What is Stress?• A significant deviation from the conditionsoptimal for life, and eliciting changes andresponses at all functional levels of theorganism.• Two waysTemporary stressPermanent stress
What Happens During Stress?
How to Recognize StressEffects of Stress1. Stressor-specific effectinvolve a well- defined target within theplant.Ex. Intense radiation causes direct damage to the thylakoidmembrane2. Non- specific effectStress responses within the plant is carried outby phytohormones.
How to Recognize Stress• Non- specific effects of stressa. Alterations in membrane properties(membrane potential, transport of substances)b. Increased respirationc. Inhibition of photosynthesisd. Growth disturbancese. Lower fertilityf. Premature senescenceg. Decrease of availability of energy
How to Recognize Stress• Intracellular decrease in availability of energy.(Due to metabolic impairment)• Less ATP is formed.• It can be calculated as an Adenylate EnergyCharge(AEC).AEC = (ATP)+ 0.5(ADP)(ATP)+(ADP)+(AMP)• AEC < 0.6 indicates deterioration in the vitalityof a plant, and a plant under stress.
Survival of Stress• Survival = Stress evasion, Resistance, Recovery
Natural Environmental Constraints• Environmental stress factors1. Abiotic factors – mainly includeclimatic factors.2. Biotic factors – Due to activity ofanimals, microorganisms or human beings.
Multiple Stresses• In nature frequently multiple stresses areinvolved.Ex. Stress arise due to combination of strongradiation, overheating, drought in openhabitat.
Radiation Stress• Two ways of radiation stress1.Excessive quantities of photosyntheticallyactive radiation.2.increased absorption of UV radiation.
Light Stress• Strong light presents the leaf with morephotochemical energy than can be utilized forphotosynthesis.• Overloading of the photosynthetic process.• Extremely high irradiance destroysphotosynthetic pigments and thylokoidstructures is called “photodamage”• Shade plants may be damaged breif exposureof strong light.
Light StressConostomum tetragonium exposed to the high light intensity
Photoinhibition• Inhibition of photosynthesis caused byexcessive radiation.• Strong light attack photosystem II• Brake down of Protein sub units• Photosynthetic electron transport isinterrupted.• Reduce efficiency of photosystem II
PhotoinhibitionAs an protective measure,• Excessive radiation energy is diverted tofluorescence and heat.• Surplus reductive capacity in chloroplast isused by “Xanthophyll Cycle”
Xanthophyll CycleThylakoid membraneLumen Stroma
A moss quenches high light energy with the pigment zeaxanthin.
a) Pellia endiviifolia did notexperienced a rise in de-epoxidized Xanthophyll.Liverwortsb) Flullania dilatata was a risein the concentration of de-epoxidized xanthophyllsthat can protect cell fromchlorophyll damagea)b)
Adaptation to Stress from Strong Light• Positioning leaves at an angle to the incominglight- Receive less radiation.• Rolling up the shoots (mosses, pteridophytes)• Dense coverings of trichomes on the uppersurface of the leaf.• Thickened walls in the epidermis and hypodermaltissue-act as diffusive filters (conifer needles &cacti)• Presence of Anthocyanin- act as darkening filters& shields the mesophyll.
Ultraviolet Radiation• Two types of UV radiationUV-A (315-400nm)UV-B (280-315nm)• UV-A is mainly photooxidative.• UV-B is in addition to photooxidative actioncauses photolesions in biomembranes.
UV Damage• Breaking down the disulfide bridges in proteinmolecules.• Dimerizing thymine groups of DNA- results indefective transcription.• Xanthophyll cycle is disrupted by inhibiting theviolaxanthine-deepoxidase
UV DamageCan be identified by• Changes in enzyme activity (increasedperoxidase activity, inhibition of cytochromeoxidase).• Poor energy status of the cell.• Lower photosynthetic yield.• Disturbed growth (reduced extension growth& pollen tube elongation).
