Osmotic Solutes Research Articles

Variation in Populus euphratica foliar carbon isotope composition and osmotic solute for different groundwater depths in an arid region of China.

Water use efficiency (WUE) is an important trait associated with plant acclimation caused by water deficits, and δ13C is a good surrogate of WUE under conditions of water deficits. Water deficiency also enhances the accumulation of compatible solutes in the leaves. In this study, variations in foliar δ(13)C values and main osmotic solutes were investigated. Those included total soluble sugar (TSS), sucrose, free proline, glycine betaine (GB), and inorganic ionic (K+, Ca2+, and Cl-) content of Populus euphratica for different groundwater depths in a Ejina desert riparian forest, China. Results indicated that foliar δ13C values in the P. euphratica for different groundwater depths ranged from -29.14±0.06 to -25.84±0.04 ‰. Foliar δ13C signatures became richer as groundwater levels declined. TSS, sucrose, free proline, GB, and K+ were accumulated in P. euphratica foliage with developing plant growth and increasing groundwater depth. Ca2+ and Cl- content increased under stronger P. euphratica transpiration rates for shallower groundwater depths (1-2.5 m) and decreased for deeper groundwater depths (greater than 3.0 m). Moreover, correlations between δ13C, osmotic solutes, and groundwater depths showed that the primary osmotic solutes were TSS, sucrose, proline, GB, and K+. Correlations also showed that δ13C was not only a useful measure for P. euphratica-integrated WUE but also could be used as an indicator reflecting some physiological osmotic indexes.

Genotypic variability in physiological, biomass and yield response to drought stressin pigeonpea.

Three pigeonpea (Cajanus cajan L. Millsp.) genotypes- GT-1, AKP-1 and PRG-158 with varying crop duration, growth habit and flowering pattern were evaluated for variability in their response for drought stress. Drought stress was imposed at initiation of flowering and the observations on biomass and seed yield parameters were recorded at harvest. The magnitude of response of individual component to drought stress was found to be genotype specific. Drought stress significantly decreased photosynthetic rate (PN), transpiration rate (Tr) and relative water content (RWC) in all the genotypes, however the magnitude of reduction differed with genotype. With drought stress, the reduction of PN was highest in GT-1 while reduction in Tr was highest inPRG-158. The genotype AKP-1, accumulated significantly higher concentrations of osmotic solutes especially proline under water deficit stress, this facilitated it to maintain higher relative water content (RWC) and lower malondialdehyde (MDA) content as compared to other genotypes. Drought stress also impacted biomass production and their partitioning to vegetative and reproductive components at harvest. There was significant variability between the genotypes for seed yield under drought stress while it was non-significant under well-watered condition. Drought stress enhanced flower drop and decreased flower to pod conversion resulting in reduced pod number and seed number in PRG-158 and GT-1. The genotype AKP-1 recorded superior performance for seed yield under stress environment due to its ability in maintaining pod and seed number as well as improved test weight (100 seed weight). Under drought stress, significant positive association of seed yield with proline, seed number, pod number and test weight clearly indicating their role in drought tolerance.

Osmoregulation-mediated differential responses of field-grown fennel genotypes to drought

