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Biology Sylvia S. Mader Michael Windelspecht
Chapter 26 Flowering Plants: Control of Growth Responses Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1
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Biology, 9th ed, Sylvia Mader
Chapter 27 Outline Control of Plant Growth/Response 26.1 Plant Hormones 26.2 Plant Responses
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Biology, 9th ed, Sylvia Mader
Chapter 27 26.1 Plant Hormones Control of Plant Growth/Response Flowering plants respond to environmental stimuli Stimuli include light, gravity, carbon dioxide levels, pathogen infection, drought, and touch Response to stimuli leads to the survival of the species. The responses can be: Short term Stomata open and close in response to light levels. Long term The response to gravity causes downward growth of the root and the upward growth of the stem.
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Response of plants to environmental stimuli involves signal transduction The binding of a molecular “signal” that initiates and amplifies a response. Signal transduction involves the following: Receptors – proteins activated by a specific signal Transduction pathway – a series of relay proteins or enzymes that amplify and transform the signal to one understood by the machinery of the cell Cellular response – the result of the transduction pathway
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Hormones Enable plant cells to communicate Are synthesized in one part of the plant Travel within phloem or from cell to cell in response to the appropriate stimulus
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Signal Transduction in Plants
Biology, 9th ed, Sylvia Mader Chapter 27 Signal Transduction in Plants Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. defense hormones hormone-binding site blue light signal 3 2 Receptor: Molecule in the plasma membrane, cytoplasm, or nucleus that receives signal and becomes activated. Response: Most often a change in gene expression or a cellular process affects plant growth and development. Transduction pathway: A series of relay proteins that amplify and convert the original signal into one that affects cellular machinery . activated phototropin relay Defense responses proteins auxin auxin carrier Responses include bending of stem 1 Gene expression changes activated auxin receptor Responses include growth of roots Cytoplasm Nucleus
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Auxins Produced in shoot apical meristem Found in young leaves, flowers, and fruits Effects of auxin on growth and development: Apically produced auxin prevents the growth of axillary buds Apical dominance Promotes growth of roots and fruit Prevents loss of leaves and fruit Promotes positive phototropism of stems
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Auxin and Phototropism
Biology, 9th ed, Sylvia Mader Chapter 27 Auxin and Phototropism Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. Coleoptile tip is intact. 2. Coleoptile tip is removed. 3. Tips are placed on agar, and auxin diffuses into the agar. 4. Agar block is placed to one side of the coleoptile. 5. Curvature occurs beneath the block.
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response How Auxins Cause Stems to Bend When a stem is exposed to unidirectional light, auxin moves to the shady sides Auxin binds to plasma membrane receptors; the complex leads to the activation of a proton pump Activated proton pumps H+ out of cell Cell wall loosens Turgor pressure increases due to the entry of water Cell enlarges
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Expansion of the Cell Wall
Biology, 9th ed, Sylvia Mader Chapter 27 Expansion of the Cell Wall Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cellulose fiber in cell wall auxin nucleus H+ enzyme (inactive) H+ H+ H+ chloroplast 1 Cytoplasm H+ H+ active enzyme H+ H2O H+ 2 turgor turgor 3
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Gibberellins are growth-promoting hormones Gibberellins cause stem elongation There are about 70 gibberellins Each differ slightly chemically The most common is gibberellic acid
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Gibberellins Cause Stem Elongation
Biology, 9th ed, Sylvia Mader Chapter 27 Gibberellins Cause Stem Elongation Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. a: © Robert E. Lyons/Visuals Unlimited; b: © Sylvan Whittwer/Visuals Unlimited
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response The cytokinins are a class of hormones that promote cell division found in dividing tissues of roots, in seeds, and in fruits have been used to prolong the life of flower cuttings as well as vegetables in storage Auxin and cytokinins interact prevent senescence (aging process)
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Interaction of Hormones
Biology, 9th ed, Sylvia Mader Chapter 27 Interaction of Hormones Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. c. d. Courtesy Alan Darvill and Stefan Eberhard, Complex Carbohydrate Research Center, University of Georgia
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Abscisic acid (ABA) is produced by any “green tissue” (i.e., tissue containing chloroplasts) sometimes called the stress hormone initiates and maintains seed and bud dormancy brings about the closure of stomata
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Abscisic Acid Promotes Closure of Stomata
Biology, 9th ed, Sylvia Mader Chapter 27 Abscisic Acid Promotes Closure of Stomata Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. inside outside H2O K+ K+ K+ Ca2+ ABA Open stoma Guard cell plasma membrane Closed stoma
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Hormones Control of Plant Growth/Response Ethylene (H2C = CH2) is a gas formed from the amino acid methionine. Effects of ethylene Abscission Ethylene stimulates certain enzymes, such as cellulase, which helps cause leaf, fruit, or flower drop Ripening of fruits Increases the activity of enzymes, such as cellulase, that soften fruits It also promotes the activity of enzymes that produce the flavor and smell of ripened fruits. Axillary bud inhibition Suppression of stem and root elongation
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Ethylene and Fruit Ripening
Biology, 9th ed, Sylvia Mader Ethylene and Fruit Ripening Chapter 27 Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gene for ethylene biosynthesis enzyme DNA ripe tomatoes harvested transcription mRNA translation functional enzyme for ethylene biosynthesis ethylene synthesis (in plant) green tomatoes harvested no ethylene synthesis
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Arabidopsis Is a Model Organism
Biology, 9th ed, Sylvia Mader Chapter 27 Arabidopsis Is a Model Organism Control of Plant Growth/Response Arabidopsis thaliana A small flowering plant related to cabbage and mustard plants Has no commercial value It has become a model organism for the study of plant molecular genetics, including signal transduction. It is small, so many hundreds of plants can be grown in a small amount of space. Generation time is short – 5-6 weeks until maturity. It normally self-pollinates, but it can easily be cross-pollinated. The number of base pairs in its DNA is relatively small.
