Effect of salinity,temperature and hypersaline conditions on the seed germination in Limonium mansanetianum an endemic and threatened Mediterranean species

Abstract

Limonium mansanetianum is catalogued as critically threatened (CR) species and it is included in Valencian Catalogue of Threatened Plant Species. Limonium mansanetianum is a gypsicolous species, which only lives in a restricted area to south-centre of Valencia province (Spain). The species is a low-branched woody shrub with summer flowering. The influence of incubation temperature (10°, 15°, 20° and 25°/20?°C) and salinity (0%–3.0% NaCl) on seed germination of L. mansanetianum was studied. Best seed germination was obtained in distilled water controls. Seed germination decreased with an increase in salinity and few seeds germinated at 2.5% and 3.0% NaCl. Optimal temperature regime for germination was 15?°C where germination in 0.5% and 1.0% NaCl was not affected. Recovery and hypersaline conditions experiments showed that L. mansanetianum seeds displayed a greater tolerance to high salinity and temperature stress before germination.     

Laboratory studies on the life-histories of four enchytraeid worms (Oligochaeta) which inhabit sewage percolating filters

The life-histories of four enchytraeid worms, Lumbricillus rivalis, Enchy-traeus coronatus, E. buchholzi, and E. albidus which occur in sewage percolating filters, were studied under laboratory conditions at 8 , 15 and 20°C. The number of ova per cocoon varied from 0 to 50 (L. rivalis), 0 to 33 (E. coronatus), 1 to 9 (E. buchholzi) and 0 to 22 (E. albidus). The mean number of ova per cocoon was highest at 15°C for all species except E. coronatus which had a highest mean value at 8°C. The number of ova in cocoons was correlated with cocoon length (P < 0.001) for all species. Cocoon production usually increased with temperature ranging from 0.8 cocoons per adult per week at 8°C to 2.0 at 20°C for L. rivalis, and from 1–4 to about 2.6 for E. coronatus and E. buchholzi. The total number of ova produced by each E. coronatus (350 at 8°C to 550 at 20°C) was similar to that produced by each L. rivalis (600 at 8°C to 350 at 20°C) and was about five times greater than the total numbers produced by the other two species. Cocoon and ova production and the number of ova per cocoon varied with the age of the adult, usually reaching a peak soon after maturity. Hatching success was low and generally 40–50 % of ova failed to develop; subsequent mortality among immature worms was about 10–20%. Growth was more rapid at the higher temperatures; L. rivalis matured in about 26 days at 20°C, the clitellum forming when the worm was 13–14 mm long; data for the other species are 13 days and 5–6 mm (E. coronatus); 16 days and 3–4 mm (E. buchholzi); 28 days and 13–14 mm (E. albidus). The maturation period at 8°C was at least twice that at 20°C. The generation period (cocoon to cocoon) was about a month at 20°C for all species except E. albidus (2 months), but as some species had longer reproductive periods than others the actual number of generations per year was highest in E. buchholzi, 7.0 per year, and lowest in E. albidus, about 3.3 per year, At 8°C all four species had between 1.4 and 2.8 generations a year. A comparison of expected and observed population densities of L. rivalis and E. coronatus in a sewage percolating filter showed that neither achieved values approaching their potential summer densities although ample food was apparently available. Of the four species studied only E. buchholzi produced viable ova without pairing.     

The effect of Sea Water and Temperature on the Germination Behaviour of Crithmum maritimum

The seeds of Crithmmm maritimum L. were germinated floating on various concentrations of sea water up to 50% at constant temperatures of 5, 10, 15, 20, and 25°C and at alternating temperatures of 5 and 15°C. 5 and 25°C. and 15 and 25°C. Significantly higher germination was obtained at alternating than at constant temperature. When two constant temperatures at which no germination occurred were alternated, good germination was obtained. There was reduced germination and increase in time of first germination as sea water concentration increased, in the absence of sea water, high temperature caused not only severe inhibition of germination but also permanent injury to the seeds. The results help to explain the germination behaviour of the species in nature.     

