The effect of salinity change on the heart rate of Mytilus edulis specimens from different ecological zones

The heart rate of specimens of Mytilus edulis (L.) both from the sublittoral and littoral zones exposed to normal and altered salinity was investigated in a long-term experiment. The heart rate was monitored by a non-invasive method for nine days. The heart rate of sublittoral mussels was higher than that of littoral ones. This suggests a higher level of metabolic activity in sublittoral mussels. When exposed to moderate hyposalinity (15 g l⁻¹) M. edulis from both zones showed a significant decrease in the heart rate with respect to the control salinity (25 g l⁻¹), but sublittoral mussels had a more prominent bradycardia. The heart beat quickly accelerated in all organisms when they were returned to the control salinity medium. Throughout the experiment, heart contractions halted with distinct periodicity in all mussels.     

Effect of the Razdol’naya River on structure of the free-living nematode community of the Amursky Bay,Sea of Japan

The effect of the Razdol’naya River on the littoral and sublittoral nematode community was studied in the innermost part of the Amursky Bay. Thanks to the seasonal abundance of juveniles of macrobenthic animals, pseudomacrobenthic species prevailed in the meiobenthos littoral community. Juvenile amphipods dominated (39.5%), the percentage of nematodes was 18.4% (45 species). The nematodes dominated in the meiobenthos community (65.7%, 71 species) at the sublittoral zone. The similarity of the species structure of littoral and sublittoral nematodes reached 36.5%. Low population density (2.6±1.7 thousand ind/m²) and poor species diversity of nematodes (7 species), the dominating form being Oncholaimium paraolium, were recorded at the littoral zone, which was subjected to direct riverine influence (1‰salinity). The correlation analysis revealed no relationship between salinity and population density of nematodes at the littoral zone. At the sublittoral zone (at stations of salinity less than 2.85‰) the parameters of population density (73.9±32.3 thousand ind/m²) and species diversity (12 species) of nematodes were the lowest, Parodontophora timmica dominated. A poor expressed dependence between the density of nematode populations and salinity was revealed. The correlation between the average size of ground particles and population density of nematodes was recorded. The greatest similarity of the species structure of littoral and sublittoral nematodes (26.67%) was recorded on gravel-sand bottoms.     

Heart Rate in the Blue Mussel <Emphasis Type="Italic">Mytilus edulis</Emphasis> (Bivalvia) under Salinity Change

The heart rate (HR) was studied applying noninvasive monitoring in the blue mussel Mytilus edulis L. from the White Sea. It was shown that the sublittoral mussels had a higher cardiac activity than the littoral mussels. Mollusks responded to a drop in salinity from 25 to 15‰ with a decrease in HR, which was more pronounced in sublittoral individuals. Acclimated mollusks sharply increased their HR upon being returned to the initial salinity (deacclimation). The cardiac activity normalized completely within two days after the beginning of the deacclimation.     

Heart rate variation patterns in some representatives of Bivalvia

The pattern of heart rate variation was studied in bivalves sublittoral (aquaculture) and littoral mussels Mytilus edulis L. and Hiatella arctica L. in a long-term experiment at constant salinity (25‰) and temperature (10°C). Periodic changes in heart rate were observed in both littoral and sublittoral mussels. Heart activity could regularly decrease up to temporary cardiac arrest. Changes in H. arctica heart rate were much less pronounced compared to mussels and no cardiac arrest was observed.     

Endophytic fungal pre-treatments of seeds alleviates salinity stress effects in soybean plants

