Plant Defense Mechanisms

Defense Mechanism In Plants

Introduction

• Plants protect themselves from various threats.

• Modified parts are used for defense.

• Defense mechanisms protect against herbivorous animals, insects, and egg-laying insects.

Types Of Defense Mechanisms

1. Thorns

2. Spines

3. Prickles

4. Shrinkage

5. Milky Latex

6. Trichomes

7. Volatile Organic Compounds (VOC’s)

Thorns

• Definition: Modified branches or stems with sharpened points.

• Example: Carissa bispinosa uses thorns as a defense mechanism.

Spines

• Definition: Modified leaves or stipules.

• Examples:

  • Modified from leaves: Opuntia sp.

  • Modified from stipules: Acacia erioloba.

Prickles

• Definition: Modified extensions from the epidermis.

• Origin: Arise from stem or leaves.

• Examples:

  • From stem: Rose.

  • From leaves: Solanum pyracanthum.

Shrinkage

• Description: Occurs when cells lose turgidity.

• Effect: Scares animals; they may avoid fast-moving shrinking plants.

• Example: Mimosa pudica.

Milky Latex

• Definition: Aqueous secretion that is poisonous.

• Examples: Found in Euphorbia pulcherrima and Opium poppy.

Trichomes

• Definition: Hair-like projections from the epidermis.

• Types:

  • Glandular hairs (poisonous).

  • Non-glandular hairs (non-poisonous but irritating).

  • Example: Capsicum pubescens (non-glandular), Cannabis sp. (glandular).

Volatile Organic Compounds (VOC’s)

• Definition: Chemical substances produced by plants as defense.

• Example: Geraniums produce quisqualic acid, which paralyzes insects feeding on the plant.