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1、Plant Environmental Stress Physiology,Fan Hai,What is Plant Stress,Plant stress is the adverse reaction of plants to environmental conditions that are unfavorable to growth,such as lack of sufficient nutrients,inadequate watering,flooding,high or low temp.,disease or insect infestation.,Stress,Bioti
2、c stress,pathogen microbesinsectsallelopathy,Abiotic stress,water,Temp.,light,droughtflooding,High temp.Low temp.：chilling,freezing,photoinhibitionUV damage,chemicals,SalinityAlkalinityInsecticide,herbicideAir pollution,Plant stresses greatly diminish crop yields,Biotic and abiotic stresses can redu
3、ce average productivity by 65%87%,Table:Average yields and record yields of 8 major crops,What is Strain,Strain is the biologic changes of plants under the influence of plant stress.Strain can be elastic or plastic depending on the degree and lasting time of stress.Elastic strain:recoverable,tempora
4、ryPlastic strain:non-recoverable,permanent,I.Damages of stress to the plant,stress,Primary damage,Secondary damage,Primary direct-damage,Primary indirect damage,（injury to the plasma lemma）,（dysfunction of metabolism）,（e.g.water stress in salt stress）,I.Damages of stress to the plant,Bio-membraneCha
5、nge in membrane phaseChange in membrane constituentsChange in membrane permeability,PhotosynthesisDecrease in PnDecrease in stomatal apertureDecrease in Fv/FmDecrease in quantum yield,RespirationChange in respiration pathE.g.Turn EMP-TCA pathway to PPP under drough,pathogen and wounding stress.Decre
6、ase in respiration rate under freezing,hot and flooding stressIncrease in respiration rate under wounding and pathogen stressUnder chilling and drought stress,the respiration rate increase first and then decrease,Changes of phytohormone levelDecrease in IAA,CTK,GBSignificant increase in ABAIncrease
7、of Eth under flooding,Oxidative stress induced by reactive oxygen species(ROS)Reactive oxygen species are highly reactive molecules containing atom oxygen.It mainly include 4 species:O2.-,OH,H2O2 and 1O2 ROS can attack chloroplast,mitochondria and other organelles.ROS can also attack membrane by cau
8、sing membrane peroxidation.,II.Plants Respond to Stress in Several Different Ways,Environmental Stress,Stress response,Tolerance,Avoidance,Escape,Stress Escape:Plant avoid the injury of stress by regulating its life cycle to avoid meeting with stress.E.g.some short-lived,desert ephemeral plants germ
9、inate,grow and flower very quickly following seasonal rains.They thus complete their life cycle during a period of adequate moisture and form dormant seeds before the onset of dry season.,Stress avoidance:plants avoid the injury of stress by building up a barrier to prevent stress factors entering t
10、he plant.E.g.alfafa survive dry habitats by sending down deep root systems that penetrate the water table.Salt-secretion halophytes secrete the salts out from the leaf thus reduce salt content in the leaf.,Stress tolerance:Plants adapt to the stress environment by regulating their metabolism and rep
11、air the damage caused by stress.E.g.Highly salt tolerant halophytes such as suaeda salsa survive salty habitat by many strategies such as high ROS scavenging ability,high osmotic adjustment ability,high ion compartmentalization ability and so on.,Adaptation vs.Acclimation,Adaptation and acclimation
12、both are means of achieving tolerance to a particular stress.Adaptation refers to heritable modifications in structure or function that increase the fitness of the organism in the stressful environment.e.g.CAM plants to desert.Acclimation refers to nonheritable physiological modifications that occur
13、 over the life of an individual.These modifications are induced by gradual exposure to the stress.E.g.slow drying increases the drought resistance of plants.The process of acclimation is known as hardening.,How plants get adapted to stress?,Osmotic adjustmentStress proteinsScavenge ROSSynthesis ABAC
14、ross-adaptation,1.Osmotic adjustment,Water deficit can be induced by many environmental conditionsDroughtSalinityCold temperatureOsmotic adjustment is a biochemical mechanism that helps plants to acclimate to drought,salinity etc.Osmotic adjustment is an active process of increasing the number of so
15、lute particles in the plant that resulting in a reduced osmotic and water potential and enables the plant to absorb water in drought and saline habitat.,Compatible solutes share specific biochemical attributesHighly solubleLow molecular weightDo not interfere with cellular metabolismNeutrally charge
16、d at physiological pHMainly distributed in the cytosol,not vacuoles,Most compatible osmolytes are AA,QACS or poly alcohols,Some compatible solutes may serve other protective functions in addition to osmotic adjustmentMinimizing the perturbing impact of ionsProtecting enzymes(pro,glycine betain)Scave
