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 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

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 Higher C metabolism results N reduces acclimation Breeding for better membranes results in more yield and allows expansion of range

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

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?

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

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

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

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

Detecting stress