Importance of N source on heat stress tolerance due to the accumulation of proline and quaternary ammonium compounds in tomato plants

Proline and quaternary ammonium compounds (QAC), in addition to being N-rich, are known to accumulate in plants under different environmental stress conditions. The accumulation of N-rich compounds in plants has been shown to confer stress resistance. The aim of our work is two-fold: first, to study the influence of temperature on proline, QAC, and choline metabolism in tomato leaves; and second, to investigate the relationship between N source applied (NO3- or NH4+) and thermal stress resistance in these plants. To do this, experiments were conducted at three different temperatures (10 degrees C, 25 degrees C, 35 degrees C); at each temperature half of the plants received NO3-, and the other half received NH4+. At 35 degrees C the plants had the lowest biomass production with respect to 25 degrees C (optimal temperature) and 10 degrees C (cold stress), suggesting that tomato plants were most affected by heat stress. At 35 degrees C, there were also high levels of choline and proline due to the activation of Delta1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine aminotransferase (OAT), and simultaneous inhibition of proline dehydrogenase (PDH) and proline oxidase (PO). However, plants with NH4+ as the N source exhibited reduced growth with respect to the plants fed with NO3-. This is interesting because, under heat stress (35 degrees C), biomass production, as well as proline and choline accumulation, in NH4+ fed plants was higher than in NO3- fed plants. From this, we concluded that tomato plants fed with NH4+ as the N source show higher tolerance to heat stress (35 degrees C) than plants fed with NO3-.     

Does grafting provide tomato plants an advantage against H2O2 production under conditions of thermal shock?

Non-grafted tomato plants ( Lycopersicon esculentum L. cv. Tmknvf₂) and grafted tomato plants ( L. esculentum L. cv. Tmknvf₂ ×  L. esculentum L. cv. RX-335) were grown for 30 days at three different temperatures (10°C, 25°C and 35°C). In the leaves of these plants, the enzymatic activities of SOD, GPX, CAT, APX, DHAR and GR were analysed, as were the concentrations of total H₂O₂, ascorbate and glutathione as well as foliar DW. Regardless of whether the plant was grafted or not, our results indicate that the thermal stress occurred mainly at 35°C, with the following effects: (1) high SOD activity; (2) H₂O₂ accumulation; (3) foliar-biomass reduction; (4) low GPX, CAT, APX, DHAR and GR activities; and (5) high concentrations of ascorbate and glutathione. In addition, our data show these effects to be much weaker in grafted than in non-grafted plants, directly reflected in greater biomass production. Therefore, the use of grafted plants under excessively high temperatures may offer an advantage over non-grafted plants in terms of resistance against thermal shock.     

Effects of Cadmium,Chromium and Lead on Growth,Metal Uptake and Antioxidative Capacity in <Emphasis Type="Italic">Typha angustifolia</Emphasis>

This study investigates the modulation of antioxidant defence system of Typha angustifolia after 30 days exposure of 1 mM chromium (Cr), cadmium (Cd), or lead (Pb). T. angustifolia showed high tolerance to heavy metal toxicity with no visual toxic symptom when exposed to metal stress, and Cd/Pb addition also increased plant height and biomass especially in Pb treatment. Along with increased Cr, Cd, and Pb uptake in metal treatments, there was enhanced uptake of plant nutrients including Ca and Fe, and Zn in Pb treatment. A significant increase in malondialdehyde (MDA) content and superoxide dismutase (SOD) and peroxidase (POD) activities were recorded in plants subjected to Cr, Cd, or Pb stress. Furthermore, Pb stress also improved catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) activities; whereas Cr stress depressed APX and GPX. The results indicate that enzymatic antioxidants and Ca/Fe uptake were important for heavy metal detoxification in T. angustifolia, stimulated antioxidative enzymes, and Ca, Fe, and Zn uptake could partially explain its hyper-Pb tolerance.     

