Overview: Angiosperm flowers can attract pollinators using visual cues and volatile chemicals reproduce sexually and asexually Symbiotic relationships are common between plants and other species Since the beginning of agriculture, plant breeders have genetically manipulated traits of wild angiosperm species by artificial selection Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A.Alternation of Generations (n  2n  n  2n) B.2n = diploid sporophyte 1.Dominant generation (what we see!) 2.Produces haploid spores by meiosis (in the sporangia-review Ch. 30!) 3.Spores divide by mitosis forming gametophyte (n) C.n= haploid gamete 1.male or female 2.mitosis in gametophyte produces sperm or eggs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

A.Reproductive structures of the angiosperm sporophyte; they attach to a part of the stem called the receptacle B.Sepals-usually green, protect the flower C.Petals-generally brightly colored, attract pollinators Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

D. Stamen 1.Anther- with pollen sacs that produce pollen grains 2.Filament-supports the anther E. Carpels (pistil) 1.A carpel has a long stigma on which pollen may land a.Style b.Ovary containing embryo sacs within ovules Copyrigt © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 38-2a Stamen Anther Filament Stigma Carpel (pistil) Style Ovary Receptacle Sepal Petal (a) Structure of an idealized flower Ovule

Complete flowers contain all four floral organs Incomplete flowers lack one or more floral organs, for example stamens or carpels Many angiosperms have mechanisms that make it difficult or impossible for a flower to self-fertilize Monoecious- both flowers on same plant (ex. corn) Dioecious species have staminate and carpellate flowers on separate plants Others have stamens and carpels that mature at different times or are arranged to prevent selfing Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig (a) Sagittaria latifolia staminate flower (left) and carpellate flower (right) (b) Oxalis alpina flowers Thrum flowerPin flower Stamens Styles Stamens

A.Pollination- pollen lands on the stigma a.Wind can be a pollinator b.Insects specific for plants they pollinate c.Some flowers self-pollinate, but most cannot. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 38-4a Abiotic Pollination by Wind Hazel staminate flowers (stamens only) Hazel carpellate flower (carpels only)

Fig. 38-4c Pollination by Moths and Butterflies Moth on yucca flower Anther Stigma

Fig. 38-4d Pollination by Flies Blowfly on carrion flower Fly egg

Fig. 38-4e Hummingbird drinking nectar of poro flower Pollination by Birds

Fig. 38-4f Long-nosed bat feeding on cactus flower at night Pollination by Bats

B. Pollen Tube grows down the carpels and discharges 2 sperm a. Double fertilization Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 38-5b Ovule Polar nuclei Egg Synergid 2 sperm i. one sperm (n) fertilizes the egg (n)  zygote (2n) formed  embryo

Fig. 38-5c Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm) ii. one sperm (n) combines with two polar nuclei (n)+ (n)  endosperm (3n) = food-storing tissue After double fertilization, each ovule develops into a seed

Structure of the Mature Seed The embryo and its food supply are enclosed by a hard, protective seed coat The seed enters a state of dormancy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C. Fruit Development (pollination triggers hormonal changes that cause the ovary to grow tremendously) a. 3n nucleus divides to form multinucleate “SUPER CELL” b. Cytokinesis forms membranes and walls between nuclei c. Rich in nutrients for developing embryo and seedling d. Fruit protects seeds and aids in dispersal (water, wind, animals) e. Other flower parts wither away as ovary grows. – If a flowers is not pollinated it will wither and fall away. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig FlowerStamen Carpels Ovary Stigma Pea flower Ovule Seed Carpel (fruitlet) Raspberry flower Stigma Ovary Stamen Pineapple inflorescenceApple flower Stigma Stamen Ovule Each segment develops from the carpel of one flower Pea fruitRaspberry fruitPineapple fruitApple fruit (a) Simple fruit(b) Aggregate fruit(c) Multiple fruit(d) Accessory fruit Sepal Petal Style Ovary (in receptacle) Sepals Seed Receptacle Remains of stamens and styles

