Accumulation Of Compatible Solutes Research Articles

Sorghum drought tolerance is enhanced by cerium oxide nanoparticles via stomatal regulation and osmolyte accumulation

Sorghum [Sorghum bicolor (L.) Moench] yield is limited by the coincidence of drought during its sensitive stages. The use of cerium oxide nanoparticles in agriculture is minimal despite its antioxidant properties. We hypothesize that drought-induced decreases in photosynthetic rate in sorghum may be associated with decreased tissue water content and organelle membrane damage. We aimed to quantify the impact of foliar application of nanoceria on transpiration rate, accumulation of compatible solutes, photosynthetic rate and reproductive success under drought stress in sorghum. In order to ascertain the mechanism by which nanoceria mitigate drought-induced inhibition of photosynthesis and reproductive success, experiments were undertaken in a factorial completely randomized design or split-plot design. Foliar spray of nanoceria under progressive soil drying conserved soil moisture by restricting the transpiration rate than water spray, indicating that nanoceria exerted strong stomatal control. Under drought stress at the seed development stage, foliar application of nanoceria at 25 mg L−1 significantly improved the photosynthetic rate (19%) compared to control by maintaining a higher tissue water content (18%) achieved by accumulating compatible solutes. The nanoceria-sprayed plants exhibited intact chloroplast and thylakoid membranes because of increased heme enzymes [catalase (53%) and peroxidase (45%)] activity, which helped in the reduction of hydrogen peroxide content (74%). Under drought, compared to water spray, nanoceria improved the seed-set percentage (24%) and individual seed mass (27%), eventually causing a higher seed yield. Thus, foliar application of nanoceria at 25 mg L−1 under drought can increase grain yield through increased photosynthesis and reproductive traits.

Coping with salinity stress: segmental group 7 chromosome introgressions from halophytic Thinopyrum species greatly enhance tolerance of recipient durum wheat.

Increased soil salinization, tightly related to global warming and drought and exacerbated by intensified irrigation supply, implies highly detrimental effects on staple food crops such as wheat. The situation is particularly alarming for durum wheat (DW), better adapted to arid/semi-arid environments yet more sensitive to salt stress than bread wheat (BW). To enhance DW salinity tolerance, we resorted to chromosomally engineered materials with introgressions from allied halophytic Thinopyrum species. "Primary" recombinant lines (RLs), having portions of their 7AL arms distally replaced by 7el1L Th. ponticum segments, and "secondary" RLs, harboring Th. elongatum 7EL insertions "nested" into 7el1L segments, in addition to near-isogenic lines lacking any alien segment (CLs), cv. Om Rabia (OR) as salt tolerant control, and BW introgression lines with either most of 7el1 or the complete 7E chromosome substitution as additional CLs, were subjected to moderate (100 mM) and intense (200 mM) salt (NaCl) stress at early growth stages. The applied stress altered cell cycle progression, determining a general increase of cells in G1 and a reduction in S phase. Assessment of morpho-physiological and biochemical traits overall showed that the presence of Thinopyrum spp. segments was associated with considerably increased salinity tolerance versus its absence. For relative water content, Na+ accumulation and K+ retention in roots and leaves, oxidative stress indicators (malondialdehyde and hydrogen peroxide) and antioxidant enzyme activities, the observed differences between stressed and unstressed RLs versus CLs was of similar magnitude in "primary" and "secondary" types, suggesting that tolerance factors might reside in defined 7el1L shared portion(s). Nonetheless, the incremental contribution of 7EL segments emerged in various instances, greatly mitigating the effects of salt stress on root and leaf growth and on the quantity of photosynthetic pigments, boosting accumulation of compatible solutes and minimizing the decrease of a powerful antioxidant like ascorbate. The seemingly synergistic effect of 7el1L + 7EL segments/genes made "secondary" RLs able to often exceed cv. OR and equal or better perform than BW lines. Thus, transfer of a suite of genes from halophytic germplasm by use of fine chromosome engineering strategies may well be the way forward to enhance salinity tolerance of glycophytes, even the sensitive DW.

