Molecular Mechanisms in Plant Stress Responses
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Questions and Answers

What is the primary role of Abscisic Acid (ABA) in plant stress responses?

  • Induces programmed cell death for better oxygen supply
  • Regulates stomatal closure to reduce water loss (correct)
  • Activates defense-related genes against pathogens
  • Promotes growth during environmental stress

Which hormone accumulates in plants under flooding conditions to aid oxygen supply?

  • Ethylene (correct)
  • Jasmonic Acid (JA)
  • Salicylic Acid (SA)
  • Auxins

How do secondary messengers function in stress signal transduction?

  • They directly activate plant hormones
  • They inhibit the expression of stress-related genes
  • They amplify the stress signal for a stronger response (correct)
  • They block the perception of stress signals

Which role do protein kinases primarily serve in the signal transduction pathways during stress?

<p>Phosphorylating target proteins to relay signals (A)</p> Signup and view all the answers

In addition to their growth functions, how do Auxins and Cytokinins contribute to stress responses?

<p>By delaying leaf senescence under stress conditions (D)</p> Signup and view all the answers

Which secondary messenger is NOT directly mentioned as a part of stress signaling?

<p>Glycolytic enzymes (B)</p> Signup and view all the answers

What is a primary function of Salicylic Acid (SA) in plants during stress conditions?

<p>Mediates responses to pathogens and abiotic stress (D)</p> Signup and view all the answers

What is the first step in the signal transduction pathway of stress responses?

<p>Perception of stress signals (D)</p> Signup and view all the answers

Flashcards

What is Abscisic Acid (ABA)?

A plant hormone that plays a central role in drought and salinity stress responses, acting as a signal to regulate stomatal closure and enhance stress tolerance.

What does Ethylene do in response to flooding?

A plant hormone that accumulates under flooding conditions, inducing adaptations like programmed cell death in root cells to create air spaces and improve oxygen supply.

What is the role of Jasmonic Acid (JA)?

A plant hormone crucial for defending against herbivores and pathogens, also aiding in antioxidant defenses during drought or temperature stress.

What is Salicylic Acid (SA) involved in?

A plant hormone that mediates responses to pathogens and also plays a role in abiotic stress like temperature fluctuations by activating defense-related genes.

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What is the role of Auxins, Gibberellins, and Cytokinins in stress?

Although primarily associated with growth, these hormones also influence responses to environmental stress. For example, cytokinins help delay leaf senescence under stress, promoting longevity and tolerance.

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What is Signal Transduction?

The process by which external stress signals are translated into cellular responses, involving multiple steps.

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What is the role of receptors in signal transduction?

They detect environmental changes like drought, salinity, or pathogen invasion, kicking off the stress response.

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What is the role of secondary messengers in signal transduction?

They amplify the stress signal, like a megaphone, initiating a stronger response within the cell.

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Study Notes

Molecular Mechanisms in Stress Responses

  • Plant hormones (phytohormones) modulate stress responses, acting as signals for defense mechanisms.
  • Abscisic Acid (ABA): A "stress hormone" crucial for drought and salinity stress by regulating stomatal closure to reduce water loss. It also modifies gene expression for stress tolerance.
  • Ethylene: Accumulates under abiotic stress like flooding, inducing programmed cell death in certain root cells to form air spaces, improving oxygen supply.
  • Jasmonic Acid (JA): Essential for defense against herbivores and pathogens; it can also activate antioxidant defenses during drought or temperature stress.
  • Salicylic Acid (SA): Mediates plant responses to pathogens and plays a role in abiotic stress like temperature fluctuations, by activating defense-related genes.
  • Auxins, Gibberellins, and Cytokinins: Primarily associated with growth but also modulate responses to environmental stress, like cytokinins delaying leaf senescence for greater tolerance.

Signal Transduction Pathways

  • Signal transduction pathways translate external stress signals into cellular responses.
  • Perception of Stress Signals: Receptors on the plasma membrane recognize environmental changes like drought, salinity, or pathogen invasion.
  • Secondary Messengers: Calcium ions (Ca2+), reactive oxygen species (ROS), and cyclic AMP (cAMP) amplify stress signals, initiating a more robust response.
  • Activation of Protein Kinases and Phosphatases: Protein kinases (e.g., MAPKs) phosphorylate target proteins, relaying the signal, balanced by phosphatases to ensure response specificity.
  • Transcriptional Regulation: Signal cascade activates transcription factors that regulate stress-responsive genes. This leads to the expression of stress proteins, antioxidants, osmoprotectants, and enzymes to combat stress.
  • Crosstalk Between Pathways: Pathways often interact creating a network allowing plants to prioritize responses based on the stress condition, ensuring efficient response to combined stress.

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Description

Explore the intricate roles of various plant hormones in regulating stress responses to environmental challenges. This quiz covers key phytohormones such as Abscisic Acid, Ethylene, and Jasmonic Acid, detailing their functions in enhancing plant resilience against abiotic and biotic stressors.

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