Germination profiling of lentil genotypes subjected to salinity stress

• Salinity is one of the most severe environmental stresses, negatively affecting productivity of salt‐sensitive crop species. Given that germination is the most critical phase in the plant life cycle, the present study aimed to determine seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt‐tolerant lentil genotypes.
• The genetic material consisted of six lentil genotypes whose adaptation to various agroclimatic conditions is not well elucidated. Salinity stress was applied by addition of NaCl at three different levels of stress, while non‐stressed plants were included as controls. Evaluation of tolerance was performed on the basis of germination percentage, seed water absorbance, root and shoot length, seedling water content, seedling vigour index and number of seedlings with an abnormal phenotype.
• Overall, our findings revealed that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the level of stress applied. It is noteworthy, however, that genotypes responded differently to the varying salinity levels. In this context, Samos proved the most salt‐tolerant genotype, indicating its possible use for cultivation under stress conditions.
• In conclusion, the determination of seed germination and early growth potential may be exploited as an efficient strategy to reveal genetic variation in lentil germplasm of unknown tolerance to salinity stress. This approach allows selection of desirable genotypes at early growth stages, thus enabling more efficient application of various breeding methods to achieve stress‐tolerant lentil genotypes.

     

胡麻资源萌发期耐盐综合性评价

筛选胡麻耐盐品种,对胡麻产业可持续发展应对盐渍胁迫具有重要现实意义。试验选用100 mmol·L^-1的NaCl溶液对28份胡麻资源种子进行胁迫,并测定发芽率、总鲜重、下胚轴鲜重、下胚轴干重、下胚轴长、胚根鲜重、胚根干重和胚根长等相关指标,通过相关性分析、因子和主成分分析、聚类分析和逐步回归分析对11个指标进行综合分析,对28份胡麻资源萌发期耐盐性做出评价,并筛选出胡麻萌发期耐盐性鉴定的关键指标。结果表明：经相关分析,11个指标中多项指标间都是极显著或显著的正相关;因子和主成分分析将11个单项指标转化成3个综合指标,第Ⅰ主成分为下胚轴长势情况,第Ⅱ主成分为胚根长势情况,第Ⅲ主成分为种子萌发情况;聚类分析将28份胡麻资源划分为4大类：耐盐型、中等耐盐型、盐敏感型和强盐敏感型。雁杂10号、轮选1号为强耐盐材料;陇亚4号、R40号、DYMS为较强耐盐材料;逐步回归分析建立了胡麻萌发期耐盐能力预测的数学评价模型,筛选出总鲜重、胚根干重、发芽指数和下胚轴长这4个鉴定指标是胡麻萌发期耐盐能力鉴定的关键指标。以这4个筛选指标计算出的预测值与综合评价计算出的综合Z值之间极显著相关（R²=0.991 8^**）,表明鉴定结果具有较高的准确性,可以代替原来11个指标对胡麻萌发期耐盐性进行评价。     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Germination responses of <Emphasis Type="Italic">Cymbopogon schoenanthus</Emphasis> to salinity

Germination studies of Cymbopogon schoenanthus (Poaceae) distributed along southern Tunisia were carried out to assess the effects of salinity. A preliminary experiment showed 30°C as the optimum germination temperature for seeds of this species. After that, seed germination was studied at different salinity levels. Our results revealed a decrease in germination percentage with increasing salinity. Germination rate, however, was maintained up to 200 mM NaCl and drastically declined at 300 mM NaCl.     

Germination responses of Diplotaxis harra to temperature and salinity

Diplotaxis harra (Forssk.) Boiss, an annual herb in the family of Brassicaceae, is widely distributed in many sandy and gypseous areas in southern Tunisia. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after seed transfer to distilled water. The germination responses of the seeds in complete darkness were determined over a wide range of temperatures (5, 10, 15, 20, 25 and 30 °C) and salinities (0, 50, 100, 150 and 200 mM NaCl). Germination was inhibited by either an increase or decrease in temperature from the optimal temperature (15 °C). Highest germination percentages were obtained under non-saline conditions and an increase in NaCl concentrations progressively inhibited seed germination. Rate of germination decreased with an increase in salinity at all temperatures but comparatively higher rates were obtained at 15 °C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 200 mM NaCl. Seeds were transferred from salt solution to distilled water after 20 days, and those from low salinities recovered at all temperatures. At NaCl concentration of 200 mM, the recovery of germination was completely inhibited.     