In the present study, four endophytic fungi (GM-1, GM-2, GM-3, and GM-4) were tested for their ability to improve soybean plant growth under salinity stress conditions. The seed germination and plant growth were higher in seeds pretreated with endophytic fungal cultures than their controls. The positive influence of fungi on plant growth was supported by gibberellins analysis of culture filtrate (CF), which showed wide diversity and various concentrations of GAs. Specifically, GA₄, GA₇, GA₈, GA₉, GA₁₂, and GA₂₀ were found in fungal CFs. Under salinity stress conditions, GM-1 significantly enhanced the length and fresh weight of soybean plants relative to other fungal treatments. GM-1 effectively mitigated the adverse effects of salinity by limiting lipid peroxidation and accumulating protein content. GM-2, GM-3, and GM-4 also counteracted the salinity induced oxidative stress in soybean plants through reduction of lipid peroxidation and enhancement of protein content, maintaining the length and fresh weight of shoots. The activities of the antioxidant enzymes catalase, superoxide dismutase and peroxidase were inhibited in salinity exposed plants, while GM-1 significantly enhanced these antioxidant enzyme activities in plants under salt stress. GM-1 treatment also showed lower levels of abscisic acid and elevated levels of salicylic acid in plants under salinity stress. Hence, GM-1 was identified as Fusarium verticillioides (teleomorph Gibberella moniliformis) isolate RK01 based on its DNA sequence homology. These results suggest that endophytic fungal (F. verticillioides) pre-treatment of soybean seeds would be an effective method to promote soybean plant growth under salinity stress conditions.     

Characterization of salt-tolerance mechanisms in mycorrhizal (Claroideoglomus etunicatum) halophytic grass,Puccinellia distans

Responses of Puccinellia distans, a halophytic grass to low (50 mM) and high (200 mM) NaCl salinity, were studied in a sand culture experiment without or with inoculation by arbuscular mycorrhizal fungus (AMF), Claroideoglomus etunicatum isolated from its saline habitat. Plant biomass was not influenced by salinity levels, while a tendency to a higher biomass was observed in AMF plants under both control and saline conditions. Leaf photosynthesis increased by both salinity and AMF inoculation. Despite higher transpiration rate, AMF plants had higher water-use efficiency under sever saline conditions. AMF inoculation decreased proline concentration, but increased significantly leaf osmotic potential. Antioxidative enzymes responded differently to the salt and AMF treatments depending on the salt concentration and plant organ. Nonetheless, salt-induced malondialdehyde accumulation in the leaves diminished by AMF colonization. K and Ca contents were not affected by salt, while fungal colonization increased K in the roots and Ca in both leaves and roots. Our results indicated that enhancement of photosynthesis and ion homeostasis is involved in the tolerance of P. distans to both low and high salinity. AMF inoculation increased plants’ tolerance by augmentation of the above mechanisms accompanied by improvement of water relations and protection against oxidative damage in the leaves.     

Effect of growth in highly salinized media on the enzymes of the photosynthetic apparatus in pea seedlings

The rate of chlorophyll formation in initially etiolated pea seedlings (Pisum sativum) that are growing in the light in salinized media is slower than in similar plants not subjected to salinity. However, the final steady state level of chlorophyll is the same under both conditions. Growth under saline conditions did not change the ratio of dry weight to wet weight in the plant leaves nor the specific concentration of soluble protein in leaf extracts. Changes in the specific activity of 11 enzymes in leaf extracts during growth in the light were measured. At least six of these enzymes are known to be part of the photosynthetic apparatus and that their synthesis is subject to photocontrol. The changes in specific activity that were observed were slower in the salt-treated plants, but the final steady state concentration of each was the same as in the control plants. It is concluded that salinity impairs growth of pea plants but that formation of enzymes and other proteins are always in balance with growth.     

Effect of salinity on soluble protein,free amino acids and nicotine contents inNicotiana rustica L.

Nicotiana rustica plants were grown under two grades of salinity conditions, 50 mM and 100 mM NaCl. High levels of NaCl added to the nutritive solution produced a progressive absorption of Na in detriment of K, thereby causing an ionic disequilibrium, particularly in leaves. The weight and longitudinal growth of plants grown under salinity conditions were lower than control plants, while their protein content was higher. Deficit of K induced by salinity increased the levels of free amino acids, especially of aspartic acid, glutamic acid and proline. On the other hand, the levels of nicotine in leaves of treated plants were lower than controls. In contrast, treatment of the plants with 100 mM NaCl induced in general an increase of nicotine in the roots. These results indicate that there was an unclear effect of salinity either on synthesis or on translocation of nicotine from roots to leves.     

