Characterization and expression of cytoplasmic copper/zinc superoxide dismutase (CuZn SOD) gene under temperature and hydrogen peroxide (H2O2) in rotifer Brachionus calyciflorus

Superoxide dismutase (SOD, EC 1.15.1.1) is an important antioxidant enzyme that protects organs from damage by reactive oxygen species (ROS). We cloned cDNA encoding SOD activated with copper/zinc (CuZn SOD) from the rotifer Brachionus calyciflorus Pallas. The full-length cDNA of CuZn SOD was 692 bp and had a 465 bp open reading frame encoding 154 amino acids. The deduced amino acid sequence of B. calyciflorus CuZn SOD showed 63.87%, 60.00%, 59.74% and 48.89% similarity with the CuZn SOD of the Ctenopharyn godonidella, Schistosoma japonicum, Drosophila melanogaster and Caenorhabditis elegans, respectively. The phylogenetic tree constructed based on the amino acid sequences of CuZn SODs from B. calyciflorus and other organisms revealed that rotifer is closely related to nematode. Analysis of the expression of CuZn SOD under different temperatures (15, 30 and 37 °C) revealed that its expression was enhanced 4.2-fold (p < 0.001) at 30 °C after 2 h, however, the lower temperature (15 °C) promoted CuZn SOD transiently (4.1-fold, p < 0.001) and then the expression of CuZn SOD decreased to normal level (p > 0.05). When exposed to H₂O₂ (0.1 mM), CuZn SOD, manganese superoxide dismutase (Mn SOD) and catalase (CAT) gene were upregulated, and in addition, the mRNA expression of CuZn SOD gene was induced instantaneously after exposure to vitamin E. It indicates that the CuZn SOD gene would be an important gene in response to oxidative and temperature stress.     

Growth attributes,biochemical modulations,antioxidant enzymatic metabolism and yield in Brassica napus varieties for salinity tolerance

Improvement in salinity tolerance of plants is of immense significance as salt stress particularly threatens the productivity of agricultural crops. This study was designed to assess the tolerance level of six Brassica napus varieties (Super, Sandal, Faisal, CON-111, AC Excel and Punjab) under different levels of salinity (0, 50, 100, 150 & 200 mM) with three replications under CRD. Salt induced osmotic stress curtailed the plant growth attributes, photosynthetic pigments and disturbed ionic homeostasis (K⁺, Na⁺, Ca^2+, Cl^-) but least disturbance as compared to control was found in Super and Sandal cultivars. Punjab canola and AC Excel canola cultivars were least tolerant to salinity because these displayed greater decline in all growth and biochemical attributes. Plants subjected to NaCl induced stress exhibited considerable decline in all attributes under study with proline as exception. Antioxidants (CAT, SOD & POD) showed an obvious change in Canola plants under stress, but greatest decline was displayed at 200 mM NaCl level in all six cultivars. Over all these attributes presented a comparatively stable trend in super and sandal cultivars. This shows presence of physiological resilience and metabolic capacity in these two cultivars to tackle salinity. Similarly, all yield attributes displayed adverse behavior under 150 mM & 200 mM salinity stress. Our results demonstrated that Super and Sandal cultivars of Brassica napus exhibit good performance in salinity tolerance and can be good option for cultivation in salt affected areas.     

Processes hindering activation of lipid peroxidation in cold-tolerant plants under hypothermia

The reasons why the rate of lipid peroxidation (POL) associated with a long-term action of low above-zero temperature (5°C, 6 days) on 6-week-old plants of two potato (Solanum tuberosum L.) cultivars (cold-tolerant cv. Desnitsa and less tolerant cv. Desiree) did not rise were investigated. Upon a long-term action of low hardening temperatures on the plants of both cultivars, there was an equilibrium between the rate of generation of superoxide anion (O₂^·− and activity of superoxide dismutase (SOD), which inactivated it with the formation of H₂O₂. Among the enzymes breaking up hydrogen peroxide, the highest activity was observed for guaiacol peroxidases, which was an order of magnitude greater than the activity of catalase. In potato cultivars, POL processes were not considerably activated; however, activities of antioxidant enzymes (SOD, catalase, and guaiacol peroxidases) in cold-tolerant cv. Desnitsa and less tolerant cv. Desiree differed. It was concluded that, upon a long-term action of hardening temperatures, cold-tolerant plants could sup-press POL processes. Moreover, a test for tolerance to damaging temperature (−3°C, 18 h) showed that detected preservation of the prooxidant/antioxidant equilibrium not only maintained vital activities at low above-zero temperatures but also elevated tolerance to short-term frosts, with this adaptability being cultivar-specific.     

