Defense Mechanisms in Plants
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Questions and Answers

How do calcium ions contribute to plant defense against Rhizoctonia?

  • They inhibit the activity of a pathogen enzyme. (correct)
  • They promote further tissue maceration.
  • They increase electrical conductivity in cells.
  • They enhance nutrient absorption.

    • What is the role of cellular respiration in resistant plant varieties after infection?

  • It inhibits the production of toxic substances.
  • It decreases metabolic activity for energy conservation.
  • It accelerates general metabolism to develop resistance. (correct)
  • It suppresses cellular communication.

    • What occurs during a hypersensitive reaction in resistant host plant cells?

  • The pathogen becomes unable to attach to the host.
  • Infection spreads rapidly throughout the plant tissue.
  • Adjoining host cells form brown granules and are killed. (correct)
  • The pathogen is directly killed by the host's immune system.

    • What determines the size and extent of lesions produced in resistant varieties of hosts?

    <p>The genetic makeup and resistance of the host plants.</p> Signup and view all the answers

    What substances are released from dead host cells that can affect pathogens?

    <p>Toxic phenols and hydrolytic enzymes.</p> Signup and view all the answers

    What is the term for a plant's ability to defend against pathogens?

    <p>Resistance</p> Signup and view all the answers

    Which type of resistance is characterized by being effective against some races of pathogens but not others?

    <p>Vertical resistance</p> Signup and view all the answers

    What type of resistance is described as incomplete but permanent?

    <p>Horizontal resistance</p> Signup and view all the answers

    What do waxes in the cuticle primarily provide for plants?

    <p>Pathogen resistance</p> Signup and view all the answers

    How is horizontal resistance controlled in plants?

    <p>By multiple genes</p> Signup and view all the answers

    Which of the following best describes the nature of vertical resistance?

    <p>Complete but not permanent</p> Signup and view all the answers

    What is the role of the wax layer in plant cuticles?

    <p>Acting as a water repellent</p> Signup and view all the answers

    What is a potential issue with cutin in the plant cuticle?

    <p>It provides little resistance due to pathogen enzymes.</p> Signup and view all the answers

    What is the function of tyloses in xylem vessels?

    <p>To obstruct the movement of pathogens.</p> Signup and view all the answers

    What results from the formation of the abscission layer in plants?

    <p>It separates diseased tissue from healthy tissue.</p> Signup and view all the answers

    How do gum deposits function in a plant's defense mechanism?

    <p>They restrict the movement of the pathogen.</p> Signup and view all the answers

    What occurs in the swelling of cell walls during pathogen invasion?

    <p>Creates an impermeable barrier to prevent further invasion.</p> Signup and view all the answers

    What role do pre-existing biochemical defenses in plants serve?

    <p>They inactivate pathogens or their toxins.</p> Signup and view all the answers

    What effect do chemical substances released by plants into their environment generally have?

    <p>They can either promote or inhibit pathogen growth.</p> Signup and view all the answers

    What is a potential consequence of the formation of callus in response to pathogen invasion?

    <p>It encloses fungal hyphae and restricts their spread.</p> Signup and view all the answers

    Which onion variety characteristic contributes to its resistance against Colletotrichum attack?

    <p>Pigmented bulb scales (red or yellow)</p> Signup and view all the answers

    What toxic compound do some flax varieties exude from their roots to combat the wilt pathogen Fusarium axysporum?

    <p>Hydrocyanides (HCN)</p> Signup and view all the answers

    What is the primary purpose of plants releasing gases and organic chemicals into the atmosphere?

    <p>To interact with the surrounding microflora and fauna.</p> Signup and view all the answers

    Which chemical compound is secreted by some varieties of gram to inhibit the growth of blight fungus?

    <p>Malic acid</p> Signup and view all the answers

    Which phytoalexin is produced in sweet potato when infected with Ceratocystis fimbriata?

    <p>Ipomeamarone</p> Signup and view all the answers

    Which of the following describes a characteristic of resistant host plant cells?

    <p>Presence of higher amounts of toxic chemical substances</p> Signup and view all the answers

    What type of compound is used by resistant plants to neutralize toxins produced by pathogens?

    <p>Fusaric acid</p> Signup and view all the answers

    What is the role of tannic acid found in tobacco plants?

    <p>It inhibits infection of tobacco mosaic virus</p> Signup and view all the answers

    Which of the following is NOT a mechanism of plant defense discussed?

    <p>Defence through nutrient absorption</p> Signup and view all the answers

    What does the absence of specific nutrients do for host plants regarding certain pathogens?

    <p>Makes host resistant to pathogens</p> Signup and view all the answers

    Which pathogen is associated with the production of Rishitin in potatoes?