Enrichment performance and salt tolerance of polyhydroxyalkanoates (PHAs) producing mixed cultures under different saline environments

The key to the resource recycling of saline wastes in form of polyhydroxyalkanoates (PHA) is to enrich mixed cultures with salt tolerance and PHA synthesis ability. However, the comparison of saline sludge from different sources and the salt tolerance mechanisms of salt-tolerant PHA producers need to be clarified. In this study, three kinds of activated sludge from different salinity environments were selected as the inoculum to enrich salt-tolerant PHA producers under aerobic dynamic feeding (ADF) mode with butyric acid dominated mixed volatile fatty acid as the substrate. The maximum PHA content (PHAm) reached 0.62 ± 0.01, 0.62 ± 0.02, and 0.55 ± 0.03 g PHA/g VSS at salinity of 0.5%, 0.8%, and 1.8%, respectively. Microbial community analysis indicated that Thauera, Paracoccus, and Prosthecobacter were dominant salt-tolerant PHA producers at low salinity, Thauera, NS9_marine, and SM1A02 were dominant salt-tolerant PHA producers at high salinity. High salinity and ADF mode had synergistic effects on selection and enrichment of salt-tolerant PHA producers. Combined correlation network with redundancy analysis indicated that trehalose synthesis genes and betaine related genes had positive correlation with PHAm, while extracellular polymeric substances (EPS) content had negative correlation with PHAm. The compatible solutes accumulation and EPS secretion were the main salt tolerance mechanisms of the PHA producers. Therefore, adding compatible solutes is an effective strategy to improve PHA synthesis in saline environment.

NPK fertilization modulates enzyme activity and mitigates the impacts of salinity on West Indian cherry.

Salt stress causes several physiological and biochemical disorders and impairs plant growth. However, adequate fertilization can improve the nutritional status and may reduce significantly the harmful effects caused by salt stress. From this perspective, this study aimed to evaluate the impact of different combinations of nitrogen, phosphorus and potassium fertilization on the antioxidant activity and accumulation of organic and inorganic solutes in West Indian cherry leaves, in the second year of production. The experimental design was in randomized blocks, with treatments distributed in a 10 × 2 factorial arrangement corresponding to ten fertilization combinations (FC) of NPK (FC1: 80-100-100%, FC2:100-100-100%, FC3:120-100-100%, FC4:140-100-100%, FC5:100-80-100%, FC6:100-120-100%, FC7:100-140-100%, FC8:100-100-80%, FC9:100-100-120%, and FC10:100-100-140% of the recommendation) and two levels of electrical conductivity of irrigation water (ECw) (0.6 and 4.0 dS m-1), with three replications. The multivariate analysis showed that irrigation with water of different electrical conductivities (0.6 and 4.0 dS m-1) resulted in different responses concerning the enzyme activity, production of organic compounds, and accumulation of inorganic solutes in the leaves. Under irrigation with low salinity water, there was greater accumulation of K+, soluble carbohydrates, and proline, and lower activity of antioxidative enzymes, especially SOD and APX. Under high salinity water, greater enzyme activity and higher concentrations of Na+ and Cl- were observed. The results indicate that the response of West Indian cherry to salinity was more towards redox homeostasis than osmotic homeostasis through the accumulation of compatible solutes. Fertilization combination FC5 (100-80-100% corresponding to 200, 24 and 80 g plant-1 of NPK) modulates the enzyme activity of SOD and APX attenuating the impacts of salinity, being an efficient combination to preserve redox homeostasis in West Indian cherry plants grown under salt stress.