Plasma osmolality and oxygen consumption of perch Perca fluviatilis in response to different salinities and temperatures

The present study determined the blood plasma osmolality and oxygen consumption of the perch Perca fluviatilis at different salinities (0, 10 and 15) and temperatures (5, 10 and 20° C). Blood plasma osmolality increased with salinity at all temperatures. Standard metabolic rate (SMR) increased with salinity at 10 and 20° C. Maximum metabolic rate (MMR) and aerobic scope was lowest at salinity of 15 at 5° C, yet at 20° C, they were lowest at a salinity of 0. A cost of osmoregulation (SMR at a salinity of 0 and 15 compared with SMR at a salinity of 10) could only be detected at a salinity of 15 at 20° C, where it was 28%. The results show that P. fluviatilis have capacity to osmoregulate in hyper‐osmotic environments. This contradicts previous studies and indicates intraspecific variability in osmoregulatory capabilities among P. fluviatilis populations or habitat origins. An apparent cost of osmoregulation (28%) at a salinity of 15 at 20° C indicates that the cost of osmoregulation in P. fluviatilis increases with temperature under hyperosmotic conditions and a power analysis showed that the cost of osmoregulation could be lower than 12·5% under other environmental conditions. The effect of salinity on MMR is possibly due to a reduction in gill permeability, initiated to reduce osmotic stress. An interaction between salinity and temperature on aerobic scope shows that high salinity habitats are energetically beneficial during warm periods (summer), whereas low salinity habitats are energetically beneficial during cold periods (winter). It is suggested, therefore, that the seasonal migrations of P. fluviatilis between brackish and fresh water is to select an environment that is optimal for metabolism and aerobic scope.     

PHYSIOLOGICAL PERFORMANCE OF FLOATING GIANT KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE): LATITUDINAL VARIABILITY IN THE EFFECTS OF TEMPERATURE AND GRAZING1

Rafts of Macrocystis pyrifera (L.) C. Agardh can act as an important dispersal vehicle for a multitude of organisms, but this mechanism requires prolonged persistence of floating kelps at the sea surface. When detached, kelps become transferred into higher temperature and irradiance regimes at the sea surface, which may negatively affect kelp physiology and thus their ability to persist for long periods after detachment. To examine the effect of water temperature and herbivory on the photosynthetic performance, pigment composition, carbonic anhydrase (CA) activity, and the nitrogen (N) and carbon (C) content of floating M. pyrifera, experiments were conducted at three sites (20° S, 30° S, 40° S) along the Chilean Pacific coast. Sporophytes of M. pyrifera were maintained at three different temperatures (ambient, ambient ? 4°C, ambient + 4°C) and in presence or absence of the amphipod Peramphithoe femorata for 14 d. CA activity decreased at 20° S and 30° S, where water temperatures and irradiances were highest. At both sites, pigment contents were substantially lower in the experimental algae than in the initial algae, an effect that was enhanced by grazers. Floating kelps at 20° S could not withstand water temperatures >24°C and sank at day 5 of experimentation. Maximal quantum yield decreased at 20° S and 30° S but remained high at 40° S. It is concluded that environmental stress is low for kelps floating under moderate temperature and irradiance conditions (i.e., at 40° S), ensuring their physiological integrity at the sea surface and, consequently, a high dispersal potential for associated biota.     

THE INFLUENCE OF SALINITY AND TEMPERATURE COVARIATION ON THE PHOTOPHYSIOLOGICAL CHARACTERISTICS OF ANTARCTIC SEA ICE MICROALGAE1

The responses of sea ice microalgae to variation in ambient irradiance (0 to 150 μE · m^?2· s^?1), temperature (–6° to + 6° C), and salinity (0 to 100 ppt) were tested to determine whether these variables act independently or in concert to influence rates of microalgal photosynthesis. The photosynthetic efficiency and maximum photosynthetic rate for sea ice microalgae increased as a function of incubation temperature between -6° and + 6° C. Furthermore, photosynthetic efficiency, maximum photosynthetic rate, and quantum yield were greatest at salinities between SO and 50 ppt. In contrast, the mean specific absorption coefficients were lowest near seawater salinities, and the saturating irradiance, I_s, appeared to be inversely proportional to salinity. Results also suggest that the effects of salinity on the growth of sea ice microalgae are independent of those elicited by temperature or light, and that the functional relationship between salinity and light or temperature is multiplicative. This information is essential to the proper formulation of algorithms used to describe algal growth in environments where light, temperature, and salinity are changing simultaneously, such as within sea ice or within the water column at the marginal ice edge zone.     