This study was aimed at examination of physiological and agronomic responses of fennel (Foeniculum vulgare Mill.) to water deficit. Twelve fennel genotypes namely ‘Kashan’, ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’, ‘Mashhad’, ‘Ardabil’, ‘Bushehr’, ‘Avicenna’, ‘Isfahan’, and ‘Yazd’ were subjected to four levels of irrigation (irrigation after 35%, 55%, 75%, and 85% depletion of available soil water) in a field study in two years. Leaf water potential, relative water content (RWC), proline, total soluble sugars, chlorophyll a (Chl a), b (Chl b), total (Chl a+b), a/b (Chl a/b) along with dry mass (DM), seed yield and its attributes and seed essential oil content were measured. Water deprivation left significant effects on all characteristics, i.e. in contrast to seed essential oil content and harvest index, the rest of the attributes were decreased significantly with drought intensification. Varietal differences in response to drought were meaningful for most of the traits; i.e. genotypic variations for DM, grain yield and stress susceptibility index (SSI) were consistent with differences among the genotypes in physiological traits such as leaf water potential, RWC, proline, soluble sugars and chl content. Genotypes were discriminated according to their response to drought and SSI. Drought tolerant genotypes (‘Yazd’, ‘Kerman, ‘Mashhad’ and ‘Shiraz’) exhibited a greater capacity for accumulation of osmotic solutes associated with higher leaf water potential and RWC, compared to drought sensitive genotypes (‘Ardabil’, ‘Avicenna’, ‘Hamadan’ and ‘Birjand’). From our findings, fennel could be appreciated as a promising species in potentiating alternative industrial-medicinal crops in the face of the eminent challenge of water scarcity in arid and semi-arid climatic regions.

A vesicle-trafficking protein commandeers Kv channel voltage sensors for voltage-dependent secretion.

Growth in plants depends on ion transport for osmotic solute uptake and secretory membrane trafficking to deliver material for wall remodelling and cell expansion. The coordination of these processes lies at the heart of the question, unresolved for more than a century, of how plants regulate cell volume and turgor. Here we report that the SNARE protein SYP121 (SYR1/PEN1), which mediates vesicle fusion at the Arabidopsis plasma membrane, binds the voltage sensor domains (VSDs) of K(+) channels to confer a voltage dependence on secretory traffic in parallel with K(+) uptake. VSD binding enhances secretion in vivo subject to voltage, and mutations affecting VSD conformation alter binding and secretion in parallel with channel gating, net K(+) concentration, osmotic content and growth. These results demonstrate a new and unexpected mechanism for secretory control, in which a subset of plant SNAREs commandeer K(+) channel VSDs to coordinate membrane trafficking with K(+) uptake for growth.

Influence of Amino Acids Mixture Application on Some Biochemical Aspects, Antioxidant Enzymes and Endogenous Polyamines of Vicia faba Plant Grown under Seawater Salinity Stress

Irrigation with diluted seawater can act as an alternate water resource and thus plays an important role in saving fresh water resources as well as promoting agriculture. Two pot experiments were conducted to elucidate the effect of foliar application with amino acid mixture (0, 500, 1000 and 1500 mg/L as AA0, AA1, AA2 and AA3, respectively) on faba bean plants irrigated with different seawater levels (0.23, 3.13 and 6.25 dS/m as S0, S1 and S2, respectively) regarding some physiological and biochemical aspects, lipid peroxidation, antioxidant enzymes and endogenous polyamines of faba bean (Vicia faba L.) plants. Irrigation of faba bean plants with different levels of seawater caused significant increases in osmotic solutes (total soluble sugars, free amino acids and proline), phenol content, lipid peroxidation, some antioxidant enzymes (IAA-oxidase, polyphenol oxidase; PPO, peroxidase; POX, super oxide dismutase; SOD, Catalase; CAT, ascorbate peroxidase; APX) and endogenous spermidine and spermine compared with control plants. At the same time, indole acetic acid (IAA), putrescine and total endogenous polyamine contents were decreased in response to different seawater levels. Under salt stress, foliar application with different concentrations stimulated the salt tolerance of faba bean plants via improving osmotic solutes (total soluble sugars, free amino acids and proline), phenolic content, IAA and endogenous polyamines, whereas lipid peroxidation and antioxidant enzymes (PPO, POX, SOD, CAT and APX) were significantly decreased. These results emphasize the potential of application of amino acids mixture in sustainable agriculture in arid and semiarid regions. In addition, it opens up new research lines aimed at obtaining maximum benefit from the amino acids under salinity or other osmotic stress conditions.

The effect of lichen-dominated biological soil crusts on growth and physiological characteristics of three plant species in a temperate desert of northwest China.

