Seawater Stress Research Articles

Microbial Community Shifts in Tea Plant Rhizosphere under Seawater Stress: Enrichment of Beneficial Taxa.

Seawater intrusion has a significant impact on the irrigation quality of agricultural water, thereby posing a threat to plant growth and development. We hypothesized that the rhizosphere of tea plants harbors beneficial microorganisms, which may improve the tolerance of tea plants to seawater stress. This study utilized 16s and ITS techniques to analyze microbial community shifts in the tea plant rhizosphere and non-rhizosphere under seawater stress conditions. The findings suggest that seawater stress leads to a reduction in microbial diversity, although the rhizosphere microbial diversity in stressed soils showed a relatively higher level. Moreover, the rhizosphere of the tea plant under seawater stress exhibited an enrichment of plant growth-promoting rhizobacteria alongside a higher presence of pathogenic fungi. Network analysis revealed that seawater stress resulted in the construction of a more complex and stable rhizosphere microbial network compared to normal conditions. Predictions of bacterial potential functions highlighted a greater diversity of functional groups, enhancing resource utilization efficiency. In general, the rhizosphere microorganisms of tea plants are jointly selected by seawater and the host. The microorganisms closely related to the rhizosphere of tea plants are retained and, at the same time, attract beneficial microorganisms that may alleviate stress. These findings provide new insights into plant responses to saline stress and have significant implications for leveraging vegetation to enhance the resilience of coastal saline soils and contribute to economic progress.

Corrosion Behavior of Al2O3-40TiO2 Coating Deposited on 20MnNiMo Steel via Atmospheric Plasma Spraying in Hydrogen Sulfide Seawater Stress Environments

In this study, an Al2O3-40TiO2 coating was deposited on 20MnNiMo steel via atmospheric plasma spraying. The corrosion behavior of the coating was investigated in both artificial seawater and a simulated environment with hydrogen sulfide and high pressure. Additionally, ion dissolution experiments were conducted to evaluate the coating’s bio-friendliness. In artificial seawater, the corrosion rate (based on the corrosion current) of the Al2O3-40TiO2 coating initially decreased before increasing. It was speculated that the blocking of corrosion products in the defect channels was helpful in delaying the progress of corrosion in the early stage. The coating had a corrosion current on the order of 10−6 A/cm2 in artificial seawater, suggesting good protection in conventional seawater environments. In the simulated environment, the corrosion rate (based on the weight loss) of the Al2O3-40TiO2 coating showed a continuously declining trend. It was deduced that, unlike corrosion products in artificial seawater, the corrosion products in the simulated environment (e.g., metal sulfide) might be more chemically stable, leading to a longer blocking effect. Therefore, a minimal corrosion rate of 0.0030 mm/a was obtained after the coating was immersed for 30 days. The amount of dissolved coated elements was negligible and there were only small amounts of dissolved non-coated elements such as Ni and Mo. The developed coating can be considered to be highly biofriendly if the non-coated area of the specimen is well sealed.

Regulation effects of indoleacetic acid on lipid production and nutrient removal of Chlorella pyrenoidosa in seawater-containing wastewater

The utilization of seawater supplemented with wastewater nutrients for microalgae cultivation represents a promising and cost-effective approach that combines the benefits of wastewater treatment and microalgal resource recovery. However, the high salt content in seawater poses a significant challenge, hindering microalgal growth and reducing the removal of nitrogen and phosphorus on a large scale. The phytohormone indoleacetic acid (IAA) was used in this study to enhance stress resistance and lipid production of Chlorella pyrenoidosa grown in seawater-wastewater medium. Compared to the control groups involving regular wastewater and seawater-containing wastewater without IAA, Chlorella pyrenoidosa cultivated in the seawater-containing wastewater supplemented with IAA exhibited remarkable outcomes. Specifically, microalgae in IAA-enhanced seawater-containing wastewater achieved the highest lipid productivity (22.67 mg L−1 d−1) along with impressive nitrogen (99.3 %) and phosphorus (97.3 %) removal rates. Moreover, their cell sedimentation ratio reached 76.6 %, indicating enhanced settling properties. Additionally, the physiological mechanism changes after exposure to seawater stress and IAA were revealed based on the changes in antioxidant enzymes, endogenous hormones, and fatty acid saturation. Furthermore, the transcriptomic analysis elucidated the molecular mechanisms underlying microalgal lipid synthesis and their response to antioxidant stress when exposed to seawater. The supplementation of IAA under seawater stress stimulated energy metabolism and the antioxidant response in microalgal cells, effectively mitigating the adverse effects of seawater stress and promoting overall algal lipid productivity. Overall, this study unveiled the potential of exogenous plant hormones, particularly IAA, in enhancing stress resistance and lipid productivity of microalgae grown in seawater-wastewater medium, which significantly contributed towards the efficient use of seawater resources for microalgae cultivation and biofuel production.

