Plant Reproduction

Chapter 30

Impacts, IssuesPlight of the Honeybee

Flowering plants coevolved with animal pollinators such as honeybees – now pesticides and other factors threaten our food supply

30.1 Reproductive Structures of Flowering Plants

Flowers are specialized reproductive shoots of angiosperm sporophytes (diploid spore-producing plant bodies that grow by mitotic cell divisions of fertilized eggs)

Spores that form by meiosis inside flowers develop into haploid gametophytes (structures in which haploid gametes form by mitosis)

Anatomy of a Flower

Petals and other flower parts are modified leaves that form in four spirals or whorls at the end of a floral shoot• Calyx: A ring of protective sepals• Corolla: A ring of petals that attracts pollinators• Stamens: Male parts of a flower• Carpels (pistils): Female parts of a flower

Stamens

Stamens consist of a filament with an anther at the tip

Anthers contain pollen sacs, in which diploid cells produce haploid spores by meiosis

Spores differentiate into pollen grains (immature male gametophytes)

Carpels

Flowers have one or several carpels, each with a sticky stigma to capture pollen grains

The ovary contains ovules which undergo meiosis to form a haploid female gametophyte

A diploid zygote forms when male and female gametophytes join in an ovary

Structure of Flowers

Fig. 30-2a (1), p. 508

Fig. 30-2a (2), p. 508

Fig. 30-2a (2), p. 508

stamen carpel

(male reproductive part) (female reproductive part)

filament anther stigma style ovary

petal (all petals combined are the flower’s corolla)

ovule (forms within ovary)

sepal (all sepals combined are flower’s calyx)

receptacle

Fig. 30-2b, p. 508

Fig. 30-2b, p. 508

carpel structure varies

ovule position varies within

ovariesovary position

varies

Animation: Flower parts

Typical Flowering Plant Life Cycle

Fig. 30-3, p. 509

mature sporophyte

(2n)germination

zygote in seed (2n)

fertilization meiosis in anther

meiosis in ovary

DIPLOID

HAPLOID

microspores (n)

megaspores (n)

eggs (n) sperm (n)

male gametophyte (n)

female gametophyte (n)

zygote in seed (2n)

fertilization DIPLOID

Fig. 30-3, p. 509

mature sporophyte

(2n)germination

meiosis in anther

meiosis in ovary

HAPLOID

eggs (n) sperm (n)

male gametophyte (n)

female gametophyte (n) Stepped Art

microspores (n)

megaspores (n)

Animation: Flowering plant life-cycle

Animation: Eudicot life cycle

Diversity of Flower Structure

Many variations in flower structure are adaptations to maximize cross-pollination• Regular and irregular flowers• Single flowers and inflorescences• Complete flowers and incomplete flowers• Perfect flowers and imperfect flowers

Diversity of Flower Structure

30.2 Flowers and Their Pollinators

Sexual reproduction in plants involves transfer of pollen, usually from one plant to another

Flowering plants coevolved with pollination vectors (agents that deliver pollen from an anther to a compatible stigma)

Pollinators are living pollination vectors such as insects, birds, or other animals

Flowers and Their Pollinators

Flower shape, pattern, color and fragrance are adaptations that attract specific animal pollinators• Bees are attracted to bright white, yellow or blue

flowers, and patterns of UV reflecting pigments• Bats and moths are attracted to certain scents

Pollinators are often rewarded for visiting a flower by obtaining nutritious pollen or sweet nectar

Flowers with Specific Animal Pollinators

Bees as Pollinators

Day and Night Pollinators

Attracting Pollinators

Animal Pollinator

30.1-30.2 Key Concepts Structure and Function of Flowers

Flowers are shoots that are specialized for reproduction

Modified leaves form their parts

Gamete-producing cells form in their reproductive structures; other parts such as petals are adapted to attract and reward pollinators