Halophilic-psychrotrophic bacteria of an Alaskan cryopeg—a model for astrobiology

Cryopegs, lenses of hypersaline unfrozen soil or water within permafrost, are a model for astrobiology, since free water can only be present on cryogenic bodies and planets in the form of brine. In this paper the diversity of aerobic halophilic-psychrotrophic microorganisms from an Alaskan cryopeg (Barrow Cape) were studied and described for the first time. This cryopeg is characterized by a constant subzero temperature (–7°C), high salinity (total mineralization is about 120 g/L) and isolation from external influences for a geologically significant period of time. Our study has revealed a large number of microorganisms capable of growth at low temperature (4°C) in a wide range of salinities from 5 to 250 g/L of NaCl, the latter being 3 times higher than the natural salt concentration of the Alaskan cryopeg. The microorganisms identified are comprised of four major phyla: Actinobacteria (genera Brevibacterium, Citricoccus, Microbacterium), Firmicutes (genus Paenibacillus), Bacteroidetes (genus Sphingobacterium), and Proteobacteria (genus Ochrobactrum).     

Variation in temperature and light but not salinity invokes antioxidant enzyme activities in germinating seeds of Salsola drummondii

Seeds with efficient antioxidant defence system show higher germination under stress conditions; however, such information is limited for the halophyte seeds. We therefore studied lipid peroxidation and antioxidant responses of a leaf-succulent halophyte Salsola drummondii during seed germination under different salinity levels (0, 200 and 800 mM NaCl), temperature (10/20, 20/30 and 25/35°C) and light regimes. Seeds absorbed water and germinated in less than 1 h in non-saline control while increases in salinity decreased the rate of water uptake as well as seed germination. Non-optimal temperatures (10/20 and 25/35°C) and complete dark condition reduced seed germination in comparison to those seeds germinated under optimal temperature (20/30°C) and 12-h photoperiod, respectively. Generally, higher lipid peroxidation and antioxidant enzyme activities were observed in seeds at non-optimal temperature and in those seeds germinated in dark. Decrease in reduced ascorbic acid content was found in highest salinity and temperature treatments, while reduced glutathione content did not change significantly with changes in salinity, temperature and light regimes. These results indicate variation in temperature and light but not salinity enhances antioxidant enzyme activities in germinating seeds of Salsola drummondii.     

Effects of salinity and temperature on ex situ germination of the threatened Gulf of St. Lawrence Aster,Symphyotrichum laurentianum Fernald (Nesom)

The threatened Gulf of St. Lawrence Aster, Symphyotrichum laurentianum Fernald (Nesom), is an annual coastal halophyte of the southern Gulf of St. Lawrence, Canada. We examined the effects of salinity (0–20 g/L) and temperature (16–30°C) on germination of S. laurentianum seeds over 32 days. The time‐course of germination was significantly affected by both salinity and temperature. At lower temperatures (16°C and 23°C), germination was inhibited by salt water at days 16 and 32. However, at 30°C germination rates after 16 days were highest at an intermediate salinity, whereas after 32 days germination was uniformly high in all salinity treatments. Overall, the effect of temperature on germination was much stronger than the effect of salinity. Delays in germination resulting from exposure to salinity or from low soil temperatures could set up strong size asymmetries between seedlings of S. laurentianum and the surrounding vegetation, leading to suppression of growing seedlings via shading. Because germination has the potential to be a significant population bottleneck for this seed‐dependent annual, conservation efforts should consider microsite suitability for germination in the management of natural populations and in the selection of sites for explants.     

Effects of salinity and temperature on Deschampsia antarctica

Deschampsia antarctica is one of two species of vascular plants native to Antarctica. Populations of D. antarctica have become established on recently exposed glacial forelands on the Antarctic Peninsula and these plants may rely upon nutrient inputs from hauled out mammals, seabirds and sea spray. However, not much is known about the ability of these plants to tolerate salinity stress. We examined the effects of salinity and temperature on growth, reproduction, chlorophyll fluorescence and water relations of D. antarctica. In addition, we analysed concentrations of free proline in leaves and roots as previous studies have found large increases in the concentration of this amino acid in response to environmental stress. The growth chamber experiment was a 3 × 3 (temperature × salinity) complete factorial. Plants were grown at three temperature regimes: 7°/7°C, 12°/7°C, and 20°/7°C day/night and three salinity levels: <0.02 decismen per metre (dS m⁻¹; “low salinity”), 2.5 dS m⁻¹ (“medium salinity”), and 5.0 dS m⁻¹ (“high salinity”) for 66 days. Warmer temperatures improved leaf and tiller production as well as leaf and root length, which is consistent with previous findings on this species. Salinity reduced final root length by 6 and 13% in the medium and high-salinity treatments, respectively. Plants growing in medium and high-salinity treatments had xylem pressures that were more negative and higher free-proline concentrations, suggesting that proline may act as an osmoregulant in D. antarctica.     

