1. PLANT GROWTH

Definition: Irreversible permanent increase in size, mass, and volume of a plant or its parts.

Types of Growth: a) Primary Growth

• Occurs in apical meristems
• Results in increase in length
• Found in roots and shoots
• Responsible for primary plant body

b) Secondary Growth

• Occurs in lateral meristems
• Results in increase in girth/thickness
• Found in dicot stems and roots
• Forms secondary plant body

Characteristics of Growth:

1. Cell Division (Mitosis)
2. Cell Elongation
3. Cell Differentiation

Plant Growth Generally is Indeterminate:

1. Characteristics of Plant Growth

• Plants have unlimited growth potential throughout their life
• Growth is indeterminate
• Due to presence of meristems in specific locations
• Called “open form of growth”

2. Meristems

• Contain cells capable of division and self-perpetuation

• Two main types: a) Primary Meristems

  • Root apical meristem
  • Shoot apical meristem
  • Responsible for primary growth
  • Causes elongation along plant axis

  b) Lateral Meristems

  • Vascular cambium
  • Cork-cambium
  • Appear later in life
  • Found in dicots and gymnosperms
  • Responsible for secondary growth

3. Growth Patterns

• Primary Growth

  • Elongation of plant along axis
  • Controlled by apical meristems

• Secondary Growth

  • Increase in girth/thickness
  • Controlled by lateral meristems
  • Occurs in dicots and gymnosperms

4. Cell Development

• Meristematic cells divide continuously
• Daughter cells lose division capacity
• These cells form permanent plant body tissues

2. GROWTH MEASUREMENT

3. Basic Definition:

• Growth is primarily the increase in protoplasm at cellular level
• Direct measurement of protoplasm increase is difficult

2. Parameters for Measuring Growth:

• Fresh weight
• Dry weight
• Length
• Area
• Volume
• Cell number

3. Examples of Growth Rates: a) Maize Root:

• Apical meristem produces 17,500+ new cells/hour
• Growth measured by cell number increase

b) Watermelon:

• Cells can increase in size by up to 350,000 times
• Growth measured by cell size increase

4. Specific Growth Measurements:

• Pollen tube: Measured by length
• Dorsiventral leaf: Measured by surface area

Growth Patterns: a) Arithmetic Growth

• Linear growth pattern
• Common in root/shoot elongation
• Formula: L = L₀ + rt (L = length, L₀ = initial length, r = growth rate, t = time)

b) Geometric Growth

• Exponential growth pattern
• Shows ‘J’ curve
• Formula: W = W₀ert (W = final size, W₀ = initial size, r = growth rate, t = time)

c) Sigmoid Growth (S-curve) Phases:

1. Lag Phase (slow growth)
2. Log/Exponential Phase (rapid growth)
3. Stationary Phase (growth stops)

Differentiation, Dedifferentiation, and Redifferentiation:

A) Differentiation

• Definition: Process where cells mature to perform specific functions
• Structural Changes: Changes in cell walls and protoplasm
• Example: Tracheary elements

B) Dedifferentiation

• Definition: Living differentiated cells regain division capacity
• Example: Formation of interfascicular cambium and cork cambium

C) Redifferentiation

• Definition: Cells from dedifferentiation mature for specific functions
• Examples: Xylem, Phloem, Cork, Pith, Cortex

D) Additional Concepts:

• Tumors: Abnormal growths from uncontrolled cell division
• Callus: Dividing parenchyma cells in tissue culture
• Open Differentiation: Different structures based on cell location

3. DEVELOPMENT IN PLANTS

4. DEFINITION AND REPRESENTATION

• Growth: Irreversible increase in mass and size
• Development: Qualitative changes leading to maturation
• Growth can be measured through:
  • Fresh/dry weight
  • Length/height
  • Surface area
  • Cell number

2. PLASTICITY

• Ability of plants to modify their growth based on environment Heterophylly Examples:
• Cotton: Juvenile vs mature leaves
• Coriander: Ground-level vs stem leaves
• Larkspur: Submerged vs aerial leaves

3. FACTORS AFFECTING GROWTH

A) EXTERNAL FACTORS:

1. Light

• Essential for photosynthesis
• Affects phototropism
• Influences flowering
• Controls chlorophyll synthesis

2. Temperature

• Affects enzyme activity
• Influences germination
• Controls flowering time
• Impacts growth rate

3. Water

• Essential for cell turgidity
• Required for photosynthesis
• Affects nutrient transport
• Influences germination

4. Oxygen

• Necessary for respiration
• Important for root growth
• Required for seed germination

B) INTERNAL FACTORS (PLANT HORMONES):

1. Auxins

• Promotes stem elongation
• Controls apical dominance
• Stimulates root formation
• Prevents leaf abscission

2. Gibberellins

• Promotes stem elongation
• Breaks seed dormancy
• Induces flowering
• Fruit development

3. Cytokinins

• Promotes cell division
• Delays senescence
• Lateral bud growth
• Chloroplast development

4. Ethylene

• Fruit ripening
• Triple response
• Leaf abscission
• Root hair formation

5. Abscisic Acid (ABA)

• Promotes dormancy
• Stomatal closure
• Stress response
• Inhibits growth

4. PHOTOPERIODISM

Short Day Plants (SDP):

• Flower when night length > critical duration
• Examples: Chrysanthemum, Rice

Long Day Plants (LDP):

• Flower when night length < critical duration
• Examples: Spinach, Wheat

Day Neutral Plants (DNP):

• Flowering independent of day length
• Examples: Tomato, Cotton

5. VERNALIZATION

• Cold treatment requirement for flowering
• Duration varies by species
• Examples: Winter wheat, Beet
• Prevents premature flowering

6. SEED DORMANCY

Causes:

1. Hard seed coat
2. Immature embryo
3. Chemical inhibitors
4. Light requirement
5. Temperature requirement

Breaking Dormancy Methods:

1. Scarification

   • Mechanical
   • Chemical (acid treatment)

2. Stratification

   • Cold treatment
   • Moist chilling

3. Other Methods:

   • Light exposure
   • Hormone treatment
   • Leaching inhibitors
   • Temperature alternation