Cd2+、Hg2+对菱幼苗生长及其超氧化物歧化酶、过氧化物酶活性的影响

利用不同浓度Ｃｄ２＋、Ｈｇ２＋处理菱幼苗,研究重金属离子对菱生长、超氧化物歧化酶（ＳＯＤ）、过氧化物酶（ＰＯＤ）活性的影响,比较Ｃｄ２＋、Ｈｇ２＋对同一植物的毒性差异。Ｃｄ２＋、Ｈｇ２＋各处理浓度均抑制菱幼苗生长,使叶绿素含量下降,但Ｃｄ２＋的抑制作用比Ｈｇ２＋的作用明显。Ｃｄ２＋、Ｈｇ２＋对ＳＯＤ、ＰＯＤ活性有不同的影响效果：Ｃｄ２＋处理最初诱导ＳＯＤ、ＰＯＤ活性升高,但随浓度加大时间延长酶活性急剧下降;Ｈｇ２＋处理的酶活性变化相对平缓,其中５μｍｏｌ／Ｌ和１０μｍｏｌ／ＬＨｇ２＋处理的ＰＯＤ活性持续上升。实验结果表明,在相同处理时间和浓度条件下,Ｃｄ２＋比Ｈｇ２＋对菱的毒性要大。依据实验结果,作者探讨了重金属对植物的毒害机制     

不同浓度Hg^2＋对睡莲的毒害影响研究

主要研究了Ｈｇ＾２＋对睡莲的外部形态及叶绿素含量、过氧化物酶活性、硝酸还原酶活性。可溶性蛋白含量等生理指标的影响。结论是：Ｈｇ＾２＋对其外部形态的毒害程度与处理浓度和时间成正相关。１－５ｍｍｏｌ／Ｌ处理使叶绿素含量、硝酸还原酶活性上升,８－１０ｍｍｏｌ／Ｌ处理则下降;１－８ｍｍｏｌ／Ｌ处理过氧化物酶活性随浓度增加而上升,１０ｍｍｏｌ／Ｌ处理则下降,但仍高于对照;可溶性蛋白含量随处理浓度增加呈下降趋     

Cd2+、Hg2+对菱幼苗生长及其超氧化物歧化酶、过氧化物酶活性的影响

利用不同浓度Ｃｄ＾２＋、Ｈｇ＾２＋处理菱幼苗,研究重金属离子对菱生长、超氧化物歧化酶（ＳＯＤ）、过氧化物酶（ＰＯＤ）活性的影响,比较了Ｃｄ＾２＋、Ｈｇ＾２＋对同一植物的毒性差异,Ｃｄ＾２＋、Ｈｇ＾＾２＋各处理浓度与均抑制菱幼苗生长,使叶绿素含量下降,Ｃｄ＾２＋的抑制作用比Ｈｇ＾２＋的作用明显。Ｃｄ＾２＋、Ｈｇ＾２＋对ＳＯＤ、ＰＯＤ活性有不同的影响效果;Ｃｄ＾２＋处理最艉地ＳＯＤ、ＰＯＤ活性升高,但     

铜胁迫对甘蔗生长及抗氧化酶活性的影响

甘蔗是重要的糖能兼用植物,同时也是潜在的重金属土壤修复植物。为了探明甘蔗对铜胁迫的生理响应,该研究采用营养液培养的方法分析了铜胁迫对甘蔗生长、叶片相对电导率、叶绿素含量及根系抗氧化酶活性等的影响。结果表明:甘蔗地上部分生物、叶绿素含量随铜浓度增加而下降,地上部分铜含量和叶片的相对电导率则随铜浓度增加而提高。根系的丙二醛(MDA)含量在胁迫24h开始发生显著的变化,在400μmol·L^-1铜处理下比对照显著增加了25.5%,随着胁迫时间的延长,丙二醛含量增加幅度上升。到胁迫72h,100μmol·L^-1铜处理的MDA含量也显著的提高。根系SOD、POD和CAT酶活性在胁迫24h开始发生显著的变化,但不同酶活性变化存在差异。SOD酶活性除了在胁迫的72h随铜浓度增加而提高,其他时间表现为在100μmol·L^-1铜处理下活性下降,随着铜浓度继续增加SOD酶活性提高,到400μmol·L^-1铜处理SOD酶活性又出现下降。POD酶活性在处理的24、48和72h表现为随浓度增加先提高后下降的趋势,但在处理7d时随铜浓度增加而提高。CAT酶活性随着浓度的升高和胁迫时间的延长而下降,到了胁迫的第7天,三个铜处理下CAT酶活性分别下降了89.98%、96.88%和98.50%。由此可见,铜胁迫严重影响甘蔗的生长,较短时间的处理就已经引起了甘蔗根系的氧化胁迫,根系中SOD、POD和CAT酶活性的变化在甘蔗对抗铜引起的氧化胁迫中起到重要作用。     