Effects of salicylic acid and cold treatments on protein levels and on the activities of antioxidant enzymes in the apoplast of winter wheat leaves

The effects of salicylic acid (SA) and cold on apoplastic protein levels and activities of apoplastic catalase (CAT), peroxidase (POX) and polyphenol oxidase (PPO) were investigated in winter wheat (Triticum aestivum cv. Dogu-88) leaves. The plants were grown with and without 10 microM SA treatment at both control (20/18 degrees C for 30 and 45-day) and cold (10/5 degrees C for 30-day and 5/3 degrees C for 45-day) acclimatisations. Molecular masses of the apoplastic polypeptides were shown ranging in size from 20 to 66 kDa on SDS-PAGE. Accumulation and pattern of the polypeptides were changed by both SA and cold. It is observed that CAT, POX and PPO activities at 45-day control leaves were higher than at 30-day. When the activities with SA and cold treatments are compared to their controls, CAT activities were decreased while POX and PPO activities were increased by both the treatments. When the activities with cold+SA treatment are compared to their cold treatments, CAT and POX activities were decreased while PPO activity was increased by SA. It is concluded that exogenous SA can be involved in cold tolerance by regulating apoplastic proteins and antioxidant enzyme activities.     

Arbuscular mycorrhizal influence on growth,photosynthetic pigments,osmotic adjustment and oxidative stress in tomato plants subjected to low temperature stress

The influence of the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on characteristics of growth, photosynthetic pigments, osmotic adjustment, membrane lipid peroxidation and activity of antioxidant enzymes in leaves of tomato (Lycopersicon esculentum cv Zhongzha105) plants was studied in pot culture under low temperature stress. The tomato plants were placed in a sand and soil mixture at 25°C for 6 weeks, and then subjected to 8°C for 1 week. AM symbiosis decreased malondialdehyde (MDA) content in leaves. The contents of photosynthetic pigments, sugars and soluble protein in leaves were higher, but leaf proline content was lower in mycorrhizal than non-mycorrhizal plants. AM colonization increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in leaves. The results indicate that the AM fungus is capable of alleviating the damage caused by low temperature stress on tomato plants by reducing membrane lipid peroxidation and increasing the photosynthetic pigments, accumulation of osmotic adjustment compounds, and antioxidant enzyme activity. Consequently, arbuscular mycorrhiza formation highly enhanced the cold tolerance of tomato plant, which increased host biomass and promoted plant growth.     

Polyamine catabolism influences antioxidative defense mechanism in shoots and roots of five wheat genotypes under high temperature stress

Effect of high temperature stress on polyamine catabolism and antioxidant enzyme activity in relation to glutathione, ascorbate and proline accumulation was studied in five wheat (Triticum aestivum L.) genotypes (differently susceptible to temperature stress). High temperature significantly increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and glutathione S-transferase (GST) in shoots of all genotypes. Higher activities of GPX in C 306, C 273 and APX in PBW 550, PBW 343 and PBW 534 demonstrate their important role in scavenging H₂O₂. Conversely, high temperature stress led to a significant decline in SOD, CAT, APX and GPX activities of roots with a subsequent increase in diamine oxidase (DAO) and polyamine oxidase (PAO) activities especially in PBW 550 and PBW 343. The concentration of ascorbic acid declined with the imposition of heat stress, however, polyamines responded to high temperature stress by increasing spermidine and spermine levels and decreasing putrescine levels. After exposure to high temperature, proline accumulation was significantly decreased in roots and increased in shoots though maximum concentration was achieved in C 306 genotype. Apparently, the wheat seedlings respond to high temperature mediated increase in reactive oxygen species (ROS) production by altering antioxidative defense mechanism and polyamine catabolism though differentially in five wheat genotypes. Among five genotypes studied, C 306 and C 273 seem to be better protected against temperature stress. The results suggested that shoots were more resistant against the destructive effects of ROS as is indicated by low levels of thiobarbituric acid reactive substances under high temperature stress.     

