Interactions between nitrogen fertilization and ozone in watermelon cultivar Reina de Corazones in open-top chambers. Effects on chlorophyll a fluorescence, lipid peroxidation, and yield

Watermelon (Citrillus lanatus) plants were grown for two consecutive years in open-top chambers with three different ozone concentrations (O₃-free air, O₃ ambient, and air with additional O₃; CFA, NFA, and NFA+O₃) and three nitrogen fertilizer concentrations [0, 14.0, and 29.6 g N per pot; N0, N1, and N2). There was an interaction between ozone and N fertilizer for the major parameters studied. O₃ and N2 treatments led to a significant decrease in maximum efficiency of photosystem 2 (PS2) photochemistry (F_v/F_m), and induced a significant decrease in the actual quantum yield of PS2 (Φ_PS2), due mainly to the increased closure of PS2 reaction centres (q_P) and to an increase in the non-photochemical quenching (NPQ). On the other hand, these plants exhibited an increased susceptibility to photoinhibition, which could be associated with an increased fraction of reduced Q_A. An increase in lipid peroxidation indicated that damage was occurring at the membrane levels. High N concentration enhanced the detrimental effects of ozone on the fluorescence parameter induction and lipid peroxidation. All these negative alterations led to a decreased yield.     

Similar Effects of Ozone on Four Cultivars of Lettuce in Open Top Chambers During Winter

Ozone is the major phytotoxic air pollutant that reduces the yield of several agricultural crops in the Spanish Mediterranean area. We studied four lettuce cultivars (Lactuca sativa L.) for the effects of different O₃ concentrations during the winter on chlorophyll (Chl) a fluorescence, lipid peroxidation, and root length in outdoor open-top chambers. Under O₃ the photosynthetic quantum conversion declined while heat emissions increased in all cultivars; these results provide more evidence of non-filtered air with additional ozone (NFA+O₃) treatment compared with non-filtered air (NFA) and charcoal filtered ozone-free air (CFA). Changes in the Chl a fluorescence may be associated with an increase in membrane lipid peroxidation as well as with observed reduction of root length under O₃ stress.     

Response of Spinach Leaves (Spinacia oleracea L.) to Ozone Measured by Gas Exchange,Chlorophyll a Fluorescence,Antioxidant Systems,and Lipid Peroxidation

Spinach (Spinacia oleracea L. cv. Clermont) leaves grown in open-top chambers and exposed to three different concentrations of ozone were measured for gas exchange, chlorophyll a fluorescence, antioxidant systems, and lipid peroxidation at the end of growing season. High O₃ concentration reduced F_v/F_m, indicating that the efficiency in the energy conversion of photosystem 2 (PS2) was altered. The rate of non-cyclic electron transport rate and the capacity to reduce the quinone pool were also affected. The development of non-photochemical quenching was not high enough to decrease the photon excess in the PS2. The limitation of photosynthetic activity was probably correlated with stomata closure and with an increase in intercellular CO₂ concentration. Under oxidative stress, superoxide dismutase (SOD) activity was stimulated in parallel with lipid peroxidation. We did not find any differences in the ascorbate (AsA) pool and ascorbate peroxidase (APX) or glutathione reductase (GR) activities between air qualities. Small, but similar responses were observed in spinach leaves exposed to ambient ozone concentration.     

Foliar Spraying with Zineb Increases Fruit Productivity and Alleviates Oxidative Stress in Two Tomato Cultivars

The effects of foliar spraying of the dithiocarbamate zineb on two cultivars of tomato grown in the field in a site with high ozone concentrations were studied by means of biomass assessment, antioxidant enzyme assays, lipid peroxidation, and chlorophyll fluorescence measurements. Zineb prevented the peroxidation of membrane lipids and decreased the activity of scavenging enzymes, which suggests that plants sprayed with zineb are subjected to lower oxidative stress than controls. The beneficial effects of zineb protection is the utilization of a larger fraction of absorbed radiant energy in photosynthesis and a larger fruit yield in plants of both cultivars.     

Effects of 2-month ozone exposure in spinach leaves on photosynthesis,antioxidant systems and lipid peroxidation

The photosynthesis response, antioxidant systems and lipid peroxidation were studied in leaves from spinach plants (Spinacia oleracea L.) in response to ozone fumigation, ambient air and charcoal filtered air treatments. The photosynthetic activity was tested through gas exchange and chlorophyll a fluorescence measurements. Ambient air and ozone fumigation caused a decrease in the photosynthetic rate (25% and 63%, respectively) mainly due to a reduced mesophyll activity, as evidenced by the increased intercellular CO₂ concentration. These data agree with a large reduction in the non-cyclic electron flow (7% and 16%), a lower capacity to reduce the quinone pool and a higher development of non-photochemical quenching upon high O₃ concentration. The results suggest that the oxidative stress produced, together with the stimulation of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11) activities and the increase in lipid peroxidation (20% and 36%, respectively), generated an alteration of the membrane properties.     

