Chapter 38 Campbell

Angiosperm Reproduction and Biotechnology

Figure 38.1 Rafflesia arnoldii, “monster flower”

of Indonesia

• Overview: To Seed or Not to Seed

• The parasitic plant Rafflesia arnoldii

– Produces enormous flowers that can produce up to 4 million seeds

• Concept 38.1: Pollination enables gametes to come together within a flower

• In angiosperms, the dominant sporophyte

– Produces spores that develop within flowers into male gametophytes (pollen grains)

– Produces female gametophytes (embryo sacs)

Figure 38.2 An overview of angiosperm reproduction

• An overview of angiosperm reproduction

Flower Structure

• Flowers

– Are the __________ shoots of the angiosperm sporophyte

– Are composed of four floral organs: sepals, petals, stamens, and carpels

Figure 38.3 Floral Variations

• Many variations in floral structure

– Have evolved during the 140 million years of angiosperm history

Gametophyte Development and Pollination

• In angiosperms

– Pollination is the transfer of pollen from an anther to a stigma

– If pollination is successful, a pollen grain produces a structure called a pollen tube, which grows down into the ovary and discharges sperm near the embryo sac

• Pollen

– Develops from microspores within

the sporangia of anthers

• Embryo sacs

– Develop from megaspores within ovules

Figure 38.4 The development of angiosperm gametophytes (pollen grains and embryo sacs)

Mechanisms That Prevent Self-Fertilization

• Many angiosperms

– Have mechanisms that make it difficult or impossible for a flower to fertilize __________

• The most common anti-selfing mechanism in flowering plants

– Is known as self-incompatibility, the ability of a plant to reject its own pollen

• Researchers are unraveling the molecular mechanisms that are 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

• Concept 38.2: After fertilization, ovules develop into seeds and ovaries into fruits

Double Fertilization

• After landing on a receptive stigma

– A pollen grain germinates and produces a pollen tube that extends down between the cells of the style toward the ovary

• The pollen tube

– Then discharges __________ sperm into the embryo sac

• In double fertilization

– One sperm fertilizes the egg

– The other sperm combines with the polar nuclei, giving rise to the food-storing endosperm

• Growth of the pollen tube and double fertilization

From Ovule to Seed

• After double fertilization

– Each ovule develops into a seed

– The ovary develops into a fruit enclosing the seed(s)

Endosperm Development

• Endosperm development

– Usually precedes embryo development

• In most monocots and some eudicots

– The endosperm __________ nutrients that can be used by the seedling after germination

• In other eudicots

– The food reserves of the endosperm are completely exported to the cotyledons

Embryo Development

• The first mitotic division of the zygote is transverse

– Splitting the fertilized egg into a basal cell and a terminal cell

Structure of the Mature Seed

• The embryo and its food supply

– Are enclosed by a hard, protective seed coat

• In a common garden bean, a eudicot

– The embryo consists of the hypocotyl, radicle, and thick cotyledons

• The seeds of other eudicots, such as castor beans

– Have similar structures, but thin cotyledons

• The embryo of a monocot

– Has a single cotyledon, a coleoptile, and a coleorhiza

From Ovary to Fruit

• A fruit

– Develops from the ovary

– Protects the enclosed seeds

– Aids in the __________ of seeds by wind or animals

• Fruits are classified into several types

– Depending on their developmental origin

Seed Germination

• As a seed matures

– It dehydrates and enters a phase referred to as dormancy

Seed Dormancy: Adaptation for Tough Times

• Seed dormancy

– Increases the chances that germination will occur at a time and place most advantageous to the seedling

• The breaking of seed dormancy

– Often requires environmental cues, such as temperature or lighting cues

From Seed to Seedling

• Germination of seeds depends on the physical process called imbibition

– The uptake of water due to low water potential of the dry seed

• The __________

– Is the first organ to emerge from the germinating seed

• In many eudicots

– A hook forms in the hypocotyl, and growth pushes the hook above ground

• Monocots

– Use a different method for breaking ground when they germinate

• The __________

– Pushes upward through the soil and into the air

Figure 38.10 Two common types of seed germination

• Concept 38.3: Many flowering plants clone themselves by asexual reproduction

• Many angiosperm species

– Reproduce both asexually and sexually

• Sexual reproduction

– Generates the genetic variation that makes evolutionary adaptation possible

• Asexual reproduction in plants

– Is called vegetative reproduction

Mechanisms of Asexual Reproduction

• Fragmentation

– Is the separation of a parent plant into parts that develop into whole plants

– Is one of the most common modes of asexual reproduction

• In some species

– The root system of a single parent gives rise to many adventitious shoots that become separate shoot systems

Vegetative Propagation and Agriculture

• Humans have devised various methods for asexual propagation of angiosperms

Clones from Cuttings

• Many kinds of plants

– Are __________ reproduced from plant fragments called __________

Grafting

• In a modification of vegetative reproduction from cuttings

– A twig or bud from one plant can be grafted onto a plant of a closely related species or a different variety of the same species

Test-Tube Cloning and Related Techniques

• Plant biologists have adopted in vitro methods

– To create and clone novel plant varieties

• In a process called protoplast fusion

– Researchers fuse protoplasts, plant cells with their cell walls removed, to create hybrid plants

• Concept 38.4: Plant biotechnology is transforming agriculture

• Plant biotechnology has two meanings

– It refers to innovations in the use of plants to make products of use to humans

– It refers to the use of genetically modified (GM) organisms in agriculture and industry

Artificial Selection

• Humans have intervened

– In the reproduction and genetic makeup of plants for thousands of years

• Maize

– Is a product of artificial selection by humans

– Is a staple in many developing countries, but is a poor source of protein

• Interspecific __________ of plants

– Is common in nature and has been used by breeders, ancient and modern, to introduce new genes

Reducing World Hunger and Malnutrition

• Genetically modified plants

– Have the potential of increasing the quality and quantity of food worldwide

The Debate over Plant Biotechnology

• There are some biologists, particularly ecologists

– Who are concerned about the unknown risks associated with the release of GM organisms (GMOs) into the environment

Issues of Human Health

• One concern is that genetic engineering

– May transfer allergens from a gene source to a plant used for food

Possible Effects on Nontarget Organisms

• Many ecologists are concerned that the growing of GM crops

– Might have unforeseen effects on nontarget organisms

Addressing the Problem of Transgene Escape

• Perhaps the most serious concern that some scientists raise about GM crops

– Is the possibility of the introduced genes escaping from a transgenic crop into related weeds through crop-to-weed hybridization

• Despite all the issues associated with GM crops

– The benefits should be considered

Animation 39.1 Fertilization

Animation 39.2 The Effect of Interrupted Days and Nights

Video 39.1 Time-lapse of flower and fruit formation

Video 39.2 Time-lapse of white lily blooming, showing sexual parts

Video 39.3 Time-lapse of red lily blooming, showing sexual parts

Video 39.4 Pollen transfer by wind