Chapter 27 Plant Reproduction and Development (Sections 27.1 - 27.5)

27.1 Plight of the Honeybee Most food crops are flowering plants, which make pollen The recent decline of honeybees used to pollinate crops is a huge threat to our agricultural economy pollinator An organism that moves pollen from one plant to another

Importance of Insect Pollinators Many plant species will not develop fruits (or only develop inferior fruits) unless they receive pollen from other flowers Figure 27.1 Importance of insect pollinators. Opposite, honeybees are efficient pollinators of a variety of flowers, including those of berry plants. Above, raspberry flowers can pollinate themselves, but the fruit that forms from a self-fertilized flower is of lower quality than that of a cross-pollinated flower. The two raspberries on the left formed from self-pollinated flowers. The one on the right formed from an insect-pollinated flower.

27.2 Reproductive Structures of Flowering Plants Petals and other parts of a typical flower are modified leaves that form in four spirals (whorls) at the end of a floral shoot flower Specialized reproductive shoot of an angiosperm sporophyte

Flower Formation The outermost whorl develops into a ring of sepals (a calyx ) Petals form in the second whorl (the corolla) A whorl of stamens (which produce male gametophytes) forms inside the ring of petals The innermost whorl of modified leaves are folded and fused into carpels (which produce female gametophytes)

Key Terms stamen Reproductive structure that produces male gametophytes In most plants it consists of a pollen-producing anther on the tip of a filament carpel Reproductive structure that produces female gametophytes Sticky or hairlike stigma together with an ovary and a style

Carpels Flowers may have one carpel, several carpels, or several groups of carpels that may be fused A swollen region (the ovary) contains one or more ovules A cell in the ovule undergoes meiosis and develops into the haploid female gametophyte

Key Terms ovary In flowering plants, the enlarged base of a carpel, inside which one or more ovules form and eggs are fertilized ovule In a seed-bearing plant, a structure in which a haploid, egg-producing female gametophyte forms After fertilization, matures into a seed

Anatomy of a Typical Flower

Anatomy of a Typical Flower stamen carpel filament anther stigma style ovary Figure 27.2 Anatomy of a typical flower. ovule (forms within ovary) petal (all petals combined are the flower’s corolla) sepal (all sepals combined are flower’s calyx) receptacle Fig. 27.2a.2, p. 430

Flower Structure Flower structure varies among different plant species

carpel structure varies ovule position varies within ovaries Flower Structure carpel structure varies Figure 27.2 Anatomy of a typical flower. ovule position varies within ovaries ovary position varies B Flower structure varies among different plant species. Fig. 27.2b, p. 430

Life Cycle of a Flowering Plant The life cycle of flowering plants is dominated by a diploid, spore-producing sporophyte Spores that form by meiosis inside flowers develop into haploid gametophytes, which produce gametes At fertilization, a diploid zygote forms when male and female gametes meet inside an ovary

Life Cycle of a Flowering Plant

Life Cycle of a Flowering Plant mature sporophyte (2n) germination zygote in seed (2n) meiosis in anther meiosis in ovary fertilization microspores (n) sperm (n) Figure 27.3 Life cycle of a typical flowering plant. male gametophyte eggs (n) megaspores (n) female gametophyte Fig. 27.3, p. 430

Life Cycle of a Flowering Plant zygote in seed (2n) mature sporophyte (2n) germination megaspores (n) microspores (n) meiosis in anther meiosis in ovary female gametophyte male gametophyte eggs (n) sperm (n) fertilization Figure 27.3 Life cycle of a typical flowering plant. Stepped Art Fig. 27.3, p. 430

Pollinators Sexual reproduction in flowering plants involves transfer of pollen, typically from one plant to another Animal pollinators pick up pollen and transfer it to the flower of a different plant A flower’s shape, pattern, color, and fragrance are adaptations that attract specific animal pollinators

Coevolution ~90% of flowering plants have coevolved animal pollinators An animal’s reward for a visit to a flower may be nectar, oils, nutritious pollen, or even sex Butterflies, hummingbirds, and honeybees feed on nectar Bats, moths, and flies are attracted to specific odors Some flowers have specializations that prevent pollination by everything other than a specific pollinator species

Coevolution Zebra orchid mimics the scent of a female wasp Female burnet moths ready to mate Figure 27.4 Intimate connections between pollinator and flower. A A zebra orchid mimics the scent of a female wasp. Male wasps follow the scent to the flower, then try to copulate with and lift the dark red mass of tissue on the lip. The wasp’s movements trigger the lip to tilt upward, which brushes the wasp’s back against the flower’s stigma and pollen. B Female burnet moths perch on purple flowers—preferably those of field scabious— when they are ready to mate. The combination of colors and patterns attracts males.