NaCl induced morpho-biochemical and anatomical changes in mulberry (<Emphasis Type="Italic">Morus</Emphasis> spp.)

Mulberry is an economically important tree, used for feeding the silkworm Bombyx mori L. Effect of different levels of NaCl on growth and development of mulberry has been studied using five mulberry genotypes selected on the basis of their performance under in vitro salinity. The study while endorsing the efficacy of in vitro screening of axillary buds of mulberry for salt tolerance, showed genotypic variability in its response to salinity. Salinity reduced growth and development of all genotypes. However, the putative tolerant genotypes showed better performance than the putative susceptible genotypes. Under low salinity (<0.5% NaCl) salt tolerant genotypes showed an increase in chlorophyll and protein concentrations, while in susceptible genotypes both were reduced by 3–58% at 0.5% NaCl and 50–64% at 1.00% NaCl. Leaf thickness increased by 16% at 1.00% NaCl in C776 and reduced by 1.0% in Mandalaya. The increase in chlorophyll concentration and leaf thickness under high salinity can be considered as preliminary selection parameters for salt tolerance in mulberry. The study confirmed the efficacy of in vitro method for screening of large number of genotypes for salt tolerance in mulberry.     

Effect of zinc nutrition on salinity-induced oxidative damages in wheat genotypes differing in zinc deficiency tolerance

Zinc deficiency and salinity are well-documented soil problems and often occur simultaneously in cultivated soils. Usually, plants respond to environmental stress factors by activating their antioxidative defense mechanisms. The antioxidative response of wheat genotypes to salinity in relation to Zn nutrition is not well understood. So, we investigated the effect of Zn nutrition on the growth, membrane permeability and sulfhydryl group (–SH groups) content of root cells and antioxidative defense mechanisms of wheat plants exposed to salt stress. In a hydroponic experiment, three bread wheat genotypes (Triticum aestivum L. cvs. Rushan, Kavir, and Cross) with different Zn-deficiency tolerance were exposed to adequate (1 μM Zn) and deficient (no Zn) Zn supply and three salinity levels (0, 60, and 120 mM NaCl). The results obtained showed that adequate Zn nutrition counteracted the detrimental effect of 60 mM NaCl level on the growth of all three wheat genotypes while it had no effect on the root and shoot growth of ‘Rushan’ and ‘Kavir’ at the 120 mM NaCl treatment. At the 0 and 60 mM NaCl treatments, Zn application decreased root membrane permeability while increased –SH group content and root activity of catalase (CAT) and superoxide dismutase (SOD) in ‘Rushan’ and ‘Kavir’. In contrast, Zn had no effect on the root membrane permeability and –SH group content of ‘Rushan’ and ‘Kavir’ exposed to the 120 mM NaCl treatment. At all salinity levels, ‘Cross’ plants supplied with Zn had lower root membrane permeability and higher –SH group content compared to those grown under Zn-deficient conditions. At the 0 and 60 salinity levels, Zn-deficient roots of Kavir and Rushan genotype leaked significantly higher amounts of Fe and K than the Zn-sufficient roots. In contrast, at the 120 mM treatment, Zn application had no effect or slightly increased Fe and K concentration in the root ion leakage of these wheat genotypes. For ‘Cross’, at all salinity levels, Zn-deficient roots leaked significantly higher amounts of Fe and K compared with the Zn-sufficient roots. The differential tolerance to salt stress among wheat genotypes examined in this study was related to their tolerance to Zn-deficiency, –SH group content, and root activity of CAT and SOD. Greater tolerance to salinity of Zn-deficiency tolerant genotype ‘Cross’ is probably associated with its greater antioxidative defense capacity.     

