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The article offers information on the International Day for the Defense of Mangroves due to the substantial loss of these coastal ecosystems that are highly productive. Topics discussed include shrubs or small trees that grow in saline coastal or brackish waters; salt-tolerant trees, also called halophytes, adapted to life in adverse coastal conditions; great environmental and socioeconomic value of mangroves; and Laguncularia racemosa provide shelter and food for marine fauna.

We have performed an extensive study on the responses to salt stress in four related Limonium halophytes with different geographic distribution patterns, during seed germination and early vegetative growth. The aims of the work were twofold: to establish the basis for the different chorology of these species, and to identify relevantmechanisms of salt tolerance dependent on the control of ion transport and osmolyte accumulation. Seeds were germinated in vitro, in the presence of increasing NaCl concentrations, and subjected to "recovery of germination" tests; germination percentages and velocity were determined to establish the relative tolerance and competitiveness of the four Limonium taxa. Salt treatments were also applied to young plants, by 1-month irrigation with NaCl up to 800 mM; then, growth parameters, levels of monovalent and divalent ions (in roots and leaves), and leaf contents of photosynthetic pigments and common osmolytes were determined in control and stressed plants of the four species. Seed germination is the most salt-sensitive developmental phase in Limonium. The different germination behavior of the investigated species appears to be responsible for their geographical range size: L. narbonense and L. virgatum, widespread throughout the Mediterranean, are the most tolerant and the most competitive at higher soil salinities; the endemic L. santapolense and L. girardianum are the most sensitive and more competitive only at lower salinities. During early vegetative growth, all taxa showed a strong tolerance to salt stress, although slightly higher in L. virgatum and L. santapolense. Salt tolerance is based on the efficient transport of Na+ and Cl- to the leaves and on the accumulation of fructose and proline for osmotic adjustment. Despite some species-specific quantitative differences, the accumulation patterns of the different ions were similar in all species, not explaining differences in tolerance, except for the apparent activation of K+ transport to the leaves at high external salinity, observed only in the most tolerant L. narbonense and L. virgatum. This specific response may be therefore relevant for salt tolerance in Limonium. The ecological implications of these results, which can contribute to a more efficient management of salt marshes conservation/regeneration programs, are also discussed. [ABSTRACT FROM AUTHOR]

Several reports have highlighted that many plant growth-promoting endophytic bacteria (PGPE) can assist their host plants in coping with various biotic and abiotic stresses. However, information about the PGPE colonizing in the halophytes is still scarce. This study was designed to isolate and characterize PGPE from salt-accumulating halophyte Salicornia europaea grown under extreme salinity and to evaluate in vitro the bacterial mechanisms related to plant growth promotion. A total of 105 isolates were obtained from the surface-sterilized roots, stems, and assimilation twigs of S. europaea. Thirty-two isolates were initially selected for their ability to produce 1-aminocyclopropane-1-carboxylate deaminase as well as other properties such as production of indole-3-acetic acid and phosphate-solubilizing activities. The 16S rRNA gene-sequencing analysis revealed that these isolates belong to 13 different genera and 19 bacterial species. For these 32 strains, seed germination and seedling growth in axenically grown S. europaea seedlings at different NaCl concentrations (50-500 mM) were quantified. Five isolates possessing significant stimulation of the host plant growth were obtained. The five isolates were identified as Bacillus endophyticus, Bacillus tequilensis, Planococcus rifietoensis, Variovorax paradoxus, and Arthrobacter agilis. All the five strains could colonize and can be reisolated from the host plant interior tissues. These results demonstrate that habitat-adapted PGPE isolated from halophyte could enhance plant growth under saline stress conditions. [ABSTRACT FROM AUTHOR]

High-throughput sequencing technology was used to reveal the composition and distribution of fungal community structure in the Yellow River Delta under bare land and four kinds of halophyte vegetation ( saline seepweed, Angiospermae, Imperata and Apocynum venetum [ A. venetum]). The results showed that the soil quality continuously improved with the succession of salt vegetation types. The soil fungi richness of mild-salt communities ( Imperata and A. venetum) was relatively higher, with Shannon index values of 5.21 and 5.84, respectively. The soil fungi richness of severe-salt-tolerant communities ( saline seepweed, Angiospermae) was relatively lower, with Shannon index values of 4.64 and 4.66, respectively. The UniFrac metric values ranged from 0.48 to 0.67 when the vegetation was in different succession stages. A total of 60,174 valid sequences were obtained for the five vegetation types, and they were classified into Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota and Mucoromycotina. Ascomycota had the greatest advantage among plant communities of Imperata and A. venetum, as indicated by relative abundances of 2.69 and 69.97 %, respectively. Basidiomycota had the greatest advantage among mild-salt communities of saline seepweed and Angiospermae, with relative abundances of 9.43 and 6.64 %, respectively. Soil physical and chemical properties were correlated with the distribution of the fungi, and Mucor was significantly correlated with soil moisture ( r = 0.985; P < 0.01). Soil quality, salt vegetation and soil fungi were influenced by each other. [ABSTRACT FROM AUTHOR]

