Sexual reproduction in Flowering Plants Flashcards
Panchanan maheshwari
Panchanan Maheshwari – Contributions to Botany
Born in November 1904 in Jaipur, Rajasthan.
Obtained D.Sc. from Allahabad University.
Inspired by Dr. W. Dudgeon, an American missionary teacher.
Specialized in embryology and tissue culture.
Popularized embryological characters in taxonomy.
Established Delhi University’s Botany Department as a research hub.
Pioneered work in test tube fertilization and intra-ovarian pollination.
Honored with Fellowship of the Royal Society (FRS) and Indian National Science Academy.
Played a key role in developing NCERT’s first Higher Secondary Biology textbooks (1964).
Pre-Fertilization Events in Flowering Plants
Floral primordium formation occurs before flowering.
Hormonal & structural changes initiate flower development.
Formation of inflorescences, leading to floral buds and flowers.
Differentiation of androecium (male) and gynoecium (female) structures.
structure of a stamen
The proximal end of the filament is attached o the thalamus or petal of the flower.
Parts of a Stamen:
Filament – Long, slender stalk attached to the thalamus or petal.
Anther – Terminal, generally bilobed structure containing pollen sacs;have 2 theca-dithecous.often a longitudianl groove run legthwise seperating the theca
Variability: Number and length of stamens vary among plant species
Sterile stamen: Called staminode (non-functional).
Attachment of Stamens:
Epipetalous – attached to petals (e.g., Brinjal).
Epiphyllous – attached to perianth (e.g., Lily).
Stamen Arrangement:
Polyandrous – Stamens free.
Monoadelphous – United into one bundle (e.g., China rose).
Diadelphous – United into two bundles (e.g., Pea).
Polyadelphous – United into more than two bundles (e.g., Citrus).
Variation in filament length seen in Salvia and Mustard.
anther
Anther:
Typically bilobed and dithecous (each lobe has two theca).
Contains four microsporangia (two in each lobe).
Microsporangia develop into pollen sacs, filled with pollen grains.
Layers of Microsporangium (in Transverse Section):
Epidermis – Protective outermost layer.
Endothecium – Helps in anther dehiscence.
Middle layers – Provide additional protection.
Tapetum – Innermost layer, nourishes developing pollen grains and may be bi-nucleate.
microsporogenesis
Microsporogenesis (Formation of Pollen Grains)
Sporogenous Tissue:
Compactly arranged homogeneous cells in the center of microsporangium.
Each cell is a potential pollen (microspore) mother cell (PMC).
Steps of Microsporogenesis:
Meiosis in PMC → Produces microspore tetrads (haploid).
Separation of Microspores → Individual pollen grains form.
Anther Maturation & Dehydration → Pollen grains are released upon dehiscence of the anther.
pollen grains
Structure of Pollen Grain
Pollen grains represent the male gametophyte.
Appearance:
Spherical, 25-50 µm in diameter.
Two-layered wall:
Exine – Outer hard layer made of sporopollenin (highly resistant, protects pollen).
Intine – Inner thin layer made of cellulose & pectin.
Special Features:
Sporopollenin: One of the most resistant organic materials; withstands extreme conditions.
Germ pores: Apertures in the exine where sporopollenin is absent; allow pollen tube formation.
2. Cells in Pollen Grain
Mature pollen grain contains two cells:
Vegetative cell:
Larger, with abundant food reserves.
Contains a large irregularly shaped nucleus.
Generative cell:
Smaller, spindle-shaped, with dense cytoplasm and a nucleus.
Divides mitotically to form two male gametes (before or after pollen release).
Pollen shedding stages:
60% of angiosperms release pollen at the 2-celled stage.
40% of species release pollen at the 3-celled stage (generative cell divides before release).
3. Pollen and Allergies
Pollen grains cause allergies in some individuals, leading to:
Asthma, bronchitis, and other respiratory disorders.
Parthenium (Carrot Grass):
Invasive species, entered India with imported wheat.
Causes pollen allergies due to its widespread presence.
Pollen Viability & Storage
Pollen grains are nutrient-rich; used in pollen tablets and syrups as food supplements.
Pollen viability (lifespan of pollen grains after release) varies:
Short-lived (e.g., Rice, Wheat) – viable for 30 minutes.
Long-lived (e.g., Rosaceae, Leguminosae, Solanaceae) – viable for months.
Pollen banks:
Pollen grains can be stored in liquid nitrogen (-196°C) for years.
