植物生理学英文课件：chapter10 stress

1、Chapter 10 Stress Physiology,Stress: Stress in physics is any force applied to an object. Stress in biology is any change in environmental conditions that might reduce or adversely change a plants growth or development. Such as freeze, chilling, heat, drought, flood, salty, pest and air pollution et

2、c. Resistance: resistance is the ability adaptive or tolerant to stress.,Adaptations involve genetic modifications The genetic changes in entire population fixed by natural selection over many generations for adaptation to the environment.Example In southwestern Endland,populations of Yorkshire fog

3、grass contain a specific genetic modification that reduces the uptake of arsenate,allowing the plants to avoid arsenic toxicity abd thrive on contaminated mine sites.In contrast,populations growing on uncontaminated soils are less likely to contain this genetic modifications.,Phenotypic plasticity:

4、Plants respond to fluctuations in environment by directly altering their morphology and physiology.This change requires no new genetic modifications, and many changes are reversible.,逆境(environmental stress)是指对植物生存与发育不利的各种环境因素的总称。逆境可分为自然逆境（natural stress)和人为逆境（anthropogenic stress).根据环境的种类又可将逆境分为生物因

5、素逆境和理化因素逆境等类型（图）植物对逆境的抵抗和忍耐能力叫植物抗逆性，简称抗性(resistance,hardiness)。,抗性是植物在对环境的逐步适应过程中形成的。由于植物没有动物那样的运动机能和神经系统，基本上是生长在固定的位置上，因此常常遭受不良环境的侵袭。但植物可用多种方式来适应逆境，以求生存与发展。植物适应逆境的方式主要表现在三个方面。,1.避逆性 指植物通过对生育周期的调整来避开逆境的干扰，在相对适宜的环境中完成其生活史。这种方式在植物进化上是十分重要的。例如夏季生长的短命植物，其渗透势比较低，且能随环境而改变自己的生育期。2.御逆性 指植物处于逆境时，其生理过程不受或少受逆境

6、的影响，仍能保持正常的生理活性。这主要是植物体营造了适宜生活的内环境，免除了外部不利条件对其的危害。这类植物通常具有根系发达，吸水、吸肥能力强，物质运输阻力小，角质层较厚，还原性物质含量高，有机物质的合成快等特点。如仙人掌，其一方面在组织内贮藏大量的水分；另一方面，在白天关闭气孔，降低蒸腾，这样就避免干旱对它的影响。3.耐逆性 指植物处于不利环境时，通过代谢反应来阻止、降低或修复由逆境造成的损伤，使其仍保持正常的生理活动。例如植物遇到干旱或低温时，细胞内的渗透物质会增加，以提高细胞抗性。,Resistance includes adaptation, avoidance and toleran

7、ce. Adaptation is permanent resistance to stress in morphology and structure, physiology and biochemistry under long-term stress condition. a well-developed aerenchyma in hydrophytes, a pattern for stomata movement in CAM plant.,Lotus and its special tissue for adaptation to submerging condition,Avo

8、idance is a manner to avoid facing with stress using neither metabolic process nor energy. Very short-life cycle plants in desert. Dormancy during the cool, hot, and drought conditions. Tolerance is a resistant reaction to reduce or repair injury with morphology , structure, physiology, biochemistry

9、 or molecular biology, when plant counters with stresses. Hardening is a gradual adaptation to stress when the plant is located in the stress condition.,Section 1. Water stress in plant 1.1 Resistance of plant to drought Drought injure: Soil drought: no rain for long time and no-available water in t

10、he soil. Air drought: RHwater absorption. If longer, soil drought occurs. Drought injury is actual injury in physiology.,Water deficits cause cell dehydration and inhibition of cell expansion Water deficits causes reduction in cell tugor and cell volume,which are associated with cellular dehydration

11、 and with the water potential of apolost becoming more negative than that of symplast.A secondary effect of cellular dehydration is that ions become more concentrated and may become cytotoxic. Cell expansion is a turgor-driven process and is extremely sensitive to water . Water-deficient plants tend