Compatible solutes determine the heat resistance of conidia

BackgroundAsexually developed fungal spores (conidia) are key for the massive proliferation and dispersal of filamentous fungi. Germination of conidia and subsequent formation of a mycelium network give rise to many societal problems related to human and animal fungal diseases, post-harvest food spoilage, loss of harvest caused by plant-pathogenic fungi and moulding of buildings. Conidia are highly stress resistant compared to the vegetative mycelium and therefore even more difficult to tackle.ResultsIn this study, complementary approaches are used to show that accumulation of mannitol and trehalose as the main compatible solutes during spore maturation is a key factor for heat resistance of conidia. Compatible solute concentrations increase during conidia maturation, correlating with increased heat resistance of mature conidia. This maturation only occurs when conidia are attached to the conidiophore. Moreover, conidia of a mutant Aspergillus niger strain, constructed by deleting genes involved in mannitol and trehalose synthesis and consequently containing low concentrations of these compatible solutes, exhibit a sixteen orders of magnitude more sensitive heat shock phenotype compared to wild-type conidia. Cultivation at elevated temperature results in adaptation of conidia with increased heat resistance. Transcriptomic and proteomic analyses revealed two putative heat shock proteins to be upregulated under these conditions. However, conidia of knock-out strains lacking these putative heat shock proteins did not show a reduced heat resistance.ConclusionsHeat stress resistance of fungal conidia is mainly determined by the compatible solute composition established during conidia maturation. To prevent heat resistant fungal spore contaminants, food processing protocols should consider environmental conditions stimulating compatible solute accumulation and potentially use compatible solute biosynthesis as a novel food preservation target.

Exogenous 5-Aminolevulinic Acid Promotes Osmotic Stress Tolerance of Walnuts by Modulating Photosynthesis, Osmotic Adjustment and Antioxidant Systems

The walnut (Juglans regia L.) is an important economic tree worldwide, often cultivated in arid and semiarid regions. Improving the drought tolerance is of significance for walnut growth, production, and economic effectiveness. 5-Aminolevulinic acid (ALA) is a novel plant growth regulator which raises plant tolerance to various stressful conditions. Here, foliage application of ALA was carried out to uncover its effect on walnuts under polyethylene glycol (PEG) 6000-stimulated osmotic stress. Our results displayed that exogenous ALA greatly promoted the chlorophyll content, photochemical activities, and gas exchange in walnuts under osmotic stress. ALA led to a considerable accumulation of compatible osmotic solutes, enabling walnuts to maintain osmotic equilibrium against drought stress. Furthermore, ALA alleviated the reactive oxygen species (ROS) damages on osmotically stressed walnuts through enhancing the antioxidant enzyme activities, as well as decreasing the ROS and malondialdehyde (MDA) content. The relative water content (RWC) in the ALA-treated leaves was higher than that of PEG-stressed, while the RWC in the substrate of ALA treatment was significantly lower than that of the PEG-stressed, further suggesting that ALA promotes plant water uptake from the substrate under osmotic stress. These demonstrate that ALA improves the photosynthesis, osmotic adjustment, antioxidant systems and, consequently, the walnuts’ drought tolerance.

Transcriptomic analysis reveals novel desiccation tolerance mechanism of Cronobacter based on type VI secretion system inhibition

Cronobacter malonaticus (C. malonaticus) is a food-borne pathogen inducing severe infections both in infants and adults, and it could survive in dry powdered infant formula (PIF) for a long time, implying its strong tolerance to desiccation. However, the thorough molecular mechanism of resistance to desiccation remains elusive. When C. malonaticus was exposed to desiccation conditions (7, 15, and 30 d), transcriptomic analysis provided a universal adaptation strategy to withstand desiccation with the increased compatible solutes accumulation, activated stress resistance-related regulators, suppressed protein export and bacterial secretion system, and reduced other unessential survival functions including adhesion, invasion, virulence, and flagellar motility. Importantly, type VI secretion system (T6SS) genes exhibited significantly downregulated expressions, as well as markedly increased survival and viability of their mutants after desiccation treatment, revealing the negative regulation of T6SS in desiccation tolerance. Meanwhile, the decreased expressions of T6SS structure genes in other six species further confirmed the vital role of T6SS in desiccation tolerance of Cronobacter spp. Thus, our studies present a novel hypothesis of desiccation resistance in Cronobacter based on type VI secretion system inhibition, causing the reduction of macromolecule secretion such as effectors and hyperosmolality development within the cytomembrane, which allow Cronobacter to survive in desiccation.