Used in crop breeding programs (similar to seed banks).
pistil or gynoecium
Structure of Pistil (Gynoecium - Female Reproductive Organ)
Gynoecium consists of one or more pistils (carpels).
Monocarpellary – Single pistil.
Multicarpellary – More than one pistil, can be:
Syncarpous – Fused carpels (e.g., Mustard, Tomato).
Apocarpous – Free carpels (e.g., Lotus, Rose).
Parts of a Pistil:
Stigma – Pollen-receiving structure.
Style – Slender stalk connecting stigma to ovary.
Ovary – Basal swollen part containing ovules (megasporangia).
Ovules arise from the placenta inside the ovarian cavity.
Number of Ovules per Ovary:
One (e.g., Wheat, Paddy, Mango).
Many (e.g., Papaya, Watermelon, Orchids).
Post-Fertilization Changes:
Ovule → Seed.
Ovary → Fruit.
2. Placentation (Arrangement of Ovules in Ovary)
Marginal – Ovules on a ridge along the ventral suture (e.g., Pea).
Axile – Ovules attached to central placenta in a multilocular ovary (e.g., China rose, Tomato, Lemon).
Parietal – Ovules on inner ovary wall; ovary is one-chambered but may develop a false septum (e.g., Mustard, Argemone).
Free Central – Ovules attached to central axis, no septa (e.g., Dianthus, Primrose).
Basal – Single ovule at the base of the ovary (e.g., Sunflower, Marigold).
megasporangium(ovule) and megasporogenesis
Structure of the Megasporangium (Ovule) in Angiosperms
The ovule (megasporangium) is a small, specialized structure found within the ovary of the pistil. It is attached to the placenta by a stalk called the funicle.
Hilum: The region where the ovule and funicle are connected.
Integuments: One or two protective layers that surround the ovule.
Micropyle: A small opening in the integuments at the tip of the ovule, which facilitates the entry of the pollen tube during fertilization.
Chalaza: The basal region of the ovule, opposite the micropyle. It represents the point where nucellus and integuments are joined.
Nucellus: A mass of diploid (2n) nutritive tissue inside the ovule, which nourishes the developing female gametophyte/embryo sac.
Female Gametophyte/Embryo Sac: The haploid structure located within the nucellus that plays a crucial role in sexual reproduction by producing the egg cell and other accessory cells needed for fertilization.
2. Megasporogenesis: Formation of Megaspores
Megasporogenesis is the process in which a single diploid (2n) Megaspore Mother Cell (MMC) inside the nucellus of the ovule undergoes meiosis to form four haploid (n) megaspores.
The MMC is large, has dense cytoplasm, and a prominent nucleus.
Meiotic Division of MMC:
First meiotic division → produces two haploid cells.
Second meiotic division → results in four haploid megaspores.
Out of the four megaspores produced:
Only one remains functional and develops into the female gametophyte/embryo sac.
The other three megaspores degenerate.
This mode of embryo sac formation is called monosporic development because only one megaspore is functional and contributes to embryo sac formation.
3. Development of the Female Gametophyte/Embryo Sac
The functional haploid (n) megaspore undergoes a series of three consecutive mitotic divisions to form the 8-nucleate, 7-celled female gametophyte/embryo sac.
Step-by-step mitotic divisions:
The nucleus of the functional megaspore divides mitotically into two nuclei that migrate to opposite poles, forming the 2-nucleate stage.
A second mitotic division results in four nuclei, forming the 4-nucleate stage.
A third mitotic division produces eight nuclei, forming the 8-nucleate stage.
Cell walls are laid down around six of the eight nuclei, leading to the organization of the embryo sac into seven cells. The remaining two nuclei remain free in the central cell.
4. Structure of the Mature Female Gametophyte/Embryo Sac
At maturity, the embryo sac is an 8-nucleate but 7-celled structure, consisting of three distinct groups of cells:
(A) Micropylar End (Egg Apparatus – 3 Cells)
One Egg Cell (n): Participates in fertilization, fusing with one of the male gametes to form the zygote (2n).
Two Synergid Cells (n): Located next to the egg cell, these have special thickenings at their tips called the filiform apparatus, which helps guide the pollen tube into the embryo sac.
(B) Central Cell (1 Large Binucleate Cell)
The largest cell of the embryo sac, containing two free polar nuclei (each n).
