1. What is Stress? Adverse factor(s) that inhibits ‘normal’ physiology
Can result in:
Reduced growth (NPP/yield)
Lower survivorship; limits distributions
Impaired response to environ. cues

2. Possible responses: move, adapt or die Stress escapers
Dormant or die; active during good times
Stress tolerators
Equilibrium w/ stress via acclimation or hardening
Acclimation - physiological modifications made over short-time (e.g. a season or the life of an individual)
Stress avoidance/resistance
Morpho-physiologic traits allow few harmful effects
Adaptation - heritable traits that increase fitness
Severity depends on rate of change, magnitude of stress and extreme

3. Chilling Tos = suboptimal Tos; not freezing; ~10o C
Big crop loss = ~$200-$350 mil/yr: cotton, subtropical fruits
Generally decreases yield or hastens spoilage
Limits (sub)tropical plants; NRG intensive to grow outside of range
Chill-sensitive plants = higher proportion of saturated fatty acids
Damage b/c membrane properties altered
Cells leak; proteins degrade
Lower C metabolism (PSN & respiration)
Leaf lesions, wilting

4. Acclimation: produce more unsaturated fatty acids
Higher C metabolism results
N reduces acclimation
Breeding for better membranes results in more yield and allows expansion of range

5. Freezing Tos - Damage from ice crystals; Cell leaks
Avoiders/tolerators acclimate to ~ -40oC by:
Increasing ABA, GA
Altering membrane properties; how?
High [solute] inside cells; AFPs in apoplast
Ice formation in apoplast; water fusion releases heat
Dehydrating xylem; tolerating dehydrated cells
Limiting ice nucleation w/in cells
Freezing process w/ supercooling

6. High Tos Few plants can live > 45oC
Leaf Tos increase when stomata closed
Heat alters membrane properties
Membranes too fluid; leakage
Inefficient PSN and respiration
Proteins denatured
Leaf ‘burn’ wilting
Acclimation:
membrane f.a? also increase cholesterol
heat shock proteins (HSP)
Molecular chaperones; stabilize protein structure
Cross protection to other stresses
Adaptations?

7. Salinity stress Occurs: Effects: Near sea water
In naturally saline soils
(old inland seas)
B/c of irrigation
10-35% ag land affected
Effects:
Toxicity of specific ions
Osmotic stress; ψs lower in soil
Alters soil structure; less O2

8. Glycophytes vs. halophytes
Halophytes are adapted to salt stress:
Alter protein synthesis (osmotin) to acclimate
Synthesize compatible solutes
Exclude salts or take up salts & excrete on surface or take up salts & sequester
Oxygenate soils with specialized roots

9. Flooding Anaerobic soils cause: ATP production ceases in roots
pH decreases in root tips
Fe toxicity
low N and S availability
Lower nutrient uptake

10. Air pollution Industrial and auto emissions
CO, SOx, NOx, ozone, volatile organics
Gases enter stomates
Disrupt guard cells; alter membranes
Some gases toxic or generate free radicals
C assimilation & PSN enzyme activity decreases

11. Detecting stress