Search

Brassinosteroid (BR) has been shown to modulate plant tolerance to various stresses. S‐nitrosoglutathione reductase (GSNOR) is involved in the plant response to environment stress by fine‐turning the level of nitric oxide (NO). However, whether GSNOR is involved in BR‐regulated Na+/K+ homeostasis to improve the salt tolerance in halophyte is unknown. Here, we firstly reported that high salinity increases the expression of BR‐biosynthesis genes and the endogenous levels of BR in mangrove Kandelia obovata. Then, salt‐induced BR triggers the activities and gene expressions of GSNOR and antioxidant enzymes, thereafter decrease the levels of malondialdehyde, hydrogen peroxide. Subsequently, BR‐mediated GSNOR negatively regulates NO contributions to the reduction of reactive oxygen species generation and induction of the gene expression related to Na+ and K+ transport, leading to the decrease of Na+/K+ ratio in the roots of K. obovata. Finally, the applications of exogenous BR, NO scavenger, BR biosynthetic inhibitor and GSNOR inhibitor further confirm the function of BR. Taken together, our result provides insight into the mechanism of BR in the response of mangrove K. obovata to high salinity via GSNOR and NO signaling pathway by reducing oxidative damage and modulating Na+/K+ homeostasis. Summary Statement: Salinity increases brassinosteroid (BR)‐biosynthesis genes expression and endogenous BR in mangrove Kandelia obovata. BR enhances the activity and gene expression of S‐nitrosoglutathione reductase that negatively regulates nitric oxide signaling and reactive oxygen species level, while, BR regulates antioxidant enzymes and Na+/K+ homeostasis. [ABSTRACT FROM AUTHOR]

Foliar water uptake (FWU) occurs in plants of diverse ecosystems; however, the diversity of pathways and their associated FWU kinetics remain poorly resolved. We characterized a novel FWU pathway in two mangrove species of the Sonneratia genus, S. alba and S. caseolaris. Further, we assessed the influence of leaf wetting duration, wet‐dry seasonality and leaf dehydration on leaf conductance to surface water (Ksurf). The symplastic tracer dye, disodium fluorescein, revealed living cells subtending and encircling leaf epidermal structures known as cork warts as a pathway of FWU entry into the leaf. Rehydration kinetics experiments revealed a novel mode of FWU, with slow and steady rates of water uptake persistent over a duration of 12 hr. Ksurf increased with longer durations of leaf wetting and was greater in leaves with more negative water potentials at the initiation of leaf wetting. Ksurf declined by 68% between wet and dry seasons. Our results suggest that FWU via cork warts in Sonneratia sp. may be rate limited and under active regulation. We conclude that FWU pathways in halophytes may require ion exclusion to avoid uptake of salt when inundated, paralleling the capacity of halophyte roots for ion selectivity during water acquisition. Epidermal cork warts function as a pathway of foliar water uptake in the mangroves Sonneratia alba and S. caseolaris. Leaf surface conductance to water increased with leaf rehydration duration, was inhibited in the dry season and increased with leaf dehydration. [ABSTRACT FROM AUTHOR]

The Plumbaginaceae (non‐core Caryophyllales) is a family well known for species adapted to a wide range of arid and saline habitats. Of its salt‐tolerant species, at least 45 are in the genus Limonium; two in each of Aegialitis, Limoniastrum and Myriolimon, and one each in Psylliostachys, Armeria, Ceratostigma, Goniolimon and Plumbago. All the halophytic members of the family have salt glands and salt glands are also common in the closely related Tamaricaceae and Frankeniaceae. The halophytic species of the three families can secrete a range of ions (Na+, K+, Ca2+, Mg2+, Cl−, HCO3−, SO42‐) and other elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Salt glands are, however, absent in salt‐tolerant members of the sister family Polygonaceae. We describe the structure of the salt glands in the three families and consider whether glands might have arisen as a means to avoid the toxicity of Na+ and/or Cl− or to regulate Ca2+ concentrations with the leaves. We conclude that the establishment of lineages with salt glands took place after the split between the Polygonaceae and its sister group the Plumbaginaceae. The Plumbaginaceae, a family within the non‐core Caryophyllales, contains over 50 halophytic species, all of which have salt glands on their leaves. It is not clear, however whether these glands evolved to regulate internal Na, (or Cl) or Ca. [ABSTRACT FROM AUTHOR]

Anatomical adaptations to high‐salinity environments in mangrove leaves may be recorded in leaf water isotopes. Recent studies observed lower 18O enrichment (ΔL) of leaf water with respect to source water in three mangrove species relative to adjacent freshwater trees, but the factors that govern this phenomenon remain unclear. To resolve this issue, we investigated leaf traits and ΔL in 15 species of true mangrove plants, 14 species of adjacent freshwater trees, and 4 species of semi‐mangrove plants at five study sites along south‐eastern coast of China. Our results confirm that ΔL was generally 3–4‰ lower for mangrove species than for adjacent freshwater or semi‐mangrove species. We hypothesized that higher leaf water content (LWC) and lower leaf stomatal density (LS) both played important roles in reducing ΔL in mangroves relative to nearby freshwater plants. Both differences acted to elongate effective leaf mixing length (L) in mangroves by about 200% and lower stomatal conductance by about 30%. Péclet models based on both LWC and LS could accurately predict ΔL. Our findings highlight the potential species‐specific anatomical determinants of ΔL (or L), which has important implications for the interpretation of environmental information from metabolites produced by leaf water isotopes in palaeoclimate research. Mangrove forests evolve typical leaf structures to adapt to high‐salinity environments, and many of these adaptations may leave imprints in leaf water isotopes. Our comprehensive field study confirmed that the isotope enrichment of leaf water (ΔL) in mangroves were generally lower than those of the adjacent nonmangrove at multiple‐site and multiple‐species scales and that leaf anatomies play key roles in determining these differences in ΔL. The potential species‐specific anatomical determinants of ΔL based on a large pool of species can be incorporated into the leaf water model, which will have considerable potential applications not only for palaeoclimate reconstruction but also in distinguishing what kinds of plants with strong Péclet effect. [ABSTRACT FROM AUTHOR]