Key Concepts Structure and Function of Flowers Flowers are shoots that are specialized for reproduction Modified leaves form their parts Gamete-producing cells develop in their reproductive structures Other parts such as petals are adapted to attract and reward pollinators

27.3 A New Generation Begins In flowering plants, fertilization has two outcomes: It results in a diploid zygote, which becomes the mature sporophyte It is the start of nutritive endosperm, which sustains rapid growth of the sporophyte seedling until true leaves form and photosynthesis begins

10 Steps in the Flowering Plant Life Cycle 1. An ovule forms inside a flower’s ovary; one cell enlarges 2. Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell 3. In one megaspore, three rounds of mitosis with no cytoplasmic division result in a single cell with eight nuclei 4. Uneven cytoplasmic divisions result in a seven-celled embryo sac (female gametophyte) with eight haploid nuclei

10 Steps in the Flowering Plant Life Cycle 5. Pollen sacs form in an anther 6. Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac 7. Mitosis and differentiation of a microspore produces a two-celled pollen grain, which enters dormancy, before being released from the anther

Key Terms megaspore Haploid spore that forms in ovule of seed plants Gives rise to an egg-producing gametophyte microspore Walled haploid spore of seed plants Gives rise to a sperm-producing gametophyte dormancy Period of temporarily suspended metabolism

10 Steps in the Flowering Plant Life Cycle 8. Pollen grains are released from the anther; one lands on a stigma and germinates (pollination): One cell in the pollen grain develops into a pollen tube The other cell develops into two haploid sperm cells 9. The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it

10 Steps in the Flowering Plant Life Cycle 10. The pollen tube reaches the ovule, penetrates it, and releases the two sperm nuclei (double fertilization) One sperm fertilizes the egg and forms a diploid zygote The other fuses with the endosperm mother cell, forming a triploid (3n) cell which gives rise to triploid endosperm

Key Terms pollination Arrival of pollen on a receptive stigma double fertilization Mode of fertilization in flowering plants in which one sperm cell fuses with the egg, and a second sperm cell fuses with the endosperm mother cell endosperm Nutritive tissue in the seeds of flowering plants

Life Cycle of a Eudicot

Life Cycle of a Eudicot An ovule forms inside a flower’s ovary. A cell in the ovule enlarges. 1 an ovule seedling ovary wall ovary seed Sporophyte (2n) Meiosis in ovary pollen tube Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate. 2 megaspores (n) endosperm mother cell (n + n) In the remaining megaspore, three rounds of mitosis with no cytoplasmic division result in a single cell with eight nuclei. 3 egg (n) Figure 27.5 Life cycle of cherry (Prunus), a eudicot. sperm (n) The pollen tube reaches the ovule, penetrates it, and releases the two sperm nuclei. One nucleus fertilizes the egg. The other fuses with the endosperm mother cell. 10 Double fertilization Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight haploid nuclei. This sac is the female gametophyte. 4 female gametophyte Fig. 27.5.1-4,10, p. 433

mature male gametophyte Life Cycle of a Eudicot pollen sac anther (cutaway view) filament Pollen sacs form in an anther. 5 a cell in the pollen sac Meiosis in anther 6 Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac. 6 microspores (n) In this plant, mitosis of a micro-spore followed by differentiation results in a two-celled pollen grain. 7 7 Figure 27.5 Life cycle of cherry (Prunus), a eudicot. Pollen grains are released from the anther. One lands on a stigma and germinates. A cell in the grain develops into a pollen tube; the other, into two haploid sperm cells. 8 8 The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it. 9 pollen tube stigma style sperm cells 9 mature male gametophyte Fig. 27.5.5-9, p. 432

