Plant Defense

Definition

Plant defense refers to the various mechanisms and strategies employed by plants to protect themselves from herbivores, pathogens, and other environmental stresses. These defense mechanisms are crucial for the survival and fitness of plants in their natural habitats.

5 Must Know Facts For Your Next Test

1. Terpenoids are a large and diverse class of plant secondary metabolites that play crucial roles in plant defense, including deterring herbivores, attracting predators of herbivores, and protecting against pathogens.
2. Plants can produce a wide variety of terpenoids, such as monoterpenoids, sesquiterpenoids, and diterpenoids, each with their unique defensive properties.
3. Phytoalexins are antimicrobial compounds produced by plants in response to pathogen attack or other stresses, helping plants defend themselves against a broad range of microorganisms.
4. Systemic Acquired Resistance (SAR) is a form of induced resistance in plants, where the entire plant becomes more resistant to a broad spectrum of pathogens after a localized infection or treatment.
5. Plant defense mechanisms can be classified into two main categories: constitutive defenses (always present) and induced defenses (activated in response to a threat).

Review Questions

• Explain the role of terpenoids in plant defense, and provide examples of their defensive functions.
  • Terpenoids are a diverse class of plant secondary metabolites that play a crucial role in plant defense mechanisms. These compounds can deter herbivores by making the plant less palatable or toxic, attract predators of herbivores to provide indirect defense, and protect the plant against pathogens by inhibiting their growth or disrupting their cellular processes. Examples of defensive terpenoids include monoterpenoids like limonene, which can repel insects, and diterpenoids like taxol, which has antimicrobial properties.
• Describe the concept of Systemic Acquired Resistance (SAR) in plants and how it contributes to their defense against pathogens.
  • Systemic Acquired Resistance (SAR) is a form of induced resistance in plants, where the entire plant becomes more resistant to a broad spectrum of pathogens after a localized infection or treatment. When a plant is exposed to a pathogen or other stressor, it can trigger the production of signaling molecules, such as salicylic acid, that are transported throughout the plant. This leads to the activation of defense-related genes and the production of antimicrobial compounds, enhancing the plant's overall resistance to future pathogen attacks. SAR is a crucial mechanism that allows plants to mount a more effective and long-lasting defense against a wide range of pathogens.
• Analyze the differences between constitutive and induced plant defense mechanisms, and explain how they work together to provide comprehensive protection for the plant.
  • Plant defense mechanisms can be classified into two main categories: constitutive defenses and induced defenses. Constitutive defenses are always present in the plant, such as physical barriers (e.g., cell walls, waxy cuticles) and preformed antimicrobial compounds. These defenses provide a baseline level of protection against potential threats. In contrast, induced defenses are activated in response to a specific threat, such as herbivore feeding or pathogen attack. These induced defenses can include the production of defensive chemicals (e.g., terpenoids, phytoalexins), the strengthening of cell walls, and the activation of signaling pathways that trigger a broader defensive response (e.g., Systemic Acquired Resistance). The combination of constitutive and induced defenses allows plants to respond effectively to a wide range of biotic and abiotic stresses, providing comprehensive protection for their survival and fitness.

Related terms

Terpenoids:

Terpenoids are a diverse class of organic compounds produced by plants, often as part of their defense system. They can have various functions, such as deterring herbivores, attracting predators of herbivores, and protecting against pathogens.

Phytoalexins: Phytoalexins are antimicrobial compounds produced by plants in response to pathogen attack or other stresses. They help plants defend themselves against a wide range of microorganisms, including bacteria, fungi, and viruses.

Systemic Acquired Resistance (SAR): Systemic Acquired Resistance is a form of induced resistance in plants, where the entire plant becomes more resistant to a broad spectrum of pathogens after a localized infection or treatment.