Efforts to breed salt tolerant crops could benefit from investigating previously unexplored traits. One of them is a tissue succulency. In this work, we have undertaken an electrophysiological and biochemical comparison of properties of mesophyll and storage parenchyma leaf tissues of a succulent halophyte species Carpobrotus rosii ("pigface"). We show that storage parenchyma cells of C. rossii act as Na+ sink and possessed both higher Na+ sequestration (298 vs. 215 mM NaCl in mesophyll) and better K+ retention ability. The latter traits was determined by the higher rate of H+‐ATPase operation and higher nonenzymatic antioxidant activity in this tissue. Na+ uptake in both tissues was insensitive to either Gd3+ or elevated Ca2+ ruling out involvement of nonselective cation channels as a major path for Na+ entry. Patch‐clamp experiments have revealed that Caprobrotus plants were capable to downregulate activity of fast vacuolar channels when exposed to saline environment; this ability was higher in the storage parenchyma cells compared with mesophyll. Also, storage parenchyma cells have constitutively lower number of open slow vacuolar channels, whereas in mesophyll, this suppression was inducible by salt. Taken together, these results provide a mechanistic basis for efficient Na+ sequestration in the succulent leaf tissues. This work explored a mechanistic basis for Na+ sequestration in the succulent leaf tissues from the halophyte species Carpobrotus rosii. It is shown that the storage parenchyma in Carpobrotus act as Na+ sink and also possessed better K+ retention ability, due to higher rate of H+‐ATPase operation and higher nonenzymatic antioxidant activity in this tissue. The storage parenchyma cells also had constitutively lower number of open slow vacuolar channels, thus preventing futile Na+ leak from the vacuole into the cytosol. [ABSTRACT FROM AUTHOR]

Salt stress causes dramatic changes in the organization and dynamic properties of membranes, however, little is known about the underlying mechanisms involved. Modified trichomes, known as epidermal bladder cells (EBC), on the leaves and stems of the halophyte Mesembryanthemum crystallinum can be successfully exploited as a single-celltype system to investigate salt-induced changes to cellular lipid composition. In this study alterations in key molecular species from different lipid classes highlighted an increase in phospholipid species, particularly those from phosphatidylcholine (PC) and phosphatidic acid (PA), where the latter is central to the synthesis of membrane lipids. Triacylglycerol (TG) species decreased during salinity, while there was little change in plastidic galactolipids. EBC transcriptomic and proteomic data mining revealed changes in genes and proteins involved in lipid metabolism and the upregulation of transcripts for PIPKIB, PI5PII, PIPKIII, and PLDd, suggested the induction of signalling processes mediated by phosphoinositides and PA. TEM and flow cytometry showed the dynamic nature of lipid droplets in these cells under salt stress. Altogether, this work indicates the metabolism of TG might play an important role in EBC response to salinity as either an energy reserve for sodium accumulation and/or driving membrane biosynthesis for EBC expansion. [ABSTRACT FROM AUTHOR]

Abstract: Soil health is essential and irreplaceable for plant growth and global food production, which has been threatened by climate change and soil degradation. Degraded coastal soils are urgently required to reclaim using new sustainable technologies. Interest in applying biochar to improve soil health and promote crop yield has rapidly increased because of its multiple benefits. However, effects of biochar addition on the saline–sodic coastal soil health and halophyte growth were poorly understood. Response of two halophytes, Sesbania (Sesbania cannabina) and Seashore mallow (Kosteletzkya virginica), to the individual or co‐application of biochar and inorganic fertilizer into a coastal soil was investigated using a 52 d pot experiment. The biochar alone or co‐application stimulated the plant growth (germination, root development, and biomass), primarily attributed to the enhanced nutrient availability from the biochar‐improved soil health. Additionally, the promoted microbial activities and bacterial community shift towards the beneficial taxa (e.g. Pseudomonas and Bacillus) in the rhizosphere also contributed to the enhanced plant growth and biomass. Our findings showed the promising significance because biochar added at an optimal level (≤5%) could be a feasible option to reclaim the degraded coastal soil, enhance plant growth and production, and increase soil health and food security. [ABSTRACT FROM AUTHOR]

The Arabidopsis U-box E3 ubiquitin ligases play an important role in the ubiquitin/26S proteasome-mediated protein degradation pathway. Recently, PUB30 has been reported to participate in the salt stress response during seed germination stage in abscisic acid (ABA)-independent manner, but the molecular mechanism remains to be elucidated. Here, we displayed that the pub30 mutant was more tolerant to salt stress during seed germination, whereas the mutant of its closest homologue PUB31 showed mild sensitivity to salt stress. PUB30 exhibited E3 ubiquitin ligase activity in vitro. PUB30 specifically interacted with BRI1 kinase inhibitor 1 (BKI1), a regulator playing dual roles in brassinosteroids signaling, in vitro and in vivo. We found that BKI1 protein was ubiquitinated and degraded by the 26S proteasome. The degradation of BKI1 was slowed down in the pub30-1 mutant compared with that in the wild type. The bki1 mutant was sensitive to salt, whereas the transgenic plants overexpressing BKI1 showed salt tolerant phenotype. All these results indicate that PUB30 negatively regulates salt tolerance probably through regulating the degradation of BKI1 and brassinosteroids signaling in Arabidopsis. [ABSTRACT FROM AUTHOR]

Hydraulic redistribution (HR), the movement of water from wet to dry patches in the soil via roots, occurs in different ecosystems and plant species. By extension of the principle that HR is driven by gradients in soil water potential, HR has been proposed to occur for plants in saline soils. Despite the inherent spatial patchiness and salinity gradients in these soils, the lack of direct evidence of HR in response to osmotic gradients prompted us to ask the question: are there physical or physiological constraints to HR for plants in saline environments? We propose that build-up of ions in the root xylem sap and in the leaf apoplast, with the latter resulting in a large predawn disequilibrium of water potential in shoots compared with roots and soil, would both impede HR. We present a conceptual model that illustrates how processes in root systems in heterogeneous salinity with water potential gradients, even if equal to those in non-saline soils, will experience a dampened magnitude of water potential gradients in the soil-plant continuum, minimizing or preventing HR. Finally, we provide an outlook for understanding the relevance of HR for plants in saline environments by addressing key research questions on plant salinity tolerance. [ABSTRACT FROM AUTHOR]

