Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Plant Reproduction Chapter 42 Copyright © McGraw-Hill Companies Permission

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Plant Reproduction

Chapter 42

Copyright © McGraw-Hill Companies Permission required for reproduction or display


Rise of the Flowering Plants

• Virtually all our food is derived, directly or indirectly, from flowering plants. Also sources of

medicine, clothing, and building materials.

• Much of early angiosperm evolution may have taken place in patches of drier or unfavorable habitat in the interior of Gondwanaland. Outcrossing may have

been important in early success.


Evolution of the Flower

• Pollen matures within the anthers and is transported to the stigma of another flower.

When pollen reaches the stigma, it germinates, and a pollen tube grows down, carrying sperm nuclei to the embryo sac.

- Seed matures within ripening fruit.



• Characteristics A complete flower has four

whorls, while an incomplete flower lacks at least one.

- Calyx, composed of sepals, makes up outermost whorl.

- Petals collectively make up the corolla.


Evolution of the Flower• Characteristics

Male part:

Stamens collectively compose androecium.

Stamens made up of filament and anther.

Female part:

Gynoecium refers to the collection of female parts in a flower.

Single or fused carpels also referred to as simple or compound pistils.

Ovules produced in pistil’s swollen ovary.

Style - Slender neck.

Stigma - Pollen-receptive structure.



• Trends in Floral Specialization Separate floral parts have fused. Floral Parts have been lost or reduced.

- Resultant of natural selection and artificial breeding.

• Trends in Floral Symmetry Many flowers of advanced groups are

bilaterally symmetrical.- Often associated with advanced

pollination systems.


Formation of Angiosperm Gametes

• Plant sexual life cycles are characterized by an alternation of generations. Diploid sporophyte gives rise to haploid

gametophyte generation.- Male gametophytes

(microgametophytes) - Pollen grains- Female gametophyte

(megagametophyte) - Embryo sac



• Angiosperms have separate structures for reproduction . Similar to animals, except:

Male and female structures usually occur together in the same individual flower.

Angiosperm reproductive structures are not permanent parts of the adult individual.



• Pollen Formation Each pollen sac contains specialized chambers enclosing

microspore mother cells.- Undergo meiosis to form four haploid microspores.

Pollen grain shapes are specialized for specific flower species.



• Embryo Sac Megaspore mother cell found within each

ovule.- Undergoes meiosis to produce four

haploid megaspores. Usually only one survives and the other

three are absorbed by the ovule. Remaining megaspore undergoes

mitosis and produces eight haploid nuclei enclosed in an embryo sac.


Pollination

• Pollination - Pollen is placed on the stigma. Early seed plants pollinated passively.

• Pollination by Animals Bees - Initially locate food sources by odor,

and then orient on a flower by its shape, color, and texture.

- May drive coevolution.

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Pollination

• Other Insects Butterflies Moths Beetles

• Birds Many plants produce large amount of nectar to

attract birds.- Hummingbirds

Red colors tend to attract birds, while carotenoids tend to attract insects because they are visible in the UV range.


Pollination

• Other Animals Bats Rodents Monkeys

• Wind-Pollinated Angiosperms Typically have small, greenish, odorless

flowers with reduced or absent corollas.


Self-Pollination

• Two basic reasons for self-pollination. Ecologically advantageous as they do not

need to be visited by animals, and thus do not have to expend energy producing attractants.

Produces more uniform progeny than outcrossing.

- Well-adapted to particular habitats.


Self-Pollination

• Factors Promoting Outcrossing Dioecious plants produce only ovules or

only pollen on a single individual. Monoecious produce both on same plant. Dichogamous - Functional stamens and

pistils present on same plant, but reach maturity at different times.


Self-Pollination

• Self-incompatibility results when pollen and stigma recognize each other as genetically related and pollen tube growth is blocked.


Fertilization• Double Fertilization results in two key developments:

Fertilization of the egg. Formation of endosperm.

• Pollen grains adhere to the stigma and grow a pollen tube that pierces the style. Grows until it reaches the ovule in the ovary.

• Tip of pollen tube bursts and releases two sperm cells. One fertilizes the egg cell forming a zygote. The other cell fuses with two polar nuclei located at the center of the embryo

sac.


Asexual Reproduction

• Vegetative Reproduction - New plants are cloned from adult parts. Runners Rhizomes Suckers Adventitious Plantlets

• Apomixis - Embryos in seeds produced asexually from the parent plant.


Life Span of Plants

• Once established, plants live for highly variable periods of time. Life span may or may not correlate with

reproductive strategy.- Woody plants which have extensive

secondary growth, nearly always live longer than herbaceous plants, which have limited to no secondary growth.


Life Span of Plants

• Annuals Annual plants grow, flower, and form fruits

and seeds within one growing season, and then die when the process is complete.

- Grow rapidly under favorable conditions. Developing flowers or embryos use

hormones signaling nutrient reallocation.


Life Span of Plants

• Biennials Biennial plants have life cycles that take

two years to complete.- Photosynthate stored in underground

storage organs during the first year.- Flowering stems are produced during

the second year.


Life Span of Plants

• Perennials Perennial plants grow year after year.

- Majority of vascular plants are perennial. Food is often stored in roots or

underground stems which can become relatively large.

- Trees and shrubs generally flower repeatedly.

Deciduous or Evergreen.


Life Span of Plants

• Organ Abscission Abscission - Shedding of

leaves or petals.- Dispense with nutrient

sinks. Shaded leaves,

petals- Evergreens usually have

complete change of leaves every two to seven years.


Life Span of Plants

• Abscission involves changes in abscission zone at the base of the petiole.

Young leaves produce hormones that inhibit development of specialized layers of cells in the abscission zone.

- Cells become impregnated with suberin.

Separation layer develops on the side of the leaf blade; cells of the separation layer divide, swell, and become gelatinous.


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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Plant Reproduction Chapter 42 Copyright © McGraw-Hill Companies Permission