Role of hydration in ovulation of common frog oocytes in vitro

Stimulation of ovulation of the common frog Rana temporaria oocytes with homologous pituitary extract caused an increase in their volume. Factors that are known to inhibit hydration in teleostean oocytes (potassium-free Ringer solution and inhibitor of Na⁺,K⁺-ATPase—ouabain), as well as aquaporin inhibitors (mercuric chloride and methylmethanethiosulphonate) inhibited also homologous pituitary extract-induced volume increase in follicle-enclosed oocytes and led to reduced percentage of ovulated oocytes. Volume of denuded oocytes remained unchanged in the course of maturation when exposed to progesterone or other treatments. The data obtained suggest that stimulation of oocyte ovulation in the common frog caused an increase in their hydration that is necessary for their ovulation but this did not occur in denuded cells.     

Effects of 24‐epibrassinolide on plant growth,osmotic regulation and ion homeostasis of salt‐stressed canola

This study evaluated effects of foliar spraying 24‐epibrassinoide (24‐EBL) on the growth of salt‐stressed canola. Seedlings at the four‐leaf stage were treated with 150 mm NaCl and different concentrations of 24‐EBL (10^?6, 10^?8, 10^?10, 10^?12 m ) for 15 days. A concentration of 10^?10 m 24‐EBL was chosen as optimal and used in a subsequent experiment on plant biomass and leaf water potential parameters. The results showed that 24‐EBL mainly promoted shoot growth of salt‐stressed plants and also ameliorated leaf water status. Foliar spraying of salt‐stressed canola with 24‐EBL increased osmotic adjustment ability in all organs, especially in younger leaves and roots. This was mainly due to an increase of free amino acid content in upper leaves, soluble sugars in middle leaves, organic acids and proline in lower leaves, all of these compounds in roots, as well as essential inorganic ions. Na⁺ and Cl^? sharply increased in different organs under salt stress, and 24‐EBL reduced their accumulation. 24‐EBL improved the uptake of K⁺, Ca²⁺, Mg²⁺ and NO₃^? in roots, which were mainly transported to upper leaves, while NO₃^? was mainly transported to middle leaves. Thus, 24‐EBL improvements in ion homeostasis of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and NO₃^?/Cl^?, especially in younger leaves and roots, could be explained. As most important parts, younger leaves and roots were the main organs protected by 24‐EBL via improvement in osmotic adjustment ability and ion homeostasis. Further, physiological status of growth of salt‐stressed canola was ameliorated after 24‐EBL treatment.     

Comparative effects of salt and alkali stresses on growth, osmotic adjustment and ionic balance of an alkali-resistant halophyte Suaeda glauca (Bge.)

Effects of salt and alkali stresses on growth, osmotic adjustment and ionic balance of Suaeda glauca (Bge.), an alkali-resistant succulent halophyte, were compared. The results showed that alkali stress clearly inhibited the growth of S. glauca. Moreover, the concentrations of Na⁺ and K⁺ both increased with increasing salinity under both stresses, suggesting no competitive inhibition between absorptions of Na⁺ and K⁺. The mechanism underlying osmotic adjustment during salt stress was similar to alkali stress in shoots. The shared essential features were that organic acids, betaine and inorganic ions (dominated by Na⁺) mostly accumulated. On the other hand, the mechanisms governing ionic balance under both stresses were different. Under salt stress, S. glauca accumulated organic acids and inorganic anions to maintain the intracellular ionic equilibrium, but the anion contribution of inorganic ions was greater than that of organic acids. However, the concentrations of inorganic anions under alkali stress were significantly lower than those under salt stress of the same intensity, suggesting that alkali stress might inhibit uptake of anions, such as NO₃ ^– and H₂PO₄ ^–. Under alkali stress, organic acids were the dominant factor in maintaining ionic equilibrium. The contribution of organic acids to anions was 74.1%, while that of inorganic anions was only 25.9%. S. glauca enhanced the synthesis of organic acids, dominated by oxalic acid, to compensate for the shortage of inorganic anions.     

