Comparative physiology of salt and water stress

Phenomic and Physiological Analysis of Salinity Effects on Lettuce

Salinity is a rising concern in many lettuce-growing regions. Lettuce (Lactuca sativa L.) is sensitive to salinity, which reduces plant biomass, and causes leaf burn and early senescence. We sought to identify physiological traits important in salt tolerance that allows lettuce adaptation to high salinity while maintaining its productivity. Based on previous salinity tolerance studies, one sensitive and one tolerant genotype each was selected from crisphead, butterhead, and romaine, as well as leaf types of cultivated lettuce and its wild relative, L. serriola L. Physiological parameters were measured four weeks after transplanting two-day old seedlings into 350 mL volume pots filled with sand, hydrated with Hoagland nutrient solution and grown in a growth chamber. Salinity treatment consisted of gradually increasing concentrations of NaCl and CaCl2 from 0 mM/0 mM at the time of transplanting, to 30 mM/15 mM at the beginning of week three, and maintaining it until harvest. Across the 10 genotypes, leaf area and fresh weight decreased 0-64% and 16-67%, respectively, under salinity compared to the control. Salinity stress increased the chlorophyll index by 4-26% in the cultivated genotypes, while decreasing it by 5-14% in the two wild accessions. Tolerant lines less affected by elevated salinity were characterized by high values of the chlorophyll fluorescence parameters Fv/Fm and instantaneous photosystem II quantum yield (QY), and lower leaf transpiration.

Morphological and metabolic responses to salt stress of rice (Oryza sativa L.) cultivars which differ in salinity tolerance

Salinization is one of the most important abiotic stressors for crop growth and productivity. Rice (Oryza sativa L.), as the major food source around the world, is very sensitive to salt, especially at seedling stage. In order to examine how salt stress influences the metabolism of rice, we compared the levels of a range of sugars and organic acids in three rice cultivars with different tolerance under salt stress over time. According to the morphological result, the shoot length and root fresh weight were only affected by salinity in the salt sensitive cultivar (Nipponbare). The responses of metabolites to salinity were time-, tissue- and cultivar-dependent. Shikimate and quinate, involved in the shikimate pathway, were dramatically decreased in the leaves of all three cultivars, which was regarded as a response to salinity. Many sugars in the leaves of the salt tolerant cultivar (Dendang and Fatmawati) showed earlier increases to salt stress compared to Nipponbare leaves. Moreover, only in the leaves of tolerant cultivars (Dendang and Fatimawati), malate was significantly decreased while sucrose was significantly increased. In Dendang roots, mannitol levels were significantly higher than in Nipponbare roots after 14 days of salt treatment, which may be attributed to its higher salt tolerance. It is proposed that these responses in the more tolerant cultivars are involved in their resistance to high salt stress which may lay the foundation for breeding tolerant rice cultivars.

Contrasting water sources and water-use efficiency in coexisting desert plants in two saline-sodic soils in northwest China

Soil degradation resulting from various types of salinity is a major environmental problem, especially in arid and semiarid regions. Exploring the water-related physiological traits of halophytes is useful for understanding the mechanisms of salt tolerance. This knowledge could be used to rehabilitate degraded arid lands. To investigate whether different types of salinity influence the water sources and water-use efficiency of desert plants (Karelinia caspia, Tamarix hohenackeri, Nitraria sibirica, Phragmites australis, Alhagi sparsifolia, Suaeda microphylla, Kalidium foliatum) in natural environments, we measured leaf gas exchange, leaf carbon and xylem oxygen isotope composition and soil oxygen isotope composition at neutral saline-sodic site (NSS) and alkaline saline-sodic site (ASS) in northwest China. The studied plants had different xylem water oxygen isotope compositions (δ¹⁸ O) and foliar carbon isotope compositions (δ¹³ C), indicating that desert plants coexist through differentiation in water use patterns. Compared to that at the NSS site, the stem water in K. caspia, A. sparsifolia and S. microphylla was depleted in ¹⁸ O at the ASS site, which indicates that plants can switch to obtain water from deeper soil layers when suffering environmental stress from both salinity and alkalinisation. Alhagi sparsifolia had higher δ¹³ C at the ASS site than at the NSS site, while K. caspia and S. microphylla had lower δ¹³ C, which may have resulted from interspecific differences in plant alkali and salt tolerance ability. Our results suggest that under severe salinity and alkalinity, plants may exploit deeper soil water to avoid ion toxicity resulting from high concentrations of soluble salts in the superficial soil layer. In managed lands, it is vital to select and cultivate different salt-tolerant or alkali-tolerant plant species in light of local conditions.

Novel Miscanthus genotypes selected for different drought tolerance phenotypes show enhanced tolerance across combinations of salinity and drought treatments

BACKGROUND AND AIMS

Water deficit and salinity stresses are often experienced by plants concurrently; however, knowledge is limited about the effects of combined salinity and water deficit stress in plants, and especially in C4 bioenergy crops. Here we aim to understand how diverse drought tolerance traits may deliver tolerance to combinations of drought and salinity in C4 crops, and identify key traits that influence the productivity and biomass composition of novel Miscanthus genotypes under such conditions.

METHODS

Novel genotypes used included M. sinensis and M. floridulus species, pre-screened for different drought responses, plus the commercial accession Miscanthus × giganteus (M×g.). Plants were grown under control treatments, single stress or combinations of water deficit and moderate salinity stress. Morphophysiological responses, including growth, yield, gas exchange and leaf water relations and contents of proline, soluble sugars, ash and lignin were tested for significant genotypic and treatment effects.

KEY RESULTS

The results indicated that plants subjected to combined stresses showed more severe responses compared with single stresses. All novel drought-tolerant genotypes and M×g. were tolerant to moderate salinity stress. Biomass production in M. sinensis genotypes was more resilient to co-occurring stresses than that in M×g. and M. floridulus, which, despite the yield penalty produced more biomass overall. A stay-green M. sinensis genotype adopted a conservative growth strategy with few significant treatment effects. Proline biosynthesis was species-specific and was triggered by salinity and co-occurring stress treatments, mainly in M. floridulus. The ash content was compartmentalized differently in leaves and stems in the novel genotypes, indicating different mechanisms of ion accumulation.

CONCLUSIONS

This study highlights the potential to select novel drought-tolerant Miscanthus genotypes that are resilient to combinations of stress and is expected to contribute to a deeper fundamental knowledge of different mechanistic responses identified for further exploitation in developing resilient Miscanthus crops.

Adaptation of Plants to Salt Stress: Characterization of Na+ and K+ Transporters and Role of CBL Gene Family in Regulating Salt Stress Response

Salinity is one of the most serious factors limiting the productivity of agricultural crops, with adverse effects on germination, plant vigor, and crop yield. This salinity may be natural or induced by agricultural activities such as irrigation or the use of certain types of fertilizer. The most detrimental effect of salinity stress is the accumulation of Na+ and Cl− ions in tissues of plants exposed to soils with high NaCl concentrations. The entry of both Na+ and Cl− into the cells causes severe ion imbalance, and excess uptake might cause significant physiological disorder(s). High Na+ concentration inhibits the uptake of K+, which is an element for plant growth and development that results in lower productivity and may even lead to death. The genetic analyses revealed K+ and Na+ transport systems such as SOS1, which belong to the CBL gene family and play a key role in the transport of Na+ from the roots to the aerial parts in the Arabidopsis plant. In this review, we mainly discuss the roles of alkaline cations K+ and Na+, Ion homeostasis-transport determinants, and their regulation. Moreover, we tried to give a synthetic overview of soil salinity, its effects on plants, and tolerance mechanisms to withstand stress.

Halotolerant Rhizobacterial Strains Mitigate the Adverse Effects of NaCl Stress in Soybean Seedlings

BACKGROUND

Salinity is one of the major abiotic constraints that hinder health and quality of crops. Conversely, halotolerant plant growth-promoting rhizospheric (PGPR) bacteria are considered biologically safe for alleviating salinity stress.

