Ch. 38: Plant Reproduction and

Biotechnology

Review: Alternation of generations in moss

Sporophyte (2n):produces haploidspores which divide by mitosisto form plants called gametophytes.

Gametophyte (n):Produces gameteswhich fertilize toform a sporophyte

I. Sexual Reproduction in plants:A. Alternation of generations in angiosperms:

B.Flowers are specialized shoots bearing reproductive organs of the angiospermsporophyte.

1.Stamen = male Carpel = female2.Pollen grain = sperm producing male gameto- phytes3.Embryo sac = egg producing female gameto- phytes

4.Complete flowers: all four organs(sepal, petals, stamen, and carpel)

5.Incomplete flowers: loacking one or moreof the floral parts (ex. Grasses lack petals)

6.Bisexual flower: possesses both stamenand carpel.

7.Unisexual flower: possesses one one sexual part-Monoecious: stamen and carpel are on the same plant but on different flowers.-Dioecious: stamen and carpel are found on different plants.

Corn: Monoecious Sagittaria: Dioecious

C.Development of the male gametophyte:1.Microsporocyte (in pollen sac of anther)

undergoes meiosis, formingfour haploid cells calledmicrospores.

2.Microspores divide once bymitosis and produces twocells, one a generative cell,the other a tube cell.a.Generative Spermb.Tube cell enclose the

generative cell and produce the pollen tube(for sperm delivery)

c.The two-celled structureis enclosed in a thickwall that has an elaborate pattern.

Pollen grainPollen becomes a mature male gametophyte when the generative cell divides to form two sperm.

D.Development of female gametophyte:1.Megasporocyte divides by meiosis to form four haploid cells.2.Only 1 survives to form the megaspore.3.Megaspore undergoes mitosis 3 times, forming one large cell with 8 haploid nuclei.4.The 8 haploid cells are enclosed in the embryo sac. 5.The 8 haploid cells become 4 types of cells: Antipodal, polar, egg, and synergids.

-Antipodal: unknown function-Synergids: flank the egg cell and assist in attracting and guiding the pollen tube.-Polar: in cytoplasm; fuses with sperm to form endosperm-Egg: fuses with sperm

E.Plants can prevent self-fertilization by:1.Dioecious plants2.Bisexual plants can have carpel and stamen

maturing at different times3.Self-incompatibility: plant rejects its own

pollen and the pollen of closely related plants.

If a pollen contains an S1 allele that matches the S1 allele in the stigma, the pollen grain will not form a pollen tube No fertilization.

S genes code for a receptor protein (R) in the ECM of the stigma. Another product of the Sgenes are protein kinases (K) embedded in the plasma membrane. Similar or same S genes self-incompatibility

F.Double fertilization gives rise to the zygoteand endosperm.

Double fertilization = 1.One sperm fuses with egg (2n) 2.Another sperm fuses with polar cells to form the endosperm (3n)

G.After fertilization, the ovule develops into a seed and the ovary develops into a fruit enclosing the seed(s).

1.Endosperm develops from the triploid nucleus, forming a milky liquid mass. Theendosperm provides nutrients for the developing embryo and germinating seed.

2.Embryo development: -Transverse split: Terminal and basal Terminal becomes most of the embryo See p. 791, fig. 38.10 for details

H.Structure of the mature seed:1.Seed coat: protective2.Hypocotyl: point

where cotyledonsattach.

3.Radicle: where thehypocotyl terminates;the embryonic root.

4.Epicotyl: shoot tipMonocots: Single cotyledon called scutellumColeorhiza: covers young rootColeoptile: covers young shoot

I. Ovary develops into fruit:1.Fruit: protects the seeds and aids in their

dispersal by wind or animals.2.Pollination triggers hormonal changes that

causes the ovary to begin its transformationinto a fruit. no pollination, no fruit Exceptions: Parthenocarpy (seedless) 3.Pericarp: thickening wall of the fruit

J. Evolutionary adaptations of seed germinationcontribute to seedling survival.

1.Seeds mature and then enter dormancy;low metabolic rate and suspension of growthand development. Seeds germinate when conditions are

favorable. Seed dormancy increases the chances of seedling survival by germinating only when conditions are favorable. Favorable cues = water, light, animal’s digestive tract

2.Germination from seed to seedling dependson “imbibition,” the uptake of water. Imbibing causes the seed to expand and

rupture its coat and also triggersmetabolic changes in the embryo thatenable it to resume growth.

3.Enzymes begin digesting the storage materials in the endosperm and cotyledonsand transfer the nutrients to the embryo.

4.First to emerge from seed is the radicle.5.Next, the shoot.6.The hypocotyl, stimulated by light,

straightens, raising the cotyledons and epicotyl.

-Imbibing causes GA (Gibberellins) to be released.-Enzymes from aleurone are released.-Enzymes hydrolyze the food storage for embryo.-Light must be available for leaves to green and plant to develop.

II. Asexual Reproduction in plants:A. Cloning: “vegetative reproduction”

-Meristematic tissue = undifferentiated cells-Parenchyma cells can divide and differentiate into specialized cells-Fragmentation: tissue from parent plant can develop into a new plant-Apomixis: Formation of seeds without flowers being fertilized. A diploid cell within the ovule matures into seeds.

B.Some plants can reproduce both asexuallyand sexually.1.Advantage of sexual: variety for success, seed dispersal and seed dormancy2.Advantage of asexual: clone rapidly, offspring are mature fragments, not frail.

C.Vegetative propagation is used extensivelyin crop, orchard, and ornamental plantfarming. Cutting of shoots/stems Grafting: stock is the plant that provides

root system; scion is the twig that is grafted in.

III.Plant Biotechnology in use of plants and theirproducts and how humans have altered plantsto suit their purposes.A.History: Neolithic (stone age) humans

artificially selected for the best corn (maize).

B.Pig farmers feed pigs with opaque-2 maize,a type of corn that is more nutritious.

C.Transgenic plants: Plants that contain genesfrom a plant of a different species.1.Disease resistant genes2.Pest resistant genes

D.Plant biotechnology has caused great public debate:1.Unknown health risks associated with genetically modified foods.2.Possible damage to other organisms that rely on foods not previously modified.3.Potential for a genetically modified crop to hybridize with a weed, producing a “superweed.”