Evaluation of orange-fleshed sweet potato (<Emphasis Type="Italic">Ipomoea batatas</Emphasis> L.) genotypes for salt tolerance through shoot apex culture under in vitro NaCl mediated salinity stress conditions

Fifteen genotypes of sweet potato were evaluated for salinity stress tolerance under in vitro NaCl mediated salinity stress conditions (MS, MS + 0.5% and MS + 1.0% NaCl). The growth parameters such as number of leaves, number of shoots, number of roots, length of plantlets and length of roots decreased significantly among the genotypes with increase in level of salinity. Of the 15 genotypes tested, six genotypes (108X1, 90/606, 90/696, CIP 8, S-30X15 and SP-61) were unable to sprout even at 0.5% NaCl and were characterized as susceptible to salt stress, three genotypes (CIP 6, 90/774 and CIP 3) which could tolerate 0.5% NaCl as moderately tolerant and six genotypes (CIP 12, CIP 13, JO 14, JP 13, SB-198/115 and Gouri) as tolerant to salinity at 1.0% NaCl. Amongst the six genotypes showing tolerance to 1.0% NaCl, the exotic genotypes––JP 13, CIP 12 and indigenous one SB-198/115 continued to exhibit significant higher values for growth parameters over the susceptible one. Based on the performance under NaCl mediated salinity stress (1.0%), the pattern of salinity tolerance in the genotypes through shoot apex culture was JP 13 > SB-198/115 > JO 14 > Gouri > CIP 12 > CIP 13. The effect of salt stress on the activity of antioxidative enzymes was studied in leaves of 8-week-old plantlets of those six genotypes, which responded at higher NaCl stress along with a susceptible genotype 90/606. In leaves of salt stressed plants, superoxide dismutase (SOD), guaiacol peroxidase (GPX) and catalase (CAT) activities increased when compared with the stress free control. The increase was more pronounced in the tolerant genotypes than that in the susceptible one. These results indicate that oxidative stress may play an important role in salt stressed sweet potato plants and that the greater protection of tolerant plants from salt induced oxidative damage results, at least in part, through the increase in the activity of antioxidant enzymes.     

Germination kinetics and seed reserve mobilization in two flax (<Emphasis Type="Italic">Linum usitatissimum</Emphasis> L.) cultivars under moderate salt stress

Because of its high contents of protein, α-linolenic-rich oil, lignans, and fiber, demand is increasing for flax(Linum usitatissi-mum L.) and flax seed oil as a food source. In this comparative survey, we examined germination and the mobilization of seed storage products (lipids and soluble proteins) of 3-d-old seedlings from two flax cultivars (N 51 and H 52) challenged with moderate salinity (up to 200 mM NaCl). At the highest salt concentration, germination appeared to be cultivar-dependent, with that of ‘N 51’ being less impaired and delayed than in ’H 52’. Sodium chloride inhibited germination via osmotic and toxic effects, so that seed viability was altered, especially in ‘H 52’. At 200 mM NaCl, lipid mobilization was delayed in the earliest germination phases. This response was associated with increased proportions of linolenic acid contents in both cultivars and more linolenic acid-rich molecular species of TAGs. Irrespective of the salt level, soluble protein contents in both cultivars decreased over time, although a salt-related precocity of protein degradation occurred at 200 mM NaCl.     

Effect of salinity on tomato (Lycopersicon esculentum Mill.) during seed germination stage

A study was conducted using ten genetically diverse genotypes along with their 45F₁ (generated by diallel mating) under normal and salt stress conditions. Although, tomato (Lycopersicon esculentum Mill.) is moderately sensitive to salinity but more attention to salinity is yet to be required in the production of tomato. In present study, germination rate, speed of germination, dry weight ratio and Na⁺/K⁺ ratio in root and shoot, were the parameters assayed on three salinity levels; control, 1.0 % NaCl and 3.0 % NaCl with Hoagland’s solution. Increasing salt stress negatively affected growth and development of tomato. When salt concentration increased, germination of tomato seed was reduced and the time needed to complete germination lengthened, root/shoot dry weight ratio was higher and Na⁺ content increased but K⁺ content decreased. Among the varieties, Sel-7 followed by Arka Vikas and crosses involving them as a parent were found to be the more tolerant genotypes in the present study on the basis of studied parameters.     