RESULTS

We isolated halotolerant PGPR strains from the rhizospheric soil of Artemisia princeps, Chenopodium ficifolium, Echinochloa crus-galli, and Oenothera biennis plants; overall, 126 strains were isolated. The plant growth-promoting traits of these isolates were studied by inoculating them with the soil used to grow soybean plants under normal and salt stress (NaCl; 200 mM) conditions. The isolates identified as positive for growth-promoting activities were subjected to molecular identification. Out of 126 isolates, five strains-Arthrobacter woluwensis (AK1), Microbacterium oxydans (AK2), Arthrobacter aurescens (AK3), Bacillus megaterium (AK4), and Bacillus aryabhattai (AK5)-were identified to be highly tolerant to salt stress and demonstrated several plant growth-promoting traits like increased production of indole-3-acetic acid (IAA), gibberellin (GA), and siderophores and increased phosphate solubilization. These strains were inoculated in the soil of soybean plants grown under salt stress (NaCl; 200 mM) and various physiological and morphological parameters of plants were studied. The results showed that the microbial inoculation elevated the antioxidant (SOD and GSH) level and K+ uptake and reduced the Na+ ion concentration. Moreover, inoculation of these microbes significantly lowered the ABA level and increased plant growth attributes and chlorophyll content in soybean plants under 200 mM NaCl stress. The salt-tolerant gene GmST1 was highly expressed with the highest expression of 42.85% in AK1-treated plants, whereas the lowest expression observed was 13.46% in AK5-treated plants. Similarly, expression of the IAA regulating gene GmLAX3 was highly depleted in salt-stressed plants by 38.92%, which was upregulated from 11.26% to 43.13% upon inoculation with the microorganism.

CONCLUSION

Our results showed that the salt stress-resistant microorganism used in these experiments could be a potential biofertilizer to mitigate the detrimental effects of salt stress in plants via regulation of phytohormones and gene expression.

Xylem-phloem hydraulic coupling explains multiple osmoregulatory responses to salt stress

Salinity is known to affect plant productivity by limiting leaf-level carbon exchange, root water uptake, and carbohydrates transport in the phloem. However, the mechanisms through which plants respond to salt exposure by adjusting leaf gas exchange and xylem-phloem flow are still mostly unexplored. A physically based model coupling xylem, leaf, and phloem flows is here developed to explain different osmoregulation patterns across species. Hydraulic coupling is controlled by leaf water potential, ψ_l , and determined under four different maximization hypotheses: water uptake (1), carbon assimilation (2), sucrose transport (3), or (4) profit function - i.e. carbon gain minus hydraulic risk. All four hypotheses assume that finite transpiration occurs, providing a further constraint on ψ_l . With increasing salinity, the model captures different transpiration patterns observed in halophytes (nonmonotonic) and glycophytes (monotonically decreasing) by reproducing the species-specific strength of xylem-leaf-phloem coupling. Salt tolerance thus emerges as plant's capability of differentiating between salt- and drought-induced hydraulic risk, and to regulate internal flows and osmolytes accordingly. Results are shown to be consistent across optimization schemes (1-3) for both halophytes and glycophytes. In halophytes, however, profit-maximization (4) predicts systematically higher ψ_l than (1-3), pointing to the need of an updated definition of hydraulic cost for halophytes under saline conditions.

Characterization of Na+ exclusion mechanism in rice under saline-alkaline stress conditions

This study was designed to elucidate the physiological responses of two rice genotypes to different pH levels under high saline stress. A salt-tolerant cultivar, FL478, and a salt-sensitive cultivar, IR29, were exposed to saline-alkaline solutions supplemented with 50 mM Na at pH 9 (severe), pH 8 (moderate), and pH 7 (mild) for three weeks. The results indicated that FL478 is relatively saline-alkaline tolerant compared to IR29, and this was evident from its higher dry mass production, lower Na⁺ concentration in the leaf blades, and maintenance of water balance under both mild and moderate saline-alkaline stress conditions. In both cultivars, Na⁺ concentrations in the leaf blades were considerably higher at pH 8 than at pH 7, indicating that high alkaline stress promoted Na⁺ accumulation under highly saline conditions. FL478 plants had lower Na⁺/K⁺ ratios in leaf blades and leaf sheaths than IR29 plants under saline-alkaline stress at both pH 7 and pH 8. To understand the mechanisms behind the difference in saline-alkaline tolerance between the two rice genotypes, transcript levels of the genes encoding Na⁺ transport proteins were analyzed. In response to mild and moderate saline-alkaline stress conditions, salt-tolerant FL478 had highly induced expression of the OsHKT1;5 gene in the roots, corresponding to lower Na⁺ accumulation in the leaf blades. Induction of high expression of the OsSOS1 gene in the roots of FL478 implied that Na may be effectively exported from cytosols to apoplasts in the roots resulting in sequestration of Na⁺ to outside of the roots and loading Na⁺ in xylem transpiration stream. On the other hand, the salt-sensitive IR29 had lower expression of the genes related to Na⁺ transporters, such as the OsHKT1;5 gene and the OsSOS1 gene, in the roots, leading to higher Na⁺ accumulation in the shoots. Expression of the determinant genes for alkaline tolerance, such as K⁺ and Fe acquisition and acidification of the rhizosphere was highly induced in FL478, but not in IR29. Thus, molecular analysis suggested that genes encoding Na⁺ transport proteins are involved in regulating Na⁺ transport under saline-alkaline stress in both salt-tolerant and salt-sensitive rice cultivars, and this is useful information for improving saline-alkaline tolerance traits of rice in the future.

Expression of AoNHX1 increases salt tolerance of rice and Arabidopsis, and bHLH transcription factors regulate AtNHX1 and AtNHX6 in Arabidopsis

Expression of AoNHX1 from the mangrove Avicennia increases salt tolerance of rice and Arabidopsis, and specific bHLH transcription factors regulate AtNHX1 and AtNHX6 in Arabidopsis to mediate the salinity response. Improving crop plants to better tolerate soil salinity is a challenging task. Mangrove trees such as Avicennia officinalis have special adaptations to thrive in high salt conditions, which include subcellular compartmentalization of ions facilitated by specialized ion transporters. We identified and characterized two genes encoding Na⁺/H⁺ exchangers AoNHX1 and AoNHX6 from Avicennia. AoNHX1 was present in the tonoplast, while, AoNHX6 was localized to the ER and Golgi. Both NHXs were induced by NaCl treatment, with AoNHX1 showing high expression levels in the leaves and AoNHX6 in the seedling roots. Yeast deletion mutants (ena1-5Δ nha1Δ nhx1Δ and ena1-5Δ nha1Δ vnx1Δ) complemented with AoNHX1 and AoNHX6 showed increased tolerance to both NaCl and KCl. Expression of AoNHX1 and AoNHX6 in the corresponding Arabidopsis mutants conferred enhanced NaCl tolerance. The underlying molecular regulatory mechanism was investigated using AtNHX1 and AtNHX6 in Arabidopsis. We identified two basic helix-loop-helix (bHLH) transcription factors AtMYC2 and AtbHLH122 as the ABA-mediated upstream regulators of AtNHX1 and AtNHX6 by chromatin immunoprecipitation. Furthermore, expression of AtNHX1 and AtNHX6 transcripts was reduced in the atmyc2 and atbhlh122 mutants. Lastly, transgenic rice seedlings harboring pUBI::AoNHX1 showed enhanced salt tolerance, suggesting that this gene can be exploited for developing salt-tolerant crops.

