Effects of nitric oxide on the germination of cucumber seeds and antioxidant enzymes under salinity stress

Effects of exogenous nitric oxide (NO) on the germination and antioxidant enzyme during cucumber seed germination were investigated under salt stress. Seeds of cucumber (Cucumis sativus L. cv. Jinyou 1) were treated with distilled water or NaCl in the presence or absence of NO donor sodium nitroprusside (SNP) during germination. Excess 50 mM NaCl reduced significantly the seed germination rate in a short term and speed of germination. When salt concentration increased, germination of cucumber seed was reduced and the time needed to complete germination lengthened. Addition of exogenous SNP in salt solution attenuated the salt stress effects in a dose-dependent manner, as indicated by accelerating the seed germination, as well as weight increase of budding seeds, and 50 μM SNP was optimal concentration. At 150 mM NaCl, the 50 μM exogenous SNP significantly increased the activities of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and protein content, while decreased the contents of malondialdehyde (MDA). There were no obvious effects of exogenous NO on peroxidase (POD, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.6) activities under salt stress. Exogenous NO also increased the SOD and CAT isozyme expression under salt stress, which was in accordance with the improved antioxidant activities in the germinating seeds. The NO-induced salt stress resistance was associated with activated enzymes, and enhanced protein content, thus decreasing MDA content. It is concluded that exogenous NO treatment on cucumber seeds may be a good option to improve seed germination under saline conditions.     

外源水杨酸对NaCl胁迫下大豆种子萌发和幼苗生长生理的影响

以大豆种子、幼苗为试验材料,采用砂培的方法,研究了0.2mmol·L-1外源水杨酸(SA)对100mmol·L-1 NaCl胁迫下大豆种子萌发、幼苗形态及生物量、膜脂过氧化和抗氧化酶活性的影响。结果显示:NaCl胁迫下,大豆种子萌发和幼苗生长受到显著抑制,且随着胁迫时间的延长(0~3d),大豆幼苗相对电解质渗漏率、硫代巴比妥酸活性产物(TBARS)含量显著升高,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性均明显降低。外源SA促进NaCl胁迫下大豆种子萌发和根茎生长,增加幼苗生物量积累,降低幼苗叶片相对电解质渗漏率和TBARS含量,增强其叶片SOD、CAT、APX活性。研究表明,NaCl胁迫能显著抑制大豆种子萌发和幼苗生长,而一定浓度的外源SA能有效提高NaCl胁迫下大豆种子活力及幼苗抗氧化酶活性,减轻膜脂过氧化程度,缓解NaCl胁迫所造成的伤害,提高大豆幼苗抗盐胁迫的能力。     

外源24-表油菜素内酯对盐胁迫下茄子种子萌发和幼苗生理特性的影响

研究了150mmol·L^-1NaCI胁迫下,外源24-表油菜素内酯（EBR）对茄子种子萌发、幼苗生长和生理特性的影响。结果表明,0．05mg·L^-1外源EBR显著缓解150mmol·L^-1NaCI胁迫伤害,使茄子种子发芽率提高了8．23％,发芽势提高15．91％,发芽指数提高了17．23％,活力指数提高了44．29％;幼苗株高、根长和植株鲜重分别提高了56．67％、23．83％和56．68％;抗氧化酶（SOD、POD、CAT和APX）活性分别增加了13．75％、24．00％、28．64％和21．46％,脯氨酸和可溶性糖含量分别提高30．96％和23．66％;MDA含量、Ｏ产生速率分别降低了29．58％和14．80％。表明0．05mg·L^-1外源EBR能显著促进盐胁迫下茄子种子萌发和幼苗生长,明显缓解叶片氧化损伤,增强茄子的耐盐能力。     

Changes in oligosaccharide content and antioxidant enzyme activities in developing bean seeds as related to acquisition of drying tolerance and seed quality.