Differential ecological responses to environmental stress in the life history phases of the isomorphic red alga Gracilaria chilensis (Rhodophyta)

In order to better understand the alternation of generations that characterizes haploid–diploid life cycles, we assessed the existence of ecological differences between the two phases (haploid gametophyte and diploid tetrasporophyte) in Gracilaria chilensis, a rhodophyte with a typical Polysiphonia-type life cycle. We investigated the effect of light intensity and salinity on viability and growth of both phases at different ontogenetic stages: juveniles and adults. In our study, the survival of juvenile gametophytes (n) was higher than the survival of juvenile tetrasporophytes (2n) despite culture conditions; however, low salinity had greater effect on carpospores (2n) than on tetraspores (n). On the other hand, a complex interaction between salinity and light intensity within each life history phase generated observed differences between juvenile growth rates. Low light was shown to trigger early onset of alteration of the holdfast growing pattern. In addition, adult tetrasporophytes showed, despite the conditions, a faster vegetative growth than female and male gametophytes. These differences between phases could have led to the complete dominance of tetrasporophyte fragments of fronds observed in G. chilensis farms. We hypothesize that Chilean fishers could have unknowingly selected for tetrasporophyte thalli during domestication of the species, thus enhancing the natural trend of tetrasporophytes dominance already present in estuarine natural populations of free-floating plants.     

Modulating role of lipids and their fatty acids in adaptation of the White Sea mussels <Emphasis Type="Italic">Mytilus edulis</Emphasis> L. to environmental salinity change

Role of lipids and fatty acids (FA) in littoral and sublittoral White Sea mussels Mytilus edulis L. was studied at various stages of reproductive cycle in the phenotypic adaptation (acclimation) to changes of the sea water salinity. The obtained data indicate differences in the mussel lipid and fatty acid spectra, which are connected both with their location (littoral or sublittoral) and with the spawning period stage (3b—release of gametes or 3c—resorption of residual sex products). Lipids and FA of both mussel groups respond to the salinity changes to the greater degree at the 3b than at the 3c stage. In the littoral mussels at the 3b and 3c stages there were revealed differently directed changes in the content of membrane lipid—cholesterol—and in the cholesterol: phospholipids ratio. In the sublittoral mussels that are less adapted to extreme action of abiotic factors, more significant changes were found in the lipid and FA compositions.     

Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile

The main aim of this study was to estimate the effects of salinity variation on the Mediterranean seagrass Posidonia oceanica (L.) Delile and its attached epiphytes. Leaf growth and survival of this plant were tested in several short-term (15 days) mesocosms experiments under controlled conditions between February 2001 and November 2001. Plants collected from shallow meadows at Alicante (SE Spain), with an ambient salinity of 36.8-38.0 psu, were placed in tanks of 300 L with an additional overhead light and exposed to different salinity treatments (ranging from 25 to 57 psu) during 15 days. To estimate the mortality and growth recuperation, in some experiments shoots were returned to control salinity (38 psu). Leaf growth was measured in the laboratory where epiphytic fauna and flora were removed from leaves, with a razor blade, to determine their biomass.P. oceanica was negatively influenced by increased salinity. Shoots showed a significant decrease in growth and survival, whereas epiphyte biomass did not show a clear response because of their high variability. Maximum leaf growth occurred between 25 and 39 psu. In addition, plants suffered considerable mortality at salinities above 42 psu and below 29 psu, with 100% mortality at 50 psu. In salinities between 39 and 46 psu, surviving plants were able to regain their original growth rate when returned to normal seawater salinity (38 psu). These results suggest that P. oceanica is one of the most sensitive seagrasses to salinity increments it is more tolerant to salinity reductions (25.0-36.4 psu), perhaps due to the terrestrial origin of seagrasses.     

Resistance of larvae of common species of White Sea invertebrates to extreme changes in salinity

This study examines the effect of sharp changes in salinity on pelagic larvae of ten common species of invertebrates from the brackish White Sea (Mollusca, Polychaeta, Echinodermata, Cnidaria, Ascidia). For five species, the low salinity resistance limit was in the range of 8–12‰: for the gastropod Littorina littorea, it was below 8‰; for Dyaphana sp. and the bivalves Hiatella arctica and Heteranomia ovata, it was more than 12‰; and for the ascidian Styela rustica, it was 16‰. About 50% of larvae of four investigated species were able to withstand high salinity and survived at 36–40 and even 50‰ (Littorina). Larvae of littoral-sublittoral species proved to be more euryhaline than larvae of sublittoral species.     