Measurement of net fluxes of ammonium and nitrate at the surface of barley roots using ion-selective microelectrodes

Neutral carrier-based liquid membrane ion-selective microelectrodes for NH₄⁺ and NO₃⁻ were developed and used to investigate inorganic nitrogen acquisition in two varieties of barley, Hordeum vulgare L. cv Olli and H. vulgare L. cv Prato, originating in cold and warm climates, respectively. In the present paper, the methods used in the fabrication of ammonium- and nitrate-selective microelectrodes are described, and their application in the study of inorganic nitrogen uptake is demonstrated. Net ionic fluxes of NH₄⁺ and NO₃⁻ were measured in the unstirred layer of solution immediately external to the root surface. The preference for the uptake of a particular ionic form was examined by measuring the net flux of the predominant form of inorganic nitrogen, with and without the alternative ion in solution. Net flux of NH₄⁺ into the cold-adapted variety remained unchanged when equimolar concentrations (200 micromolar) of NH₄⁺ and NO₃⁻ were present. Similarly, net flux of NO₃⁻ into the warm-adapted variety was not affected when NH₄⁺ was also present in solution. The high temporal and spatial resolution afforded by ammonium- and nitrate-selective microelectrodes permits a detailed examination of inorganic nitrogen acquisition and its component ionic interactions.     

Osmoadaptation in Representatives of Haloalkaliphilic Bacteria from Soda Lakes

The adaptation of microorganisms to life in brines allows two strategies: the accumulation of organic osmoregulators in the cell (as in many moderate halophiles, halomonads in particular) or the accumulation of inorganic ions at extremely high intracellular concentrations (as, for example, in haloanaerobes). To reveal the regularities of osmoregulation in haloalkaliphiles developing in soda lakes, Halomonas campisalis Z-7398-2 and Halomonas sp. AIR-2 were chosen as representatives of halomonads, and Natroniella acetigena, as a representative of haloanaerobes. It was established that, in alkaliphilic halomonads, the intracellular concentrations of inorganic ions are insufficient for counterbalancing the environmental osmotic pressure and balance is attained due to the accumulation of organic osmoregulators, such as ectoine and betaine. On the contrary, the alkaliphilic haloanaerobe N. acetigena employs K⁺, Na⁺, and Cl^? ions for osmoregulation. High intracellular salt concentrations increasing with the content of Na⁺ in the medium were revealed in this organism. At a concentration of 1.91 M Na⁺ in the medium, N. acetigena accumulated 0.83 M K⁺, 0.91 M Na⁺, and 0.29 M Cl^? in cells, and, with an increase in the Na⁺ content in the medium to 2.59 M, it accumulated 0.94 M K⁺, 1.98 M Na⁺, and 0.89 M Cl^?, which counterbalanced the external osmotic pressure and provided for cell turgor. Thus, it was shown that alkaliphilic microorganisms use osmoregulation strategies similar to those of halophiles and these mechanisms are independent of the mechanism of pH homeostasis.     

Regulation of ion concentration by Drosophila hydei Na+, K+, Ca2+, and Cl-

The ionic composition of the haemolymph of osmotically unencumbered larvae of Drosophila hydei shows a pattern that is typical (Bone, 1944) for highly developed phytophagous insect larvae: 36 mval/l. Cl^?; 56 mval/l. Na⁺; 31 mval/l. K⁺; approximately 18 mval/l. Ca²⁺ at an osmolality of 299 mOsmol/l.The larvae are able to maintain their most favourable ionic concentrations in the haemolymph after experimental osmotic stress in hypertonic as well as in hypotonic media. The reactions are most distinct with an increase or decrease of Cl^? concentration of the external medium. Characteristic regulating processes begin, and the Cl^? concentration of the haemolymph adjusts to the ‘standard’ again. The principal lapse shows the functional representation of an intensely suppressed oscillation. There seems to be a two-point regulation which requires the existence of a Cl^? ion depot and the existence of Cl^?-sensitive receptors.     

