Lecture8.plant_responses

Lecture8.plant_responses - Plant Responses • A potato...

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Unformatted text preview: Plant Responses • A potato left growing in darkness produces shoots that look unhealthy and lacks elongated roots • These are morphological adaptations for growing in darkness, collectively called etiolation • After exposure to light, a potato undergoes changes called de-etiolation , in which shoots and roots grow normally • A potato’s response to light is an example of cell- signal processing • The stages are reception, transduction, and response Signal transduction pathways link signal reception to response • For a stimulus to elicit a response, certain cells must have an appropriate receptor Reception • Internal and external signals are detected by receptors, proteins that change in response to specific stimuli • Receptor involved in de-etiolation – a type of phytochrome located in the cytoplasm • Studies of the Aurea tomato mutant – Greens less than wild-type tomatoes when exposed to light • Has lower than normal levels of phytochrome – Injections of phytochrome produces normal de- etiolation Transduction • Second messengers transfer and amplify signals from receptors to proteins that cause responses – In de-etiolation (greening) • The light signal activates at least two transduction pathways • Increased level of second messengers – cGMP and Ca +2 Response • A signal transduction pathway leads to regulation of one or more cellular activities – In de-etiolation • transduction pathways lead to the production of proteins that function in de- etiolation • In most cases, these responses to stimulation involve increased activity of enzymes – In de-etioloation • Many enzymes that function in certain signal responses are directly involved in photosynthesis • Other enzymes are involved in supplying chemical precursors for chlorophyll production • Other proteins affect the levels of plant hormones Plant Hormones • Hormones are chemical signals that are produced in one part of the body, transported to other parts, bind to specific receptors, and trigger responses in target cells and tissues Plant Hormones – Required in minute quantities – Concentration and rate of transport changes in response to stimuli – Plant responses are usually governed by the interaction of two or more hormones • In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells • Some mediate short-term physiological responses • Each hormone has multiple effect depending on its site of action, its concentration, and the developmental stage of the plant Major Classes of Hormone • Auxin • Cytokinins • Gibberillens • Brassinosteroids • Abscisic acid • Ethylene Systems Biology and Hormone Interactions • Interactions between hormones and signal transduction pathways make it hard to predict how genetic manipulation will affect a plant Responses to Light...
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This note was uploaded on 11/02/2010 for the course CHEM 51LA 56555 taught by Professor Guan during the Spring '10 term at UC Irvine.

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Lecture8.plant_responses - Plant Responses • A potato...

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