PLANT STRESS DUETO EXTREMETEMPETURES24
KINETIC ENERGY OF MOLECULES= HEATKINETICENERGY OFMOLECULESHIGH ENERGYLOW ENERGYHEATCOLD25
Temperature balance on earth by,Solar radiationair currentHeat and Cold effect• Metabolic activity• Growth• Viability• Distribution,of a plant.26
Critical temperature Thresholds• Activity limit(5-25 0C)• Lethal limit– Cold– Heat27
HeatHighest temperature on earth- 80oCLethal limit- 40-70oCHigh temperatures arise by,• Higher solar radiation• Volcanic phenomena• Hot pools• Fires29
Functional disturbance of heat• Damage physiochemical state of biomembranes and the conformations of proteinmolecules.– Disturbance in photosynthesis– Disturbance in transport– Disturbance in mitochondrial respiration30
Heat Tolerance• Evasion of strong sunlight– Thick cutine layer• Heat insulating bark– Thick fibrous bark– Rough suberized bark– Silica in cell walls– Peripheral cambium layer• Dense leaf sheaths covering the basal buds• Withdrawal to underground organs• Transpirational cooling31
Most effective form of heatprotection is provide by,Heat shock proteins32
Type of heat resistanceThree types• Heat sensitive species• Relatively heat resistant eukaryotes• Heat tolerance prokaryotes33
Coldlowest temperature on earth= -90oCLethal limit= +5 - -90oClow temperatures arise by,• Low solar radiations34
Functional disturbance of coldAbove the freezing pointBy Decrease the speed of chemical reactions• Uptake of water and nutrients restricted• Less metabolic energy• Less biosynthesis• assimilation reduced• Growth stops35
The first main detectable result oflow temperature is,cessation of cytoplasmicstreaming36
Mostly effect on chilling sensitiveplants. It happens in stepwise37Primary effect:-LIQUID CRYSTALINE BIO MEMBRANES → SOLID GELLInitial reversible processes:-DAMAGE TO THE FUNCTIONALITY OF ORGANSCLOROPLAST- INHIBIT PHOTOSINTHESISMITOCHONDRIA- INCREASE RESPIRATIONFinal irreversible processes:-INSUFFICIENT CARBOHUDRATESIMPAIRED ION BALANCEIMBALANCE IN METABOLISMACCUMILATION OF TOXIC SUBSTANCESINJURY AND DEATH OF CELLS
Type of chilling sensitive plants• Partially sensitive plants• Totally sensitive plants38
Below the freezing pointFROST OCCUR PERIODICALLY ANDEPISODICALLY ON EARTHby the ice formation• Cytoplasm destroy by ice crystals• Block the vascular bundles• Ice nucleation active bacteria attack39
By ice formation less water in theplant = Desiccation conditionarise40
It results,• Unfrozen solution reach abnormallyhigh concentration• Toxic effect• Enzymes get inactive• Bio membranes are overtaxed bothosmotically and by the volume reduction41
Freezing of cells• intercellular • Extracellular42
Low temperature tolerance• No thermal insulation (no heat losses)– Dense growth surrounding the regenerative buds– Giant rosette• Abscission of sensitive organs• Depression of freezing point• Super cooling• Trans located ice formation (extra tissuefreezing)43
EVOLUTION OF VASCULAR PLANTSFOR FROSTHappen in a stepwise process45First step:COLD ADAPTATION OF ENZYMES AND MEMBRANESSecond step:IMPROVING THE SUPERCOOLING CAPACITY
Survival capacity• Younger plants are more sensitive• Reproductive organs are more sensitive• Underground organs are also quite sensitive• Above ground shoot is the least sensitive part46
Winter desiccationWinter conditions may result in damage due todesiccation.This happen by,• Frozen soil• Snow and ice47
Effects of winter desiccation• Plants can not take up enough water andnutrient• Loss water by stomatal transpiration• Xylem transpiration make cavities of the watercolumns in the conducting vessels• Block the passage of water through the xylem• Chronic damages in plant tissues48
Harmful effect of long periods beneathice or snow• Low CO2 and O2 permeability of ice sheets• Stop the gas exchange of plant• Respiratory CO2 increase and O2 decrease within the plant• Hypoxia• Toxic substances accumulate• Pathogenic effect49
Oxygen Deficiency in the Soil.DroughtSalt Stress
Oxygen Deficiency in the Soil.Lack of sufficient oxygen in the soil.Extensive areas of land are temporarily inundate byflood waters of large rivers, small rivers or streamsrepeatedly overflow their banks.the plants cover of valley soils is often buried of longperiod of times.Soils are compacted and become impermeable as a resultof construction activities.