Osmotic acclimation of the brackish water xanthophyceae,Vaucheria dichotoma (L.) MARTIUS: Inorganic ion composition and amino acids

The salinity tolerance ofVaucheria dichotoma, a siphonous Xanthophycean alga was investigated. The alga survived an external osmotic potential range between 74 and 1, 176 mOsmol (ca. 2.5 and 40.0 ppt. (parts per thousand]). Turgor pressure was regulated in salinities ranging from 74 to 441 mOsmol. With further increase of the salinity, turgor pressure decreased from 153 to 9 mOsmol (0.44 to 0.08 MPa). At 441 mOsmol salinity the major intracellular ions were present in the following concentrations (mM/l cell water): K⁺, 145; Na⁺; 90; sulphate, 91; Cl⁻, 91. Under the most severe salinity stress (1,176 mOsmol) the ionic concentration increased to (mM/l cell water): K⁺, 250; Na⁺, 75; sulphate, 35; Cl⁻, 351. The content of amino acids: alanine (Ala), threonine (Thr and glutamic acid (Glu) was lower, nerver exceeding 5–11 mM, however; the concentrations were positively correlated with salinity.     

Analytical and experimental studies on the relationship between Na+, K+, and water uptake during volume increases associated with Fundulus oocyte maturation in vitro

Summary Oocytes of marine and estuarine teleosts often undergo pronounced volume increases during the maturation phase of development that precedes ovulation and fertilization. To examine the physiological correlates of these volume increases, prematuration follicles of the saltmarsh teleost, Fundulus heteroclitus, were cultured in vitro with a maturation-inducing steroid (17-hydroxy-20-dihydroprogesterone). Mean follicle volume rose significantly (75%) during a 40-h incubation period. Similar to the situation previously found in vivo, uptake of water by the maturing follicle was responsible for this volume increase in vitro, with the water content increasing from 62% to 78% of the total follicle mass. The follicle contents of two probable osmotic effectors-Na⁺ and K⁺-also rose, the increase in K⁺ being twice that of Na⁺. The influx of K⁺ even exceeded water uptake, resulting in a net increase in the concentration of this cation. It thus appears that the influx of these cations, in particular K⁺, is a major cause of the uptake of osmotically obligated water and subsequent volume increase experienced by maturing F. heteroclitus follicles. In a search for operant mechanisms, it was found that follicle hydration, but not maturation, was strictly dependent on external K⁺ in a concentration-dependent manner. The mechanism by which K⁺ accumulates in the follicle was insensitive to ouabain, so that a typical Na⁺, K⁺-ATPase mechanism does not appear to be involved. The ability of external K⁺ to promote follicle hydration was gradually lost during the maturation process as the oocyte dissociated from the surrounding granulosa cells in preparation for ovulation. Removal of all associated somatic cells prior to maturation prevented subsequent steroid-initiated hydration but not maturation. The results suggest that K⁺ may be translocated from surrounding granulosa cells to the oocyte via gap junctions during maturation.Abbreviations GVBD germinal vesicle breakdown     

Effect of salinity on osmotic adjustment,proline accumulation and possible role of ornithine-δ-aminotransferase in proline biosynthesis in <Emphasis Type="Italic">Cakile maritima</Emphasis>

The short time response to salt stress was studied in Cakile maritima. Plants were exposed to different salt concentrations (0, 100, 200 and 400 mM NaCl) and harvested after 4, 24, 72 and 168 h of treatment. Before harvesting plants, tissue hydration, osmotic potential, inorganic and organic solute contents, and ornithine-δ-aminotransferase activity were measured. Plants of C. maritima maintained turgor and tissue hydration at low osmotic potential mainly at 400 mM NaCl. The results showed that, in leaves and stems, Na⁺ content increased significantly after the first 4 h of treatment. However, in roots, the increase of Na⁺ content remained relatively unchanged with increasing salt. The K⁺ content decreased sharply at 200 and 400 mM NaCl with treatment duration. This decrease was more pronounced in roots. The content of proline and amino acids increased with increasing salinity and treatment duration. These results indicated that the accumulation of inorganic and organic compounds was a central adaptive mechanism by which C. maritima maintained intracellular ionic balance under saline conditions. However, their percentage contribution to total osmotic adjustment varies from organ to organ; for example, Na⁺ accumulation mainly contributes in osmotic adjustment of stem tissue (60%). Proline contribution to osmotic adjustment reached 36% in roots. In all organs, proline as well as δ-OAT activity increased with salt concentration and treatment duration. Under normal growth conditions, δ-OAT is mainly involved in the mobilization of nitrogen required for plant growth. However, the highly significant positive correlation between proline and δ-OAT activity under salt-stress conditions suggests that ornithine pathway contributed to proline synthesis.     