Seeds of bean (Phaseolus vulgaris cv. Vernel) were collected throughout their development on the plant and dried at 15 degrees C and 75% relative humidity to a final moisture content of about 16% (fresh weight basis) to determine whether the onset of tolerance to this drying condition was related to changes in soluble sugars or the activities of the main antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR). Measurements of soluble sugars and enzyme activities were made after drying the seeds, and drying tolerance was evaluated by the ability of dried seeds to germinate and to produce normal seedlings. Seeds became tolerant to drying at 45 d after anthesis, a time marking physiological maturity. At physiological maturity, the moisture content of seeds was about 50-55% (fresh weight basis) and seed dry matter reached about 190 mg per seed. Seed vigour, evaluated by controlled deterioration and conductivity measurements, continued to increase after seed mass maturity, but decreased when seeds remained thereafter for more than 7 d on the plant. Acquisition of drying tolerance was coincident with an accumulation of raffinose and stachyose. Dried-tolerant seeds were also characterized by a high amount of sucrose, the most abundant sugar, and by a low content of monosaccharides. The (raffinose+stachyose)/sucrose ratio increased during seed filling, reaching a value close to 1 when all the seeds became tolerant to drying, and maintaining this proportion during the final stages of maturation. Acquisition of drying tolerance was also related to a reorientation of the enzymatic antioxidant defence system. Drying-tolerant dried seeds displayed high CAT and GR activities and low SOD and APX activities, while the opposite condition was observed in immature dried seeds. The shift in antioxidant enzymes corresponded to the beginning of the maturation-drying phase. These results suggest that oligosaccharide metabolism and enzymatic antioxidant defences may be involved in acquisition of drying tolerance during bean seed development, but are not related to seed vigour.     

一氧化氮对渗透胁迫下小麦种子萌发及其活性氧代谢的影响

一氧化氮供体硝普钠(Sodium nitroprusside,SNP)能明显地促进渗透胁迫下小麦(Triticum aestivum L.)种子萌发、胚根和胚芽伸长,提高萌发过程中淀粉酶和内肽酶的活力,加速贮藏物质的降解;胁迫解除后,仍能使种子维持较高的活力.此外,SNP还能显著诱导渗透胁迫下CAT、APX活力的上升和脯氨酸含量积累,抑制LOX活力,从而提高渗透胁迫下小麦种子萌发过程中抗氧化能力.进一步研究还发现,SNP诱导切胚半粒小麦种子萌发早期(6h)的淀粉酶活力上升可能与GA3无直接关系.     

一氧化氮对渗透胁迫下小麦种子萌发及其活性氧代谢的影响

一氧化氮供体硝普钠(Sodium nitroprusside,SNP)能明显地促进渗透胁迫下小麦(Triticum aestivum L.)种子萌发、胚根和胚芽伸长,提高萌发过程中淀粉酶和内肽酶的活力,加速贮藏物质的降解：胁迫解除后,仍能使种子维持较高的活力。此外,SNP还能显著诱导渗透胁迫下CAT、APX活力的上升和脯氨酸含量积累,抑制LOX活力,从而提高渗透胁迫下小麦种子萌发过程中抗氧化能力。进一步研究还发现,SNP诱导切胚半粒小麦种子萌发早期(6h)的淀粉酶活力上升可能与GA3无直接关系。     

Ca^2＋对小麦萌发及幼苗抗盐性的效应

以冬小麦（Triticum aestivum）临远077038为材料, 研究了施入外源Ca^2＋对150、200、250及350 mmol·L^-1NaCl胁迫下小麦种子萌发及幼苗生长发育的影响。结果表明： 20 mmol·L^-1CaCl2浸种能够提高小麦在150–250 mmol·L^-1盐胁迫下种子的发芽率, 并能增强其生长势; 当NaCl浓度为350 mmol·L^-1时, 小麦种子不能萌发, 且在以上浓度的NaCl胁迫下, 小麦种子均不能发育成苗。对NaCl胁迫下的小麦幼苗施入外源Ca^2＋后, 提高了幼苗膜稳定性, 降低了膜脂过氧化程度, 从而减轻了盐胁迫对幼苗膜的伤害, 表现为电导率降低、MDA含量降低及SOD和POD活性提高, 并且提高了幼苗的呼吸强度及叶绿素含量, 促进了幼苗生长及生物量的积累; Ca^2＋的缓解效应随着盐胁迫的加剧逐渐减弱, 在浓度为350 mmol·L^-1的盐胁迫下, 幼苗的生物量显著低于对照。以上结果表明, 与水处理相比, 20 mmol·L^-1CaCl2处理能够更大程度地促进小麦的生长发育。     

基于叶片生理指标的小麦芽期耐盐性评价

土壤盐渍化严重影响小麦生产,提高小麦耐盐性是应对土壤盐渍化的主要生物途径之一.小麦芽期亦是对盐分较为敏感的时期,小麦芽期耐盐性的强弱对盐碱地小麦种植至关重要.为探讨利用叶片生理指标进行小麦芽期耐盐性评价的可行性,该文以沧麦6005及其73个叠氮化钠诱变家系为试验材料,在超纯水和40％人工海水条件下,对芽期叶片中脯氨酸、...     