Salicylic acid and trehalose attenuate salt toxicity in Brassica juncea L. by activating the stress defense mechanism

Two significant soil degradation processes that pose a hazard to our ecosystems are soil salinization and sodification. The information on potential of salicylic acid (SA) and trehalose (Tre) to induce abiotic stress signaling and triggers physio-biochemical responses in crop plants is limited. Therefore, the present study was aimed to investigate the efficacy of 5 μM SA and/or 10 mM Tre in improving the growth, photosynthesis, ion homeostasis, nutrient acquisition, antioxidant defense system and yield of mustard plants growing under sodium chloride (NaCl) stress (0, 50, 100 and 150 mM NaCl). The data showed that increasing NaCl stress concentration decreased growth, photosynthesis, membrane permeability, ion homeostasis and yield in a dose-dependent manner while increasing considerably enzymatic antioxidant enzyme activities, compatible solute accumulation, sodium ion and oxidative stress biomarkers linearly with increasing NaCl stress concentration. The spray of SA, Tre, and SA + Tre played diversified roles in enhancing NaCl stress tolerance in mustard at morpho-physiological and biochemical levels. The combined SA + Tre application proved best and completely neutralized the NaCl stress-induced suppression in growth, photosynthesis, ion homeostasis, nutrient acquisition and yield by significantly enhancing the activities of enzymatic antioxidants, compatible solutes accumulation, water status and membrane permeability, while reducing considerably osmotic stress, reactive oxygen species generation, lipid peroxidation, cell death and sodium uptake in mustard. The SA + Tre application enhanced relative water content by 23%, net photosynthetic rate by 48%, superoxide dismutase activity by 51% and seed yield per plant by 64%, while decreased superoxide anion content by 26%, sodium ion content by 36% and malondialdehyde content by 25% over 0 mM NaCl treatment. Our findings indicate that the co-application of SA + Tre can be a suitable approach to palliate the ill effect of NaCl stress in mustard plants.

On the bioprotective effects of 3-hydroxybutyrate: Thermodynamic study of binary 3HB-water systems

Microorganisms must face various inconvenient conditions; therefore, they developed several approaches for protection. Such a strategy also involves the accumulation of compatible solutes, also called osmolytes. It has been proved that the monomer unit 3-hydroxybutyrate (3HB), which is present in sufficient concentration in poly(3-hydroxybutyrate) (PHB)-accumulating cells, serves as a chemical chaperone protecting enzymes against heat and oxidative stress and as a cryoprotectant for enzymes, bacterial cells, and yeast. The stress robustness of the cells is also strongly dependent on the behavior and state of intracellular water, especially during stress exposure. For a better understanding of the protective mechanism and effect of strongly hydrophilic 3HB in solutions at a wide range of temperatures, a binary phase diagram of system sodium 3HB (Na3HB)-water in equilibrium and the state diagrams showing the glass transitions in the system were constructed. To investigate the activity of water in various compositions of the Na3HB/water system, three experimental techniques have been used (dynamic water sorption analysis, water activity measurements, and sorption calorimetry). First, Na3HB proved its hydrophilic nature, which is very comparable with known compatible solutes (trehalose). Results of differential scanning calorimetry demonstrated that Na3HB is also highly effective in depressing the freezing point and generating a large amount of nonfrozen water (1.35 g of water per gram of Na3HB). Therefore, Na3HB represents a very effective cryoprotectant that can be widely used for numerous applications.

Effect of Salicylic Acid on Physicochemical Parameters and Accumulation of Compatible Solutes in Three Genotypes of Cowpea under Arsenic Stress

Cowpea is a legume widely cultivated across the world but its growth may be limited by contamination with non-essential elements among which are arsenic. The present study was designed to examine the effect of salicylic acid on physicochemical parameters and accumulation of compatible solutes in cowpea under arsenic stress.

A genomic approach to analyze the cold adaptation of yeasts isolated from Italian Alps.