Heat Stress and Spermidine: Effect on Chlorophyll Fluorescence in Tomato Plants

Two tomato (Lycopersicon esculentum L.) cultivars: Robin (tolerant) and Roma (sensitive to heat stress) were studied. Chlorophyll fluorescence induction parameters (F_v/F_p, A_max, and Rfd) at 25 °C showed that the PS2 activity was similar for both cultivars. The parameters, measured at 38 °C, decreased in both cultivars, but more in cv. Roma. Exogenous application of 4 mM spermidine improved the plant heat-resistance in both cultivars, and especially in cv. Roma. Analysis of chlorophyll fluorescence changes during linear increase in temperature showed that cv. Robin plants have higher ability to hardening and higher resistance to thermal damage of the pigment-protein complexes structure and the activity of PS2 than cv. Roma.     

Protective Role of Selenium on Pepper Exposed to Cadmium Stress During Reproductive Stage

The aim of the present study was to examine the effects of exogenous selenium (Se) supplementation on the tolerance of pepper (Capsicum annuum L.) cv. Suryamukhi Cluster plants to cadmium (Cd) phytotoxicity at the reproductive stage. The pepper plants were supplied with Cd (0, 0.25 or 0.50 mM) and Se (0, 3 or 7 μM), individually or simultaneously, three times during the experiment. The obtained results show that Cd had deleterious effect on pepper plants at the reproductive stage. However, Se supplementation improved the flower number, fruit number and fruit diameter in plants exposed to 0.50 mM Cd. Moreover, both Se concentrations used in 0.25 mM Cd-treated plants and 3 μM Se in 0.50 mM Cd-treated plants enhanced fruit yield per plant as compared to Cd-alone treatment. The chlorophyll concentrations significantly increased in the fruits of Cd-exposed plants after Se addition. However, Se supplementation reduced total carotenoids and total soluble solid (TSS) concentrations in the pepper fruits exposed to Cd. Selenium also generally enhanced the total antioxidant activity of pepper fruits subjected to Cd. Both Se concentrations used increased mean productivity (MP), stress tolerance index (STI) and yield stability index (YSI) in plants grown in the medium containing 0.25 mM Cd. At low concentration (3 μM), Se significantly increased geometric mean productivity (GMP), STI and YSI of plant exposed to 0.50 mM Cd. The highest Cd concentration in the fruits was achieved at 0.50 mM Cd and Se application significantly reduced Cd accumulation in the Cd-exposed plants. Our results indicate that application of Se can alleviate Cd toxicity in pepper plants at the reproductive stage by restricting Cd accumulation in fruits, enhancing their antioxidant activity and thus improving the reproductive and stress tolerance parameters.     

Peroxidase activities of two rice cultivars differing in salinity tolerance as affected by proline and NaCl

Proline content, ion accumulation, cell wall and soluble peroxidase activities were determined in control and salt-treated calli (150 nM NaCl) and whole plants (30 mM NaCl) of two rice cultivars (salt sensitive cv. IKP and salt tolerant cv. Aiwu). Under salinity, the highest accumulation of Na⁺, Cl^? and proline occurred in calli, roots and younger leaves of cv. IKP, coupled with the highest decrease in K⁺ content; accumulations of Na⁺ and Cl^? were restricted to older leaves in cv. Aiwu. Relative growth rates of calli and roots or shoots from both cultivars were not linked to peroxidase activities. High concentrations (1 M) of exogenously applied glycerol did not inhibitin vitro activities of soluble peroxidase extracted from control and salt-treated calli or plants. Conversely, 35–55% (in cv. IKP) or 60–80% (in cv. Aiwu) of soluble peroxidase activities were found in presence of isosmotic proline concentration. There were no differences between proline and glycerol effects onin vitro cell wall peroxidase activities.     