Biocrusts (biological soil crusts) cover open spaces between vascular plants in most arid and semi-arid areas. Information on effects of biocrusts on seedling growth is controversial, and there is little information on their effects on plant growth and physiology. We examined impacts of biocrusts on growth and physiological characteristics of three habitat-typical plants, Erodium oxyrhynchum, Alyssum linifolium and Hyalea pulchella, growing in the Gurbantunggut Desert, northwest China. The influence of biocrusts on plant biomass, leaf area, leaf relative water content, photosynthesis, maximum quantum efficiency of PSII (F(v)/F(m)), chlorophyll, osmotic solutes (soluble sugars, protein, proline) and antioxidant enzymes (superoxide dismutase, catalase, peroxidase) was investigated on sites with or without biocrust cover. Biomass, leaf area, leaf water content, photosynthesis, F(v)/F(m) and chlorophyll content in crusted soils were higher than in uncrusted soils during early growth and lower later in the growth period. Soluble sugars, proline and antioxidant enzyme activity were always higher in crusted than in uncrusted soils, while soluble protein content was always lower. These findings indicate that biocrusts have different effects on these three ephemeral species during growth in this desert, primarily via effects on soil moisture, and possibly on soil nutrients. The influence of biocrusts changes during plant development: in early plant growth, biocrusts had either positive or no effect on growth and physiological parameters. However, biocrusts tended to negatively influence plants during later growth. Our results provide insights to explain why previous studies have found different effects of biocrusts on vascular plant growth.

A homolog of Class IV HD-Zip transcription factors, EsHdzip1, confers drought resistance in tobacco via enhanced the capacity of water conserving and absorbing

Previous studies have indicated that homeodomain-leucine zipper (HD-Zip) transcription factors play important roles during abiotic stress, but there is no information on the functions of HD-Zip genes in a new model plant Eutrema salsugineum for studying plant abiotic stress tolerance. Here, EsHdzip1 (GenBank No. XM_006390503) belonging to the Class IV subgroup of HD-Zip transcription factor family was isolated from E. salsugineum and characterized for its physiological roles under drought stress conditions. Transgenic tobacco plants overexpressing EsHdzip1 exhibited increased drought resistance with promoted root growth and reduction of water loss. Furthermore, these transgenic plants had lower ion leakage (IL), malondialdehyde (MDA), and reactive oxygen species (ROS) accumulation, but higher content of osmotic solutes (proline and total soluble sugars) and activities of antioxidant enzymes including superoxide dismutase (SOD) and ascorbate peroxidase (APX) relative to wild-type (WT) plants when subjected to drought stress treatments. The content of abscisic acid (ABA) was also observed to be remarkably higher in the transgenic lines than WT plants under drought stress conditions. In addition, the expression levels of three important stress-related genes (NtP5CS, NtERD10C, and NtLEA5) involved in the osmotic adjustment and water maintenance were significantly higher than WT plants under drought stress conditions. Therefore, we have revealed important roles of the EsHdzip1 gene in response to drought stress, suggesting that this gene has a great potential for improving plant drought tolerance by engineering manipulation.

Are Aquaporins the Missing Transmembrane Osmosensors?

Regulation of cell volume is central to homeostasis. It is assumed to begin with the detection of a change in water potential across the bounding membrane, but it is not clear how this is accomplished. While examples of general osmoreceptors (which sense osmotic pressure in one phase) and stretch-activated ion channels (which require swelling of a cell or organelle) are known, effective volume regulation requires true transmembrane osmosensors (TMOs) which directly detect a water potential difference spanning a membrane. At present, no TMO molecule has been unambiguously identified, and clear evidence for mammalian TMOs is notably lacking. In this paper, we set out a theory of TMOs which requires a water channel spanning the membrane that excludes the major osmotic solutes, responds directly without the need for any other process such as swelling, and signals to other molecules associated with the magnitude of changing osmotic differences. The most likely molecules that are fit for this purpose and which are also ubiquitous in eukaryotic cells are aquaporins (AQPs). We review experimental evidence from several systems which indicates that AQPs are essential elements in regulation and may be functioning as TMOs; i.e. the first step in an osmosensing sequence that signals osmotic imbalance in a cell or organelle. We extend this concept to several systems of current interest in which the cellular involvement of AQPs as simple water channels is puzzling or counter-intuitive. We suggest that, apart from regulatory volume changes in cells, AQPs may also be acting as TMOs in red cells, secretory granules and microorganisms.