Effect of 24-epibrassinolide on drought stress-induced changes in Chorispora bungeana

Brassinosteroids (BRs) have been proposed to increase the resistance of plants to drought stress. The effect of foliar application of 0.1 μM 24-epibrassinolide (EBR) on chlorophyll (Chl) content, photosystem 2 (PS 2) photochemistry, membrane permeability, lipid peroxidation, relative water content (RWC), proline content, and the antioxidant system in drought-stressed Chorispora bungeana plants was investigated. The results showed that polyethylene glycol (PEG) induced water stress decreased RWC, Chl content and variable to maximum Chl fluorescence ratio (F_v/F_m) less in plants pretreated with EBR than in non-pretreated plants. In addition, lipid peroxidation, measured in terms of malondialdehyde content, membrane permeability and proline content in drought-stressed plants were less increased in EBR pretreated plants, while antioxidative enzyme activities and reduced ascorbate and glutathione contents were more increased in EBR pretreated than in non-pretreated plants. These results suggested that EBR could improve plant growth under drought stress     

Effects of Nitrogen Deficiency on Gas Exchange,Chlorophyll Fluorescence,and Antioxidant Enzymes in Leaves of Rice Plants

Gas exchange, chlorophyll (Chl) fluorescence, and contents of photosynthetic pigments, soluble proteins (ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO), and antioxidant enzymes were characterized in the fully expanded 6^th leaves in rice seedlings grown on either complete (CK) or on nitrogen-deficient nutrient (N-deficiency) solutions during a 20-chase period. Compared with the control plants, the lower photosynthetic capacity at saturation irradiance (P _max) was accompanied by an increase in intercellular CO₂ concentration (C_i), indicating that in N-deficient plants the decline in P _max was not due to stomatal limitation but due to the reduced carboxylation efficiency. The fluorescence parameters _PS2, F_v/F_m, electron transport rate (ETR), and q_P showed the same tendency as P _max in N-deficient plants. Correspondingly, a higher q_N paralleled the rise of the ratio of carotenoid (Car) to Chl contents. However, F_v/F_m was still diminished, suggesting that photoinhibition did occur in the photosystem 2 (PS2) reaction centres. In addition, the activities of antioxidant enzymes on a fresh mass basis were gradually lowered, leading to the aggravation of membrane lipid peroxidation with the proceeding N-deficiency. The accumulation of malonyldialdehyde resulted in the lessening of Chl and soluble protein content. Analyses of regression showed PS2 excitation pressure (1 - q_P) was linearly correlated with the content of Chl and inversely with soluble protein (particularly RuBPCO) content. There was a lag phase in the increase of PS2 excitation pressure compared to the decrease of RuBPCO content. Therefore, the increased excitation pressure under N-deficiency is probably the result of saturation of the electron transport chain due to the limitation of the use of reductants by the Calvin cycle. Rice plants responded to N-deficiency and high irradiance by decreasing light-harvesting capacity and by increasing thermal dissipation of absorbed energy.     

Activity of Photosystem 2, Lipid Peroxidation,and the Enzymatic Antioxidant Protective System in Heat Shocked Barley Seedlings

The impact of heat shock on minimising the activity of photosystem 2 (PS2) initiating high lipid peroxidation (POL) level and consequently changes in the enzymatic-antioxidant protective system was studied in seedlings of two Egyptian cultivars of barley (Giza 124 and 125). Heat doses (35 and 45 °C for 2, 4, 6, and 8 h) decreased chlorophyll (Chl) contents coupled with an increase in Chl a/b ratio, diminished Hill reaction activity, and quenched Chl a fluorescence emission spectra. These parameters reflect the disturbance of the structure, composition, and function of the photosynthetic apparatus as well as the activity of PS2. POL level, as dependent on the balance between pro- and anti-oxidant systems, was directly correlated with temperature, exposure time, and their interaction. Heat shock caused an increase in the electric conductivity of cell membrane, and malonyldialdehyde content (a peroxidation product) coupled with the disappearance of the polyunsaturated linolenic acid (C_18:3), reflecting the peroxidation of membrane lipids which led to the loss of membrane selective permeability. Moreover, it induced distinct and significant changes in activities of antioxidant enzymes. Superoxide dismutase and peroxidase activities have been progressively enhanced by moderate and elevated heat doses, but the most elevated one (45 °C for 8 h) showed a decrease in activities of both enzymes. In contrast, catalase activity was reduced with all heat shocks.     

