Angiosperm Reproduction Study Notes

Focus on understanding reproduction and domestication of flowering plants.
Learning Outcomes:
- Characterize features of the angiosperm life cycle.
- Compare and contrast sexual and asexual reproduction in plants.
- Explain how breeding and genetic engineering are used to modify plants.

Definition: Angiosperms are seed plants with reproductive structures called flowers and fruits.
Characteristics:
- Most widespread and diverse group of plants.
- Classified under the single phylum known as Anthophyta (Greek: "anthos" means flower).

Pollination: Pollen grain is transferred from an anther to a stigma by biotic or abiotic vectors.
Fertilization: A pollen tube delivers sperm to an ovule, leading to the fertilization of an egg.
Seed Development: The fertilized ovule develops into a seed containing an embryo and a food supply.
Fruit Formation: The ovary develops into a fruit that encloses the seeds for dispersal.
Germination: The seed germinates, leading to the development of a new plant.

General Structure: A specialized shoot with leaves modified to form four types of floral organs:
- Sepals: Sterile parts that enclose the unopened flower.
- Petals: Sterile parts that attract pollinators.
- Stamens: Fertile parts that produce pollen, comprising a filament and an anther.
- Carpels/Pistils: Fertile parts producing ovules, consisting of an ovary (with ovules), style, and stigma.

Carpels (Megasporophylls):
- Contain one or more carpels; a single carpel is referred to as a simple pistil, while fused carpels constitute a compound pistil.
Ovary: Houses ovules; after fertilization, ovules convert into seeds while the ovary thickens into a fruit.

Stamens (Microsporophylls):
- Anthers have chambers called microsporangia (pollen sacs) that produce pollen.

Gametophyte Development:
- Reduced to a few cells and depends on the sporophyte for nutrients.
- Male gametophyte: Pollen grain, formed in the anther.
- Female gametophyte: Embryo sac, formed inside the megasporangium.
Pollination:
- Pollen grain transfers to stigma and germinates to produce a pollen tube.
- The tube grows down the style toward the micropyle, attracted by synergids.
Double Fertilization:
- One sperm fertilizes the egg to form a zygote, while the other fuses with polar nuclei to create endosperm.
Seed Development:
- Ovules develop into seeds and the ovary into fruit.

Double Fertilization ensures that endosperm only develops in ovules with fertilized eggs. The endosperm serves as food-storing tissue for the seed.
Angiosperms utilize coevolution as part of their reproduction strategy, where flowers and pollinators evolve in tandem.

A mature seed consists of:
- Dormant Embryo: Surrounded by stored food (endosperm) and protective layers.
- Nutritional Reserves: Stored proteins, oils, and starch.
The ovary develops into a fruit, which aids in seed dispersal by animals or wind.

Parts of Fruits:
- Exocarp: Outermost skin or covering.
- Mesocarp: Middle part of the fruit.
- Endocarp: Innermost part of the fruit.
- Together known as the pericarp.
Types of Fruits:
- Simple Fruits: Develop from a single or several fused carpels.
- Aggregate Fruits: Result from a single flower with multiple separate carpels.
- Multiple Fruits: Develop from a cluster of flowers (inflorescence).
- Accessory Fruits: Develop from floral tissues other than the ovary.

Importance of Seed Dispersal: Ensures competition for nutrients and light away from parent plants.
Methods of Dispersal:
- Water: Some seeds float, allowing for dispersal by water.
- Wind: Lightweight seeds can be carried by wind (e.g., dandelions).
- Animals: Many seeds are dispersed by animals that eat them.

Fragmentation: Parent separates into parts that develop into whole plants.
Adventitious Shoots: Root systems of parent plants may produce separate shoot systems.
Apomixis: Producing diploid seeds without fertilization, allowing for dispersal benefits.

Asexual Reproduction:
- Efficient in stable environments; clones inherit parent's genes but may risk local extinction due to uniform genetics.
Sexual Reproduction:
- Generates genetic variation, critical for evolutionary adaptation; however, only a fraction of seedlings survive.

Spatial separation: stamen and carpel on different flowers.
Temporal separation: stamen and carpel mature at different times.
Self-incompatibility: plants can reject own pollen or pollen from closely related individuals based on S-genes affecting pollen uptake.

Humans have influenced plant reproduction and genetics for millennia, notably through artificial selection.
Plant Breeding Techniques:
- Hybridization introduces genetic variation; mutagenesis used to induce beneficial traits.

Two meanings:
- General: Innovations utilizing plants for useful products.
- Specific: Utilization of GMOs in agriculture/industry.
Transgenic Organisms: Engineered to express genes from other species.

Addressing global hunger through increased production, improved nutritional quality, and environmental benefits.
Golden rice: Addresses vitamin A deficiencies in populations that rely on rice as a staple food.

Potential to reduce fossil fuel dependency by engineering high-yield crops for biofuel production, lowering greenhouse gas emissions.

Concerns largely arise from misinformation:
- No evidence of adverse health effects from GM plants.
- Risks of transgene escape into wild relatives.
- Example: Glyphosate-resistant Agrostis stolonifera hybridizing with wild types, raising concerns in 2003.