Background: Soil salinity affects growth and yield of crop plants. Plants respond to salinity by physiological and biochemical adjustments through a coordinated regulation and expression of a cascade of genes. Recently, halophytes have attracted attention of the biologists to understand their salt adaptation mechanisms. Spartina alterniflora (smooth cordgrass) is a Louisiana native monocot halophyte that can withstand salinity up to double the strength of sea water. To dissect the molecular mechanisms underlying its salinity adaptation, leaf and root transcriptome of S. alterniflora was sequenced using 454/GS-FLX. Results: Altogether, 770,690 high quality reads with an average length 324-bp were assembled de novo into 73,131 contigs (average 577-bp long) with 5.9X sequence coverage. Most unigenes (95 %) annotated to proteins with known functions, and had more than 90 % similarity to rice genes. About 28 % unigenes were considered specific to S. alterniflora. Digital expression profiles revealed significant enrichment (P < 0.01) of transporters, vacuolar proton pump members and transcription factors under salt stress, which suggested the role of ion homeostasis and transcriptional regulation in the salinity adaptation of this grass. Also, 10,805 SSRs markers from 9457 unigenes were generated and validated through genetic diversity analysis among 13 accessions of S. alterniflora. Conclusions: The present study explores the transcriptome of S. alterniflora to understand the gene regulation under salt stress in halophytes. The sequenced transcriptome (control and salt-regulated) of S. alterniflora provides a platform for further gene finding studies in grasses. This study and our previously published studies suggested that S. alterniflora is a rich reservoir of salt tolerance genes that can be used to develop salt tolerant cereal crops, especially rice, a major food crop of global importance. [ABSTRACT FROM AUTHOR]

Qualitative and quantitative compositions of esterified fatty acids (FAs) in the total lipids from the leaves, shoots, and roots of halophile plants, such as suaeda ( Suaeda altissima), samphire ( Salicornia europaea), and wormwood ( Artemisia lerchiana), collected in their natural environments were estimated by GLC techniques. It was shown that the vegetative organs of these halophytes contained 24 FA species, and 16 of them were tentatively identified as the very-long-chain FAs (VLCFAs). There were four VLCFA groups, viz. C20, C21, C22, and C23, each including saturated, mono-, and diunsaturated components; C24 and C25 FAs were also present. The concentration of VLCFAs in the total FAs comprised 4–64%. In vegetative organs of higher plants not subjected to genetic transformation, such a high VLCFA content was found for the first time. Saturated and even-numbered components predominated among the VLCFAs, and the roots exceeded severalfold the above-ground organs in the total VLCFA content. Possible pathways of VLCFA biosynthesis in plants, VLCFA content in the vegetative tissues, and the physiological role of membrane lipid FA composition in the plant salt metabolism are discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, salt tolerance was investigated in Odyssea paucinervis Staph, an ecologically important C4 grass that is widely distributed in saline and arid areas of southern Africa. Plants were subjected to 0.2%, 10%, 20%, 40%, 60% and 80% sea water dilutions (or 0.076, 3.8, 7.6, 15.2, 22.8, and 30.4 parts per thousand) for 11 weeks. Increase in salinity from 0.2% to 20% sea water had no effect on total dry biomass accumulation, while further increase in salinity to 80% sea water significantly decreased biomass by over 50%. Morphological changes induced by salinity included reductions in the number of culms, leaves and internodes as well as decreases in internode length and leaf length:leaf width ratios. Carbon dioxide exchange, leaf conductance and transpiration decreased at salinities of 40% and higher, while quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and intrinsic photosynthetic efficiency generally decreased at salinities of 60% and higher compared to 0.2% sea water. Concentrations of Na+ and Cl− increased significantly with salinity increase in both roots and shoots. Na+/K+ ratios in the roots and shoots ranged from 0.66 to 3.28 and increased with increase in substrate salinity. The maximal rate of secretion at 80% sea water was 415nmolcm−2 d−1 for Na+ and 763nmolm−2 d−1 for Cl− with high selectivity for these two ions. Predawn and midday ψ decreased with increase in salinity and were more negative than those of the treatment solutions. The concentration of proline increased with increase in salinity in both roots and shoots. The data clearly indicated that O. paucinervis is a highly salt-tolerant species that is morphologically and physiologically adapted to a saline environment. [Copyright &y& Elsevier]

Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings of K. sieversiana were treated with varying (0–400 mM) salt stress (1:1 molar ratio of NaCl to Na2SO4) and alkali stress (1:1 molar ratio of NaHCO3 to Na2CO3). The concentrations of various solutes in fresh shoots, including Na+, K+, Ca2+, Mg2+, Cl−, SO, NO, H2PO, betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 [g g−1 Dry weight (DW)] even under the highest salt or alkali stress. At salinity levels >240 mM, proline concentrations increased dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations of Na+ and K+ all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na+, K+ and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm. On the other hand, the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkali-resistant gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora. [ABSTRACT FROM AUTHOR]

Abstract: Cynara cardunculus L. is a robust thistle widespread in arid and semi-arid regions where high salinity is frequently present, but information about salt stress tolerance in this plant is almost null. This study examines the effect of salts (NaCl and KCl) on the growth, ion and other solutes accumulation and distribution through the plant. Moreover, Na+ and Rb+ (K+) uptake and translocation in the presence of specific water stress were determined. Moderately high concentrations of salt decreased the weight of the plant. However, a differential effect between NaCl and KCl was found. High concentrations of K+ produced higher deleterious effects than the same amounts of Na+. KCl was more toxic for the plant, probably because of the high accumulation of K+ ions in the plant. Osmotic adjustment was mainly due to inorganic ions and not to other organic solutes. Water stress promoted Na+ but not Rb+ (K+) uptake and translocation to the shoot. It is proposed that strategies present in halophytic plants to cope with high salt can be found in C. cardunculus although this plant cannot be considered as a typical halophyte. [Copyright &y& Elsevier]

From the ice plant, Mesembryanthemum crystallinum, McHKT1 was isolated encoding a protein 41–61% identical to other plant HKT1-like sequences previously described as potassium or sodium/potassium transporters. McHKT1 acts as a potassium transporter in yeast with specificity similar to that of wheat HKT1. In Xenopus oocytes it transports cations with a specificity Rb+ > Cs+ > [K+ = Na+ = Li+]. McHKT1 is exclusively localized to the plasma membrane. The isoform isolated is most highly expressed in leaves and is present in stems, flowers and seed pods but absent from the root where, according to immunological data, a second isoform exists which does not cross-hybridize with the leaf form in RNA blots at high stringency. McHKT1 transcript amounts increase during the first 6–10 h of stress and then decline to pre-stress levels with kinetics reminiscent of the initial influx of sodium into this halophyte. Immunocytological localization showed strong signals in the leaf vasculature and surrounding mesophyll cells but low-intensity signals are also detected in other cell types. In roots, McHKT is mainly confined to endodermis and stele. Possible functions of McHKT1 in ion homeostasis in the halophytic ice plant are discussed. [ABSTRACT FROM AUTHOR]

In this review I will describe the importance of seed banks and the population dynamics of seeds on the distribution of species in saline habitats. The main questions being examined in this review include: 1. Does the seed bank represent the flora of the entire salinity gradient or is it restricted to the species in each zonal community? 2. Is the size and species composition of the persistent seed bank regulated by the degree of salt stress in habitats along an environmental gradient? 3. Does the population dynamics of seeds influence the temporal and spatial distribution of plant species in saline habitats? Seed banks may be transient or persistent depending upon the physiological responses of species and the soil environment in which the seeds are found. The formation of zonal communities in salt marsh environments is affected by changes in soil salinity and flooding along an elevational gradient. Population dynamics of seeds have been found to determine the spatial and temporal distribution of species along salinity gradients. The flora and relative density of species of zonal communities are significantly dependent upon the stress tolerance of species at different stages of development and the presence of transient or persistent seed banks. The occurrence of a seed bank is related to the salinity tolerance of species at the germination stage of development, a seeds ability to tolerate hypersaline conditions and flooding, and whether or not species are able to maintain a persistent seed bank until hypersaline conditions are alleviated. [ABSTRACT FROM AUTHOR]

We have investigated conditions leading to the degradation of glycinebetaine in Aphanothece halophytica and have shown the activity of betaine-homocysteine methyltransferase (BHMT). The intracellular glycinebetaine level was decreased approximately 50% after 36 h salt downshock from 2.0 m NaCl medium to 0.5 m NaCl medium. A slight additional decrease of glycinebetaine occurred when salt downshock was combined with dark treatment. The omission of carbon and nitrogen sources in the growth medium further decreased intracellular glycinebetaine. The activity of BHMT increased from 0 to 460 nmol h-1mg-1 after 3 h salt downshock. Higher strength of salt downshock resulted in higher activity of the enzyme. Small increase of the enzyme activity was also observed when A. halophytica was deprived of carbon and nitrogen sources in the growth medium. [ABSTRACT FROM AUTHOR]

