Plant Defense Mechanisms and Pathogenesis
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Questions and Answers

What is the primary role of defense mechanisms in plants?

  • To improve nutrient absorption
  • To ensure survival against parasites and abiotic stresses (correct)
  • To enhance photosynthesis efficiency
  • To promote growth and reproduction

How do plants typically respond to pathogen invasion?

  • By speeding up growth
  • By forming physical and chemical barriers (correct)
  • By increasing photosynthetic rates
  • By altering nutrient composition in leaves

What type of trait do plants possess that helps them resist pathogen attack?

  • Environmental adaptation
  • Adaptive characteristic acquired through experience
  • Random genetic mutation
  • Heritable trait that allows natural resistance (correct)

What is co-evolution in the context of plant defense mechanisms?

<p>The mutual adaptation of plants and pathogens through their coexistence (C)</p> Signup and view all the answers

What are preexisting barriers in plants?

<p>Inherited structures that resist pathogen penetration (B)</p> Signup and view all the answers

What is the first line of defense in plants against pathogens?

<p>The epidermis of the plant (B)</p> Signup and view all the answers

What function does the cuticle serve in plant defense mechanisms?

<p>It provides a physical barrier against pathogens (C)</p> Signup and view all the answers

How do wax layers on plants help in defense against pathogens?

<p>They create a negative charge that repels airborne spores (A)</p> Signup and view all the answers

What role does the epidermis play when a pathogen attempts to invade a plant?

<p>It serves as a barrier between the pathogen and the internal tissues (D)</p> Signup and view all the answers

Which of the following structures primarily helps in the pre-existing defense against a pathogen's penetration?

<p>The cutin layer of the cuticle (A)</p> Signup and view all the answers

What defines pre-existing structural barriers in plant defense?

<p>Intrinsic structures present before pathogen attack (A)</p> Signup and view all the answers

Which enzyme is known to help some pathogens penetrate plant tissues more effectively?

<p>Cutinase (D)</p> Signup and view all the answers

What happens to the retention of water on plant surfaces due to the wax and cuticle?

<p>It decreases, making conditions less favorable for spore germination (A)</p> Signup and view all the answers

What role do inhibitory substances play in the environment?

<p>They encourage certain groups to dominate and can act as antagonists to pathogens. (B)</p> Signup and view all the answers

Which compounds are specifically mentioned as contributing to a plant's resistance against parasitic fungi?

<p>Phenolic compounds and tannins. (A)</p> Signup and view all the answers

How do saponins contribute to plant defense against fungal pathogens?

<p>They have antifungal membranolytic activity preventing infection. (B)</p> Signup and view all the answers

What is the significance of recognition factors in plant-pathogen interactions?

<p>They enable pathogens to recognize and adhere to specific host plants. (B)</p> Signup and view all the answers

Which of the following is true about preformed plant proteins?

<p>They serve as inhibitors of pathogen enzymes. (D)</p> Signup and view all the answers

What action do hydrolytic enzymes performed by plant surface cells have on pathogens?

<p>They break down the cell walls of the pathogens. (D)</p> Signup and view all the answers

In which type of plants are pre-existing toxic substances often found in higher concentrations?

<p>Resistant varieties. (A)</p> Signup and view all the answers

What is the first step in the infection process for pathogens?

<p>Cell-to-cell communication between the host and pathogens. (C)</p> Signup and view all the answers

What is the purpose of lignification in plants during an infection?

<p>To create an impermeable barrier against pathogen penetration (B)</p> Signup and view all the answers

Which of the following best describes suberization in plants?

<p>Isolation of infected cells from healthy tissues (B)</p> Signup and view all the answers

What role does the abscission layer play in plant defense mechanisms?

<p>It aids in shedding infected tissues or parts (B)</p> Signup and view all the answers

What is the purpose of tyloses in the plant defense response?

<p>To mechanically block the vessels and limit pathogen spread (D)</p> Signup and view all the answers

Which mechanism is observed when carbohydrates are synthesized as part of plant defense?

<p>Development of secondary walls and papillae (A)</p> Signup and view all the answers

What is the function of callose deposition in plant cellular defense?

<p>To form a protective sheath around pathogen points of entry (A)</p> Signup and view all the answers

How do gums and vascular gels contribute to the defense against pathogens?

<p>By blocking nutrient flow to the pathogen (A)</p> Signup and view all the answers

Induced cellular defenses have what limitation during plant defense?

<p>They have a limited role compared to physical barriers (D)</p> Signup and view all the answers

What role do host-specific toxins play in host-parasite interactions?

<p>They attach to sensitive sites in the cell, causing disease. (B)</p> Signup and view all the answers

Why are some parasites only able to grow on specific varieties of plants?

<p>Only certain plants contain the essential nutrients and growth factors. (B)</p> Signup and view all the answers

What is the primary function of pre-existing defence mechanisms in plants?

