Effects of NaCl stress on proline and cation accumulation in salt sensitive and tolerant turfgrasses

Summary Concentrations of proline, sodium and potassium in shoot tissues of five turfgrass species were measured following exposure to 170 mM NaCl salinity stress. Salt tolerant ‘Fults’ alkaligrass and ‘Dawson’ red fescue restricted the accumulation of Na-ions to significatnly low levels compared to the salt sensitive Kentucky bluegrasses (‘Adelphi’ and ‘Ram I’) and ‘Jamestown’ red fescue. Accumulation of proline began in all species within 24 h of initiation of salt stress but at a more rapid rate and higher overall concentration for ‘Fults’ alkaligrass. Proline levels were variable and too low in relation to sodium accumulations to have any significant osmoregulatory role in salt tolerance among all cultivars tested with the possible exception of alkaligrass.     

The ultrastructure of the plasmodesmata of the salt glands ofTamarix as revealed by transmission and freeze-fracture electron microscopy

Summary Numerous plasmodesmata occur in the walls between the secretory cells ofTamarix salt glands. The plasmalemma bounds the plasmodesmata and is continuous from cell to cell. In freeze-fracture, the e-face of the plasmalemma within the plasmodesmata is virtually devoid of intramembranous particles while, in contrast, the p-face is decidedly enriched with particles. The axial components appear to be a tightly curved membrane bilayer, as judged from measurements and their appearance in freeze-fracture, and the e-face of this membrane is also devoid of particles. Observations from both thin sections and freeze-fracture replicas indicate the presence of a circular cluster of six particles around the axial component near the cytoplasmic termini of the plasmodesmata. These particles extend from the p-face of the axial component to the p-face of the plasmalemma. These observations are summarized in a model.     

不同生态环境野生大豆的结构比较研究

对生长在不同生态环境的蝶形花科Ｆａｂａｃｅａｅ 大豆属Ｇｌｙｃｉｎｅ 的两个野生大豆Ｇ．ｓｏｊａ 品系进行了扫描电镜观察及比较研究．结果表明,生长在盐渍生态环境的野生大豆茎和叶体表都具有盐腺,盐腺圆球型,基部有一个小柄,着生在盐生野生大豆茎、叶表皮外切向壁的胞间层处．幼嫩的盐腺靠泌盐孔泌盐,成熟的盐腺靠整体破碎释盐．而生长在黑土地生态环境的野生大豆的茎和叶外切向壁未发现有泌盐的盐腺,其茎叶的表皮都呈现出平滑状态．因此两种不同生态环境的同科同属植物在微观结构上显示出明显差异．     

盐胁迫下苗期与拔节期碱茅植株生长及与离子关系的比较研究

 用不同浓度NaCl溶液处理碱茅植株,测定和比较苗期与拔节期植株的生物量,K、Na与Cl含量和吸收与运输速率。苗期与拔节期植株的地上生物量分别在66及134mmol／L浓度下达最大值,根系生物量在66mmol／L下达最大值,根／冠比在苗期随盐浓度增加线性降低,而拔节期显著低于苗期且不受盐浓度影响。拔节期植株Na、Cl含量及由此产生的渗透调节能力、以及K,Na与C1的吸收与运输速率均高于苗期,而K／Na比及对K离子的选择性则低于苗期,两生长期植株K含量无显著差异。苗期与拔节期植株对K都存在着选择性吸收与运输,且吸收与运输速率与相对生长率呈显著正相关;苗期植株的Na与Cl吸收与运输速率与相对生长率无关,而拔节期呈显著正相关。从盐胁迫下,K、Na与Cl离子含量变化及由此产生的渗透反应分析,Cl主要用于维持植株的“基础”渗透势,在高胁迫下也参与渗透调节;Na主要用于维持植株的渗透调节;而K从数值上不参与渗透调节,在维持植株的“基础”渗透势中的作用也较小。     

Structural and histochemical changes in the salivary glands of Rhipicephalus appendiculatus during feeding