Silicon improves salinity tolerance in wheat plants

Durum wheat (Triticum durum cv. Gediz-75) and bread wheat (Triticum aestivum cv. Izmir-85) were grown in a complete nutrient solution in a growth room to investigate effect of silicone supplied to the nutrient solution on plants grown at salt stress. The experiment was a 2 × 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicone (Si) in nutrient solution, 0.25 and 0.50 mM, as Na₂SiO₃. The plants grown at 100 mM NaCl produced less dry matter and chlorophyll content than those without NaCl. Supplementary Si at both 0.25 and 0.5 mM ameliorated the negative effects of salinity on plant dry matter and chlorophyll content. Membrane permeability and proline content in leaves increased with addition of 100 mM NaCl and these increases were decreased with Si treatments. Sodium (Na) concentration in plant tissues increased in both leaves and roots of plants in the high NaCl treatment and Si treatments lowered significantly the concentrations of Na in both leaves and roots. Bread wheat was more tolerant to salinity than durum wheat. The accumulation of Na in roots indicates a possible mechanism whereby bread wheat copes with salinity in the rooting medium and/or may indicate the existence of an inhibition mechanism of Na transport to leaves. Concentrations of both Ca and K were lower in the plants grown at high NaCl than in those in the control treatment and these two element concentrations were increased by Si treatments in both shoots and roots but remained lower than control values in most cases.     

Salicylic acid-mediated changes in photosynthesis,nutrients content and antioxidant metabolism in two mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> L.) cultivars differing in salt tolerance

Mustard (Brassica juncea L.) cultivars Alankar (salt-tolerant) and PBM16 (salt-sensitive) plants were grown with 50 mM NaCl and were sprayed with 0.1, 0.5, and 1.0 mM salicylic acid (SA) to study the physiological processes determining salt tolerance and to observe the influence of SA application on the alleviation of NaCl-induced adverse effects. The content of leaf Na⁺, Cl⁻, H₂O₂, TBARS, and electrolyte leakage and the activity of SOD were higher in PBM16 than Alankar. In contrast, nutrients content, activity of APX and GR, glutathione content, photosynthetic and growth characteristics were higher in Alankar. Treatment of 50 mM NaCl resulted in increase of Na⁺ and Cl⁻, oxidative stress, activity of antioxidant enzymes and glutathione content, while nutrients content, photosynthetic, and growth characteristics decreased in both the cultivars. Application of 0.5 mM SA alleviated the negative effects of 50 mM NaCl maximally, but 1.0 mM SA proved inhibitory. The effect of SA was more conspicuous in Alankar than PBM16. It is concluded that the higher tolerance of Alankar was due to its lower leaf Na⁺ and Cl⁻ content, higher nutrients content, and efficient antioxidant metabolism. The application of 0.5 mM SA substantially alleviated salt-induced adverse effects in Alankar.     

The alteration of mRNA expression of SOD and GPX genes,and proteins in tomato (Lycopersicon esculentum Mill) under stress of NaCl and/or ZnO nanoparticles

Five cultivars of tomato having different levels of salt stress tolerance were exposed to different treatments of NaCl (0, 3 and 6 g L⁻¹) and ZnO-NPs (0, 15 and 30 mg L⁻¹). Treatments with NaCl at both 3 and 6 g L⁻¹ suppressed the mRNA levels of superoxide dismutase (SOD) and glutathione peroxidase (GPX) genes in all cultivars while plants treated with ZnO-NPs in the presence of NaCl, showed increments in the mRNA expression levels. This indicated that ZnO-NPs had a positive response on plant metabolism under salt stress. Superior expression levels of mRNA were observed in the salt tolerant cultivars, Sandpoint and Edkawy while the lowest level was detected in the salt sensitive cultivar, Anna Aasa. SDS–PAGE showed clear differences in patterns of protein expression among the cultivars. A negative protein marker for salt sensitivity and ZnO-NPs was detected in cv. Anna Aasa at a molecular weight of 19.162 kDa, while the tolerant cultivar Edkawy had two positive markers at molecular weights of 74.991 and 79.735 kDa.     