Exogenous ascorbic acid mitigates accumulation of abscisic acid, proline and polyamine under osmotic stress in maize leaves

The effects of osmotic stress (polyethylene glycol, PEG 6000) and exogenous ascorbic acid (ASC) on abscisic acid (ABA), some osmolytes (proline and polyamine), and gene expression of polyamine metabolic enzymes arginine decarboxylase (ADC), S-adenosylmethionine decarboxylase (SAMDC) and polyamine oxidase (PAO1) were assessed in the leaves of Zea mays L. seedlings. ASC (0.1 mM) was hydroponically applied to detached maize seedlings. ASC application scavenged endogenous hydrogen peroxide level and ameliorated leaf water status and stomatal conductance under osmotic stress. Lipid peroxidation, ABA and osmolyte accumulation were mitigated by ASC treatment. For osmolytes, the alleviation of polyamine accumulation was more obvious than that of the proline. Therefore, gene expressions of polyamine metabolic enzymes were investigated. Compared to control seedlings, down-regulation of SAMDC and ADC gene expressions were determined in ASC + PEG-applied seedlings while PAO1 gene expression increased. These results indicated that exogenous ASC influenced polyamine metabolism. ASC application under the osmotic stress ameliorated osmotic solute levels and ABA concentration in maize.

Drought stress mitigation by foliar application of salicylic acid and their interactive effects on physiological characteristics of fennel (Foeniculum vulgare Mill.) genotypes

This study was aimed at characterization of physiological responses of fennel to water deficit and exogenous application of salicylic acid (SA). Six fennel genotypes namely ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’, and ‘Yazd’ were subjected to two levels of irrigation (irrigation after 35 and 75 % depletion of available soil water) and three levels of SA (0.0, 0.5, and 1.0 mM). Leaf water potential, relative water content (RWC), proline, total soluble carbohydrates, chlorophyll a (Chl a), b (Chl b), total (Chl a + b), a/b (Chl a/b) and carotenoids contents, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) specific activities along with seed yield per plant and seed essential oil content were measured. Water deprivation left significant effects on all characteristics, i.e., in contrast to the antioxidative enzymes activities and seed essential oil content, the rest of the attributes were decreased significantly with water deficit. Drought-tolerant genotypes (‘Yazd’ and ‘Shiraz’) exhibited higher accumulation of osmotic solutes and carotenoids along with higher leaf water potential, RWC, and antioxidant enzymes activities (CAT, APX, and SOD) than drought sensitive genotypes (‘Hamadan’ and ‘Birjand’). SA affected the activities of antioxidant enzymes and increased water potential, RWC, leaf osmolytes, chlorophyll and carotenoids, and seed essential oil content; the extent of the increases appeared greater when fennel was grown under drought. All the above effects helped the seed yield of fennel genotypes to increase with increase in SA level and led to the conclusion that drought-induced harmful effects on fennel could be alleviated by exogenously applied SA.

