Half-strength Seawater Research Articles

Performances of Boro Rice as Affected by Different Concentrations of Marine Water

Salinity is one of the most devastating abiotic stresses limiting crop production. Considering this issue, a pot experiment was conducted at Sher-e-Bangla Agricultural University, Dhaka, Bangladesh during the boro season (2017-2018) using two rice(Oryza sativa L.) varieties, namely BRRI dhan28 (salt sensitive) and BRRI dhan47 (salt tolerant),to assess the effects of varied salinity levels on the growth and the performance of the rice varieties under salt stress conditions. Four salinity treatments were used in this experiment, viz. control S0 (only freshwater), quarter-strength marine water S1 (three-parts freshwater and one-part marine water; 7.5 ds m−1), half-strength marine water S2 (half freshwater and half marine water; 15 ds m−1), and full-strength marine water S3 (only marine water; 30 ds m−1).These mixtures were used for irrigation purposes throughout the life cycle of the plants. Salt stress significantly decreased the plant height, relative water content (RWC) of leaves, number of effective tillers hill−1, number of filled grains panicle−1, 1000-grain weight, grain yield, straw yield, and biological yield of the rice. In both rice types, plant growth and yield were reduced as the salinity level increased. Grain yields decreased by 50, 90, and 100% in BRRI dhan28 when irrigated with quarter strength, half strength, and full-strength seawater, respectively, but decreased by 27, 50, and 72%, respectively, in BRRI dhan47. Similarly, other yield attributes had higher reductions in BRRI dhan28 under salt stress conditions than BRRI dhan47. However, irrigation with marine water in rice might lead to some straw yield but produced little to no grain.

Is Pitcairnia halophila really a halophyte? Evidence from a germination and growth experiment

AbstractMany bromeliads occur in habitats that are potentially affected by salt. Pitcairnia halophila is a particularly interesting case in this context due to its growing sites in the spray zone of coastal cliffs in Central America. We conducted an experimental/observational study that explored the physiological and ecological basis of the occurrence of this species. Germination of P. halophila was as affected by increasing salinity as that of congeneric species from other natural growing sites, but seedling growth was less impaired in comparison and remained positive even at exposure to half-strength seawater. Interestingly, in situ plant nutrient concentrations documented over an entire growing season suggest that this capacity to tolerate salt stress is not tested at the natural growing site – Na+ concentrations were consistently low in leaves and shoots and comparable to those of seedlings watered with distilled water in the laboratory. We conclude that P. halophila shows the physiological ability to deal with medium levels of salinity, but ecological conditions at the humid tropical growing site allow these plants to avoid salt stress entirely in spite of the close proximity to the sea.

Continuous gastric saline perfusion elicits cardiovascular responses in freshwater rainbow trout (Oncorhynchus mykiss)

When in seawater, rainbow trout (Oncorhynchus mykiss) drink to avoid dehydration and display stroke volume (SV) mediated elevations in cardiac output (CO) and an increased proportion of CO is diverted to the gastrointestinal tract as compared to when in freshwater. These cardiovascular alterations are associated with distinct reductions in systemic and gastrointestinal vascular resistance (RSys and RGI, respectively). Although increased gastrointestinal blood flow (GBF) is likely essential for osmoregulation in seawater, the sensory functions and mechanisms driving the vascular resistance changes and other associated cardiovascular changes in euryhaline fishes remain poorly understood. Here, we examined whether internal gastrointestinal mechanisms responsive to osmotic changes mediate the cardiovascular changes typically observed in seawater, by comparing the cardiovascular responses of freshwater-acclimated rainbow trout receiving continuous (for 4 days) gastric perfusion with half-strength seawater (½ SW, ~ 17 ppt) to control fish (i.e., no perfusion). We show that perfusion with ½ SW causes significantly larger increases in CO, SV and GBF, as well as reductions in RSys and RGI, compared with the control, whilst there were no significant differences in blood composition between treatments. Taken together, our data suggest that increased gastrointestinal luminal osmolality is sensed directly in the gut, and at least partly, mediates cardiovascular responses previously observed in SW acclimated rainbow trout. Even though a potential role of mechano-receptor stimulation from gastrointestinal volume loading in eliciting these cardiovascular responses cannot be excluded, our study indicates the presence of internal gastrointestinal milieu-sensing mechanisms that affect cardiovascular responses when environmental salinity changes.