Microorganisms including yeasts are responsible for mineralization of organic matter in cold regions, and their characterization is critical to elucidate the ecology of such environments on Earth. Strategies developed by yeasts to survive in cold environments have been increasingly studied in the last years and applied to different biotechnological applications, but their knowledge is still limited. Microbial adaptations to cold include the synthesis of cryoprotective compounds, as well as the presence of a high number of genes encoding the synthesis of proteins/enzymes characterized by a reduced proline content and highly flexible and large catalytic active sites. This study is a comparative genomic study on the adaptations of yeasts isolated from the Italian Alps, considering their growth kinetics. The optimal temperature for growth (OTG), growth rate (Gr), and draft genome sizes considerably varied (OTG, 10°C-20°C; Gr, 0.071-0.0726; genomes, 20.7-21.5 Mpb; %GC, 50.9-61.5). A direct relationship was observed between calculated protein flexibilities and OTG, but not for Gr. Putative genes encoding for cold stress response were found, as well as high numbers of genes encoding for general, oxidative, and osmotic stresses. The cold response genes found in the studied yeasts play roles in cell membrane adaptation, compatible solute accumulation, RNA structure changes, and protein folding, i.e., dihydrolipoamide dehydrogenase, glycogen synthase, omega-6 fatty acid, stearoyl-CoA desaturase, ATP-dependent RNA helicase, and elongation of very-long-chain fatty acids. A redundancy for several putative genes was found, higher for P-loop containing nucleoside triphosphate hydrolase, alpha/beta hydrolase, armadillo repeat-containing proteins, and the major facilitator superfamily protein. Hundreds of thousands of small open reading frames (SmORFs) were found in all studied yeasts, especially in Phenoliferia glacialis. Gene clusters encoding for the synthesis of secondary metabolites such as terpene, non-ribosomal peptide, and type III polyketide were predicted in four, three, and two studied yeasts, respectively.

Exogenous aspartic acid alleviates salt stress-induced decline in growth by enhancing antioxidants and compatible solutes while reducing reactive oxygen species in wheat.

Salinity is the primary environmental stress that adversely affects plants' growth and productivity in many areas of the world. Published research validated the role of aspartic acid in improving plant tolerance against salinity stress. Therefore, in the present work, factorial pot trials in a completely randomized design were conducted to examine the potential role of exogenous application of aspartic acid (Asp) in increasing the tolerance of wheat (Triticum aestivum L.) plants against salt stress. Wheat plants were sown with different levels of salinity (0, 30, or 60 mM NaCl) and treated with three levels of exogenous application of foliar spray of aspartic acid (Asp) (0, 0.4, 0.6, or 0.8 mM). Results of the study indicated that salinity stress decreased growth attributes like shoot length, leaf area, and shoot biomass along with photosynthesis pigments and endogenous indole acetic acid. NaCl stress reduced the total content of carbohydrates, flavonoid, beta carotene, lycopene, and free radical scavenging activity (DPPH%). However, Asp application enhanced photosynthetic pigments and endogenous indole acetic acid, consequently improving plant leaf area, leading to higher biomass dry weight either under salt-stressed or non-stressed plants. Exogenous application of Asp, up-regulate the antioxidant system viz. antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and nitrate reductase), and non-enzymatic antioxidants (ascorbate, glutathione, total phenolic content, total flavonoid content, beta carotene, lycopene) contents resulted in declined in reactive oxygen species (ROS). The decreased ROS in Asp-treated plants resulted in reduced hydrogen peroxide, lipid peroxidation (MDA), and aldehyde under salt or non-salt stress conditions. Furthermore, Asp foliar application increased compatible solute accumulation (amino acids, proline, total soluble sugar, and total carbohydrates) and increased radical scavenging activity of DPPH and enzymatic ABTS. Results revealed that the quadratic regression model explained 100% of the shoot dry weight (SDW) yield variation. With an increase in Asp application level by 1.0 mM, the SDW was projected to upsurge through 956 mg/plant. In the quadratic curve model, if Asp is applied at a level of 0.95 mM, the SDW is probably 2.13 g plant-1. This study concluded that the exogenous application of aspartic acid mitigated the adverse effect of salt stress damage on wheat plants and provided economic benefits.