Domestication influences morphological and physiological responses to salinity in Brassica oleracea seedlings

Brassica oleracea cultivars include important vegetable and forage crops grown worldwide, whereas the wild counterpart occurs naturally on European sea cliffs. Domestication and selection processes have led to phenotypic and genetic divergence between domesticated plants and their wild ancestors that inhabit coastal areas and are exposed to saline conditions. Salinity is one of the most limiting factors for crop production. However, little is known about how salinity affects plants in relation to domestication of B. oleracea. The objective of this study was to determine the influence of domestication status (wild, landrace or cultivar) on the response of different B. oleracea crops to salinity, as measured by seed germination, plant growth, water content and mineral concentration parameters at the seedling stage. For this purpose, two independent pot experiments were conducted with six accessions of B. oleracea, including cabbage (group capitata) and kale (group acephala), in a growth chamber under controlled environmental conditions. In both taxonomic groups, differences in domestication status and salt stress significantly affected all major process such as germination, changes in dry matter, water relations and mineral uptake. In the acephala experiment, the domestication × salinity interaction significantly affected water content parameters and shoot Na+ allocation. At early stages of development, wild plants are more succulent than cultivated plants and have a higher capacity to maintain lower Na+ concentrations in their shoots in response to increasing levels of salinity. Different responses of domesticated and cultivated accessions in relation to these traits indicated a high level of natural variation in wild B. oleracea. Exclusion of Na+ from shoots and increasing succulence may enhance salt tolerance in B. oleracea exposed to extreme salinity in the long term. The wild germplasm can potentially be used to improve the salt tolerance of crops by the identification of useful genes and incorporation of these into salinity-sensitive cultivars.

Bacteria-assisted phytoremediation of fuel oil and lead co-contaminated soil in the salt-stressed condition by chromolaena odorata and Micrococcus luteus

Bioremediation of lead-petroleum co-contaminated soil under salt-stressed condition has been investigated. In this study, the co-contaminated soil (780 mg kg^-1 Pb and 27,000 mg kg^-1 TPHs) under the high salinity (EC 7.79 ds m^-1) was used as a model soil to be remediated by Chromolaena odorata inoculated with Micrococcus luteus. The results showed that salt stress caused a marked reduction in dry biomass and stem height, and high accumulation of proline. The presence of salt did not affect the total amount of chlorophyll in plant tissues. No toxicity symptoms were evident from plant morphology after three months of exposure. Drastic differences in the accumulation patterns of Pb in C. odorata grown on saline and non-saline soils were observed and indicated that salinity negatively affected Pb uptake and accumulation. A high rate of degradation of TPHs was observed in non-saline soils with or without bacterial inoculation. Salinity stress showed no significant different in the proportion of TPH degradation with added or non-added M. luteus. The tolerance of C. odorata and M. luteus to moderate concentrations of Pb and fuel oil made them very good candidates for the use in bacteria-assisted phytoremediation of lead-fuel oil co-contaminated soils under the mild saline soils.

Comparative physiological and metabolomic analyses reveal mechanisms of Aspergillus aculeatus-mediated abiotic stress tolerance in tall fescue

Aspergillus aculeatus has been shown to stimulate plant growth, but its role in plants abiotic stress tolerance and the underlying mechanisms are not fully documented. In this study, we investigated the mechanisms of A.aculeatus-mediated drought, heat and salt stress tolerance in tall fescue. The results showed that A.aculeatus inoculation improved drought and heat stress tolerance in tall fescue as observed from its effect on turf quality (TQ) and leaf relative water content (LWC). In the same stress conditions, A.aculeatus alleviated reactive oxygen species (ROS) induced burst and cell damage, as indicated by lower H₂O₂, electrolyte leakage (EL) and malondialdehyde (MDA) levels. Additionally, the A.aculeatus inoculated plants exhibited higher photosynthetic efficiency than uninoculated plants under drought, heat and salt stress conditions. The fungus reduced the uptake of Na⁺, and inoculated plants showed lower Na⁺/K⁺, Na⁺/Ca²⁺and Na⁺/Mg²⁺ ratios compared to uninoculated ones under salt stress. Furthermore, comparative metabolomic analysis showed that A.aculeatus exclusively increased amino acid (such as proline and glycine) and sugar (such as glucose, fructose, sorbose, and talose) accumulation under drought and heat stress. However, there were no differences between inoculated and uninoculated plants except for changes in H₂O₂ level, Na⁺ in the root and photosynthetic efficiency under salt stress. Taken together, this study provides the first evidence of the protective roles of A.aculeatus in the tall fescue response to abiotic stresses, partially via protection of photosynthesis and modulation of metabolic homeostasis.

Stimulating antioxidant defenses, antioxidant gene expression, and salt tolerance in Pisum sativum seedling by pretreatment using licorice root extract (LRE) as an organic biostimulant

Plant extracts have recently been used as exogenous adjuvants to strengthen the endogenous plant defense systems when they grow under different environmental stresses, including salinity. The study aimed at determining the effects of seed soaking using licorice root extract (LRE) on photosynthesis and antioxidant defense systems, including transcript levels of enzyme-encoding genes in pea seedling grown under 150 mM NaCl-salinity. Salt stress reduced seedling growth, photosynthesis attributes, and K+ content, and increased oxidative stress (O2•‒ and H2O2, and MDA), Na+, and Cl-, along with an increase in antioxidative defense activities compared to control. However, LRE pretreatment enhanced seedling growth, photosynthetic attributes (chlorophylls, carotenoids, Fv/Fm, Pn, Tr, and gs), ascorbate and glutathione and their redox states, proline, soluble sugars, α-TOC, and enzyme activities compared to stressed control. LRE pretreatment also upregulated transcript levels of CAT-, SOD-, APX-, GR-, DHAR-, and PrxQ-encoding genes in salt-stressed seedlings, decreasing oxidative stress and Na+ and Cl- contents and increasing K+ content and K+/Na+ ratio.

Potassium-induced decrease in cytosolic Na+ alleviates deleterious effects of salt stress on wheat (Triticum aestivum L.)

Accumulation of NaCl in soil causes osmotic stress in plants, and sodium (Na⁺ ) and chloride (Cl^- ) cause ion toxicity, but also reduce the potassium (K⁺ ) uptake by plant roots and stimulate the K⁺ efflux through the cell membrane. Thus, decreased K⁺ /Na⁺ ratio in plant tissue lead us to hypothesise that elevated levels of K⁺ in nutrient medium enhance this ratio in plant tissue and cytosol to improve enzyme activation, osmoregulation and charge balance. In this study, wheat was cultivated at different concentrations of K⁺ (2.2, 4.4 or 8.8 mm) with or without salinity (1, 60 or 120 mm NaCl) and the effects on growth, root and shoot Na⁺ and K⁺ distribution and grain yield were determined. Also, the cytosolic Na⁺ concentration was investigated, as well as photosynthesis rate and water potential. Salinity reduced fresh weight of both shoots and roots and dry weight of roots. The grain yield was significantly reduced under Na⁺ stress and improved with elevated K⁺ fertilisation. Elevated K⁺ level during cultivation prevented the accumulation of Na⁺ into the cytosol of both shoot and root protoplasts. Wheat growth at vegetative stage was transiently reduced at the highest K⁺ concentration, perhaps due to plants' efforts to overcome a high solute concentration in the plant tissue, nevertheless grain yield was increased at both K⁺ levels. In conclusion, a moderately elevated K⁺ application to wheat seedlings reduces tissue as well as cytosolic Na⁺ concentration and enhances wheat growth and grain yield by mitigating the deleterious effects of Na⁺ toxicity.