The effects of copper, manganese and zinc on plant growth and elemental accumulation in the manganese-hyperaccumulator Phytolacca americana

Synchrotron radiation X-ray fluorescence (SRXRF) and inductively coupled plasma mass spectrometry were used to estimate major, minor and trace elements in Cu-, Zn- and Mn-treated Phytolacca americana. The effects of the addition of Cu, Zn and Mn on morphological parameters, such as root length, shoot height, and fresh and dry weights of shoots and roots, were also examined. In addition, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (GPX) and catalase (CAT) and the expression of Fe-SOD, Cu/Zn-SOD, metallothionein-2 and glutathione S-transferase (GST) exposed to the highest amounts of Cu, Zn or Mn were detected. Our results confirmed the following: (1) Zn supplementation leads to chlorosis, disturbed elemental homeostasis and decreased concentrations of micro- and macroelements such as Fe, Mg, Mn, Ca and K. Cu competed with Fe, Mn and Zn uptake in plants supplemented with 25μM Cu. However, no antagonistic interactions took place between Cu, Zn, Mn and Fe uptake in plants supplemented with 100μM Cu. Mn supplementation at various concentrations had no negative effects on elemental deficits. Mn was co-located with high concentrations of Fe and Zn in mature leaves and the concentrations of macro elements were unchanged. (2) P. americana supplemented with increased concentrations of Zn and Cu exhibited lower biomass production and reduced plant growth. (3) When plants were supplemented with the highest Zn and Cu concentrations, symptoms of toxicity corresponded to decreased SOD or CAT activities and increased APX and GPX activities. However, Mn tolerance corresponded to increased SOD and CAT activities and decreased POD and APX activities. Our study revealed that heavy metals partially exert toxicity by disturbing the nutrient balance and modifying enzyme activities that induce damage in plants. However, P. americana has evolved hyper accumulating mechanisms to maintain elemental balance and redox homeostasis under excess Mn.     

Modulation of Antioxidant Machinery and the Methylglyoxal Detoxification System in Selenium-Supplemented Brassica napus Seedlings Confers Tolerance to High Temperature Stress

We investigated the protective role of selenium (Se) in minimizing high temperature-induced damages to rapeseed (Brassica napus L. cv. BINA Sarisha 3) seedlings. Ten-day-old seedlings which had been supplemented with Se (25 μM Na₂SeO₄) or not were grown separately under control temperature (25 °C) or high temperature (38 °C) for a period of 24 or 48 h in nutrient solution. Heat stress caused decrease in chlorophyll and leaf relative water content (RWC) and increased malondialdehyde (MDA), hydrogen peroxide (H₂O₂), proline (Pro), and methylglyoxal (MG) contents. Ascorbate (AsA) content decreased at any duration of heat treatment. The content of reduced glutathione (GSH) increased only at 24 h of stress, while glutathione disulfide (GSSG) markedly increased at both duration of heat exposure with associated decrease in GSH/GSSG ratio. Upon heat treatment the activities of ascorbate peroxidase (APX), glutathione S-transferase (GST) and glyoxalase I (Gly I) were increased, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and catalase (CAT) were decreased. The activities of glutathione reductase (GR) and glutathione peroxidase (GPX) remained unchanged under heat stress. However, heat-treated seedlings which were supplemented with Se significantly decreased the lipid peroxidation, H₂O₂, and MG content and enhanced the content of chlorophyll, Pro, RWC, AsA, and GSH as well as the GSH/GSSG ratio. Selenium supplemented heat-treated seedlings also showed enhanced activities of MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II as compared to heat-treated seedlings without Se supplementation. This study concludes that exogenous Se application confers heat stress tolerance in rapeseed seedlings by upregulating the antioxidant defense mechanism and methylglyoxal detoxification system.     

