Plant Reproduction and Diversity

Angiosperm Reproduction: Double Fertilization and Endosperm

• Central Cell:

  • Large central cell with two haploid nuclei.
  • Formed after mitosis without cytokinesis.
  • Significant for double fertilization.

• Other Cells:

  • Antipodal Cells: Three cells that do nothing.
  • Egg: The middle cell at the bottom near the opening of the megagametophyte.
  • Synergids: Two flanking cells beside the egg. They release chemical signals to attract the pollen tube.

• Pollen Tube and Fertilization:

  • Pollen tube grows into one of the synergids, releasing two haploid sperm.
  • One sperm fuses with the egg to form a diploid zygote.
  • The other sperm combines with the two haploid nuclei of the central cell to form a triploid cell.

• Endosperm:

  • The triploid cell resulting from fertilization is called the endosperm.
  • It grows mitotically and surrounds the embryo.
  • Provides nutrition for the embryo before the seed sprouts.

• Seed and Fruit Development:

  • The ovule becomes the seed.
  • The ovary gives rise to the fruit.

Challenges in Perfect Flowers: Self-Pollination

• Perfect Flowers:

  • Flowers like lilies, daffodils, and tulips have both male (pollen) and female parts.

• Self-Pollination Problem:

  • Pollen can easily pollinate the same flower or other flowers on the same plant.
  • This reduces genetic variation, undermining the purpose of sexual reproduction.
  • It's like asexual reproduction, which is less efficient than methods like cuttings or runners.

• Homozygosity:

  • Self-pollination can increase homozygosity, concentrating deleterious recessive alleles.
  • In diploid organisms, a good allele can compensate for a bad one, but interbreeding increases the chances of inheriting two bad alleles.

• Self-Fertilization Prevention:

  • Most flowering plants have mechanisms to prevent self-fertilization.
  • Mendel's pea plants were an exception because they readily self-pollinate, allowing him to create true-breeding strains.

Mechanisms to Prevent Self-Fertilization

• Pollination vs. Fertilization:

  • Pollination: Pollen is delivered to the flower.
  • Fertilization: Pollen tube grows, sperm are generated, and double fertilization occurs.

• Physical Separation:

  • Dioecious Plants: Separate male and female flowers on different plants (two houses).
    • Example: Date palms.
  • Monoecious Plants: Imperfect flowers (male and female) on the same plant (one house), or male and female flowers are separated on the same plant (e.g., zucchini).

• Genetic Self-Incompatibility:

  • Molecular mechanisms prevent pollen tube growth after pollination.
  • Pollination occurs when pollen lands on the stigma.
  • Plants inhibit pollen tube growth to prevent self-fertilization.

• Molecular Fingerprint

  • A locus on a plant chromosome controls surface proteins (determinant genes).
  • Proteins on the pollen grain and stigma must match and dock; made by surface of the pollen grain and the carpal.
  • If the proteins match (from the same sporophyte), a signal cascade inhibits pollen tube growth.
  • If they don't match, the pollen tube grows.
  • The genetics are so exquisite that this will distinguish between individuals of the same species.
  • These are like fingerprints, so two apple trees nearby cannot self-pollinate, self-fertilize.

Balancing Separation and Reproduction

• Extreme Separation:

  • If you are male and get transported somewhere far, without a female plant you will go extinct.

• Preventing Self-Pollination/Fertilization as a Balancing Act:

  • Balancing complete separation, and finding out which methods to use best.

Double Fertilization Revisited

• Process:

  • Synergids attract the pollen tube.
  • Generative cell divides to produce sperm.
  • One sperm combines with the central cell to form the triploid endosperm.
  • The other combines with the egg to form the diploid zygote.

• Key Traits:

  • Egg retained in parent gametophyte tissues (streptophyte).
  • Embryo initially retained in parent gametophyte tissues (embryophyte).

• Seed Structure:

  • Ovule turns into the seed.
  • Seed surrounded by triploid endosperm.
  • Gymnosperms: Seed surrounded by nucellus (megasporangium).
  • Seed inside integuments (modified leaves).

• Fruit Formation:

  • Ovary enlarges and becomes the fruit.

Fruit Function: Seed Dispersal

• Purpose of Fruit:

  • Not protection (the seed is already protected).
  • Distribution or dispersal of the seed.

• Examples of Seed Dispersal:

  • Explosions (e.g., violet flower seeds).
  • Wind dispersal (e.g., dandelion fluff).
  • Animal dispersal (e.g., burs sticking to fur).
  • Water dispersal (e.g., coconuts).

• Technical Definition of Fruit:

  • Modified ovary wall that disperses the seed.

• Examples Evaluation:

  • Tomato: Fruit.
  • Pear: Fruit.
  • Potato: Not a fruit (storage organ).
  • Banana: Fruit (remnants of seeds in commercial bananas).
  • Cucumber: Fruit.
  • Snow Pea: Fruit (pea pod is the fruit).
  • Sunflower Seed: Not a fruit (the husk and part of the sunflower are the fruit).
  • Almond: The hard shell is the fruit, the almond itself is the seed.
  • Peanut: The husky part is the fruit, then the seeds are inside.

Seed Dormancy and Germination

• Seed as a Resting Structure:

  • It's ready to germinate when conditions are right.

• Regulation of Germination:

  • Tightly regulated to prevent sprouting at disadvantageous times.
  • Under hormonal growth control.

• Key Hormones:

  • Abscisic Acid (ABA): Promotes seed dormancy.
  • Gibberellins (GA): Trigger seed sprouting.
  • The balance between ABA and GA determines dormancy or germination.