The salivary glands of the brown ear tick of cattle, R. appendiculatus, from both sexes and at all stages of feeding, were examined as whole glands and as sections for ultrastructural and histochemical changes. The type 1 acinus consists of a basal labyrinth formed by the interdigitations of a central cell and four peripheral cells. These cells form a specialized border with a central constrictor cell which surrounds the acinar duct. The plasma membrane of the central cell is exposed to the duct. The type 1 acini do not appear to secrete active saliva components involved in feeding. The type 2 acini undergo a great increase in synthetic and secretory activity during feeding in both sexes and secrete a lipoprotein probably to form part of the attachment cone and also glycoproteins and esterases of unknown functions. The type 3 acini of both sexes also secrete a lipoprotein probably to form part of the attachment cone. The f cells of these acini in the females transiently secrete a glycoprotein of unknown function and then transform to become part of a water excreting unit. In the males the secretory activity of the granular cells of the type 2 and 3 acini is maintained for further attachments. The type 4 acini of the males accumulate masses of proteinaceous granules. The system of interstitial cells and intercellular spaces in types 2, 3 and 4 acini is large and increasingly active during feeding.     

Osmoregulatory mechanisms of the Australian freshwater crocodile, Crocodylus johnstoni, in freshwater and estuarine habitats

The estuary of the Limmen Bight River in Australia's Northern Territory is home to an unusual salt water-adapted population of the Australian `freshwater' crocodile, Crocodylus johnstoni. Crocodiles were captured from tidal reaches of the estuary ranging in salinity from 0.5–24‰ and from several permanent fresh water reaches more or less remote from saline waters. C. johnstoni is an effective osmoregulator in moderately saline waters and has osmoregulatory mechanisms very similar to its more marine-adapted relative, the estuarine crocodile Crocodylus porosus. Fasted C. johnstoni in brackish water appear to lose little sodium in cloacal urine, relying on their lingual salt glands for excretion of excess sodium chloride. The lingual glands show clear evidence of short-term and long-term acclimation to salt water. Like estuarine crocodiles, C. johnstoni drinks fresh water and will not drink sea water. Gross sodium and water fluxes in brackish water are very similar to those in other crocodilians, suggesting differences in integumental permeability are not a major influence on osmoregulatory differences between crocodilians. The data reinforce the hypothesis that crocodylids differ fundamentally from alligatorids in the structure and function of the renal-cloacal-salt gland complex and are of interest in current debate over the evolutionary and zoogeographical history of the eusuchian crocodilians. Accepted: 25 February 1999     

Osmoregulation by the broad-snouted caiman, Caiman latirostris, in estuarine habitat in southern Brazil

The broad-snouted caiman Caiman latirostris, of South America mostly frequents freshwater but occurs also in estuaries. Nothing of substance is known of its osmoregulatory physiology but, in the light of accumulating evidence that alligatorids lack specialised adaptations for life in hyperosmotic waters, we anticipated its physiology would be more similar to that of Alligator mississippiensis than the euryhaline Crocodylus porosus, which has both lingual salt glands and a more complex renal:cloacal system. This proved to be the case. Caiman captured in estuaries of the Ilha do Cardoso in southern Brazil were effective hypo-osmotic osmoregulators in salinities of 0–24 ppt (seawater = 35 ppt). Plasma osmolarity, sodium and chloride were similar to those in other crocodilians and not influenced by salinity. Plasma urea was low and did not vary with salinity. We found no evidence of lingual or other salt glands. Urinary electrolyte concentrations varied considerably with salinity and in ways reminiscent of A. mississippiensis but very different from C. porosus. Ca. latirostris dehydrated in seawater more rapidly than C. porosus and had substantially higher integumental permeability to water. Caiman did not drink seawater but rehydrated rapidly when returned to freshwater (FW). We found small caiman (<500 g) only in very low salinities (<3 ppt) and larger caiman closer to the sea. We postulate that medium to large Ca. latirostris can take advantage of the feeding opportunities presented by the estuarine mangal despite lacking the physiological specialisations of crocodylids. Two individuals which we re-sighted by chance had travelled at least 600 m in 2–3 days, showing that every caiman we captured or saw was within easy reach of FW. Most likely their habitation of the estuary and its mangal is achieved through a combination of low surface area:volume ratio, relatively impermeable skin, and periodic access to FW. Accepted: 11 May 1998     

