Plant Growth and Development

Introduction

• Plant growth and development is an easy chapter.
• We will complete it with quality.
• The rest of the chapters are planned for next week.

Plant Growth Regulator

Definition

• Plant growth regulators or phytohormones are small simple compounds.
• Diversity in chemical composition.
• Divided into growth promoters and inhibitors.

Promoters

• Auxin, gibberellins, cytokinins.
• Promote cell division, cell elongation, flowering, seed germination.

Inhibitors

• Abscisic acid (ABA), ethylene.
• Promote dormancy and senescence.

Auxin

Discovery and Properties

• Charles Darwin and Francis Darwin experimented on canary grass.
• A chemical is produced at the tip for phototropism.
• FW Went isolated auxin.

Functions

• Promotes apical dominance.
• Prevents senescence of young leaves.

Gibberellins

Discovery and Properties

• Observed in rice plants by a Japanese farmer.
• Isolated from fungus.

Functions

• Increases the shape and size of grapes and apples.
• Increases the length of sugar cane.
• Promotes respiration and ripening.

Cytokinins

Discovery

• Skoog experimented on tobacco cells.

Functions

• Inhibits apical dominance.
• Promotes cell division in tissue culture.

Abscisic Acid (ABA)

Properties

• Growth inhibitor.
• Acts as a stress hormone.

Functions

• Closes stomata to reduce transpiration.
• Inhibits seed germination.

Ethylene

Properties

• Gaseous hormone.
• Fruit ripening hormone.

Functions

• Promotes phototropism, senescence.
• Shows triple response in plant growth.

Growth Patterns

Arithmetic and Geometric Growth

• In arithmetic, one cell divides, in geometric, all do.
• Geometric is faster.

Sigmoid Growth Curve

• Followed in living organisms.
• Lag phase, log phase, stationary phase are present.

Other Important Topics

Plasticity and Heterophylly

• Plasticity means following different growth patterns to have different types of leaves.

Research on these topics provides extensive information on plant growth and development.