Enhancing growth of mangrove seedlings in the environmentally extreme Arabian Gulf using treated sewage sludge

The response of mangrove (Avicennia marina) seedlings to treated (wet) sludge from a sewage treatment plant (STP) was tested in a randomized block design experiment at a tree nursery on Mubarraz Island in the Arabian Gulf. The growth response of seedlings to half-strength and full-strength STP sludge was monitored over 103 days and compared with the response to freshwater, seawater and half-strength seawater treatments. Sludge treatments resulted in significantly greater plant growth, leaf number, leaf biomass and root biomass than the other treatments did. The positive effect of STP sludge on seedling growth is attributed to enhanced levels of total nitrogen (8.9 ± 0.1 mg l−1) and total phosphorus (7.8 ± 0.2 mg l−1) in the sludge and its low salinity. These results suggest that sludge from sewage treatment plants may be beneficially used in mangrove nurseries and plantations in this arid region, where soils are nutrient-poor and fresh water is scarce.

Sucrose-to-ethanol microalgae-based platform using seawater

Microalgal biomass is increasingly considered a promising feedstock for the production of bioethanol because it has simpler biochemical composition and structural features than plant feedstocks. However, it still requires hazardous and/or expensive acid or enzymatic saccharification processes before its conversion into ethanol by fermentation. To bypass this limitation, we identified microalgal strains that accumulate up to 10% (w/w) of sucrose, a readily fermentable sugar. Conditions were optimized to produce sucrose in half-strength seawater, as well as efficient extraction by very mild procedures, and conversion into ethanol. We present a model based on cultivation in environmental photobioreactors that predicted a productivity of 4200 L ethanol·ha−1·year−1 in raceway ponds in Brazil, approaching the average sucrose and ethanol productivity from sugarcane.

Labyrinthulomycota from Brazilian mangrove swamps and coastal waters

Abstract The phylum Labyrinthulomycota is composed of three distinct groups of fungus-like organisms: the labyrinthulids, the thraustochytrids and the aplanochytrids. They are present in marine and brackish waters as saprobes and/or parasites. In recent years, there was an increased interest in studying these organisms due to the ability that some have to produce large amounts of lipids, particularly polyunsaturated fatty acids. However, in spite of their importance and diversity, in Brazil only four species were reported in the 1970s. Due to their ecological and economic importance globally and the limited knowledge of them in the country, this study aimed to evaluate the diversity of the Labyrinthulomycota in mangrove swamps and coastal waters of São Paulo State, Brazil. The specimens were isolated from water and leaf samples using different methodologies, and purified in an agar medium prepared with half-strength sterile seawater, peptone, yeast extract and glucose. After purification, they were identified by means of morphology and phylogenetic analysis of the SSU rDNA region. A total of 193 specimens representing five genera were observed, 26 specimens were incorporated into the culture collections and 29 sequences of the SSU rDNA region were deposited in GenBank. Labyrinthula sp., Aurantiochytrium sp., Parietichytrium sarkarianum and Thraustochytrium striatum are new records for Brazil, contributing to our knowledge of the diversity of fungus-like organisms in the country.

Is the reduced growth of the halophyte Suaeda maritima under hypoxia due to toxicity of iron or manganese?

For most plants, submergence in water is a rare occurrence, but for plants that grow on salt marshes flooding with seawater may be a twice-daily event. This is the case for plants of the halophyte Suaeda maritima, growing at low elevations on salt marshes. These plants are, however, smaller than those growing at higher elevations, where flooding is less frequent and the soil better drained. We investigated whether the reduced growth brought about by flooding with saline water was a consequence of toxicity of manganese or iron. Seedlings of S. maritima were grown both in a solid medium (a mixture of salt-marsh mud and sand) that was either submerged twice a day or continuously flooded with half-strength seawater and in a hydroponic solution where the oxygen concentration was adjusted by bubbling with nitrogen or air. Hypoxia, reduced the growth of plants in both solid and liquid media and resulted in increases in manganese and iron in the shoots and roots. Experiments in culture solution showed that elevated levels of manganese were unlikely to be toxic, but that iron did reach toxic concentrations in flooded plants.