汞对萝卜种子发芽及幼苗某些生理特性的影响

研究了重金属汞离子(Hg^2 )对萝卜种子发芽及幼苗某些生理特性的影响。结果表明,随着汞离子浓度的增加和处理时间的延长,萝卜种子的发芽率和发芽指数以及幼苗的生长势和生长量均明显下降。幼苗子叶叶绿素a、b的含量下降。幼苗根系、茎叶过氧化物酶的活性则明显升高。     

库拉索芦荟幼苗对海水胁迫的响应

采用砂培试验,研究库拉索芦荟（Aloe vera）幼苗对海水胁迫的响应特征。结果表明：（1）30％海水处理20d,库拉索芦荟幼苗的干重与对照无显著差异,而30％海水处理库拉索芦荟的根干重明显高于10％海水及淡水处理;（2）海水胁迫下,库拉索芦荟幼苗中离子区域化明显：从地下部和地上部来看,Na^＋、Cl^＋明显在芦荟根部积累,海水比例越高,根部Na^＋、Cl^＋含量越大,而K^＋却相反;海水胁迫下芦荟地上部分功能叶片中Na^＋、Cl^＋含量最低,K^＋含量最高,而淡水处理从老叶到新叶,Na^＋、Cl^＋含量总是呈下降趋势,而K^＋正好相反;随海水胁迫在库拉索幼苗中Ca^2＋含量下降,而Mg^2＋含量七升;（3）随海水胁迫时间增加芦荟叶片质膜透性呈显著上升,MDA含量呈波动变化。     

Cd2+胁迫对石菖蒲生理生化特性的影响

通过水堵实验,研究了不同浓度(0、50、200、400μmol/L)下和不同时间内(3、7、11d)Cd2+对石菖蒲(Acorus ta-tarinowii Sehott)叶片抗氧酶活性、叶绿素含量、脂质过氧化程度以及脯氨酸含量的影响.结果表明:(1)超氧化物歧化酶(SOD)活性在3d时随着胁迫浓度的增大而增加,但7d和11d时都是在50 μmol/L浓度下达到峰值,然后降低,但都高于对照;除400μmol/L处理下SOD随胁迫时间延长呈先降后升的趋势外,其余浓度处理下均升高.(2)过氧化物酶(POD)活性在胁迫3d和7d时均随着胁迫浓度的增大而增加,11d时在200 μmol/L处理下达到峰值,然后降低;各浓度处理组均随着胁迫时间的延长POD活性呈下降趋势.(3)过氧化氢酶(CAT)活性在不同时间内随着胁迫浓度的增加呈先增后降趋势,并且各浓度处理组的CAT均随胁迫时间的延长而增加.(4)叶绿素含量在不同胁迫时间内均在200μmol/L处理下达到峰值,然后降低;除400μmol/L处理下的叶绿素随胁迫时间延长而增加外,其余浓度处理组均呈下降趋势.(5)丙二醛(MDA)含量和脯氨酸(Pro)含量均随着胁迫浓度的增加和胁迫时间的延长而增加.研究结果分析表明石菖蒲对Cd2+胁迫有一定的耐受性.     