Effect of Power Ultrasound and Pulsed Vacuum Treatments on the Dehydration Kinetics, Distribution, and Status of Water in Osmotically Dehydrated Strawberry: a Combined NMR and DSC Study

The effect of power ultrasound and pulsed vacuum (PV) treatments on the dehydration kinetics and the status of water during osmotic dehydration of strawberries was investigated. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to determine the spatial distribution and status of water within the cellular and intercellular spaces. Differential scanning calorimetry (DSC) was used to determine the freezing point depression and the amount of frozen water. Osmotic treatment was performed by immersing the samples in 25 and 50 % (w/w) sucrose solutions at 40 °C for 3 h. Water loss and solid gain of strawberry samples were measured and the data were fitted by Peleg’s model. The Peleg’s model fitted the experimental water loss and solid gain kinetics data well (R 2 > 0.98). At a given sucrose concentration, the highest water loss and the highest decrease in firmness occurred while using ultrasound treatment, while the highest solid gain and the highest firmness values were achieved by pulsed vacuum treatment. LF-NMR signals were able to quantify the effect of water-osmotic solute exchange on the cell compartments (vacuole, cytoplasm plus intercellular space, and cell wall). The LF-NMR data showed that the relative space occupied by the vacuole decreased and the relative space occupied by the cytoplasm and intercellular space were increased due to these osmotic treatments. MRI results indicated that a bright “water strip” appeared in the periphery of all the osmotically dehydrated samples. DSC results showed that the decrease in water content and the increase in the osmotic solutes depressed the initial freezing point and the freezable water content in osmotically dehydrated strawberry.

ABSTRACT 229

Background and aims: Controlled hypernatremia can play a role in the management of intracranial hypertension, and can be accomplished with CRRT using hypernatremic replacement fluids. The ability to predict the therapeutic result of a hypernatremic CRRT prescription can help develop operating parameters. Aims: The aim of this study was to develop a mathematical model of CRRT to predict sodium levels with hypernatremic replacement fluids. Methods: A multiscale mathematical model was developed for the simulation of sodium, citrate and bicarbonate dynamics. This model consists of a finite element analysis model with partial differential equations for fluid and solute handling in the hemofilter coupled to a multi-compartment model based on ordinary differential equations that describes fluid and solute handling in the body. The model incorporates blood and dialysate flow, protein transport and osmotic pressure, solute reflection, and diffusive and convective solute transport as well as distribution, transport and elimination of sodium, citrate, and bicarbonate in body compartments. Approval was waived by the IRB. Results: A 3 year old 23 kg pediatric patient with post-traumatic intracranial hypertension was managed with controlled hypernatremia using CVVHD with sodium concentration in replacement fluid and dialysate of 160 mMol/L. Anticoagulation was 4% trisodium citrate. Serum sodium was monitored every 2 hours. Simulations over the initial 12 hours were run using the same operating conditions. Comparison of recorded and predicted sodium levels revealed good agreement over the simulation period. Conclusions: This multiscale model predicted sodium levels during hypertonic CVVHD with reasonable accuracy, taking into account multiple factors affecting sodium levels.

Experimental values and correlations of some thermal properties of fresh and osmotically dehydrated stone fruits

Nectarines, plums and peaches were dehydrated with osmotic solutions (glucose at 60°Brix or sorbitol at 60°Brix) at temperature of 35°C for scheduled periods (0.5, 1, 2, 4, 6, 8 h). Thermal properties of fresh and osmotically dehydrated fruits were measured by DSC where samples were heated from −40°C to 40°C at a rate of 2°C min−1. In this work, we obtained experimental data on the variation of water content and soluble solids during the osmotic dehydration of nectarines, peaches and plums in solutions of glucose or sorbitol; experimental data for enthalpy of fresh and osmotically dehydrated nectarines, plums and peaches as a function of temperature and type of osmotic solute; correlations for initial freezing temperature of osmotically dehydrated stone fruits as a function of water content and type of dehydrating solute and correlations between heat capacity or enthalpy and temperature for some fresh and osmotically dehydrated stone fruits.

