Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Plant Stress Physiology Stress=an external factor that exerts a disadvantageous influence on plantsChapter 26Because of stress resulting from suboptimal climatic and soil conditions, the yield of field-grown crops in the United states in only 22% of their genetic potential (Boyer 1982)123 Biomass (g. DW)ShadeHigh LightShadeHigh Light**pH 5.5pH 4Sugar mapleRed mapleA plant’s ability to cope with an unfavorable environmentStress toleranceAcclimation: physiological adjustment in response to a prior stress (hardening) that increases tolerance- rapid responseAdaptation: a genetically determined level of stress resistance acquired by selection of adaptive traitsStress toleranceAfter LambersRate of processStressStress responseAcclimationAdaptationMinDayMonthGenerationEvolutionary timeLeaf area injury1.21.82.40.050.100.15YellWicaVoyaRomoSaguYoseSekiMnfCuvaInduDewaAlplBerrang et al.R2=0.92Ozone concentrationExamples of adaptation and acclimationAdaptation to ozone in aspenAcclimation to heat stress in riceWaterDrought (long term stress) or water deficit (short term stress)FloodingOxygen deficiencyTemperatureHeatChillingMineral stressNutrient deficiencyIon toxicitySalt stressEnvironmental stressesFlooding reduces root respiration due to low O2 (damage 24 hrs)Hypoxia tolerance: Fermentation metabolism: O2 independent but yields little ATP Greater energy use efficiencyHypoxia avoidance: Root aerenchyma: air spaces in root cortex How would aerenchyma slow hypoxia? PneumatophoresFlooding stressPneumatophoresAerenchymaWater deficit: water content of a tissue or cell that is below the highest water content exhibited at the most hydrated stateStrategies for dealing with severe water deficitDesiccation toleranceAbility to function while dehydratedDrought escapeComplete life cycle before drought onsetDesiccation postponementAbility to maintain tissue hydration Water deficit Decrease leaf area (lower water demand) Stomatal control Osmotic adjustment Leaf movements Leaf wax depositionHow?Decrease leaf area by dropping mature leavesPlant responses to water deficitDecrease leaf area by slowing leaf expansion rate Plant responses to water deficit How would a plant slow its leaf expansion rate under water deficit?ChapparalEastern ForestPlant responses to water deficit Adaptive traits: leaf size decreases and leaf thickness increases in dryer biomes; in wetter more light competitive biomes leaf tend to be thinner and largerOsmotic adjustment Solutes accumulation in cell drives water uptake Solutes:Inorganic ions, especially K+Restricted to vacuoles to avoid cytosolic enzyme inactivationCompatible solutes-organic ionsAmino acidsSugar alcoholsGlycine betaineOsmotic adjustment develops slowly and helps plants maintain water balance during water deficitPlant responses to water deficitPlant responses to water deficit Leaf movements Leaf wax depositionStomatal limitationsStomata close increasing resistance to CO2 diffusionBiochemical limitationsNegative effect on the enzymes that drive photosynthesisTranslocation limitationsResource arrival and photosynthate exportWater deficit limits photosynthetic capacity051015200 .1 .2 .3gs (mol m-2 s-1)Photosynthesis (µmol m-2 s-1)R2=0.94Nutrient deficienciesN and P deficiency primary constraint to plant growth world-wideOn acid soils deficiencies of Ca, Mg, K commonIon toxicitiesAcid soils- Al and Mn toxicity are commonSalt stress- arid environmentsMineral stressSalt stressSaline soils have excess mineralsSaline soil solutions create low osmotic potential (osmotic stress)- roots struggle to get soil moistureHigh concentrations of Na+, Cl- or SO42- inactivates cytosolic enzymes and photosynthesisHigh levels of salts can change soil structureSalts bind with clays which leads to soil compactionHalophytes: salt tolerant plantsPlants that naturally grow and thrive in the presence of high levels of salts in the soil and/or waterLocations such as coasts, mangrove swamps (seawater), saline semi-arid and arid deserts, marshes and sloughsMangroves1) Osmotic adjustment using compatible solutesHow do they do it?Plant responses to salt stress2) Salt toleranceLeaf excretion concentration/abscissioncompartmentation-vacuolecellular extrusion3) Salt avoidanceIon exclusionPlants that complete their reproductive life cycle during rainy season (lower salt concentrations)Heat stressProtein denaturation and membrane damagePlant responses to heat stressCellular levelHormone involvementABA and ethylene—mutants are sensitive to heat stressAdaptation to heat stress is mediated by cytosolic Ca+2HSF- transcription factorHeat shock proteins- chaperonesAnatomical and morphological Reflective leaf hairsLeaf waxes & cuticleLeaf rolling or movementChanges in leaf morphologyMore small, highly dissected leavesChilling and freezing stress Membrane properties change in response to chilling injuryProper membrane fluidity allows membrane proteins to continue functioningPlant responses to freeze stressCellular responsesHormone involvementABA—exogenous treatment increases cold toleranceC-repeat binding factor- transcription factor100+ genes upregulated in response to cold stressAntifreeze proteins-slow ice crystal formationSucrose and proteins—stabilize proteins and membranesIce nucleation by bacteriaChapter 25 Homework QuestionsDefine stress tolerance and outline the two general strategies that plants use to cope with stress.Explain the three general strategies that plants use to deal with drought stress. Which of these strategies has made cheat grass so successful? If you were breeding plants to be drought tolerant, identify three traits you would select.Identify the mineral stresses you would expect to see in acidic soils and in arid soils. Explain three ways in which saline soils can impair plant function. Identify two ways (for both tolerance and avoidance) in which plants tolerate and avoid salt stress. Using transport proteins on the plasma membrane and the vacuole membrane (tonoplast) bioengineer a way to maintain low salt concentrations in the cytosol of root cells growing in saline soils. Also explain how you will get water into the cytosol with such high solute concentrations in the soil.Explain how extreme temperatures impair physiological function and explain the