Plant Gorwth and Developlement

Plant Gorwth and Developlement - PLANT GROWTH AND...

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PLANT GROWTH AND DEVELOPMENT (CHAPTER 37) Phototropism o Growth in response to the direction of light (positive) o Bending triggered by blue light (<500nm) o Photoreceptors called phototropins (light activated kinases) are phosphorylated and lead to signal cascade o Similar mechanism for stomata opening in response to light Gravitropism o Growth in response to gravity o Most stems tip grow away from earth’s center (negative gravitropism); most root tips show positive gravitropism) (NB: root cap removal)- amyoplasts in specialized cells cooect at the bottom of the root cap in response to gravity. Not in some mutants however. Thigmotropism o Growth in response to contact with a solid object: Mechanical stimulus helping a climbing plant twine or curl Production of tendrils E.g. vine Plant Hormones o Organic compounds produced by plants o :<10 (-6) mol/L o Act as highly specific chemical signals Response occurs close o hormone production, not at a distance Small molecules not macromolecules o Elicit responses that regulate growth and development at a particular concentration And inhibit at another concentration Mechanisms
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o Many a plant hormones bind to enzyme-linked receptor s in the plasma membrane Auxin o Auxin binds to receptor in plasma membrane Catalyzes attachment of ubitiquin to repressor proteins Repressor proteins are targeted for destruction o Genes repressed by these proteins are now activated Genes transcription and translation Changing cell growth and development o TIR1 = transport inhibitor response 1 receptor; an F-box protein (with a specific sequence that tabs ubiquitiin). Ubiquitin destruction of certain proteins. Darwin’s experiment (1870s) (Phototropism experiments on grass seedings) o Coleoptile exposed to light, bends toward light o Covered coleoptiles tip, plant didn’t bend o Cut off coleoptiles tip, plant didn’t bend o Bottom of coleoptiles shielded from light, only coleoptiles tip bent o NB: coleoptiles is protective sheath that covers stem o First evidence that Grass coleoptile tip is needed for bending in the presence of light Conclusion: some kind of substance is transmitted from the upper part to the lower part to bend Fritz Went’s Experiment
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Plant Gorwth and Developlement - PLANT GROWTH AND...

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