Oxygen consumption and haematology of juvenile shortnose sturgeonAcipenser brevirostrumduring an acute 24 h saltwater challenge

This study focused on the acute physiological responses to saltwater exposure in juvenile shortnose sturgeon Acipenser brevirostrum. In two separate laboratory experiments, 2 year-old A. brevirostrum were exposed to either full (32) or half-strength (16) seawater for up to 24 h. First, oxygen consumption rates were used to estimate the metabolic costs over 24 h. Secondly, blood and muscle samples were analysed at 6, 12 and 24 h for water loss, various measures of osmoregulatory status (plasma osmolality and ions) and other standard haematological variables. Juveniles exposed to full-strength seawater showed significant decreases in oxygen consumption rates during the 24 h exposure. Furthermore, seawater-exposed fish had significantly increased plasma osmolality, ions (Na(+) and Cl(-)) and a 17% decrease in total wet mass over the 24 h exposure period. To a lesser extent, increases in osmolality, ions and mass loss were observed in fish exposed to half-strength seawater but no changes to oxygen consumption. Cortisol was also significantly increased in fish exposed to full-strength seawater. While plasma protein was elevated following 24 h in full-strength seawater, haemoglobin, haematocrit and plasma glucose levels did not change with increased salinity. These results imply an inability of juvenile A. brevirostrum to regulate water and ions in full-strength seawater within 24 h. Nonetheless, no mortality occurred in any exposure, suggesting that juvenile A. brevirostrum can tolerate short periods in saline environments.

The effect of combined salinity and waterlogging on the halophyte Suaeda maritima: The role of antioxidants

Suaeda maritima is a halophytic plant and its habitat is salt marsh. In order to adapt to saline or waterlogged conditions, plants have evolved mechanisms that include antioxidant protection. However, the combined effect of salinity and waterlogging on antioxidants in S. maritima is unknown. The aim of this study was therefore to investigate the effect of saline-flooding on levels of glutathione and phenolic compounds (antioxidants) and the correlation between their concentration and activity in S. maritima shoots grown in their natural habitat and in a glasshouse.Shoots were collected from two different elevations (and so different degrees of flooding) of a salt marsh while other plants were grown in half strength seawater in the controlled conditions of a glasshouse for 8 weeks (drained and flooded). Shoot samples were used to measure dry weight, glutathione and its reduction state, malonyldialdehyde content (MDA), polyphenol content, superoxide anion and 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) scavenging activity in the shoots of S. maritima.Growth of S. maritima was greater in plants growing on the high marsh than at a lower elevation and in drained medium as opposed to waterlogged conditions in the glasshouse. Waterlogging caused an increase in glutathione and its reduction state. The glutathione half-cell redox potential (EGSSG/2GSH) was more negative in plant shoots grown under waterlogged conditions than in plants grown under normal conditions. Higher DPPH and superoxide anion scavenging activity was associated with high antioxidant concentrations (glutathione and polyphenols).Conclusions. Under saline-flooded conditions in the field and in the glasshouse, plants produced a higher concentration of antioxidants than under drained conditions. These result indicated that antioxidant molecules play an important role in S. maritima plants under combined salinity and waterlogging stress.

A Thermostable Metal-Tolerant Laccase with Bioremediation Potential from a Marine-Derived Fungus

