Molecular Mechanisms in Plant Stress Responses

Study Notes

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 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.