Fig a Coconut Dispersal by Water

Fig b Tumbleweed Dispersal by Wind Winged fruit of maple Dandelion “parachute” Winged seed of Asian climbing gourd

Fig c Dispersal by Animals Seeds carried to ant nest Seeds buried in caches Seeds in feces Barbed fruit

D. Embryo Development a. zygote divides by mitosis b. cotyledons begin to form c. embryo elongates and embryonic root and meristem form. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 38-9a (a) Common garden bean Seed coat Radicle Hypocotyl Cotyledon Hypocotyl Epicotyl Foliage leaves Cotyledon Hypocotyl

Fig. 38-9b (b) Maize Radicle Foliage leaves Coleoptile

Concept 38.2: Plants reproduce sexually, asexually, or both Many angiosperm species reproduce both asexually and sexually Sexual reproduction results in offspring that are genetically different from their parents Asexual reproduction results in a clone of genetically identical organisms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Mechanisms of Asexual Reproduction Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction In some species, a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Apomixis is the asexual production of seeds from a diploid cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Advantages and Disadvantages of Asexual Versus Sexual Reproduction Asexual reproduction is also called vegetative reproduction Asexual reproduction can be beneficial to a successful plant in a stable environment However, a clone of plants is vulnerable to local extinction if there is an environmental change Sexual reproduction generates genetic variation that makes evolutionary adaptation possible However, only a fraction of seedlings survive Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Mechanisms That Prevent Self-Fertilization Many angiosperms have mechanisms that make it difficult or impossible for a flower to self-fertilize Dioecious species have staminate and carpellate flowers on separate plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Others have stamens and carpels that mature at different times or are arranged to prevent selfing Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The most common is self-incompatibility, a plant’s ability to reject its own pollen Researchers are unraveling the molecular mechanisms involved in self-incompatibility Some plants reject pollen that has an S-gene matching an allele in the stigma cells Recognition of self pollen triggers a signal transduction pathway leading to a block in growth of a pollen tube Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Clones from Cuttings Many kinds of plants are asexually reproduced from plant fragments called cuttings A callus is a mass of dividing undifferentiated cells that forms where a stem is cut and produces adventitious roots Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Test-Tube Cloning and Related Techniques Plant biologists have adopted in vitro methods to create and clone novel plant varieties Transgenic plants are genetically modified (GM) to express a gene from another organism Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Vegetative Propagation and Agriculture Humans have devised methods for asexual propagation of angiosperms 3 methods are based on the ability of plants to form adventitious roots or shoots 1.Many kinds of plants are asexually reproduced from plant fragments called cuttings 2.Grafting: A twig or bud can be grafted onto a plant of a closely related species or variety 3.Transgenic plants are genetically modified (GM) to express a gene from another organism Plant biologists have adopted in vitro methods to create and clone novel plant varieties – Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 38.3: Humans modify crops by breeding and genetic engineering Plant biotechnology has two meanings: – In a general sense, it refers to innovations in the use of plants to make useful products – In a specific sense, it refers to use of GM organisms in agriculture and industry Modern plant biotechnology is not limited to transfer of genes between closely related species or varieties of the same species Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Biofuels are made by the fermentation and distillation of plant materials such as cellulose Biofuels can be produced by rapidly growing crops Reducing Fossil Fuel Dependency Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Reducing World Hunger and Malnutrition Genetically modified plants may increase the quality and quantity of food worldwide Transgenic crops have been developed that: – Produce proteins to defend them against insect pests – Tolerate herbicides – Resist specific diseases Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Genetically modified rice Ordinary rice “Golden Rice”

Issues: One concern is that genetic engineering may transfer allergens from a gene source to a plant used for food Many ecologists are concerned that the growing of GM crops might have unforeseen effects on nontarget organisms Perhaps the most serious concern is the possibility of introduced genes escaping into related weeds through crop-to-weed hybridization Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Efforts are underway to prevent this by introducing: – Male sterility – Apomixis – Transgenes into chloroplast DNA (not transferred by pollen) – Strict self-pollination Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings