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Mar. 1st st , 2011 B4730/5730 Plant Physiological Ecology

Mar. 1st st , 2011 B4730/5730 Plant Physiological Ecology. Organ Water Relations. Components of Water Potential. By definition, 0 (units) is water potential of pure water under standard conditions Osmotic (solute) potential ( Ψ π ) is the water potential in solution due to dissolved materials

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Mar. 1st st , 2011 B4730/5730 Plant Physiological Ecology

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  1. Mar. 1stst, 2011B4730/5730Plant Physiological Ecology Organ Water Relations

  2. Components of Water Potential • By definition, 0 (units) is water potential of pure water under standard conditions • Osmotic (solute) potential (Ψπ) is the water potential in solution due to dissolved materials • Hydrostatic or pressure potential (ΨP) is the physical pressure potential • Matric potential (ΨM) force with which water is adsorbed onto surfaces, especially soil • Gravity potential (Ψg) force of water due to gravity • Water Potential in energy or pressure units • Ψ = Ψπ + ΨP + ΨM +Ψg

  3. Water Relations of Cells • Ψ in cells can only be regulated by Ψπ and ΨP, but ΨP must be positive • Osmotic regulation through compatible solutes • Changes in cell-wall elasticity • greater elasticity allows more loss of water before ΨP is zero • ε = dV/dΨ • Reflection coefficient δ • Selectivity of a solute • Water moves across membranes faster than predicted by diffusion gradients • aquaporins

  4. Vacuoles, Apoplast, Symplast • Vacuoles moderate cell water relations • Provide water and solute storage • Reservoir • Apoplast is a continuous aqueous connection that does not cross cell membranes • Cell wall included in apoplast • Symplast is a sometimes discontinuous aqueous connection of water that must cross at least one membrane • plasmodesmata

  5. Katsuhara et al Funct Pl Bio 2008

  6. Sunflower Mesophyll Cells Hydrated and Dehydrated (Kramer and Boyer 1995) Chara corallina Ye et al. PCE 2005

  7. Osmotic Adjustment • Cell water balance may be maintained by lowering osmotic (solute) potential • Compatible solutes • Mineral adjustments • Ion charge and size • Organic synthesis, especially proline • Energy and N expensive • Hypotheses for adaptation include N storage and osmotic adjustment

  8. Trotel et al Plant Science 1996; Brassica rapa leaf discs (RLD)

  9. Leaf Anatomy and Water Relations • Water transported to leaves through xylem in veins • Phloem connection • Leaf water potential drives water transport to leaves • Low water potential changes cell biochemistry • Stomates restrict water loss • Do not respond directly to vpd • Unknown water potential signal

  10. Root Anatomy and Water Relations • Tradeoffs between safety and efficiency • Exodermis • Roots hairs, mycorrhizae • Casparian strip • Apoplast and symplast • Transcellular • Endodermis • Root branching • Stele • Secondary growth, cambium • Xylem and phloem • Root cap

  11. Agave deserti; North et al. 2004 PCE

  12. Root Water and Aquaporins Transport Agave deserti; North et al. 2004 PCE

  13. Pressure Volume Curves • Relationship between tissue pressure and volume describe effect of dehydration • Uses Boyle-Mariotte Law that PV=constant • Ψ is substitute for pressure • Extrapolation to Ψπ • Relative Water Content substitute for volume • Graphs drawn with 1/RWC • ε derived from nonlinearity between full turgor and turgor loss point • Osmotic adjustment shifts turgor loss point to lower RWC

  14. Niinemets Ecology 2001

  15. Glyricidia sepium Brodribb & Holbrook Plant Phys. 2003

  16. Brodribb & Holbrook Plant Phys. 2003; dotted lines 80% and 20% maximum gs

  17. Salt Effects Phillyrea latifolia; Tattini et al. 2002

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