Epidermal bladder cells (EBCs) have been postulated to assist halophytes in coping with saline environments. However, little direct supporting evidence is available. Here, Chenopodium quinoa plants were grown under saline conditions for 5 weeks. One day prior to salinity treatment, EBCs from all leaves and petioles were gently removed by using a soft cosmetic brush and physiological, ionic and metabolic changes in brushed and non-brushed leaves were compared. Gentle removal of EBC neither initiated wound metabolism nor affected the physiology and biochemistry of control-grown plants but did have a pronounced effect on salt-grown plants, resulting in a salt-sensitive phenotype. Of 91 detected metabolites, more than half were significantly affected by salinity. Removal of EBC dramatically modified these metabolic changes, with the biggest differences reported for gamma-aminobutyric acid (GABA), proline, sucrose and inositol, affecting ion transport across cellular membranes (as shown in electrophysiological experiments). This work provides the first direct evidence for a role of EBC in salt tolerance in halophytes and attributes this to (1) a key role of EBC as a salt dump for external sequestration of sodium; (2) improved K+ retention in leaf mesophyll and (3) EBC as a storage space for several metabolites known to modulate plant ionic relations. [ABSTRACT FROM AUTHOR]

Protein phosphatase 2A (PP2A) is an enzyme consisting of three subunits: a scaffolding A subunit, a regulatory B subunit and a catalytic C subunit. PP2As were shown to play diverse roles in eukaryotes. In this study, the function of the Arabidopsis PP2A-C5 gene that encodes the catalytic subunit 5 of PP2A was studied using both loss-of-function and gain-of-function analyses. Loss-of-function mutant pp2a-c5-1 displayed more impaired growth during root and shoot development, whereas overexpression of PP2A-C5 conferred better root and shoot growth under different salt treatments, indicating that PP2A-C5 plays an important role in plant growth under salt conditions. Double knockout mutants of pp2a-c5-1 and salt overly sensitive ( sos) mutants sos1-1, sos2-2 or sos3-1 showed additive sensitivity to NaCl, indicating that PP2A-C5 functions in a pathway different from the SOS signalling pathway. Using yeast two-hybrid analysis, four vacuolar membrane chloride channel (CLC) proteins, AtCLCa, AtCLCb, AtCLCc and AtCLCg, were found to interact with PP2A-C5. Moreover, overexpression of AtCLCc leads to increased salt tolerance and Cl− accumulation in transgenic Arabidopsis plants. These data indicate that PP2A-C5-mediated better growth under salt conditions might involve up-regulation of CLC activities on vacuolar membranes and that PP2A-C5 could be used for improving salt tolerance in crops. [ABSTRACT FROM AUTHOR]

Salt respiration is defined as the increase of respiration under early salt stress. However, the response of respiration varies depending on the degree of salt tolerance and salt stress. It has been hypothesized that the activity of the alternative pathway may increase preventing over-reduction of the ubiquinone pool in response to salinity, which in turn can increase respiration. Three genotypes of Medicago truncatula are reputed as differently responsive to salinity: TN1.11, A17 and TN6.18. We used the oxygen-isotope fractionation technique to study the in vivo respiratory activities of the cytochrome oxidase pathway (COP) and the alternative oxidase pathway (AOP) in leaves and roots of these genotypes treated with severe salt stress (300 mM) during 1 and 3 days. In parallel, AOX capacity, gas exchange measurements, relative water content and metabolomics were determined in control and treated plants. Our study shows for first time that salt respiration is induced by the triggered AOP in response to salinity. Moreover, this phenomenon coincides with increased levels of metabolites such as amino and organic acids, and is shown to be related with higher photosynthetic rate and water content in TN6.18. [ABSTRACT FROM AUTHOR]

The halophilic mangrove species Kandelia candel is an excellent model for understanding why halophytes thrive in high salinity. Preliminary transcriptomic analyses revealed that genes involved in diverse functions, such as in phenylpropanoid and amino acid metabolisms, and those in DNA replication and damage repair were highly responsive to salt stress. Proteomic analyses revealed that the proteins involved in light reaction of photosynthesis, amino acid and carbohydrate metabolisms, secondary metabolite biosynthesis and posttranslational modification showed increased levels in response to salt stress. The metabolisms of phenylpropanoids and amino acids under salt stress were systematically examined based on the preliminary omics analyses. The activities of phenylpropanoid biosynthetic enzymes and the contents of phenols, flavonoids, anthocyanins and lignins were significantly increased under salt stress. In the free amino acid pool, glutamate was the most abundant. Together with γ-aminobutyric acid, glutamate levels further increased, while proline levels remained unchanged in response to salt stress. These findings point to the potential importance of phenylpropanoids and free amino acids in salt tolerance of K. candel that have been observed, but not systemically investigated at the levels of gene expression, enzyme activity and metabolite accumulation in glycophytes and non-tree halophytes. [ABSTRACT FROM AUTHOR]

Extremophile plants are valuable sources of genes conferring tolerance traits, which can be explored to improve stress tolerance of crops. Lepidium crassifolium is a halophytic relative of the model plant Arabidopsis thaliana, and displays tolerance to salt, osmotic and oxidative stresses. We have employed the modified Conditional cDNA Overexpression System to transfer a cDNA library from L. crassifolium to the glycophyte A. thaliana. By screening for salt, osmotic and oxidative stress tolerance through in vitro growth assays and non-destructive chlorophyll fluorescence imaging, 20 Arabidopsis lines were identified with superior performance under restrictive conditions. Several cDNA inserts were cloned and confirmed to be responsible for the enhanced tolerance by analysing independent transgenic lines. Examples include full-length cDNAs encoding proteins with high homologies to GDSL-lipase/esterase or acyl CoA-binding protein or proteins without known function, which could confer tolerance to one or several stress conditions. Our results confirm that random gene transfer from stress tolerant to sensitive plant species is a valuable tool to discover novel genes with potential for biotechnological applications. [ABSTRACT FROM AUTHOR]