Osmotic dehydration of fruits in food industrial: A review

Osmotic dehydration (OD) is an operation used for the partial removal of water from plant tissues by immersion in a hypertonic solution, sugar and/or salt solution, to reduce the moisture content of foods before actual drying process. Research applications of osmotic dehydration to food processing in technology and in component transfer mechanisms are being carried out in several countries. This technique is a partial dehydration process to give the product a quality improvement over the conventional drying process. Osmotic dehydration is affected by several factors such as osmotic agent, solute concentration, temperature, time, size, and shape and tissue compactness of the material, agitation and solution/sample ratio. The osmotic dehydration step can be done before, during or after the conventional drying process to enhance the mass transfer rate or to shorten the duration of drying time the quality of osmotically dehydrated products is better and shrinkage is considerably lower as compared to products from conventional drying processes. This technique helps to conserve the overall energy relative to other drying procedures. In this review, the mechanism of osmotic dehydration is described. In addition, some factors that affect on mass transfer during osmotic dehydration reviewed. The major objective of this paper is to discuss the advantage of osmotic dehydration in terms of energy reduction.

Comparison of ectoine synthesis regulation in secreting and non-secreting strains of Halomonas

Ectoine is an osmotic pressure compatible solute. It is synthesized by Halomonas and other microorganisms in a hypertonic environment. As a stabilizing agent of cells proteins, nucleic acids and other biological products, ectoine has wide applications. Therefore, an efficient production method for ectoine is in great demand. Ectoine is overproduced by Halomonas salina DSM 5928, an ectoine-secreting strain, in which the synthesis of ectoine is not limited by its intracellular threshold concentration. In order to explain the mechanism of secretion of ectoine, the response to NaCl stress, and the release and uptake kinetics of ectoine were compared between H. salina DSM 5928 and Halomonas elongata DSM 2581, a non-ectoine-secreting strain. Moreover, the ectoine binding protein TeaA from each of these two strains was cloned and expressed, and binding abilities were examined in vitro. The results indicated that H. salina DSM 5928 and H. elongata DSM 2581 respond to NaCl in the medium in different ways. Compared with H. elongata DSM 2581, the amount of ectoine released was higher and the uptake of ectoine under NaCl stress was lower in H. salina DSM 5928. In addition, the binding ability of TeaA to ectoine in H. salina DSM 5928 was also lower. These results reveal the secretion mechanism of ectoine as well as critical regulation and control factors involved in ectoine synthesis.

Osmotic dehydration pretreatment for improving the quality attributes of frozen mango: effects of different osmotic solutes and concentrations on the samples

SummaryThe effect of osmotic dehydration pretreatment on the quality attributes (e.g. colour, hardness, drip loss, vitamin C content and pH) of frozen mango cuboids in different osmotic solutions (sucrose, glucose and maltose) and concentrations (30, 45 and 60% (wt/wt)) was investigated. Results revealed that melting temperature of mango cuboids was affected by both solute type and solid mass fraction. In addition, the dehydrofrozen samples pretreated in maltose had higher quality in vitamin C content (increasing by 23.5–73.0%), colour (colour change reducing by 2.6–39.2%) and drip loss (reducing by 0.7–9.7%) than those pretreated in other osmotic solutions. The cuboids pretreated in glucose displayed higher hardness (increasing by 16.4–36.2%). Based on principal component analysis and group distance, osmotic dehydration in 45% maltose was proposed as the most favourable freezing conditions with the highest sensory score (6.8). The current work indicates osmotic dehydration significantly improves frozen mango quality.

Exogenous hydrogen peroxide increases dry matter production, mineral content and level of osmotic solutes in young maize leaves and alleviates deleterious effects of copper stress.