The soil atmosphere is low in Oxygen in anycase,Anaerobic microorganisms take over .Creating a strongly reducing milieu which Fe2+ ,Mn2+, H2S, Sulphides ,Lactic acid ,Butyric acid are present intoxic concentration.Nitrogen turnover in the soil.
Functional Disturbances and Patterns ofInjuryroots are capable of respiring anaerobically,continuous for some hours irregularities in metabolismoccur.partial pressure of Oxygen drops to 1-5 kPa (Hypoxia)Alternative respiratory pathway is activate.The energy status of the adenylate system dropssubstantially.
Root growth stops.Root tips entering the low Oxygen zone die offAdventitious root developed.Older part of the root systems often develop corkyintumescences and swollen lenticels.
Total and near total Oxygen deficiency (anoxia)Respiration switches to anaerobic dissimilationIn the absence of terminal oxidationAcetaldehyde and ethanol accumulate.Abscisic acid, ethylene and ethylene precursors areformed in larger amount.Evoking in the leaves partial stomatal closure.Epinasty and often abscission.Cellular membrane systems brake down.Mitochondia and microbodies disintegrate and their enzymesare partially inhibited.
Surviving Oxygen DeficiencyMany plants can germinate, roots and grow in oxygen deficientsoil because they have developed certain adaptations to meetconditions in an toxic environment.Functional adaptation Morphologicaladaptation
Functional adaptationincrease in alcohol dehydrogenase (ADH) duringanaerobiosis.Protein metabolism is adjusted within a few hoursafter gene activation
Morphological adaptationA hypoxic milieu consist in the development in ventilatingtissue (aerenchyma) with a continuous systems ofintercellular spaces.The volume of intercellular system in the root parenchyma,swamp plants – 20%-60%well-aerated plant – <10%Well aerated roots may even loss oxygen to the surroundingsoil, It can detoxify harmful reducing substances :Fe2+ Fe111- oxide.Aeration is also furthered by temperature gradients.
Plants growing on very dense and poorly aerated soils developa system of laterally spreading roots near the surface.In the flooded regions submerged parts of trunks andbranches put out dense bundles of water roots.poplar, willow, alder, ash
In mangrove plants,In the form of lenticels-covered respiratory roots(pneumatophores) with a large amount of aerenchyma.Knee roots that produced above the surface of the soil andstanding water.
DroughtA period without appreciable precipitation, during with thewater content of the soil is reduced to such an extent thatplants suffer from lack of water.Low precipitation and high evaporation.Strong evaporation caused by dryness of the air andhigh levels of radiation.
The dry region of the earth
Functional disturbance and patterns of InjuryDecrease in turgor and a slowing down of growth processDecrease in cell volumeMost strongly inhibited enzyme is nitrate reductase.plants that have been treated with nitrogen containingfertilizer in drought.Nitrogen fixation is more sensitive to drought.Increase in concentration of the cell sap.Progressive dehydration of the protoplasm
Protein metabolism and synthesis of amino acids areimpaired.Supresses cell divisionSlow down mitosis- S phase being affected most.During pollen development, the meioses exhibitchromosome anomalies- specially metaphase and anaphase.Drought lower pollen fertility.
During drought,Initiate stomatal closerUnder the influence of hormone synthesized in theleaves and roots in response to droughtChanges occur in the allocation of assimilatesThe ratio of shoot to roots growth is alteredCharacteristic morphogenetic features developReproductive processes become predominantSenescence is acceleratedOlder leaves dry out and shed
In wilt,The reduction of cell volumeIncreasing concentration of the intercellular solutes-ionsIn the final phase preceding cellular disruptionThe central vacuole splits up into small fragmentaryvacuolesThe thylakoids in the chloroplasts and the mitochondrialcristae first of all swell and are later break downThe nuclear membrane becomes distended and thepolyribosome disintegrateDrought stress in tobacco
Survival of DroughtDrought resistancethe capacity of a plant to withstand period of dryness, and isa complex characteristics.xerophytes
Desiccation Avoidancedesiccation is delayed by all those mechanismsthat enable the plant to maintain a favorable tissue watercontent as long as possible despite dryness of air andsoil.uptake of water from the soilreduced loss of water
Water uptakeextensive root system with a large active surface area isimproved further by rapid growth into deeper soil layerthe seedling of woody plants in dry regions may havetap roots ten times as long as the shootgrasses in such places develop a dense root system andsend their threadlike roots to depths of some meters.