The combined effects of temperature,salinity, and declining oxygen tension on oxygen consumption in the marine pulmonate Amphibola crenata (Gmelin, 1791)

Oxygen consumption of Amphibola crenata (Gmelin) was measured in various salinity-temperature combinations (< 0.1‰ to 41‰ salinity and 5 to 30°C) in air, and following exposure to declining oxygen tensions. In all experimental conditions, respiration varied with the 0.44 power of the body weight (sd = 0.14). The aquatic rate was consistently higher than the aerial rate of oxygen consumption, although at 30 °C the two rates were similar. Oxygen consumption increased with temperature up to 25 °C in all salinities; the lowest values were recorded at temperatures below 10 °C and at 30 °C in the most dilute medium. At all exposure temperatures, the oxygen consumption of Amphibola decreased regularly with salinity down to 0.1 ‰, and following exposure to concentrated sea water (41‰). Salinity had the least effect at 15 °C which was the acclimation temperature. In general, all of the temperature coefficients (Q₁₀ values) were low, < 1.65. However, Q₁₀ values above 2.8 were recorded at a salinity of 17.8‰ between 10 and 15 °C. Oxygen consumption of all size classes of Amphibola was more temperature dependent in air than in water and small individuals show a greater difference between their aerial and aquatic rates than larger snails. The rates of oxygen consumption in declining oxygen tensions were expressed as fractions of the rates in air saturated sea water at each experimental salinity-temperature combination. The quadratic coefficient B₂ becomes increasingly more negative with both decreasing salinity and temperatures up to 20 °C. At higher temperatures (25 and 30 °C) the response is reversed such that O₂ uptake in snails becomes increasingly independent of declining oxygen tensions at higher salinities. On exposure to a salinity of 4‰, Amphibola showed no systematic response to declining oxygen tension with respect to temperature. The ability of Amphibola to maintain its rate of oxygen consumption in a wide range of environmental conditions is discussed in relation to its potential for invading terrestrial habitats and its widespread distribution on New Zealand's intertidal mudflats.     

Diffusion in plant cuticles as affected by temperature and size of organic solutes: similarity and diversity among species

Mobilities of lipophilic organic solutes in cuticular membranes (CM) isolated from mature leaves of Citrus aurantium L., Citrus grandis L., Hedera helix L., IIex aquifolium L., Ilex paraguariensis St.-Hil., Mains domestica Borkh., Prunus armeniaca L., Primus laurocerasus L., Pyrus communis L., Pyrus pyrifolia (Burm. f.) Nakai, Stephanotis florihunda Brongn. and Strophantus gratus Baill. were measured over a temperature range of 15–78°C. In this range, solute mobilities increased up to 1000-fold, which corresponds to temperature coefficients Q₁₀ of 3 (IAA in P. armeniaca) to 14 (cholesterol in H. helix). For most species, Arrhenius graphs showed good linearity up to 40°C, and up to 78°C for some species, while for others activation energies declined with increasing temperature. However, no distinct phase transitions caused by sudden structural changes in the CM were observed. In three species we examined whether heating to 70°C changed solute mobility irreversibly by comparing Arrhenius graphs for two successive experiments with the same CM. The two graphs were very similar for P. laurocerasus, while mobilities in the second graph were somewhat reduced for C. aurantium and greatly increased (at 25 and 35°C) for H. helix. This indicates rearrangements of at least some wax constituents when heated to high temperatures. The activation energies of diffusion (E_D) ranged from 75 to 189 KJ mol^?11 depending on species and solute size. Size selectivity and variability between cuticles decreased with increasing temperature, and this is caused by differences in (E_D). An excellent correlation between the pre-exponential factor of the Arrhenius equation and E_D was observed, which is evidence that organic solutes differing greatly in molecular size (130–349 cm³ mol^?1) and cuticle/water partition coefficient (25–10⁸) use similar diffusion paths in the CM of all 12 plant species tested. Diffusion occurs in regions with identical physicochemical properties and differs only in magnitude.     