Laccase, an oxidoreductive enzyme, is important in bioremediation. Although marine fungi are potential sources of enzymes for industrial applications, they have been inadequately explored. The fungus MTCC 5159, isolated from decaying mangrove wood and identified as Cerrena unicolor based on the D1/D2 region of 28S and the 18S ribosomal DNA sequence, decolorized several synthetic dyes. Partially purified laccase reduced lignin content from sugarcane bagasse pulp by 36% within 24 h at 30 degrees C. Laccase was the major lignin-degrading enzyme (approximately 24,000 U L(-1)) produced when grown in low-nitrogen medium with half-strength seawater. Three laccases, Lac I, Lac II, and Lac III, of differing molecular masses were produced. Each of these, further resolved into four isozymes by anion exchange chromatography. The N-terminal amino acid sequence of the major isozyme, Lac IId showed 70-85% homology to laccases from basidiomycetes. It contained an N-linked glycan content of 17%. The optimum pH and temperature for Lac IId were 3 and 70 degrees C, respectively, the half-life at 70 degrees C being 90 min. The enzyme was most stable at pH 9 and retained >60% of its activity up to 180 min at 50 degrees C and 60 degrees C. The enzyme was not inhibited by Pb, Fe, Ni, Li, Co, and Cd at 1 mmol. This is the first report on the characterization of thermostable metal-tolerant laccase from a marine-derived fungus with a potential for industrial application.

Biophysical properties of salmonid alphaviruses: influence of temperature and pH on virus survival

A series of laboratory studies were undertaken to investigate the survival of salmonid alphaviruses (SAV) under a range of conditions relevant to waste disposal, persistence and spread in the field, and to laboratory studies and testing. SAV was found to be rapidly inactivated in the presence of high levels of organic matter at 60 degrees C at pH 7.2 and at pH 4 and pH 12 at 4 degrees C, suggesting that composting, ensiling and alkaline hydrolysis would all be effective at inactivating virus in fish waste. Testing was conducted under sterile conditions at 4, 10, 15 and 20 degrees C in sea water, half-strength sea water and fresh (hard) water, both in the absence and the presence of added organic matter. Virus survival was shown to be inversely related to temperature, and to be reduced by the presence of organic matter. Calculated half lives (t(1/2)) under these conditions ranged from 61.0 to 1.5 days. Testing in non-sterile sea water resulted in reduced t(1/2) values. The half life of SAV in serum was also found to be inversely related to temperature, emphasizing the need for rapid shipment of samples at 4 degrees C to laboratories for virus isolation studies.

Metabolic organization of freshwater, euryhaline, and marine elasmobranchs: implications for the evolution of energy metabolism in sharks and rays

To test the hypothesis that the preference for ketone bodies rather than lipids as oxidative fuel in elasmobranchs evolved in response to the appearance of urea-based osmoregulation, we measured total non-esterified fatty acids (NEFA) in plasma as well as maximal activities of enzymes of intermediary metabolism in tissues from marine and freshwater elasmobranchs, including: the river stingray Potamotrygon motoro (<1 mmol l(-1) plasma urea); the marine stingray Taeniura lymma, and the marine shark Chiloscyllium punctatum (>300 mmol l(-1) plasma urea); and the euryhaline freshwater stingray Himantura signifer, which possesses intermediate levels of urea. H. signifer also were acclimated to half-strength seawater (15 per thousand) for 2 weeks to ascertain the metabolic effects of the higher urea level that results from salinity acclimation. Our results do not support the urea hypothesis. Enzyme activities and plasma NEFA in salinity-challenged H. signifer were largely unchanged from the freshwater controls, and the freshwater elasmobranchs did not show an enhanced capacity for extrahepatic lipid oxidation relative to the marine species. Importantly, and contrary to previous studies, extrahepatic lipid oxidation does occur in elasmobranchs, based on high carnitine palmitoyl transferase (CPT) activities in kidney and rectal gland. Heart CPT in the stingrays was detectable but low, indicating some capacity for lipid oxidation. CPT was undetectable in red muscle, and almost undetectable in heart, from C. punctatum as well as in white muscle from T. lymma. We propose a revised model of tissue-specific lipid oxidation in elasmobranchs, with high levels in liver, kidney and rectal gland, low or undetectable levels in heart, and none in red or white muscle. Plasma NEFA levels were low in all species, as previously noted in elasmobranchs. D-beta-hydroxybutyrate dehydrogenase (d-beta-HBDH) was high in most tissues confirming the importance of ketone bodies in elasmobranchs. However, very low d-beta-HBDH in kidney from T. lymma indicates that interspecific variability in ketone body utilization occurs. A negative relationship was observed across species between liver glutamate dehydrogenase activity and tissue or plasma urea levels, suggesting that glutamate is preferentially deaminated in freshwater elasmobranchs because it does not need to be shunted to urea production as in marine elasmobranchs.