After fertilization, the two polar nuclei fuse with the second male gamete, forming the triploid (3n) Primary Endosperm Nucleus (PEN), which develops into endosperm (nutritive tissue for the developing embryo).
(C) Chalazal End (3 Antipodal Cells)
Three Antipodal Cells (n): Located at the opposite end (chalazal end) of the embryo sac.
Function remains unclear, but they degenerate after fertilization.
key features
Key Features of Megasporogenesis and Embryo Sac Formation
Only one megaspore remains functional and develops into the female gametophyte/embryo sac (Monosporic Development).
Embryo sac is 8-nucleate but 7-celled at maturity.
Synergids guide the pollen tube using the filiform apparatus.
Polar nuclei fuse with a male gamete to form the endosperm (triploid, 3n).
Fertilization leads to the formation of a diploid zygote (2n), which develops into the embryo.
Ploidy Levels of Different Cells in the Ovule and Female Gametophyte/Embryo Sac
Ploidy Levels of Different Cells in the Ovule and Female Gametophyte/Embryo Sac
Structure Ploidy Level
Nucellus Diploid (2n)
Megaspore Mother Cell (MMC) Diploid (2n)
Functional Megaspore Haploid (n)
Egg Cell Haploid (n)
Synergid Cells Haploid (n)
Antipodal Cells Haploid (n)
Polar Nuclei (before fertilization) Haploid (n) each
Primary Endosperm Nucleus (after fertilization) Triploid (3n)
Zygote (after fertilization) Diploid (2n)
pollination
Pollination: Transfer of pollen grains from the anther to the stigma of a pistil.
Types of Pollination:
Autogamy (Self-Pollination):
Pollen transferred within the same flower.
Requires synchrony in pollen release and stigma receptivity.
Occurs in:
Chasmogamous flowers: Open flowers with exposed anthers and stigma.
Cleistogamous flowers: Flowers do not open, ensuring self-pollination (e.g., Viola, Oxalis, Commelina).
Geitonogamy:
Pollen from one flower to the stigma of another flower on the same plant.
Functionally cross-pollination, but genetically self-pollination.
Xenogamy (Cross-Pollination):
Pollen transferred from anther of one plant to stigma of another plant.
Ensures genetic recombination.
2. Agents of Pollination
Abiotic (Non-Living) Agents:
Wind Pollination (Anemophily):
Common in grasses (e.g., maize, wheat).
Flowers:
Light, non-sticky pollen grains carried by wind.
Well-exposed stamens for easy pollen dispersal.
Large, feathery stigma to trap airborne pollen.
Single ovule per ovary; inflorescence with numerous flowers (e.g., corn cob tassels).
Water Pollination (Hydrophily):
Rare in flowering plants (~30 genera, mostly monocots).
Two types:
Surface Hydrophily: Pollen floats on water surface (e.g., freshwater-Vallisneria and hydrilla).
Submerged Hydrophily: Pollen released inside water (e.g.,marine seagrasses-Zostera).
Features:
Pollen protected by mucilaginous covering.
Flowers not showy, no nectar production.
Biotic (Living) Agents:
Insects-moths,wasps,beetles,flies; birds(hummingbirds and sunbirds), bats,reptiles(garden lizard and gecko lizard),arboreal rodents
Majority of flowering plants rely on biotic agents for pollination.
3. Features of Wind and Water-Pollinated Flowers
Not brightly colored (colorful petals attract insects, not needed here).
Do not produce nectar (nectar attracts pollinators, unnecessary for wind/water pollination).
pollination by animals
Flashcards on Pollination by Animals and Outbreeding Devices
1. Pollination by Animals (Zoophily)
- Majority of flowering plants use animals as pollinators.
- Common pollinating agents:
- Insects: Bees, butterflies, flies, beetles, wasps, ants, moths.
- Birds: Sunbirds, hummingbirds.
- Mammals: Bats, primates (e.g., lemurs), arboreal rodents.
- Reptiles: Gecko lizards, garden lizards.
- Adaptations of Animal-Pollinated Flowers:
- Large, colorful, fragrant flowers rich in nectar.
- Small flowers occur in clusters (inflorescences) to attract pollinators.
- Flies and beetles are attracted to foul-smelling flowers.
- Sticky pollen grains attach to pollinators’ bodies.
- Special Pollination Mechanisms:
- Amorphophallus: Provides a safe place for insects to lay eggs.
- Yucca and Moth: Mutualistic relationship—moth lays eggs in the ovary locule and pollinates the flower.
