles
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.Important Things to Note About Angiosperm Life Cycles
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.Important Things to Note About Angiosperm Life Cycles
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.
The generative cell forms sperm.
The tube cell, enclosing the generative cell, produces the pollen tube, which delivers sperm to the egg.
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.Fate of the Endosperm
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
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)
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).Functions of the Fruit
Length of dormancy
Signals triggering the end of dormancy.
occurrence of water
period of cold temperature
Asexual and Sexual Reproduction in the Life Histories of Plants
the sum of all of the changes that progressively elaborate an organism’s body; involves growth, morphogenesis, and cellular differentiation
an irreversible increase in size resulting from increases in cell number and size
the development of form
the specialization of cells into different types with different functionsSome Definitions Related to Plant Development
Plant morphogenesis involves oriented cell division and growth but not the migration of cells to different parts of the plant body.Lifelong Morphogenesis
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.Role of the Cytoskeleton in the Orientation of Cell Division
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.Cellular Differentiation in Plants
Genetic Basis for Pattern Formation in Flower Development