Download Feb. 22

Feb. 22nd, 2011
B4730/5730
Plant Physiological Ecology
Cell Water Relations
Tournier et al Pl. J. 06
Pinus taeda;
Johnsen et al PCE 2007
Iglesias et al Phys Plant 02
Citrus unshiu
Mencuccini & Holta;
New Phyt 2010
grassland;
Bahn et al
New Phyt 2009
Gough et al Biosci 2008
Importance of Water
• Unique Physical Properties
– Hydrogen bonding
– cohesion, adhesion, surface tension,
universal solvent
– High specific heat and heat of vaporization
– Expands when frozen
– Incompressible
• In plants, 80-95% of biomass, transport
medium, provides rigidity
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
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
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
Katsuhara et al Funct Pl Bio 2008
Sunflower Mesophyll
Cells Hydrated and
Dehydrated (Kramer
and Boyer 1995)
Chara corallina Ye et al. PCE 2005
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
Trotel et al Plant Science 1996; Brassica rapa leaf discs (RLD)