Intracellular Solutes,Photosynthesis and Respiration of the Green Alga Blidingia minima in Response to Salinity Stress

The effects of different salinities ranging from 7–68‰ on the internal inorganic and organic solute concentrations, and on the photosynthesis and respiration have been investigated in the green alga Bladingia minima (Näg. ex Kütz.) Kylin. The levels of the main osmotic solutes K⁺, sucrose and proline increased with increasing salinities and vice versa, while Na⁺, Mg²⁺, Cl^? and PO^3–₄ played a minor role in the osmotic acclimation. In contrast to related Enteromorpha species, B. minima exhibited high NO^?₃ concentrations, which decreased under hypo- and hypersaline conditions. B. minima differs also from Enteromorpha by accumulating the tertiary sulphonium compound DMSP in osmotically significant amounts under gentle hypersaline conditions. B. minima revealed typical characteristics of a “sun-plant” having a high light compensation point together with a saturation of photosynthesis at high photon flux densities. The alga showed a broad photosynthetic stability under osmotic stress; only with extreme hypersaline conditions was photosynthesis partly inhibited. The rate of respiration remained constant in hypersaline media, and was stimulated under hyposaline conditions.     

Accumulation of inorganic and organic osmolytes and their role in osmotic adjustment in NaCl-stressed vetiver grass seedlings

The accumulation of inorganic and organic osmolytes and their role in osmotic adjustment were investigated in roots and leaves of vetiver grass (Vetiveria zizanioides) seedlings stressed with 100, 200, and 300 mM NaCl for 9 days. The results showed that, although the contents of inorganic (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and H₂PO₃⁻)) and organic (soluble sugar, organic acids, and free amino acids) osmolytes all increased with NaCl concentration, the contribution of inorganic ions (mainly Na⁺, K⁺, and Cl⁻) to osmotic adjustment was higher (71.50–80.56% of total) than that of organic solutes (19.43–28.50%). The contribution of inorganic ions increased and that of organic solutes decreased in roots with the enhanced NaCl concentration, whereas the case in leaves was opposite. On the other hand, the osmotic adjustment was only effective for vetiver grass seedlings under moderate saline stress (less than 200 mM NaCl).     

Comparative effects of osmotic-, salt- and alkali stress on growth,photosynthesis, and osmotic adjustment of cotton plants

In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K⁺, NO₃ ⁻, and H₂PO₄ ⁻ under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role.     

Osmotic adjustment in three succulent species of Zygophyllaceae

Three species, Zygophyllum album L., Z. coccineum L. and Z. simplex L., from family Zygophyllaceae were collected from two locations in Egypt to study their response to environmental conditions. Organic solutes (amino acids, soluble proteins and soluble sugars) and inorganic solutes (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, PO₄^3? and SO₄^2?) were estimated to study their role in osmotic adjustment under the effect of drought and salinity. The study showed that Z. coccineum is most tolerant for drought and salinity than Z. simplex. Z. coccineum was dependent on soluble proteins and soluble sugars, to increase its content of bound water, to undergo water deficit in desert. Z. simplex accumulated inorganic solutes more than Z. coccineum and less organic solutes. Amino acids content increased in Z. coccineum and Z. simplex survived in saline conditions to play a role in osmotic adjustment. Under the effect of salinity, all the studied species showed a tendency and high capacity to accumulate inorganic solutes. The main inorganic salutes were Ca²⁺, Mg²⁺ and Cl^?. The role of Na⁺ was less than Ca²⁺ and Mg²⁺. Z. album and Z. simplex preferred Mg²⁺ more than Z. coccineum which preferred Ca²⁺.     

