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Stress Physiology Chapter 25 Water stress drought

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Stress Physiology Chapter 25 Water stress drought tolerance Heat stress and heat shock Chilling and freezing Salinity O2 deficiency Responses to water stress ... – PowerPoint PPT presentation

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Title: Stress Physiology Chapter 25 Water stress drought


1
Stress Physiology Chapter 25
Water stress drought tolerance Heat stress and
heat shock Chilling and freezing Salinity O2
deficiency
2
  • Responses to water stress
  • Osmotic adjustment
  • Stomatal closure
  • hydropassive - guard cell dehydration
  • hydroactive - guard cell metabolism ABA,
    solutes, etc.
  • Leaf abscision and reduced leaf growth
  • reduces surface area for water loss
  • Smaller leaves lose more heat via convective heat
    loss
  • Increased root growth
  • with reduced leaf expansion, more C transported
    to roots
  • increases water supply
  • Increased wax deposition on leaf surface
  • reduces cuticular transpiration, increases
    reflection

3
Also many responses at the cellular
level Proteins increase and decrease in
response to water stress One special group of
proteins LEA-proteins (late embryogenesis
abundant) Accumulate in dehydrating leaves, and
during seed ripening Function protection of
membranes (hydrophylic proteins) prevention of
destructive crystallization of proteins
4

Table 25.3
2. Heat Stress And Thermotolerance
5
Energy loss Reradiation Convection Conduction Tr
anspiration Energy storage
6

Atriplex Tidestromia
Photosynthesis declines before respiration
Ion leakage is a sign of membrane damage due to
high temps. (or freezing.)
Fig. 25.10
7
  • What happens when plant tissues reach harmful
    temperatures?
  • Membranes lose function because they become too
    fluid.
  • Soluble proteins may denature, degrading function
  • Membrane-bound proteins may become dysfunctional
    because of denaturation or excessive membrane
    fluidity.
  • These effects can be seen in the changes in
    photosynthesis, respiration, and ion leakage of
    membranes.

Fig. 1.5
8
  • Adaptive or acclimation responses to high
    temperatures
  • Vertical leaf orientation
  • Leaf pubescence
  • Altered membrane fatty acids
  • more saturated fatty acids that dont melt as
    readily
  • 4. Production of heat shock proteins (HSPs) in
    response
  • to rapid heat stress
  • molecular chaperones, increase enzymes
    resistance to denaturation help maintain proper
    protein folding

9
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10
3. Chilling and freezing stress Symptoms
Slower growth Leaf necrosis or damage Soggy
looking leaves Inhibition of photosynthesis,
translocation, increased degradation of
proteins The central problem - loss of membrane
function. Chilling can cause membranes to lose
fluidity. Freezing can rupture membranes (ice
crystals) Extracellular ice can dehydrate
protoplast Freezing induced xylem embolisms can
result from air bubbles released from ice as it
thaws.
11
Chilling sensitive Corn Phaseolus
bean Rice Tomato Cotton etc
12
Young root sections Incubate at 25C for
24h Measure conductivity Kill roots at high
temperature Measure conductivity
Nayyar et al. 2005 - chickpea
13
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14
Membrane fatty acid composition determines
fluidity at different temperatures.
Saturated f.a. have no double bonds all
carbons are saturated with -H. Ratio of chain
lengthdbl. bonds determines melting point

15
Longer chains and fewer double bonds mean higher
melting temperature
Palmitic 160 (major constituent of palm oil)
16
Acclimation and adaptation response to low
temperatures include an increase in membrane
unsaturated fatty acids. Chilling-resistant
species have higher unsatd/satd ratio.
Oleic acid is 181, Pea shoot is 17.8 not 12.8
17
summary of fatty acids High unsaturated
melts early, good for cold Low unsaturated
melts late, good for hot
18
Pinus aristata, S.F. Peaks
What makes arctic and alpine species tolerant of
freezing? How is that overwintering buds (e.g.
winter deciduous trees) tolerate
temperatures that would kill summer leaves and
buds?
19
Frost tolerance increases as buds harden for
winter.
ABA is thought to induce hardening
20
Dealing with chilling and freezing
stress 1.Altered membrane fatty acids 2. Solute
accumulation can lower freezing
point. antifreeze compounds 3. Limiting ice
nucleation using antifreeze proteins that slow
ice formation. 4. deep supercooling
mechanisms that prevent ice formation down to
-400C! 5. ABA seems to induce freezing tolerance.
21
Hardening in hardwood forest species 1- short
days, low temperature induction of chilling
tolerance - stops growth, remove water from
xylem 2- freezing tolerant to -50 to
-100C Deep super cooling no ice formation
above -40C. Oak, elm, maple, beech, pear,
apple, Engelmann spruce, subalpine fir. Cross
tolerance They are also extremely dehydration
resistant. Again LEA and HSP proteins may be
involved. Some of the anti-freeze proteins are
also involved in pathogen attacks!! Spring
freeze tolerance is lost quickly spring damage
to flower buds!!
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