Varied tolerance to NaCl salinity is related to biochemical changes in two contrasting lettuce genotypes

Salt stress perturbs a multitude of physiological processes such as photosynthesis and growth. To understand the biochemical changes associated with physiological and cellular adaptations to salinity, two lettuce varieties (Verte and Romaine) were grown in a hydroponics culture system supplemented with 0, 100 or 200 mM NaCl. Verte displayed better growth under 100 mM NaCl compared to Romaine, but both genotypes registered relatively similar reductions in growth under 200 mM NaCl treatment. Both varieties showed differences in net photosynthetic activity in the absence of salt and 8 days after salt treatment. These differences diminished subsequently under prolonged salt stress (14 days). Verte showed enhanced leaf proline and restricted total cations especially Na⁺, lesser malondialdehyde (MDA) formation and lignification in the roots under 100 mM NaCl salinity. Membrane damage estimated by electrolyte leakage increased with elevated salt concentrations in roots of both varieties, but Verte had significantly lower electrolyte leakage relative to Romaine under 100 mM NaCl. Moreover, Verte also accumulated greater levels of carotenoids under increasing NaCl concentrations compared to Romaine. Taken together, these findings suggest that the greater tolerance of Verte to 100 mM NaCl is related to the more restricted accumulation of total cations and toxic Na⁺ in the roots and enhanced levels of antioxidative metabolites in root and leaf tissue.     

Extracts of the Brown Alga Dictyota dichotoma (Hudson) J.V. Lamouroux Alleviate Salt Stress in Rice (Oryza sativa L.) During Germination

Algal extracts provide a safe regime for enhancing crop productivity under stressful conditions. The present study evaluated the efficiency of aqueous and ethanolic extracts of the brown alga Dictyota dichotoma in alleviation of salt stress on germination of rice seeds. Firstly, seeds were germinated using the aqueous extract of D. dichotoma at concentrations of 0, 5, 10, 20, and 50 g L⁻¹, prepared either at room temperature (RTE) or by boiling (BLE). The % germination of rice increased from 84% in non-treated seeds to 100% when treated with 20 g L⁻¹ BLE, although this treatment caused reduced uniformity of germination. Embryo growth was maximum at 20 g L⁻¹ of both extracts with superiority of BLE over RTE. In the second experiment, the effect of 20 g L⁻¹ aqueous and ethanolic extracts relative to a balanced nutrient supply on germination of seeds treated with 0, 40, 90, and 170 mM NaCl was investigated. Salinity reduced % germination with delayed onset but high uniformity of germination, whereas algal amendments counterbalanced the effect of salinity to a greater extent relative to the nutrient supply. Upon withdrawal of salt stress, seeds promptly recovered, with more efficient recovery of seeds exposed to 170 mM than from 90 mM NaCl. The lower recovery of salt-treated seeds compared with the control seed germination suggests that rice suffered from the toxic ion effect of salinity on embryo rather than from the osmotic effect. Extracts of D. dichotoma can enhance and also alleviate salinity stress on rice seed germination.

     

Thellungilla halophila is more adaptive to salinity than Arabidopsis thaliana at stages of seed germination and seedling establishment

Thellungiella halophila is a salt tolerant relative of Arabidopsis thaliana with high genetic and morphological similarity. In the present study, effects of salinity on germination and seedling growth of T. halophila and A. thaliana were compared. The present results showed that the salinity inhibited seed germination in both species. Unexpectedly, percentages of seed germination in A. thaliana were higher than T. halophila in a range of 0?C200?mM NaCl. Seeds of both species could not germinate when the concentration of NaCl was over 200?mM. However, when compared with A. thaliana, seeds of T. halophila did not suffer ion toxicity, as evidenced by the higher final germination rate after ungerminated seeds pretreated with NaCl were transferred to distilled water. Seedlings of T. halophila were more salt tolerant than those of A. thaliana, e.g., seedlings of T. halophila had better plant growth (root length, fresh and dry mass), higher chlorophyll content, less MDA content and higher proline content and K⁺/Na⁺ ratio under salinity. These results indicate that T. halophila is more salt tolerant than A. thaliana during both seed germination and seedling stages and explain why A. thaliana is excluded from saline locations and T. halophila can survive in saline soils.     

Does salt stress increase the ability of the exotic legume Acacia longifolia to compete with native legumes in sand dune ecosystems?