Exploring the potential of halotolerant bacteria from coastal regions to mitigate salinity stress in wheat: physiological, molecular, and biochemical insights.

Salinity stress, a significant global abiotic stress, is caused by various factors such as irrigation with saline water, fertilizer overuse, and drought conditions, resulting in reduced agricultural production and sustainability. In this study, we investigated the use of halotolerant bacteria from coastal regions characterized by high salinity as a solution to address the major environmental challenge of salinity stress. To identify effective microbial strains, we isolated and characterized 81 halophilic bacteria from various sources, such as plants, rhizosphere, algae, lichen, sea sediments, and sea water. We screened these bacterial strains for their plant growth-promoting activities, such as indole acetic acid (IAA), phosphate solubilization, and siderophore production. Similarly, the evaluation of bacterial isolates through bioassay revealed that approximately 22% of the endophytic isolates and 14% of rhizospheric isolates exhibited a favorable influence on seed germination and seedling growth. Among the tested isolates, GREB3, GRRB3, and SPSB2 displayed a significant improvement in all growth parameters compared to the control. As a result, these three isolates were utilized to evaluate their efficacy in alleviating the negative impacts of salt stress (150 mM, 300 mM, and seawater (SW)) on the growth of wheat plants. The result showed that shoot length significantly increased in plants inoculated with bacterial isolates up to 15% (GREB3), 16% (GRRB3), and 24% (SPSB2), respectively, compared to the control. The SPSB2 strain was particularly effective in promoting plant growth and alleviating salt stress. All the isolates exhibited a more promotory effect on root length than shoot length. Under salt stress conditions, the GRRB3 strain significantly impacted root length, leading to a boost of up to 6%, 5%, and 3.8% at 150 mM, 300 mM, and seawater stress levels, respectively. The bacterial isolates also positively impacted the plant's secondary metabolites and antioxidant enzymes. The study also identified the WDREB2 gene as highly upregulated under salt stress, whereas DREB6 was downregulated. These findings demonstrate the potential of beneficial microbes as a sustainable approach to mitigate salinity stress in agriculture.

Spectral Reflectance Indices’ Performance to Identify Seawater Salinity Tolerance in Bread Wheat Genotypes Using Genotype by Yield*Trait Biplot Approach

Salinity stress harms crop yield and productivity worldwide. This study aimed to identify genotypes with higher grain yield and/or salinity tolerance from forty bread wheat genotypes evaluated under seawater diluted at 4.0, 8.0, or 12.0 dS/m or control (0.4 dS/m) in the 2019/20 and 2020/21 seasons. Six elite genotypes, namely 6, 16, 31, 33, 34, and 36, were chosen and tested in a lysimeter under diluted seawater stress in 2020/21. The results showed significant differences (p ≤ 0.01) among the genotypes for the traits grain yield (GY), harvest index (HI), chlorophyll content index (CCI), chlorophyll fluorescence parameter Fv/Fm, and their interaction with salinity treatments. Additionally, significant differences (p ≤ 0.01) were detected among ten genotypes for all agronomic traits along with spectral reflectance indices (SRI), e.g., curvature index (CI), normalized difference vegetation index (NDVI), triangular vegetation index (TVI), modified chlorophyll absorption reflectance index (MCARI), and their interaction with salinity treatments. Genotype by traits (GT) and genotype by yield*trait (GYT) biplots are useful for genotypes screening and selection based on grain yield and other associated traits (agronomic, physiological traits, and spectral reflectance indices combinations) as well as genotypes by stress tolerance indices (GSTI). In conclusion, this study identified that genotypes 6, 16, 31, 33, 34, and 36 in the 2019/20 season and genotypes 2 and 1 performed better than Kharchia 65 and Sakha 8 in the 2020/21 season, which detected as superior genotypes and might be recommended for sowing and/or inclusion in the breeding program in salt-affected soils. It was possible to draw the conclusion that spectral reflectance indices were efficient at identifying genotypic variance.

