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CHAPTER 38 PLANT REPRODUCTION

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CHAPTER 38 PLANT REPRODUCTION. Angiosperm 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.

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CHAPTER 38 PLANT REPRODUCTION

Angiosperm Reproduction & Biotechnology

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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.

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

Classification of Flowers
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).

Monoecious Versus Dioecious
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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.

pollen grains
Pollen Grains
  • This is a pollen grain, an immature male gametophyte.
barriers to self fertilization
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.
the genetic basis for the inhibition of self fertilization
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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embryo

endosperm

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 before 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
the ovary develops into a fruit adapted for seed dispersal
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)

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).

Functions of the Fruit
fig 38 10

Fig. 38-10

Types of Fruits

Stigma

Style

Carpels

Petal

Stamen

Flower

Ovary

Stamen

Stamen

Sepal

Stigma

Ovary

(in receptacle)

Ovule

Ovule

Pea flower

Raspberry flower

Pineapple inflorescence

Apple flower

Each segment

develops

from the

carpel

of one

flower

Remains of

stamens and styles

Carpel

(fruitlet)

Sepals

Stigma

Seed

Ovary

Stamen

Seed

Receptacle

Pea fruit

Raspberry fruit

Pineapple fruit

Apple fruit

(a) Simple fruit

(b) Aggregate fruit

(c) Multiple fruit

(d) Accessory fruit

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

Seed Dormancy
asexual propagation of plants in agriculture
Shoot or stem cuttings generate roots.

Cloning from single leaves.

Potato eyes used to generate whole potato plants.

Plant tissue culture.

Grafting.

Asexual Propagation of Plants in Agriculture
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Plant Tissue Culture: Plant biotechnologists have adopted in vitro methods to create and clone novel plants varieties.
monoculture risks and benefits
MonocultureRisks and Benefits

Potato blight

Phytophthora infestans

Irish Potato Famine (1845)

fig 38 18

Fig. 38-18

Genetically modified rice

Ordinary rice

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Make plants disease resistant

Use less pesticides and herbicides

Create plants that are more nutritious

Improve crop yields

Drought resistance

Medicine

Bioengineering

Latest plant developments

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Inadvertent consequences: allergies (nuts)

Ethics: patents and ownership of genes

Herbicide tolerance- fear of producing a herbicide resistant weed that could get out of control

Loss of biodiversity

Food safety

Cutting choices for vegetarians

Cross pollination with human food crops

Bioengineering Plants

Risks

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