Protective roles of nitric oxide on germination and antioxidant metabolism in wheat seeds under copper stress

Nitric oxide (NO) is a multifunctional gaseous signal in plant. In the present study, we found that pretreatment with NO could significantly improve wheat seeds germination and alleviate oxidative stress against copper toxicity. With the enhancement of copper stress, the germination percentage of wheat seeds decreased gradually. Pretreatment during wheat seed imbibition with sodium nitroprusside (SNP), an NO donor, could greatly reverse the inhibitory effect of the following copper stress to wheat seeds germination. SNP-pretreated seeds also tended to retain higher amylase activities than that of the control without SNP pretreatment. On the other hand, there was no apparent difference in the activities of esterase in wheat seeds pretreated with or without SNP. Further investigations showed that pretreatment with NO donor dramatically stimulated the activities of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6), decreased the activities of lipoxygenases, sustained a lower level of malondialdehyde, and interfered with hydrogen peroxide (H₂O₂) excessive accumulation compared with the control, thereby enhancing the antioxidative capacity in wheat seeds under copper stress. In addition, the seed copper contents were not significant different between those pretreated with SNP and the controls, inferring that protective roles of NO was not responsible for preventing Cu uptake. Kang-Di Hu and Lan-Ying Hu contributed equally to this paper.     

外源5-氨基乙酰丙酸对盐胁迫下菘蓝种子萌发及幼苗抗氧化酶活性的影响

采用砂培方式,研究了外源5-氨基乙酰丙酸(ALA)对盐胁迫下菘蓝种子的萌发、幼苗叶片的可溶性糖含量、丙二醛(MDA)含量及其抗氧化酶活性的影响,探讨ALA缓解菘蓝受盐胁迫伤害的响应机制。结果显示:(1)菘蓝种子萌发及幼苗生长在100 mmol·L^-1 NaCl胁迫下受到明显的抑制,种子发芽率、发芽势、发芽指数、活力指数与自然含水量均显著降低,丙二醛含量、可溶性糖含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)活性显著升高。(2)盐胁迫下适宜浓度的ALA处理显著提高了种子萌发率、自然含水量及SOD、POD和CAT活性,降低了可溶性糖和丙二醛的含量,并以16.7 mg·L^-1 ALA处理盐胁迫下菘蓝种子的发芽率、发芽势最大,其幼苗的SOD、POD、CAT活性最强。研究表明,盐胁迫显著抑制菘蓝种子的萌发及幼苗生长,适宜浓度的ALA能够有效缓解盐胁迫对菘蓝种子萌发及幼苗生长的伤害,提高植株的抗盐性,并以16.7 mg·L^-1 ALA处理效果最佳。     

外源糖浸种缓解盐胁迫下玉米种子萌发

以玉米品种‘垦玉6号’为材料,在150 mmol·L^-1NaCl胁迫条件下,研究葡萄糖(Glc)和蔗糖(Suc)浸种对玉米种子萌发阶段耐盐性的影响.结果表明: 盐胁迫下,0.5 mmol·L^-1 Glc、Suc浸种可促进玉米种子萌发及幼苗早期生长,其中Glc浸种玉米胚芽和胚根长及相应干质量增加到盐处理的1.5、1.3、2.1、1.8倍;Suc浸种玉米分别增加到1.7、1.3、2.7、1.9倍;盐胁迫下Glc、Suc浸种可减少胚芽中硫代巴比妥酸反应物(TBARS)和过氧化氢(H2O2)含量,与盐处理相比分别降低24.9%、20.6%;Glc、Suc浸种可显著提高盐胁迫下玉米胚芽超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、谷胱甘肽过氧化物酶(GPX)、谷胱甘肽还原酶(GR)的活性,并诱导葡萄糖6 磷酸脱氢酶(G6PDH)活性的升高,其中Glc浸种玉米SOD、APX、GPX、GR、G6PDH活性较盐处理分别提高66.2%、62.9%、32.0%、38.5%、50.5%,Suc浸种玉米较盐处理分别提高67.5%、59.8%、30.0%、38.5%、50.4%;Glc、Suc浸种胚芽中抗坏血酸 (ASA)、谷胱甘肽(GSH)含量及ASA/DHA、GSH/GSSG显著提高,其中G6PDH活性与外源糖诱导的较强的抗氧化能力密切相关.Glc、Suc浸种还可提高盐胁迫下玉米胚芽中K⁺/Na⁺,分别为盐处理的2.3、2.4倍.外源 Glc、Suc浸种可通过提高玉米种子抗氧化能力及维持体内K⁺和Na⁺离子平衡缓解盐胁迫对玉米种子萌发的抑制效应.     

