Plant Reproduction Chapter 30

Impacts, Issues Plight 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

stamencarpel (male reproductive part) (female reproductive part) filamentantherstigmastyleovary 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

carpel structure varies ovule position varies within ovaries ovary 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) fertilizationDIPLOID 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

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 (a-d), p. 512

pollen sacanther (cutaway view) filament forerunner of one of the microspores A Pollen sacs form in the mature sporophyte. meiosis Diploid Stage Haploid 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 tube stigma Mature Male Gametophyte sperm cells (male gametes) carpel

A Pollen sacs form in the mature sporophyte. pollen sacanther (cutaway view) filament forerunner of one of the microspores meiosis Diploid Stage Fig (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 stigma Mature Male Gametophyte carpel sperm 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 (e-i), p. 513

an ovule ovary wall cell inside ovule tissue Sporophyte seedling (2n) seed coat embryo (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) seed Diploid Stage double fertilization meiosis Haploid 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 (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 ovule ovary 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 coat embryo (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

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

Fig a, p. 515 many ovules inside ovary wall embryo endosperminteguments 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 b, 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 c, p. 515 root apical meristem embryo endosperm shoot tipcotyledons C The developing embryo is torpedo-shaped when the enlarging cotyledons bend inside the ovule.

Fig d, 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 , 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

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