Salinity effects on photosynthesis in isolated mesophyll cells of cowpea leaves

Mesophyll cells from leaves of cowpea (Vigna unquiculata [L.] Walp.) plants grown under saline conditions were isolated and used for the determination of photosynthetic CO₂ fixation. Maximal CO₂ fixation rate was obtained when the osmotic potential of both cell isolation and CO₂ fixation assay media were close to leaf osmotic potential, yielding a zero turgor pressure. Hypotonic and hypertonic media decreased the rate of photosynthesis regardless of the salinity level during plant growth. No decrease in photosynthesis was obtained for NaCl concentrations up to 87 moles per cubic meter in the plant growing media and only a 30% decrease was found at 130 moles per cubic meter when the osmotic potential of cell isolation and CO₂ fixation media were optimal. The inhibition was reversible when stress was relieved. At 173 moles per cubic meter NaCl, photosynthesis was severely and irreversibly inhibited. This inhibition was attributed to toxic effects caused by high Cl⁻ and Na⁺ accumulation in the leaves. Uptake of sorbitol by intact cells was insignificant, and therefore not associated with cell volume changes. The light response curve of cells from low salinity grown plants was similar to the controls. Cells from plants grown at 173 moles per cubic meter NaCl were light saturated at a lower radiant flux density than were cells from lower salinity levels.     

环境因子对小球藻(Chlorella sp. XQ-20044)光合作用的影响

小球藻（Chlorella sp.XQ-20044）是一株具有应用潜力的产油微藻,本文利用测定净光合放氧速率的方法研究了光照强度、温度、pH值和盐度对其光合作用的影响。研究结果表明：小球藻适宜的光照强度为500~1200 μmol·m^-2·s^-1,光补偿点约30 μmol·m^-2·s^-1,光饱和点在600 μmol·m^-2·s^-1附近;光合作用适宜的温度范围为30~42.5℃,最适温度为40℃;适宜的pH值范围7.0~10.0,最适pH值为8.0;适宜盐度范围0.1~0.3 mol/L,最适盐度为0.2 mol/L。从光合作用特性来看,小球藻能适应较强的光照强度、较高的温度、偏碱性和较高的盐度环境,其中可耐受较高盐度的特性,有助于预防敌害生物的污染,对于实现规模培养,特别是利用开放系统进行规模培养较为有利。     

LIGHT,TEMPERATURE AND SALINITY EFFECTS ON GROWTH,LEAF ANATOMY AND PHOTOSYNTHESIS OF DISTICHLIS SPICATA (L.) GREENE

The effects of light, temperature, and salinity on growth, net CO₂ exchange and leaf anatomy of Distichlis spicata were investigated in controlled environment chambers. When plants were grown at low light, growth rates were significantly reduced by high substrate salinity or low temperature. However, when plants were grown at high light, growth rates were not significantly affected by temperature or salinity. The capacity for high light to overcome depressed growth at high salinity cannot be explained completely by rates of net photosynthesis, since high salinity caused decreases in net photosynthesis at all environmental conditions. This salinity-induced decrease in net photosynthesis was caused largely by stomatal closure, although plants grown at low temperature and low light showed significant increases in internal leaf resistance to CO₂ exchange. Increased salinity resulted in generally thicker leaves with lower stomatal density but no significant differences in the ratio of mesophyll cell surface area to leaf area. Salinity and light during growth did not significantly affect rates of dark respiration. The mechanisms by which Distichlis spicata tolerates salt appear to be closely coulpled to the utilization of light energy. Salt-induced leaf succulence is of questionable importance to gas exchange at high salinity in this C₄ species.     