2. Pollen/Nectar Robbers
- Some insects consume pollen/nectar without pollinating.
- These insects are called pollen/nectar robbers.
- Only those that come in contact with both anthers and stigma bring about pollination.
3. Outbreeding Devices
- Why prevent self-pollination?
- Inbreeding depression reduces genetic diversity and vigor.
- Plants have evolved mechanisms to encourage cross-pollination.
- Mechanisms to Prevent Self-Pollination:
1. Pollen Release and Stigma Receptivity Mismatch:
- Pollen is released before stigma matures or vice versa.
- Prevents autogamy (self-pollination).
2. Anther and Stigma Placement Differences:
- Prevents self-pollination by spatial separation.
3. Self-Incompatibility:
- Genetic mechanism prevents self-pollen from germinating or growing in the pistil.
4. Unisexual Flowers:
- Monoecious Plants (e.g., Maize, Castor): Male and female flowers on the same plant, prevents autogamy but not geitonogamy.
- Dioecious Plants (e.g., Papaya): Male and female flowers on separate plants, preventing both autogamy and geitonogamy.
pollen pistil interaction
Flashcards on Pollen-Pistil Interaction & Artificial Hybridisation
1. Pollen-Pistil Interaction
- Pollination does not ensure fertilisation; the right type of pollen must land on the stigma.
- The pistil recognises pollen as either:
- Compatible (right type, same species) → Accepted, post-pollination events occur.
- Incompatible (wrong type, different species/self-incompatible) → Rejected, prevents germination or pollen tube growth.
- This recognition is mediated by chemical interactions between pollen and pistil components.
- Pollen tube formation:
- After pollination, pollen germinates on stigma and forms a pollen tube through one of its germ pores.
- Pollen tube grows through the stigma and style, reaching the ovary.
- Pollen tube entry:
- Enters ovule through the micropyle.
- Guided by the filiform apparatus of the synergids.
- Types of Pollen at Shedding:
- Two-celled pollen (Vegetative cell + Generative cell): Generative cell divides into two male gametes during pollen tube growth.
- Three-celled pollen: Already contains two male gametes.
- Importance:
- Understanding pollen-pistil interaction helps breeders manipulate fertilisation in hybrid production.
3. Artificial Hybridisation in Crop Improvement
- Used by breeders to cross different species/genera to create superior varieties.
- Ensures only desired pollen fertilises the stigma.
- Two Key Techniques:
1. Emasculation (For Bisexual Flowers):
- Removal of anthers from flower buds before dehiscence (using forceps).
2. Bagging (For Both Bisexual & Unisexual Flowers):
- Covering flowers with butter paper bags to prevent contamination by unwanted pollen.
- After stigma attains receptivity, dust it with desired pollen.
- Rebag the flower and allow fruit development.
double fertilization and post fertilization events
Flashcards on Double Fertilisation & Post-Fertilisation Events
1. Double Fertilisation (Unique to Flowering Plants)
- Process:
- Pollen tube enters synergid → releases two male gametes.
- One male gamete fuses with the egg cell nucleus → Syngamy → forms diploid zygote.
- Other male gamete fuses with two polar nuclei → Triple fusion → forms triploid Primary Endosperm Nucleus (PEN).
- Terminology:
- Double fertilisation = Syngamy + Triple Fusion.
- Unique to angiosperms (flowering plants).
- Post-fusion events:
- Zygote → develops into the embryo.
- Primary Endosperm Cell (PEC) → develops into endosperm (nutritive tissue).
2. Post-Fertilisation Events
- Includes endosperm and embryo development, ovule maturation into seed, and ovary maturation into fruit.
A) Endosperm Development (Precedes Embryo Development)
- Primary Endosperm Cell (PEC) divides repeatedly → forms triploid endosperm tissue (stores nutrients).
- Types of Endosperm Development:
1. Free-nuclear endosperm → PEN undergoes nuclear divisions without cell wall formation (e.g., coconut water = free nuclei).
2. Cellular endosperm → cell walls form later (e.g., coconut kernel).
- Fate of Endosperm:
- Completely consumed before seed maturation (e.g., pea, groundnut, beans).
- Persists in mature seed and used during germination (e.g., castor, coconut, cereals like wheat, rice, maize).
3. Embryo Development
- Occurs at micropylar end of the embryo sac (where zygote is located).
- Stages of Embryogeny:
1. Zygote → Proembryo.
2. Globular stage → Heart-shaped stage → Mature embryo.
A) Dicotyledonous Embryo Structure
- Embryonal axis with two cotyledons.