Decolorization of molasses spent wash by the white-rot fungus Flavodon flavus, isolated from a marine habitat.

Flavodon flavus (Klotzsch) Ryvarden, a basidiomycete (NIOCC strain 312) isolated from decomposing leaves of a sea grass, decolorized pigments in molasses spent wash (MSW) by 80% after 8 days of incubation, when used at concentrations of 10% and 50%. Decolorizing activity was also present in media prepared with half-strength seawater (equivalent to 15 ppt salinity). Decolorizing activity was seen in low-nitrogen medium, nutrient-rich medium and in sugarcane bagasse medium. The percentage decolorization of MSW was highest when glucose or sucrose was used as the carbon source in the low-nitrogen medium. The production of lignin-modifying enzymes, manganese-dependent peroxidase (MNP) and laccase decreased in a medium containing MSW. MNP production and MSW decolorization were inversely correlated, suggesting no role for MNP in MSW decolorization. The decolorization of MSW was not effective when F. flavus was immobilized in calcium alginate beads. Decolorization was achieved best in oxygenated cultures. Besides color, total phenolics and chemical oxygen demand were reduced by 50% in MSW treated with F. flavus, suggesting its potential in the bioremediation of effluents.

Temperature, pH and electrolyte sensitivity, and heat, UV and disinfectant inactivation of sea bass ( Dicentrarchuslabrax) neuropathy nodavirus

The effect of temperature, pH and electrolytes on the stability of two Mediterranean sea bass neuropathy nodavirus isolates (SBNN) and the inactivation of SBNN by heating, exposure to ultraviolet radiation and chemical disinfectants was investigated in vitro using a striped snakehead fish cell line (SSN-1) for virus propagation and assay. The two nodavirus isolates showed no significant differences in response to the procedures examined. Nodavirus held in cell culture medium containing 5% foetal bovine serum was effectively inactivated within 4 days at 37°C and 3 months at 25°C but showed no significant loss of titre over 6 months at 15°C and still retained a measurable level of infectivity after storage for 1 year at this temperature. Virus suspensions in distilled water tolerated exposure to pH 2–11 with no significant loss of titre over 24 h. Thereafter, a steady diminution in infectivity was noted at pH 11 from day 3 and at pH 2 from day 15 onwards, but no loss of titre was recorded between pH 3–7 over 6 weeks storage. Infectivity titres fell gradually at a very similar rate for virus held at 15°C in balanced salt solution and full- and half-strength seawater over a 6-month test period. Virus held in freshwater, however, was markedly less stable and no viable virus could be detected after 6 months storage. SBNN was susceptible to heat treatment at 60°C within 30 min with no viable virus detected after 1 h. UV irradiation at an intensity of 440 μW/cm 2 resulted in a 99.9% linear reduction in virus titre after 8 min exposure. Treatment with 2% formalin was not totally effective even after 6 hours exposure at 15°C although virus titre was reduced. The effect of chlorine, iodine and peroxygen on SBNN at 15°C was noticeably different when organic matter in the form of foetal bovine serum (FBS) was present in the virus diluent. Suspensions of virus in distilled water were completely inactivated within 5 min by 50 ppm chlorine and 25 ppm iodine. Virus in Hanks' BSS+FBS, however, showed only a marginal loss in infectivity following similar treatments and significant levels of infectivity were still detectable after 30 min exposure to 100 ppm of either disinfectant. Treatment with an acid peroxygen disinfectant rapidly reduced virus infectivity in both distilled water and serum supplemented diluent within 5 min but infectious virus was not totally eliminated even after exposure for 30 min.

