Plant Hormones - Module 3 Signals Chemical Electric...

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Module 3: Signals, Chemical & Electric Communication Among Cells
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Plant Hormones Key Concepts Signal transduction pathways link signal reception to response Plant hormones help coordinate growth, development, and responses to stimuli Responses to light are critical for plant success Plants respond to a wide variety of stimuli other than light
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Potato Etiolation and De- etiolation A potato left growing in darkness will produce shoots that do not appear healthy, and will lack elongated roots These are morphological adaptations for growing in darkness collectively referred to as etiolation After the potato is exposed to light the plant undergoes profound changes called de- etiolation, in which shoots and roots grow normally
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What are hormones? 1. Chemical compound, small molecules 2. Mobile 3. Potent ! (just 10 -6 to 10 -5 mol/L)
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There Are Some Differences Between Animal and Plant Hormones Plant hormones are not produced in glands (animal hormones are) but they are transported around the plant to act on distant tissues (just as animal hormones can travel in the bloodstream to site of action) Plant hormones - can produce different responses in different tissues. A plant hormone often achieves its effect in combination with other plant hormones; the ratios are critical Plant hormones are small, simple molecules but animal hormones are large, complex molecules There are many types of animal hormones but there are only five classical plant hormones: gibberellins, abscisic acid, ethylene, auxins and cytokinins. Plus recent discoveries. Plant hormones are also known as plant growth substances or plant growth regulators
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Cell Signal Processing 1. Signal (hormone or stimulus) 2. Signal received 3. Amplified 4. (Chemical) Response
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The Discovery of Plant Hormones Any growth response that results in curvatures of whole plant organs toward or away from a stimulus is called a tropism and is often caused by hormones Charles Darwin and his son Francis conducted some of the earliest experiments on phototropism, a plant’s response to light, in the late 19th century For example, the bending of a grass seedling toward light begins with the plant sensing the direction, quantity, & color of the light
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Charles Darwin and Son Francis used canary grass seedlings grown in dark. Seedlings ‘blindfolded’ and illuminated from one side. Coleoptile responds to light only when top is exposed Conclusion: Plant’s ‘eye’ is in the tip, sends message to region of bending 1913, Peter Boysen-Jensen conducted an experiment to determine how the signal for phototropism is transmitted. Boysen-Jensen observed that a phototropic response occurred if the tip was separated by gelatin (permeable barrier) but not if separated by an impermeable barrier (mica). Conclusion: results suggested signal is
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Plant Hormones - Module 3 Signals Chemical Electric...

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