Identification and functional analysis of proteins in response to light intensity, temperature and water potential in Brassica rapa hypocotyl

Hypocotyl elongation is an early event in plant growth and development and is sensitive to fluctuations in light, temperature, water potential and nutrients. Most research on hypocotyl elongation has focused on the regulatory mechanism of a single environment factor. However, information about combined effects of multi-environment factors remains unavailable, and overlapping sites of the environmental factors signaling pathways in the regulation of hypocotyl elongation remain unclear. To identify how cross-talks among light intensity, temperature and water potential regulate hypocotyl elongation in Brassica rapa L. ssp. chinesis, a comprehensive isobaric tag for relative and absolute quantitation-based proteomic approach was adopted. In total, 7259 proteins were quantified, and 378 differentially expressed proteins (DEPs) were responsive to all three environmental factors. The DEPs were involved in a variety of biochemical processes, including signal transduction, cytoskeletal organization, carbohydrate metabolism, cell wall organization, protein modification and transport. The DEPs did not function in isolation, but acted in a large and complex interaction network to affect hypocotyl elongation. Among the DEPs, phyB was outstanding for its significant fold change in quantity and complex interaction networks with other proteins. In addition, changes of sensitivity to environmental factors in phyB-9 suggested a key role in the regulation of hypocotyl elongation. Overall, the data presented in this study show a profile of proteins interaction network in response to light intensity, temperature and water potential and provides molecular basis of hypocotyl elongation in B. rapa.

Silicon attenuates sodium toxicity by improving nutritional efficiency in sorghum and sunflower plants

Salt stress is known to negatively affect the fundamental processes in plants, reducing their growth and yield. The role of Silicon (Si) to protect the sorghum and sunflower plants against salinity stress was assessed. The objective of this study was to evaluate the effects of different forms of Si application on the uptake and use efficiency of macronutrients and micronutrients in sorghum and sunflower plants under salinity stress under greenhouse conditions. Two experiments were conducted using sorghum and sunflower under greenhouse conditions. Four Si levels were applied to plants: no Si application; foliar application of 28.6 mmol.L^-1; root application of 2.0 mmol.L^-1; and combined Si application with both via nutrient solution and foliar spraying. Each Si treatment was applied in the absence and presence of NaCl (100 mM). Thirty days after treatments, sodium (Na⁺) and Si accumulation, nutrient uptake and use efficiency, and the roots and total plant dry weight were measured. Salinity stress induced nutritional imbalance and decreased dry weight production in both plant species. Our results showed that Si application alleviated the salinity stress by decreased Na⁺ uptake and increased nutritional efficiency, thereby favoring the total plant dry weight in sorghum by 27% and sunflower by 41%. This occurred when Si was applied either via root or in combination via root and foliar application, respectively. Collectively, our findings indicate that Si application can attenuate the deleterious effects of salt stress and increase yield in sorghum and sunflower plants in a sustainable manner.

Physiological responses of Goji berry (Lycium barbarum L.) to saline-alkaline soil from Qinghai region, China

Recently, Goji berry (Lycium barbarum L.) has been extensively cultivated to improve the fragile ecological environment and increase the income of residents in Qinghai Province, northwestern China. However, few studies have focused on the physiological responses of Goji berry under salt stress and alkali stress. Gas exchange, photosynthetic pigments, and chlorophyll fluorescence were evaluated in response to neutral (NaCl) and alkali (NaHCO3) salt stresses. Nine irrigation treatments were applied over 30 days and included 0(Control group), 50, 100, 200, and 300 mM NaCl and NaHCO3. The results showed that salt and alkali stress reduced all the indicators and that alkali stress was more harmful to Goji berry than salt stress under the same solution concentrations. The salt tolerance and alkali resistance thresholds were identified when the index value exceeded the 50% standard of the control group, and threshold values of 246.3 ± 2.9 mM and 108.4.7 ± 2.1 mM, respectively, were determined by regression analysis. These results were used to identify the optimal water content for Goji berry. The minimum soil water content to cultivate Goji berry should be 16.22% and 23.37% under mild and moderate salt stress soils, respectively, and 29.10% and 42.68% under mild and moderate alkali stress soil, respectively.

Assessing trait contribution and mapping novel QTL for salinity tolerance using the Bangladeshi rice landrace Capsule

BACKGROUND

Salinity is one of the most widespread abiotic stresses affecting rice productivity worldwide. The purpose of this study was to establish the relative importance of different traits associated with salinity tolerance in rice and to identify new quantitative trait loci (QTL) conferring tolerance to salinity at seedling stage. A total of 231 F_2:3 plants derived from a cross between a sensitive variety BRRI dhan29 (BR29 hereafter) and Capsule, a salt tolerant Bangladeshi indica landrace, were evaluated under salt stress in a phytotron.

RESULTS

Out of the 231 F₂ plants, 47 highly tolerant and 47 most sensitive lines were selected, representing the two extreme tails of the phenotypic distribution. These 94 plants were genotyped for 105 simple sequence repeat (SSR) and insertion/deletion (InDel) markers. A genetic linkage map spanning approximately 1442.9 cM of the 12 linkage groups with an average marker distance of 13.7 cM was constructed. QTL were identified on the long arm of chromosome 1 for Na⁺ concentration, K⁺ concentration, Na⁺-K⁺ ratio and survival; chromosome 3 for Na⁺ concentration, survival and overall phenotypic evaluation using the Standard Evaluation system (SES); and chromosome 5 for SES. A total of 6 pairwise epistatic interactions were also detected between QTL-linked and QTL-unlinked regions. Graphical genotyping indicated an association between the phenotypes of the extreme families and their QTL genotypes. Path coefficient analysis revealed that Na⁺ concentration, survival, Na⁺-K⁺ ratio and the overall phenotypic performance (SES score) are the major traits associated with salinity tolerance of Capsule.

CONCLUSIONS

Capsule provides an alternative source of salinity tolerance aside from Pokkali and Nona Bokra, the two Indian salt tolerant landraces traditionally used for breeding salt tolerant rice varieties. Pyramiding the new QTL identified in this study with previously discovered loci, such as Saltol, will facilitate breeding varieties that are highly tolerant of salt stress.

Effect of salinity stress on bioactive compounds and antioxidant activity of wheat microgreen extract under organic cultivation conditions

This study was conducted to confirm the effects of salinity stress on bioactive compounds and antioxidant activity of wheat microgreen extract. The microgreens were cultivated for 8 days in organic media with different concentrations of Na [0 (control), 12.5, 25, 50, and 100 mM from sodium chloride] which was contained in a growth chamber with controlled temperature (20/15 °C, day/night), light (14/10 h, light/dark; intensity 150 μmol·m^-2·s^-1 with quantum dot light-emitting diodes), and humidity (60%). Treatment with increasing concentrations of Na resulted in an increase in the Na content of microgreens. Treatment with 12.5 mM of NaCl significantly maximized β-carotene (1.21 μg/mL), phenolic acid (41.70 μg/mL), flavonoid (165.47 μg/mL), and vitamin C (29.51 μg/mL) levels and the nitrite-scavenging activities (37.33%) in wheat microgreen extracts. In addition, the salt-stress caused due to treatment with 25 mM of NaCl resulted in the highest anthocyanin (51.43 μg/mL), 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (89.31%), and 2,2-diphenyl-1-picrylhydrazyl (63.28%) radical-scavenging activity. Therefore, attaining adequate levels of salt-stress may be useful for the industrial manufacturing of new products from wheat microgreen extract.

