干旱胁迫下沙生灌木花棒的抗氧化保护响应研究

采用盆栽试验,测定了在不同土壤水分胁迫程度和胁迫时间下花棒苗抗氧化保护酶(SOD、CAT、POD、APX)活性和抗氧化物(AsA、GSH、Car)含量,并用隶属函数值法综合评价了试验条件下花棒苗的抗氧化能力。结果显示:(1)与同期适宜水分处理相比,花棒苗的抗氧化保护酶活性在中度和重度干旱胁迫30d时均显著增加;胁迫60d时,POD活性均显著降低,而其余酶活性仍增加(重度胁迫)或显著增加(中度胁迫);胁迫90d时,中度胁迫处理除APX活性持平外,其余酶活性仍显著升高,而重度胁迫处理的SOD活性持平、POD活性显著增加、CAT和APX活性均显著降低。(2)相对于同期适宜水分处理,干旱胁迫30d时,中度胁迫处理的花棒苗AsA、Car、GSH含量分别显著增加、稍有增加和显著降低,而重度胁迫的AsA显著增加,Car和GSH含量均显著降低;胁迫60d时,中度胁迫处理的AsA、Car、GSH含量分别显著增加、稍有降低和稍有提高,而重度胁迫的AsA、Car、GSH含量分别显著增加、稍有增加和显著降低;胁迫90d时,中度胁迫处理的AsA含量显著增加,Car和GSH含量均稍有提高,而重度胁迫的AsA含量稍有下降,Car和GSH含量则持平。(3)花棒苗的MDA含量在干旱胁迫过程中均比适宜水分处理增加,且中后期达到显著水平。(4)花棒苗抗氧化能力在干旱胁迫30d表现为重度干旱>中度干旱>适宜水分,胁迫60d为中度干旱>重度干旱>适宜水分,胁迫90d时为中度干旱>适宜水分>重度干旱。研究表明,花棒苗在中度干旱胁迫下能调动自身抗氧化保护酶类与抗氧化物质并提高其抗氧化能力,消除或减轻干旱诱导的活性氧毒害;重度干旱胁迫下的花棒苗在胁迫前中期亦能增强自身的抗氧化能力,但在胁迫后期因部分活性氧清除机制受到破坏而使抗氧化能力降低。     

不同耐铝型杉木幼苗叶片抗氧化系统对铝胁迫的响应特征

为探讨铝胁迫对杉木抗坏血酸-谷胱甘肽(AsA-GSH)循环的影响,明确AsA-GSH循环在杉木耐铝性中的作用,以耐铝(YX26)和铝敏感型(YX5)杉木家系为材料,分析了铝胁迫对不同耐铝型杉木叶片氧化损伤、抗氧化酶活性和AsA-GSH循环系统的影响。结果表明:(1)铝胁迫显著增加杉木叶片丙二醛(MDA)含量,而且YX5叶片中MDA含量增幅显著大于YX26。(2)铝胁迫不同程度增加了2个杉木家系叶片过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)和单脱氢抗坏血酸还原酶(MDAR)活性以及抗坏血酸(AsA)、脱氢抗坏血酸(DHA)、还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量,而且除AsA含量外,铝胁迫下YX26中上述酶活性和非酶性抗氧化剂含量的增幅均大于YX5。(3)铝胁迫下YX5叶片中过氧化氢酶(CAT)和脱氢抗坏血酸还原酶(DHAR)的活性受到显著抑制,而YX26中这两个酶的活性却有所增加,且YX26中的DHAR活性显著高于对照。(4)铝胁迫抑制了2个杉木家系超氧化物歧化酶(SOD)活性,但YX26中SOD活性的降幅小于YX5。研究认为,铝胁迫下通过维持AsA-GSH循环酶活性和非酶性抗氧化系统的高效运转,增强自身活性氧清除能力是耐铝型杉木家系具有较强铝耐能力的生理基础。     

NaCl胁迫下AM真菌对滨梅叶片中抗坏血酸-谷胱甘肽循环的影响

以接种Glomus mosseae的滨梅幼苗为试材,研究了AM真菌对2.0%NaCl胁迫下滨梅叶片抗坏血酸-谷胱甘肽循环系统的影响。结果显示,NaCl胁迫下滨梅幼苗叶片H2O2含量呈增加趋势,但接种菌幼苗叶片H2O2含量显著低于未接种苗的。NaCl胁迫下菌根苗叶片抗氧化酶(APX、DHAR和GR)活性、AsA和GSH含量、氧化还原力(AsA/DHA值和GSH/GSSG值)均显著高于未接种苗。这表明,NaCl胁迫下,AM真菌能促进滨梅叶AsA-GSH循环快速有效地运转,维持体内抗氧化物质较强的再生能力,从而提高抗氧化胁迫能力,菌根苗表现出较强的耐盐性。     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸-谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明:外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

