1.27.10 - Transpiration and water potential low Two...

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1 Transpiration and water potential 1) ‘Pushing’ via Active transport-pump solutes into roots- costs energy Two mechanisms to get water into roots: water follows osmotically, raising root pressure… Ψ Transpiration and water potential Soil -0.3 MPa Root xylem -0.6 MPa Ψ Ψ Ψ Ψ Ψ Ψ Outside air -10 to -100 MPa Ψ Trunk xylem -0.8 to -1.5 MPa Leaf cells -1 to -3 MPa low high Leaf air space -7 MPa 2) ‘pulling’ of water; effects of water potential due to transpiration during photosynthesis Plant control systems Plants are complex and live in changing and often unpredictable environments. Control and coordination is essential for proper development and growth (roots grow down, shoots grow up; there should be ‘balance’ between root system and shoot system) • respond to predictable environmental changes (day-night, seasonal, etc: when to grow or open leaves, produce flowers, set fruit, etc.) • respond 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 Δ 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.
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2 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: hormone receptor cytoplasmic enzyme 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: 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 activity of existing proteins, transporters, etc: Signal transduction pathway (“2nd messenger” system) in cytoplasm 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
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3 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 receptor (in nucleus) 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 Mechanisms of hormone function Plant hormones influence their target cells in two general ways (same for animal hormones):
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1.27.10 - Transpiration and water potential low Two...

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