    <p>Phytophthora infestans</p> Signup and view all the answers

    Which fungus fails to produce appresoria in pure culture medium without nutrients from susceptible hosts?

    <p><em>Rhizoctonia solani</em></p> Signup and view all the answers

    What role do auxins play in the defense of resistant plant varieties?

    <p>Inhibiting the actions of fungi</p> Signup and view all the answers

    What is the significance of the absence of common antigen in host responses?

    <p>It enables production of antibodies against foreign proteins</p> Signup and view all the answers

    In which plant is the phytoalexin phaseolin produced when infected?

    <p>Phaseolus vulgaris</p> Signup and view all the answers

    Which fungal disease is linked to the production of medicarpin in alfalfa?

    <p>Infections by many fungi</p> Signup and view all the answers

    What type of compounds modify pathogen enzymes in resistant plant varieties?

    <p>Phenolic compounds</p> Signup and view all the answers

    What happens when antigens common to a pathogen are not present in a host plant?

    <p>The plant develops resistance to that particular pathogen.</p> Signup and view all the answers

    What role does β-glycosidase play in the defense mechanism of resistant apple varieties?

    <p>It acts on glucoside phloridzin to release phloretin.</p> Signup and view all the answers

    Which of the following statements about phytoalexins is true?

    <p>They are produced in response to mechanical or chemical injury.</p> Signup and view all the answers

    What is a primary observation associated with the response of plants to infection regarding phenolic compounds?

    <p>There is an increase in phenolic compound concentration.</p> Signup and view all the answers

    Which of the following plants has been observed to increase phenolic compound levels when infected by Verticillium?

    <p>Cotton</p> Signup and view all the answers

    Who coined the term 'phytoalexins' and in which year?

    <p>Muller and Borger in 1940</p> Signup and view all the answers

    What is a key factor that influences the quantity of phytoalexin biosynthesis?

    <p>The concentration of inoculum</p> Signup and view all the answers

    In the context of plant defense, what is the nature of compounds like phloretin after being released from glucosides?

    <p>They are extremely toxic and harmful to pathogens.</p> Signup and view all the answers

    Study Notes

    Defense Mechanisms in Plants

    • Plants have natural defenses against pathogens.
    • Resistance is the ability of a plant to restrict pathogen establishment and activity.
    • Susceptibility is the opposite of resistance.
    • Two main types of resistance are horizontal and vertical.

    Horizontal Resistance

    • General resistance across all pathogen races.
    • Incomplete but permanent resistance.
    • Controlled by multiple, complementary genes (polygenic).
    • Mechanisms of defense are less efficient.

    Vertical Resistance

    • Resistance effective against specific pathogen races.
    • Complete but not permanent.
    • Controlled by one or a few genes (mono- or oligogenic).
    • Mechanisms of defense are more efficient.

    Defense Mechanisms Categories

    • Morphological/Structural: Physical barriers preventing pathogen entry.
    • Biochemical: Chemical compounds inhibiting pathogen growth.

    Morphological/Structural Mechanisms

    • Pre-existing structural defenses.
      • Waxes and cuticles: Prevent pathogen entry, hydrophobic surfaces.
      • Epidermal cell wall structure: Thick, tough cell walls.
      • Stomata: Small size and lip-like structures limit pathogen entry.
      • Lenticels and other openings: Structures that limit pathogen entry.
      • Internal structures: Thick inner cell walls and sclerenchyma.
      • Post-infectional structural defenses
      • Cork layers: Layers formed in response to infection.
      • Tyloses: Cell wall protrusions in xylem vessels.
      • Abscission layers: Separation of infected areas.
      • Gum deposition: Barriers to restrict the pathogen.

    Biochemical Defense Mechanisms

    • Toxic chemicals in plant cells.
      • Phenols, saponins, sulphur compounds: Inhibit pathogen growth.
    • Presence of inhibitors in plant environment.
      • Organic chemicals: Prevent pathogen growth or attract beneficial microbes.
    • Absence of essential nutrients for pathogen growth.
    • Release of phenols from non-toxic glucosides.
    • Synthesis of phenols in response to infection.
    • Production of phytoalexins.
      • Phytoalexins: Compounds produced in response to infection that are toxic to the pathogen.
    • Defense through altered respiration and hypersensitive responses.
      • Increased respiration rate following infection can lead to resistance.
      • Hypersensitive response: Killing of host cells surrounding infection to prevent spread.
    • Defense through growth substances.

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    Defence Mechanisms in Plants PDF

    Description

    Explore the fascinating world of plant defense mechanisms against pathogens. This quiz covers horizontal and vertical resistance, as well as the various structural and biochemical defenses plants employ. Test your knowledge on how plants protect themselves and the genetic factors involved.

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