木薯华南8号组培苗对盐胁迫的生理响应

以NaCl胁迫生长的木薯(Manihot esculenta)华南8号(SC8)组培苗为材料,研究不同浓度(0、5、20、35、50 mmol·L-1及R50 mmol·L-1)NaCl处理对SC8组培苗的生长状况及叶绿素、过氧化氢(H2 O2)、丙二醛(MDA)含量,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)活性的影响.结果表明:≤20 mmol·L-1的NaCl胁迫60 d对SC8组培苗的生长基本无影响;≥35 mmol·L-1的NaCl胁迫60 d抑制了SC8组培苗的生长,但高浓度(50 mmol·L-1)胁迫30 d后正常培养30 d,可以使SC8组培苗的长势得到恢复.叶绿素和MDA含量在≤35 mmol·L-1 NaCl处理下较对照出现积累现象,随NaCl浓度升高(≥50 mmol·L-1)含量开始下降;与对照相比,H2 O2含量在NaCl胁迫下未出现积累现象.NaCl胁迫下,POD、CAT和APX活性较对照均有所提高;较高浓度的NaCl处理下,SOD、CAT和APX活性开始降低.实时荧光定量PCR结果表明,≥50 mmol·L-1NaCl胁迫下,SOD、CAT、POD和APX的表达水平较对照出现上升现象.这说明短时间的盐胁迫不会对木薯造成致死伤害,可以通过调节生理指标的活性来提高木薯的耐盐性.     

Proline Metabolism and Cross-Tolerance to Salinity and Heat Stress in Germinating Wheat Seeds

Germination/growth of wheat (Triticum aestivum L., cv. Zimai 1) seeds and changes in the levels of proline and protein as well as in activities of key enzymes involved in proline metabolism in response to salinity-, heat-stresses and their cross-stress were studied. With decreasing water potential caused by increasing concentrations of NaCl, germination percentage, fresh weight of seedlings and protein amount markedly decreased, whereas proline amount slightly increased. The activities of pyrroline-5-carboxylate synthetase (P5CS), ornithine aminotransferase (OAT), and proline dehydrogenase (PDH) peaked at ?0.2 MPa water potential. Germination percentage and amounts of proline and protein increased as germination temperature elevated to 25°C from 15°C, and decreased above 25°C; fresh weight of seedlings increased to 30°C from 15°C, and decreased above 30°C. However, the activities of P5CS, OAT and PDH gradually decreased with elevaing temperature. Seeds pretreated at 33°C or in ?0.8 MPa NaCl solution for various time length increased tolerance to subsequent salt + water stress or heat stress, as measured by germination percentage and fresh weight of seedlings 5 days after beginning of experiment. The acquisition of cross-tolerance resulting in limitation of negative stress effects does not relate directly to proline level and activities of P5CS, OAT and PDH involved in proline metabolism. Proline amount as measured four days or later after stress imposition cannot be considered a symptom of salt-, water- and heat-stress injury or an indicator of the resistance.     