Deuterium depletions between stem water and source water have been observed in coastal halophyte plants and in multiple species under greenhouse conditions. However, the location(s) of the isotope fractionation is not clear yet and it is uncertain whether deuterium fractionation appears in other natural environments. In this study, through two extensive field campaigns utilizing a common dryland riparian tree species Populus euphratica Oliv., we showed that no significant δ18O differences were found between water source and various plant components, in accord with previous studies. We also found that no deuterium fractionation occurred during P. euphratica water uptake by comparing the deuterium composition (δD) of groundwater and xylem sap. However, remarkable δD differences (up to 26.4‰) between xylem sap and twig water, root water and core water provided direct evidence that deuterium fractionation occurred between xylem sap and root or stem tissue water. This study indicates that deuterium fractionation could be a common phenomenon in drylands, which has important implications in plant water source identification, palaeoclimate reconstruction based on wood cellulose and evapotranspiration partitioning using δD of stem water. [ABSTRACT FROM AUTHOR]

Silicon ( Si) is generally considered a beneficial element for the growth of higher plants, especially under stress conditions, but the mechanisms remain unclear. Here, we tested the hypothesis that Si improves salt tolerance through mediating important metabolism processes rather than acting as a mere mechanical barrier. Seedlings of sorghum ( S orghum bicolor L.) growing in hydroponic culture were treated with Na Cl (100 m m) combined with or without Si (0.83 m m). The result showed that supplemental Si enhanced sorghum salt tolerance by decreasing Na+ accumulation. Simultaneously, polyamine ( PA) levels were increased and ethylene precursor (1-aminocyclopropane-1-carboxylic acid: ACC) concentrations were decreased. Several key PA synthesis genes were up-regulated by Si under salt stress. To further confirm the role of PA in Si-mediated salt tolerance, seedlings were exposed to spermidine ( Spd) or a PA synthesis inhibitor (dicyclohexylammonium sulphate, DCHA) combined with salt and Si. Exogenous Spd showed similar effects as Si under salt stress whereas exogenous DCHA eliminated Si-enhanced salt tolerance and the beneficial effect of Si in decreasing Na+ accumulation. These results indicate that PAs and ACC are involved in Si-induced salt tolerance in sorghum and provide evidence that Si plays an active role in mediating salt tolerance. [ABSTRACT FROM AUTHOR]

With the expansion of saline land worldwide, it is essential to establish a model halophyte to study the salt-tolerance mechanism. The salt glands in the epidermis of L imonium bicolor (a recretohalophyte) play a pivotal role in salt tolerance by secreting excess salts from tissues. Despite the importance of salt secretion, nothing is known about the molecular mechanisms of salt gland development. In this study, we applied RNA sequencing to profile early leaf development using five distinct developmental stages, which were quantified by successive collections of the first true leaves of L . bicolor with precise spatial and temporal resolution. Specific gene expression patterns were identified for each developmental stage. In particular, we found that genes controlling salt gland differentiation in L . bicolor may evolve in a trichome formation, which was also confirmed by mutants with increased salt gland densities. Genes involved in the special ultrastructure of salt glands were also elucidated. Twenty-six genes were proposed to participate in salt gland differentiation. Our dataset sheds light on the molecular processes underpinning salt gland development and thus represents a first step towards the bioengineering of active salt-secretion capacity in crops. [ABSTRACT FROM AUTHOR]

Very little is known about the adaptation mechanism of Chenopodiaceae H alogeton glomeratus, a succulent annual halophyte, under saline conditions. In this study, we investigated the morphological and physiological adaptation mechanisms of seedlings exposed to different concentrations of NaCl treatment for 21 d. Our results revealed that H . glomeratus has a robust ability to tolerate salt; its optimal growth occurs under approximately 100 m m NaCl conditions. Salt crystals were deposited in water-storage tissue under saline conditions. We speculate that osmotic adjustment may be the primary mechanism of salt tolerance in H . glomeratus, which transports toxic ions such as sodium into specific salt-storage cells and compartmentalizes them in large vacuoles to maintain the water content of tissues and the succulence of the leaves. To investigate the molecular response mechanisms to salt stress in H . glomeratus, we conducted a comparative proteomic analysis of seedling leaves that had been exposed to 200 m m NaCl for 24 h, 72 h and 7 d. Forty-nine protein spots, exhibiting significant changes in abundance after stress, were identified using matrix-assisted laser desorption ionization tandem time-of-flight mass spectrometry ( MALDI- TOF/ TOF MS/ MS) and similarity searches across EST database of H . glomeratus. These stress-responsive proteins were categorized into nine functional groups, such as photosynthesis, carbohydrate and energy metabolism, and stress and defence response. [ABSTRACT FROM AUTHOR]

γ-Aminobutyric acid ( GABA) accumulates in many plant species in response to environmental stress. However, the physiological function of GABA or its metabolic pathway ( GABA shunt) in plants remains largely unclear. Here, the genes, including glutamate decarboxylases ( SlGADs), GABA transaminases ( SlGABA - T s) and succinic semialdehyde dehydrogenase ( SlSSADH), controlling three steps of the metabolic pathway of GABA, were studied through virus-induced gene silencing approach in tomato. Silencing of SlGADs ( GABA biosynthetic genes) and SlGABA - T s ( GABA catabolic genes) led to increased accumulation of reactive oxygen species ( ROS) as well as salt sensitivity under 200 m m NaCl treatment. Targeted quantitative analysis of metabolites revealed that GABA decreased and increased in the SlGADs- and SlGABA - T s-silenced plants, respectively, whereas succinate (the final product of GABA metabolism) decreased in both silenced plants. Contrarily, SlSSADH-silenced plants, also defective in GABA degradation process, showed dwarf phenotype, curled leaves and enhanced accumulation of ROS in normal conditions, suggesting the involvement of a bypath for succinic semialdehyde catabolism to γ-hydroxybutyrate as reported previously in A rabidopsis, were less sensitive to salt stress. These results suggest that GABA shunt is involved in salt tolerance of tomato, probably by affecting the homeostasis of metabolites such as succinate and γ-hydroxybutyrate and subsequent ROS accumulation under salt stress. [ABSTRACT FROM AUTHOR]