12、 to become rehydrated at night.,MPa,0,-0.5,-1.0,-1.5,-2.0,Cell elongation(-) Cell wall synthesis(-) Protein synthesis(-) Chlorophyll synthesis(-) ABA synthesis(+) Seed germination(-) Stomatal opening(-) CO2 assimilation(-) respiration(-) Proline accumulation(+),Metabolism relevant to water sensitive

13、 to range of water Inhibit (-) promotion (+),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. 1.1.1 Mechanism of drought injure 1.1.1.1 Membrane damage. Like senescence, biomembr

14、ane changes in states, such as hexagonal phase and become leaked.,Hydrophilic groups of lipid aggregate together (Hexagonal phase ),drought,Re-watering,1.1.1.2. Metabolic disorder （1）Redistribution of water among organs：,(2)Photosynthesis decreases, while respiration rises after lowering Starvation

15、to death. a. assimilate SC ，Photorespiration，electron transfer activity and PSP .In sunflower,-1.1MPa，ET and PSP decrease obviously，1.7MPa, PSP is 0. b. inhibition by photoassimilate feedback.,（3）Decrease in nuclear acids and proteins. Protease activity，free aa，RNAase activity，RNA hydrolysis ,DNA co

16、ntent falls down. （4）Pro accumulation： Pro from protein hydrolysis;synthesis，oxidation. Pro function： detoxication of NH3;bound water .,（5）Changes in plant hormones，promoters，inhibitors，esp. ABA. （6）Poisonous agents accumulation. NH3 and amines. 1.1.1.3 Mechanical injure Cytoplasm is broken down. Fo

17、rmation of SS.,1.1.2 Mechanisms of resistance to drought and the methods to increase the resistance 1.1.2.1. Mechanisms of resistance （1）Morphology： increase in water absorption and transportation , declination of transpiration. a. Developed root system and higher ratio of root to shoot开源,b. Thick l

18、eaf , smaller leaf area and thick cuticle节流. c. Developed bundle and veins，smaller and more stomata流畅,（2）Physiology and biochemistry a. Stomatal regulation： ABA accumulationstomatal closure ex. Tomato (flacca)-dhns, (sitiens)-PI-PII mutants; Potato (droopy)-PI-PII mutants b. Increase in capacity of

19、resistance to dehydration of cytoplasm Rapid accumulation of Pro, glycinebetaine Lea protein, dehydrin, osmotin and ion etc.,1.1.2.2. Methods to increase the resistance （1）Selection of cultivars with high resistance to drought，high yield and quality. （2）drought hardening： “Seedling drought”, “seedli

20、ng starvation”, “double sprout”. Seed priming(种子引发): a special technology to control seed water absorption and re-drying slowly,（3）Suitable fertilizer application： Application of more P、K to plants. （4）Chemical regents application Soaking in 0.25% CaCl2 or 0.05%ZnSO4 solution. Application of plant s

21、ubstance: ABA, CCC etc,2.2 Resistance of plant to flood Flood injury: moisture injury and flooding injury. Moisture injury is caused by soil space filled with water and without air. flooding injury: whole plant or part of shoot is submerged to water while flooding,2.2.1 Injures of flood to plant Flo

22、od is actual deficiency in O2 Anything increases in soluble O2, the injury will decrease. And anything decreases in soluble O2, the injury will increase Such as slowly streaming water less damage than static water.,(1) Injury in morphology and anatomy by O2 deficiency：growth，leaf yellowish (nutritio

23、n deficiency），root darkness（low Eh），epinasty（Eth), air root(IAA, Eth), stem hollow (tissue degradation caused by Eth ）. Soil hypoxia and anoxia damage plant roots directly by inhibiting cellular respiration. (2) Injury in metabolism by O2 deficiency: Anaerobic respiration，toxicants: alcohol ，acetald