Synthesizing glycine betaine via choline oxidation pathway as an osmoprotectant strategy in Haloferacales

The accumulation of organic compatible solutes, such as glycine betaine, is one of the osmoprotective strategies used by halophilic archaea to adapt to high salinity. The uptake of glycine betaine from the external environment using various transporters has been widely studied in different halophilic archaea. However, the de novo biosynthesis of glycine betaine and its distribution in halophilic archaea remain unclear. In this study, an extremely halophilic archaea strain, named Halorubrum sp. 2020YC2 and previously isolated from a salt-lake sample, was identified with complete choline oxidation pathway genes. Halorubrum sp. 2020YC2 could synthesize and accumulate 1.56–4.25 μmol per mg of protein of glycine betaine in a defined medium, with its content increasing along with increasing salinity. The intracellular content of glycine betaine remained relatively stable at different salinities when another exogenous solute such as trehalose was provided. The metabolic profile and transcriptional results strongly suggested that the intracellular glycine betaine was derived from serine, which came from the glycolytic intermediate 3-phosphoglycerate when glucose was used as the sole carbon source. Out of 205 available genomes of halophilic archaea, genes encoding the choline oxidation pathway were identified in 30 genomes, and more than half of the strains belonging to order Haloferacales contained the choline oxidation pathway. Phylogenetic analysis further indicated that this pathway evolved from halophilic Proteobacteria, and its absence in some genera indicated a possible gene loss event during evolution. The analysis of reported culture data of halophilic archaea strains eventually demonstrated that the presence of the choline oxidation pathway had no significant effects on the adaptation of Haloferacales to high salinity habitats. Therefore, the de novo biosynthesis of glycine betaine via the choline oxidation pathway could be an auxiliary osmoprotective strategy in halophilic archaea.

Water retention and metabolic changes improve desiccation tolerance in Barbacenia graminifolia (Velloziaceae).

Barbacenia graminifolia is a Velloziaceae species endemic to the campos rupestres in Serra do Cipó, Minas Gerais state (Brazil). This biome is characterised by high irradiance and limited water conditions. Unlike other resurrection plants, B. graminifolia can maintain a high hydric status (>80%) after 28 days of water suppression before desiccation. We investigated the physiological and metabolic mechanisms associated with structural changes that allow B. graminifolia to maintain hydration under a prolonged water deficit and to recover after desiccation. After 30 days of water deficit, desiccated plants exhibited chlorophyll degradation, a 178.4% and 193.7% increase in total carotenoids and MDA, respectively, and twice the CAT and APX activity compared to hydrated plants. The metabolite profile showed increased amino acids, carbohydrates, saturated fatty acids and benzoic acids during dehydration, while trichloroacetic acid cycle acids were higher in hydrated and rehydrated plants. Anatomical and ultrastructural data corroborated the physiological and metabolic changes and revealed the presence of mucilaginous cells with high water retention capacity. Our data indicated that combined strategies of assimilatory metabolism shutdown, accumulation of compatible solutes and antioxidant compounds, increase in hydrophilic molecules, changes in the composition of membrane lipids and remodelling of cell organelles conditioned the efficiency of B. graminifolia in delaying water loss, tolerating further desiccation and quickly recovering after rehydration. These attributes evidence that this species is well adapted to cope with adverse environmental conditions, mainly directing the metabolism to an efficient antioxidant response and improving its capacity to retain water during the dry season.

ProX from marine Synechococcus spp. show a sole preference for glycine-betaine with differential affinity between ecotypes.

Osmotic stress, caused by high or fluctuating salt concentrations, is a crucial abiotic factor affecting microbial growth in aquatic habitats. Many organisms utilize common responses to osmotic stress, generally requiring active extrusion of toxic inorganic ions and accumulation of compatible solutes to protect cellular machinery. We heterologously expressed and purified predicted osmoprotectant, proline/glycine betaine-binding proteins (ProX) from two phylogenetically distinct Synechococcus spp. MITS9220 and WH8102. Homologues of this protein are conserved only among Prochlorococcus LLIV and Synechococcus clade I, III and CRD1 strains. Our biophysical characterization show Synechococcus ProX exists as a dimer, with specificity solely for glycine betaine but not to other osmoprotectants tested. We discovered that MITS9220_ProX has a 10-fold higher affinity to glycine betaine than WH8102_ProX, which is further elevated (24-fold) in high salt conditions. The stronger affinity and effect of ionic strength on MITS9220_ProX glycine betaine binding but not on WH8102_ProX alludes to a novel regulatory mechanism, providing critical functional insights into the phylogenetic divergence of picocyanobacterial ProX proteins that may be necessary for their ecological success.