Growth responses and genetic variation among highly ecologically diverse spring wheat genotypes grown under seawater stress.

Most of the freshwaters worldwide are used for agriculture. Freshwater sources are expected to decline and will not suffice to support the food production needed for the growing population. Therefore, growing crops with seawater might constitute a solution. However, very little work has been done on the effect of seawater stress on wheat, an important cereal crop. The present study aimed to determine whether particular wheat genotypes provided better resistance to seawater stress. A set of 80 highly diverse spring wheat genotypes collected from different countries in Europe, Asia, Africa, North and South America was exposed to 50% seawater stress at the early growth stage. Four seeding shoot and root traits were scored for all genotypes. High genetic variations were found among all genotypes for the epicotyl length (EL), hypocotyl length (HL), number of radicles (NOR), and fresh weight (FW). Eight genotypes with high-performance scores of seedling traits were selected. The correlation analyses revealed highly significant correlations among all traits scored in this study. The strongest correlation was found between the NOR and the other seeding traits. Thus, the NOR might be an important adaptive trait for seawater tolerance. The genetic diversity among all genotypes was investigated based on genetic distance. A wide range of genetic distances among all genotypes was found. There was also a great genetic distance among the eight selected genotypes. In particular, the genetic distance between ATRI 5310 (France) and the other seven genotypes was the greatest. Such high genetic diversity might be utilized to select highly divergent genotypes for crossing in a future breeding program. The present study provides very useful information on the presence of different genetic resources in wheat for seawater tolerance.

Salinity Stress Effects on Some Morpho-Physiological and Biochemical Traits of Basak

Soil salinity has long been regarded as one of the most serious environmental constraints limiting agricultural crop growth and productivity. The goal of this study was to analyze the morpho-physiological and biochemical alterations of basak plants at varying salinity levels by a pot experiment. The experiment was set up in a Randomized Complete Block Design (RCBD) with five replications. The three different salinity levels (4 dS/m, 8 dS/m and 12 dS/m) and control (tap water) comprised the four different treatments in this investigation. The study showed that all parameters viz growth, physiological and biochemical were influenced significantly by different seawater induced saline treatments over time. Different morpho-physiological features, such as plant height, number of leaves, number of branches, and total dry matter (TDM) were shown to be decreased with increasing salinity as compared to control. However, chlorophyll (Chl) a, Chl-b, total Chl and carbohydrate content of basak plants were also negatively associated with increasing different seawater induced salinity levels. In response to seawater stress plants accumulate several biochemical compounds. In that case, the accumulation of proline (Pro), total phenol, MDA content and total antioxidant activities were found to be highest when plants were exposed to the uppermost salinity level i.e. 12 dS/m. Collectively, the findings reveal that, while seawater-induced salinity had a substantial impact on basak growth and biochemical parameters, all plants were able to endure a wide range of salinity levels, demonstrating the basak plant's ability to cope with salt-induced membrane damage.

Study on Stress Corrosion Properties of 1Cr17Ni2 Stainless Steel

1Cr17Ni2 stainless steel is used in aviation, ships, machinery, and other fields. However, stress corrosion will lead to its strength reduction, thus failure. In this paper, we studied the stress corrosion resistance of 1Cr17Ni2 stainless steel bolts and nuts using fasteners’ stress corrosion test method and fasteners’ stress corrosion test method in a simulated environment with the accelerated stress corrosion test method of fasteners. The influence of seawater concentration, temperature, stress, test duration, and other parameters was fully considered during the test. The test results showed that 1Cr17Ni2 stainless steel would appear to stress corrosion crack under a specific corrosive environment, but the occurrence probability was not high. Therefore, in the complex seawater salt fog environment, the stress corrosion of 1Cr17Ni2 stainless steel cannot be ignored, which provides a practical reference for applying 1Cr17Ni2 stainless steel in a complex environment.

