Introduction to Development

Development refers to all the changes that occur in an organism during its life cycle, starting from seed germination, followed by growth, maturation, flowering, seed formation, and finally senescence (aging).

Key Point: Development is not just increase in size. It includes structural, functional, and physiological changes.

Development is the sum of two processes:

  • Growth → Increase in size and mass
  • Differentiation → Specialisation of cells

Differentiation, Dedifferentiation, and Redifferentiation

These processes explain how plant cells change their structure and function during development.

1. Differentiation

  • Meaning: The process by which meristematic cells mature and become structurally and functionally specialised.

  • What happens:

  • Changes in cell wall thickness

  • Changes in protoplasm

  • Cells lose the ability to divide

  • Example: Formation of tracheary elements (xylem vessels)

  • Cells elongate

  • Protoplasm is lost

  • Thick, lignified secondary walls are formed for water transport

  • Result: Formation of primary permanent tissues like parenchyma, collenchyma, sclerenchyma, primary xylem, and primary phloem.

Exam Line: Differentiation leads to functional specialisation of cells.

2. Dedifferentiation

  • Meaning: The process by which living, mature, differentiated cells regain the ability to divide under specific conditions.

  • Important Point: Dedifferentiated cells do not lose their identity, but regain divisional capacity.

  • Examples:

  • Formation of interfascicular cambium from medullary ray parenchyma

  • Formation of cork cambium (phellogen) from cortical parenchyma

  • Result: Formation of secondary meristems

Exam Line: Dedifferentiation is essential for secondary growth.

3. Redifferentiation

  • Meaning: Cells produced by secondary meristems differentiate again, lose the ability to divide, and perform specific functions.

  • Examples:

  • Vascular cambium → Secondary xylem and secondary phloem

  • Cork cambium → Cork (phellem) and phelloderm

  • Result: Formation of secondary permanent tissues

Key Idea: Dedifferentiation is followed by redifferentiation.

Plasticity

Plasticity is the ability of plants to modify their growth and development in response to environmental conditions or different phases of life.

Plants can produce different structures from the same genotype.

Heterophylly – An Example of Plasticity

Heterophylly means the presence of different types of leaves in the same plant.

Types of Heterophylly

  1. Developmental Heterophylly
  • Leaf shape changes during different stages of plant life
  • Juvenile and adult leaves are different
  • Examples: Cotton, Coriander, Larkspur
  1. Environmental Heterophylly
  • Leaf shape changes due to environmental conditions
  • Example: Buttercup (Ranunculus)
  • Terrestrial leaves → Broad
  • Aquatic leaves → Highly dissected

Important Point: Buttercup is an example of environmental heterophylly.

Important Notes

  • Development = Growth + Differentiation
  • Differentiation is irreversible
  • Dedifferentiation forms secondary meristems
  • Plasticity shows adaptability of plants

Differentiation & Development

DEVELOPMENT = GROWTH + DIFFERENTIATION

3 D's (In Order):

  1. Differentiation → Specialisation
  2. Dedifferentiation → Regain division
  3. Redifferentiation → Specialise again

KEY ASSOCIATIONS

  • Differentiation → Permanent tissues
  • Dedifferentiation → Secondary meristems
  • Redifferentiation → Secondary permanent tissues

PLASTICITY Ability to form different structures

HETEROPHYLLY

  • Developmental → Cotton, Coriander
  • Environmental → Buttercup (Ranunculus)

ONE-LINER FOR EXAM: Plants show plasticity due to their sessile nature

💡 Questions and Answers

Q1. Define differentiation, dedifferentiation, and redifferentiation.

A1:

  • Differentiation: Process in which meristematic cells mature and become specialised to perform specific functions.
  • Dedifferentiation: Mature living cells regain the ability to divide and form secondary meristems.
  • Redifferentiation: Cells formed from secondary meristems again lose divisional capacity and become specialised tissues.

Q2: What is development in plants?

A2: Development is the sum of all changes that occur during a plant’s life cycle. It includes both growth (increase in size) and differentiation (specialisation of cells).

Q3: What is plasticity? Give one example.

A3: Plasticity is the ability of plants to alter their growth pattern in response to environmental conditions or life stages. Buttercup shows plasticity by producing different leaf shapes in aquatic and terrestrial conditions.

Q4: Why is dedifferentiation important in plants?

A4: Dedifferentiation is important because it helps in secondary growth and repair. It allows formation of secondary meristems like cambium, which increase the girth of the plant.

Q5: Differentiate between developmental and environmental heterophylly.

A5:

  • Developmental heterophylly: Leaf shape changes with age (Cotton, Coriander).
  • Environmental heterophylly: Leaf shape changes with environment (Buttercup).