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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
Possible responses: move, adapt or dieStress 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
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
Acclimation: produce more unsaturated fatty acids
Breeding for better membranes results in more yield and allows expansion of range
Higher C metabolism results
N reduces acclimation
Freezing Tos- Damage from ice crystals; Cell leaksAvoiders/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
High TosFew plants can live > 45oCLeaf Tos increase when stomata closedHeat alters membrane properties
– Membranes too fluid; leakage– Inefficient PSN and respiration– Proteins denatured– Leaf ‘burn’ wilting
Acclimation:1)membrane f.a? also increase cholesterol 2)heat shock proteins (HSP)
– Molecular chaperones; stabilize protein structure– Cross protection to other stresses
Adaptations?
Salinity stressOccurs:
– 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
Glycophytes vs. halophytesHalophytes 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
FloodingAnaerobic soils cause:
– ATP production ceases in roots
– pH decreases in root tips
– Fe toxicity
– low N and S availability
– Lower nutrient uptake
Air pollutionIndustrial 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
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