Cellular penetration of fluorescently labeled superoxide dismutases of various origins.

BACKGROUND: Using fluorescently labeled superoxide dismutase (SOD) and flow cytometry, we have shown previously that the enzyme CuZn SOD (EC 1.15.1.1) from bovine erythrocytes binds rapidly to the cell surface with slow uptake into the cell during the following hours. The degree of labeling was most important for monocytes in comparison to other blood cells (erythrocytes, lymphocytes, and neutrophils) and fibroblasts. In agreement with the flow-cytometric findings, the inhibition of superoxide production was more important for SOD-pretreated monocytes than for neutrophils, as demonstrated with the cytochrome c reduction assay. It was thus of interest to confirm the observed differences between monocytes and neutrophils with confocal laser microscopy, study in greater detail the kinetics of binding, penetration, and intracellular localization of the enzyme, and compare the results obtained with bovine CuZn SOD with those from SODs of other origins and carrying different active sites. MATERIALS AND METHODS: Recombinant human (rh), bovine, and equine CuZn SODs, as well as rh and E. coli Mn SODs, were studied before use with respect to specific activity and purity (HPLC, SDS-PAGE electrophoresis). Fluorescein isothiocyanate was covalently conjugated to the various SODs for study with high-resolution confocal scanning laser microscopy. Superoxide production by monocytes and neutrophils was measured with the cytochrome c assay. RESULTS: As expected from our experiments with flow cytometry, only rare neutrophils were labeled with FITC-SOD, even with the longest incubation time of 3 hr and the highest dose of 1500 units/ml. In addition, they showed a localized fluorescence pattern that was quite different from the diffuse punctate fluorescence pattern of monocytes. Lymphocytes were not labeled at all. The rapid binding to the cellular surface of monocytes was confirmed, and even after 5 min of preincubation, FITC-SOD was found on a small percentage of monocytes. This was correlated with a reduction in superoxide release after phorbolmyristate acetate (PMA) stimulation by 40%. An interesting finding was the perinuclear accumulation of the penetrated SOD after the longest pretreatment of 3 hr, suggesting a barrier against further progression. Indeed, through confocal microscopy we were able to exclude any fluorescence at the nuclear level. While the fluorescence labeling patterns and the kinetics of penetration were quite similar for bovine, equine, and rh CuZn SOD, the Mn SODs showed poor labeling, correlated with a weak inhibitory effect on cytochrome c reduction, which was not statistically significant. CONCLUSIONS: The rapid binding of native CuZn SODs on the surface of monocytes, leading to reduced superoxide release by these cells, explains the observation that beneficial effects of injected SOD lasted for months despite rapid clearance of the enzyme from the bloodstream, according to pharmacodynamic studies. The preferential binding to monocytes, in contrast to neutrophils, may play a role in chronic inflammatory diseases in which the monocytes are in an activated state. The differences in binding capacity between CuZn SODs and Mn SODs, correlated with different inhibitory effects of superoxide production by monocytes, may also have therapeutic significance.     

Purification of Two Superoxide Dismutase Isozymes and Their Subcellular Localization in Needles and Roots of Norway Spruce (Picea abies L.) Trees

Two isozymes of superoxide dismutase (SOD; EC 1.15.1.1) were purified from Norway spruce (Picea abies L.) needles to apparent electrophoretic homogeneity. Purification factors were 354 for SOD I and 265 for SOD II. The native molecular mass of both purified enzymes was approximately 33 kD, as determined by gel filtration. The subunit molecular weights, as estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, were 20,000 for SOD I and 16,000 for SOD II in the presence of 2-mercaptoethanol, and 15,800 and 15,000, respectively, in its absence. These results indicate that the native enzymes were homodimers whose subunits contained intrachain disulfide bonds. Isoelectric points determined by nondenaturing isoelectric focusing were 4.5 and 5.5 for SOD I and II, respectively. NH₂-terminal sequence analysis of the first 22 to 23 amino acids revealed 70 to 75% sequence identity with chloroplastic CuZn SODs from other plant species for SOD I, and 75% sequence identity with the cytosolic CuZn SOD from Scots pine for SOD II. SOD I was the major activity in needles and it was associated with chloroplasts. SOD II activity was dominant in roots.     