Physiological responses of the xero‐halophyte Salsola drummondii to seasonal alterations of environmental conditions in a salt desert

AbstractGlobal climate changes of rising temperature are threatening food security by causing desertification in many arid and semi‐arid regions. Morpho‐physiological adaptations in xero‐halophytes under extreme conditions such as high temperature, drought, and salinity could provide information for producing more resilient cash crops. This study examined seasonal variations in growth, photosynthesis, antioxidant defense, water, and ion relations of the xero‐halophyte Salsola drummondii in its natural habitat. The resistance of Sa. drummondii to seasonal alterations was related to plant interactions with soil and atmosphere. Leaf succulence, organic weight, photosynthesis, water use efficiency, compatible solutes, and antioxidant enzyme activities correlated well with precipitation, soil moisture, and electrical conductivity. Photosynthesis and stomatal conductance increased during the monsoon period with low vapor pressure deficit and moderate temperature. Sa. drummondii responded to reduced water availability by decreasing leaf succulence, xylem pressure, and osmotic potentials like a typical C4 plant displaying water and energy‐saving seasonal adjustment. C4 mode of photosynthesis, higher antioxidant enzyme activities, and accumulation of compatible solutes could be involved in protection against photo‐oxidative stress. This study highlights the importance of physiological and biochemical adaptations of Sa. drummondii to seasonal alterations in a salt desert and could serve as a model for future crop development in arid‐saline habitats.

Zn alleviated salt toxicity in Solanum lycopersicum L. seedlings by reducing Na+ transfer, improving gas exchange, defense system and Zn contents

Soil secondary salinization is a serious menace that has significant influence on the sustainability of agriculture and threatens food security around the world. Zinc (Zn) as an essential plant nutrient associated with many physio-biochemical processes in plants and improve resistance against various abiotic stresses. The role of Zn in acclimation of Solanum lycopersicum L. challenged with salt stress is miserly understood. A hydroponic study was performed with two tomato varieties (Riogrande and Sungold) exposed to the salinity stress (0 mM and 160 mM NaCl) under two Zn concentrations (15 μM and 30 μM ZnSO4). The results revealed that salt stress exerted strongly negative impacts on root and shoot length, fresh and dry biomass, plant water relations, membrane stability, chlorophyll contents, Na+/K+ ratio along with inferior gas exchange attributes and activities of antioxidant enzymes. Moreover, Riogrande was found to be more resistant to salinity stress than Sungold. However, Zn supply significantly alleviated the hazardous effects of salinity by altering compatible solutes accumulation, photosynthetic activity, water relation, soluble sugar contents and providing antioxidant defense against salt stress. The salinity + Zn2 treatment more obviously enhanced RWC (19.0%), MSI (30.8%), SPAD value (17.8%), and activities of SOD (31.7%), POD (28.5%), APX (64.5%) and CAT (23.3%) in Riogrande than Sungold, compared with the corresponding salinity treatment alone. In addition, salinity + Zn2 treatment significantly (P > 0.05) ameliorated salinity stress due to the depreciation in Na+/K+ ratio by 63.3% and 40.8%, Na+ ion relocation from root to shoot by 10.4% and 6.4%, and thereby significantly reduced Na+ ion accumulation by 47.4% and 16.3% in the leaves of Riogrande and Sungold respectively, compared to the salinity treatment alone. Therefore, it was obvious that 30 μM Zn concentration was more effective to induce resistance against salinity stress than 15 μM Zn concentration. Conclusively, it can be reported that exogenous Zn application helps tomato plant to combat adverse saline conditions by modulating photosynthetic and antioxidant capacity along with reduced Na+ uptake at the root surface of tomato plant.