24、ehyde，NH3，lactate , H2S. Photosynthesis stomatal block, inhibition of CO2 entrance .,(3) Nutrition disorder： Absorption ，soil N、P、K、Ca loss but H2S、Fe、Mn ，microelements toxication. (4) Changes in plant hormones：IAA and CTK .ACC synthesis in root and release of Eth in shoot. (5) Mechanical damage and

25、 infection by harmful organism.,2.2.2 Mechanism of resistance to flood Resistance is different in plants:hydrophytesland plants，ricerapebarley; Oryza.sativa indica O.sativa japonica ，and in growth stages : seedling other stages, “寸麦不怕尺水,尺麦怕寸水”. (1) Tolerance in tissues：Well-developed aerenchyma.,(2)

26、 Tolerance in metabolism：Mitochondria well develops in anaerobic conditions, succinic acid dehydrogenase，tolerance to ethanol ; PPP instead of EMP，NR，Glutamate dehydrogenase .,Immediately drainage is necessary after flood: The drainage should be done late if strong sunlight. It is necessary to wash

27、the soil attaching the plant and apply N、P、K to plant after drainage.,Eco-hydroponics左图-生态水培番茄幼苗 右图-不同处理番茄植株:左-生态水培,中间-常规水培(不充气),右-常规水培(充气).,Section 2 Temperature stress Temperature stress: Low or high temperature, called frost injury or heat injury, respectively. 2.1 Frost ( freezing )injury The in

28、jury is caused by low temperature below freezing point (0), companied with frost.,冻害发生的温度限度，可因植物种类、生育时期、生理状态、组织器官及其经受低温的时间长短而有很大差异。大麦、小麦、燕麦、苜蓿等越冬作物一般可忍耐-7-12的严寒；有些树木，如白桦、网脉柳可以经受-45的严冬而不死；种子的抗冻性很强，在短时期内可经受-100以下冷冻而仍保持其发芽能力；某些植物的愈伤组织在液氮下，即在-196低温下保存4个月之久仍有活性。 一般剧烈的降温和升温，以及连续的冷冻，对植物的危害较大；缓慢的降温与升温解冻，植物受

29、害较轻。植物受冻害时，叶片就像烫伤一样，细胞失去膨压，组织柔软、叶色变褐，最终干枯死亡。,2.1.1 Mechanism of freezing (frost )injury 2.1.1.1.Freezing:(intercellular and intracellular freezing) (1) Intercellular freezing,Freezing,Intercellular freezing occurs when temperature falls gradually down.,ice,(1)原生质过度脱水，使蛋白质变性或原生质发生不可逆的凝胶化。由于胞外出现冰晶，于是随

30、冰核的形成，细胞间隙内水蒸汽压降低，但胞内含水量较大，蒸汽压仍然较高，这个压力差的梯度使胞内水分外溢，而到胞间后水分又结冰，使冰晶愈结愈大，细胞内水分不断被冰块夺取，终于使原生质发生严重脱水。(2)冰晶体对细胞的机械损伤。由于冰晶体的逐渐膨大，它对细胞造成的机械压力会使细胞变形，甚至可能将细胞壁和质膜挤碎，使原生质暴露于胞外而受冻害，同时细胞亚微结构遭受破坏，区域化被打破，酶活动无秩序，影响代谢的正常进行。 在冰点温度的植物体会由于水分随着水势梯度流动，穿过质体膜进入细胞壁和细胞间空隙，而造成细胞内水分匮乏。阻止细胞质结晶冰的形成，导致细胞死亡。相反，细胞会脱水，非原生质体发生结冰。（3）解冻

31、过快对细胞的损伤。结冰的植物遇气温缓慢回升，对细胞的影响不会太大。若遇温度骤然回升，冰晶迅速融化，细胞壁易于恢复原状，而原生质尚来不及吸水膨胀，有可能被撕裂损伤。例如葱和白菜叶等突然遇高热化冻后，立即瘫软成泥，就是这种原因造成的。,胞内结冰对细胞的危害更为直接。因为原生质是有高度精细结构的组织，冰晶形成以及融化时对质膜与细胞器以及整个细胞质产生破坏作用。胞内结冰常给植物带来致命的损伤。,（2）Intracellular Freezing : Intracellular freezing often occurs when temperature falls suddenly down. Ice

