chapter 30

Reproduction and Domestication of Flowering Plants

Chapter Overview

  • Exploration of unique features of the angiosperm life cycle

    • Flowers

    • Double Fertilization

    • Fruits

  • Description of asexual and sexual reproduction of plants

  • Explanation of crop modification through genetic engineering and breeding

Reminders

  • Padlet due tonight

  • Exam on March 23

  • Quiz due Friday

Key Concepts and Definitions

1. Drought Stress and Water Blockage

  • Cavitation: A blockage in the water channels of the xylem caused by drought stress or freezing conditions.

    • Other terms provided:

    • Excavation

    • Embolism

    • Cabolicism

2. Transpiration Rate Regulation

  • True or False: The rate of transpiration is regulated by stomata.

3. Plant Sugar Dynamics

  • Sink: An organ that is a net consumer or storer of sugar, such as a tuber or bulb.

    • Other options included:

    • Source

    • Cavity

    • Vessel Element

4. Role of Rhizobacteria and Endophytes

  • These enhance plant growth by:

    • Producing growth-stimulating chemicals

    • Producing antibiotics that protect roots from disease

    • Absorbing toxic metals

    • Making nutrients more bioavailable to roots

5. Contrast in Mycorrhizal Types

  • Ectomycorrhizae vs. Arbuscular Mycorrhizae: Differences in structure and function, specifically in symbiotic relationships with plants.

Unique Features of the Angiosperm Life Cycle

1. Flowers

  • Anther: The part of the stamen where pollen is produced.

2. Double Fertilization

  • Involves formation of:

    • Pollen grains (n)

    • Embryo sac (n)

    • Seed coat (2n)

    • Endosperm (3n)

3. Fruits

  • Structures that evolve from the ovary and enclose seeds.

4. The 3 F’s: Flowers, Double Fertilization, and Fruits

Alternation of Generations

Overview

  • Plant life cycles alternate between multicellular haploid (n) and multicellular diploid (2n) generations.

    • Diploid sporophytes (2n) produce spores (n) by meiosis, leading to haploid gametophytes (n).

    • Gametophytes produce gametes (n) by mitosis.

    • Fertilization results in a new sporophyte.

In Angiosperms

  • The sporophyte is the dominant generation; gametophytes are reduced and nutrient-dependent.

  • Characterized by flowers, double fertilization, and fruits.

Flower Structure and Function

  • Four Floral Organs: Carpels (female), Stamens (male), Petals, and Sepals.

    • Floral organs are attached to a stem part called the receptacle.

  • Pistil: A single carpel or a group of fused carpels.

  • Stamen: Comprises a filament and anther.

Complete vs. Incomplete Flowers

  • Complete Flowers: Contain all four floral organs.

  • Incomplete Flowers: Lack one or more floral organs, such as male or female features.

  • Clusters of flowers are termed inflorescences.

Flower Formation and Development

  • Floral development synchronizes with outbreeding.

  • Transition from vegetative to reproductive growth is initiated by environmental and internal signals.

  • Floral identity genes regulate flower formation; mutations can lead to abnormal development.

ABC Hypothesis

  • Explains flower organ formation through three classes of organ identity genes:

    • A genes: Produce sepals and petals.

    • B genes: Produce petals and stamens.

    • C genes: Produce stamens and carpels.

  • Plant individuals lacking A, B, or C gene activity will show abnormal floral development.

Major Stages of the Angiosperm Life Cycle

  • Gametophyte development (female and male)

  • Pollination and double fertilization

  • Seed development and embryo formation

Double Fertilization Explained

  • Occurs when two sperm from a pollen grain fertilize the egg cell and combine with polar nuclei.

  • Results in:

    • Zygote (2n)

    • Endosperm (3n)

  • Ensures the endosperm develops only when fertilization occurs.

Seed Development and Structure

1. Mature Seed Components

  • Consists of a dormant embryo, stored food, and protective layers.

    • Endosperm and embryo development follow specific sequences:

    • Endosperm develops before embryo in most monocots and some eudicots.

2. Seed Germination

  • Begins when environmental conditions are optimal.

  • Imbibition: Uptake of water that initiates germination.

    • The radicle (embryonic root) emerges first, followed by shoot tip.

Vegetative Growth and Flowering

  • Growth arises from the shoot apical meristem.

  • Environmental cues convert shoot apical meristems into floral meristems.

Fruit Structure and Function

  • A fruit is a mature ovary, aiding in seed dispersal.

  • Classification includes:

    • Dry or fleshy fruits

    • Simple, aggregate, or multiple fruits

    • Accessory fruits contain additional floral parts along with ovaries.

Seed Dispersal Mechanisms

  • Dispersal occurs via:

    • Water

    • Wind with adaptations for buoyancy or structure

    • Animals through ingestion or attachment

Reproductive Strategies in Flowering Plants

Sexual vs Asexual Reproduction

  • Many angiosperm species can reproduce both ways.

  • Sexual Reproduction: Creates genetic diversity.

  • Asexual Reproduction: Results in clones, stable in consistent environments.

Mechanisms of Asexual Reproduction

  • Fragmentation and apomixis are common methods.

  • Apomixis: Asexual seed production from diploid cells.

Advantages and Disadvantages

  • Asexual benefits in stable environments; risk in variable conditions.

  • Sexual reproduction fosters genetic variation but fewer seedlings survive.

Self-Fertilization and Incompatibility

  • Some plants self-fertilize; mechanisms exist to prevent selfing in many angiosperms.

  • Self-incompatibility is when a plant rejects its own pollen.

Plant Breeding and Genetic Engineering

  • Human intervention in plant reproduction spans centuries.

  • Breeding through hybridization introduces desirable traits.

  • Genetic engineering techniques utilize transgenic organisms.

    • Example: Antifreeze gene from Arctic flounder introduced into strawberries for freeze resistance.

Genetic Perspectives on Food Production

  • Genetically modified plants may enhance food quality and yield, such as:

    • Bt crops that produce insecticidal proteins

    • Herbicide-resistant plants

  • Example of “Golden Rice” addressing vitamin A deficiency, and transgenic cassava enhancing nutrients and reducing toxins.

Conclusion

  • The chapter discusses key aspects of angiosperm reproduction, highlighting their complexity and importance in both natural ecosystems and agricultural practices.