Insect cross-tolerance to freezing and drought stress: role of metabolic rearrangement.

The accumulation of trehalose has been suggested as a mechanism underlying insect cross-tolerance to cold/freezing and drought. Here we show that exposing diapausing larvae of the drosophilid fly, Chymomyza costata to dry conditions significantly stimulates their freeze tolerance. It does not, however, improve their tolerance to desiccation, nor does it significantly affect trehalose concentrations. Next, we use metabolomics to compare the complex alterations to intermediary metabolism pathways in response to three environmental factors with different ecological meanings: environmental drought (an environmental stressor causing mortality), decreasing ambient temperatures (an acclimation stimulus for improvement of cold hardiness), and short days (an environmental signal inducing diapause). We show that all three factors trigger qualitatively similar metabolic rearrangement and a similar phenotypic outcome-improved larval freeze tolerance. The similarities in metabolic response include (but are not restricted to) the accumulation of typical compatible solutes and the accumulation of energy-rich molecules (phosphagens). Based on these results, we suggest that transition to metabolic suppression (a state in which chemical energy demand is relatively low but need for stabilization of macromolecules is high) represents a common axis of metabolic pathway reorganization towards accumulation of non-toxic cytoprotective compounds, which in turn stimulates larval freeze tolerance.

Utilization and accumulation of compatible solutes in Halomonas pacifica: a species of moderately halophilic bacteria isolated from a saline lake in South Libya.

When grown in high salt concentrations, halophilic bacteria often accumulate compatible solutes, which have major applications in biotechnology because they stabilize cells and proteins. Four Gram-negative bacterial strains, belonging to the family Halomonadaceae, were isolated from Qaberoun and Um-Alma lakes in South Libya using high-salinity medium. The strains were identified using 16S rRNA gene sequencing as belonging to Halomonas pacifica (strain ABQ1), Halomonas venusta (ABQ2), Halomonas elongata (ABU1) and Halomonas salifodinae (ABU2). H. pacifica ABQ1 is a moderate halophile (salinity range 0.05 to 2.5 M NaCl), with a broad tolerance to pH (7 to 9) and temperature (25–37 °C). Addition of the compatible solutes glycine betaine (betaine) and ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) to the medium had a positive effect on growth of H. pacifica at 2 M NaCl. In rich LB medium, betaine was the major compatible solute accumulated, with ectoine only being accumulated at salinities in excess of 1 M NaCl. In minimal M9 medium, betaine was not produced, but increasing amounts of ectoine were synthesized with increasing salinity, and hydroxyectoine [(4S,5S)−5-hydroxy-2-methyl-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid] was also synthesized when the cells were grown in very high salt. We have thus identified H. pacifica as a producer of ectoine and hydroxyectoine, with more being produced at higher salinities. As industrial demand for these compatible solutes continues to increase, this system has biotechnological potential.

Physiological reaction and chemical composition of Stachys schtschegleevii Sosn. essential oil under water deficit.

Stachys schtschegleevii Sosn. is an endemic medicinal plant belonging to the Lamiaceae family and mainly grown in North-western Iran. Drought stress is an important factor in reducing the yield of medicinal herbs. Water-stress tolerance involves subtle changes in cellular biochemistry. It appears to be the result of the accumulation of compatible solutes and of chemical compositions that can be rapidly induced by osmotic stress. For this purpose, the effect of different irrigation regimes (well-watered and irrigation after depletion of 40% and 70% of field capacity (FC)) were studied in S. schtschegleevii. The experiment was conducted in a randomized complete block design in three replications. The results showed that water-deficit had negative effects on shoot dry matter, relative water content, and photosynthetic pigments of the exposed plants. The essential oil (EO) content under water-deficit had an increasing trend. Water-deficit significantly increased total phenol content, proline, H2O2, and malondialdehyde contents. Linalool, β-pinene oxide, α-campholenal and germacrene-D were the major compounds of essential oils (EOs) affected by water-deficit stress. Finally, although water deficiency reduces the shoot dry matter yield of the S. schtschegleevii, the accumulation of EO increased as a plant response to water-deficit stress.