Role of organic acids in the formation of the ionic composition in developing glycophyte leaves

The ionic composition in the leaves of some glycophyte plants (Phaseolus vulgaris L., Lycopersicon esculentum L., and Amaranthus cruentus L.) was studied during leaf development. Plants were grown in a stationary hydroponic culture; a growth medium contained equimolar concentrations of inorganic ions (NO ₃ ^? , Cl^?, SO ₄ ^2? , H₂PO ₄ ^? , K⁺, Ca²⁺, Mg²⁺, and Na⁺) equal to 5 mg-equiv./l for each ion. In the juvenile leaf, the main ions were K⁺ and water-soluble anions of organic acids represented mainly by di-and tricarboxylic acids in kidney bean and tomato and oxalic acid in amaranth. An increase in the total amount of organic anions, coinciding with the accumulation of bivalent cations, was registered in leaves of glycophytes during their development. Mature and senescing leaves of tomato and kidney bean accumulated mainly di-and tricarboxylic acid salts with the prevalence of Ca²⁺ ions. In amaranth leaves, the formation of water-insoluble (acid-soluble) oxalate pool containing Ca²⁺ ions (mature leaves) or Ca²⁺ and Mg²⁺ ions (senescing leaves) was registered. The priority role of the metabolism of organic acids in the formation of the ionic composition of glycophyte leaves during their development is discussed. It is supposed that the species-specific ionic composition of glycophyte leaves at different developmental stages is due mainly to the pattern of carbon metabolism causing the accumulation either of di-and tricarboxylic acids or oxalic acid.     

Contamination on sandflats and the decoupling of linked ecological functions

Benthic macrofauna can influence inputs and transformations of energy and matter in estuaries, affecting both the stocks of vital materials (e.g. carbon, oxygen) and the rates of key processes (e.g. organic matter decomposition, nutrient uptake). Although a number of studies have identified shifts in functional groups or biological traits in relation to anthropogenic stressors, there have been few field‐based assessments of changes in functioning associated with stress gradients. We used a comparative experimental approach to investigate functioning on two sandflats with differing exposures to urban contaminants. Apart from significant differences in sediment contaminant concentrations (43.2 ± 1.8 mg kg^?1 Zn and 15.6 ± 0.9 mg kg^?1 Pb at the Pollen site; 17.7 ± 0.7 mg kg^?1 Zn and 7.9 ± 0.9 mg kg^?1 Pb at the Waiheke site), the two sandflats were readily comparable: both had similar sediment grain size distributions and were dominated by the same macrofaunal species; and both were in non‐eutrophic New Zealand marine reserves with low ambient sediment organic matter content. To better understand the effects of contaminants on biologically mediated transformations of organic matter into inorganic nutrients, we manipulated sediment organic matter content and macrofaunal abundance in standardized treatments at each site. Fluxes of oxygen and ammonium, which are linked to key sandflat processes such as organic matter decomposition and benthic photosynthesis, were measured as response variables 1 week after the experimental manipulations. We predicted more efficient organic matter processing on the uncontaminated flat and thus expected to see elevated ammonium efflux in response to organic enrichment treatments at this site. Higher rates of benthic photosynthesis were predicted for plots with higher ammonium efflux, as ammonium is a readily utilizable form of limiting inorganic nitrogen. We documented significant positive relationships between ammonium uptake and benthic primary production on the uncontaminated flat, but weaker/insignificant relationships at the contaminated site. Our data were consistent with theories of increased variability and a decoupling of system processes with increasing amounts of stress.     