高山离子芥试管苗在PEG-6000模拟干旱条件下的生理响应

以高山离子芥(Chorispora bungeana)为试材,采用固液培养法,设置对照(不添加PEG-6000,CK)、5%PEG-6000、10%PEG-6000、20%PEG-6000、40%PEG-6000五个干旱处理水平,研究了不同浓度PEG-6000模拟干旱环境下,对高山离子芥幼苗生理生化特性的影响。结果表明:干旱胁迫下,随着不同的处理时间,脯氨酸含量始终保持上升的趋势且含量显著高于对照;可溶性蛋白的含量也有波动,呈现先上升后下降的趋势;丙二醛(MDA)含量,随着时间的延长,呈现先升高再下降的趋势且含量显著高于对照。幼苗叶片叶绿素总含量呈现先升高后下降的趋势,在浓度为40%PEG-6000胁迫下,叶绿素总含量均显著低于对照;叶绿素a则有显著降低的趋势;叶绿素b在浓度为5%PEG-6000胁迫下显著升高,在浓度为10%、20%、40%PEG-6000胁迫下也呈现显著升高的趋势;但其含量总体低于叶绿素a;Chla/Chlb的值经历了先升高后下降的趋势且均高于对照。在各浓度及不同时间处理胁迫下,高山离子芥叶片K+、Na+、Ca2+、Mg2+含量有明显波动:K+、Ca2在5%和10%PEG-6000胁迫6、12、24、48、72h后均显著高于对照,而40%PEG-6000胁迫后均显著低于对照。Na+在5%PEG-6000各时间段胁迫后含量较对照有所增加,在其它浓度和时间处理下其含量均低于对照;而Mg2+含量在40%PEG-6000胁迫下虽有下降趋势但均显著高于对照。表明在干旱胁迫下,高山离子芥通过改变渗透调节物、光合系统中叶绿素含量及离子含量等,启动应对外界干旱环境的耐旱响应机制,从生理角度揭示了高山离子芥响应耐旱的生理生态机理。     

重金属对蚕豆的细胞遗传学毒理作用和对蚕豆根尖微核技术的探讨

Ｐｂ２＋ 、Ｃｄ２＋ 和Ｈｇ２＋ 显著地缩短蚕豆（Ｖｉｃｉａ ｆａｂａ Ｌ．）根尖细胞分裂的持续时间,延长细胞间期的时间间隔,在总体上延长了细胞分裂周期;除Ｈｇ２＋ 随浓度升高一直表现为对有丝分裂抑制外,在Ｐｂ２＋ 、Ｃｄ２＋ 和Ｚｎ２＋ 浓度分别小于１．０、０．０１、１０．０ ｐｐｍ 时,细胞有丝分裂指数随处理浓度升高而上升,当超出上述浓度时则随浓度升高而下降;微核率（ＭＣＮＦ）在Ｐｂ２＋ 、Ｃｄ２＋ 、Ｈｇ２＋ 和Ｚｎ２＋ 的浓度分别小于１．０、５．０、０．５０、１００．０ ｐｐｍ 时,染色体畸变率（ＣＡＦ）在Ｐｂ２＋ 、Ｃｄ２＋ 、Ｈｇ２＋ 和Ｚｎ２＋ 的浓度分别小于５．０、５．０、０．５０、１００．０ ｐｐｍ 时,这两参数随处理浓度的升高而增大;超过上述浓度后,则随处理浓度升高而下降。Ｍｎ２＋ 对各项参数无显著影响。对蚕豆根尖细胞遗传学毒性顺序为Ｈｇ２＋ ＞ Ｃｄ２＋ ＞ Ｐｂ２＋ ＞ Ｚｎ２＋ ＞ Ｍｎ２＋ 。经综合分析,３ 个参数在不同剂量范围下相关性程度有很大的差异。认为蚕豆根尖微核技术检测危险化学品和监测环境污染时取得可靠结果的条件是：受检物质在检测条件下不严重抑制细胞分裂和ＣＡＦ和ＭＣＮＦ呈正相关     

NaCl胁迫对灰绿藜中保护酶活性及MDA含量的影响

目的：研究NaCl胁迫对灰绿藜（Chenopodium glaucum L.）各部位中保护酶活性及MDA含量的影响。方法：对灰绿藜进行控制条件下的NaCl胁迫实验,测定分析不同NaCl浓度下（0、100、200、300、400和500mmol/L）各部位中3种保护性酶活性及MDA含量变化。结果：随着NaCl浓度的增大,灰绿藜根茎叶中的保护酶活性均在一定范围内随着盐浓度的升高而增加;根、茎、叶中的MDA含量均迅速升高;随着NaCl胁迫时间的延长,叶中酶活性的趋势较为平缓或者下降;而根和茎中的酶活性则随着时间的延长逐渐上升;根中MDA的含量与胁迫初期相比,没有较明显的变化;而茎和叶中的MDA含量则有明显下降的趋势。结论：随着NaCl浓度的增大,细胞膜的膜脂过氧化程度得到加强;而随着NaCl胁迫时间的延长,细胞膜的受损程度可得到一定缓解。     

Changes in hydrogen peroxide content and activities of antioxidant enzymes in tomato seedlings exposed to mercury

