Detailed Notes on Plant Responses to Internal & External Signals
Goals: Understand plant responses to stimuli and mechanisms of immunity.
Outcomes:
Explain auxin's role in cell elongation and development.
Describe key plant hormones: cytokinins, gibberellins, ethylene.
Define photomorphogenesis and photoperiodism's impact on flowering.
Explain plant immune responses: PAMP-triggered and effector-triggered immunity.
Stimuli and Stationary Life:
Plants alter growth in response to stimuli (unlike animal movement).
Example: Dodder seedlings bend towards host plants.
Plant Hormones:
Auxin (IAA): Stimulates stem elongation, root formation, regulates fruit development.
Cytokinins: Promote cell division, lateral bud growth, and delay leaf senescence.
Gibberellins (GA): Stimulate stem elongation, fruit growth, seed germination.
Abscisic Acid (ABA): Inhibits growth, promotes stomatal closure, and seed dormancy.
Ethylene: Regulates fruit ripening, leaf abscission, and stress responses.
Brassinosteroids: Promote cell expansion and division, inhibit phloem differentiation.
Jasmonates: Involved in responses to herbivory; regulates fruit, pollen, and root growth.
Strigolactones: Control apical dominance and mycorrhizal interaction.
Phototropism and Hormone Discovery:
Phototropism: Growth towards light via auxin.
Acid Growth Hypothesis: Explains auxin-induced cell elongation through cell wall loosening and turgor pressure increase.
Responses to Light:
Photomorphogenesis: Light affects growth; red/blue light are key.
Phytochromes: Regulate responses like seed germination and flowering.
Flowering Control:
Photoperiodism: Relative length of light/dark influences flowering.
Short-day and long-day plants rely on specific night lengths for flowering.
Plant Immunity:
First defense: Epidermis barrier.
PAMP-triggered Immunity: Recognizes pathogen patterns leading to antimicrobial responses.
Effector-triggered Immunity: Response to pathogen effectors; involves resistance genes and systemic acquired resistance for widespread defense.