ABSTRACT Tolerance to boron (B) is still not completely understood. We tested here the hypothesis that Thellungiella halophila, an Arabidopsis thaliana-related 'extremophile' plant, with abundance of B in its natural environment, is tolerant to B, and examined the potential mechanisms of this tolerance. With 1-10 m m B applied ([B]ext) to Thellungiella and Arabidopsis grown in hydroponics, the steady-state accumulated B concentration ([B]int) in the root was below [B]ext, and was similar in both, suggesting both extrude B actively. Whether grown in soil or hydroponically, the shoot [B]int was higher in Arabidopsis than in Thellungiella, suggesting more effective net B exclusion by Thellungiella root. Arabidopsis exhibited toxicity symptoms including reduced shoot fresh weight (FW), but Thellungiella was not affected, even at similar levels of shoot-accumulated [B]int (about 10 to 40 m m B in 'shoot water'), suggesting additional B tolerance mechanism in Thellungiella shoot. At [B]ext = 5 m m, the summed shoot concentration of the potentially B-binding polyhydroxyl metabolites (malic acid, fructose, glucose, sucrose and citric acid) in Arabidopsis was below [B]int, but in Thellungiella it was over twofold higher than [B]int, and therefore likely to allow appreciable 1:2 boron-metabolite complexation in the shoot. This, we suggest, is an important component of Thellungiella B tolerance mechanism. [ABSTRACT FROM AUTHOR]

Suaeda salsa is a leaf-succulent euhalophytic plant capable of surviving under seawater salinity. Here, we report the isolation and functional analysis of a novel Suaeda gene (designated as SsTypA1) encoding a member of the TypA/BipA GTPase gene family. The steady-state transcript level of SsTypA1 in S. salsa was up-regulated in response to various external stressors. Expression of SsTypA1 was restricted to the epidermal layers of the leaf and stem in S. salsa, and SsTypA1–green fluorescence protein (GFP) fusion proteins were targeted to the chloroplasts of tobacco leaves. Ectopic over-expression of SsTypA1 rendered the transgenic tobacco plants with significantly increased tolerance to oxidative stress, and this was accompanied by a reduction in H2O2 content. Enzymatic and Western blot analyses revealed that the activity and amount of the thylakoid-bound NAD(P)H dehydrogenase (NDH) complex in the chloroplasts of leaf cells were enhanced. Additionally, an in vitro assay demonstrated that SsTypA1 bound to GTP and possessed GTPase activity that was stimulated by the presence of chloroplast 70S ribosomes. Together, these results suggest that SsTypA1 may play a critical role in the development of oxidative stress tolerance, perhaps as a translational regulator of the stress-responsive proteins involved in reactive oxygen species (ROS) suppression in chloroplast. [ABSTRACT FROM AUTHOR]

In flood-tolerant species, a common response to inundation is growth of adventitious roots into the water column. The capacity for these roots to become photosynthetically active has received scant attention. The experiments presented here show the aquatic adventitious roots of the flood-tolerant, halophytic stem-succulent, Tecticornia pergranulata (subfamily Salicornioideae, Chenopodiaceae) are photosynthetic and quantify for the first time the photosynthetic capacity of aquatic roots for a terrestrial species. Fluorescence microscopy was used to determine the presence of chloroplasts within cells of aquatic roots. Net O2 production by excised aquatic roots, when underwater, was measured with varying light and CO2 regimes; the apparent maximum capacity ( Pmax) for underwater net photosynthesis in aquatic roots was 0.45 µmol O2 m−2 s−1. The photosynthetic potential of these roots was supported by the immunolocalization of PsbA, the major protein of photosystem II, and ribulose-1-5-bisphosphate carboxylase/oxygenase (Rubisco) in root protein extracts. Chlorophyllous aquatic roots of T. pergranulata are photosynthetically active, and such activity is a previously unrecognized source of O2, and potentially carbohydrates, in flooded and submerged plants. [ABSTRACT FROM AUTHOR]

Salt-sensitive glycophytes and salt-tolerant halophytes employ common mechanisms to cope with salinity, and it is hypothesized that differences in salt tolerance arise because of changes in the regulation of a basic set of salt tolerance genes. We explored the expression of genes involved in two key salt tolerance mechanisms in Arabidopsis thaliana and the halophytic A. thaliana relative model system (ARMS), Thellungiella halophila. Salt overly sensitive 1 (SOS1) is a plasma membrane Na+/H+ antiporter that retrieves and loads Na+ ions from and into the xylem. Shoot SOS1 transcript was more strongly induced by salt in T. halophila while root SOS1 was constitutively higher in unstressed T. halophila. This is consistent with a lower salt-induced rise in T. halophila xylem sap Na+ concentration than in A. thaliana. Thellungiella halophila contained higher unstressed levels of the compatible osmolyte proline than A. thaliana, while under salt stress, T. halophila accumulated more proline mainly in shoots. Expression of the A. thaliana ortholog of proline dehydrogenase (PDH), involved in proline catabolism, was undetectable in T. halophila shoots. The PDH enzyme activity was lower and T. halophila seedlings were hypersensitive to exogenous proline, indicating repression of proline catabolism in T. halophila. Our results suggest that differential gene expression between glycophytes and halophytes contributes to the salt tolerance of halophytes. [ABSTRACT FROM AUTHOR]

Xylem sap salinity and conductivity were examined in two mangrove ecosystem tree species . For Avicennia germinans, extracted xylem sap osmotic potentials ranged from −0.24 to −1.36 MPa versus −0.14 to −0.56 MPa for Conocarpus erectus. Xylem sap of Conocarpus did not vary in osmotic potential between sites nor between predawn and midday. In Avicennia, values were more negative at midday than predawn, and also more negative at hypersaline than hyposaline sites. After removing embolisms, specific conductivity ( Ks) was measured as a function of salinity of the artificial xylem sap perfusion. For both species the lowest Ks values, about 70% of the maximum Ks, were obtained when stems were perfused with deionized water (0 m m; 0.0 MPa) or with a 557-m m saline solution (−2.4 MPa). Higher Ks values were obtained in the range from −0.3 to −1.2 MPa, with a peak at −0.82 ± 0.08 MPa for Avicennia and −0.75 ± 0.08 MPa for Conocarpus. The variations in Ks values with minima both at very low and very high salt concentrations were consistent with published results for swelling and shrinking of synthetic hydrogels, suggesting native hydrogels in pit membranes of vessels could help regulate conductivity. [ABSTRACT FROM AUTHOR]