Thirty-day-old seedlings of tomato (Lycopersicon esculentum Mill.) were treated with various Hg concentrations (0, 10, and 50 μM) for up to 20 days, and the hypothesis that Hg induces oxidative stress leading to the reduction of biomass and chlorophyll content in leaves was examined. The accumulation of Hg in seedlings increased with external Hg concentration and exposure time, and Hg content in roots exposed to 50 μM Hg for 20 days was about 27-fold higher than that in shoots. Furthermore, Hg exposure not only reduced biomass and chlorophyll levels in leaves but also caused an overall increase of endogenous H₂O₂, lipid peroxidation products (malondialdehyde), and antioxidant emzymes activities such as superoxide dismutase, catalase, and peroxidase in leaves and roots. Our results suggest that the suppression of growth and the reduction of chlorophyll levels in tomato seedlings exposed to toxic Hg levels may be caused by an enhanced production of active oxygen species and subsequent high lipid peroxidation.     

Pb~(2+)、Cr~(6+)、Hg~(2+)和Cu~(2+)对碱蓬幼苗生长及生理生化指标的影响

以水培法及分光光度法培养、测定碱蓬幼苗在重金属胁迫下的株高、鲜重及根数,叶绿素、可溶性蛋白和丙二醛含量等各项生长指标以及过氧化物酶、过氧化氢酶的活性变化.结果表明:Pb2+、Cr6+、Hg2+和Cu2+使碱蓬植株生长出现明显抑制效果的临界浓度分别为:45 mg/kg、15 mg/kg、10 mg/kg和5 mg/kg。此浓度胁迫下,碱蓬植株鲜重降低25%~30%、根数减少12%~34%。重金属处理后,碱蓬的叶绿素和可溶性蛋白含量下降、丙二醛含量上升,且处理与对照间差异显著。Pb2+、Cr6+、Hg2+、Cu2+处理的叶绿素总量分别是对照的61%、59%、55%和67%,可溶性蛋白含量分别是对照的66.7%、58.3%、41.7%和75%,而丙二醛含量分别是对照的167%、147%、114%和131%。4种重金属胁迫下的碱蓬植株体内过氧化物酶活性均高于对照,而过氧化氢酶活性低于对照。     

硝基苯酚胁迫下外源褪黑素对水稻幼苗生长及生理特性的影响

采用液体培养实验方法,研究硝基苯酚胁迫对水稻(Oryza sativa L.)幼苗生长、抗氧化特性、光系统Ⅱ(PSⅡ)光合特性的影响,以及添加外源褪黑素对缓解硝基苯酚胁迫的作用。结果显示,随着硝基苯酚胁迫浓度的升高,水稻幼苗株高、根长、地下部干重、地上部干重、全株干重和叶片PSⅡ实际光化学效率[Y(Ⅱ)]、光化学淬灭系数(q P)、PSⅡ电子传递速率(ETR)、叶绿素含量均有所下降,而叶片非光化学淬灭系数(qN、NPQ)上升;同时,根系活性氧[过氧化氢(H_2O_2)和超氧阴离子(O·-2)]积累量、抗氧化酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)]活性,以及渗透调节物质(可溶性蛋白和可溶性糖)含量呈先升高后降低的趋势。在非硝基苯酚胁迫下,与对照组相比,添加外源褪黑素显著提高了幼苗地下部干重、根系可溶性糖含量和SOD活性、叶片PSⅡ光化学效率和叶绿素含量。与单独添加硝基苯酚处理相比,硝基苯酚+褪黑素复合处理显著缓解了硝基苯酚胁迫对幼苗生长、叶片PSⅡ光化学效率和叶绿素合成的抑制作用;降低了根系活性氧水平、抗氧化酶活性和渗透调节物质含量。研究结果表明添加外源褪黑素能够显著缓解硝基苯酚胁迫对水稻幼苗生长、根系活性氧水平、抗氧化酶活性、叶片PSⅡ光化学效率及叶绿素合成的不良影响,提高水稻幼苗对硝基苯酚胁迫的适应性。     