- Epicotyl (above cotyledons) → terminates in plumule (stem tip).
- Hypocotyl (below cotyledons) → terminates in radicle (root tip, covered by root cap).
B) Monocotyledonous Embryo Structure
- Single cotyledon (Scutellum), located laterally to embryonal axis.
- Epicotyl has shoot apex + leaf primordia enclosed in coleoptile.
- Radicle and root cap enclosed in coleorhiza.
4. Observing Embryos in Seeds (Simple Experiment)
- Materials: Seeds of wheat, maize, peas, chickpeas, groundnut.
- Procedure:
- Soak seeds in water overnight.
- Split them open and observe embryo and seed structures.
post fertilixation events-seed and fruit formation
Flashcards on Seed & Fruit Formation
1. Seed: The Final Product of Sexual Reproduction
- Definition: A fertilized ovule enclosed within a fruit.
- Structure:
- Seed coat(s) (formed from hardened integuments).
- Embryo (consisting of cotyledon(s) and embryo axis).
- Micropyle (small pore in seed coat for water and oxygen entry).
- Types of Seeds:
1. Non-albuminous seeds: No residual endosperm (e.g., pea, groundnut).
2. Albuminous seeds: Endosperm persists (e.g., wheat, maize, barley, castor).
3. Perisperm: Persistent nucellus remnants (e.g., black pepper, beet).
2. Seed Dormancy & Germination
- Maturation process:
- Water content reduces to 10-15%.
- Metabolic activity slows → Dormancy (inactive embryo).
- When conditions are favorable (water, oxygen, suitable temperature), the seed germinates.
3. Fruit Formation & Types
- Transformation Process:
- Ovules → Develop into seeds.
- Ovary → Develops into fruit.
- Ovary wall → Develops into pericarp (fruit wall).
- Types of Fruits:
1. True Fruits: Develop only from the ovary (e.g., mango, orange, guava).
2. False Fruits: Develop from ovary + other floral parts (e.g., apple, strawberry, cashew).
3. Parthenocarpic Fruits: Develop without fertilization (e.g., banana).
- Induced artificially using growth hormones → Produces seedless fruits.
4. Importance & Advantages of Seeds
- Independence from Water: Fertilization and seed formation occur without water.
- Seed Dispersal & Colonization: Seeds travel to new habitats, promoting plant distribution.
- Food Reserves: Nourish the young seedling until it can photosynthesize.
- Protection: The hard seed coat shields the embryo.
- Genetic Variation: Seeds arise from sexual reproduction, promoting genetic diversity.
5. Seed Viability & Longevity
- Variable lifespan:
- Some seeds lose viability within months.
- Many species have seeds that remain viable for years.
- Some seeds remain viable for hundreds to thousands of years:
- Lupinus arcticus → 10,000 years (Arctic Tundra).
- Phoenix dactylifera (Date Palm) → 2,000 years (Excavated from King Herod’s palace).
6. Massive Reproductive Capacity in Plants
- Questions to consider:
- How many eggs in an embryo sac?
- How many embryo sacs in an ovule?
- How many ovules in an ovary?
- How many ovaries in a flower?
- How many flowers in a tree?
- Examples of high seed production:
- Orchid fruits → Contain thousands of tiny seeds.
- Parasitic plants (e.g., Orobanche, Striga) → Produce large numbers of seeds.
- Ficus tree → Develops from a tiny seed and produces billions of seeds over its lifetime.
apomixis and polyembryony
Flashcards on Apomixis & Polyembryony
1. Apomixis: Asexual Seed Formation
- Definition: Formation of seeds without fertilization (e.g., Asteraceae, grasses).
- Mechanism:
- Diploid egg cell forms without reduction division and develops into an embryo.
- Nucellar cells around the embryo sac divide and develop into additional embryos (Citrus, Mango).
- Relation to Asexual Reproduction:
- Mimics sexual reproduction but does not involve fertilization.
- Produces genetically identical offspring (clones).
2. Polyembryony: Multiple Embryos in One Seed
- Definition: Presence of more than one embryo in a single seed.
- Causes:
- Additional nucellar cells develop into embryos (Citrus, Mango).
- Example:
- Orange seeds contain multiple embryos of various sizes & shapes.
3. Importance of Apomixis in Hybrid Seed Industry
- Hybrid Crops:
- High productivity, but hybrid seeds must be produced every year.