Mitigation of Salinity Stress Effects on Growth, Physio-Chemical Parameters and Yield of Snapbean (<i>Phaseolus vulgaris</i> L.) by Exogenous Application of Glycine Betaine

Pots experiment was carried out during season 2017 at greenhouse of the Agric. Bot. Dep., Fac. of Agric., Zagazig Univ., Egypt to evaluate the effect of glycine betaine (GB) application under salinity stress (50 and100 mM NaCl) on growth, physio-chemical analysis and yield of snap bean cv. Bronco. A complete randomized blocks design was used in this search with three replications. Growth parameters, chlorophyll content and green pod yield were significantly decreased with subjecting plants to NaCl. However foliar application of GB detoxified the stress generated by NaCl and significantly improved the above mention parameters. Salinity stress increased the electrolyte leakage (EL) and decreased membrane stability index (MSI) and relative water content (RWC). While foliar application of GB was improved MSI and RWC and minimized EL. Proline content and antioxidant enzymes significantly increased in the response to NaCl stress as well as GB application.

iTRAQ protein profile analysis of young and old leaves of cotton (Gossypium hirsutum L.) differing in response to alkali stress

Proteins will provide a new perspective and deeper understanding for the research of crop alkali tolerance. The aims of this study were to determine and identify the differentially abundant proteins and adaptive mechanisms to alkali tolerance between young and old leaves of cotton. The 4704 proteins were identified, in which 1490 were significantly changed in young leaves and 563 were changed in old leaves in response to alkali stress. The differentially abundant proteins were classified into 10 functional categories in the young leaves, and only 3 functional categories were involved in the old leaves. In the photoreaction system, the accumulations of differential proteins, especially Psb proteins, were higher in young leaves than in old leaves. Compared with old leaves, the carbon metabolism was enhanced significantly through an increased chlorophyll content and increased expression of key proteins for carbon metabolism in young leaves. Furthermore, alkali stress revealed more complex effects on the nitrogen metabolism in young leaves than that in old leaves. Our results demonstrated that during adaptation of cotton to alkali stress, young and old leaves have distinct mechanisms of molecular metabolism regulation. The metabolic flexibility was more remarkable in young leaves than in old leaves; therefore, the alkali tolerance of young leaves is more efficient. These data will increase our understanding of alkali-tolerant mechanisms in higher plants.

Nitrogen alleviates salinity toxicity in Solanum lycopersicum seedlings by regulating ROS homeostasis

The present study was aimed to investigate adaptation in physiology and biochemistry of Solanum lycopersicum seedlings under NaCl (NaCl₀; 0.0 g NaCl kg^-1 sand, NaCl₁; 0.3 g NaCl/kg sand and NaCl₂; 0.5 g NaCl/kg sand) stress, simultaneously supplemented with different (deprived; 0 mg/kg sand, LN; 105 mg/kg sand, MN; 210 mg/kg sand and HN; 270 mg/kg sand) levels of nitrogen (N). NaCl at both doses caused significant loss in growth, K⁺ content, K⁺/Na⁺ ratio, total chlorophyll and photosynthetic oxygen evolution. Further, N supplementation influences growth of test seedlings, that attained maximum growth in HN followed by MN, LN and deprived N conditions. N at HN level significantly declined Na⁺ accumulation in the cell and enhanced level of K⁺. NaCl treatment enhanced level of oxidative stress biomarkers: superoxide radical (O₂^•-), hydrogen peroxide (H₂O₂), MDA equivalents contents and electrolyte leakage in leaf as well as root despite enhanced activity of SOD, POD, CAT and GST, and enzymes participating in the ascorbate-glutathione cycle (AsA-GSH cycle) viz. APX, DHAR and GR. At the same time, higher contents of total AsA (AsA + DHA) and total GSH (GSH + GSSG), and maintained ratios of AsA/DHA and GSH/GSSG in HN fed seedlings were observed. Overall, the results suggest that HN supplementation was able in alleviating NaCl induced toxicity in test seedlings which was mainly due to the up-regulation of the AsA-GSH cycle, K⁺ and K⁺/Na⁺ ratio, which resulted into better growth performance of HN fed seedlings under NaCl stress while reverse was noticed for LN and deprive N conditions.

Differences of Acer platanoides L. and Tilia cordata Mill. Response patterns/survival strategies during cultivation in extremely polluted mining sludge - A pot trial

The study aimed to evaluate the physiological mechanisms underlying differences in metals and metalloid uptake and tolerance of two tree species cultivated in mining waste material. Two-year old Acer platanoides L. and Tilia cordata Mill. were cultivated in mining sludge characterized by high pH, salinity and an extremely high concentration of As. Both species were able to develop leaves from leafless seedlings, however, their total biomass was greatly reduced in comparison to control plants, following the severe disturbances in chlorophyll content. Phytoextraction abilities were observed for T. cordata for Ba, Nb, Rb and Se, and phytostabilisation was stated for Pd, Ru, Sc and Sm for both species, Ba and Nd for A. platonoides and Be for T. cordata only. Metal exclusion was observed for the majority of detected elements indicating an intense limitation of metal transport to photosynthetic tissue. A diversified uptake of elements was accompanied by a species-specific pattern of physiological reaction during the cultivation in sludge. Organic ligands (glutatnione and low-molecular-weight organic acids) were suppressed in A. platanoides, and enhanced biosynthesis of phenolic compounds was observed for both species, being more pronounced in T. cordata. Despite its higher accumulation of key metabolites for plant reaction to oxidative stress, such as phenolic acids, flavonoids and organic ligands, T. cordata exhibited relatively lower tolerance to sludge, probably due to the increased uptake and translocation rate of toxic metal/loids to aerial organs and/or restricted accumulation of salicylic acid which is known to play a decisive role in mechanisms of plant tolerance.

Evaluating rice for salinity using pot-culture provides a systematic tolerance assessment at the seedling stage

BACKGROUND

Rice (Oryza sativa L.) is one of the major staple food crops consumed globally. However, rice production is severely affected by high salinity levels, particularly at the seedling stage. A good solution would be the development of an efficient screening methodology to identify genotypes possessing genes for salt tolerance.

RESULT

A new salinity tolerance screening technique using rice seedlings in pot-culture was tested. This method controls soil heterogeneity by using pure sand as a growth medium and minimizes unexpected extreme weather conditions with a movable shelter. Seventy-four rice genotypes were screened at three salinity treatments including high salt stress (electrical conductivity (EC) 12 dSm^- 1), moderate salt stress (EC 6 dSm^- 1), and control (no salt stress), imposed 1 week after emergence. Several shoot and root morpho-physiological traits were measured at 37 days after sowing. A wide range of variability was observed among genotypes for measured traits with root traits being identified as the best descriptors for tolerance to salt stress conditions. Salt stress response indices (SSRI) were used to classify the 74 rice genotypes; 7 genotypes (9.46%) were identified as salt sensitive, 27 (36.48%) each as low and moderately salt tolerant, and 13 (17.57%) as highly salt tolerant. Genotypes FED 473 and IR85427 were identified as the most salt tolerant and salt sensitive, respectively. These results were further confirmed by principal component analysis (PCA) for accuracy and reliability.

CONCLUSION

Although tolerant genotypes still need to be confirmed in field studies and tolerance mechanisms identified at the molecular level, information gained from this study could help rice breeders and other scientists to accelerate breeding by selecting appropriate donor parents, progenies and potential genotypes at early growth stages necessary for salinity tolerance research.

Evaluating rice for salinity using pot-culture provides a systematic tolerance assessment at the seedling stage

BACKGROUND

Rice (Oryza sativa L.) is one of the major staple food crops consumed globally. However, rice production is severely affected by high salinity levels, particularly at the seedling stage. A good solution would be the development of an efficient screening methodology to identify genotypes possessing genes for salt tolerance.

RESULT

A new salinity tolerance screening technique using rice seedlings in pot-culture was tested. This method controls soil heterogeneity by using pure sand as a growth medium and minimizes unexpected extreme weather conditions with a movable shelter. Seventy-four rice genotypes were screened at three salinity treatments including high salt stress (electrical conductivity (EC) 12 dSm^- 1), moderate salt stress (EC 6 dSm^- 1), and control (no salt stress), imposed 1 week after emergence. Several shoot and root morpho-physiological traits were measured at 37 days after sowing. A wide range of variability was observed among genotypes for measured traits with root traits being identified as the best descriptors for tolerance to salt stress conditions. Salt stress response indices (SSRI) were used to classify the 74 rice genotypes; 7 genotypes (9.46%) were identified as salt sensitive, 27 (36.48%) each as low and moderately salt tolerant, and 13 (17.57%) as highly salt tolerant. Genotypes FED 473 and IR85427 were identified as the most salt tolerant and salt sensitive, respectively. These results were further confirmed by principal component analysis (PCA) for accuracy and reliability.