硫化氢对盐碱胁迫下裸燕麦叶片抗坏血酸-谷胱甘肽循环的调控效应

盐碱胁迫是植物遭受的常见非生物胁迫之一,气体信号硫化氢(H₂S)在植物响应盐碱胁迫中发挥着重要作用。为探讨H₂S对盐碱胁迫下裸燕麦抗坏血酸(AsA)-谷胱甘肽(GSH)循环的调控效应,以品种‘定莜9号’为材料,研究了喷施H₂S供体硫氢化钠(NaHS)或H₂S合成抑制剂羟胺(HA)对盐碱混合胁迫下植株生长、叶片活性氧、膜脂过氧化和AsA-GSH循环中抗氧化物质和关键酶的影响。结果表明: 喷施50 μmol·L^-1 NaHS可缓解50 mmol·L^-1盐碱混合胁迫对裸燕麦生长的抑制,降低超氧阴离子、H₂O₂、丙二醛、氧化型抗坏血酸(DHA)、还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量,提高AsA/DHA和GSH/GSSG,而对还原型抗坏血酸(AsA)含量无显著影响。喷施NaHS还提高了盐碱混合胁迫下裸燕麦叶片AsA合成关键酶L-半乳糖脱氢酶(GalDH)和L-半乳糖-1,4-内酯脱氢酶(GalLDH)及AsA-GSH循环中单脱氢抗坏血酸还原酶(MDHAR)活性,降低了抗坏血酸过氧化物酶(APX)和脱氢抗坏血酸还原酶(DHAR)活性,而对抗坏血酸氧化酶(AO)和谷胱甘肽还原酶(GR)活性的影响不大。增添HA后部分或完全解除了喷施NaHS的上述作用。这说明H₂S可通过促进AsA合成和增强MDHAR活性提高AsA-GSH循环效率,降低盐碱胁迫对裸燕麦的氧化伤害。     

NaCl胁迫对茄子嫁接幼苗叶片抗坏血酸和谷胱甘肽代谢的影响

以Torvum Vigor为砧木,栽培品种苏崎茄为接穗,研究NaCl胁迫对茄子嫁接苗和自根苗抗氧化物质含量和H2O2产生及清除酶活性的影响.结果表明;(1)NaCl胁迫可诱导叶片中H2O2的产生,导致膜脂过氧化产物丙二醛(MDA)的积累,嫁接苗叶片中H2O2和MDA的含量显著低于自根苗.(2)在NaCl胁迫下,嫁接苗叶片中谷胱甘肽还原酶(GR)和抗坏血酸过氧化物酶(APX)活性上升,自根苗则下降;NaCl胁迫促进了嫁接苗还原型抗坏血酸(AsA)和还原型谷胱甘肽(GSH)的合成,嫁接苗叶片中AsA和GSH的含量显著高于自根苗.由此认为,茄子嫁接苗耐盐性优于自根苗的原因之一在于嫁接苗保持较快的AsA-GSH循环,从而保证GSH和AsA的再生以减轻氧化损伤.     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明：外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L^-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L^-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

不同抗性苹果砧木叶片抗坏血酸代谢对干旱胁迫的响应

以抗旱性强的苹果砧木新疆野苹果[Malus sieversii (Ledeb.) Roem.]和抗旱性弱的平邑甜茶[M.hupehensis (Panlp.) Reld.]叶片为试材,在20%PEG-6000模拟干旱胁迫条件下,研究了抗坏血酸(AsA)含量、氧化还原状态、合成和代谢相关酶活性对干旱胁迫的响应。结果显示,在正常水分条件下,新疆野苹果和平邑甜茶叶片间AsA含量及代谢相关酶活性差异不显著。干旱胁迫过程中,二者之间叶片AsA、谷胱甘肽(GSH)、总谷胱甘肽和总抗坏血酸含量变化趋势基本一致,但新疆野苹果叶片中的含量增加幅度明显大于平邑甜茶;且与平邑甜茶相比,新疆野苹果叶片具有较高的L-半乳糖酸-1,4-内酯脱氢酶(GalLDH)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR)活性及AsA/DHA(脱氢抗坏酸)和GSH/GSSG(氧化型谷胱甘肽)比率。研究表明,干旱胁迫下,新疆野苹果能够维持较高的AsA合成和再生能力,并具有维持高AsA水平特性,这可能与其具有较强的抗旱性相关。     

