Plant Growth Stages and Germination

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Questions and Answers

What is the primary function of the tube nucleus in the pollen grain?

To divide into two male gametes

To provide nutrients for the pollen grain

To guide the growth of the pollen tube (correct)

To remain dormant during the germination process

During megasporogenesis, how many megaspores remain functional after the meiotic division of the megasporocyte?

Three

Four

One (correct)

Two

Which part of the embryo sac is formed from the three cells at the micropylar end?

Polar nuclei

Zygote nucleus

Synergids and egg cell (correct)

Antipodal cells

What happens to the generative nucleus during the process of fertilization?

It divides into two male gametes Signup and view all the answers

Which of the following is an example of a self-pollinated crop?

Peach Signup and view all the answers

What is the completed structure of the matured embryo sac?

7-celled and 8-nucleated Signup and view all the answers

In cross-pollination, what does the term 'heterogamy' specifically refer to?

Transfer of pollen between flowers of different plants Signup and view all the answers

What is the outcome of fertilization?

The fusion of male and female gamete nuclei Signup and view all the answers

What is the primary outcome of double fertilization in flowering plants?

Development of endosperm and a zygote Signup and view all the answers

What happens to the synergids if the egg cell is fertilized?

They undergo disintegration immediately Signup and view all the answers

What is the fate of the ovary after fertilization?

It becomes the fruit Signup and view all the answers

Which of the following is true regarding seed dormancy?

Seeds remain viable but do not germinate under favorable conditions Signup and view all the answers

Which floral parts will typically wither and drop off after fertilization?

Sepals, petals, and stamens Signup and view all the answers

What is defined as the process of aging in plants that leads to death of the whole plant?

Complete senescence Signup and view all the answers

What do the integuments develop into after fertilization?

Seed coat Signup and view all the answers

What distinguishes senescence from seed dormancy in plants?

Senescence involves gradual decay and death of plant parts Signup and view all the answers

Which pigment is responsible for both light absorption and floral induction in plants?

Phytochrome Signup and view all the answers

What type of growth is characterized by the emergence of both cotyledons and hypocotyls above the ground?

Epigeal growth Signup and view all the answers

During which stage does a plant experience vigorous growth but cannot undergo reproductive type of growth?

Juvenile stage Signup and view all the answers

What is a key characteristic of the transition stage in plant development?

Receptivity to external conditions Signup and view all the answers

What process refers to the formation of pollen grains within a microsporangium?

Microsporogenesis Signup and view all the answers

What type of tissues undergo meiotic divisions to form haploid microspores?

Sporogenous tissue Signup and view all the answers

Which of the following is not a characteristic of the juvenile stage of plant growth?

Induced to reproductive growth Signup and view all the answers

In which phase does a plant begin producing flowers, fruits, and seeds?

Maturity stage Signup and view all the answers

Which type of dormancy is characterized by both physiological and physical blocks?

Double dormancy Signup and view all the answers

What is the purpose of stratification in seed germination?

To expose seeds to varying temperatures to break dormancy Signup and view all the answers

What chemical is commonly associated with physiological dormancy?

Abscisic acid Signup and view all the answers

Which method involves mechanically altering the seed coat to promote water and gas exchange?

Scarification Signup and view all the answers

What is the role of chemical scarification in breaking seed dormancy?

It penetrates the hard seed coat with acids. Signup and view all the answers

Which temperature range is used in cold stratification?

5-10°C Signup and view all the answers

What is the main goal of determining seed viability?

To assess the potential for the seeds to germinate and reproduce. Signup and view all the answers

What happens to seeds during warm stratification?

They are exposed to microbial decomposition. Signup and view all the answers

What is a characteristic of recalcitrant seeds?

They tolerate only slight desiccation. Signup and view all the answers

What should be combined with sawdust to store recalcitrant seeds effectively?

Moistened charcoal and low temperatures. Signup and view all the answers

Which factor contributes to the longevity of orthodox seeds during storage?

Storing in air-tight containers with desiccants. Signup and view all the answers

According to Harrington's Thumb Rules, how does decreasing moisture content affect seed storage life?

It doubles the storage life for every 1% decrease. Signup and view all the answers

What is one of Liebig’s Law of Minimum principles?

Any deficiency in essential nutrients limits plant growth. Signup and view all the answers

Which of the following is an effective method to protect seeds from microorganisms during long-term storage?

Coating them with fungicides. Signup and view all the answers

What role do desiccants play in seed storage?

They absorb moisture to maintain dryness. Signup and view all the answers

Which of the following storage containers provides the best protection for seeds?

Aluminum and vacuum-sealed cans. Signup and view all the answers

Study Notes

Light and Germination

Light intensity and light quality influence germination.
The chemical reaction is controlled by the wavelength of light absorbed by the Phytochrome pigment.

Seedling Stage

The stage between germination and the juvenile stage.
Epigeal growth (dicot plants): cotyledons and hypocotyl are raised above ground, cotyledons provide food for the plant.
Hypogeal growth (monocot plants): plumule and hypocotyl emerge above ground, cotyledons remain below soil.