CONCLUSION

Although tolerant genotypes still need to be confirmed in field studies and tolerance mechanisms identified at the molecular level, information gained from this study could help rice breeders and other scientists to accelerate breeding by selecting appropriate donor parents, progenies and potential genotypes at early growth stages necessary for salinity tolerance research.

Response of seedling growth and physiology of Sorghum bicolor (L.) Moench to saline-alkali stress

Soil salinization is a serious problem that affects the seedling growth in many regions. A greenhouse experiment was carried to investigate the adaptation ability of seedlings (Sorghum bicolor (L.) Moench.) in coastal saline alkaline environment. Seedlings of sorghum were treated by different salt and alkali stress (NaCl: Na₂SO₄: NaHCO₃ were 2:1:0, 2:1:1, 2:1:2). The treatments consisted of three levels of salinity (100, 200 and 300 mmol/L) and pH values were 7.08, 8.78 and 9.04. The results showed that the seedlings of sorghum have good adaptability to salt stress under low pH (pH ≤7.08). The plant height, the maximum leave areas of seedlings all dropped and root length first ascended and then descended with the increasing of salt and alkali stress. The contents of Chlorophyll b degraded significantly under salt and alkali stress. Salt and alkali stress stimulated the accumulation of organic solutes (proline and protein) and inorganic ions (Na⁺, Cl^-, SO₄^2-). Our results showed that salt and alkali stress have significant effect on growth indexes except root length and the interaction effect has significantly on physiology.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

Contrasting Effects of NaCl and NaHCO3 Stresses on Seed Germination, Seedling Growth, Photosynthesis, and Osmoregulators of the Common Bean (Phaseolus vulgaris L.)

The common bean (Phaseolus vulgaris L.), the most important food legume for human nutrition globally, contributes greatly to the improvement of soil fertility in semi-dry lands where most of the soil is already salinized or alkalized, such as in the Songnen Plain of China. In this study, we investigated the effects of salt stress (neutral and alkaline) on the salt-tolerant common bean. Seed germination, seedling growth, photosynthesis, and osmotic adjustment were assessed. Neutral and alkaline salt growth environments were simulated using NaCl and NaHCO3, respectively. The results indicated that at ≥60 mmol·L−1, both NaCl and NaHCO3 caused significant delays in seedling emergence and decreased seedling emergence rates. NaHCO3 stress suppressed seedling survival regardless of concentration; however, only NaCl concentrations >60 mmol·L−1 had the same effect. Alkaline salt stress remarkably suppressed photosynthesis and seedling establishment. The common bean compensated for the increase in inorganic anion concentration (influx of Na+) by synthesizing more organic acids and soluble sugars. This adaptive mechanism enabled the common bean to balance the large inflow of cations for maintaining a stable cell pH environment under alkaline salt stress.

Arbuscular Mycorrhizal Fungi Confer Salt Tolerance in Giant Reed (Arundo donax L.) Plants Grown Under Low Phosphorus by Reducing Leaf Na+ Concentration and Improving Phosphorus Use Efficiency

Salinization is one of the major causes of agricultural soil degradation worldwide. In arid and semi-arid regions with calcareous soils, phosphorus (P) deficiency further worsens the quality of salinized soils. Nonetheless, nutrient poor soils could be suitable of producing second-generation energy crops. Due to its high biomass production, Arundo donax L. (giant reed) is one of the most promising species for energy and second-generation biofuel production. A. donax can be propagated by micropropagation, an in vitro technique that produces high number of homogeneous plantlets. However, crop establishment is often compromised due to poor plantlet acclimatization to the soil environment. Arbuscular mycorrhizal fungi (AM) are components of soil-plant systems able to increase root phosphorus uptake and to confer the plant an increase tolerance to salinity with a consequent enhancement effect of plant growth and yield. In the present study, the relative importance of the early symbiosis establishment between AM fungi and A. donax micropropagated plantlets in the response to salt stress under low phosphorus availability was determined. A commercial inoculum which contained two different AM fungi species: Rhizophagus intraradices and Funneliformis mosseae was used. AM-symbionts (AM) and non-symbionts plants were grown at two phosphorus [2.5 μM (C) and 0.5 mM (P)] and three NaCl (1, 75 and 150 mM) concentrations in a room chamber under controlled conditions. After 5 weeks, AM root colonization was 60, 26 and 15% in 1, 75 and 150 mM NaCl-treated plants, respectively. At 1 and 75 mM NaCl, AM plants showed increased growth. In all saline treatments, AM plants had decreased Na+ uptake, Na+ root-to-shoot translocation, Na+/K+ ratio and increased P and K use efficiencies with respect to C and P plants. AM improved the nutritional status of A. donax plants by enhancing nutrient use efficiency rather than nutrient uptake. Increased phosphorus use efficiency in AM plants could have benefited ion (Na+ and K+) uptake and/or allocation and ultimately ameliorate the plant's response to saline conditions.

Omeprazole Promotes Chloride Exclusion and Induces Salt Tolerance in Greenhouse Basil

The role of small bioactive molecules (<500 Da) in mechanisms improving resource use efficiency in plants under stress conditions draws increasing interest. One such molecule is omeprazole (OMP), a benzimidazole derivative and inhibitor of animal proton pumps shown to improve nitrate uptake and exclusion of toxic ions, especially of chloride from the cytosol of salt-stressed leaves. Currently, OMP was applied as substrate drench at two rates (0 or 10 μM) on hydroponic basil (Ocimum basilicum L. cv. Genovese) grown under decreasing NO3−:Cl− ratio (80:20, 60:40, 40:60, or 20:80). Chloride concentration and stomatal resistance increased while transpiration, net CO2 assimilation rate and beneficial ions (NO3−, PO43−, and SO42−) decreased with reduced NO3−:Cl− ratio under the 0 μM OMP treatment. The negative effects of chloride were not only mitigated by the 10 μM OMP application in all treatments, with the exception of 20:80 NO3−:Cl−, but plant growth at 80:20, 60:40, and 40:60 NO3−:Cl− ratios receiving OMP application showed maximum fresh yield (+13%, 24%, and 22%, respectively), shoot (+10%, 25%, and 21%, respectively) and root (+32%, 76%, and 75%, respectively) biomass compared to the corresponding untreated treatments. OMP was not directly involved in ion homeostasis and compartmentalization of vacuolar or apoplastic chloride. However, it was active in limiting chloride loading into the shoot, as manifested by the lower chloride concentration in the 80:20, 60:40, and 40:60 NO3−:Cl− treatments compared to the respective controls (−41%, −37%, and −24%), favoring instead that of nitrate and potassium while also boosting photosynthetic activity. Despite its unequivocally beneficial effect on plants, the large-scale application of OMP is currently limited by the molecule’s high cost. However, further studies are warranted to unravel the molecular mechanisms of OMP-induced reduction of chloride loading to shoot and improved salt tolerance.

Effect of day time climatic conditions associated with different 2,4-D formulations on spray deposition and weed control

The aim of this study was to evaluate the effect of time of the day and their associated climatic conditions on spray deposition of two 2,4-D formulations, as well as the influence on weed control. The experiment was installed in the field in complete randomized design. Treatments were arranged in factorial design 8 × 2, with 20 repetitions. First factor corresponded to different application time (1:00, 4:00, 7:00, 10:00, 13:00, 16:00, 19:00, and 22:00) with their respective climatic conditions. The second factor consisted of two formulations of 2,4-D applied at 776 g a.e. ha-1 (2,4-D amine and 2,4-D choline salt with Colex-D™ Technology) + glyphosate (816 g a.e. ha-1). There was more spray deposition when 2,4-D choline formulation was used, and such differences were more evident for applications performed under adverse climatic conditions. More spray deposition was found in applications performed at times of day with more favorable temperature and humidity of the air conditions. Only the initial control of the evaluated species was affected by the time of application.