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Biology, 9th ed, Sylvia Mader
Chapter 27 26.2 Plant Responses Control of Plant Growth/Response Tropism Plant growth toward or away from a unidirectional stimulus Positive tropism is growth toward the stimulus Negative tropism is growth away from the stimulus Gravitropism - movement in response to gravity Phototropism - movement in response to light Thigmotropism - movement in response to touch
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Gravitropism When a plant is placed on its side, the stem grows upward, opposite of the pull of gravity Stems with root caps grow downward Response depends on sensors called statoliths Auxin may be responsible for: gravitropism of roots and shoots
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Biology, 9th ed, Sylvia Mader
Gravitropism Chapter 27 Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. gravity a: © Kingsley Stern; b: Courtesy Malcolm Wilkins, Glascow University; c: © BioPhot c. 25 mm
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Phototropism Positive phototropism of stems Occurs because cells on the shady side of the stem elongate due to the presence of auxin A pigment absorbing blue light initiates phototropism
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Biology, 9th ed, Sylvia Mader
Chapter 27 Phototropin Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 cytoplasm 2 3 blue light blue light blue light ADP transduction pathway phot phot phot P A T P ATP plasma membrane
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Thigmotropism Unusual growth due to contact with solid objects Coiling of tendrils Thigmomorphogenesis occurs when the entire plant responds to the presence of environmental stimuli Wind Rain
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Biology, 9th ed, Sylvia Mader
Chapter 27 Coiling Response Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © John D. Cunningham/Visuals Unlimited
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Nastic movements: Do not involve growth and Are not dependent on the stimulus direction Turgor movements result from touch, shaking, or thermal stimulation Mimosa pudica Venus flytrap Sleep movements: Occur daily in response to light and dark changes Circadian rhythm
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Biology, 9th ed, Sylvia Mader
Chapter 27 Turgor Movement Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pulvinus vascular tissue cell retaining turgor cell losing turgor Before After © John Kaprielian/Photo Researchers, Inc.6
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Circadian rhythms: Biological rhythms with a 24-hour cycle Tend to be persistent Rhythm is maintained in the absence of environmental stimuli Caused by a biological clock
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Sleep Movements and Circadian Rhythms
Biology, 9th ed, Sylvia Mader Chapter 27 Sleep Movements and Circadian Rhythms Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prayer plant (morning) Prayer plant (night) a. Morning glory (morning) Morning glory (night) b. Circadian Rhythm flowers open Period (about 24 hours) flowers close 12 24 36 48 Time (hours) (Top, both): © Tom McHugh/Photo Researchers, Inc.(Bottom left): © BIOS A. Thais/Peter Arnold, Inc.; (Bottom right): © BIOS Pierre Huguet/Peter Arnold, Inc. c.
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Photoperiodism: Any physiological response prompted by changes in day or night length influences flowering in some plants requires participation of a biological clock and a plant photoreceptor called phytochrome
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Biology, 9th ed, Sylvia Mader
Chapter 27 Plant Responses Control of Plant Growth/Response Phytochrome is a blue-green leaf pigment that alternately exists in two forms Phytochrome red (Pr) is inactive Phytochrome far-red (Pfr) is active Conversion of forms allows a plant to detect photoperiod changes Also promotes seed germination and inhibits stem elongation
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Wound Response in Tomato
Biology, 9th ed, Sylvia Mader Chapter 27 Wound Response in Tomato Control of Plant Growth/Response Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. systemin cytoplasm membrane- bound receptor proteinase inhibitors lipase wounded leaf membrane lipids systemin release salicylic acid nucleus jasmonic acid activation of proteinase inhibitor genes transduction pathway
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