Hg2+和Cd2+胁迫对满江红生理和细胞超微结构的影响

研究了在梯度浓度Hg2+和Cd2+胁迫下,满江红(Azolla imbricata (Roxb.) Nakai)的叶绿素含量、叶绿素a/b比值、光合放氧速率、呼吸速率、抗氧化酶系(超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD))和细胞超微结构受Hg2+和Cd2+的毒害影响.结果显示:随着胁迫程度的增大,叶绿素含量、叶绿素a/b比值、光合放氧速率明显下降,呼吸速率均在2 mg/L浓度下达到峰值,尔后下降; SOD、CAT、POD的活性均出现不同程度的应激性升高(除POD在Cd2+处理时下降),尔后下降.电镜观察发现,随着污染物浓度的增加和胁迫时间的延长,叶绿体出现膨大、破损和解体;线粒体嵴突膨胀和线粒体变形及空泡化;核染色质凝集,核仁消失,核膜破裂.实验结果表明: Hg2+和Cd2+污染不仅损害植物的生理活性,而且也破坏细胞的超微结构,最终导致植物死亡;随着Hg2+和Cd2+胁迫的增大,细胞超微结构的损伤程度和植物的生理变化是同步的;植物受毒害的程度表现出明显的剂量效应关系;在同一处理时间和浓度下,Cd2+对满江红的毒性大于Hg2+.Hg2+对满江红的致死浓度为3.5～4.0 mg/L,Cd2+为3.0～3.5 mg/L.对满江红鱼腥藻(Anabaena azollae Strasburger)细胞的超微结构变化观察表明,满江红鱼腥藻对Hg2+和Cd2+的耐受性明显高于满江红.     

Hg^2＋和Cd^2＋胁迫对满江红生理和细胞超微结构的影响

研究了在梯度浓度Hg^2 和Cd^2 胁迫下,满江红（Azolla imbricata(Roxb.)Nakai)的叶绿素含量,叶绿素a/b比值,光合放氧速率,呼吸速率,抗氧化酶系（超氧化物歧化酶（SOD）,过氧化氢酶（CAT）,过氧化物酶（POD）和细胞超微结构受He^2 和Cd^2 的毒害影响。结果显示：随着胁迫程度的增大,叶绿素含量,叶绿素a/b比值,光合放氧速率明显下降,呼吸速率均在2mg/L浓度下达到峰值,尔后下降;SOD,CAT,POD的活性均出现不同程度的应激性升高（除POD在Cd^2 处理时下降）,尔后下降,电镜观察发现,随着污染物浓度的增加和胁迫时间的延长,叶绿体出现膨大,破损和解体;线粒体嵴突膨胀和线粒体变形及空泡化;核染色质凝集,核仁消失。核膜破裂,实验结果表明：Hg^2 和Cd^2 污染不仅损害植物的生理活性,而且也破坏细胞的超微结构,最终导致植物死亡,随着Hg^2 和Cd^2 为3.0-3.5mg/L。对满江红鱼腥藻（Anabaena azollae Strasburger)细胞的超微结构变化观察表明,满江红鱼腥藻对Hg^2 和Cd^2 的耐受性明显高于满江红。     

Characterization of mercury-induced stress biomarkers in Fagopyrum tataricum plants

The effect of mercury stress on antioxidant enzymes, lipid peroxidation, photosynthetic pigments, hydrogen peroxide content, osmolytes, and growth parameters in Tartary buckwheat were investigated. The effect of Hg-exposure was found to be time (15 and 30 days) and concentration (0, 25, 50, and 75 μM) dependent. Hg was readily absorbed by seedlings with higher content in roots and it resulted in reduction of root and shoot length. The root and shoot Hg uptakes were significantly and directly correlated with each other. However, the fresh mass and biomass increased up to 50 μM Hg-treatment at both time periods. A significant positive correlation was observed between biomass accumulation with relative water content. Hg levels were positively correlated with the production of hydrogen peroxide in leaves as evidenced by 3, 3-diaminobenzidine (DAB)-mediated tissue fingerprinting. The osmolyte levels in general were elevated except for proline and protein which showed a decline at 75 μM Hg-treatment at 30-days. Amongst the photosynthetic pigments, chlorophyll showed a decline while as carotenoid and anthocyanin levels were elevated. The activity of antioxidant enzymes such as ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), Glutathione-s-transferase (GST) and superoxide dismutase (SOD) were positively correlated with Hg-treatment except SOD, which declined at 75 μM Hg-treatment in 30-days old seedlings. Catalase (CAT) activity showed a positive correlation up to 50 μM Hg-treatment but at 75 μM Hg-stress it decreases at both 15 and 30 days.     