32、 results in the direct injury in cytoplasm, biomembrane and organelle, and damages to cell compartmentation and metabolic disorder. Much more serious damage is caused by Intracellular freezing than by intercellular freezing. 2.1.1.2 damage of protein: Sulfhydryl group hypothesis（disulfide bridge hyp

33、othesis ）,Before freezing frozen defrozen,SH HS,S S,SH H S,SS,SS,SS,SS,HS,SH,SS,Injury by formation of sulfhydryl group hypothesis,Supported Exp： (1) SS一increase and soluble SH decrease after plant tissue faces to freezing. (2) LessSSand SH of protein in the resistant-freeze plants. (3) The plant wi

34、th freeSH, glutathione, is more resistant to freeze. (4) Artificial SH, mercapthanol increases resistance of plant to low temperature.,2.1.1.3.Damage of biomembrane Electric conductivity，cell material leakage，photochemical activity and ATP production , while photoinhibition ，CF1 and PC depart from t

35、he membrane. Change in state of lipid and protein denuturation,膜对结冰最敏感，如柑橘的细胞在-4.4-6.7时所有的膜(质膜、液泡膜、 体和线粒体)都被破坏，小麦根分生细胞结冰后线粒体膜也发生显著的损伤。低温造成细胞间结冰时，可产生脱水、机械和渗透三种胁迫，这三种胁迫同时作用，使蛋白质变性或改变膜中蛋白和膜脂的排列，膜受到伤害，透性增大，溶质大量外流。另一方面膜脂相变使得一部分与膜结合的酶游离而失去活性，光合磷酸化和氧化磷酸化解偶联，ATP形成明显下降，引起代谢失调，严重的则使植株死亡.,2.1.2 Chilling injury

36、 Chilling injury in tropical or subtropical plant is caused by temperature above 0 (freezing point ). Maize, cotton rice seedling10. Rice pollen-mother cell division，23 for O. sativa indica and 20 for O. sativa japonica. Banana tree13. Oak tree5.,2.1.2.1. Change in state of lipid,Electric conductivi

37、ty as an index for resistance to low temperature in production,2.1.2.2. Metabolism disorder （1）Uptake function of roots declines and water balance disorders Transpirationwater absorption. The plant loss water and leaf curls青枯死苗（水稻）. （2）Photosynthetic rate lowers . Photosynthesis respiration, starvat

38、ion to death黄枯死苗. Rubisco losses activity under low temperature，PSP uncouples and free radicals breaks out.,（3）Aerobic respiration decreases and anaerobic respiration increases. Cytaa3 activity , respiratory electron transport and phosphorylation activities . Ethanol toxification. （4） Organic substa

39、nce degrades. protease，protein，RNA、ATP .,2.1.3 Physiological reaction of plant to low temperature (1) Water content, metabolism, growth decrease . Total water content，bound water，free water and ratio (free water/bound water) . (2) Protective substances increase. NADPHreducesSS to SH，ATP and sugar, b

40、ound water.,(3) Unsaturated fatty acids increase in membrane. Unsaturated fatty acids and saturated one . (4) ABA，GA, dormancy appears. (5) Proteins-resistant to freezing accumulations. Freezing resistant protein Ice-BoxThe genes expression induced by freezefreeze-resistant protein.,植物在长期进化过程中，在生长习性

41、和生理生化方面都对低温具有特殊的适应方式。如一年生植物主要以干燥种子形式越冬；大多数多年生草本植物越冬时地上部死亡，而以埋藏于土壤中的延存器官(如鳞茎、块茎等)渡过冬天；大多数木本植物或冬季作物除了在形态上形成或加强保护组织(如芽鳞片、木栓层等)和落叶外，主要在生理生化上有所适应，增强抗寒力。,2.1.2.4 Methods to increase the resistance to low temperature. (1) The resistant cultivars. (2) Low temperature hardening. (3) Chemical control. ABA ,CC