外源α-萘乙酸对花期长期干旱大豆叶片抗氧化系统的影响

以不同耐旱型品种‘南农99-6’和‘科丰1号’大豆为材料,2012年在南京农业大学牌楼试验站进行为期110 d的盆栽试验,研究大豆花期叶面喷施α-萘乙酸(NAA)对长期干旱条件下大豆植株抗氧化系统的影响.结果表明:干旱胁迫显著降低了大豆地上部干物质量,叶片中丙二醛(MDA)含量及活性氧(ROS)水平显著升高,同时,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDHAR)、谷胱甘肽还原酶(GR)和谷胱甘肽过氧化物酶(GPX)活性,还原型抗坏血酸(AsA)、还原型谷胱甘肽(GSH)含量及AsA/DHA(双脱氢抗坏血酸)和GSH/GSSG(氧化型谷胱甘肽)比值显著升高,其中‘科丰1号’大豆的抗氧化能力更高,从而维持较低的ROS水平和MDA含量.NAA可显著提高叶片中的APX、POD、CAT、MDHAR活性及AsA/DHA、GSH/GSSG比值,其中‘科丰1号’大豆叶片的脱氢抗坏血栓还原酶(DHAR)活性和AsA含量极显著增加.     

5-氨基乙酰丙酸(ALA)对盐胁迫下葡萄叶片中AsA-GSH循环的影响

以两个耐盐程度不同的葡萄品种‘夏黑’(耐盐性较弱)和‘里扎马特’(耐盐性较强)为材料,分析了不同浓度ALA对不同浓度盐胁迫下葡萄叶片中AsA-GSH循环的影响。研究表明:喷施75 mg·L-1 ALA可显著提高2 g·kg-1盐胁迫下‘夏黑’葡萄叶片中抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)的活性以及还原型抗坏血酸(As A)、还原型谷胱甘肽(GSH)含量和AsA/DHA、GSH/GSSG比值,显著降低氢抗坏血酸(DHA)与氧化型谷胱甘肽(GSSG)含量;而喷施150 mg·L-1 ALA可显著提高4 g·kg-1盐胁迫下‘里扎马特’葡萄叶片中APX、GR、MDHAR、DHAR的活性以及AsA、GSH含量和AsA/DHA、GSH/GSSG比值,显著降低DHA与GSSG含量。     

外源α-萘乙酸对花期长期干旱大豆叶片抗氧化系统的影响

以不同耐旱型品种‘南农99-6’和‘科丰1号’大豆为材料,2012年在南京农业大学牌楼试验站进行为期110 d的盆栽试验,研究大豆花期叶面喷施α-萘乙酸(NAA)对长期干旱条件下大豆植株抗氧化系统的影响.结果表明: 干旱胁迫显著降低了大豆地上部干物质量,叶片中丙二醛(MDA)含量及活性氧(ROS)水平显著升高,同时,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶（MDHAR）、谷胱甘肽还原酶(GR)和谷胱甘肽过氧化物酶(GPX)活性,还原型抗坏血酸(AsA)、还原型谷胱甘肽(GSH)含量及AsA/DHA(双脱氢抗坏血酸)和GSH/GSSG(氧化型谷胱甘肽)比值显著升高,其中‘科丰1号’大豆的抗氧化能力更高,从而维持较低的ROS水平和MDA含量.NAA可显著提高叶片中的APX、POD、CAT、MDHAR活性及AsA/DHA、GSH/GSSG比值,其中‘科丰1号’大豆叶片的脱氢抗坏血栓还原酶（DHAR）活性和AsA含量极显著增加.     

