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SFR 100 - Lecture #19 : Plant Response to Signals Topic #19 Plant Response to Signals (Campbell and Reece 821-849) I. II. Objectives A. Review basic requirements for stimulus and response B. Learn the basic plant hormones and their functions. C. Summarize how plants respond to environmental stimuli. Flow of information in plants. A. Three steps. B. Scale of response 1. Plant 2. Cell page 1 SFR 100 - Lecture #19 : Plant Response to Signals III. Classes of plant hormones and cell level response. A. B. C. Overview 1. Chemical signals that coordinate organism functions 2. Minute amounts result in major changes 3. Variability in function. Auxin. 1. IAA. 2. Stimulates cell wall elongation. 3. Produced in apical buds. 4. Seeds - involved in germination 5. Commercial applications. Cytokinins. page 2 SFR 100 - Lecture #19 : Plant Response to Signals D. Gibberellins. E. Abscisic acid (ABA). F. 1. Produced in leaves and developing seeds 2. Associated with dormancy. 3. Stomata control Ethylene. 1. Produced by tissue under stress. 2. Apoptosis - programmed cell death. a) Cells respond to ethylene by page 3 SFR 100 - Lecture #19 : Plant Response to Signals IV. b) Leaf abscission - many breakdown products reabsorbed. c) Fruit ripening. Plant Hormone Interactions. A. Apical dominance. B. Shoot and root growth, differentiation . 1. Shoots. 2. Roots. 3. Ratios. 4. Dormancy. page 4 SFR 100 - Lecture #19 : Plant Response to Signals V. Flowering and photoperiodism. A. Phytochrome. 1. Protein complex with chromophore 2. Chromophore has two forms. 3. VI. a) Pr b) Pfr Ratio for day and night. B. Photoperiodism - flowering dependent on night length. C. Appropriate stimulus will result in meristem forming flower parts Responses to other environmental stimuli A. Phototropism. B. Gravitropism. page 5 SFR 100 - Lecture #19 : Plant Response to Signals VII. C. Drought - ABA and guard cells D. Damage (including pests) Key Terms. flow of information stimulus communication response hormone auxin IAA indoleacetic acid cytokinin gibberellin abscisic acid dormancy ethylene Apoptosis abscission layer apical dominance Phytochrome chromophore Pr Pfr photoperiodism long night plant short night plant phototropism gravitropism periderm page 6