Interaction between Light Intensity and NaCl Salinity and Their Effects on Growth, CO(2) Assimilation, and Photosynthate Conversion in Young Broad Beans

Seedings of Vicia faba were grown for four weeks at two different light intensities (55 and 105 watts per square meter) in a saline (50 millimolar NaCl) and nonsaline nutrient solution. NaCl salinity depressed growth and restricted protein formation, CO₂ assimilation, and especially the incorporation of photosynthates into the lipid fraction. Conversion of photosynthates in leaves was much more affected by salinity than was photosynthate turnover in roots. The detrimental effect of NaCl salinity on growth, protein formation, and CO₂ assimilation was greater under low than under high light conditions. Plants of the high light intensity treatment were more capable of excluding Na⁺ and Cl⁻ and accumulating nutrient cation species (Ca²⁺, K⁺, Mg²⁺) than plants grown under low light intensity. It is suggested that the improved ionic status provided better conditions for protein synthesis, CO₂ assimilation, and especially for the conversion of photosynthates into lipids.     

Arbuscular mycorrhizal symbiosis regulates physiology and performance of <Emphasis Type="Italic">Digitaria eriantha</Emphasis> plants subjected to abiotic stresses by modulating antioxidant and jasmonate levels

This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.     

盐地碱蓬二型性种子及其幼苗对盐渍环境的适应性

研究了盐地碱蓬二型性种子中离子含量与刚萌发幼苗耐盐性之间的关系,以及盐分对砂培盐地碱蓬二型性种子的幼苗生长、离子含量及光合特性的影响.棕色种子中离子含量显著高于黑色种子.与对照相比,100和400 mmol/L NaCl对棕色种子幼苗伸长没有抑制作用,却显著抑制黑色种子幼苗的伸长.NaCl处理下棕色种子的幼苗地上部分干重和主茎一级分枝数比黑色种子幼苗高,但二型性种子的幼苗叶片中离子含量、叶绿素含量及光合放氧速率却没有明显差异.上述结果说明盐地碱蓬棕色种子较高的离子含量可能是棕色种子刚萌发幼苗耐盐性较强的重要原因.棕色种子幼苗较高的生物量可能与其较多的分枝数有关.二型种子的这些特征可能决定了其在群落建成中所起到的不同作用.     

The seaweed flora of a young semi-enclosed sea: The Baltic. Salinity as a possible agent of flora divergence

The salinity tolerances of Baltic and Atlantic populations ofFucus vesiculosus andChorda filum have been measured using net photosynthesis as an index of tissue damage. AtlanticFucus proved to have a broader salinity tolerance than AtlanticChorda, a result which is consistent with others published on the tolerances of intertidal and sublittoral marine species. The optimum salinity for all Atlantic plants was 11 or 34‰, but that of all Baltic plants was 6‰. BalticFucus andChorda were different in breadth of tolerance, in spite of the fact that they inhabit the same sublittoral habitat. This difference is interpreted in relation to their respective life-forms,Fucus being perennial andChorda annual.Fucus is therefore present as a macrothallus at all times of year, including the critical low-salinity period of the spring ice-melt.Chorda evades damage by existing as a resistent microthallus at this time. It is concluded that the distinctive character of Baltic marine algae deserves nomenclatural recognition at some level below that of the species. The rank of subspecies would appear the most appropriate of those listed in the Code, but none of those available is able adequately to express the patterns of variation now being reported. Paper presented at the XIV International Botanical Congress (Berlin, 24 July-1 August, 1987), Symposium 6-15, “Biogeography of marine benthic algae”.     

Overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica enhances growth rate as well as abiotic stress tolerance of poplar plants

The DnaK/Hsp70 family is a molecular chaperone that binds non-native states of other proteins, and concerns to various physiological processes in the bacterial, plant and animal cells. Previously, we showed that overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica (ApDnaK) enhances tolerance to abiotic stresses such as high salinity and high temperature in tobacco plants. Here, we tested the transformation of poplar (Populus alba) with ApDnaK for enhancing the growth of transformed poplar plants. Under control growth conditions, transgenic poplar plants exhibited similar growth rates with the wild-type plants during young seedlings under low light intensity, whereas they showed faster growth, larger plant size, and higher cellulose contents when poplar plants were grown under high light intensity. Transgenic young poplar plants exhibited more rapid recovery from the stresses of high salinity, drought, and low temperature compared with those of the wild type plants when poplar plants were grown under low light intensity. These results suggest that ApDnaK could be useful to enhance the growth rate as well as to increase the stress tolerance.