30.3 A New Generation Begins

Male gametophytes form in pollen grains• Diploid spore-producing cells form in pollen sacs• Diploid cells undergo meiosis to form four haploid

microspores• Mitosis and differentiation of microspores produce

pollen grains consisting of two cells

Female Gamete Production

Female gametes form in ovules• A mass of tissue (ovule) grows in an ovary• One cell undergoes meiosis, forming four haploid

megaspores, three of which disintegrate• One megaspore undergoes mitosis to form the

female gametophyte, which contains one haploid egg, five other haploid cells, and one endosperm mother cell with two nuclei (n + n)

Pollination

Pollination occurs when a pollen grain arrives on a receptive stigma and germinates• One cell in the pollen grain develops into the

pollen tube, which grows toward the ovule• The other cell undergoes mitosis to produce two

sperm cells (male gametes)• A pollen tube containing male gametes

constitutes the mature male gametophyte

Fertilization

Flowering plants undergo double fertilization • Pollen tube releases sperm into the embryo sac• One sperm cell fertilizes the egg, producing a

diploid zygote• The other sperm fuses with the endosperm

mother cell, forming a tripod (3n) cell which is the start of endosperm, a nutritious tissue that nourishes the embryo sporophyte

Life Cycle: Eudicot

Fig. 30-8 (a-d), p. 512

Fig. 30-8 (a-d), p. 512

pollen sac anther (cutaway view)

filament

forerunner of one of the microspores

A Pollen sacs form in the mature sporophyte.

meiosisDiploid StageHaploid Stage

B Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac.

C In this plant, mitosis of a microspore (with no cytoplasmic division) followed by differentiation results in a two-celled, haploid pollen grain.

D A pollen grain released from the anther lands on a stigma and germinates. One cell in the grain develops into a pollen tube; the other gives rise to two sperm cells, which are carried by the pollen tube into the tissues of the carpel.

pollen tubestigma

Mature Male Gametophyte sperm cells

(male gametes)carpel

A Pollen sacs form in the mature sporophyte.

pollen sac anther (cutaway view)

filament

forerunner of one of the microspores

meiosisDiploid Stage

Fig. 30-8 (a-d), p. 512

Stepped Art

Haploid Stage

B Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac.

D A pollen grain released from the anther lands on a stigma and germinates. One cell in the grain develops into a pollen tube; the other gives rise to two sperm cells, which are carried by the pollen tube into the tissues of the carpel.

pollen tube

stigmaMature Male

Gametophyte

carpelsperm cells (male gametes)

C In this plant, mitosis of a microspore (with no cytoplasmic division) followed by differentiation results in a two-celled, haploid pollen grain.

Fig. 30-8 (e-i), p. 513

Fig. 30-8 (e-i), p. 513

an ovuleovary wall

cell inside ovule tissueSporophyte

seedling (2n)

seed coatembryo (2n)

E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges.

ovary (cutaway view)

seedDiploid Stage

double fertilization meiosisHaploid Stage

F Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate.

pollen tube

G In the remaining megaspore, three rounds of mitosis without cytoplasmic division produce a single cell that contains eight haploid nuclei.

Female Gametophyte

endosperm mother cell (n + n)

egg (n)

I The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.

H Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight nuclei—the female gametophyte.

endosperm (3n)

Fig. 30-8 (e-i), p. 513

Diploid Stage

E In a flower of a mature sporophyte, an ovule forms inside an ovary. One of the cells in the ovule enlarges.

cell inside ovule tissue

an ovuleovary wall

ovary (cutaway view)

meiosis

Stepped Art

Haploid Stage

F Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate.

H Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight nuclei—the female gametophyte.