Responses of growth and antioxidant systems in <Emphasis Type="Italic">Carthamus</Emphasis><Emphasis Type="Italic">tinctorius</Emphasis> L. under water deficit stress

An investigation was carried out to find out the extent of changes occurred in two safflower (Carthamus tinctorius L.) cultivars in response to water deficit stress. Two safflower cultivars namely IL.111 and Isfahan were used for the study. Thirty days after sowing, plants were grown under soil moisture corresponding to 100, 85, 70 and 55% field capacity for next 30 days. Water deficit treatments significantly decreased the shoot length, shoot dry matter, root dry matter, relative growth rate, leaf relative water content (LRWC) and leaf water potential (Ψ_W), whereas root length, root-to-shoot ratio, lipid peroxidation and antioxidant compounds such as ascorbic acid (AA), α-tocopherol (α-Toc) and reduced glutathione (GSH) and superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and peroxidase (POX, EC 1.11.1.7) activities were increased. Water deficit stressed plants maintained higher levels of compounds and scavenging enzymes. Significant differences were observed between cultivars and irrigation levels treatments. The cv. IL.111 could be considered more tolerant to water stress than cv. Isfahan, registering greater biomass, LRWC and leaf water potential (Ψ_W), associated with high antioxidant activity.     

Enhancement of superoxide dismutase activity in the leaves of white clover (Trifolium repens L.) in response to polyethylene glycol-induced water stress

Effects of polyethylene glycol (PEG)-induced water stress on the activities of total leaf superoxide dismutase (SOD) and chloroplast SOD (including thylakoid-bound SOD and stroma SOD) are described in white clover (Trifolium repens L.) grown in solution culture from rooted cuttings. Both leaf SOD and chloroplast SOD activities were markedly enhanced with increasing concentration of PEG stress, generating osmotic potentials around the roots 0, −0.5, −1.0, −1.5 MPa. The effects increased with time up to 72 h. Chloroplast Fe-containing SOD represented about 30% of the total leaf SOD activity in the control plants and a significant increase in chloroplast SOD activity was found during the stress period. This accounted for about 35.5–71.1% of the total leaf SOD activity. The proportion of chloroplast SOD in total leaf SOD not only increased with the decreasing of osmotic potential, but also increased with incubation time. Furthermore, the increase in thylakoid-bound SOD activity was much higher than that of stroma SOD in chloroplast of plants under water stress. The enhanced chloroplastic SOD activity, especially thylakoid-bound SOD activity, demonstrated in Trifolium repens suggests that Fe-SOD located in chloroplasts play a more important role than cytosolic Cu/Zn-containing SODs in scavenging O₂ ⁻.     

Ectopic expression of an osmotin gene leads to enhanced salt tolerance in transgenic chilli pepper (<Emphasis Type="Italic">Capsicum annum</Emphasis> L.)

Plants, when exposed to abiotic or biotic stress, produce several pathogenesis-related proteins to counteract the effects of stress. Osmotin is one of the important pathogenesis-related proteins induced during several stress conditions. We have developed improved salt stress tolerant transgenic chilli pepper plants (Capsicum annum L. var. Aiswarya 2103) by ectopic expression of the Nicotiana tabaccum osmotin gene using Agrobacterium tumefaciens EHA105 as a vector. Four-week-old chilli pepper leaves were used as an explant and A. tumefaciens EHA105 harboring pBINASCOSM plasmid that contains osmotin gene under the control of CaMV 35S promoter and npt II as a selectable marker was used in co-cultivation. Transgene integration and expression were analyzed using molecular, immunochemical, and biochemical assays. PCR and Southern blot analysis confirmed that osmotin gene has been successfully integrated into the genome of chilli pepper plants. The osmotin gene was stably segregated and expressed in T₂ generation transgenic chilli pepper plants, and it was confirmed by Western blot analysis. Biochemical assays of these putative transgenic plants revealed enhanced levels of chlorophyll, proline, glycinebetaine, APX, SOD, DHAR, MDHAR, GR, and relative water content. Yield potential of the putative transgenic chilli pepper plants was evaluated under salinity stress conditions in a green house. The putative transgenic chilli pepper plants overexpressing the osmotin gene were morphologically similar to wild-type plants and produced 3.32 kg chilli pepper fruits per plant at 300 mM NaCl concentration.     