Reduction of transpirationModulative adptationtimely closure stomatawhen leaves growing under conditions of waterdeficiency develop smaller but more densely distributedstomata.
The leaves have more densely cutinized epidermal wallsCovered with thicker layer of wax.Stomata are present only on the under side of the leavessmalleroften hidden beneath dense hair or in depressionBoundary layer resistance is increased and the air outside thestomata become moistureRolling the leaves
Salt stressSalt stress may have be a first chemical stressfactor encountered during the evolution of life on earth.Saline habitatsthe presents of an abnormally high content ofreadily soluble saltAquatic saline habitat: Oceans, salt lakes, saline pondsIn land: saline soil
Effect of high salt concentration on plantsThe burden of high salt concentrations for plant is due toosmotic retention of water and to specific ionic effect onthe protoplasm.An excess of Na+ and Cl- in the protoplasm lead todisturbance in the ionic balanceIon specific effects on enzyme protein andmembrane.
Too little energy is produced by photophosphorylationand phosphorylation in respiratory chainNitrogen elimination is impairedProtein metabolism is disturbedAccumulation of diamines such as putrescinecadaverine,polyamines
Functional disturbancePhotosynthesis is impairedStomata closureEffect of salt in chloroplast in particular on electrontransport and secondary processRespiration increased or decreased – rootEnzyme system of glycolysis and the tricarboxylic acidcycle are more sensitive than alternative metabolicpathways.When the NaCl content of the soil is high the uptake ofmineral nutrients NO3- , K+ , Ca2+ is reduced.
Extreme salt stressInhibition of root growthBud opening is delayedShoot are stuntedLeaves are smallCell die and necrosis appear in roots, buds, leaf margins andshoot tipsThe leaves become yellow and dry before the growingseason has ended and whole portion of the shoot dry out.Lower level of cytokininIncreased abscisic acid senescence
Survival of Saline habitatsplant growing in saline habitat cannot evade theeffects of salt and must therefore develop at least somedegree of resistance to it.Salt resistance is ability of a plant either to avoid,salt regulationexcessive amount of salt from reaching theprotoplasmto tolerate the toxic and osmotic effect associatedwith the increased ion concentration.
Regulation of the salt content1. Salt exclusion: In some mangrove- transport barriers of theroots prevent the salinity of the water in the conductingsystem from becoming too high.Prosopis farctacrop plantshalophorbic species2. Salt elimination : A plant can rid itself of excess salt ,releasing volatile methyl halides – exclusion by glands excretion of salt at the shoot shedding parts heavily loaded with saltmarine phytoplanktonmacro algae
3. Salt redistribution:Na+ and Cl- can be readily translocated in thephloem , so that the high concentration arising in activelytranspiring leaves can be diluted by throughout the plant.4. Salt tolerance : the protoplasmic compartment ofresistance to salt stress.
Anthropogenic stressMan made pollutants and their impact on thephytosphere.Due to human activities plants exposed to greateramounts of harmful substances.
Human activities…• Results of industrial processes.• Traffic.• Chemicals used in agriculture and household,fertilizers, pesticides.• Excessive consumption of fossil fuels-emmission of green house gases.• Catastrophic accidents-nuclear reactoractivities, oil spills.
• PollutantA contaminant of air, water or soil that has anadverse effect on an organism.1.Naturally occurring pollutants2.Anthropogenic pollutantsInstead of one pollutant activity combinedactivity of pollutants.Ex: Photo oxidant complex + SO2 (g),+ heavymetals
Naturally occurring harmful substances in higherconcentrations.• SO2 (g),NO2 (g),H2S (g),O3 (g)• Dust.• Heavy metals.Ultimate result is environmental stress.EcosystemsCountriesContinentsEntire globe
• High input of pollutants within a short periodof time = acute damages• Exposure to low concentrated pollutants for alonger period of time = Chronic damagePollution InjuryThe extent which vital(physiological &biochemical) functions are affected.