mature male gametophyte Life Cycle of a Eudicot pollen sac anther (cutaway view) filament a cell in the pollen sac Pollen sacs form in an anther. 5 Meiosis in anther Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac. 6 microspores (n) In this plant, mitosis of a micro-spore followed by differentiation results in a two-celled pollen grain. 7 Figure 27.5 Life cycle of cherry (Prunus), a eudicot. Pollen grains are released from the anther. One lands on a stigma and germinates. A cell in the grain develops into a pollen tube; the other, into two haploid sperm cells. 8 The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it. 9 pollen tube stigma style sperm cells mature male gametophyte Stepped Art Fig. 27.5.5-9, p. 432

ANIMATION: Pollination 32

ANIMATION: Plant Life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

27.4 From Zygotes to Seeds and Fruits After fertilization, mitotic cell divisions transform a zygote into an embryo sporophyte encased in a seed As embryos develop inside the ovules of flowering plants, tissues around them form fruits Water, wind, and animals disperse seeds in fruits

The Embryo Sporophyte Forms Double fertilization produces a zygote, which develops into an embryo sporophyte, and a triploid (3n) cell, which develops into nutrient-containing endosperm When the embryo matures, layers of integuments separate from the ovary wall and become a protective seed coat The embryo sporophyte, its reserves of food, and the seed coat become a mature ovule (seed)

A Seed seed Embryo sporophyte of a seed plant packaged with nutritive tissue inside a protective coat

A Seed root apical meristem seed coat embryo shoot tip cotyledons Figure 27.6 Seed of shepherd’s purse (Capsella), a eudicot. Fig. 27.6, p. 434

Fruits Fruits include seed-containing “vegetables” such as beans, tomatoes, grains, and squash Simple fruits(e.g. pea pod) form from a single ovary Aggregate fruits (e.g. strawberry) form from separate ovaries of one flower Multiple fruits (e.g. pineapple) form from fused ovaries of separate flowers fruit A seed-containing mature ovary of a flowering plant Often with accessory tissues

Parts of a Fruit

Parts of a Fruit tissue derived from ovary wall carpel wall seed Figure 27.7 Parts of a fruit that develop from parts of a flower. Left, the tissues of an orange (Citrus) develop from the ovary wall. Right, the flesh of an apple (Malus) is an enlarged receptacle. enlarged receptacle Fig. 27.7, p. 434

Aggregate Fruits

Aggregate Fruits Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits. Fig. 27.8a, p. 435

Aggregate Fruits Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits. Fig. 27.8b, p. 435

Aggregate Fruits Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits. Fig. 27.8c, p. 435

Categories of Fruits Based on tissues: True fruits develop from the ovary wall Accessory fruits include the ovary and other parts developed from petals, sepals, stamens, or receptacles Based on appearance: Dry fruits (e.g. acorns, grains, strawberries) Fleshy fruits (e.g. cherries, berries, apples)

Function of Fruits The function of a fruit is to protect and disperse seeds Specific dispersal vectors are reflected in a fruit’s form: Water: Water-repellent outer layers Wind: Lightweight with breeze-catching specializations Animals: Hooks or spines that stick to feathers, feet, or fur Animal feces: Colorful, fleshy, fragrant fruits

Key Concepts Plant Sexual Reproduction In flowering plants, pollination is followed by double fertilization After fertilization, ovules mature into seeds As seeds develop, tissues of the ovary and other parts of the flower mature into fruits, which function to disperse seeds

ABC Video: Doomsday Vault Seed Collection

Animation: Double Fertilization

27.5 Asexual Reproduction in Plants Most flowering plants can reproduce by vegetative reproduction, a form of asexual reproduction that produces genetically identical offspring Triploid species are sterile and can only reproduce asexually vegetative reproduction Growth of new roots and shoots from extensions or fragments of a parent plant

Tissue Culture Propagation An entire plant may be cloned from a single cell with tissue culture propagation This technique is used to improve food crops and to propagate rare ornamental plants such as orchids tissue culture propagation Laboratory method in which body cells are induced to divide and form an embryo

Key Concepts Asexual Reproduction of 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