42、C，PP330，Amo-1618. (4) Others. PK application, keep warm with artificial materials-protected cultivation.,2.2 High temperature stress and heat resistance of plants Cold-favored plants: some alga，bacteria and fungi，meets heat injury at 1520 . Temperature-mediate plant: most of crops35. Temperature-fav

43、ored plants， some alga，bacteria 65100，many CAM plants50. Heat injury is a damage to the temperature- mediate plant by high temperature above 35.,喜冷植物：例如某些藻类、细菌和真菌，生长温度为在零上低温(020)，当温度在1520以上即受高温伤害。中生植物：例如水生和阴生的高等植物，地衣和苔藓等，生长温度为1030，超过35就会受伤。喜温植物：其中有些植物在45以上就受伤害，称为适度喜温植物，例如陆生高等植物，某些隐花植物；有些植物则在65100才受害

44、，称为极度喜温植物，例如蓝绿藻、真菌和细菌等。,植物受高温伤害后会出现各种症状：树干(特别是向阳部分)干燥、裂开；叶片出现死班，叶色变褐、变黄、鲜果（如葡萄、番茄等)烧伤，后来受伤处与健康处之间形成木栓，有时甚至整个果实死亡；出现雄性不育，花序或子房脱落等异常现象。高温对植物的危害是复杂的、多方面的，归纳起来可分为直接危害与间接危害两个方面。,2.2.1 Reasons for heat injure 2.2.1.1. Indirect damage （1）Starvation Temperature compensation point: Pn is equal to zero at hig

45、h temperature Respiration is much larger than photosynthesis. 高温下呼吸作用大于光合作用，即消耗多于合成，如马铃薯的光合适温为30，而呼吸适温接近50。,Pn,Rd (molm-2s-1),Total photosynthetic rate,Pn,Respiration rate,(2) Toxication 高温使氧气的溶解度减小，抑制植物的有氧呼吸，同时积累无氧呼吸所产生的有毒物质，如乙醇、乙醛等。如果提高高温时的氧分压，则可显著减轻热害。氨(NH3)毒也是高温的常见现象。高温抑制含氮化合物的合成，促进蛋白质的降解，使体内氨过度

46、积累而毒害细胞。Ethanol or acetaldehyde, free radicals. (3) 高温使某些生化环节发生障碍，使得植物生长所必需的活性物质如维生素，核苷酸缺乏，从而引起植物生长不良或出现伤害。deficiency of biotins Biotins，Vitamins . (4) 高温一方面使细胞产生了自溶的水解酶类，或溶酶体破裂释放出水解酶使蛋白质分解；另一方面破坏了氧化磷酸化的偶联，因而丧失了为蛋白质生物合成提供能量的能力。此外，高温还破坏核糖体和核酸的生物活性，从根本上降低蛋白质的合成能力。damage of nuclear acids and proteins,2

47、.2.1.2. Direct damage （1）Protein denaturation Configuration damage The degree in denaturation is positively related to water content in plant tissue. Dry seed is able to resist to 7080. 高温破坏蛋白质空间构型，由于维持蛋白质空间构型的氢键和疏水键键能较低，所以高温易使蛋白质失去二级与三级结构，蛋白质分子展开，失去其原有的生物学特性。蛋白质变性最初是可逆的，在持续高温下，很快转变为不可逆的凝聚状态 2.脂类液化生

48、物膜主要由蛋白质和脂类组成，它们之间靠静电或疏水键相联系。高温能打断这些键，把膜中的脂类释放出来，形成一些液化的小囊泡，从而破坏了膜的结构，使膜失去半透性和主动吸收的特性。脂类液化程度决定了脂肪酸的饱和程度，饱和脂肪酸愈多愈不易液化，耐热性愈强。经比较，耐热藻类的饱和脂肪酸含量显著比中生藻类的高。,（2）Lipid liquefaction,High temperature,liquefaction,2.2.2 Mechanism of heat resistance (1) High stability of protein under heat stress. muchSS (2) Low