High-efficiency biofuel production by mixing seawater and domestic sewage to culture freshwater microalgae

Although microalgae biofuel has many advantages, its production is faced with difficulties regarding algal cell harvesting and low lipid content. In this experiment, mixtures of seawater and domestic sewage were prepared for the cultivation of freshwater microalgae. The results showed that the proportion of seawater had an important effect on the precipitation and biofuel production of the microalgae. The increasing proportion of seawater in the mixed wastewater improved the sedimentation performance and lipid content of microalgae, but the growth of microalgae was greatly inhibited under 80% seawater stress. Therefore, the highest algal lipid productivity of 10.74 mg L-1 d-1 was achieved in the wastewater containing 60% seawater, which was 2.15-fold higher than that of the control. Furthermore, the fatty acid saturation and the C16-C18 fatty acid proportion of the microalgae cultured in wastewater containing 60% seawater were relatively ideal, which was beneficial for improving the quality of biodiesel. Therefore, wastewater containing 60% seawater was the most favourable for the cultivation of biofuel-producing microalgae. The mechanism by which seawater improved the precipitation performance of freshwater microalgae was also investigated. The addition of seawater to the sewage increased the cell diameter of the microalgae, reduced the zeta potential of microalgal colloids, and promoted the synthesis of extracellular polymeric substances by the microalgal cells. Thus, the precipitation performance of the microalgae cells was effectively improved. The pigment contents and antioxidant enzyme activities of the microalgae were also determined, and it was found that the glutathione peroxidase activity of microalgae increased under certain seawater stress, indicating that glutathione peroxidase played an indispensable role in the removal of reactive oxygen species produced by seawater stress.

Flow cytometry-based study of model marine microalgal consortia revealed an ecological advantage of siderophore utilization by the dinoflagellate Amphidinium carterae

Investigations of phytoplankton responses to iron stress in seawater are complicated by the fact that iron concentrations do not necessarily reflect bioavailability. Most studies to date have been based on single species or field samples and are problematic to interpret. Here, we report results from an experimental cocultivation model system that enabled us to evaluate interspecific competition as a function of iron content and form, and to study the effect of nutritional conditions on the proteomic profiles of individual species. Our study revealed that the dinoflagellate Amphidinium carterae was able to utilize iron from a hydroxamate siderophore, a strategy that could provide an ecological advantage in environments where siderophores present an important source of iron. Additionally, proteomic analysis allowed us to identify a potential candidate protein involved in iron acquisition from hydroxamate siderophores, a strategy that is largely unknown in eukaryotic phytoplankton.

Primary, secondary, and tertiary stress responses of juvenile seahorse Hippocampus reidi exposed to acute acid stress in brackish and seawater.

Seahorse Hippocampus reidi is a vulnerable species, inhabiting estuarine and coastal waters. The safety of acidic environments for fish has been considered in terms of ocean acidification in nature and decreasing pH in intensive aquaculture systems. This study aimed to investigate the effects of acute exposition (96h) of juvenile seahorses to different pH (5, 6, 7, and 8) in brackish (BW - salinity 11) or seawater (SW - salinity 33). For that, we studied the responses of cortisol, oxidative stress, and survival, thus covering primary, secondary, and tertiary stress responses. In SW, cortisol levels were not altered for fish maintained at pH5 and 8. However, in BW, cortisol was higher for fish kept at pH5. Regarding secondary stress responses, only GST activity increased with acidification in SW. However, acidification in BW caused biochemical alterations at enzymatic level (SOD, GST, GPx) and glutathione metabolism, accompanied by reduction of antioxidant capacity (TEAC) and increased lipid peroxidation (TBARS). Survival was always above 90% and it did not differ significantly among pH levels. Our results suggest that H. reidi juveniles are more vulnerable to acidic exposure in BW than in SW.

Enhancement of Seawater Stress Tolerance in Barley by the Endophytic Fungus Aspergillus ochraceus.