Effects of Paclobutrazol on Response of Two Barley Cultivars to Salt Stress

The seeds of two barley (Hordeum vulgare L.) cultivars (a drought resistant cv. Tokak-137/57 and a drought sensitive cv. Erginel-90) were imbibed either in distilled water (control) or in a solution containing 40 mg dm⁻³ paclobutrazol (PBZ) and air dried. Seeds were germinated and grown in a glasshouse for 21 d and seedlings were subjected to salt stress by treating them with 100 and 200 mM NaCl for 12 d. The height of shoots was significantly decreased and root length was increased in PBZ-treated plants prior and after NaCl stress for 12 d leading to an increase in root to shoot ratio. Leaf chlorophyll and carotenoid contents in PBZ treated plants were increased in controls and especially in plants subjected to salt stress. PBZ induced increase in superoxide dismutase (SOD) activities was higher in cv. Tokak-157/37, than in cv. Erginel-90. However, an increase in SOD activity was not accompanied by an increase in peroxidase activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water availability effects on antioxidant enzyme activities, lipid peroxidation, and reducing sugar contents of alfalfa (Medicago sativa L.)

To understand alfalfa (Medicago sativa L.) reactions to osmotic stress, solutions with −0.5, −1 and −1.5 MPa osmotic potentials using PEG (Poly ethyleneglycol) and distilled water as control were prepared. In a germination test, eleven alfalfa cultivar seeds were allowed to germinate in these solutions. M. sativa cv. Yazdi and M. sativa cv. Gharayonje, selected as tolerant and sensitive cultivars, respectively, and were used for further studies. In all PEG solutions, root and shoot dry weights decreased in both cultivars. Under different levels of osmotic stress, root to shoot ratio increased significantly in Yazdi, whereas this parameter showed no significant differences in Gharayonje. Yazdi cultivar also showed higher activities of SOD (Superoxide dismutase), APX (Ascorbate peroxidase), CAT (Catalase), POD (Peroxidase), and higher reducing sugar contents of leaves in comparison with Gharayonje. These higher antioxidant activities help the tolerant cultivar to decrease oxidative damages of osmotic stress to membrane lipids as compared with its sensitive counterpart. As a result, electrolyte leakage and the amounts of MDA (Malondialdehyde), were higher in Gharayonje. This study highlights the importance of enzymatic and non-enzymatic antioxidant systems in scavenging reactive oxygen species which is caused by osmotic stress. It is seems that antioxidant systems are more active in tolerant cultivars than those of sensitive ones.     

Photosynthetic characteristics and enzymatic antioxidant capacity of leaves from wheat cultivars exposed to drought