Antioxidant response to drought in red and white clover

Antioxidant response to drought in red (Trifolium pratense L., cv. ??Start??) and white clover (Trifolium repens L, cv. ??Haifa?? and cv. ??Debut??) grown as soil cultures was evaluated in water-deprived and recovered plants. Drought provoked oxidative stress in leaves confirmed by the considerable changes in electrolyte leakage, malondialdehyde, hydrogen peroxides and proline contents. Immunoblot of ??-1-pyrroline-5-carboxylate synthetase (P5CS), which catalyzes the first two steps in proline biosynthesis, revealed strong induction of the enzyme in red clover plants submitted to drought. Water-deprived white clover plants exhibited distinct P5CS profiles. This was related to different drought tolerance of the studied T. repens cultivars. Isoenzyme analyses of superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) demonstrated certain differences in antioxidant defence among the tested varieties. It was confirmed that MnSOD (in both T. repens and T pratense) and FeSOD (in T. repens) isoforms were the most affected by drought. The red clover cultivar ??Start?? exhibited the lowest FeSOD and POX activities which could contribute to its poor performance under water deprivation.     

Biochemical markers of oxidative stress in Perna viridis exposed to mercury and temperature

Oxidative damage and antioxidant properties have been studied in Perna viridis subjected to short-term exposure to Hg along with temperature (72h) and long-term temperature exposures (14 days) as pollution biomarkers. The elevated thiobarbituric acid reactive substances (TBA-RS) levels observed in gills and digestive gland under exposure to Hg, individually and combined with temperature, as also long-term temperature stress have been assigned to the oxidative damage resulting in lipid peroxidation (LPX). Increased activities of antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase (GST) both in gills and digestive glands under long-term exposures to temperatures are more prominent to heat rather than cold stress suggesting activation of physiological mechanism to scavenge the ROS produced during heat stress. Also decreased values of reduced glutathione (GSH) on long exposures to temperature stress indicate utilisation of this antioxidant, either to scavenge oxiradicals or act in combination with other enzymes, was more than its production capacity under heat stress. The results suggest that temperature variation does alter the active oxygen metabolism by modulating antioxidant enzyme activities, which can be used as biomarker to detect sublethal effects of pollution.     

Exogenous hydrogen peroxide enhanced the thermotolerance of Festuca arundinacea and Lolium perenne by increasing the antioxidative capacity

Heat stress is one of the most detrimental environment stresses for plants. Hydrogen peroxide (H₂O₂) is produced quickly in response to various stresses and likely plays a positive role in transmitting stress signal in organisms. This investigation addressed whether an exogenous H₂O₂ application would affect the heat response of turfgrasses and induce acclimation. Tall fescue (Festuca arundinacea cv. Barlexas) and perennial ryegrass (Lolium perenne cv. Accent), two important cool-season turfgrasses and forages, were sprayed with 10 mM H₂O₂ before they were treated with heat stress (38/30 °C, day/night) and compared with plants maintained at control temperatures (26/15 °C, day/night). Prior to the initiation of heat stress, H₂O₂ pretreatment increased the activities of guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione-dependent peroxidase (GPX) and the ascorbate and glutathione pool, and it decreased the GSH/GSSG ratio. During the heat stress process, pretreated plants from both grasses exhibited higher turfgrass quality and relative water content, and they experienced lower oxidative damage and H₂O₂ levels. Moreover, the activities of APX, GR, GPX and glutathione-S-transferase increased significantly in response to H₂O₂ pretreatment under heat stress. These results suggested that H₂O₂ most likely participated in the transduction of redox signaling and induced the antioxidative defense system, including various enzymatic and nonenzymatic H₂O₂ scavengers. The scavengers played important roles in improving the thermotolerance of tall fescue and perennial ryegrasses.     