Effect of Drought Stress on Certain Morphological and Physiological Characteristics of a Resistant and a Sensitive Canola Cultivar

Water stress is one of the main abiotic factors that reduces plant growth, mainly due to high evaporative demand and low water availability. In order to evaluate the effects of drought stress on certain morphological and physiological characteristics of two canola cultivars, we conducted a factorial experiment based on a completely randomized design. The findings show that drought stress exacerbations result in the plant's response to stress due to increased canola resistance caused by changes in plant pigments, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase and malondialdehyde, glucose, galactose, rhamnose and xylose. These in turn ultimately influence the morphological characteristics of canola. Drought stress reduces the concentration of carotenoids, chlorophyll a, chlorophyll b, total chlorophylls; however, glucose, galactose, rhamnose, xylose, proline, catalase, ascorbate peroxidase, peroxidase, superoxide dismutase, malondialdehyde (in leaves and roots) and the chlorophyll a and b ratios were increased. Reduction of plant height, stem height, root length, fresh and dry weight of canola treated with 300 g/l PEG compared to non‐treatment were 0.264, 0.236, 0.394, 0.183 and 0.395, respectively. From the two canola cultivars, the morphological characteristics of the NIMA increased compared to the Ks7 cultivar. Interaction effects of cultivar and drought stress showed that NIMA cultivar without treatment had the highest number of morphological characteristics such as carotenoid concentration, chlorophyll a, chlorophyll b, total chlorophylls a and b, whereas the cultivar with 300 g/l PEG (drought stress) had the highest amount of proline, malondialdehyde, soluble sugars and enzymes in leaves and roots. Increasing activity of oxidative enzymes and soluble sugars in canola under drought stress could be a sign of their relative tolerance to drought stress.     

Antioxidant system activation by mercury in Pfaffia glomerata plantlets

Oxidative stress caused by mercury (Hg) was investigated in Pfaffia glomerata plantlets grown in nutrient solution using sand as substrate. Thirty-day-old acclimated plants were treated for 9 days with four Hg levels (0, 1, 25 and 50 μM) in the substrate. Parameters such as growth, tissue Hg concentration, toxicity indicators (δ-aminolevulinic acid dehidratase, δ-ALA-D, activity), oxidative damage markers (TBARS, lipid peroxidation, and H₂O₂ concentration) and enzymatic (superoxide dismutase, SOD, catalase, CAT, and ascorbate peroxidase, APX) and non-enzymatic (non-protein thiols, NPSH, ascorbic acid, AsA, and proline concentration) antioxidants were investigated. Tissue Hg concentration increased with Hg levels. Root and shoot fresh weight and δ-ALA-D activity were significantly decreased at 50 μM Hg, and chlorophyll and carotenoid concentration were not affected. Shoot H₂O₂ concentration increased curvilinearly with Hg levels, whereas lipid peroxidation increased at 25 and 50 μM Hg, respectively, in roots and shoots. SOD activity showed a straight correlation with H₂O₂ concentration, whereas CAT activity increased only in shoots at 1 and 50 μM Hg. Shoot APX activity was either decreased at 1 μM Hg or increased at 50 μM Hg. Conversely, root APX activity was only increased at 1 μM Hg. In general, AsA, NPSH and proline concentrations increased upon addition of Hg, with the exception of proline in roots, which decreased. These changes in enzymatic and non-enzymatic antioxidants had a significant protective effect on P. glomerata plantlets under mild Hg-stressed conditions.     

Metabolic adaptations to mercury-induced oxidative stress in roots of Medicago sativa L

Alfalfa (Medicago sativa) roots were treated with mercuric ions in a concentration- and time-dependent manner, and lipid peroxidation was studied biochemically as well as histochemically along with other physiological responses. Histochemical staining with Schiff's reagent and Evans blue revealed that the peroxidation of membrane lipids and loss of plasma membrane integrity in Hg-treated roots occurred in the meristem and the elongation zone. The histochemical observations were supported by the quantitative determinations of thiobarbituric acid reactive substances (TBARS). However, under the mercuric ions stress, the alfalfa plants showed no significant alteration of hydrogen peroxide in roots. Analysis of lipoxygenase activity by non-denaturing polyacrylamide gel electrophoresis (PAGE) showed that there were two isoforms in the root of alfalfa plants, but they showed quite different patterns under the Hg exposure. Also, using non-denaturing PAGE, activities of superoxide dismutase (SOD) and peroxidase (POD) were determined in roots after treatment with Hg ions. The total activities of SOD and POD increased in roots after Hg treatment of roots. Activity of ascorbate peroxides (APX) was stimulated at relatively high concentration of Hg (40microM), and after prolonged Hg exposure (20microM, 24h). In contrast, glutathione reductase activity was depressed at higher concentrations of Hg (10-20microM). Treatments of seedlings with 10-40microM Hg decreased the ascorbate and glutathione amounts but increased total non-protein thiols. The above results indicated that Hg exerted its toxic effect on the root growth of alfalfa by induction of oxidative stress.