Visible damage depend on manyfactors of the plant.1. Plant species.2. Growth form.3. Age of the plant.4. Phase of activity.5. General vigour(physical strength & good health.6. Climatic and edaptic condition.7. Chemical nature.8. Concentration of the pollutant.9. Time and duration of the action of the pollutant.
Air born pollutants• SO2 (g),NOx (g), PAN (peroxyacetylnitrate),Hydrogenhelides, NH3(g), hydrocarbons, tarfumes, soot, dust.Symptoms of damage• Non specific.• Many symptoms interact with other plantstress factors.
• At noon stomata are fully open atmosphericpollutant concentration is high in noondamage is higher.• At night plants recover from the injuriousimmisions.
Early recognition of pollution damage1. Accumulation of toxic compounds/substances in theplant tissues.2. Reduction of buffering capacity of tissues.3. Erosion of epicuticular wax .4. Decreation /incretion of certain enzyme activities.5. Qualitative and quantitative shifts amongmetabolites.6. Appearance of stress hormones– Ex: ethylene7. Respiration incretion/decreation8. Photosynthetic disturbance.9. Alteration of stomatal opening and closure.10. Diminished allocation of photosynthetes to the rootsystem.
When the pollutant in immediatevicinity..1. Occurrence of chlorosis.2. Leaf discoloration.3. Tissue necrosis.4. Death of entire plant.•Reduce productivity anddefective fertility.•Less growth in cambial tissues.•Foliage become sparser.•Water transpiration interfered.
SO2 (g) –cause most of the damageNatural sources-volcanic emissions, S containingores, biological decay and forest fires.Man-made sources-fossil fuel combustion,smelting, manufacture of sulfuric acid.SO2 (g) is there in the environment since the plantsbeginning.-Plants have been adapted to tolerateSO2 (g) for some extent.Entry into plants.1. Enter the leaf through opened stomata.2. By over-coming the cuticular resistance.(if thestomata are closed)
Damage by SO2 (g)SO2 (g)low externalconcentrationTrigger a loss of turgor inepidermal cellsStomata openTranspiration high• High externalconcentration• Stomata closure• Low transpiration
• SO2 (g) diffuse similar as CO2 (g) .Atmospheric SO2 (g)Dissolved in guard cell wall water SO2 (g) +H2O(l)HSO3-(aq) + SO32-(aq)Chloroplast: Cytosol: Vacuole96 : 3 : 1
Sulphur compounds(SO2(g),H2S (g) )detoxification01.) SO32-(aq) SO42-(aq)SO32-(aq) remaining will effected by thephotosynthetic sulphur metabolismCovert to sulphur containing aminoacids.(cysteine, methionone)Call wall peroxidases.
Harmful effects of SO2 (g)1. SO32-(aq) Level in chloroplast rise.2. SO2(g) ,occupies binding sites in RUBPcarboxylases.secondary process of photosynthesis inhibits.3.The tertiary structure of the enzymes aredisturbed.4. SO32-(aq) SO42-(aq)Super oxide radicals generate, if not excludedrapidly chlorophyll will be destroyed.photooxidation
Mechanisms of resistance of SO2 (g)stress* can be passive or active processesPassiveNon specific, not usually relatedto a particular pollutant.1. Regular development of newleaves with short functionallife span.Ex:deciduouswoody plants• Thallophytes also havestructural, chemicalcharacteristics reduce theentry of SO2ActiveStressor specific processes.1. High buffering capacity-fromincreased uptake of alkali &alkali earth cations.2. Binding to 2ry products ofmetabolism.3. Metabolic use of Sulphur anddetoxifying oxidativereactions.4. C4 syndrome.Evergreentrees withneedles
Ever green tree s with needles Deciduous woody plants
C4 syndromeC4 grass1.Miscanthus sinensis2.Andropogon virginicusModerate resistant C31.Polygonaceae2.Metrosideros collina in HawaiiSome plants have theability to grow in thevicinity of volcanicvents
Species-specific sensitivity to immissions.• Different species• Individual varieties and ecotypes• Different life stagesSO2 (g) Resistant plant species introduce topolluted areas.Highly sensitive plants to SO2 (g) Indicatororganisms toindicate SO2 (g)pollution.
