Chapter 30 Movement of Water and Solutes in Plants

1
Chapter 30Movement of Water and Solutes
in Plants
2
Basics

• Water movement in X (upward)
• taken up by roots
• evaporated from lvs/non-woody stems
• transpiration (T) evaporation of water from
  plant
• 2 steps
• evaporation of water from CW surface to airspaces
  w/i leaf
• diffusion of water vapor from air space into atm.
• as water moves from leaf, more pulled up from
  roots via X
• controlled by stomata
• Photosynthate (sugar) mvmt in P (downward)
• source-sink (lvs to roots)
• sugar removed 1st, followed by water

3
Water and Nutrient Movement

• Plants utilize more water than animals per wt
• animals recirculate
• plants have 1-way path from root to shoot (99
  loss)
• deciduous tree transpires 50-100 G/day
• unavoidable evil
• balance water loss w/
  CO2
  acquisition via stomata
• cuticle leaf covering,
  impervious to
  water and CO2

4
Stomata

• Stomata pores in leaf surface
• bordered by guard cells
• used to regulate water loss and CO2 intake
  (12,000/cm2)
• some water loss via lenticels
• interior of stomata is spongy mesophyll
• lots of air space
• ? humidity

5
Stomata

• Turgor pressure pressure due to water mvmt into
  cell
• Turgor pressure in guard cells determines
  stomatal aperture
• determined by mvmt of water into and out of leaf
  along ?w gradient dictated by solutes
• solutes actively ? in guard cells
• water moves into cell stomata open
• solute conc. ?
• water moves out of cell
  stomata close

6
Stomata

• Factors affecting stomatal aperture
• water loss/gain
• abscisic acid (ABA)
• produced in roots/mesophyll cells
• ? ABA close
• circadian rhythms
• light open, dark close
• CAM plants are opposite
• ?CO2 close, ?CO2 open
• ? temp. close
• ? temp ? respiration ?CO2

7
Transpiration Rates

• Transpiration
• doubles every 10C ?, up to 35C when stomata close
• Humidity
• T rate proportional to VPD
• T ? w/ ? humidity
• relates to leaf morphology
• Air current/wind
• boundary layer
• thick boundary layer ? T
• blow humid air away from leaf surface
• cooling
• drying

8
Cohesion-Tension Theory

• Sequence of events
• water evaporates from CW surfaces of air spaces
  w/i leaf and replaced by water w/i cell
• due to loss of water, solute conc. ? w/i cell
• ?w ?
• water moves from adjacent cells w/ ? ?w
• continuum of ?w throughout plant
• ? ?w due to T results in gradient from
  atmosphere to soil via
  plant tissues
• H-bonding allows water pulled
  up through plant
• cohesive properties
• allows water to be pulled (tension)
• adhesive properties
• X walls attract water

9
Cavitations and Embolisms

• Upward transport of water depends on continuous
  water column
• Cavitation breakdown of
  continuous water column
• Embolism filling of X element
  w/ air bubble
• cannot conduct water
• large vessels most susceptible
• due to physical damage
• insect/breakage/freezing
• airseeding air sucked in
  from adjacent X
  element
• larger pores more susceptible

10
Cavitations and Embolisms

• Pit membranes help prevent cavitation of entire
  column
• keep it localized
• due to surface tension btwn air/water
  meniscus in tiny pores
  of pit membranes
  or blocked by torus

11
Measurements

• Pressure bomb/chamber
• measures tension in leaf/twig
• when plant organ removed, water retracts
• apply pressure until sap comes to
  surface of cut plant part
• pressure applied tension in plant

12
Measurements

• Dendrometer
• measures change in trunk diameter
• delay in skrinkage in lower trunk relative to
  higher on trunk
• Sap flow gauge
• measures water flow past specific pt
• heating element/thermocouple used to determine
  rate of T
• 16 - 45m/day in trees
  w/ wide
  vessels
• 1- 6m/day in trees
  w/ narrow
  vessels

13
Water Entry

• Root hair functions
• anchorage
• important for water uptake
• greatly ? SA, greater contact
• Pathways for water entry
• apoplastic btwn cells via CW
• symplastic btwn protoplast via
  plasmodesmata
• transcellular cell to cell,
  vacuole to
  vacuole

14
Root Pressure and Hydraulic Lift

• Root pressure pressure in roots due
  to excessive osmosis of
  water into X
  when T is low
• guttation exudation of water
  from hydathodes
• stomata cant close on leaf margins
• water exudation from wounds/stumps
• Hydraulic lift txf water from moist area in
  soil to dry areas via
  plant roots
• good for smaller, adjacent plants w/o
  deep root systems
• desert plants