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2: Water and Plant Cells (water potential contributing factors…

- - - - O covalent bonded 2 H atoms
        
        O very electronegative
        
        partial positive O
        
        partial negative H
        
        electrons
        
        O=6
        
        H=1
  - - - Hbonds=rubberbands
        
        absorb some energy
        
        leaves less E to raise temp
      - buffers temp fluctuations #
    - - due to cohesion
        
        adhesion is attraction to nonself
        
        capillary action # #
        
        contact angle
      - water greater attraction to self then air #
      - E required to increase SA at gas-liquid interface
      - units
        
        Jm^(-2)
        
        Nm^(-1)
      - produce force that pull water through vascular system #
    - - water small
      - polar #
    - - transpiration #
      - decreases as temp increases
      - helps cool surfaces #
    - - negative hydrostatic pressure #
        
        MPa
        
        1MPa=9.9atm
        
        1Pa=1Nm^(-2)
        
        1Pa=1Jm^(-3)
      - cavitation
      - 20MPa to break water column #
- - - - Js= flux density
        
        =amount of substance crossing a cross-sectional area per unit of time
        
        mol m^(-2) s^(-1)
      - \( \Delta\) Cs=concentration of substance s
      - \( \Delta\)X separation distance
        
        time required to diffuse a distance increases as the square of that distance
      - \( \Delta\)cs=diffusion coeeficient
        
        increase with temp
        
        air faster than liquid
      - negative sign indicates movement down concentration gradient
- - - - J m^(-3)
  - - - Psi s = solute concentration
        
        solute potential = osmotic potetnial
        
        solutes increase free energy decrease
        
        R=gas constant
        
        =8.32 J mol^(-1)K^(-1)
        
        T= absolute temperature (K)
        
        cs = solute concentration
        
        osmolarity
        
        moles of total dissolved solutes per volume of water mol L^(-1)
        
        neg. sign indicates that dissolved solutes reduce Psi of a solution relative to reference state of pure water
        
        for 'ideal' solutions only
      - psi P = pressure
        
        pressure potential
        
        hydrostatic pressure on free energy of water
        
        pos psiP, increases Psi
        
        neg PsiP, decreases Psi
        
        neg p = tension #
        
        += turgor pressure
      - Psi g = gravity
        
        #
        
        h=height
        
        pw=density of water
        
        g=acceleration due to gravity
        
        pwg=0.01MPa m^(-1)
      - simplified for cells
        
        psi g negligible
        
        matric potential
        
        psi m
        
        combine psi s and psi p`
        
        used for
        
        seeds
        
        dry soils
        
        when water exists in very thin layer (1-2 molecules thick)
  - - - vapor pressure of water in equilibrium with the sample
      - transfer of water vapor btw sample & solution of known psi s
    - - directly
        
        liquid filled microcapillary attached to pressure sensor
      - estimate
        
        difference between Psi and psi s
- - - - inhibits growth
      - inhibit photosynthesis
      - cell expansion largely affected
        
        shoot growth decrease while root growth increase
        
        adaptation, not a constraint
    - - accumulation of solutes in cytoplasm and vacuoles
      - maintains turgor despite low \( \Psi\)
  - - - lowers cell \( \Psi\)
        
        enables roots to extract water from saline water without allowing excessive levels of salts to ener at the same time
  - - - stretch activated signaling molecules in membranes
- - - - increase in solutes
        
        lower osmotic potential (psi s)
        
        decrease psi
      - flaccid cell
        
        no turgor pressure
      - reference set to 0MPa
    - - put cell into higher concentration environment
      - put cell under higher pressure
        
        RO water
  - - - <260 water molecules
  - - - herbs -0.2 to -1MPa
      - trees & shrubs-0.2 to -2.5 MPa
    - - well watered
        
        garden plants (lettuce) >-0.5MPa
        
        low solute concentration
        
        -0.8 to -1.2 MPa typical
        
        woody plants
        
        psi s tends to be lower
        
        higher cell solute concentration
        
        permits low midday psi without loss of turgor
      - apoplastic cell solution
        
        cell walls & xylem
        
        dilute
        
        typically -0.1 to 0MPa
        
        can be high in high salinity environments
        
        can be high in developing fruits
    - - well watered
        
        tyically 0.1 to 3MPa
        
        depends on psi s
        
        wilting occurs when turgor go towards 0
        
        very low turgor can result in mechanical damage of cell wall
- - - - approaches zero as rel. cell volume dereases by 10-15%
    - - volume homeostasis due to cell wall #
      - usually little change
        
        change in psi
        
        results in large change in psi p
      - pressure-volume curve
    - - epsilon
      - change in psi p for given change in relative volume
      - large \( \epsilon\)= stiff cells
        
        larger changes in psi p for same change in cell volume as cells with smaller \( \epsilon\)
  - - - half time of water transport across membrane
        
        short half time = fast equilibration
        
        typical cell 1-10s
      - V= volume of cell
      - A=cell surface area
      - Lp=hydraulic conductivity of membrane
        
        m^3 m^(-2) s^(-1) MPa^(-1)
    - - cannot change direction
      - can be "gated"
        
        respond to pH, Ca2+, etc
        
        cells able to regulate permeability to water
  - - - inner cells have thinner walls
        
        more flexible, lower \( \epsilon\)
        
        greater water loss during drought #
        
        atypical loss of solutes in storage cells
        
        help maintain hydrated photosynthetic tissue
      - outer photosynthetic cells thicker walls
        
        less water loss than inner cells