An Enhancing Effect of Exogenous Mannitol on the Antioxidant Enzyme Activities in Roots of Wheat Under Salt Stress

The role of mannitol as an osmoprotectant, a radical scavenger, a stabilizer of protein and membrane structure, and protector of photosynthesis under abiotic stress has already been well described. In this article we show that mannitol applied exogenously to salt-stressed wheat, which normally cannot synthesize mannitol, improved their salt tolerance by enhancing activities of antioxidant enzymes. Wheat seedlings (3 days old) grown in 100 mM mannitol (corresponding to −0.224 MPa) for 24 h were subjected to 100 mM NaCl treatment for 5 days. The effect of exogenously applied mannitol on the salt tolerance of plants in view of growth, lipid peroxidation levels, and activities of antioxidant enzymes in the roots of salt-sensitive wheat (Triticum aestivum L. cv. Kızıltan-91) plants with or without mannitol was studied. Although root growth decreased under salt stress, this effect could be alleviated by mannitol pretreatment. Peroxidase (POX) and ascorbate peroxidase (APX) activities increased, whereas superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) activities decreased in Kızıltan-91 under salt stress. However, activities of antioxidant enzymes such as SOD, POX, CAT, APX, and GR increased with mannitol pretreatment under salt stress. Although root tissue extracts of salt-stressed wheat plants exhibited only nine different SOD isozyme bands of which two were identified as Cu/Zn-SOD and Mn-SOD, mannitol treatment caused the appearance of 11 different SOD activity bands. On the other hand, five different POX isozyme bands were determined in all treatments. Enhanced peroxidation of lipid membranes under salt stress conditions was reduced by pretreatment with mannitol. We suggest that exogenous application of mannitol could alleviate salt-induced oxidative damage by enhancing antioxidant enzyme activities in the roots of salt-sensitive Kızıltan-91.     

Possible Involvement of Reactive Oxygen Species Scavenging Enzymes in Desiccation Sensitivity of Antiaris toxicaria Seeds and Axes

The relationships among desiccation sensitivities of Antiaris toxicaria seeds and axes, changes in activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase, (TBA)-reactive substance were studied. Desiccation tolerance of seeds and axes decreased with dehydration. Desiccation tolerance of axes was higher than that of seeds, and that of epicotyls was higher than radicles. Activities of SOD, CAT and DHAR of seeds increased during the initial phase of dehydration, and then decreased with further dehydration, whereas activities of APX and GR decreased with dehydration. These five enzyme activities of axes, however, increased during the initial phase of dehydration, and then decreased with further dehydration. The rate of superoxide radical production, and the contents of H2O2 and TBA-reactive products of seeds and axes gradually increased with dehydration. These results show that the A. toxicaria seed is a typical recalcitrant seed. Loss of desiccation tolerance in seeds and axes was correlated with activities of seeds and axes.     

不同脱水速率对木奶果种子脱水敏感性及抗氧化酶活性的影响

研究了脱水速率对木奶果种子脱水敏感性和抗氧化酶活性的影响。木奶果种子初始含水量高达1.72gH2O·g^-1DW,萌发率为86.67%。含水量降至0.90gH2O·g^-1DW左右时,慢速脱水种子的萌发率为97.78%,而快速脱水的种子萌发率仅为64.44%。快速脱水至含水量为0.76gH2O·g^-1DW时萌发率为21.67%,而慢速脱水至0.68gH2O·g^-1DW时,萌发率仍高达55.56%。确定了木奶果种子是对慢速脱水耐受性更高的顽拗性种子。在种子脱水过程中,相对电解质渗透速率和脂质过氧化产物（TBARs）都呈升高趋势,但慢速脱水后的种子,其TBARs升高的速率较快速脱水的慢。快速脱水的种子中超氧化岐化酶（SOD）、脱氢抗坏血酸还原酶（DHAR）和抗坏血酸过氧化物酶（APX）的活性较慢速脱水的高,而过氧化氢酶（CAT）活性较慢速脱水的低,未检测出谷胱甘肽还原酶（GR）的活性。这些结果表明,在木奶果种子脱水耐性获得过程中过氧化氢酶比其他抗氧化酶作用更大。     

NaCl胁迫对螺旋藻生长及抗氧化酶活性的影响

在0.1％～5.0％NaCl浓度范围的培养基中培养极大螺旋藻(Spirulina maxima),发现NaCl浓度高于2.0％时螺旋藻生长受到明显抑制。培养7天后测定超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(ASA-POD)、过氧化氢酶(CAT)活性和丙二醛(MDA)含量。结果表明：在盐胁迫下,SOD酶活性升高;抗坏血酸过氧化物酶和过氧化氢酶活性在低盐胁迫下活性升高,高盐胁迫下抗坏血酸过氧化物酶活性迅速降低,过氧化物酶则完全失活;MDA含量先随盐胁迫程度增加而降低,后随盐胁迫的进一步增强恢复至对照水平。     

Enhanced tolerance to sulfur dioxide and salt stress of transgenic Chinese cabbage plants expressing both superoxide dismutase and catalase in chloroplasts.