17、nging ROS(pro,mannitol,sorbitol),2.Stress proteins,HSPs(Heat shock proteins)CRP(Cold regulated proteins)anaerobic peptidesLEAs(late embryogenensis abundant proteins)OsmotinPathogenesis-related proteins,3.Scavenging ROS,Enzymes：SOD（superocide dismutase)CAT(Catalase)POD(Ascorbic acid Peroxidase)Oxidan
18、ts：caroteneVit EDMSOVit C GSH,4.ABA-stress hormone,Keep membrane stabilityPromote synthesis of osmolytesReduce water lossIncrease water conductivity,Cross-adaptation,Cross-adaptation mains exposure of an organism to a given adverse environment modifies its response to other adverse factors.E.g.expos
19、ure of plants to various stresses such as chilling temperature,heat,drought,and radiation conferred resistance to other stresses.,Causes of cross-adaptation,ABA is induced under many stresses.Stress induces many stress proteins,and stress protein functions in many stresses.Osmolytes are induced by m
20、any stressesMembrane change.ROS scavenging system is activated.,III.Freezing Stress,Freezing injury is caused by low temp.0Supercooling,Intercellular crystallizationIce crystals form between cells.Intracellular crystallizationIce crystals form in the cell.,Freezing Injury:Direct injury:injury by cry
21、stal formationIndirect injury:dehydration,suffocatingInjury mechanism:Membrane injuryMechanical injury-SH theory,Strategies of increasing plant freezing tolerance:Lower water contentReduce photosynthesisIncrease ABA/GBDormantIncrease osmolytesAll the above can be attained by cold hardening,IV.Chilli
22、ng Stress,Caused by low temp.0DamageMembrane phaseRoot water absorption abilityDysfunction of respiration,accumulation of ethanol.Dysfunction of metabolism,Mechanism of chilling injury:membrane phase transition:LC phaseGel phase,Liquid crystalline phase.The typical phase in biological membranes.The
23、lipids have both lateral and kinetic motion and contain membrane proteins,Gel phase.The membrane lipids have less kinetic energy and lateral motion than in the liquid crystalline phase resulting in a regular spacing between the acyl tails,Strategies of improving plant chilling tolerance:Increase IUF
24、A(index of unsaturated fatty acid),which leads to the decrease of phase transition temp.Synthesis of chilling-tolerant isoenzymes.,V.Drought Stress,Drought stress includes:Soil drought,no rain for long time and no-available water in the soil.Air drought,RHwater absorption.If longer,soil drought occu
25、rs.,Symptoms in plant facing to drought：stun,red color in base，small cell and leaf area，leaf yellowish and abscission.Young leaves or/and reproductive organs wilt to death.,Mechanisms of drought stress:Membrane damageMetabolic disorder:Water redistribution in the organPhotosynthesis reductionRespira
26、tion rises then dropsDecrease in nuclear acids and proteins Accumulation of prolineABA accumulationMechanical damageFormation of S-S,Strategies of increasing drought resistanceStress avoidance:absorption of water,declination of transpiration and increase in water transportation.Developed root system
27、 and higher ratio of root to shootThick leaf,smaller leaf area and thick cuticleAccumulation of ABA and stomatal controlStress toleranceOsmotic adjustmentChange of photosynthetic pathway,VI.Flood stress,Injury of flood:(Secondary injury)Anaerobic stress:anaerobic respiration ethanolEthylene evolving
28、,(1)Injury in morphology and anatomy by O2 deficiency：growth，leaf yellowish(nutrition deficiency），epinasty（Eth),stem hollow(tissue degradation caused by Eth）.(2)Injury in metabolism by O2 deficiency，photosynthesis stomatal block,inhibition of CO2 entrance.Anaerobic respiration，toxicants:alcohol，acet
29、aldehyde，NH3，lactate,H2S,(3)Nutrition disorder：absorption，soil N、P、K、Ca loss but H2S、Fe、Mn，microelements poison。(4)Changes in plant hormones：IAA and CTK。ACC synthesis in root and release of Eth in shoot.,Mechanism of flood resistanceWell-developed aerenchymaMore lenticlesMore adventitiouse root,白骨壤的
30、气生根,红海榄的支柱根(prop roots)，支柱根具有支撑和呼吸的功能，根中的通气组织相当发达，下陷的气孔、皮孔等都有助于体内外气体交换。,VII.Salt stress,Salt stress includes 3 aspects:Ionic stress:Na+Cl-Drought stressMetabolic disorder:Ch1 and Rubisco，protein degradation,Pro，NH4+poison,Mechanism of salt resistance:Salt avoidance:Salt secretionSalt dilutionSalt re
31、clusionSalt tolerance:Osmotic adjustmentROS scavenging,VIII.Pathogen stress,Pathogen stress to plants:Water balance disorderRespiration(PPP)Photosynthesis Abnormal growth,Plant resistance to pathogen stress:Local resistance system:supersensitlve reactionphytoalexinchintinasepathogenesis related proteinaccumulation of lignin and callusoxidative burstSystem acquired resistanceSend the signal to other parts of plant,and thus the plant is immune or alerted to the stress.,