臭氧胁迫对大豆叶片抗坏血酸-谷胱甘肽循环的影响

由于城市化的加剧导致近地面臭氧（O3）浓度日益增加,对植物生长和生态系统的功能产生了显著影响,因此准确评估近地层O3浓度升高对植物的影响具有重要意义。本文利用开顶式气室（OTCs）,系统探讨了模拟O3胁迫下大豆抗氧化系统抗坏血酸（AsA）-谷胱甘肽（GSH）循环清除活性氧（ROS）的机制及其对植株生长发育的影响。结果表明,在整个生育期内,与对照相比, 80?10 nL?L-1和110?10 nL?L-1 O3可以使大豆叶片丙二醛（MDA）含量、相对电导率增大,超氧阴离子（O2 ）产生速率、过氧化氢（H2O2）含量升高,超氧化物歧化酶（SOD）活性减弱; AsA-GSH循环中的AsA、GSH含量减少,脱氢抗坏血酸（DHA）、氧化型谷胱甘肽（GSSG）含量增加,过氧化物酶（APX）、单脱氢抗坏血酸还原酶（MDHAR）、谷胱甘肽还原酶（GR）活性呈现出前期增强后期减弱趋势,而脱氢抗坏血酸还原酶（DHAR）活性呈现出增强-减弱-增强的趋势。以上结果说明,O3浓度升高促进了大豆叶片ROS的代谢速率,降低了AsA-GSH循环效率,表明抗氧化系统不能长时间忍受高浓度O3带来的氧化伤害,从而使膜脂过氧化程度加重,对大豆表现为伤害效应。     

外源γ-氨基丁酸调控甜瓜叶绿体活性氧代谢应对短期盐碱胁迫

以甜瓜品种‘金辉1号’为试材,采用深液流水培法,研究外源γ 氨基丁酸(GABA)对短期盐碱胁迫下甜瓜幼苗叶绿体活性氧代谢的调控作用.结果表明: 盐碱胁迫显著提高了甜瓜叶绿体内光合色素、丙二醛(MDA)和过氧化氢(H₂O₂)含量及超氧阴离子(O^-_·2)产生速率;增加抗坏血酸(AsA)和谷胱甘肽(GSH)等抗氧化物质含量;明显抑制H⁺-ATP酶(H⁺-ATPase)和H⁺ 焦磷酸酶(H⁺-PPiase)活性.外源叶面喷施GABA有效抑制了盐碱胁迫引起的叶绿体内O^-_·2、H₂O₂和MDA的积累,缓解了光合色素增加的趋势;显著提高SOD和AsA GSH循环各个酶的活性,增加了AsA和GSH库,降低了AsA/DHA和GSH/GSSH比值,增强了H⁺-ATPase和H⁺-PPiase 活性.表明外源GABA能加快叶绿体内活性氧代谢,促进AsA-GSH循环的运转,维持细胞膜的渗透性,进而缓解了盐碱胁迫引起的氧化伤害.     

Selenium Pretreatment Upregulates the Antioxidant Defense and Methylglyoxal Detoxification System and Confers Enhanced Tolerance to Drought Stress in Rapeseed Seedlings

In order to observe the possible regulatory role of selenium (Se) in relation to the changes in ascorbate (AsA) glutathione (GSH) levels and to the activities of antioxidant and glyoxalase pathway enzymes, rapeseed (Brassica napus) seedlings were grown in Petri dishes. A set of 10-day-old seedlings was pretreated with 25 μM Se (Sodium selenate) for 48 h. Two levels of drought stress (10% and 20% PEG) were imposed separately as well as on Se-pretreated seedlings, which were grown for another 48 h. Drought stress, at any level, caused a significant increase in GSH and glutathione disulfide (GSSG) content; however, the AsA content increased only under mild stress. The activity of ascorbate peroxidase (APX) was not affected by drought stress. The monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) activity increased only under mild stress (10% PEG). The activity of dehydroascorbate reductase (DHAR), glutathione S-transferase (GST), glutathione peroxidase (GPX), and glyoxalase I (Gly I) activity significantly increased under any level of drought stress, while catalase (CAT) and glyoxalase II (Gly II) activity decreased. A sharp increase in hydrogen peroxide (H₂O₂) and lipid peroxidation (MDA content) was induced by drought stress. On the other hand, Se-pretreated seedlings exposed to drought stress showed a rise in AsA and GSH content, maintained a high GSH/GSSG ratio, and evidenced increased activities of APX, DHAR, MDHAR, GR, GST, GPX, CAT, Gly I, and Gly II as compared with the drought-stressed plants without Se. These seedlings showed a concomitant decrease in GSSG content, H₂O₂, and the level of lipid peroxidation. The results indicate that the exogenous application of Se increased the tolerance of the plants to drought-induced oxidative damage by enhancing their antioxidant defense and methylglyoxal detoxification systems.     