Sand dune ecosystems are one of the areas most affected by the introduction of invasive species which represents a threat for biodiversity conservation. Their invasion patterns and spread may depend on their salinity tolerance, besides other factors. To test this hypothesis, we investigated the effects of salt stress on seed germination and on the activity of antioxidant enzymes (catalase, CAT; ascorbate peroxidase, APX; peroxidase, POX; and glutathione reductase, GR) in two legume species, an invasive, Acacia longifolia (Andrews.) Willd., and a native, Ulex europaeus (L.), very common in the sand dunes of the coast of Portugal. Salt stress was induced by adding NaCl at different concentrations, 0, 50, 100 and 200 mM, for 15 days. Results showed that the highest germination percentages were obtained in distilled water (control) and that, with increasing salt concentration, seed germination was delayed and decreased in both species. Inhibition of germination was higher in the native species, only 3% of seeds germinated at 100 mM and no seeds germinated at 200 mM NaCl. In the invasive species, the reduction was higher at 200 mM NaCl (16%). Considering the coefficient of germination velocity, a decrease in both species with increasing NaCl concentration was observed. The CAT and GR activities decreased in A. longifolia with increasing salinity. In turn, APX activity significantly increased as NaCl concentration increased while the POX activities declined at the highest NaCl concentration. On the other hand, at 50 mM NaCl lower activity of CAT and APX and higher GR and POX were found in U. europaeus. In both species, protein content increased as NaCl concentration increased. In addition, it seems that APX activities play an essential role in the scavenging reactive oxygen species (ROS). These results suggest that the seeds of the invasive legume A. longifolia are more tolerant to salinity than the native legume U. europaeus, and seem better equipped to handle the physiological stress of high salinity, which may contribute to its invasive ability in sand dunes.     

Effects of seed priming with ascorbic acid to mitigate salinity stress on three wheat (Triticum aestivum L.) cultivars.

In this study, the effect of seed priming using ascorbic acid (ASA) on three commercial wheat cultivars i.e., Punjab-2011, Faisalabad-2008, and Ujala-2016 under salinity stress in both homogenous and heterogeneous environments has been investigated. It revealed that different levels of salinity have significantly reduced the growth attributes like percent germination, germination index, radical & plumule length, seed vigor index (In-vitro), seedling length, fresh & dry weight, and total chlorophyll content (In-vivo) with subsequent treatments. Salinity stress was induced by using NaCl in three different concentrations (100, 150, and 200 mM). Seeds of the three cultivars primed with 50, 100, and 150 mg/L ascorbic-acids have not only improved percent germination but also considerably reduced germination time and increased germination index (GI) indicating the potential for tolerating saline conditions. Seedling growth (seedling length, Fresh weight, and dry weight) of seeds primed with 50, 100, and 150 mg/L (ASA) was significantly higher than other non-primed seeds under the prevailing saline conditions. Hormonal priming with different concentrations of ascorbic acid was effective, nevertheless, the best results were obtained with 100 and 150 mg/L (ASA) concentrations. We concluded that the delay in germination and seedling growth was mainly due to excessive Na⁺ accumulation in the seeds of wheat cultivars. On the other hand, seed priming with various concentrations of ascorbic acid has proved to be effective in inducing salt tolerance in terms of germination parameters, seedling characteristics, and chlorophyll retention in the three local commercial wheat cultivars.     

Modulation of symbiotic efficiency and nodular antioxidant enzyme activities in two <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> genotypes under salinity

To analyse nodular expression of antioxidant enzymes depending on plant genotype and salinity, two Phaseolus vulgaris genotypes, tolerant BAT477 and sensitive COCOT, were inoculated with the reference strain Rhizobium tropici CIAT899 and grown under 25 and 50 mM NaCl. Plant growth, nodulation and nitrogen fixing activity measured by the acetylene reducing activity (ARA) as an indicator of nitrogenase (E.C. 1.7.9.92) activity were more affected by salt concentrations in COCOT than in BAT477, particularly with 50 mM NaCl. Electrophoresis analysis of antioxidant enzymes in nodules, roots and free-living rhizobia showed that only catalase (CAT E.C. 1.11.1.6) isoenzymes varied with genotype. The sensitive genotype showed lower antioxidant enzyme activities than tolerant genotype and it was more affected by salinity. In the tolerant genotype catalase and ascorbate peroxidase (APX, E.C. 1.11.1.11) were inhibited by salt stress, whereas superoxide dismutase (SOD, E.C. 1.15.1.1) and peroxidase (POX, E.C. 1.11.1.7) were activated by salinity. Statistical analysis allowed suggesting that tolerance to salinity is associated with a differential regulation of distinct superoxide dismutase and peroxidase activities.     