Contributions of inorganic ions,soluble carbohydrates,and multiatomic alcohols to water homeostasis in <Emphasis Type="Italic">Artemisia lerchiana</Emphasis> and <Emphasis Type="Italic">A. pauciflora</Emphasis>

Two morphological forms of wormwood Artemisia lerchiana (f. erecta and f. nutans) and A. pauciflora Web. (morphological form erecta) were grown on sand culture at a range of NaCl concentrations in the nutrient medium and then assayed for Na⁺, K⁺, and Cl^? content in various organs. In addition, the content of mono-, di-, and trisaccharides and multiatomic alcohols (mannitol and glycerol); water content; and organ biomass were determined. All plants examined showed high NaCl tolerance, comparable to that of halophytes. They were able to maintain high tissue hydration under conditions of salinity-induced growth suppression. The intracellular osmotic pressure in wormwood organs was mainly determined by the presence of Na⁺, K⁺, and Cl^?, as well as by mono-, di-, and trisaccharides, mannitol, and glycerol. The high content of Na⁺ and Cl^? in wormwood organs was also observed in the absence of salinity, which implies the ability of these organs to absorb ions from diluted NaCl solutions and accumulate ions in cells of their tissues. With the increase in salinity, the content of Na⁺ and Cl^? in roots and leaves increased to even higher levels. It is concluded that the ability of wormwood plants to absorb and accumulate inorganic ions provides for sustainable high intracellular osmotic pressure and, accordingly, low water potential under drought and salinity conditions. Growing plants under high salinity lowered the content of monosaccharides in parallel with accumulation of the trisaccharide raffinose. It is supposed that soluble carbohydrates and multiatomic alcohols are not only significant for osmoregulation but also perform a protective function in wormwood plants. The lower osmotic pressure in root cells compared to that in leaf cells of all plants examined was mainly due to the gradient distribution of K⁺ and Cl^? between roots and leaves. The two Artemisia species and two morphological forms of A. lerchiana did not differ appreciably in the ways of water balance regulation. It is found that different morphologies of two A. lerchiana forms are unrelated to variations in intracellular osmotic and turgor pressures.     

Water chemistry and nutrient budgets in an undisturbed evergreen rainforest of Southern Chile

In a pristine evergreen rainforest of Nothofagus betuloides, located at the Cordillera de los Andes in southern Chile (41?°S), concentrations and fluxes of nutrients in bulk precipitation, cloud water, throughfall water, stemflow water, soil infiltration and percolation water and runoff water were measured. The main objectives of this study were to investigate canopy–soil–atmosphere interactions and to calculate input–output budgets. From May 1999 till April 2000, the experimental watershed received 8121?mm water (86% incident precipitation, 14% cloud water), of which the canopy intercepted 16%. Runoff water volume amounted 9527?mm. Bulk deposition of inorganic (DIN) and organic (DON) nitrogen amounted 3.6?kg?ha^?1?year^?1 and 8.2?kg?ha^?1?year^?1 respectively. Occult deposition (clouds?+?fog) contributes for 40% to the atmospheric nitrogen input (bulk?+?occult deposition) of the forest. An important part of the atmospheric ammonium deposition is retained within the canopy or converted to nitrate or organic nitrogen by epiphytic bacteria or lichens. Also the export of inorganic (0.9?kg?ha^?1?year^?1) and organic (5.2?kg?ha^?1?year^?1) nitrogen via runoff is lower than the input to the forest floor via throughfall and stemflow water (3.2?kg?DIN?ha^?1?year^?1 and 5.6?kg?DON?ha^?1?year^?1). The low concentrations of NO-₃ and NH+₄ under the rooting depth suggest an effective biological immobilization by vegetation and soil microflora. Dry deposition and foliar leaching of base cations (K⁺, Ca²⁺, Mg²⁺) was estimated using a canopy budget model. Bulk deposition accounted for about 50% of the total atmospheric input. Calculated dry and occult deposition are both of equal value (about 25%). Foliar leaching of K⁺, Ca²⁺, and Mg²⁺ accounted for 45%, 38% and 6% of throughfall deposition respectively. On an annual basis, the experimental watershed was a net source for Na⁺, Ca²⁺ and Mg²⁺.     

Urinary bladder, ionic composition of seminal fluid and urine with characterization of sperm motility in tench (Tinca tinca L.)