Two durum (Triticum durum L.), Barakatli-95 and Garagylchyg-2; and two bread (Triticum aestivum L.) wheat cultivars, Azamatli-95 and Giymatli-2/17 with different sensitivities to drought were grown in the field on a wide area under normal irrigation and severe water deficit. Drought caused a more pronounced inhibition in photosynthetic parameters in the more sensitive cvs Garagylchyg-2 and Giymatli-2/17 compared with the tolerant cvs Barakatli-95 and Azamatli-95. Upon dehydration, a decline in total chlorophyll and relative water content was evident in all cultivars, especially in later periods of ontogenesis. Potential quantum yield of PS II (F(v)/F(m) ratio) in cv Azamatli-95 was maximal during stalk emergency stage at the beginning of drought. This parameter increased in cv Garagylchyg-2, while in tolerant cultivar Barakatli-95 significant changes were not observed. Contrary to other wheat genotypes in Giymatli-2/17 drought caused a decrease in PS II quantum yield. Drought-tolerant cultivars showed a significant increase in CAT activity as compared to control plants. In durum wheat cultivars maximal activity of CAT was observed at the milk ripeness and in bread wheat cultivars at the end of flowering. APX activity also increased in drought-treated leaves: in tolerant wheat genotypes maximal activity occurred at the end of flowering, in sensitive ones at the end of ear formation. GR activity increased in the tolerant cultivars under drought stress at all stages of ontogenesis. SOD activity significantly decreased in sensitive cultivars and remained at the control level or increased in resistant ones. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Effect of salt on malondialdehyde and antioxidant enzymes in seedling roots of Jerusalem artichoke (<Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L.)

Two cultivars of Jerusalem artichoke (Helianthus tuberosus L.) differing in genotype, Red skin (cv. R., salt-tolerant but low-yield) and White skin (cv. W., salt-sensitive but high-yield), were used to investigate malondialdehyde (MDA) content and antioxidant enzyme activity changes in their roots under a hydroponic culture system with 250 mM NaCl. The results showed that MDA contents in roots of the two genotypes increased, but MDA content of cv. R. was higher than that of cv. W. Changes in all antioxidant enzymes in roots of both varieties exhibited a similar trend, namely increased initially and then decreased. However, there were still some differences existing between the two cultivars. In other words, activities of the other two antioxidant enzymes except catalase (CAT) and peroxidase (POD) in roots of cv. R. were less than controls at 48 h, while all others except ascorbate peroxidase (APX) in roots of cv. W. were greater than controls. The peak of superoxide dismutase (SOD) activity of cv. W. was observed to appear earlier than that of cv. R. CAT activity of cv. W. was significantly greater than the value of cv. R. and the latter showed a moderate trend. POD activity of cv. R. obtained the maximum at 6 h, whereas the peak of cv. W. displayed at 24 h. APX activity of cv. R. declined more than that of cv. W. These results suggested that there was a lower efficiency of scavenging reactive oxygen species (ROS) in cv. R. roots. Concomitantly, salt stress caused more severe damage to roots of cv. R. Antioxidant enzymes in roots were inadequate to elucidate salt-tolerance mechanisms of the whole plant.     

Osmolyte accumulation in different rape genotypes under sodium chloride salinity

Physiological mechanisms of two rape (Brassica napus L.) genotype adaptation to chlorine salinity were investigated. The plants of two cultivars (Olga and Westar) differing in salt tolerance were grown in the pots filled with Perlite on the Hoagland and Snyder’s medium under controlled conditions. At a stage of 3–4 true leaves, the plants experienced 7-day-long salinity induced by a single addition of NaCl to the nutrient medium in order to attain desired final salt concentration (from 50 to 400 mM). The obtained results showed that a greater salt tolerance of cv. Olga plants (as compared with cv. Westar) could be accounted for by a capability of their root cells to uptake water under high salinity (300–400 mM NaCl), which is evident from a greater content of water in the tissues of cv. Olga. This was ensured by a sharp fall of the osmotic potential of the cellular contents (down to −2.3 MPa) at a low water potential of nutrient solution owing to more active uptake of Na⁺ (57–61 μeq/g fr wt) and K⁺ (210–270 μeq/g fr wt) as well as active accumulation of proline (30–50 μmol/g fr wt). The latter is caused by a reduced activity of proline dehydrogenase and retarded degradation of this osmolyte. It is important that, in contrast to less tolerant genotype, the rape plants of salt-resistant cultivar were able to maintain the K⁺/Na⁺ ratio at a rather high level at salinity of different degree, which made it possible to preserve ionic homeostasis under adverse conditions. Original Russian Text ? A.M. Mokhamed, G.N. Raldugina, V.P. Kholodova, Vl.V. Kuznetsov, 2006, published in Fiziologiya Rastenii, 2006, Vol. 53, No. 5, pp. 732–738.