Abstract Mesembryanthemum crystallinum L. (Aizoaceae) is a drought- and salt-tolerant halophyte that is able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200–1500 µ mol m-2 s-1 ) it displays a rapid cell-specific accumulation of plant secondary metabolites in the upper leaf epidermis; a phenomenon that is not detectable with salt or drought treatment. The accumulation of these compounds, the betacyanins and acylated flavonol glycosides, increases if the plants are exposed to polychromatic radiation with a progressively decreasing short-wave cut-off in the ultraviolet range. The response is localized in the epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. It is demonstrated that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential decrease of the response function of the plant with increasing wavelength. [ABSTRACT FROM AUTHOR]

Two sympatric subspecies of the xerohalophyte Atriplex canescens Pursh. (Nutt.) were compared for 84 d in out- door salinity trials in their native coastal desert environment in Sonora, Mexico. Subspecies linearis grows naturally on sea water in the high intertidal zone of estuaries while subspecies canescens grows on dunes. In lysimeter pot experiments, ssp. linearis exhibited 50% growth reduction when the mean root zone salinity reached 1160 mol m-3 NaCl compared to just 760 mol m-3 for ssp. canescens. When irrigated with sea water in a flood plot, ssp. linearis had 50% higher growth rates than ssp. canescens. The specialization of ssp. linearis for a saline environment was associated with greater net transport of Nat from root to shoot, greater Na+ accumulation in the leaves and a higher Na:K ratio in the leaves compared to ssp. canescens. On the other hand, the two subspecies achieved approximately the same degree of osmotic adjustment in the leaves, equal to two to three times the external salinity, and had similar water use efficiencies. Even at relatively low salinities, both subspecies accumulated larger quantities of Na+ for osmotic adjustment than K+. The results suggest that breeding for Na+ accumulation rather than exclusion might be the more effective strategy for improving salt tolerance of conventional crop plants. [ABSTRACT FROM AUTHOR]

The relationship between Na+ accumulation and salt tolerance was tested by comparing subspecies of the halophyte, Atriplex canescens (fourwing saltbush), that differed markedly in Na+ content and Na:K ratios. Above ground tissues of one low-sodium and two high-sodium subspecies were compared with respect to cation accumulation, osmotic adjustment and growth along a salinity gradient In greenhouse trials. Plants of each subspecies were grown for 80d on 2.2, 180, 540 and 720 mol m-3 NaCl. At harvest, A. canescens ssp. canescens had significantly lower NC levels, higher K+ levels and lower Na:K ratios in leaf and stem tissues than A. canescens ssp. macropoda and linearis over the salinity range (P < 0.05 or 0.01). Na:K ratios in leaves of the latter two, high-sodium, subspecies were approximately 2 on the lowest salinity treatment and ranged from 5 to 10 on the more saline solutions. By contrast, Na:K ratios in leaves of the low-sodium subspecies canescens, were only 0.4 on the lowest salinity and ranged narrowly from 1.7 to 2.3 at higher salinities. However, despite different patterns of Na+ and K+ accumulation, all three subspecies exhibited equally high salt tolerance and had similar osmotic pressures in their leaves or stems over the salinity range. Contrary to expectations, high salt tolerance was not necessarily dependent on high levels of Na+ accumulation in this species. [ABSTRACT FROM AUTHOR]

Sporobolus virginicus (L.) Kunth robust form, is a coastal C4 grass species in tropical and subtropical regions. An artificial freeze test was used to determine the response of tissue exposed to low temperature. The response was monitored by three methods: measuring respiration rates as carbon dioxide flux before and after freezing, conducting a triphenyl tetrazolium chloride (TTC) viability assay, and observing growth of tissue cultures and the regrowth of shoots and roots from rhizome buds. The TTC assay overpredicted the survival temperature in rhizomes, when based on a 50% of control as lethal value, but was a good indicator of survival in callus and suspension cultures. Respiration rates of callus tissue declined with low temperature exposure and paralleled the 'ITC results. Rhizome tissue however had a more complex respiratory response. High, post-freeze, respiration rates during thawing of rhizomes at +5.0°C were correlated with injury, detected both by a TTC assay and by the measurement of carbon dioxide flux. High respiration rates, measured after the thawing period, due to disabled rhizomes that were ultimately inviable, provide an explanation for the overprediction of the TTC assay. S. virginicus was found to be freeze-sensitive, LT[SUB50]=-2.5°C, with no hardening ability and it was concluded that cellular resistance defines the limits of freezing tolerance. However, avoidance of freezing strain through an underground perenniating organ probably allows S. virginicus to survive on the polar end of its range where episodic frosts may decrease temperatures to the lower limits of the cellular tolerance of a species. [ABSTRACT FROM AUTHOR]

Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m[SUP-3] NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m[SUP-3] Nacl was only 20% of that in plants at low salinity. Both the Na[SUP+] and K[SUP+] content of leaves and roots increased with external salinity. There was no change in the Na[SUP+]/K[SUP+] ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na[SUP+] ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO[SUB2] and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO[SUB2] concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity. [ABSTRACT FROM AUTHOR]

lncreasing atmospheric CO2 may result in alleviation of salinity stress in salt-sensitive plants. In order to assess the effect of enriched CO2 on salinity stress in Andropogon glomeratus, a C4 non-halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm3 m-3 CO2 with 0 or 100molm-3 NaC1 watering treatments. Increases in leal area and biomass with increasing CO2 were measured in salt-stressed plants, while decreases in these same parametcrs were measured in non-saltstressed plants. Tillering increased substantially with increasing CO2 in salt-stressed plants, resulting in the increased biomass. Six weeks following initiation of treatments, there was no difference in photosynthesis on a leal area basis with increasing CO2 in saltstressed plants, although short-term increases probably occurred. Stomatal conductance decreased with increasing CO2 in salt-stressed plants, resulting in higher water-use efficiency, and may have improved the diurnal water status of the plants. Concentrations of Na+ andC1- were higher in salt stressed-plants while the converse was found for K+. There were no differences in leaf ion content between CO2 treatments in the salt-stressed plants. Decreases in photosynthesis in salt-stressed plants occurred primarily as a result of decreased internal (nonstomatal) conductance. [ABSTRACT FROM AUTHOR]