<p>To help ward off most microbes as nonpathogens. (A)</p> Signup and view all the answers

How do induced defence mechanisms operate in plants?

<p>They function at multiple levels, including biochemical and cellular. (D)</p> Signup and view all the answers

What might happen if a pathogen avoids eliciting the active defence response in plants?

<p>The plant can become diseased due to the toxins. (B)</p> Signup and view all the answers

What type of defense mechanism does the ability of the plant to mount an active response rely on?

<p>Genomic control. (D)</p> Signup and view all the answers

What is the effect of metabolic toxins secreted by a pathogen in relation to plant defence?

<p>They inhibit the plant's ability to elicit active defence response. (A)</p> Signup and view all the answers

What determines the location of receptor-proteins in plant cells during pathogen attack?

<p>The specific genome of the plant. (B)</p> Signup and view all the answers

What enzyme is primarily involved in producing phenols, phytoalexins, and lignin in response to pathogens?

<p>Phenyl ammonia lyase (PAL) (A)</p> Signup and view all the answers

How do phenolic compounds contribute to plant defense against pathogens?

<p>They neutralize pathogen's enzymes. (C)</p> Signup and view all the answers

In the context of plant responses to infection, what metabolic pathway is typically altered to enhance defense substances?

<p>Shikmic acid pathway (D)</p> Signup and view all the answers

What is the role of catechol-tannin in the defense of immature grape fruits?

<p>It inhibits enzymes produced by pathogens. (B)</p> Signup and view all the answers

What is one way plants can resist toxins produced by pathogens?

<p>Detoxification of the toxins. (B)</p> Signup and view all the answers

How does the respiration process change in diseased tissues?

<p>It increases and shifts to the pentose pathway. (B)</p> Signup and view all the answers

What is a characteristic of specialized obligate parasites compared to necrotrophs and hemibiotrophs?

<p>They do not use toxins. (D)</p> Signup and view all the answers

What is the significance of the speed and amount of synthesized defense products in plants?

<p>It impacts the creation of defensive barriers. (B)</p> Signup and view all the answers

Flashcards

Plant Defense Mechanisms

The ways plants resist pathogens and other harmful factors.

Pre-infection Barriers

Physical and chemical defenses in plants that prevent pathogen entry.

Post-infection Response

Plant defenses triggered when a pathogen penetrates the pre-existing barriers.

Co-evolution

The evolution of plants and pathogens alongside each other, driving the development of defenses.

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Resistance

A plant's ability to withstand or prevent the negative effects of pathogens or stressors.

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Pre-existing structural defenses

First line of defense in plants, present on the surface to prevent pathogen entry.

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Cuticle and Wax

Protective layers on the plant surface that prevents pathogen entry and water retention.

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Cutin

Fatty acid component of the cuticle that repels spores.

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Waxes

Long chain compounds in the cuticle that prevent water retention and spore germination.

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Epidermis

The first layer of living plant cells exposed to pathogens.

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Cutinase

Enzyme produced by some pathogens to dissolve cutin.

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Pathogen penetration

Process by which pathogens enter the plant.

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Pre-existing internal structural barriers

Internal plant defenses that pathogens encounter after penetrating the surface layers.

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Plant Exudates

Substances released by plants that influence surrounding microbes.

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Inhibitory Substances

Substances in plant exudates that reduce microbial growth or promote antagonistic interactions.

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Pre-existing Toxic Substances

Plant chemicals present in cells that contribute to resistance.

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Recognition Factors

Plant surface components that determine if a pathogen is recognized as a host.

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Fungal Pathogens

Microorganisms that cause diseases in plants.

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Saponins

Plant compounds that disrupt fungal cell membranes.

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Hydrolytic Enzymes

Enzymes that break down cell wall components.

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Cell-to-Cell Communication

Exchange of signals between plant and pathogen cells to initiate the infection process.

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Host Specific Toxins

Toxins produced by pathogens that target specific host receptors, causing symptoms and disease.

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Essential Nutrients

Nutrients crucial for pathogen growth and reproduction, often only available in certain host plants.

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Pre-existing Defenses

Plants' initial, structural and biochemical defenses to ward off non-pathogens.

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Induced Defenses

Plant defenses activated in response to pathogens, either specific or non-specific.

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Biochemical Defenses

Chemical mechanisms employed by plants to combat pathogens.

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Cellular Level Defenses

Plant defenses occurring within individual plant cells.

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Tissue Level Defenses

Plant defenses that target entire tissues in the fight against pathogens.

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Disease Cause

Disease occurs when pre-existing defenses fail to stop pathogens or when pathogens disable active defenses by producing toxins or other mechanisms.

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Induced structural defense

Plant responses to infection by creating barriers to further pathogen growth and spread within cells

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Lignification

Hardening of cell walls with lignin, creating a barrier to pathogen penetration and nutrient movement.

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Suberization

Formation of a corky layer around infected cells, isolating them from healthy tissue.