硝普钠对缺铁和硝酸盐胁迫下番茄幼苗生长及生理特性的影响

采用营养液培养方法,研究外源NO供体(硝普钠,SNP)对缺铁和硝酸盐胁迫番茄幼苗生长、养分吸收及抗氧化酶活性的影响.结果表明: 处理7 d后,缺铁使番茄幼苗生长受到抑制,叶绿素a、b、类萝卜素含量显著降低,出现明显失绿症状;降低叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)的活性,电解质渗漏率、丙二醛含量明显增加,脯氨酸和可溶性糖含量变化不显著,幼苗叶片和根中N、P、K、Ca、Mg、Fe含量比对照处理有不同程度的减少.硝酸盐和缺铁双重胁迫对番茄幼苗生长抑制加剧,叶绿素a、b、类萝卜素含量、SOD、POD和CAT活性显著降低,电解质渗漏率、脯氨酸、可溶性糖和丙二醛含量明显增加;番茄幼苗叶片和根中N、P、Mg、Fe含量显著减少,而K、Ca含量显著增加. 与不添加处理相比,添加0.1 mmol·L^-1 SNP处理使胁迫番茄幼苗的生长抑制明显缓解.添加0.1 mmol·L^-1 SF(亚铁氰化钠)的处理在SOD、POD和CAT等指标上也表现出一定程度的缓解或促进作用,但其他生理指标没有表现出缓解或促进作用,原因是SF中也含有铁离子.     

Effects of calcium on antioxidant activities and water relations associated with heat tolerance in two cool-season grasses

Calcium (Ca2+) may be involved in plant tolerance to heat stress by regulating antioxidant metabolism or/and water relations. This study was designed to examine whether external Ca2+ treatment would improve heat tolerance in two C(3), cool-season grass species, tall fescue (Festuca arundinacea L.) and Kentucky bluegrass (Poa pratensis L.), and to determine the physiological mechanisms of Ca2+ effects on grass tolerance to heat stress. Grasses were treated with CaCl(2) (10 mM) or H(2)O by foliar application and then exposed to heat stress (35/30 degrees C) in growth chambers. Some of the Ca2+ -untreated plants were maintained at 20/15 degrees C as the temperature control. Heat stress reduced grass quality, relative water content (RWC), and chlorophyll (Chl) content of leaves in both species, but Ca2+ treatment increased all three factors under heat stress. The Ca2+ concentration in cell saps increased with heat stress and with external Ca2+ treatment in both species. Osmotic potential increased with heat stress, but external Ca2+ treatment had no effect. Osmotic adjustment increased during short-term heat stress, but then decreased with a prolonged period of stress; it was not influenced by Ca2+ treatment. The activity of superoxide dismutase (SOD) in both species increased transiently at 12 d of heat stress and then remained at a level similar to that of the control. External Ca2+ treatment had no effect on SOD activity. The activities of catalase (CAT), ascorbate peroxidase (AP), and glutathione reductase (GR) of both species decreased during heat stress. Plants treated with Ca2+ under heat stress had higher CAT, GR and AP activities than untreated plants. Lesser amounts of malondialdehyde (MDA) accumulated in Ca2+ -treated plants than in untreated plants during extended periods of heat stress. The results suggested that exogenous Ca2+ treatment enhanced heat tolerance in both tall fescue and Kentucky bluegrass. This enhancement was related to the maintenance of antioxidant activities and a decrease in membrane lipid peroxidation, but not to the regulation of osmotic potential and osmotic adjustment.     

Enhancement of oxidative stress tolerance in transgenic tobacco plants overproducing Fe-superoxide dismutase in chloroplasts.

A chimeric gene consisting of the coding sequence for chloroplastic Fe superoxide dismutase (FeSOD) from Arabidopsis thaliana, coupled to the chloroplast targeting sequence from the pea ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit, was expressed in Nicotiana tabacum cv Petit Havana SR1. Expression of the transgenic FeSOD protected both the plasmalemma and photosystem II against superoxide generated during illumination of leaf discs impregnated with methyl viologen. By contrast, overproduction of a mitochondrial MnSOD from Nicotiana plumbaginifolia in the chloroplasts of cv SR1 protected only the plasmalemma, but not photosystem II, against methyl viologen (L. Slooten, K. Capiau, W. Van Camp, M. Van Montagu, C. Sybesma, D. Inzé [1995] Plant Physiol 107: 737-750). The difference in effectiveness correlates with different membrane affinities of the transgenic FeSOD and MnSOD. Overproduction of FeSOD does not confer tolerance to H2O2, singlet oxygen, chilling-induced photoinhibition in leaf disc assays, or to salt stress at the whole plant level. In nontransgenic plants, salt stress led to a 2- to 3-fold increase in activity, on a protein basis, of FeSOD, cytosolic and chloroplastic Cu/ZnSOD, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. In FeSOD-overproducing plants under salt stress, the induction of cytosolic and chloroplastic Cu/ZnSOD was suppressed, whereas induction of a water-soluble chloroplastic ascorbate peroxidase isozyme was promoted.     