Salt-tolerant grasses and a sedge were grown at three salinities in a controlled-environment greenhouse. They were measured for growth rate, ash content, water content and cations. Fourteen species from the genera Sporobolus, Aeluropus, Leptochloa, Paspalurn, Puccinellia, Herdeum, Elymus, Distichlis and Spartina survived up to the highest salt treatment (540 mol m-3 NaC1). These were designated halophytes. Eleven species from the genera Triticum, Phragmites, Dactylotenium, Cynodon, Polypogon, Panicum, Jovea and Heleocharis only survived up to 180 mol m-3 NaCl and were designated salt-tolerant glycophytes. All species except Distichlis palrneri grew fastest on the non-saline control treatment. All species tended to have higher Na+ contents and lower K+ and water contents on saline treatments compared to control plants. Halophytes differed from glycophytes in having statistically significant lower water contents on the non-saline treatment, and lower ash contents and Na:K ratios on 180 mol m-3. However, the range of values among species was greater than the differences between halophytes and glycophytes. All species appeared to use Na+ accumulation and loss of water as the main means of osmotic adjustment. Three halophytic species were grown for a longer period of time to check the above results. The osmolality of the cell sap was measured directly by the vapour pressure method and compared to calculated values based on Na+ K+ and water contents (and assuming a balancing anion such as Cl-). Na+ and K+ alone could account for greater than 75% of the osmotic potential at all salinities. Hence, the accumulation of organic solutes did not appear to be an important factor in the osmotic adjustment of these species. The results support the conclusion that grasses coordinate Na+ uptake and water loss to maintain a constant osmotic potential gradient between the shoot tissues and the external solution. The results were compared to a previous study with dicotyledonous halophytes at the same location. [ABSTRACT FROM AUTHOR]

Stacking of thylakoid membranes in vitro was assessed using electron microscopy. Grana stacks of spinach thylakoids formed when 5 mol m-3 MgCl2 was present, but no stacking of thylakoids from the mangrove Avicennia marina occurred in the presence of 10mol m-3 MgCl2. Isolation of mangrove thylakoids with a high osmotic strength medium did not induce grana formation if the mediunl consisted only of sorbitol or glycinebetaine. Addition of cations to the high osmotic strength medium did induce some loose-grana formation, with divalent cations being more effective than monovalent cations. Glycinebetaine was a better osmoticum than sorbitol for grana formation provided divalent cations had been added. Oxygen evolution activity of the preparations was influenced by the amount of membrane stacking, with the preparations with the greatest amount of stacked membrane having the highest activity. Isolation with sorbitol or glycinebetaine based media did not alter this pattern, nor did assay in sorbitol or glycinebetaine. Mangrove thylakoids have a requirement for both a high osmotic strength and divalent cations for grana formation in vitro which may be related to the low water potential of the plant environment in vivo. [ABSTRACT FROM AUTHOR]

A study of the growth of the maritime halophyte Aster tripolium L. has been carried out over a range of salinity treatments. The regression approach to growth analysis using frequent small harvests has been used to allow 'continuous' measurement of growth over a period of 36d. Salinity was applied with the major ions present in ratios typical of those found in seawater. Growth was inhibited in terms of both dry weight production and leaf expansion at salinity levels equivalent to 0.625 strength sea water (full culture solution 300) and above, with the greatest effect being seen in terms of leaf area. Aster tripolium did not show increased succulence at high salinity, leaf fresh weight to dry weight ratio in fact declined, whilst leaf fresh weight per unit area remained constant. It should be noted that the plants exhibit low growth rates due to the low light intensity used. [ABSTRACT FROM AUTHOR]

Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m-3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na+K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight:dry weight (FW:DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW: DW to result in a constant shoot (Na + K) concentration on a water basis. Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na+K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed. [ABSTRACT FROM AUTHOR]

The 'tidal salt marsh' ecotype of the halophyte Aster tripolium L. was grown in a nutrient solution with either a continuous or an intermittent NO-3 supply with either Cl- or SO2-4 as the alternative anion. With increasing periods of NO-3supply per week the rate of the dry weight increment increased. When NO-3 was supplied for longer than 48 h per week, the dry weight and the organic-N content in the shoots hardly increased, whereas the NO-3 content in shoots and roots increased further. With alternated supply of a nutrient solution containing NO-3 with one containing Cl-, the internal NO-3 content in the shoot was lower than in shoots grown in solutions in which NO-3 alternated with SO2-4. It is concluded, that NO-3does not have a specific function in osmoregulation. [ABSTRACT FROM AUTHOR]

Shifts in δ13C of the graminaceous C3 halophyte Puccinellia nuttalliana (Schultes) Hitch. can be induced by salinization. To investigate this phenomenon, three approaches were taken: assay of carboxylases, CO2-enrichment studies, and gas exchange analysis. Although ribulose-1,5-bisphosphate carboxylase activity decreased with salinity, phosphoenolpyruvate carboxylase activity did not increase and its levels were not atypical of C3 plants. When plants were grown at four NaCl concentrations under atmospheres of 310 and 1300 cm3 m-3 CO2, the CO2-enrichment enhanced the effects of salinity on δ13C. This is consistent with a biophysical explanation for salt-induced shifts in δ13C, whereby there is a steepening of the CO2 diffusion gradient into the leaf. Gas exchange analysis indicated that intercellular CO2 concentrations were depressed in the leaves of salt-affected plants. This resulted from a greatly decreased stomatal conductance coupled with only small effects on intrinsic photosynthetic capacity. Water-use efficiency was enhanced. [ABSTRACT FROM AUTHOR]