Effects of Salinity and Temperature on Seed Germination in a Japanese Endangered Halophyte Triglochin maritimum (Juncaginaceae)

Triglochin maritimum (Juncaginaceae). Germination tests were carried out at three salinity levels (0,200,400 mM NaCl in which seeds were exposed to increasing- or decreasing temperatures. Effects of moist-chilling pretreatment (stratification) in 0,200 and 400 mM NaCl on seed germination at 0,200 and 400 mM NaCl, respectively, were also examined. Under the highest salinity condition (400 mM NaCl), no germination was observed. The seeds germinated very well (88%) in fresh-water after 5-month moist-chilling pretreatment. Longer moist-chilling pretreatment resulted in higher germination percentages. Moist chilling pretreatment in 0,200 and 400 mM NaCl for 5 month enhanced germination percentages to 10% (in 400 mM NaCl) –88% (in 0 mM NaCl). Received 10 December 1998/ Accepted in revised form 8 October 1999     

Alleviation of Seed Dormancy in the Desert ForbZygophyllum simplexL. from Pakistan

Zygophyllum simplexL. is a succulent annual that grows on thecoastal and inland saline flats around Karachi, Pakistan. Theseeds are moderately salt tolerant during germination. GerminationofZygophyllum simplexseeds under various salinity, proline,betaine, GA and kinetin treatments was determined. Proline (0.1and 1 mM) and betaine (0.1 and 1 mM) alleviated the innate dormancyof seeds, and germination reached 60–70% compared to 12%in the control set. At low salinity compatible osmotica alleviatedsome effects of salinity, but at higher NaCl concentrationsboth proline and betaine were ineffective. Gibberellic acid(0.3 and 3 mM) and kinetin (0.05 and 0.5 mM) substantially alleviatedboth innate as well as salinity-induced seed dormancy. At highersalinity (125 mM), low concentrations of kinetin (0.05 mM) andhigh concentrations of GA (3 mM) were more effective. GA completelyalleviated the effect of salinity at all concentrations used. Betaine; desert; dormancy; forb; GA; germination; halophyte; kinetin; proline; seeds; Zygophyllum simplex     

Alleviation of salt stress by plant growth regulators and IAA producing bacteria in wheat

The action of phytohormone producing bacteria and plant growth regulators on germination and seedling growth of wheat under saline conditions were studied. Seed dormancy enforced by salinity (100 mM NaCl) was substantially alleviated and the germination was promoted by gibberellin, auxin, zeatin, and ethephon from 54 to 97%. The IAA producing bacterial strains Pseudomonas aureantiaca TSAU22, Pseudomonas extremorientalis TSAU6 and Pseudomonas extremorientalis TSAU20 significantly increased seedling root growth up to 25% in non-salinated conditions and up to 52% at 100 mM NaCl, compared to control plants. It is concluded that growth regulators considerably alleviated salinity-induced dormancy of wheat seeds. The facts mentioned above make it possible to recommend root colonizing bacteria that produce phytohormone to alleviate salt stress of wheat grown under conditions of soil salinity.     

Comparative physiological and biochemical evaluation of salt and nickel tolerance mechanisms in two contrasting tomato genotypes

Plant tolerance against a combination of abiotic stresses is a complex phenomenon, which involves various mechanisms. Physiological and biochemical analyses of salinity (NaCl) and nickel (Ni) tolerance in two contrasting tomato genotypes were performed in a hydroponics experiment. The tomato genotypes selected were proved to be tolerant (Naqeeb) and sensitive (Nadir) to both salinity and Ni stress in our previous experiment. The tomato genotypes were exposed to combinations of NaCl (0, 75 and 150 mM) and Ni (0, 15, and 20 mg l⁻¹) for 28 days. The results revealed that the tolerant and sensitive tomato genotypes showed similar response to NaCl and Ni stress; however, the level of response was significantly different in both genotypes. The tolerant tomato genotype showed less reduction in growth than the sensitive genotype against both NaCl and Ni stress. Root and shoot ionic analysis showed a decrease in Na and increase in K concentration by increasing Ni levels in the growth medium. Moreover, accumulation of Na and Ni in tissues showed a decrease in membrane stability index and an increase in malondialdehyde contents. The activity of superoxide dismutase, catalase, peroxidase and glutathione reductase under NaCl and Ni stress was significantly higher in the tolerant compared to the sensitive genotype. Enhanced activity of many antioxidant enzymes in Naqeeb under stress conditions is among the other mechanisms that enabled the genotype to better detoxify reactive oxygen species and therefore Naqeeb tolerated the stresses better than Nadir.