Induction of new isoforms of superoxide dismutase and catalase enzymes in the flag leaf of wheat during monocarpic senescence.

Leaf senescence is a programmed cell death phenomenon and involves oxidative stress. Superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT EC 1.11.1.6) activities were studied in the flag leaf of Triticum aestivum cv. Kundan at different stages of grain development. Both SOD and CAT activities showed a decline during monocarpic senescence. Three SOD isozymes were observed in the cytosol, of which one isozyme was observed in the chloroplasts as well. Mitochondria showed the presence of three low abundant SOD isoforms. Inhibitor studies revealed the cytosolic and chloroplastic isoforms to be Cu/Zn SODs. In mitochondria however, two isozymes were MnSOD and one of them appeared to be FeSOD. These isoforms present in the mitochondria increased in activity as senescence progressed. Three isoforms of CAT were observed in peroxisomes which responded differentially during monocarpic senescence. The changes in the kind and pattern of the antioxidant enzymes supported the ordered sequence of events during leaf senescence. This is the first report showing an increase in mitochondrial FeSOD activity during leaf senescence.     

Possible Involvement of Anti-Oxidant Enzymes in the Cross-Tolerance of the Germination/Growth of Wheat Seeds to Salinity and Heat Stress

The germination/growth of wheat （Triticum aestivum L. cv. Zimai 1） seeds and changes in the activities of superoxide dismutase （SOD）, ascorbate peroxidase （APX）, and catalase （CAT）, as well as in the content of thiobarbituric acid-reactive substances （TBARS）, in response to salt and heat stress, as well as cross-stress, were investigated in the present study. With increasing temperature and decreasing water potential caused by NaCI solution, the germination percentage of seeds and the fresh weight of seedlings decreased markedly, SOD activity increased, activities of APX and CAT decreased distinctly, and the TBARS content increased gradually. Seeds pretreated at 33℃ for different times displayed increased tolerance to subsequent salt stress, enhanced SOD, APX, and CAT activities, and decreased TBARS content. Seeds pretreated at -0.8 MPa NaCI for different times displayed increased tolerance to subsequent heat stress and marked increases in SOD, APX, and CAT activities, which were associated with decreased TBARS content. It is considered that the common component in the cross-tolerance of the germination and growth of wheat seeds to salinity and heat stress is the anti-oxidant enzyme system.     

镉对长江华溪蟹肝胰腺抗氧化酶活力的影响

重金属对环境的污染已成为全球面临的首要问题之一,其中镉(Cd2 )是一种广泛存在的毒性污染物,能通过消化道和呼吸道进入生物体,对机体造成损伤(Zyadah and Abdel-Baky,2000)。研究表明,Cd2 可以通过Ca2 通道穿过细胞膜进入机体(Roesijadi and Robinson,1994),诱导产生大量自由基和活性氧(ROS),从而形成氧胁迫(Toppi andGabbrielli,1994;Hegedus et al.,2001)。ROS可以与体内脂质、蛋白质和核酸反应,导致脂质过氧化、细胞膜损伤并且影响多种酶的活力,对生物体造成威胁。由于在水生生态系统中生物富集污染物的作用明显,故相对于陆地生…     

High temperature effects on photosynthetic activity of two tomato cultivars with different heat susceptibility