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Abscission layers

Gaps that allow plants to shed infected leaves or fruits, removing the pathogen.

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Tyloses

Protrusions of xylem cells that block xylem vessels, preventing pathogen movement.

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Gum deposition

Accumulation of gums and gels that block intercellular spaces, trapping pathogens.

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Induced cellular defense

Plant responses to infection by changing cell walls and creating barriers to pathogen spread inside cells.

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Callose deposition

Formation of a carbohydrate layer around pathogens and haustoria slowing pathogen attack.

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Enzyme Role in Resistance

Enzymes are crucial for synthesizing defense compounds in plants against pathogens. Phenol-oxidizing enzymes play a vital role in this process and their activity significantly influences resistance.

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PAL Enzyme Function

Phenyl ammonia lyase (PAL) synthesizes important components like phenols, phytoalexins, and lignin in plants, strengthening their defense mechanisms.

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Resistance Mechanism Speed

Effectiveness of plant resistance relies on the rapid production and diffusion of defense substances to affected and neighboring cells to create protective barriers.

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Pathogen Toxin Action

Pathogens use toxins and enzymes to damage host tissues. Necrotrophs/hemi-biotrophs use more of these substances than obligate parasites.

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Plant Defense Inhibitors

Plants defend by producing phenols, tannins, and protein enzymes that inhibit the pathogens' enzymes and toxins, making pathogens less harmful.

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Altered Host Metabolism

Plants alter their metabolic pathways (stress response) to combat pathogens. This includes increases in specific enzymes and compounds.

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Shikimic Acid Pathway

Key metabolic pathway in plants for creating defense compounds, alongside modified acetate pathways.

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Induced Host Resistance

Plants universally react to pathogen attacks by either creating defensive structures or biochemical changes.

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Study Notes

Defense Mechanisms in Plants

  • Plants employ various defense mechanisms to resist pathogens and environmental stresses.
  • Plants are the primary producers, converting solar energy into chemical energy.
  • Coevolution with pathogens has led to the development of robust defense mechanisms.
  • Defense mechanisms are crucial for plant survival in challenging environments.

Pathogenesis and Host Response

  • Host-parasite interactions trigger plant defense mechanisms.
  • Plants exhibit structural and chemical defenses in response to pathogens.
  • These initial responses occur upon contact with pathogens.

Pre-Existing Structural Defenses

  • Plant surfaces, like the cuticle and epidermal waxes, act as a first line of defense.
  • These barriers prevent pathogen penetration.
  • Internal structural barriers also exist in the host to resist invasion.

Wax and Cuticle

  • Cutin and waxes form the cuticle, deterring pathogen entry and spore germination.
  • Waxy surfaces also prevent water loss.

Epidermal Layer

  • Epidermis, with its tough cell walls, prevents entry of pathogens.
  • The cell walls contain various compounds that obstruct penetration.
  • Features like stomata, hydathodes, and trichomes potentially help deter pathogens.

Defense Mechanisms: Induced or Active

  • Induced defense mechanisms activate in response to pathogen attack.
  • This response involves plant cell changes and chemical production.

Lignification

  • Lignified cell walls obstruct pathogen invasion, making the plant less susceptible.
  • This strategy impedes pathogen growth and proliferation.

Suberization

  • Suberized cells create a barrier to isolates infected cells from healthy ones.
  • Corky layer formation from suberization is an example of a natural healing response.

Abscission Layer

  • Abscission layers help plants shed infected or damaged parts.
  • This mechanism prevents the spread of disease to non-infected areas.

Tyloses

  • Tyloses are protrusions that block vascular vessels preventing pathogen spread.
  • This blockage hampers the pathogen's ability to get around the plant.

Gum Deposition

  • Gums or vascular gels accumulate and fill spaces in plant tissues, starving pathogens.

Induced Biochemical Defenses

  • Plant cells produce toxins and chemicals to contain pathogens.
  • These substances can damage or kill invading pathogens.
  • Phenolic substances, tannins, and fatty acids act as effective inhibitors.
  • Phytoalexins are specific toxic compounds produced during disease.

Inhibitors and Toxin Production

  • Plants produce inhibitors to inhibit pathogen enzymes.
  • These inhibitors interfere with pathogen development and survival.
  • These toxins directly combat or inhibit pathogen activities.

Role of Altered Biosynthesis

  • Altered metabolic pathways in the host make the plant less susceptible to infection.
  • Changes occur in response to disease or stress.
  • Constitutive or induced defenses are put into play.

Systemic Acquired Resistance (SAR)

  • A systemic response to pathogen attack, creating a generalized defense.
  • This response involves specific signal molecules and biochemical changes.

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Defence Mechanisms In Plants PDF

Description

Explore the various defense mechanisms employed by plants to resist pathogens and environmental stresses. This quiz covers coevolution with pathogens, structural and chemical defenses, and how plants respond to host-parasite interactions. Test your knowledge on how these strategies are crucial for plant survival.

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