Reduced salinities compromise the thermal tolerance of hypersaline specialist diving beetles

Inland saline waters are globally threatened habitats that harbour unique assemblages of specialist invertebrates. In many Mediterranean regions, irrigation associated with intensive agriculture is lowering the salinity of these habitats, resulting in the loss of their specialist biota, although the mechanisms by which reductions in salinity lead to species loss are poorly understood. In the present study, the effects of reduced salinity on the temperature tolerance and thermal acclimatory abilities of two related species of hypersaline water beetles, Nebrioporus baeticus (Schaum) and Nebrioporus ceresyi (Aubé), are explored. Both upper (UTL) and lower thermal limits (LTL) are assessed, and both salinity and temperature are found to influence the thermal biology of Nebrioporus. Mean UTLs are greater in individuals of both species acclimated at high salinities, with salinity appearing to be more important than acclimation temperature in determining UTL. In both taxa, the lowest mean LTLs are recorded in individuals acclimated at the highest salinities and lowest temperatures; temperature‐dependent acclimation is only reported after exposure to relatively high salinities. The data show that salinity influences the thermal tolerance and acclimatory ability of these hypersaline beetles, and that lowered salinity compromises the ability of adult Nebrioporus to cope with both heat and cold. Such an effect may partly explain why specialist species are lost from hypersaline habitats subject to salinity reductions, and suggests that ongoing reduction in salinity may compromise the ability of such specialist taxa to cope with rapid climate change.     

Exposure of goldsinny, rock cook and corkwing wrasse to low temperature and low salinity: survival, blood physiology and seasonal variation

Wrasse used as cleaner fish with farmed Atlantic salmon Salmo salar can be subjected to large and rapid temperature and salinity fluctuations in late autumn and early winter, when summer-warmed surface water is affected by early snowmelt episodes. Because of their containment in sea cages, wrasse which are essentially acclimated to summer temperatures may be rapidly exposed to winter conditions. Short-term tolerance of low temperature and low salinity by three species of wrasse, goldsinny Ctenolabrus rupestris rock cook Centrolabrus exoletus corkwing Crenilabrus melops caught during the summer, and winter-caught corkwing, was investigated. A 3–day period at 30 or 32‰ salinity and temperature 8, 6 or 4° C (for summer-caught fish; 4° C only for winter-caught) was followed by a decline in salinity to 24, 16 or 8‰ over c. 36 h, followed by a further 24 h at these salinities held constant, at each of the three temperatures. Controls in 30 or 32‰ were maintained at 8, 6 or 4° C. Mortality of summer-caught corkwing and rock cook was high at 4° C, whereas the influence of salinity on mortality was small. Mortality of goldsinny was low or zero in all treatments. Surviving corkwing and rock cook after 3 days at 4° C and 32‰ salinity had elevated plasma osmolality: in summer-caught corkwing, plasma [Cl°] and [Na⁺] were high, whereas in rock cook only [Na⁺] was high. Haematocrit was low in summer-caught corkwing, high in rock cook. In survivors of all three species at the end of the experiment, values of all these parameters were comparable with those of fish at the beginning of the experiment, except that survivors at low salinity (8, 16‰) had low plasma osmolality, at all temperatures, and in surviving rock cook in these treatments haematocrit was high and plasma [Cl^?] was low. Winter-caught corkwing had higher osmolality, [Na⁺] and [Cl^?] than summer-caught corkwing; there was no difference in haematocrit. Survival of wintercaught corkwing exposed to four salinities at 4° C was much higher than that of summercaught corkwing under the same conditions. Little change in blood physiology was recorded for winter-caught corkwing, with only fish subjected to 8‰ and 4° C showing signs of osmoregulatory stress. The interspecific and seasonal differences in survival and blood physiology at low temperature and low salinity are discussed in relation to wrasse survival over winter, both in the field and in salmon farms.     