Effects of wastewater discharge on microbial populations and enzyme activities in mangrove soils

Soil leaching experiments were conducted to assess the impact of discharging wastewater, of two salinities, on bacterial population sizes and microbial activities in mangrove soils. Synthetic wastewater, prepared in either deionized water or half-strength seawater, was applied to trays containing mangrove soils three times a week for a total of 12 weeks. Results show that the mangrove soils were capable of removing pollutants such as Cu, Zn, Cd, P and N from the wastewater. The total counts of both aerobic and anaerobic heterotrophic bacteria, nitrifiers and denitrifiers in mangrove soils receiving wastewater were significantly higher than those found in the control soils. The adenosine triphosphate (ATP) content and the activity of dehydrogenase and alkaline phosphatase in soils were also not affected by wastewater treatment. This indicates that the organic matter and nutrients present in wastewater did cause a large increase in bacterial growth in soils. The retention of heavy metals did not show any harmful effect in the first 10 weeks of this study as any inhibitory effect due to heavy metals might have been overshadowed by the stimulatory effects of the nutrients. The mangrove soils receiving wastewater prepared in deionized water (fresh water) generally had higher population sizes of various bacterial functional groups and supported more microbial activities than that treated with saline wastewater. These results suggest that the wastewater inputs (in particular, organic matter and nutrient) and salinity would have more significant effects on the microbial activities in mangrove soils than heavy metals.

Effects of Salinity on Sperm Motility, Fertilization, and Development in the Pacific Herring, Clupea pallasi.

We investigated the effects of salinity on fertilization and early development in a population of Pacific herring, Clupea pallasi, that migrate from oceanic waters into the San Francisco Bay estuary to spawn. The salinity range for fertilization fell between 8 and 28 ppt, with an optimal range of about 12 to 24 ppt. In comparison, the range for a population of C. harengus membras (Airisto Sound, Finland) that reside year-round in the Baltic Sea was 4 to 24 ppt. Roles for both Na+ and K+ were indicated in C. pallasi fertilization since increasing Na+ in the presence of 10 mM K+ (concentration of seawater) mimicked the effects of increased overall salinity, whereas reduced effects were obtained if [K+] was held at 5 mM (that of half-strength seawater). The initiation of C. pallasi sperm motility by components of the egg chorion, a prerequisite for fertilization, was inhibited at both elevated (28 and 32 ppt) and reduced (4 and 8 ppt) salinities. Embryonic development through larval hatching in C. pallasi exhibited a salinity tolerance similar to that of fertilization; optimum development was obtained at salinities between 8 and 24 ppt. A comparison of developmental progression in 3.5, 14, and 28 ppt seawater revealed that salinity effects became evident during the post-gastrulation stages of development and that progression to hatching was delayed in both the lower and higher salinities for those embryos that completed development.

Study on the Nature of Starfish Larval Muscle CellsIn Vitro

Abstract We describe a culture method in which larval muscle cells of the starfish Asterias amurensis develop from epithelial cells, probably deriving from the coelomic pouches. The nature of the muscle which appears in the culture is described morphologically, physiologically and ultrastructurally. Cells were dissociated from the late gastrula stage, treated with 0.6 M of glycine in half-strength sea water free of Ca2+ and Mg2+ for 12 hr, and cultured for various periods. Elongated cells appeared after about a week from small aggregates of epithelial cells which were found among the mesenchymal network on the 1st day of culture. The characteristics of the elongated cells are as follows: (1) they possess two or more arms; (2) they adhere to the cultural substratum, mesenchyme cells, and themselves at all parts of the cell body; (3) they contract in response to acetylcholine; (4) they contain an abundance of fibrous actin and myosin throughout their cytoplasm; (5) the cytoplasm contains bundles of thick (1...