The effect of Mg2+, Na+, K+ ouabain and pH on ATPase activity of purified membrane fractions enriched in plasmalemma fragments from Hordeum vulgare L. (glycophyte) and Halocnemum strobilaceum L. (halophyte) was studied. Membrane ATPases from both plants were synergistically activated by K+ and Na+ in the presence of Mg2+. The maximum activity of the enzymes were observed at the ratio Na/K = 2-3. Ouabain (10-4 M) almost completely eliminated the (Na+ + K+)-stimulated component of the ATPase activity. The Na, K, Mg-ATPase of Hordeum had a single pH optimum (pH 8), but that of the Halocnemum had two optima(pH 6 and 8). It appears that similar enzymes operate in the cells of both plants studied. The higher Na, K, Mg-ATPase activity of the halophyte compared to that of the glycophyte suggests the involvement of the enzyme in the extrusion of Na+ from the cytoplasm of cells of both plants. [ABSTRACT FROM AUTHOR]

The occurrence of glutamine synthetase, glutamate synthase and glutamate dehydrogenase in a range of halophytic higher plants has been investigated. Ferredoxin-dependent glutamate synthase was found in shoot tissue of all the species examined. Root tissue glutamate synthase was active with both reduced pyridine nucleotides and reduced ferredoxin. The levels of enzymes present in the majority of species are consistent with the view that ammonia assimilation occurs via the combined action of glutamine synthetase and glutamate synthase. An increase in external salinity lowers the levels of glutamine synthetase and glutamate dehydrogenase of root tissue but increases the level of shoot glutamine synthetase. [ABSTRACT FROM AUTHOR]

Pyruvate kinase enzymes were partially purified from leaves of halophytes, Atriplex gmelini C. A. Mey., Chenopodium acuminatum Wild, and Spergularia salina J. et C. Presl., grown hydroponically in the presence of 250 mM NaCl in a greenhouse, to determine their Km values for potassium. The values were all ca 10−3M, as also reported for the glycophyte enzymes. However, the Km values were reduced by 60 to 70% by the addition of betaine to a concentration of 1 M. [ABSTRACT FROM AUTHOR]

The present paper reports a study into the activity of nitrate reductase in plants of Suaeda maritima. The growth of S. maritima in the upper salt-marsh appears nitrogen limited, going from the upper to lower marsh there is a three-fold increase in total nitrogen of the plants. Nitrogen status and the activity of nitrate reductase are related. Plants from the lower marsh contain a fifty times higher level of enzyme than those from the upper marsh. By feeding nitrate to plants at different sites in the marsh it was possible to induce high nitrate reductase activity in plants that previously contained low levels of the enzyme. At all sites there is an equal potential to induce nitrate reductase. The induction experiments with plants in situ suggest that in this marsh nitrate availability is the main factor limiting the growth of S. maritima in the upper marsh. [ABSTRACT FROM AUTHOR]

The composition of lipids from the aerial parts of two species of halophytes from the family Chenopodiaceae, Halostachys caspica C. A. Mey. and Halocharis hispida Bge. was determined. Neutral lipids (NL, 62.1 and 54.2%, respectively) dominated the total lipids (TL) of these plants. More than a third of the NL were esters of aliphatic alcohols and phytosterols (FAE). Fatty acids 16:0, 18:1, and 18:2 dominated the acids of FAE; 16:0, 18:1, and 18:3, the phospholipids. The principal fatty acids of glycolipids were unsaturated acids (68.3 and 75.1%) with linolenic acid dominating (44.9 and 43.5%). [ABSTRACT FROM AUTHOR]

In Israel Najas marina L. grows mainly in fresh water habitats. The halophytic nature of a population from one such habitat was investigated. NaCl had a positive effect on the growth of Najas, with an optimal concentration of 37-55 mM. Germination percentage was only slightly reduced by NaCl up to a concentration of 74 mM. It is thus concluded that the populations of Najas in Israel retain their halophytic nature. In fresh water habitats, M grows under suboptimal NaCl concentrations. [ABSTRACT FROM AUTHOR]

Median and lateral seeds of Salicornia europaea L. were separately analysed for their sizes and nutrient reserves. The mean air-dry weight of a single median and lateral seed was 0.31 and 0.25 mg, respectively. The composition as well as the concentration of the nutrient reserves were similar in both seed types. The bulk of the cations was derived from K+, followed by Mg2+, Na+ and Ca2+. The chloride content was somewhat higher than the sodium content, and phosphate was equalled by acid soluble Ca2+ and Mg2+. Starchy compounds and sucrose were present in equal amounts, each of them accounted for about 50% of the carbohydrates. Glucose and fructose were less than 1%. Protein-nitrogen (ethanol-insoluble N) was about 34 g (kg dry seeds)-1. About 7 g (kg dry seeds)-1 was ethanol-soluble nitrogen, of which 10% was derived from amino acids. The total lipid content was more than 290 g (kg dry seeds)-1, 65% were calculated to be glycerides. More than 90% of the fatty acids consisted of linoleic and oleic acids, the majority (72%) of which was linoleic acid. [ABSTRACT FROM AUTHOR]