Accumulation of Free Proline at Low Temperatures

The accumulation of free proline in the first leaves of barley, Hordeum distichum L., and wheat, Triticum aestivum L., in response to a range of low temperatures was examined with 10-day-old plants. In barley (cv. Prior) no proline accumulated at 8°C or above, but in wheat (cv. Gabo) proline accumulated at 12°C and lower temperatures. In barley, the first leaf survived for 29 days following transfer to 5°C and continued to accumulate proline throughout this period. In contrast, the first leaves of plants maintained at 20°C survived for 13 days only and accumulated no proline. Proline accumulation at low temperature was shown to be light-dependent, both in intact plants and excised leaf sections, and the light requirement could not be replaced by supplying leaf segments with precursors of proline. Proline accumulation in response to water stress was not light-dependent at 20°C but was at 5°C. Inter-specific and intra-specific variation in the extent of accumulation in response to low temperature was also examined. Considerable variation was encountered but there was no clear relationship with geographical distribution or chilling sensitivity for the species and no correlation with accumulation in response to water stress in the cultivars of barley examined.     

Nutrient and water flux in a small arctic watershed: an overview

The “Response, Resistance, Resilience to, and Recovery from Disturbance in Arctic Ecosystems” (R4D) program initially concentrated on impacts of altered water and nutrient inputs on tussock tundra vegetation. The intensive site is at Imnavait Creek (68°C 37′ N, 149° 17′ E), near Toolik Lake. Alaska in the foothills of the Brooks Range, approximately 200 km south of Prudhoe Bay. Tussock tundra was selected for initial study because it has an extensive distribution in the Alaskan Arctic (80% of the arctic region), the majority of the pipeline corridor north of the Brooks Range passes through tussock tundra, and disturbances of arctic tundra are expected to occur in the future. Also important is that 18% of the circumpolar arctic primary productivity and 47% of the circumpolar arctic stored carbon are in tussock tundra. Water and nutrient additions were performed because they frequently accompany disturbance and development in the Arctic. Emphasis was placed on determining responses of physical, physiological, and ecosystem processes to environmental change in such a way that extrapolations to other areas would be facilitated. The hills near Imnavait Creek are covered by glacial till of the Sagavanirktok River glaciation. with a deep organic layer on the less exposed hill slopes and valleys. The vegetation is dominated by Eriophorum vaginatum L., Betula nana L., Vaccirtium uliginosum L, Vaccinium viiis-idaea L., Ledum palustre L., Salix pulcbra L., and Sphagnum spp. Winds were rarely calm but seldom exceed 17 m s^?1, generally from the east-southeast to the south-southwest (66%). Precipitation in 1986 was 344 mm, about half of which was snowfall. Mean temperature in 1986 was ?8.1°C, with an absolute minimum of ?43°C. Mean July temperature was between 9.8 and 13.7°C. Nutrients are more mobile than previously thought, moving an estimated 10 m downslope in the first growing season. It underscores the importance of the winter environment to biological and hydrological processes. Greater water flow results in increased plant growth rates, leaf area, and biomass. Effects of changes in nutrient and water supply on photosynthesis were minimal. Where increases in productivity took place, they occurred more likely as a result of changes in allocation patterns, including an initial redirection of carbohydrate stores to new leaf development, than from increases in photosynthetic rates. The work reported here indicates that the downslope transmission of nutrient and water flow effects caused by altered drainage and nutrient supply may result in a larger area of impact than previously thought.     

Modulation of physiological performance by temperature and salinity in the sugar kelp Saccharina latissima

The sugar kelp Saccharina latissima experiences a wide range of environmental conditions along its geographical and vertical distribution range. Temperature and salinity are two critical drivers influencing growth, photosynthesis and biochemical composition. Moreover, interactive effects might modify the results described for single effects. In shallow water coastal systems, exposure to rising temperatures and low salinity are expected as consequence of global warming, increased precipitation and coastal run‐off. To understand the acclimation mechanisms of S. latissima to changes in temperature and salinity and their interactions, we performed a mechanistic laboratory experiment in which juvenile sporophytes from Brittany, France were exposed to a combination of three temperatures (0, 8 and 15°C) and two salinity levels (20 and 30 psu (practical salinity units)). After a temperature acclimation of 7 days, sporophytes were exposed to low salinity (20 psu) for a period of 11 days. Growth, and maximal quantum yield of photosystem II (Fv/Fm), pigments, mannitol content and C:N ratio were measured over time. We report for the first time in S. latissima a fivefold increase in the osmolyte mannitol in response to low temperature (0°C) compared to 8 and 15°C that may have ecological and economic implications. Low temperatures significantly affected all parameters, mostly in a negative way. Chlorophyll a, the accessory pigment pool, growth and Fv/Fm were significantly lower at 0°C, while the de‐epoxidation state of the xanthophyll cycle was increased at both 0 and 8°C compared to 15°C. Mannitol content and growth decreased with decreased salinity; in contrast, pigment content and Fv/Fm were to a large extent irresponsive to salinity. In comparison to S. latissima originating from an Arctic population, despite some reported differences, this study reveals a remarkably similar impact of temperature and salinity variation, reflecting the large degree of adaptability in this species.     