49、er water content (3) High contents of saturated fatty acids. (4) High contents of organic acids. CAMhigh tolerance to heat due to high organic acid contents. Decrease or avoid NH3 toxification.,(5)Form of heat shock proteins (HSPs or hsps) Heat shock proteins are a newly synthesizing set of proteins

50、 that organisms ranging from bacteria to humans respond to high temperature. Functions: protect or repair proteins, nuclear acids and biomembrane from heat injury. More than 30 HSPs, 15-27kD, some are chaperons,(一)内部因素不同生长习性的植物的耐热性不同。一般说来，生长在干燥炎热环境下的植物耐热性高于生长在潮湿冷凉环境下的植物。例如C4植物起源于热带或亚热带地区，其耐热性一般高于C3植

51、物。C4植物光合最适温度为4045，也高于C3植物(2025)。因此C4植物温度补偿点高，在45高温下仍有净光合的生产，而C3植物温度补偿点低，当温度升高到30以上时常已无净光合生产。植物不同的生育时期、部位，其耐热性也有差异。成长叶片的耐热性大于嫩叶，更大于衰老叶；种子休眠时耐热性最强，随着种子吸水膨胀，耐热性下降；果实越趋成熟，耐热性越强；油料种子对高温的抵抗力大于淀粉种子；细胞汁液含水量(自由水)越少，蛋白质分子越变性，耐热性越强。耐热性强的植物在代谢上的基本特点是构成原生质的蛋白质对热稳定。蛋白质的热稳定性主要决定于化学键的牢固程度与键能大小。凡是疏水键、二硫键越多的蛋白质，其抗热性就

52、越强，这种蛋白质在较高温度下不会发生不可逆的变性与凝聚。同时，耐热植物体内合成蛋白质的速度很快，可以及时补偿因热害而造成的蛋白质的损耗。生长在沙漠、干热地区的一些植物，在高温下产生较多的有机酸，有机酸与NH4+结合可消除NH3的毒害。一般植物也有以增加有机酸来提高耐热能力的。,温度对植物耐热性有直接影响。如干旱环境下生长的藓类，在夏天高温时，耐热性强，冬天低温时，耐热性差。高温锻炼有可能提高植物的抗热性。如把一种鸭跖草栽培在28下5周，其叶片耐热性与对照(生长在20下5周)相比，从47变成51，提高了4。将组织培养材料进行高温锻炼，也能提高其耐热性。将萌动的种子放在适当高温下锻炼一定时间，然后

53、播种，可以提高作物的抗热性。高温处理会诱导植物形成热击蛋白。有的研究表明热击蛋白的形成与植物抗热性呈显著正相关，也有的研究指出热击蛋白有稳定细胞膜结构与保护线粒体的功能，所以热击蛋白的种类与数量可以作为植物抗热性的生化指标。 矿质营养与耐热性的关系较复杂。通过对白花酢浆草等植物的测定得知，氮素过多，其耐热性减低；而营养缺乏的植物其热死温度反而提高，其原因可能是氮素充足增加了植物细胞含水量。,Section3 Salt stress and resistance to salt 1/51/3 of total cultivated land suffers from salt stress. O

54、ver 1% of salt content in Reclaimed tideland (海涂地) ，0.20.25% of salt content in the northern basic soil (碱土). 世界上盐碱土面积很大，约有4亿公顷。我国盐碱土主要分布于北方和沿海地区，约2千万公顷，另外还有7百万公顷的盐化土壤。一般盐土含盐量在0.2%0.5%时就已对植物生长不利，而盐土表层含盐量往往可达0.6%10%。如果能提高作物抗盐力，并改良盐碱土，那么这将对农业生产的发展产生极大的推动力。,根据植物的耐盐能力，可将植物分为盐生植物(halophyte)和甜土植物(glycophy