The starch concentration in mature leaves of the halophyte Suaeda maritima increased from 4.7 to 7.3 mg mg-1 chlorophyll when sodium chloride (680 mol m-3 was added to the solution in which the plants were grown. This effect of salinity on the starch: chlorophyll ratio was greater in young than in old leaves. Electron micrographs showed the starch to be in the chloroplasts and this was confirmed by measurements on isolated chloroplasts. Total phosphorus concentration (mg mg-1 chlorophyll) in leaves of all ages from plants of S. maritima decreased on salinization of the growth medium suggesting an inverse relationship between phosphorus and starch concentrations. However, although leaf starch concentration varied with leaf age, phosphorus concentration did not. The cause of starch accumulation in chloroplasts at salinities which are optimal for growth (340 mol m-3) remains unclear. [ABSTRACT FROM AUTHOR]

A method is described here for isolating protoplasts and vacuoles from leaves of the halophyte Suaeda maritima. Integrity of the protoplasts and vacuoles was tested by staining and shown to be more than 75%, while use of biochemical markers, staining and light microscopy suggested a high degree of purity of the vacuoles. Phosphatase and NADH cytochrome-c-reductase were associated with vacuoles; phosphatase showed an eight-fold enrichment and NADH cytochrome-c-reductase a 3.5-fold enrichment relative to protoplasts. The vacuoles contained only 15% of the protein in protoplasts. [ABSTRACT FROM AUTHOR]

Growth rates and levels of minerals, and Na+, K+, Mg++, Ca++, and water were measured in dicotyledonous halophytes grown along a salinity gradient from fresh water to 720 mol m-3Nacl in a controlled environment greenhouse. Ten test species from the families Chenopodiaceae, Aizoaceae, and Batidaceae exhibited growth stimulation by 180 mol m-3 Nacl and were classified as euhalophytes. Ten others from the families Chenopodiaceae, Aizoceae, Asteraceae, Brassicaceae, Polygonaceae, Boraginaceae, Malvaceae, and Plumbaginaceae showed their best growth on fresh water and were clssified miohalphytes. Salt, and particularly sodium, accumulated in all halophytes but to a significantly greater extent among euhalphytes than miohalophytes. The water content of most species increased when grown on 180 mol m-3 Nacl compared to fresh water; but at higher salinities some of the species underwent dehydration. Dehydration of the succulent S. europaea was not coupled to a proportional decrease in growth. Water content and cation ordinated to produce a constant osmotic potential gradient within the shoot tissues relative to the external salinity. In contrast, miohalphytes did not appear to regulate osmotic potential as closely as euhalophytes. [ABSTRACT FROM AUTHOR]

Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. At pH 5 was not susceptible to inhibition by KCl or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m-3. At pH 8 stimulation occurred at 50 mol m-3 but concentrations above 100 mol m-3depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L at pH 5 showed maximal stimulation at 25 to 50 mol m-3 of NaCl or KCl; concentrations higher than 150 mol m-3 dsepressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m-3 NaCl or KCl while the threshold for inhibition was reduced to 15 mol m-3. With increasing salt concentation the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the diffrence between tratement and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPasee activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity. [ABSTRACT FROM AUTHOR]

The levels of soluble carbohydrates, polyols, betaines and free proline have been determined in different organs of sixteen plants collected on coastal salt marshes. Among the carbohydrates, sucrose, fructose and glucose accumulated at quite high levels. Sucrose is particularly abundant in the monocots Juncus maritima, Phragmiles communis and Scirpus maritimus. Maltose is quite abundant in Atriplex hastata and rhamnose in Plantago maritima roots. High levels of polyols were detected in Aster tripolium, Juncus maritimus, Plantago maritima and Phragmites communis. According to their capacity to accumulate carbohydrates and (or) nitrogenous solutes, halophytic higher plants can be divided into three main groups: (1) species producing high levels of soluble carbohydrates only, (2) species accumulating both carbohydrates and nitrogenous compounds, (3) species producing more nitrogenous solutes than soluble carbohydrates. The possible functions of these various organic solutes, including a role in equalizing the relative water potentials of cytoplasm and vacuole and to lower the internal potential, are discussed. [ABSTRACT FROM AUTHOR]

The chemical compositions of a number of halophytes from salt marshes on Ynys Môn (Anglesey), Wales, and of some related mesophytes and sand dune plants have been determined. Analyses of the inorganic ions broadly confirmed the existence of a characteristic chemical composition of many monocotyleclonous salt-marsh plants in that they contain high levels of potassium and relatively low levels of sodium. In contrast to most dicotyleclonous halophytes, especially members of the Chenopodiacease, the monocots restrict the entry of inorganic ions and use high levels of soluble sugars to maintain an adequate solute potential. Low calcium levels were not found to be a feature of these plants, as was previously reported. The large amounts of sugars found in the monocotyledonous plants suggested that they must be located mainly in the vacuoles, in contrast to glycinebetaine which is thought to accumulate principally in the cytoplasm of the salt-accumulating Chenopodiaceae. The monocotyledonous halophytes which accumulate proline differ from the normal monocotyledonous physiotype in the accumulation of larger quantities of sodium. Triglochin maritima is one species of this type, and Puccinellia maritima a less extreme example. Spartina spp. accumulating glycinebetaine and β-dimethylsulphoniopropionate also have unusually high inorganic ion contents for monocots. Several salt marsh plants contained large quantities of amino acids other than proline. As with ionic composition, the nature of the organic solutes broadly followed taxonomic lines. The usefulness of the physiotype concept is discussed. [ABSTRACT FROM AUTHOR]

Fluxes of sodium across the plasmalemma and tonoplast of the roots of Eleocharis uniglumis have been measured using 22Na. E. uniglumis (one gumed spike rush) was collected from and estuarine habitat where is was growing in a wide range of salinities (1 mM-50 mM Na). Compartmental analysis was used to determine sodium concentrations in the cytoplasm and the vacuole. Application of the Ussing-Teorell equation revealed the presence of sodium pumps in the plasmalemma and the tonoplast. Active sodium transport into the cytoplasm from the vacuole. In contrast to halophytes, high levels of sodium appeared to be accumulated in the cytoplasm of E. uniglumis roots. [ABSTRACT FROM AUTHOR]