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Biology 1030 Winter 2009 Coordination Chapter 39 (788-817) Scott circa 2009 Stimuli • External signals – Environmental cues • Internal signals – Growth regulators 1. Reception 2 Transduction 2. Transd ction 3. Response Scott circa 2009 1 Biology 1030 Winter 2009 Photoreception • Etiolation – Diversion of energy 1 Stems 1. 2. Leaves 3. Roots • De-etiolation – Rediversion of energy 1 Stems 1. 2. Leaves 3. Roots Scott circa 2009 De-etiolation • Light receptor – Phytochrome • Signal transduction pathway – – – – Cyclic GMP Calcium Protein kinases Transcription factors TF 1 PK 1 activated Phytochrome activated by light cGMP TF 2 PK 2 activated • Response Transcription Translation – Greening Ca2+ channel opened Greening Ca2+ Scott circa 2009 2 Biology 1030 Winter 2009 Mechanical Stimuli • Chronic stimuli – Wind, obstacles – Thigmomorphogenesis • Acute stimuli – Mimosa pudica – Rapid leaf movements Scott circa 2009 Mechanical Stimuli • Pulvinus – Motor organ – Each leaflet • Changes in turgor • Action potential – Cell-cell communications Scott circa 2009 3 Biology 1030 Winter 2009 Predators • Physical defences • Chemical Ch i l defences d f 4 Recruitment of parasitoid wasps that lay their eggs within caterpillars • Predator recruitment 1. 2. 3. 4. Injury Signal transduction Response Attack on herbivore 1 Wounding 2 Signal transduction pathway 1 Chemical in saliva 3 Synthesis and release of volatile attractants Scott circa 2009 Plant Growth Regulators • Internal coordination growth regulator? g • What is a g • What do plant growth regulators do? • Active growth regions • Transportation – – – – – – Scott circa 2009 4 Biology 1030 Winter 2009 Plant Growth Regulators • • • • • • Table 39.1 Auxin (IAA) Cytokinins Gibb Gibberellins lli Ethylene Abscissic acid Brassinosteroids • Concentration dependent • A fine balance Scott circa 2009 Auxin • Shoot apical meristem & Leaf primordia – Root apical meristem • Functions – Cell elongation • Phototropism • Gravitropism – Shoot apical p dominance – Lateral roots Scott circa 2009 5 Biology 1030 Winter 2009 Acid-Growth Hypothesis • Induction of cell elongation 1. Membrane proton pumps 2. Cell wall acidification 3. Expansin activation – Separation of microfibrils 4. Wall enzyme activation – Cleavage of crosslinks 5. Cell wall loosening • Turgor > wall pressure Scott circa 2009 Phototropism • Shoots – positive • In I grasses 1. Shoot apical meristem 2. Lateral transport 3. Cell elongation 4. Stem bends • Other plants – Growth inhibitors Scott circa 2009 6 Biology 1030 Winter 2009 Gravitropism • Positive versus negative • Statoliths St t lith – Dense starch granules 1. Cytoskeletal distortion 2. Auxin 3. Lateral transport 4 Growth inhibition 4. • Plants without statoliths Scott circa 2009 Cytokinins • Root apical meristems – Embryos & Fruits • Cell division at meristems – Cytokinesis • Cytokinin:auxin ratio – Callus – More cytokinin – roots – More auxin – shoots Scott circa 2009 7 Biology 1030 Winter 2009 Apical Dominance • Auxin – Terminal bud • Facilitated diffusion – Axillary bud inhibition • Cytokinins – Roots – Stimulates cell division • Axillary bud activation – Removal of shoot apical meristem – Addition of auxin Scott circa 2009 Gibberellins (GA) • Roots & young leaves • Stem St and d leaf l f growth th – Cell wall loosening – Foolish rice & bolting cabbage • Fruit growth Scott circa 2009 8 Biology 1030 Winter 2009 Imbibation • Gibberellins from embryo 1 Aleurone 1. Al 2. Amylase 3. Energy gy for embryo y Scott circa 2009 Abscisic Acid (ABA) • Not involved with leaf abscission • Slows Sl growth th – Drought tolerance – Seed dormancy 1. High concentration 2. Imbibition 3. Embryo development Scott circa 2009 9 Biology 1030 Winter 2009 Ethylene • Gaseous growth regulator • Stress response St – Drought, physical pressure, injury – Induction by auxin – Fruit ripening Scott circa 2009 Triple Response • Growth obstacles – Ethylene production • Avoidance – Morphological changes • Normal growth Scott circa 2009 10 Biology 1030 Winter 2009 Leaf Abscission • Growth regulator balance – Auxin & ethylene 1. 2. 3. 4. Auxin concentration Sensitivity to ethylene Cell wall breakdown Cork layer Scott circa 2009 Fruit Ripening • Ripe fruit • Cell C ll wall ll material t i l • Starches • Scents & colours y • Ethylene • Ripening ripening p g ethylene – Feedback Scott circa 2009 11
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