To explore the possibility of overcoming the highly phytotoxic effect of SO(2) and salt stress, we introduced the maize Cu/ZnSOD and/or CAT genes into chloroplasts of Chinese cabbage (Brassica campestris L. ssp. pekinensis cv. Tropical Pride) (referred to as SOD, CAT and SOD+CAT plants). SOD+CAT plants showed enhanced tolerance to 400 ppb SO(2), and visible damage was one-sixth that of wild-type (CK) plants. In addition, when SOD+CAT plants were exposed to a high salt treatment of 200 mM NaCl for 4 weeks, the photosynthetic activity of the plants decreased by only 6%, whereas that of CK plants decreased by 72%. SOD plants had higher total APX and GR activities than CK plants. As expected, SOD plants showed levels of protection from SO(2) and salt stress that were moderately improved compared to CK plants. However, CAT plants showed inhibition of APX activity and provided only limited improvements in plant stress tolerance. Moreover, SOD+CAT plants accumulated more K(+), Ca(2+) and Mg(2+) and less Na(+) in their leaves compared with those of CK plants. These results suggest that the expression of SOD and CAT simultaneously is suitable for the introduction of increased multiple stress protection.     

Thermotolerance and antioxidant response induced by heat acclimation in <Emphasis Type="Italic">Freesia</Emphasis> seedlings

Followed a heat acclimation pretreatment, seedlings of Freesia hybrida ‘Shangnong Jinghuanghou’ were exposed to heat stress at 38°C for 6 h treatment and then recovered at 22°C for 72 h to study the impact of heat acclimation (30°C) on thermotolerance under heat stress. The results showed that the pretreated seedlings performed better under heat stress than control. Heat acclimation could slow down the decrease of chlorophyll contents under heat stress and recover better. Higher levels of soluble sugar and proline and slight lower level of soluble protein were observed in pretreated seedlings. After recovery, similar levels of proline and soluble protein were maintained in all seedlings. However, a higher level of soluble sugar was maintained in pretreated seedlings. MDA content and EL showed a stable level in pretreated seedlings while a significant increase in control, followed by a significant decrease after recovery. Significant different responses of SOD, POD, CAT, and APX activities were observed in pretreated seedlings and control. Heat acclimation led to higher activities of these enzymes and a significant response of antioxidant enzyme activities occurred in a time-dependent manner under heat stress. Exposure to high temperature caused a significant increase in SOD and APX activity, and much higher levels in SOD and APX activity were observed in pretreated seedlings compared to control during heat stress. A slight difference in change pattern of POD and CAT activity was presented. The highest activities of POD and CAT were observed at 4 and 6 h of heat stress in pretreated seedlings and control, respectively. After 72 h recovery, the activities of all tested enzymes decreased to similar levels in all seedlings.     

The effect of NaCl on antioxidant enzyme activities in potato seedlings

The effect of NaCl on the growth and activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were investigated in the seedlings of four potato cultivars (Agria, Kennebec; relatively salt tolerant, Diamant and Ajax; relatively salt sensitive). The shoot fresh mass of Agria and Kennebec did not changed at 50 mM NaCl, whereas in Diamant and Ajax it decreased to 50 % of that in the controls. In Agria and Kennebec, SOD activity increased at 50 mM NaCl, but no significant changes observed in Diamant and Ajax. At higher NaCl concentration, SOD activity reduced in all cultivars. CAT and POD activities increased in all cultivars under salt stress. Unlike the other cultivars, in Ajax seedlings, APX activity increased in response to NaCl stress. We also observed new POD and SOD isoenzyme activities and changes in isoenzyme compositions under salt stress. These results suggest that salt-tolerant potato cultivars may have a better protection against reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes (especially SOD) under salt stress.