Althenia Filiformis Petit: Azione Della Temperatura e Dell'Acqua di Mare Sulla Germinazione

Abstract

Effects of temperature and sea water on germination behaviour of Althenia filiformis Petit seeds. - Germination capacity and energy of Althenia filiformis Petit seeds have been investigated, 90 and 180 days after ripening, to carry out a preliminary study on ecology of this species.

This species, halophite and hydrophyte, is spreaded along the coast shores of middle-west mediterranean sea and atlantic shores of Morocco, Spain, Portugal and France.

Seeds were soaked in the dark, at 10°, 20°, 30°C, in solutions at different salt concentration: sea water; sea water diluted in deionized water at ratios (v/v) 1: 2, 1: 4, 1: 8; sea water plus 26 gr/l NaCl; deionized water, as control.

The experimental results show that germination is reduced and delayed when seeds are soaked in progressively concentrated salt solutions; in sea water plus 26 gr/l NaCl seed germination is inhibited.

Seeds pretreated by soaking at 3°C for 10 days in sea water diluted (1:1) by deionized water did not show, when soaked in salt solution at weak and middle concentration, any delay in germination in comparison with unpretreated seeds. On the contrary, pretreated and unpretreated seeds sown in sea water at 30°C had shown, 180 days after ripening, a significant depression in germination values as compared with seeds sown at 20°C.     

PROTEINS IMMUNOLOGICALLY RELATED TO DEHYDRINS IN FUCOID ALGAE

Adult fucoid algae on Atlantic shores have well-characterized, species-specific tolerances to the varying levels of desiccation that occur from the low to high intertidal zones; however, less is known about embryonic tolerances and their mechanistic basis. We investigated this by 1) exposing embryos of Fucus evanescens C. Agardh, F. spiralis L., and F. vesiculosus L. from the Maine shore to osmotic desiccation in hypersaline seawater and 2) examining whether these embryos contain species-specific dehydrins, proteins first identified in higher plants that are hypothesized to confer tolerance to dehydration. Embryonic survival when cultured in hypersaline seawater >100 practical salinity units (psu) correlated with the position of these species in the intertidal zone (F. spiralis > F. vesiculosus > F. evanescens), but all 1-day-old embryos of these species tolerated treatment with 100 psu or lower seawater. Proteins (17–105 kDa) immunologically related to dehydrins were detected on western blots with dehydrin antibodies raised against a synthetic peptide representing the conserved motif of dehydrins in higher plants. These proteins were constitutive and unstable when subjected to prolonged (>15 min) temperatures above 55° C, unlike most higher plant dehydrins, which are inducible and remain soluble at 75°–100° C. The presence of these proteins was species- and stage-specific. Sperm of F. vesiculosus had a characteristic protein of 76 kDa, whereas eggs and embryos (6 h to 3 days old) had a 92-kDa protein. By 1 week of age, expression of the 92-kDa protein decreased, and the 35-kDa protein of adults was present. Embryos of A. nodosum L. and Pelvetia compressa J. Agardh DeToni contained an 85-kDa protein rather than the 92-kDa protein of Fucus embryos (F. distichus L., F. evanescens, F. spiralis, and F. vesiculosus). The 92-kDa protein became more abundant in embryos exposed to hyperosmotic seawater at 50 psu (F. evanescens and F. vesiculosus) or 150 psu (F. spiralis); however, dehydrin-like proteins of some molecular masses decreased in abundance simultaneously. Further characterization of these proteins is required to establish whether they protect embryos against intertidal desiccation.