Juvenile Stage

Vigorous growth phase where the plant isn't readily induced to reproduce.
Characterized by:
- Exponential growth
- Inability to reproduce
- Rejuvenation ability
- Development of morphological characteristics (e.g., thorniness)
- Non-receptiveness to external stimuli

Transition Stage

The plant gradually transitions from juvenile to mature characteristics.
Characterized by:
- Decrease in growth rate
- Receptiveness to external conditions
- Decreased rejuvenation ability

Maturity Stage

Plant becomes capable of flowering (reproductive phase).

Reproductive Phase

Microsporogenesis: Formation of microspores (pollen grains)
- Sporogenous tissue (2n) undergoes meiosis to form microspore tetrads (4n).
- Microspores develop into pollen grains (male gametes), containing generative and tube nuclei.
- Pollen grains are released from the anther.
Megasporogenesis & Megagametogenesis:
- Megasporocyte (2n) divides meiotically to form four megaspores, three degenerate.
- The remaining functional megaspore divides mitotically to form the embryo sac (7-celled, 8-nucleated).
- The embryo sac contains:
  - Egg apparatus (2 synergids, 1 egg cell)
  - 2 polar nuclei
  - 3 antipodal cells
Pollination: Transfer of pollen from stamen to stigma.
- Pollen germinates on the stigma, forming a pollen tube.
- The generative nucleus divides into two male gametes (sperm cells).
Methods of Pollination:
- Self-Pollination (augamy): Pollen from stamens to pistils within the same flower or plant (e.g., grapes, peach, tomato).
- Cross Pollination (heterogamy): Pollen from stamens of one plant to the pistil of another plant (e.g., apple, cabbage, cucumber).
Fertilization: Fusion of male and female gametes.
- One sperm cell fuses with the egg cell forming a zygote (embryo).
- The other sperm cell fuses with the two polar nuclei forming the endosperm nucleus (endosperm of seed).
Double Fertilization: Two sets of fertilization occur in flowering plants.
Fate of Floral Parts after Fertilization:
- Sepals, petals, and stamens wither and drop off.
- Ovary becomes the fruit:
  - Ovary wall becomes fruit wall
  - Ovule becomes seed
  - Integuments become seed coat (testa)
  - Fertilized egg becomes embryo

Senescence

Erosive process accompanying aging before death.
Whole plant/complete senescence: Aging and death of the entire plant except the seeds.
Organ/partial senescence: Deterioration and death of specific organs (leaves, fruits, flowers).

Seed Dormancy

Viable seed fails to germinate despite favorable conditions.
Types of Seed Dormancy:
- Physiological/Internal dormancy: Due to internal factors like inhibitors (ABA, coumarin) or immature embryo.
- Physical dormancy: Hard seed coat preventing water and oxygen intake.
- Double dormancy: Both physical and physiological blocks present.
Breaking Physical Dormancy:
- Stratification: Exposing imbibed seeds to specific temperatures:
  - Warm stratification (15-25°C)
  - Cold stratification (5-10°C)
- Scarification: Altering the seed coat:
  - Mechanical methods (abrasion)
  - Hot water treatment
  - Chemical scarification (sulfuric acid)
- Dry storage: For seeds not germinating immediately after harvest.
- Embryo culture: Aseptic growth of excised embryo in artificial media.

Seed Viability

Measure of how many seeds in a batch are alive and can develop into reproductive plants.
Determination of seed viability:
- Germination tests
- Biochemical tests (quicker, but less accurate than germination tests)

Maintaining Viability of Recalcitrant Seeds

Cannot withstand drying, sensitive to chilling.
Store in sawdust moistened to 10% at 7-10°C.
Moistened charcoal or a mixture of charcoal and sterilized sawdust at low temperature (7-10°C).

Maintaining Viability of Orthodox Seeds

Can endure extreme freezing and drying.
Maintenance methods:
- Proper drying to decrease moisture content.
- Low-temperature storage.
- Low oxygen levels.
- Air-tight containers with desiccants.
Harrington’s Thumb Rules:
- Each 1% decrease in moisture content doubles seed storage life.
- Each 5.6°C decrease in storage temperature doubles seed storage life.

Seed Storage

Protect seeds with fungicides for long-term storage.
Use various containers: polyethylene, cellophane, aluminum, vacuum-sealed cans.
For home storage, use airtight cans or bottles.

Liebig’s Law of Minimum

Plant growth is limited by the nutrient in shortest supply, even if other nutrients are abundant.
Example: Insufficient micronutrients can hinder growth even with ample nitrogen and phosphorus.

The Law of Limiting Factors

Plant growth is controlled by the factor in shortest supply, not necessarily the nutrient in shortest supply.

The Law of Diminishing Returns

As the amount of a limiting factor increases, the rate of plant growth increases initially, but eventually levels off and may even decrease.

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Description

Explore the intricacies of plant growth stages from germination to maturity. Understand how light influences germination and the differences between epigeal and hypogeal growth. Delve into the characteristics of juvenile and transition stages of plant development.