EsHO 1 mediated mitigation of NaCl induced oxidative stress and correlation between ROS, antioxidants and HO 1 in seedlings of Eruca sativa: underutilized oil yielding crop of arid region

Study have focused on NaCl induced HO 1 production and its co-relation to ROS and antioxidant regulation in Eruca sativa. Seedlings were subjected to NaCl stress ranges from 10 to 150 mM. After 96 h of treatment, plants samples were harvested to evaluate the cellular equilibrium and salt tolerance mechanisms through morphological, stress parameters, non enzymatic and antioxidant enzymes. The HO 1 activity was found to be highest at 75 mM NaCl in leaves and roots which were 2.49 and 2.02 folds respectively. The expression of EsHO 1 was also observed and the higher expression was recorded in roots than leaves. The overall activity of other antioxidants (APX and proline) was also found to be higher at 75 mM concentration. The highest HO 1 activity with other antioxidants indicates the decline in LPX and ROS at 75 mM NaCl. The present study concluded that HO 1 helps in amelioration of NaCl stress by working within a group of antioxidants that create the defense machinery in seedlings of E. sativa by manipulating various physiological processes of plants. These findings for the first time suggest the protective role of HO 1 in scavenging ROS in E. sativa under salinity stress.

Comparative analyses of albumin/globulin grain proteome fraction in differentially salt-tolerant Tunisian barley landraces reveals genotype-specific and defined abundant proteins

Salinity is one of the major abiotic stresses threatening crop production and yield worldwide. Breeding programmes are therefore needed to improve yield under cultivation in soil. Traits from locally adopted landraces provide a resource to assist breeding of novel elite genotypes. Here, we examine differentially expressed proteins by performing comparative proteomic profiling of the albumin/globulin grain fraction of Tunisian barley genotype landraces with contrasting salinity tolerance. Tunisian barley Boulifa (B, tolerant) and Testour (T, sensitive) mature grains were assessed in 2-DE profiles. Differentially expressed spots, with an abundance enhanced 1.5-fold in the grain, were subjected to MALDI TOF/TOF MS for identification. Distinctiveness between tolerant and sensitive genotypes was proved in the albumin/globulin fraction using PCA; 64 spots showed significant differential abundance. Increased accumulation of 40 spots was confirmed in Boulifa with, interestingly, four genotype-specific spots. Two of these four spots were sHSP. Proteins with highest abundance were serpin Z7, 16.9 KDa Class I HSP and phosphogluconolactonase 2. Proteins such as expansin, kiwellin, kinesin and succinyl-CoA ligase were identified for the first time in barley grain. Moreover, ß-amylase, LEA family and others were identified as abundant in Boulifa. On the other hand, proteins more accumulated in Testour are implicated mainly in ROS scavenging and protease inhibition. Our results clearly indicate proteomic contrast between the two selected genotypes. With identification of specific HSP, high abundant stress-protective and other defined proteins, we provide biochemical traits that will support breeding programmes to address the threat of salinity in agricultural production.

Quality of lettuce Lactuca sativa (var. Tropicana M1) grown with two low-salinity shrimp effluents

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Control lettuce showed higher levels of proline than lettuce from other treatments.

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Well water lettuce exhibited higher levels of phenols than that from other treatments.

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Lettuce with low-salinity shrimp effluent exhibit a quality comparable to the control.

In a previous study, we investigated the use of shrimp effluents from well water (WW) and diluted seawater (DSW) (both with 2.7 dS m⁻¹ electrical conductivity (EC)), and a hydroponic solution (HS) as the control treatment in greenhouse lettuce production. This new paper completes the previous one by focusing on the quality of lettuce harvested. Compared to the lettuce from the other treatments, WW-lettuce exhibited higher levels of phenolic compounds and a higher antioxidant capacity, mainly in the soluble fraction. The lettuce cultivated with DSW showed no significant difference in total phenolics and flavonoids with respect to the HS lettuce. These results reveal that the functional properties (antioxidant properties, polyphenols and flavonoid content) are even better in the lettuce produced with WW and DSW shrimp effluents. In contrast, agronomical properties (weight, number of leaves and yield) were found to be better in the case of lettuce grown with the hydroponic solution (control).

Salinity Stress Alters Root Morphology and Root Hair Traits in Brassica napus

Plant roots show morphological plasticity and play a substantial role in tolerance to various edaphic stresses. The aim of this study was to explore salinity-induced morphogenic responses of root traits and root hairs of two rapeseed varieties, BARI Sarisha-8 and Binasarisha-5, at the reproductive stage and perceive the effects on their reproductive growth. The experiment was conducted in a hydroponic culture. Two treatments, 0 mM NaCl as control and 100 mM NaCl, were imposed 55 d after germination. Plants exposed to 100 mM NaCl for seven days displayed greater damage in the leaves, flowers, and siliquae compared to control. Length of root hairs on first-order and third-order lateral roots, density of root hairs on first-order lateral roots, and length of third-order lateral roots were significantly greater by 91%, 22%, 29%, and 48%, respectively, in the treated condition compared to the control. An increase in estimated root surface area by 20% under salt stress conditions indicated that the spontaneous responses of plants to uptake more water and nutrients allowed a plant to cope with stressful conditions. The results of this study suggest that any future stress breeding programs should consider plasticity of root traits intensively.

Optimizing irrigation and nitrogen fertilization for seed yield in western wheatgrass [Pascopyrum smithii (Rydb.) Á. Löve] using a large multi-factorial field design

It is crucial for agricultural production to identify the trigger that switches plants from vegetative to reproductive growth. Agricultural sustainability in semiarid regions is challenged by nitrogen (N) fertilizer overuse, inadequate soil water, and heavy carbon emissions. Previous studies focused on the short-term effects of a single application of N and water but have not investigated the long-term effects of different irrigation and N fertilizer regimens on crop yields and yield components. N application is routinely coupled with water availability, and crop yields can be maximized by optimizing both. We examined the growth of western wheatgrass [Pascopyrum smithii (Rydb.) Á. Löve], a temperate-region forage and turf grass, using multiple different combinations of N fertilizer [(NH4)2·CO3] and irrigation levels over 3 years to determine optimal field management. We conducted multifactorial, orthogonally designed field experiments with large sample sizes, and measured fertile tillers m-2 (Y1), spikelets/fertile tillers (Y2), florets/spikelet (Y3), seed numbers/spikelet (Y4), seed weight (Y5), and seed yield (Z) to study factors associated with the switch between vegetative and reproductive growth. Fertilization had a greater effect on seed yield and yield components than irrigation. Y1 had the strongest positive effect on Z, whereas Y5 had a negative effect on Z. Irrigation and fertilization affected Z, Y1, and Y5. Fertilizer concentrations were positively correlated with Z, Y1, and Y5, whereas irrigation levels were negatively correlated. The ridge regression linear model results suggested N application rate and irrigation had antagonistic effects on Y1 (X3 = 867.6-4.23×X2; R2 = 0.988, F = Infinity, P<0.0001). We conclude that the optimal amount of N fertilizer and irrigation was 156 kg ha-1 + 115 mm for seed yield, 120 kg ha-1 + 146 mm for spikelets/fertile tillers, and 108 kg ha-1 + 119 mm for seed numbers/spikelets. These results will improve yield and reduce agricultural inputs for P. smithii in semiarid and arid regions, thereby reducing fertilizer pollution and conserving water.

