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

Detecting stress