55、te)。盐生植物是盐渍生境中的天然植物类群，这类植物在形态上常表现为肉质化，吸收的盐分主要积累在叶肉细胞的液泡中，通过在细胞质中合成有机溶质来维持与液泡的渗透平衡。绝大多数农作物属甜土植物，甜土植物在受到盐胁迫时会发生危害,3.1Mechanism of salt injure 1. Physiological drought-osmotic stress. 甜土植物在土壤含盐量达0.2%0.25%时，出现吸水困难；含盐量高于0.4%时，植物就易外渗脱水，生长矮小，叶色暗绿。在大气相对湿度较低的情况下，随蒸腾的加强，盐害更为严重。 2. Single salt toxicity .Na+ an

56、d Cl-，SO4. 盐碱土中Na+、Cl-、Mg2-、SO42-等含量过高，会引起K+、HPO42-或NO3-等离子的缺乏。Na+浓度过高时，植物对K+的吸收减少，同时也易发生磷和Ca2+的缺乏症。植物对离子的不平衡吸收，不仅使植物发生营养失调，抑制了生长，而且还会产生单盐毒害作用。 3. Metabolic damage：Ch1 and Rubisco, protein degradation,Pro，NH4+ poison.,1.避盐植物回避盐胁迫的抗盐方式称为避盐。它可通过被动拒盐、主动排盐和稀释盐分来达到避盐的目的。（1）拒盐一些植物对某些盐离子的透性很小，在一定浓度的盐分范围内，根

57、本不吸收或很少吸收盐分。也有些植物拒盐只发生在局部组织，如根吸收的盐类只积累在根细胞的液泡内，不向地上部分运转，地上部分“拒绝”吸收。（2）排盐：也称泌盐，指植物将吸收的盐分主动排泄到茎叶的表面，而后被雨水冲刷脱落，防止过多盐分在体内的积累。盐生植物排盐主要通过盐腺，玉米、高粱等作物都有排盐作用。此外有些植物将吸收的盐分转移到老叶中积累，最后脱落叶片以此来阻止盐分在体内的过量积累。（3）稀盐：指通过吸收水分或加快生长速率来稀释细胞内盐分的浓度。如红树虽然每天接受1.7mmolL-1盐分，但叶片的盐浓度保持恒定(510560mmolL-1)。肉质化的植物靠细胞内大量贮水来冲淡盐的浓度。,2.耐盐

58、指通过生理或代谢过程来适应细胞内的高盐环境。（1）耐渗透胁迫：通过细胞的渗透调节以适应由盐渍而产生的水分逆境。植物耐盐的主要机理是盐分在细胞内的区域化分配，盐分在液泡中积累可降低其对功能细胞器的伤害。有的植物将吸收的盐分离子积累在液泡里。植物也可通过合成可溶性糖、甜菜碱、脯氨酸等渗透物质，来降低细胞渗透势和水势，从而防止细胞脱水。 （2）营养元素平衡：有些植物在盐渍时能增加对K+的吸收，有的蓝绿藻能随Na+供应的增而加大对N的吸收，所以它们在盐胁迫下能较好地保持营养元素的平衡。 （3）代谢稳定性：在较高盐浓度中某些植物仍能保持酶活性的稳定，维持正常的代谢。例如菜豆的光合磷酸化作用受高浓度NaC

59、l抑制，而玉米、向日葵、欧洲海蓬子等在高浓度NaCl下反而剌激光合磷酸化作用。（4）与盐结合：通过代谢产物与盐类结合，减少游离离子对原生质的破坏作用。细胞中的清蛋白可提高亲水胶体对盐类凝固作用的抵抗力，从而避免原生质受电解质影响而凝固,3.2.1.Mechanism of resistance to salt,Halophytes,Salt- tolerant nonhalophytes,sensitive nonhalophyte,Fig. Idealized growth responses of halophytes, salt- tolerant nonhalophytes and sensitive nonhalophytes to salt concentration (From Hopkins and Huner, 2004),Halophytes grow in high salt soil. Suaeda maritima and marshgrass (Spartina sp.) Salt regulator, such as mangrove(红树林)，do not absorb salt but