plant control

plant control - Plant control systems Plants are complex...

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Plant control systems Plants are complex and can be very large, and live in changing and often unpredictable environments. Control and coordination is essential: development and growth in appropriate ways (roots grow down, shoots grow up; there should be ‘balance’ between root system and shoot system) response to predictable environmental changes (day-night, seasonal, etc: when to grow or open leaves, produce flowers, set fruit, etc.) response to unpredictable environmental changes (wind, rain, attack by herbivores or pathogens, etc.) Plant control systems Responses at the cellular level (signal transduction) stimulus reception transduction cellular response activation of cytoplasmic or membrane proteins; change in transcription or translation ! protein function ‘second messenger’ intracellular relay; a signal amplification system binding or other interaction of stimulus with receptor protein The stimulus may be an environmental or internal factor A chemical signal produced in one body region that travels to and has an effect on target cells in another body region is a hormone. Mechanisms of hormone function Plant hormones influence their target cells in two general ways (same for animal hormones): change the activity of existing proteins, transporters, etc: altered protein function Response Signal transduction pathway (“2nd messenger” system) in cytoplasm hormone binds to membrane receptor Mechanisms of hormone function Plant hormones influence their target cells in two general ways (same for animal hormones): change the rate of synthesis of proteins: hormone crosses membrane, binds to receptor in nucleus altered protein function Response changed translation Changed transcription
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Mechanisms of hormone function A classic hormonal-mediated response to an external stimulus: Phototropism -- bending towards light -- in growing seedlings One of the earliest examinations of hormone function; hormones first demonstrated about 100 years ago in plants and animals. Control no tip opaque tip transparent cover tip cover; opaque base shield Phototropism in coleoptiles Darwin & Darwin, 1880 These experiments show that the tip of the coleoptile is the site of the response to light. Control no tip opaque tip transparent gelatin mica block cover tip cover; block (impermeable) opaque base shield Phototropism in coleoptiles Darwins, 1880; Boysen-Jensen 1913 These experiments indicate that a mobile chemical activated by light is the signal for bending and growth. Control agar block agar block offset blocks w/o auxin with auxin cause curving (no growth) (growth) Phototropism in coleoptiles Darwins, 1880; Boysen-Jensen 1913; Went 1926 These experiments suggest that the distribution of the chemical signal is responsible for bending.
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This note was uploaded on 07/31/2008 for the course BIO 5B taught by Professor Chappell during the Spring '07 term at UC Riverside.

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plant control - Plant control systems Plants are complex...

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