Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 39. Plant Response AP Biology 2004-2005 Plant Reactions Stimuli & a Stationary Life animals respond to stimuli by changing behavior move toward positive stimuli move away from negative stimuli AP Biology plants respond to stimuli by adjusting growth & development 2004-2005 What mechanism causes this response? grown in dark AP Biology 1 week exposure to light 2004-2005 Signal Transduction Pathway model signal triggers receptor receptor triggers internal cellular messengers & then cellular response receptor signal pathway (2° messengers) response What kinds of molecules are theBiology receptors? AP 2004-2005 Signal Transduction Pathway example 1. Light signal is detected by the phytochrome receptor, which then activates least 2 uses cGMP as a 2nd 2. Oneatpathway signal transduction pathways messenger to activate 3. Both pathways leada protein kinase. to expression of genes The pathway forother proteins that involves increases Ca2+ that function in in cytoplasmic greening activates a different response of plant. protein kinase. AP Biology 2004-2005 Plant hormones Chemical signals that coordinate different parts of an organism only minute amounts are required produced by 1 part of body transported to another part binds to specific receptor triggers response in target cells & tissues AP Biology 2004-2005 Plant hormones auxins cytokinins gibberellins brassinosteroids abscisic acid ethylene AP Biology 2004-2005 Phototropism Growth towards light Went 1926 AP Biology 2004-2005 Auxin Indolacetic acid (IAA) stimulates cell elongation near apical meristems enhances apical dominance classical explanation of phototropism asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side AP Biology 2004-2005 Zones of meristem growth shoot AP Biology root 2004-2005 Cytokinins Family of hormones modified forms of adenine produced in roots, fruits & embryos Effects control of cell division & differentiation enhances apical dominance interaction of AP Biology auxin & cytokinins 2004-2005 Gibberellins Family of hormones over 100 different gibberellins identified Effects stem elongation fruit growth seed germination AP Biology 2004-2005 Abscisic acid (ABA) Effects slows growth seed dormancy high concentrations of ABA germination only after ABA is inactivated down or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture AP Biology drought tolerance rapid stomate closing 2004-2005 Ethylene Ethylene is a gas released by plant cells Multiple effects response to mechanical stress triple response slow stem elongation thickening of stem curvature to horizontal growth apoptosis leaf abscission fruit ripening AP Biology 2004-2005 Apoptosis & Leaf abscission Balance of ethylene & auxin many events in plants involve pre-programmed cell death death of annual plant after flowering differentiation of xylem vessels What is the evolutionary advantage of loss of leaves in autumn? loss of cytosol shedding of autumn leaves AP Biology 2004-2005 Fruit ripening Hard, tart fruit protects developing seed from herbivores Ripe, sweet, soft fruit attracts animals to disperse seed burst of ethylene triggers ripening process breakdown of cell wall = softening conversion of starch to sugar = sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production AP Biology 2004-2005 Applications Truth in folk wisdom! one bad apple spoils the whole bunch ripening apple releases ethylene to speed ripening of fruit nearby Ripen green bananas by bagging them with an apple Climate control storage of apples AP Biology high CO2 storage = reduces ethylene production 2004-2005 Responses to light Photomorphogenesis effect of light on plant growth Light detection intensity direction wavelength blue-light receptors phytochromes (red-light receptors) Why does it make “biological sense” that red & blue light have greater effects on plants response that other wavelengths? AP Biology 2004-2005 Phytochrome photoreceptors Molecular switch reaction to red light conversion of Pr Pfr in sunlight stimulates germination, flowering, branching… conversion of Pfr Pr in dark inhibits response, & stimulates other responses: growth in height Light induced Chromophore Photorecptor Kinase activity Phytochrome Phytochrome Response: Vertical growth AP Biology 2004-2005 Practical Application Why do you plant lettuce seed by scattering them on the ground instead of burying seed? What is the evolutionary advantage to lettuce seeds? AP Biology 2004-2005 Flowering Response Triggered by photoperiod relative lengths of day & night night length—“critical period”— is trigger Plant is sensitive to red light exposure What is the evolutionary advantage of photoperiodism? AP Biology Short-day plants Long-day plants Synchronizes plant responses to 2004-2005 season Is there a flowering hormone? Plant on left is induced to flower & then grafted onto plant on right plant on right is triggered to flower What can you conclude? AP Biology 2004-2005 Circadian rhythms Internal (endogenous) 24-hour cycles 4 O’clock Noon Midnight Morning glory AP Biology 2004-2005 Responses to gravity How does a sprouting shoot “know” to grow towards the surface from underground? environmental cues? roots = positive gravitropism shoots = negative gravitropism settling of statoliths (dense starch grains) may detect gravity AP Biology 2004-2005 Responses to touch Thigmotropism Mimosa (Sensitive plant) closes leaves in response to touch AP Biology Caused by changes in osmotic pressure = rapid loss of K+ = rapid loss of H2O = 2004-2005 loss of turgor in cells Plant defenses Defenses against herbivores AP Biology 2004-2005 Plant defenses Defenses against herbivores Parasitoid wasp larvae emerging from a caterpillar AP Biology 2004-2005 Plant defenses Defenses against pathogens AP Biology 2004-2005