乙烯与NO互作对镉胁迫下荷花的抗坏血酸-谷胱甘肽循环的影响

以荷花‘微山湖红莲’实生苗为试验材料,研究镉(Cd,50 μmol·L^-1)胁迫下,外源乙烯前体1-氨基环丙烷羧酸(ACC,100 μmol·L^-1)、ACC与一氧化氮合酶(NOS)抑制剂N-硝基-L-精氨酸(L-NNA,200 μmol·L^-1)、ACC与硝酸还原酶(NR)抑制剂钨酸钠(Tu,1 mmol·L^-1),ACC与一氧化氮(NO)清除剂2-苯基-4,4,5,5-四甲基咪唑啉-3-氧代-1-氧(PTIO,200 μmol·L^-1),外源NO供体硝普钠(SNP,500 μmol·L^-1)、SNP与乙烯信号转导抑制剂硫代硫酸银(STS,100 μmol·L^-1)处理下荷花幼苗叶片的受害程度及抗坏血酸(AsA)-谷胱甘肽(GSH)循环的变化情况.结果表明: Cd胁迫下,荷花叶片受害症状明显,其相对电导率、丙二醛(MDA)、AsA和GSH含量显著上升,抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)活性明显降低;ACC的添加进一步增加了Cd对荷花叶片的毒害症状,并加剧了4种抗氧化酶活性的降低,但增加了抗氧化剂的含量;SNP的添加对荷花叶片的伤害起到加重作用,并导致GR和MDHAR活性降低以及AsA和GSH含量的升高;PTIO可显著提高Cd和ACC复合处理下荷花叶片APX、GR、MDHAR和DHAR的活性并降低AsA和GSH的含量,而L-NNA和Tu效果不如PTIO明显;STS可显著缓解Cd和SNP复合处理下荷花叶片的毒害症状,并提高4种抗氧化酶的活性、降低AsA和GSH的含量.由此说明,乙烯和NO在AsA-GSH循环中存在互作,二者相互促进,共同调控AsA-GSH循环,进而参与调控荷花对Cd胁迫的响应.     

Spermidine application enhances tomato seedling tolerance to salinity-alkalinity stress by modifying chloroplast antioxidant systems

The purpose of this study was to elucidate whether exogenous spermidine (Spd) protection of tomato (Solanum lycopersicum L.) seedlings under salinity-alkalinity stress is associated with antioxidant enzymes in the chloroplast. The effects of exogenous Spd on antioxidant enzyme activity and antioxidant content in the chloroplast were evaluated in seedlings of salt-sensitive ecotype (Zhongza 9) grown in a 75 mM salinity-alkalinity solution, with or without 0.25 mM Spd foliar spraying. Results showed that salinity-alkalinity stress increased MDA content, superoxide anion O₂^?- generation rate, superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) activities and ratio of AsA/DHA and reduced contents of ascorbate (AsA), dehydroascorbate (DHA), AsA+DHA, glutathione (GSH), oxidized glutathione (GSSG), GSH+GSSG, dehydroascorbate reductase (DHAR) activity and ratio of GSH/GSSG in chloroplasts. The exogenous Spd application combined with salinity-alkalinity stress decreased the O₂^?- generation rate and MDA content compared to salinity-alkalinity stress alone. The exogenous Spd also increased AsA-GSH cycle components and increased all antioxidant enzyme activities in most cases. Therefore, exogenous Spd alleviates salinity-alkalinity stress damage using antioxidant enzymes and non-enzymatic systems in chloroplasts.     

The Response of Antioxidant Enzymes in Cellular Organelles in Cucumber (Cucumis sativus L.) Leaves to Methyl Viologen-induced Photo-oxidative Stress

In order to clarify the response of antioxidant systems in various cellular organelles to photo-oxidative stress, the activities of superoxide dismutase (SOD) and enzymes of the ascorbate–glutathione (AsA-GSH) cycle were investigated in chloroplasts, mitochondria and cytosol of cucumber leaves subjected to methyl viologen (MV) treatment. Photo-oxidation by MV resulted in significant reductions in net photosynthetic rate (Pn) and increases in the ratio of the quantum efficiency of photosystem II (PSII), Φ_PSII to that of the quantum efficiency of CO₂ fixation (ΦCO₂), followed by increased activities of SOD, and a general increase of AsA-GSH cycle enzymes in chloroplasts, mitochondria and cytosol. These increases were however, most significant in chloroplasts. There were also significant increases in dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) except that the content of ascorbate (AsA) in chloroplasts and cytosol was slightly decreased and little effected, respectively. However, GSSG in mitochondria and GSH in cytosol were little influenced by the MV treatment. The activity of ascorbate oxidase (AO) in these organelles was independent of the MV treatment while the activity of l-galactono-1,4- lactone dehydrogenase (GLDH) in mitochondria was slightly inhibited by MV treatment. These results indicate that disturbance of electron transport in chloroplasts by MV influenced the metabolism of whole cell by a crosstalk signaling system and that the AsA-GSH cycle played a primary role in sustaining the levels of AsA.