Symbiotic plant-fungi interaction is a promising approach to alleviate salt stress in plants. Moreover, endophytic fungi are well known to promote the growth of various crop plants. Herein, seven fungal endophytes were screened for salt tolerance; the results revealed that Aspergillus ochraceus showed a great potentiality in terms of salt tolerance, up to 200 g L−1. The indole acetic acid (IAA) production antioxidant capacity and antifungal activity of A. ochraceus were evaluated, in vitro, under two levels of seawater stress, 15 and 30% (v/v; seawater/distilled water). The results illustrated that A. ochraceus could produce about 146 and 176 µg mL−1 IAA in 15 and 30% seawater, respectively. The yield of IAA by A. ochraceus at 30% seawater was significantly higher at all tryptophan concentrations, as compared with that at 15% seawater. Moreover, the antioxidant activity of ethyl acetate extract of A. ochraceus (1000 µg mL−1) at 15 and 30% seawater was 95.83 ± 1.25 and 98.33 ± 0.57%, respectively. Crude extracts of A. ochraceus obtained at 15 and 30% seawater exhibited significant antifungal activity against F. oxysporum, compared to distilled water. The irrigation of barley plants with seawater (15 and 30%) caused notable declines in most morphological indices, pigments, sugars, proteins, and yield characteristics, while increasing the contents of proline, malondialdehyde, and hydrogen peroxide and the activities of antioxidant enzymes. On the other hand, the application of A. ochraceus mitigated the harmful effects of seawater on the growth and physiology of barley plants. Therefore, this study suggests that the endophytic fungus A. ochraceus MT089958 could be applied as a strategy for mitigating the stress imposed by seawater irrigation in barley plants and, therefore, improving crop growth and productivity.

Growth and transcriptome analysis of tomato under seawater stress

The tomato industry has been seriously affected by continuous soil salinization and seawater irritation. This study analyzed the salt tolerance mechanism of tomato from physiological and molecular aspects and screened out the salt tolerance genes; this information provides a foundation for future research on tomato salt tolerance and environmental adaptability. In this study, tomato was used as the experimental material, and treated with seawater accounted for 0%, 10%, 20%, or 30% of the nutrient solution volume respectively. The results showed that when the seawater percentage was less than 20%, it had little effect on the growth of tomato; when the seawater percentage was more than 20%, it could severely inhibit tomato growth, thereby affecting the ion balance in plants. The results showed that 33,810 unigenes were obtained after transcriptome high-throughput sequencing and assembly. In total, 31,631 unigenes were successfully annotated by comparison of the obtained unigenes with six gene databases. According to the Gene Ontology (GO) database, unigenes in the tomato transcriptome could be roughly divided into three categories (biological process, cellular component, and molecular function) with 45 branches. Analyzing genetic differences revealed that 509 unigenes were significantly differentially expressed under seawater stress, among which 40.67% were up-regulated and 59.33% were down-regulated. Moreover, we also found that the differentially expressed genes (DEGs) were mainly enriched in six pathways: growth, response to stimulus, signaling, membrane, transcription factor activity and protein binding. The expression profiles of the selected DEGs in the samples were characterized and verified by qRT-PCR. These DEGs and metabolic pathways may play an important role in salt tolerance of tomato. The functional characteristics of these genes and pathways will provide a new target for improving salt tolerance of tomato through gene regulation.

Application of hemin-induced growth and biochemical modifications in Hassawi okra (Abelmoschus esculentus L.) grown in seawater salinity

The present study investigated the possible protective role of hemin (75 µM) on okra (Abelmoschus esculentus L.) plants grown under diluted seawater (seawater/normal water) in plastic bags on loam soil and compost (1:1). Four levels of seawater were prepared by diluting seawater to give 1.8, 3.6, 5.4 and 7.2 dsm-1. Okra plants were irrigated with these concentrations of seawater. The effects of seawater salinity on okra plants were evaluated by determining growth parameters, superoxide dismutase (SOD) activity, catalase (CAT) activity ascrobate content, α-amylase, protease and lipid peroxidation in the presence or absence of hemin. The study found that seawater salinity resulted in a high level of lipid peroxidation, which was associated with significant decrease in growth parameters and protease activity. The activity of SOD, CAT and ascorbate content were increased significantly, compared to control plants. Alleviation effect of hemin was obvious on growth parameters at most salinity levels. This was associated by enhancement of CAT and α-amylase activities and reduction of lipid peroxidation compared to the corresponding untreated salinized plants. So hemin could play a central function as a signal molecule in salt tolerance of okra plants. The results of this study demonstrated that okra can be grown successfully using diluted seawater and the different antioxidants could partially alleviate the harmful effects of seawater stress that reflected on growth and some physiological changes of okra plant. According to these findings, it can be pronounced that the treatment of salinized okra with hemin (75 µM) may reduce the negative impact of light salinity stress.