A small urinary bladder attached to the seminal duct in caudal part of the abdominal cavity was registered for the first time in dissected males of tench. The urinary bladder wall was of whitish color and the bladder contained 0.5–2 ml of urine. When collected in the experiment, the tench sperm was white‐colored. Spermatozoa density is highly variable due to contamination by urine, and the latter additionally activates spontaneous motility of the spermatozoa. Seminal fluid contains ions such as Na⁺ (18.4 ± 1.3 mm ), K⁺ (1.9 ± 0.6 mm ), Ca²⁺ (0.6 ± 0.2 mm ) and Mg²⁺ (0.5 ± 0.1 mm ), leading to osmolality of 230 ± 82 mOsmol kg^?1 depending on the dilution by urine. Urea was detected in urine samples uncontaminated by sperm with an osmolality of 85 ± 58 mOsmol kg^?1. Urine also contained high concentrations of ions such as Na⁺ (30.9 ± 8.9 mm ), K⁺ (4.3 ± 2.9 mm ), Ca²⁺ (0.9 ± 0.5 mm ) and Mg²⁺ (0.6 ± 0.2 mm ). The spontaneous sperm activation by urine was up to 100%, but could be prevented by collection in an immobilizing solution. Motility was observed for 90–100% spermatozoa just after their transfer to distilled water or in a swimming medium (SM, 30–45 mm KCl) with a velocity of 120–140 μm s^?1. A flagellar beat frequency of 60–70 Hz and forward motility lasted up to 80 s in distilled water, and up to 180 s in SM at room temperature.     

Iodine contributes to osmotic acclimatisation in the kelp Laminaria digitata (Phaeophyceae)

Iodide (I^?) retained by the brown macroalga Laminaria digitata at millimolar levels, possesses antioxidant activities, but the wider physiological significance of its accumulation remains poorly understood. In its natural habitat in the lower intertidal, L. digitata experiences salinity changes and osmotic homeostasis is achieved by regulating the organic osmolyte mannitol. However, I^? may also holds an osmotic function. Here, impacts of hypo- and hypersaline conditions on I^? release from, and accumulation by, L. digitata were assessed. Additionally, mannitol accumulation was determined at high salinities, and physiological responses to externally elevated iodine concentrations and salinities were characterised by chl a fluorometry. Net I^? release rates increased with decreasing salinity. I^? was accumulated at normal (35 S _A) and high salinities (50 S _A); this coincided with enhanced rETR_max and q_P causing pronounced photoprotection capabilities via NPQ. At 50 S _A elevated tissue iodine levels impeded the well-established response of mannitol accumulation and prevented photoinhibition. Contrarily, low tissue iodine levels limited photoprotection capabilities and resulted in photoinhibition at 50 S _A, even though mannitol was accumulated. The results indicate a, so far, undescribed osmotic function of I^? in L. digitata and, thus, multifunctional principles of this halogen in kelps. The osmotic function of mannitol may have been substituted by that of I^? under hypersaline conditions, suggesting a complementary role of inorganic and organic solutes under salinity stress. This study also provides first evidence that iodine accumulation in L. digitata positively affects photo-physiology.     

Response to short-term inundation with isoosmotic solutions of seawater and sorbitol in a C4 nonhalophyte: evidence for a salt tolerance mechanism

Summary To examine the importance of Na⁺ and Cl^- to osmotic adjustment in a salt-tolerant ecotype of the C₄ nonhalophyte Andropogon glomeratus, plants were watered with sorbitol, a neutral osmoticum, and synthetic seawater, for five days. Gas exchange measurements were made during the course of the watering treatment and during a recovery period following treatment. Leaf osmotic adjustment occurred only in plants watered with seawater, and was associated with an increase in Na⁺ and Cl^- concentrations. Estimates of the molar concentrations indicated these ions could account for 95% of the leaf osmotic adjustment. Net photosynthetic CO₂ uptake was less effected during the watering treatment, and photosynthetic recovery was greater following the treatment in plants watered with seawater. Photosynthetic inhibition was related primarily to metabolic factors, including a decrease in carboxylation efficiency. A model is presented for a mechanism promoting tolerance to transient seawater inundation in A. glomeratus.