Influence of salt stress on growth,lipid peroxidation and antioxidative enzyme activity in borage (Borago officinalis L.)

Abstract

The effects of increasing salt concentrations on the growth, electrolyte leakage, lipid peroxidation, and major antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) of borage plants were investigated. Plants were grown in half strength of Hoagland nutrient solution added with 0, 25, 50, and 75 mM of NaCl. Most measured parameters were affected by salinity. Increasing salt levels caused a significant reduction in leaf area, stem length, stem diameter, flower number, and dry masses of different organs. Growth of borage plants, in terms of dry weight, was affected. As a consequence of salinity stress, lipid peroxidation and membrane permeability was increased. Antioxidant activity showed an increase in the activity of superoxide dismutase, a non-induced activity of catalase and ascorbate peroxidase, and a slight increase in glutathione reductase activity. The results indicate that borage plants appear to be sensitive to salt stress, since enzymes related to antioxidant enzymatic defense system in treated leaves should be highly active.     

Physiological responses to drought and shade in two contrasting Picea asperata populations

The responses of photosynthetic gas exchange, chlorophyll fluorescence, activities of antioxidant enzymes and lipid membrane peroxidation of two contrasting Picea asperata Mast. populations to 30% of full sunlight (shade) and full sunlight (sun) were investigated under well-watered and drought conditions. Two contrasting populations were from the wet and dry climate regions in China, respectively. For both populations tested, drought resulted in lower needle relative water content (RWC), CO₂ assimilation rate ( A ), stomatal conductance ( gs ) and effective PSII quantum yield ( Y ), and higher non-photochemical quenching ( qN ), superoxide dismutase (SOD), ascorbate peroxidase (APX) activities as well as malondialdehyde (MDA) levels and electrolyte leakage in sun plants, whereas these changes were not significant in shade plants. For the wet climate population, shade plants showed higher chlorophyll contents (Chl a , Chl b and Chl a + b ) than sun plants under both well-watered and drought conditions. Our study results implied that shade, applied together with drought, ameliorated the detrimental effects of drought. On the other hand, compared with the wet climate population, the dry climate population was more tolerant to drought in the sun treatment, as indicated by less decreases in A and mass-based leaf nitrogen content ( N _mass), more responsive stomata, greater capacity for non-radiative dissipation of excitation energy as heat (analysed by qN ), and higher level of antioxidant enzyme activities as well as lower MDA content and electrolyte leakage. These results demonstrated that the different physiological strategies were employed by the P. asperata populations from contrasting climate regions when the plants were exposed to drought and shade.     

Plant shading increases lipid peroxidation and intensifies senescence-induced changes in photosynthesis and activities of ascorbate peroxidase and glutathione reductase in wheat

Plants of spring wheat (Triticum aestivum L. cv. Saxana) were grown during the autumn. Over the growth phase of three leaves (37 d after sowing), some of the plants were shaded and the plants were grown at 100 (control without shading), 70, and 40 % photosynthetically active radiation. Over 12 d, chlorophyll (Chl) and total protein (TP) contents, rate of CO₂ assimilation (P _N), maximal efficiency of photosystem 2 photochemistry (F_V/F_P), level of lipid peroxidation, and activities of antioxidative enzymes ascorbate peroxidase (APX) and glutathione reductase (GR) were followed in the 1_st, 2_nd, and 3_rd leaves (counted according to their emergence). In un-shaded plants, the Chl and TP contents, P _N, and F_V/F_P decreased during plant ageing. Further, lipid peroxidation increased, while the APX and GR activities related to the fresh mass (FM) decreased. The APX activity related to the TP content increased in the 3_rd leaves. The plant shading accelerated senescence including the increase in lipid peroxidation especially in the 1^st leaves and intensified the changes in APX and GR activities. We suggest that in the 2_nd and 3_rd leaves a degradation of APX was slowed down, which could reflect a tendency to maintain the antioxidant protection in chloroplasts of these leaves.     