Eustress with H2O2 Facilitates Plant Growth by Improving Tolerance to Salt Stress in Two Wheat Cultivars.

In this study, the positive role of hydrogen peroxide (H2O2) pretreatment in mitigating the adverse impacts of seawater stress has been evaluated in two wheat (Triticum aestivum L.) cultivars, namely Gemmiza 11 as a salt-sensitive and Misr 1 as a salt-tolerant cultivar, with contrasting phenotypes in response to the salinity stress. Under normal conditions, wheat seeds eustress with H2O2 have shown significant effects on the improvement of plant growth parameters, such as dry weight and root and shoot lengths. Under salt stress conditions, seeds eustress with H2O2 have shown a reduction in damage to plant growth and physiological parameters as compared to the seeds kept as un-primed in both wheat cultivars. In addition, eustress of seeds with H2O2 has induced an increment in the pigments content, proline level and mineral uptake (K+, Ca2+ and Mg2+). Moreover, seeds eustress with H2O2 have shown significant decrement in Na+ content uptake in plants and that subsequently reduced lipid peroxidation. Seawater stress has increased the activity of the antioxidant system based on catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) in both cultivars, except POD in Gemmiza 11. Similarly, the application of H2O2 has further enhanced the activity of the antioxidant system in stressed plants and this enhancement of the antioxidant system further reduced Na+ content in plants and subsequently increased the growth parameters. Results of inter-simple sequence repeat (ISSR) markers have shown clear differentiation among the treatments and have provided strong evidence in support of the hypothesis proposed in this study that H2O2 eustress improves seed tolerance and enhances plant growth parameters under seawater stress.

Priming of Silybum marianum (L.) Gaertn seeds with H2O2 and magnetic field ameliorates seawater stress

Silybum marianum (L.) Gaertn is an important medicinal plant and has been used as a traditional medicine for diseases of the liver and biliary tract. The effects of seed priming by H2O2 (Haloprimig) and magnetic field (Magnetopriming, MF) on the impacts of seawater concentration were tested using S. marianum at the vegetative stage. These plant species accumulate flavonoids especially slimarine that is used in liver treatment. Some soaked S. marianum seeds were subjected to 0.18 T MF for different time durations (0, 10, 20 and 30 min) and other seeds were soaked in different concentrations of H2O2 (0, 80,160 and 240μM) for 8h. H2O2 priming increased growth and development under water irrigation more than under sea water stress. Moreover, our results uncovered statistical evidence that the priming seeds with H2O2 and MF increased the tolerance of S. marianum to salinity. In summary, we provide clear evidence that seawater stress caused a highly significant reduction in the growth parameters and stimulation in proline and phenolic compounds. It was concluded that, application of H2O2 and MF of S. marianum could scavenge or alleviate the harmful effects of salinity stress at early seedling stage and alleviate the oxidative damage leading to improvements in physiological attributes for the plant growth under sea water stress.

Accumulation capacity of ions in cabbage (Brassica oleracea L.) supplied with sea water

Cabbage seedlings were grown hydroponically to study the effects of different concentrations of seawater on the seedling growth, ion content under one-fourth strength Hoagland's nutrient solution in the greenhouse. The biomass of various organs of cabbage seedlings as well as the whole plants was significantly higher in the treatments with 1 g and 2 g sea salt/L than the no-salt control, but the treatments with 4, 5 or 6 g sea salt/L caused a decrease in growth. Root/shoot ratio remained at the level of control regardless of the sea salt treatment. Na+ and Cl- concentration in different parts of cabbage seedlings increased significantly, whereas K+ and Ca2+ concentration generally increased at low concentrations of sea salt and then decreased with increasing seawater concentration. Sodium and K+ concentrations were significantly higher in the stems than roots and leaves regardless of the sea salt treatment. The sea salt treatment increased Mg2+ concentration in stems and leaves of cabbage seedlings. An increase in Na+ and Cl- concentration in roots, stems and leaves of cabbage seedlings was the main contributor to declining ratios of K+/Na+, Ca2+/Na+ and Mg2+/Na+. The obtained data suggest that cabbage seedlings have strong ability to sustain seawater stress by the regulation of transport and distribution of ions.