BackgroundThe effects of exogenously applied H2O2 on growth, water status, the mineral ion content (Na+, K+, Ca2+, Mg2+ and Cu2+), proline, total sugars and soluble proteins were assessed in leaves of maize (Zea mays L.) cultivars, Akpinar and Pegaso exposed to excess copper (0.5 mM). Seedlings were grown in equal-sizes plastic pots and irrigated with Hoagland nutrient solution containing H2O2 or/and copper. Different treatments taken for pot experiments were named as the control (C), H2O2 treatment only (H2O2), excess Cu (Cu) and, Cu stress combined with H2O2 pretreatment (Cu + H2O2).ResultsTreatment of H2O2 caused the increases in growth, water content, mineral concentration, proline, total sugar and soluble protein contents compared to the control groups in the leaves of both cultivars. Yet excess copper caused reductions in the growth, leaf water potential, Na+, K+, Ca+, Mg2+ concentrations and soluble protein levels but increases in proline, total soluble sugars and Cu2+ contents compared to the control group. Dry matter, leaf water potential and mineral content of Cu + H2O2 group revealed a lower decrease than Cu group ones. A higher increase was also observed in proline and total sugar contents of Cu + H2O2 group than Cu group ones in both cultivars.ConclusionsThese data revealed that exogenous H2O2 might increase the dry matter production and the mineral ion distribution in maize seedlings. Moreover, osmotic regulation might be involved in alleviation of copper toxicity of maize leaves by pretreatment of H2O2.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-26) contains supplementary material, which is available to authorized users.

Spontaneous autophoretic motion of isotropic particles

Suspended colloidal particles interacting chemically with a solute can self-propel by autophoretic motion when they are asymmetrically patterned (Janus colloids). Here we demonstrate theoretically that such anisotropy is not necessary for locomotion and that the nonlinear interplay between surface osmotic flows and solute advection can produce spontaneous and self-sustained motion of isotropic particles. Solving the classical autophoretic framework for isotropic particles, we show that, for given material properties, there exists a critical particle size (or Péclet number) above which spontaneous symmetry-breaking and autophoretic motion occur. A hierarchy of instabilities is further identified for quantized critical Péclet numbers.

Thoughts on the “missing link” between saltworks biology and solat salt quality

Although solar salterns worldwide use seawater of identical chemical composition as the raw material for salt production, the size and quality of the halite crystals that precipitate in the crystallizer ponds is highly variable. Biological processes have been implicated to be responsible for the differences observed, but the “missing link” between saltworks biology and solar salt quality has never unequivocally been identified. This paper presents an overview of the different organic chemicals that are formed by the members of the microbial communities in saltern evaporation and crystallizer ponds as osmotic stabilizers as well as different compounds formed during further microbial metabolism of those osmotic solutes. Examination of the in situ concentrations and the possible role of glycerol, glycine betaine, ectoine, dihydroxyacetone, acetate, lactate, and other organic compounds failed to identify one or more compounds that may accumulate at concentrations high enough to significantly modify the formation of sodium chloride crystals in the salterns and to negatively influence the quality of the salt produced.

Glycine betaine is the main organic osmotic solute in a stratified microbial community in a hypersaline evaporitic gypsum crust

We have examined the organic osmotic solutes content within the stratified microbial communities in an evaporitic gypsum crust found in an evaporation pond (~194g/l total dissolved salts) of the salterns of the Israel Salt Company, Eilat. We extracted intracellular solutes from the upper three pigmented layers of the crust: a yellow-orange layer dominated by unicellular cyanobacteria, a green layer with filamentous cyanobacteria, and a layer colored red-purple by purple sulfur bacteria; dense communities of heterotrophic bacteria were present in all layers. The solutes were analyzed by Raman spectroscopy, (1)H and (13)C nuclear magnetic resonance, and HPLC. All layers contained glycine betaine as the only detectable osmotic solute; ectoine and other solutes known to be produced by many halophilic and halotolerant prokaryotes were not found. In this first attempt to assess the osmotic solute content within complex natural communities of halophilic microorganisms, the predominant role of glycine betaine as an osmolyte was established. Most heterotrophic bacteria cannot produce glycine betaine but preferentially use it when it is supplied. Presence of glycine betaine produced by the photoautotrophic members of the community, therefore, may relieve the heterotrophs from the need to synthesize other compounds at a high-energy cost.