Studies on the physiology of somatolactin secretion in red drum and Atlantic croaker

The effects of exposure to water of different salinities and calcium concentrations, and to various backgrounds and illuminations on somatolactin (SL) levels in juvenile red drum (Sciaenops ocellatus) were investigated using a recently developed red drum SL radioimmunoassay. Plasma SL concentrations were also monitored in wild-caught Atlantic croaker (Micropogonias undulatus) during gonadal recrudescence. No correlations were obtained between plasma SL concentrations and different salinities, external calcium concentrations or reproductive condition in these sciaenid fishes. Plasma SL concentrations remained low (<1 ng ml-1) in red drum 1h, 1 day and 1 week after exposure to full strength seawater (salinity 37%, calcium 1290 ppm), half strength seawater (salinity 18%, calcium 744 ppm), fresh water (salinity 1%, calcium 260 ppm) or soft water (salinity 0%, calcium 0 ppm). Circulating levels of SL did not change significantly in wild-caught croaker at the onset of vitellogenesis. However, by the end of ovarian recrudescence (late-yolk globule stage), plasma SL levels were significantly lower than those observed in females with immature (perinucleolar) oocytes. In contrast, plasma SL levels showed marked differences in red drum exposed to various backgrounds and illuminations. Plasma SL was lower in red drum kept in a light background (<1 ng ml-1) than in those kept in a black background or in the dark (1.4-6.9 ng ml-1). The highest plasma SL concentration (4–30 ng ml-1) was obtained in red drum kept in a black background without illumination. These results suggest that SL is involved in the adaptation of the red drum to various backgrounds and illumination levels. SL may not have an important role during the reproductive cycle and adaptation to water of different salinities and calcium concentrations in sciaenid fishes.

A Rapid Adaptation to Low Salinity of Inland-Colonizing Populations of the Littoral Grass Leymus arenarius

Ecological studies on salt tolerance in plants have focused mainly on population differentiation with limited information on the timescale and genetic basis of this adaptation. This study reports on rapid adaptation of the littoral grass Leymus arenarius (lymegrass) to low salinity that has been found since 1967 to colonize the roadsides studied in Finland. Roadsides offer an open microenvironment similar to that of the beach. Thirty-four roadside and littoral populations were differentiated by germinating seeds at 300 mM NaCl, ca. half-strength seawater. Seeds of inland and sub-maritime populations had significantly (P < .001) less salt tolerance than littoral populations. The shortest distances of the habitats from the seashores showed significant (P < .001) negative correlation with the germination ability at 300 mM NaCl. Electrophoretic patterns of endospermal glycosylated proteins of high-molar-mass leymins were significantly (P < .01) correlated to total germination at 300 mM NaCl. Inland populations usually had three bands of the high-molar-mass leymins, but six bands of leymins were found in seeds of the most salt tolerant population. The rapid adaptation of lymegrass seed germination to low salinity indicates that only a few genes are involved in its salt tolerance and that the activity of such genes provides a load where salt tolerance is unnecessary. Alternatively, salinity in the habitat may control the expression of some genes.

Heat flux, oxygen flux, and mitochondrial redox state as a function of oxygen availability and ciliary activity in excised gills of Mytilus edulis.

The ciliated gill of bivalve molluscs is situated at an interface between animal and environment. Cilia propel water past the gills to deliver oxygen and nutrition to the animal. Ciliary activity is driven by dynein ATPases and requires a continual supply of ATP at a rate sufficient to match the rate of ATP hydrolysis. Control of the balance between ATP supply and demand in the ciliated gill, and how this balance may be altered by environmental stresses, is unknown. In this pilot study, metabolic flux of excised gills from the marine mussel Mytilus edulis was examined in response to oxygen availability and to serotonin-stimulated ciliary activity. Heat flux and oxygen flux were measured simultaneously with calorespirometry. In parallel experiments, the redox state of mitochondrial cytochromes was determined with in vivo spectrophotometry. Above 4 kPa pO2, heat flux was supported by aerobic metabolism. Anoxic heat flux was less than 5% of aerobic heat flux. Heat and oxygen fluxes nearly doubled in gills in the presence of 10 microM serotonin; however, half-maximal pO2 for heat and oxygen fluxes and for reduction of mitochondrial cytochromes remained unchanged from control levels. In gills having inactive cilia in half-strength seawater, half-maximal pO2 for heat and oxygen fluxes and for cytochrome reduction nearly doubled compared with valves in full-strength seawater. These data indicate that limitation to oxygen delivery imposed by boundary layers may be reduced when ciliary beat frequency is elevated, leading to enhanced oxygen flux to intracellular mitochondrial which matches the increased energy demand by the cilia.