The functional activities of the photosynthetic apparatus of two tomato cultivars of different thermotolerance were investigated after a short period of high temperature treatment. Seedlings of two tomato genotypes, Lycopersicon esculentum var. Campbell-28 and the wild thermotolerant Nagcarlang, were grown under a photoperiod of 16h at 25 degrees C and dark period of 8h at 20 degrees C. At the fourth true leaf stage, a group of plants was exposed to heat stress of 45 degrees C for 2 h. The heat shock treatment caused important reductions of the net photosynthetic rate (Pn) of Campbell-28 plants due to non-stomatal components. These non-stomatal effects were not evident in Nagcarlang-treated plants. This reduction in the CO2 assimilation rate observed in Campbell-28 was generated by affections in the Calvin cycle and also in the PSII functioning. No changes in these parameters were observed in the thermotolerant genotype after the stress. Injury to the plasma membrane because of the heat stress was evident only in the Campbell-28 genotype. Heat led to a sun-type adaptation response of the photosynthesis pigment apparatus for the Nagcarlang genotype, but not for Campbell-28, and thus an increase in chlorophyll a/b ratio and a decrease in chlorophyll/carotenoid ratio were shown in Nagcarlang stressed plants.     

钙和水杨酸对亚高温胁迫下番茄叶片保护酶活性的调控作用

为了明确Ca²⁺和水杨酸对番茄耐亚高温特性的调控作用,在番茄第1花序第1花开花当天进行昼间亚高温（35 ℃）胁迫处理,并在亚高温处理区喷施10 mmol·L^-1CaCl₂和0.2 mmol·L^-1水杨酸（SA）水溶液,以25 ℃喷施清水为对照,研究叶片保护酶活性（SOD、POD和CAT）和可溶性蛋白质含量的变化.结果表明：亚高温处理使叶片中SOD、CAT、POD活性降低,在处理结束时,SOD、CAT、POD活性分别比对照降低了14.82%、31.84%和 26.34%.而亚高温条件下喷施CaCl₂和SA可以显著降低番茄叶片MDA含量,提高SOD、POD和CAT活性,并使这些指标达到或超过对照水平.说明Ca²⁺和水杨酸对亚高温条件下番茄植株叶片保护酶活性具有正调控作用,这种调控作用可能对亚高温条件下番茄的光合系统起到保护作用.     

Differential responses of the activities of antioxidant enzymes to thermal stresses between two invasive Eupatorium species in China

The effect of thermal stress on the antioxidant system was Investigated in two invasive plants, Eupatorlum adenophorum Spreng. and E. odoratum L. The former is sensitive to high temperature, whereas the latter is sensitive to low temperature.Our aim was to explore the relationship between the response of antioxidant enzymes and temperature In the two Invasive weeds with different distribution patterns in China. Plants were transferred from glasshouse to growth chambers at a constant 25 ℃ for 1 week to acclimatize to the environment. For the heat treatments, temperature was Increased stepwise to 30, 35, 38 and finally to 42 ℃. For the cold treatments, temperature was decreased stepwise to 20, 15,10 and finally to 5 ℃.Plants were kept In the growth chambers for 24 h at each temperature step. In E. adenophorum, the coordinated Increase of the activities of antioxidant enzymes was effective In protecting the plant from the eccumulatlon of active oxygen species (AOS) at low temperature, but the activities of catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX),glutathione reductase (GR), and monodehydroascorbate reductase (MDAR) were not accompanied by the Increase of super-oxide dismutase (SOD) during the heat treatments. As a result, the level of lipid peroxidation in E. adenophorum was higher under heat stress than under cold stress. In E. odoratum, however, the lesser degree of membrane damage, as indicated by low monodehydroascorbate content, and the coordinated Increase of the oxygen. Dstoxlfying enzymes were observed in hest-treated plants, but the antioxidant enzymes were unable to operate in cold stress. This indicates that the plants have a higher capacity for scavenging oxygen radicals in heat stress than in cold stress. The different responses of antloxidant enzymes may be one of the possible mechanisms of the differences in temperature sensitivities of the two plant species.