• Hormone Imbalance:

  • Scale Tip: As abscisic acid tips, its way inhibiting, cascading, and pushing it to the down end.

Agricultural Significance of Seed Sprouting

• Problem of Vivipary:

  • Seeds sprout while still attached to the parent plant. Causes losses because it will be mush compost and not wheat.
  • It is fine in mangroves, just not economically useful.

• Economic Impact:

  • Ruins crops like wheat, soybeans, and corn.
  • Requires methods to prevent sprouting and maintain seed dormancy.

• Solutions:

  • Spraying hormones that shift balance towards abscisic acid.

Angiosperm vs. Gymnosperm Life Cycles

• Structural Differences:

  • Angiosperms have an ovary that becomes a fruit.
  • Gymnosperms do not have fruits.

• Similarities in pollen grain:

  • Microgametophyte does not have antheridia.

• Archegonia

  • Gymnosperms have archegonia in the megagametophyte from meiosis.

Angiosperm Diversity and Dominance

• Species Count:

  • 300,000 to 450,000 species of angiosperms.
  • Far more than mosses (15,000), ferns (12,000), or gymnosperms (1,000).

• Mesozoic Era:

  • The last time gymnosperms were dominant

• Evolutionary Fitness:

  • Number of offspring produced is biggest determination factor, not size or age.

• Less Energetically Expensive.

  • There's a lot of stuff, like ATP, burned in cell divisions.
  • Angiosperms have fewer cells to make structures, unlike big complicated gymnosperms.

• Flowers May Abort: Angiosperms have flexibility:

  • Gymnosperms commit to reproduction a year in advance, cannot be changed.
  • Angiosperms are free to put up and abort ovules as the reproductive conditions seem right and wrong, respectively.

• Mutualism:

  • Angiosperms have elaborate mutualisms, such as symbiotic relationship, with pollinators to get help with their life cycle to create new species.

Pollination Strategies in Angiosperms

• Animal Pollinators Role : Mutualism with Pollinators

  • Wind Pollination: Conifers and others spend resources into producing huge pollen clouds but is not necessarily going to be delivered to flowers, and might not even be the same kind (ABIOTIC).
  • Hummingbird: Manipulation of animals, high specificity (BIOTIC).

• Animal Attraction and Morphology Adaptation:

  • Morphology: Specialization coevolved with certain pollinators.
  • Reward: Flowers produce food like nectar with almost all the diet consists of of nectar.
  • Choice: Being attractive to one animal will make you less attractive to another animal.
    Tube allows a flower to hold more nectar than if the flower is just flat, so it's more efficient.
    They are specializing to a smaller group.
    Bees and butterflies are more plentiful.

• Ultraviolet Vision:

  • Insects see ultraviolet light, revealing patterns on flowers that guide them towards pollen.

• Pollinator Constancy:

  • Generalists: Pollinators are not going to one species, but to the prettiest flower they can find.
  • Dead End: May bring the wrong pollen to flower.
    Generalists are better than wind.
  • Super Specialists: Guarantees they are going to plant of the correct species.

• Specialist and Generalist Comparison:

  • The flowers are only blooming one time of the year, doesn't really care what the animal finds.
    They just know the nectar is always available.

Specialized Pollination: Nectar Bats

• Bats that eat nectar, nocturnal flower, curves to dust it with pollen.

Pollination Oddities, Mimic

• Deception by Orchids: Orchids have rewards, then take back the rewards. They also trick into thinking this is going to reward, but it disappears.
  Food deception, trick the animal using signal without the reward.
  Sexual deception, flowers that looked liked the mate or the wasp or another pollinator. Takes advantage
  How the flower knows what the bee looks like goes through coevolution.
  Steps:
  *Leaf turns to odor.
  *The mates that don't look the same get punished, the same get rewarded
  *Is the insect going to adapt.

• Manipulation of Behavior. 853: The relationship Between Animals has Led to Big Radiations

• Carnivorous Plants:

  • Poor adaptation to all soil types.

  • In nitrogen depleted soil: Attracts animal pollinators and animals to trap.

  • Doesnt want to Eat Pollinators:
    Has to attract different animal attractants and different types.

    • Example water: Smells Like Nasty

Phylogeny Quick Review

• Angiosperms mostly belong to 2 groups:
  97% are made of eucots and monocots.

*Important Plants to Eat:
Rice, Cononut, Wheat, Corn, Maze, Potato, Sweet Potato, Cassava, Sugarcane, Sugar beet, Soy Bean, Bean, and Banana.
75% of people of World Population Eat Rice as Half of Their Calories Daily
Also for Medicine, Drugs, and the environment.
The Environment: Mudslide, roots of the tree help to hold the soil together.

# Roots

• Monocots have fibery roots: 623. pull the grass
• Dicot (2) cot (Catalean: 633) has Taproots.
  *Also app called SEEK: Can point the camera at an organism to recognize (Only in good picture quality.

The Tree

*Euocots comprise 75% of Plants, versus monocots on 22%%.
*Monocots: Grasses, bamboo, palms, and beautiful flowers.
Aquatic Grass: The oldest genoytpe organism (has ten thousand years of replication.

*Grass Glade (Called Paceae) comprises 70% of crops

*Eudicot, 75 %, trees except for for pine and palm, Rafflesia (biggest single floweres (Is parasitic.
* 670 Video with trash Rafflesia, and Rhizanthes loit which is family.
* Ghost flower native to pgh that grows underground and is 855.21