- Hybrid progeny undergo segregation, losing hybrid characters.
- Apomixis in Hybrid Crops:
- Prevents segregation, ensuring genetic uniformity in offspring.
- Farmers can reuse hybrid seeds without buying new seeds annually.
- Research Focus:
- Understanding genetics of apomixis.
- Transferring apomictic genes into hybrid crops for cost-effective farming.
answer to questions to consider
Answers to Questions on Plant Reproductive Capacity
1️⃣ How many eggs are present in an embryo sac?
One egg cell per embryo sac.
2️⃣ How many embryo sacs are present in an ovule?
One embryo sac per ovule.
3️⃣ How many ovules are present in an ovary?
The number varies by species:
Wheat, rice, maize → One ovule per ovary.
Pea, tomato, orange → Multiple ovules per ovary.
4️⃣ How many ovaries are present in a typical flower?
A flower generally has one ovary, but some flowers have multiple ovaries (e.g., raspberry).
5️⃣ How many flowers are present on a tree?
The number varies widely depending on species, age, and environmental conditions.
Small trees (e.g., guava, lemon) → Hundreds of flowers.
Large trees (e.g., mango, banyan, ficus) → Thousands to millions of flowers over their lifetime.
💡 Key Insight: A single large tree (like Ficus) can produce billions of seeds over its lifespan, highlighting the massive reproductive potential of flowering plants.
summary
Here are the additional flashcards covering the missing points:
Structure:
- A typical anther is bilobed, dithecous, and tetrasporangiate.
- Each anther lobe contains two microsporangia, making a total of four microsporangia per anther.
- Microsporangia develop into pollen sacs that produce pollen grains.
Wall Layers of Microsporangium:
1. Epidermis – Outermost protective layer.
2. Endothecium – Provides mechanical support; helps in dehiscence (splitting) of the anther.
3. Middle Layers – Degenerate to provide nutrients.
4. Tapetum – Nourishes developing pollen grains; has binucleate cells.
Sporogenous Tissue:
- Located at the center of the microsporangium.
- Cells undergo meiosis (microsporogenesis) to produce haploid microspores, which develop into pollen grains.
Structure of Pollen Grain:
- Two-layered wall:
1. Exine – Thick outer layer made of sporopollenin (highly resistant, protects pollen).
2. Intine – Inner thin layer made of cellulose and pectin.
- Germ Pores: Openings in exine that allow pollen tube formation.
Development & Shedding:
- At the time of shedding, pollen grains may be:
1. Two-celled stage: Vegetative cell (large, provides nourishment) + Generative cell (divides to form two male gametes).
2. Three-celled stage: Vegetative cell + Two male gametes (already formed).
Main Components of Ovule:
- Funicle – Stalk that attaches the ovule to the ovary.
- Integuments – Protective layers that form the seed coat.
- Micropyle – Small opening in the integuments; allows water, air, and pollen tube entry.
- Nucellus – Central mass of cells; provides nourishment to the developing embryo sac.
- Archesporium – A single cell in the nucellus that forms the megaspore mother cell.
Development of Female Gametophyte (Embryo Sac):
- The megaspore mother cell undergoes meiosis, forming four haploid megaspores.
- Only one megaspore survives and undergoes mitotic divisions to form the 7-celled, 8-nucleate embryo sac.
- Zygote Formation: The zygote forms at the micropylar end.
- Proembryo Stage: First few cell divisions of the zygote.
- Globular Stage: Embryo takes a spherical shape.
- Heart-shaped Stage: Two cotyledons begin to form (in dicots).
- Mature Embryo Stage: Fully developed embryo with cotyledons, epicotyl, and hypocotyl.
Dicot Embryo Structure:
- Two cotyledons (store nutrients).
- Epicotyl (above cotyledon level, develops into shoot).
- Hypocotyl (below cotyledons, develops into root).
- Radicle (future root, covered by root cap).
Monocot Embryo Structure:
- Single cotyledon (Scutellum) – Transfers nutrients from endosperm.
- Coleorhiza – Protects the root.
- Coleoptile – Protects the shoot.
Apomixis:
- Formation of seeds without fertilization.
- Occurs in some grasses and citrus plants.
- Produces genetically identical offspring.
- Important in horticulture and agriculture as it maintains desirable traits.
Polyembryony:
- Formation of multiple embryos in one seed.
- Seen in citrus and mango.
- Results in more than one seedling from a single seed.