Induction of tolerance to salinity in wheat genotypes by plant growth promoting endophytes: Involvement of ACC deaminase and antioxidant enzymes

Plant growth-promoting endophytes (PGPEs) can colonize the internal tissues of plants and are capable of promoting plant growth. These bacteria can improve plant tolerance against various biotic and abiotic stresses via the expression of antioxidant enzymes and the production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Two salt-tolerant PGPEs, Kocuria rhizophila: KF875448 (14ASP) and Cronobacter sakazakii: KM042090 (OF115), with ACC deaminase activity were investigated for their potential to ameliorate plant salinity stress. The wheat varieties Pasban 90 and Khirman were subjected to two levels of salt stress (80 and 160 mM NaCl) under greenhouse conditions by using a completely randomized design. Analyses of plant growth parameters, antioxidant enzyme activities, chlorophyll and plant mineral contents were conducted to investigate the stress tolerance induced by the PGPEs. The ACC utilization by the PGPEs directly relates to the promotion of plant growth due to the lowering of excess ethylene production under salt stress. High levels of NaCl exhibited negative effects in both varieties. However, inoculation with PGPEs increased the morphological traits and antioxidant activities of the plants while decreasing the Na⁺ contents in all treatments compared to uninoculated treatment. Wheat variety Pasban 90 was more tolerant than Khirman in to salt stress in all the measured morphological and biochemical parameters, while the bacterial strain OF115 performed significantly better in all morphological and biochemical parameters, such as fresh dry weight, root shoot length, proline and chlorophyll contents, compared to strain 14ASP. The K⁺/Na⁺ ratio in the tissues of bacterial treated plants was higher than the control, probably in order to maintain the nutrient balance. The results of our study revealed that the inoculation of plants by ACC deaminase-producing PGPEs is a potential tool for the enhancement of plant growth and stress tolerance. Moreover, endophytic bacteria allied with host plants are capable of enduring high saline conditions and can interact with plants in a very efficient way.

Wounding induces tomato Ve1 R-gene expression

In tomato, Ve1 gene expression is induced specifically by physical damage or plant wounding, resulting in a defense/stress cascade that mimics responses during Verticillium colonization and wilt. In tomato, Verticillium resistance is determined by the Ve gene locus, which encodes two leucine-rich repeat-receptor-like proteins (Ve1, Ve2); the Ve1 gene is induced differentially while Ve2 is constitutively expressed throughout disease development. These profiles have been observed even during compatible Verticillium interactions, colonization by some bacterial pathogens, and growth of transgenic tomato plants expressing the fungal Ave1 effector, suggesting broader roles in disease and/or stress. Here, we have examined further Ve gene expression in resistant and susceptible plants under abiotic stress, including a water deficit, salinity and physical damage. Using both quantitative RT-PCR and label-free LC-MS methods, changes have been evaluated at both the mRNA and protein levels. The results indicate that Ve1 gene expression responds specifically to physical damage or plant wounding, resulting in a defense/stress cascade that resembles observations during Verticillium colonization. In addition, the elimination or reduction of Ve1 or Ve2 gene function also result in proteomic responses that occur with wilt pathogen and continue to be consistent with an antagonistic relationship between the two genes. Mutational analyses also indicate the plant wounding hormone, systemin, is not required, while jasmonic acid again appears to play a direct role in induction of the Ve1 gene.

Interplaying roles of silicon and proline effectively improve salt and cadmium stress tolerance in Phaseolus vulgaris plant

The interplaying defensive roles of silicon (Si) and proline (Pro) in improving growth and yield attributes, physio-biochemical attributes, and antioxidant defense systems in common bean plant grown under saline (NaCl) and/or cadmium (Cd²⁺) stress were assessed. Seed were sown in plastic pots filled with sand-free ions as a growing medium that watered with a ½-strength Hoagland's nutrient solution. Twenty five days after planting, pots were split into 4 plots; control (no stress), 150 mM NaCl (salt stress), 1.5 mM Cd²⁺ in CdCl₂ (Cd²⁺ stress), and 100 mM NaCl + 1.0 mM Cd²⁺ (salt + Cd²⁺ stress). Four treatments; foliar spray with distilled water, 6 mM Si (in K₂SiO₃.nH₂O) solution, 6 mM Pro solution, and a combination of Si and Pro were allotted under each of the 4 plots. The experimental layout was a completely randomized design with 15 replicates. Compared to control, NaCl or Cd²⁺ stress significantly (P ≤ 0.05) reduced plant growth and yield attributes, leaf contents of chlorophylls, carotenoids, N, P, and K⁺, K⁺/Na⁺ ratio, RWC, MSI, Pn and Tr, while elevated significantly leaf EL, leaf contents of proline, soluble sugar, glutathione, MDA, Na⁺, and root, leaf and pod contents of Cd²⁺. The activities of antioxidant enzymes were also raised. The combined stress (NaCl + Cd²⁺) was more influential. Addition of Si and/or Pro for common bean plants under NaCl and/or Cd²⁺ stress significantly enhanced all investigated attributes of physiology, morphology, and biochemistry, and further increased the activities of antioxidant enzymes. Supplementation of Si + Pro was the best treatment having more positive influential, especially reducing the Cd²⁺ content in Phaseolus vulgaris pods to the limits (0.27 mg kg^-1) for legumes. Therefore, this combined treatment is recommended to use for alleviating environmental stress effects, especially salinity and Cd²⁺ for common bean production.

Effects of moderate soil salinity on osmotic adjustment and energy strategy in soybean under drought stress

Under drought and soil salinity, plants usually respond to accumulate inorganic and organic osmolytes for adaptation, that would induce changes in energy consumption strategy of plants. Moderate soil salinity would enable plants to lower energy consumption for osmotic adjustment by passively absorbing more Na+. This action would keep more energies for growth of drought-stressed plants. Thus, Na+ accumulation might be an energy-efficient strategy for plants to cope with drought was speculated. To support this speculation, we assessed the effects of soil salinity on osmotic adjustment and energy utilization under drought in this study. Our results indicated that the ratio and content of inorganic osmolytes was significantly higher under drought-saline stress (D + S) than those under single drought stress (D), while the osmolarity and contents of organic osmolytes of D + S were significantly lower than those of D. This indicated that moderate soil salinity could enable soybean seedlings to consume relatively lower energies to produce less organic osmolytes and accumulate more inorganic ions for osmotic adjustment coping with drought. Meanwhile the water content, cell turgor, ash content, and specific leaf area and biomass of D + S were significantly higher than those of D, but the leaf construction cost of D + S was significantly lower than those of D. This suggested that moderate soil salinity could enhance water retention, and reduce the photoassimilate and energy consumption of droughty soybean seedlings. This work would help to understand the positive effects of moderate soil salinity on plant growth on the level of osmotic adjustment and energy consumption strategy.

Cytotoxic effect of protic ionic liquids in HepG2 and HaCat human cells: in vitro and in silico studies

Protic ionic liquids (PILs) are innovative chemical compounds, which due to their peculiar nature and amazing physico-chemical properties, have been studied as potential sustainable solvents in many areas of modern science, such as in the industrial fields of textile dyeing, pharmaceuticals, biotechnology, energy and many others. Due to their more than probable large-scale use in a short space of time, a wider analysis in terms of ecotoxicity and biological safety to humans has been attracting significant attention, once many ionic liquids were found to be "a little less than green compounds" towards cells and living organisms. The aim of this study is to investigate the cytotoxicity of 13 recently synthesized PILs, as well as to reinforce knowledge in terms of key thermodynamic magnitudes. All the studied compounds were tested for their in vitro toxic activities on two human cell lines (normal keratinocytes HaCaT and hepatocytes HepG2). In addition, due to the enormous number of possible combinations of anions and cations that can form ionic liquids, a group contribution QSAR model has been tested in order to predict their cytotoxicity. The estimated and experimental values were adequately correlated (correlation coefficient R 2 = 0.9260). The experimental obtained results showed their remarkable low toxicity for the studied in vitro systems.