Female Gametophyte

I The pollen tube grows down through stigma, style, and ovary tissues, then penetrates the ovule and releases two sperm nuclei.

endosperm mother cell (n + n)

pollen tube

egg (n)

G In the remaining megaspore, three rounds of mitosis without cytoplasmic division produce a single cell that contains eight haploid nuclei.

seed

double fertilization

seed coatembryo (2n)endosperm (3n)

Sporo-phyte

seedling (2n)

30.4 Flower Sex

Recognition proteins on epidermal cells of the stigma bind to molecules in the pollen grain coat

Species-specific molecular signals from the stigma stimulate pollen germination and guide pollen-tube growth to the egg

In some species, the specificity of the signal also limits self-pollination

Pollen Tube Growth

30.3-30.4 Key Concepts Gamete Formation and Fertilization

Male and female gametophytes develop inside the reproductive parts of flowers

In flowering plants, pollination is followed by double fertilization

As in animals, signals are key to sex

30.5 Seed Formation

After fertilization, mitotic cell divisions transform the zygote into an embryo sporophyte • Endosperm becomes enriched with nutrients• Ovule’s integuments develop into a seed coat

Seed (mature ovule)• An embryo sporophyte and nutritious endosperm

encased in a seed coat

Seeds as Food

As an embryo is developing, the parent plant transfers nutrients to the ovule• Eudicot embryos transfer nutrients to two

cotyledons, which nourish seedling sporophytes• Monocot embryos use endosperm after

germination

Humans also get nutrition from seeds (grains)• Embryo (germ) contains protein and vitamins• Endosperm contains mostly starch

Embryonic Development: Eudicot

Embryonic Development: Eudicot

Embryonic Development: Eudicot

Embryonic Development: Eudicot

Fig. 30-10a, p. 515

many ovules inside ovary wall

embryo

endosperm integuments

A After fertilization, a Capsella flower’s ovary develops into a fruit. Surrounded by integuments, an embryo forms inside each of the ovary’s many ovules.

Fig. 30-10b, p. 515

embryo

endosperm

B The embryo is heart-shaped when cotyledons start forming. Endosperm tissue expands as the parent plant transfers nutrients into it.

Fig. 30-10c, p. 515

root apical meristem

embryo

endosperm

shoot tip cotyledons

C The developing embryo is torpedo-shaped when the enlarging cotyledons bend inside the ovule.

Fig. 30-10d, p. 515

seed coat

embryo

cotyledons

D A layered seed coat that formed from the layers of integuments surrounds the mature embryo sporophyte. In eudicots like Capsella, nutrients have been transferred from endosperm into two cotyledons.

Animation: Eudicot seed development

30.6 Fruits

As embryos develop inside the ovules of flowering plants, tissues around them form fruits

Fruit• A mature, seed-containing ovary, with or without

accessory tissues that develop from other parts of a flower

Fruit Development

Fig. 30-11, p. 516

tissue derived from

ovary wall

carpel wall

seed

enlarged receptacle

Mature Fruits

Seed Dispersal

Fruits function to protect and disperse seeds

Fruits are adapted to certain dispersal vectors• Mobile organisms such as birds or insects• Environmental factors such as wind or water

Adaptations for Fruit Dispersal

Three Ways to Classify Fruits

Table 30-2, p. 517

Stepped Art

Aggregate Fruits

30.5-30.6 Key Concepts Seeds and Fruits

After fertilization, ovules mature into seeds, each an embryo sporophyte and tissues that nourish and protect it

As seeds develop, tissues of the ovary and often other parts of the flower mature into fruits, which function in seed dispersal

30.7 Asexual Reproduction of Flowering Plants

Vegetative reproduction• Asexual reproduction in which new roots and

shoots grow from a parent plant or pieces of it• Permits rapid production of genetically identical

offspring (clones)

Clones of Quaking Aspen

Root suckers sprout after aboveground parts are damaged or removed

Agricultural Applications

Cuttings and grafting• Offspring have the same desirable traits as the

parent plant

Tissue culture propagation• Cloning an entire plant from a single cell

Seedless fruits• Mutations that result in arrested seed

development or triploidy produce sterile fruit

Grafted Apple Trees

30.7 Key Concepts Asexual Reproduction in Plants

Many species of plants reproduce asexually by vegetative reproduction

Humans take advantage of this natural tendency by propagating plants asexually for agriculture and research

Animation: Apple fruit structure

Animation: Bee-attracting flower pattern

Animation: Double fertilization

Animation: Floral structure and function

Animation: Microspores to pollen

Animation: Pollination

Video: Imperiled sexual partners