Uptake by the plant• Through opened stomata.• NO2(g) diffuse through cuticle, much fasterthan SO2(g) .• O3 (g) dissociate to O2(g) in the outer wall of theepidermis.• NO(g) ,NO2 (g) NO3-(aq) ,NO2-(aq) with watertaken up actively by living cells
Events within the cell.• NO3-(aq) amino acids.* SO2 (g) inhibit the actionof Nitrite reductase.• Additional source of nitrates-advantageous.• Acidification of cells/leaves-disadvantageous.Nitrite reductase enzymeToxicity of nitrates
O3(g)• O3(g) O2(g) + O.• Peroxides,-effect on plasma membrane.-other bio membranes.Transfer processimpaired.Necrosis,growthreduction,lessyields
Heavy metalcontamination of soil,waterCreate long term problemsmetals = Zn,Pb,Ni,Co,Cr,CuMetalloids = Mn,Cd,Se,ASAccumulation inorganisms, circulatein food chains.
Common heavy metal sources1. Industrial zones.2. Heavy vehicle traffic.3. Sewage sludge.4. Emissions of dust from metal processingindustries.5. Waste water-Cd,Zn,Fe,Pb,Cu,Cr,Hg
Uptake and toxic effects• Uptake is mainly by roots.-can’t stop the enter of heavy metal completely.-need to plants as micro elements.
Toxicity due to..1. Interference with electron transport inrespiration an photosynthesis.2. Inactivation of vital enzymes.
Possible mechanisms of resistance• Natural heavy metal exposures, plants growing on,a. Metal ores.b. Serpentine soils.c. Strongly acidic soils.Adaptations.1. Immobilization in cell wall.2. Obstruct permeation across the cell membrane.3. Formation of chelates.4. Compartmentalization in vacuoles.5. Active export.
6. Characteristic patterns of iso-enzymes-element specific resistance.7. Genetic plasticity, with several resistancegenes-resistant to several heavy metals.*these plant can be used to re-vegetation of stronglyheavy metal contaminated area.Ex:Agrostis tenuis Festuca ovina Silene vulgaris
Bioindicators of pollution impact• Bioindicators are organisms or communities oforganisms that are sensitive to pollution stress andrespond by alteration in their vital processes or byaccumulation of the pollutant.Bioindicators•Indicator organisms- respond to theirsurroundings, depending on their specific requirements•Test organisms- high degree of sensitivity to certainpollutants.•Monitor organisms- specific responses to pollutants can becon be used for qualitative & quantitative detection ofstress situations.
Accumulation of heavy metals influencedby ..1. Meteorological factors2. Edaphic factors -Influenced by the soil rather than by theclimate.3. Habitat related factors- growth form and rooting pattern.Heavy metal indicators= metallophytes.Ex: Eichhornia crassipes
Reasons for forest decline1. Ageing of the stand.2. Episodic damage by pests.3. Extremes of climate.4. Inappropriate management.5. Interruption of mineral recycling.6. Exhaustion of soil nutrients.7. Toxicity caused by identifiable local emitters.
forest decline• Depend on the,1. Tree species.2. Growth form.3. The site.4. Type of the soil.5. Geological origin.6. Superimposition of various stress types.
Symptoms of forest decline1. Anomalous growth.2. Discoloration of needles and leaves.3. Necrosis of isolated areas of needles, leaves,branches.4. Shedding of leaves.(thinning of crown, barenessof the hanging branches).5. Dieback of leader and branch tips.6. Increasing the shallowness of the root system.
Causes of forest decline.• Acidic effect of precipitations.Direct acid damage1. necrosis of margin of leaf2. destruction of the cuticle and cuticular waxes.3. acidification of the apoplast– affect the distributionof phytohormornes.4. fine root chromosome anormalities during celldivision.5. cells damage dissolution of cell walls tissuedisruption.
Effect of atmospheric pollutants on theecosystems and at the global level.1. Acid precipitations
Green house effect• provides temperature necessary to supportthe life on earth.• Green house gases1. CO2(g)2. H2O(g)3. CH4(g)4. O3(g)5. N2O(g)