Antioxidant status in herbaceous plants growing under elevated CO2 in mini-FACE rings

Here we present studies on the antioxidant status of a semi-natural grassland community, permanently growing in mini-FACE rings under elevated concentrations of atmospheric CO₂ (560 μmol mol⁻¹). In general, in leaves of Dactylis glomerata L. and Trifolium repens L., no differences between ambient and elevated CO₂ were detected as concerns protein content, activity of oxidant-scavenging enzymes (catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase), and lipid peroxidation. The activity of antioxidant-regenerating enzymes (monodehydroascorbate reductase, dehydroascorbate reductase and glutathione disulfide reductase) and the content of antioxidants (ascorbic acid, dehydroascorbic acid, reduced glutathione and glutathione disulfide) showed remarkable variability between leaves from plants grown in ambient and CO₂-enriched mini-FACE rings. Thus, in general it can be concluded that the effects of elevated CO₂ at environmentally relevant concentrations on the leaf antioxidant status of a grassland community are extremely variable, species-specific and rather limited.     

Antioxidant defense in the leaves of C3 and C4 plants under salinity stress

The effect of salt stress (50, 100 and 150 m M of NaCl) on the activity of superoxide dismutase (SOD, EC. 1.15.1.1), ascorbate peroxidase (APX, EC. 1.11.1.11), glutathione reductase (GR, EC. 1.6.4.2) enzymes and also on the rate of lipid peroxidation in terms of thiobarbituric acid-reactive substances (TBARS) content and photosynthetic capacity in two wheat (C3 plants) and two maize (C4 plants) varieties was studied. In the non-salined control plants, the antioxidant enzymes activities were significantly higher for maize than for wheat. Adding salt to the nutrient solution increased the level of antioxidants in leaves of both maize and wheat. The first substantial response to salinity was found for SOD on the 2nd day, whereas changes occurred for APX on the 4th day and for GR on the 4th/5th day of salt treatment. Although SOD activity increased considerably more in wheat (C3), it never reached as high levels as in maize (C4) grown in the same treatment combinations. The total increase in APX activity was similar for wheat and maize, whereas GR activity was higher in leaves of maize. Lipid peroxidation analyses showed an increase in TBARS contents in both plants' species grown under salinity that corresponded to the damage that occurred in secondary oxidative stress. However, as a result of advanced antioxidant defense in maize, the TBARS quantities did not elevate to as high level as in wheat. Chlorophyll fluorescence measurements revealed a considerable decrease in the efficiency of PS II and electron-transport chain (ETC). Assimilation rate of CO₂ decreased in both plant groups; however, in C4 maize, we observed a much better capacity to preserve the photosynthetic apparatus against overproduction of ROS. Results suggest that efficient antioxidant defense plays an important role in maize, the C₄ plant, resistance to environmental stresses like salinity or drought.     

Stress induced injury and antioxidant enzymes in relation to drought tolerance in wheat genotypes

The role of plant antioxidant system in water stress tolerance was studied in three contrasting wheat genotypes. Water stress imposed at different stages after anthesis resulted in a general increase in lipid peroxidation (LPO) and decrease in membrane stability index (MSI), and contents of chlorophylls (Chl) and carotenoids (Car). Antioxidant enzymes like glutathione reductase and ascorbate peroxidase significantly increased under water stress. Genotype C 306, which had highest glutathione reductase and ascorbate peroxidase activity, also showed lowest LPO and highest MSI, and Chl and Car contents under water stress in comparison to susceptible genotype HD 2329, which showed lowest antioxidant enzyme activity as well as MSI, Chl and Car contents and highest LPO. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Thus, the relative tolerance of a genotype to water stress as reflected by its comparatively lower LPO and higher MSI, Chl and Car contents is closely associated with its antioxidant enzyme system. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of additional red irradiation on the photosynthetic apparatus of <Emphasis Type="Italic">Pisum sativum</Emphasis>

Pisum sativum (L.) plants were grown under “white” luminescent lamps, W [45 μ mol(quantum) m⁻² s⁻¹] or under the same irradiation supplemented with narrow spectrum red light-emitting diodes (LEDs), RE [λ_max = 660 nm, Δλ = 20 nm, 40 μmol(quantum) m⁻² s⁻¹]. Significant differences in the chlorophyll (Chl) a fluorescence parameters, degree of State 1–State 2 transition, and the pigment-protein contents were found in plants grown under differing spectral composition. Addition of red LEDs to the “white light” resulted in higher effective quantum yield of photosystem 2 (PS2), i.e. F′_v/F′_m, linear electron transport (ϕ_PS2), photochemical quenching (q_P), and lower non-photochemical quenching (q_N as well as NPQ). The RE plants were characterised by higher degree State 1–State 2 transition, i.e. they were more effective in radiant energy utilisation. Judging from the data of “green” electrophoresis of Chl containing pigment-protein complexes of plants grown under various irradiation qualities, the percentage of Chl in photosystem 2 (PS2) reaction centre complexes in RE plants was higher and there was no difference in the total Chl bound with Chl-proteins of light-harvesting complexes (LHC2). Because the ratio between oligomeric and monomeric LHC2 forms was higher in RE plants, we suggest higher LHC2 stability in these ones.     