Enhancement of dimethylsulfide production by anoxic stress in natural seawater

AbstractDimethylsulfide (DMS) is produced by phytoplankton in the ocean and plays an important role in biogeochemical cycles and climate system of the Earth. Previous field studies reported a possible relationship between DMS enhancement and anoxic condition, although the governing processes are still to be identified. Here we show the first direct evidence for the enhancement of DMS production by natural planktonic assemblages caused by anoxic stress. Under the anoxic condition, DMS production was considerably enhanced and DMS bacterial consumption was inhibited, resulting in an eightfold higher rate of gross DMS production than that under the oxic condition. Our results demonstrated that anoxic stress is one of important “environmental factors” in the marine DMS dynamics, suggesting the possible global importance due to ubiquity of anoxic conditions in the coastal oceans. This process would become more important in the future due to expansion of coastal hypoxic and anoxic zones by global warming.

Jasmonate-induced tolerance of Hassawi okra seedlings to salinity in brackish water

Jasmonic acid (JA) critically participates in modulating plant responses to salt stress. Here, the protective role of JA against dilute seawater stress was investigated for Hassawi okra seedlings in pot experiments under controlled growth conditions. Seeds were soaked in 50 µM JA. The seedlings were irrigated with different dilutions of seawater (0–40 %) for 3 weeks. Okra seedlings pretreated with JA tolerated brackish water up to the level of 10 %, and survived up to 40 %, while they exhibited damage and finally death if untreated. On the other hand, the level of 5 % seawater favorably affected the growth parameters compared to the fresh water control. The beneficial effect of JA was manifested by higher biomass, photosynthetic pigment and osmoprotectant levels, and decreased general stress markers such as ion leakage and lipid peroxidation. In addition, mineral composition was altered and the activity of some antioxidant enzymes improved. In conclusion, our results indicate that JA affects plant acclimation to sublethal salinity stress by brackish water. Since seed germination and seedling establishment are critical steps in plant growth, it is recommended to consider priming with JA as measure to ameliorate the detrimental effects of seawater stress and to improve Hassawi okra seedlings tolerance when irrigating with brackish water.

Influence of different intensities of magnetic field on germination, vegetative growth and some physiological aspects of salinity-stressed cucumber

Two experiments were designed to investigate the effect of different static magnetic fields and 10% seawater stress on seed germination of cucumber (Cucumis sativus L. var. Beit Alpha), seedling vigour, vegetative growth and some biochemical aspects. Salinity stress reduced seeds germination, seedlings fresh mass and seedlings vigour by about 30%, 54%, and 70 % respectively. Moreover, salinity significantly reduced the depletion in seedling dry mass in comparison with control. The magnetic fields of 50 mT for ½ h and 100 mT for 30 s improved seed germination, seedlings fresh mass and seedlings vigour under salinity stress by about 30%, 50% and 150%, respectively in comparison with salinity treatment alone. Conversely, the dual treatment of 200 mT for 1/2 h and salinity stress had more reduction effect on cucumber than salinity alone. In general, the magnetic fields of 50 mT 30 s, 100 mT 1/2 h and 200 mT 30 s had a non significant effect on seed germination. Except for 50 mT 30 s intensity which had a promotive effect, the effect of all used magnetic fields on shoot biomass and chlorophylls content were comparable with those for seedlings fresh mass. The positive effect of magnetic fields seemed to be attributed to the enhancement in total amylase activity, soluble sugars, RNA, K+/Na+ ratio and chlorophylls level. On the contrary, magnetic treatments decreased peroxidase activity, total proteins and electrolytes leakage under salinity stress conditions. However, all magnetic intensities increased Fe content, in spite of being independent of magnetic intensity or exposure period.