Angiosperm Reproduction

Angiosperms Sporophyte = dominant generation Gametophytes the large plant that we see Gametophytes reduced in size Develop within flowers depend on the sporophyte for nutrients Male gametophytes (pollen grains) female gametophytes (embryo sacs) Video: Flower Blooming (time lapse) Video: Time Lapse of Flowering Plant Life Cycle

Stigma Anther Carpel Stamen Style Filament Ovary Sepal Petal LE 38-2a Stigma Anther Carpel Stamen Style Filament Ovary Sepal Petal Key Haploid (n) Receptacle Diploid (2n) An idealized flower

Germinated pollen grain (n) (male gametophyte) Anther LE 38-2b Germinated pollen grain (n) (male gametophyte) Anther Ovary Pollen tube Ovule Embryo sac (n) (female gametophyte) FERTILIZATION Egg (n) Mature sporophyte plant (2n) Sperm (n) Zygote (2n) Seed Key Seed Haploid (n) Diploid (2n) Embryo (2n) (sporophyte) Germinating seed Simple fruit Simplified angiosperm life cycle

Flower Structure Flowers reproductive shoots angiosperm sporophyte They consist of four floral organs: Sepals Petals Stamens Carpels

LE 38-3a SYMMETRY OVARY LOCATION FLORAL DISTRIBUTION Bilateral symmetry (orchid) Lupine inflorescence Superior ovary Radial symmetry (daffodil) Sunflower inflorescence Semi-inferior ovary Inferior ovary Sepal Fused petals

REPRODUCTIVE VARIATIONS LE 38-3b REPRODUCTIVE VARIATIONS Maize, a monoecious species Dioecious Sagittaria latifolia (common arrowhead)

Video: Bat Pollinating Agave Plant Video: Bee Pollinating pollination transfer of pollen from an anther to a stigma If successful: pollen grain produces a pollen tube grows down into the ovary discharges sperm near the embryo sac Pollen develops from microspores within sporangia of anthers Video: Bat Pollinating Agave Plant Video: Bee Pollinating

LE 38-4 Development of a male gametophyte (pollen grain) Development of a female gametophyte (embryo sac) Pollen sac (microsporangium) Mega- sporangium Micro- sporocyte Ovule Mega- sporocyte MEIOSIS Integuments Micropyle Micro- spores (4) Surviving megaspore Each of 4 microspores Female gametophyte (embryo sac) MITOSIS Ovule Antipodal cells (3) Generative cell (will form 2 sperm) Male gametophyte (pollen grain) Polar nuclei (2) Egg (1) Nucleus of tube cell Integuments Synergids (2) 20 µm Ragweed pollen grain (colorized SEM) Key to labels Embryo sac 75 µm Haploid (n) 100 µm (LM) Diploid (2n) (LM)

Embryo sacs develop from megaspores within ovules

Prevention of Self-Fertilization self-incompatibility ability to reject its own pollen Pollen with S-gene matching stigma cell gene are rejected triggers a signal transduction pathway block in growth of a pollen tube

Pin flower Thrum flower LE 38-5 Stigma Stigma Anther with pollen Pin flower Thrum flower

Animation: Plant Fertilization Double Fertilization Pollen lands on a receptive stigma Produces pollen tube extends between the cells of the style toward the ovary pollen tube discharges two sperm into the embryo sac One sperm fertilizes the egg other combines with the polar nuclei creates endosperm (3N) Animation: Plant Fertilization

LE 38-6 Pollen grain Stigma Pollen tube If a pollen grain 2 sperm germinates, a pollen tube grows down the style toward the ovary. 2 sperm Style Ovary Ovule (containing female gametophyte, or embryo sac) Polar nuclei Egg Micropyle Ovule Polar nuclei The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule. Egg Two sperm about to be discharged One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei of the embryo sac’s large central cell, forming a triploid cell that develops into the nutritive tissue called endosperm. Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm)

Animation: Seed Development From Ovule to Seed each ovule develops into a seed ovary develops into a fruit Animation: Seed Development

LE 38-7 Ovule Endosperm nucleus Integuments Zygote Zygote Terminal cell Basal cell Proembryo Suspensor Basal cell Cotyledons Shoot apex Root apex Seed coat Endosperm Suspensor

Common garden bean, a eudicot with thick cotyledons LE 38-8a Seed coat Epicotyl Hypocotyl Radicle Cotyledons Common garden bean, a eudicot with thick cotyledons

Castor bean, a eudicot with thin cotyledons LE 38-8b Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle Castor bean, a eudicot with thin cotyledons

Pericarp fused Scutellum with seed coat (cotyledon) Endosperm LE 38-8c Pericarp fused with seed coat Scutellum (cotyledon) Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle Maize, a monocot

Animation: Fruit Development From Ovary to Fruit fruit = ripened ovary protects the enclosed seeds aids in seed dispersal by wind or animals fruit are classification Simple Aggregate Multiple Animation: Fruit Development

Ovary Stamen Stigma Ovule Pea flower Seed Pea fruit Simple fruit LE 38-9a Ovary Stamen Stigma Ovule Pea flower Seed Pea fruit Simple fruit

Carpels Stamen Raspberry flower Carpel (fruitlet) Stigma Ovary Stamen LE 38-9b Carpels Stamen Raspberry flower Carpel (fruitlet) Stigma Ovary Stamen Raspberry fruit Aggregate fruit

Pineapple inflorescence LE 38-9c Flower Pineapple inflorescence Each segment develops from the carpel of one flower Pineapple fruit Multiple fruit

Seed Germination Dehydration of seed Dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling

Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon Radicle Seed coat Common garden bean

LE 38-10b Foliage leaves Coleoptile Coleoptile Radicle Maize

Reproduction Sexual reproduction Asexual reproduction generates genetic variation makes evolutionary adaptation possible Asexual reproduction called vegetative reproduction Mechanisms Fragmentation separation of a parent plant into parts that develop into whole plants adventitious shoots a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems

Agriculture Vegetative Propagation Grafting asexual reproduction from plant fragments (cuttings) Grafting A twig or bud can be grafted onto a plant of a closely related species or variety

Artificial Selection Humans intervention as a selective force Ex. Maize Hybridization

Reducing World Hunger and Malnutrition Genetically modified plants may: increase the quality of food Increase quantity of food worldwide

Genetically modified rice LE 38-16 Genetically modified rice Ordinary rice