The effects of ethylene, depressed oxygen and elevated carbon dioxide on antioxidant profiles of senescing spinach leaves

It has been suggested that antioxidants play a role in regulating or modulating senescence dynamics of plant tissues. Ethylene has been shown to promote early plant senescence while controlled atmospheres (CA; reduced O2 levels and elevated CO2 levels) can delay its onset and/or severity. In order to examine the possible importance of various antioxidants in the regulation of senescence, detached spinach (Spinacia oleracea L.) leaves were stored for 35 d at 10 degrees C in one of three different atmospheres: (1) ambient air (0.3% CO2, 21.5% O2, 78.5% N2), (2) ambient air + 10 ppm ethylene to promote senescence, or (3) CA (10% CO2, 0.8% O2 and 89.2% N2) to delay senescence. At weekly intervals, material was assessed for activities of the antioxidant enzymes ascorbate peroxidase (ASPX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6), dehydroascorbate reductase (DHAR; EC 1.8.5.4), glutathione reductase (GR; EC 1.6.4.2), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and superoxide dismutase (SOD; EC 1.15.1.1), and concentrations of the water-soluble antioxidant compounds ascorbate and glutathione. Indicators of the rate and severity of senescence (lipid peroxidation, chlorophyll, and soluble protein levels) were also determined. Results indicated that the rate and severity of senescence was similar between the leaves stored in ambient air or CA until day 35, at which point the ambient air-stored leaves exhibited a sharp increase in lipid peroxidation. Tissues under both storage regimes demonstrated significant declines only in levels of ASPX, CAT, and ascorbate. Glutathione content in the CA-stored tissue also significantly dropped, but only on day 35. In contrast, spinach leaves stored in ambient air + ethylene experienced a rapid decrease in levels of all the antioxidants assessed except SOD. Declines in levels of ASPX, CAT, and ascorbate over the 35 d storage period regardless of the composition of the storage atmosphere suggests that regulation of H2O2 levels plays an important role in both the dynamics and severity of post-harvest senescence of spinach.     

Response to ozone in two lettuce varieties on chlorophyll a fluorescence, photosynthetic pigments and lipid peroxidation.

The effect of different O3 concentrations on two lettuce (Lactuca sativa L.) varieties (Valladolid and Morella) was investigated through chlorophyll (Chl) a fluorescence parameters, photosynthetic pigments (Chl a, b and total carotenoid), lipid peroxidation and crop yield. Ozone fumigation caused: a decrease in maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm) in mature leaves, a reduction in the non-cyclic electron flow (phiPSII) and a lower capacity to reoxidize the QA pool (qP). These reductions were significant in the Valladolid var. but not in the Morella var. A significant decrease in Chl a, b and in the total carotenoids was observed in the Valladolid var. but not in the Morella var. mainly under O3 fumigation conditions. We observed that the NPQ parameter did not increase in parallel to the qP reduction seen in the Valladolid var. O3 fumigation with respect to air charcoal filtered air conditions. This fact could be associated with a lower capacity for dissipation of non-radiative excess energy and it may be closely correlated with significant decreases in photosynthetic pigment concentration. A decrease in NPQ from air ozone-free to ozone fumigation in the Morella var. can be explained by the need to maintain the photochemical quenching under O3 stress. It may also be associated with a slight increase in photosynthetic pigments. The differences between the two varieties may indicate that the Valladolid var. is more susceptible to O3 damage.     

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.     

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.     

Response of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt-dependent oxidative stress: The root antioxidative system

The response of the antioxidant system to salt stress was studied in the roots of the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (Lem) and its wild salt-tolerant relative L. pennellii (Corr.) D'Arcy accession Atico (Lpa). Roots of control and salt (100 m M NaCl)-stressed plants were sampled at various times after commencement of salinization. A gradual increase in the membrane lipid peroxidation in salt-stressed root of Lem was accompanied with decreased activities of the antioxidant enzymes: superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and decreased contents of the antioxidants ascorbate and glutathione and their redox states. In contrast, increased activities of the SOD, CAT, APX, monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and increased contents of the reduced forms of ascorbate and glutathione and their redox states were found in salt-stressed roots of Lpa, in which the level of membrane lipid peroxidation remained unchanged. It seems that the better protection of Lpa roots from salt-induced oxidative damage results, at least partially, from the increased activity of their antioxidative system.