Salt gland blood flow in the hatchling green turtle, Chelonia mydas

Microsphere and morphometric techniques were used to investigate any circulatory changes that accompany secretion by the salt glands of hatchling Chelonia mydas. Salt glands were activated by a salt load of 27.0 mmol NaCl kg body mass (BM)⁻¹, resulting in a mean sodium secretion rate of 4.14 ± 0.11 mmol Na kg BM⁻¹ h⁻¹ for a single gland. Microsphere entrapment was approximately 160–180 times greater in the active salt gland than the inactive gland, inferring a similar change in blood flow through salt gland capillaries. The concentration of microspheres trapped in the salt gland was significantly correlated with the rate of tear production (ml kg BM⁻¹ h⁻¹) and the total rate of sodium secretion (mmol Na kg BM⁻¹ h⁻¹) but not with tear sodium concentration (mmol Na l⁻¹). Adrenaline (500 μg kg BM⁻¹) inhibited tear production within 2 min and reduced microsphere entrapment by approximately 95% compared with active glands. The volume of filled blood vessels increased from 0.03 ± 0.01% of secretory lobe volume in inactive salt gland sections to 0.70 ± 0.11% in active gland sections. The results demonstrate that capillary blood flow in the salt gland of C. mydas can regulate the activity of the gland as a whole. Accepted: 12 July 2000     

Evidence that up-regulation of the parotid Na+-K+-2Cl- cotransporter by hypertonic shrinkage is not duplicated by isotonic shrinkage

The application of Ca2+ mobilizing secretagogues to rat parotid acini results in a significant decrease in cell volume (15-30%) due to isotonic salt loss. It is often assumed that the effects of such an isotonic volume decrease can be mimicked by anisotonic cell shrinkage. We demonstrate that the Na+-K+-2Cl- cotransporter in these cells is up-regulated by Ca2+ mobilizing secretagogues as well as by cell shrinkage in hypertonic media. However, we find that although the protein kinase inhibitors staurosporine (0.3 M) and K252a (0.6 M) significantly blunt the latter up-regulation, they are without effect on the former. These observations suggest that hypertonic and isotonic shrinkage do not result in the activation of the same intracellular signalling pathways, and indicate that anisotonic volume perturbations may not provide good experimental models of physiologic isotonic volume changes.     

Arterial hypotension in ducks adapted to high salt intake

Summary A homogeneous group of 8-week-old Pekin ducks was divided into two groups: saltwater (SW) ducks received salt water of gradually increasing salinity (200–600 mOsm·kg^-1) from the 8th to 20th week of age; freshwater (FW) ducks were maintained on fresh water but otherwise treated identically. During the course of salt-adaptation SW ducks increased plasma osmolality, Na⁺ and Cl^- levels, and concentrations of the osmoregulatory peptide hormones arginine vasotocin and angiotensin II. The apparent volume of inulin distribution decreased in SW ducks, but blood volume was not reduced. SW ducks also developed arterial hypotension, bradycardia, and reduced cardiac output in the course of salt adaptation. This depressed cardiovascular performance was associated with enhanced vagal restraint of cardiac function and reduced plasma concentrations of norepinephrine. Salt water adaptation did not alter the degrees to which mean arterial pressure and heart rate changed in response to intravenous bolus injections of catecholamines. The same applied to the osmoregulatory peptides which were, however, effective only at supraphysiological concentrations. The Pekin duck, as a bird predisposed for adaptation to high salt loads, presumably adapts to chronic hypertonic saline intake by resetting the central autonomic control of blood pressure to a lower level.Abbreviations FW ducks fresh water ducks - SW ducks salt water ducks - ANGI angiotensin II - AVT arginine vasotocin - MAP mean arterial pressure - HR heart rate - IV intravenous - CO cardiac output - SV stroke volume - TPR total peripheral resistance - ISp virtual inulin space - ECFV extracellular fluid volume     

The effect of salty diets and gradual transfer to sea water on osmotic adaptation, gill Na+, K+-ATPase activation, and survival of brook charr, Salvelinus fontinalis, Mitchill

The intensity and duration of the period of osmotic disturbance during introduction of brook charr into sea water were decreased by introducing the fish according to a gradient of salinity over a period of 6 days. Survival in summer increased from 25 to 90% with the use of a salinity gradient. However, kinetics and levels of activation of the gill Na⁺, K⁺-ATPase were not affected by the mode used for introducing brook charr into sea water. Neither was its level of activity modified by the use of a salted diet when the fish were in fresh water. The addition of 8 and 12% of salt to the diet prevented the plasma electrolyte surge of concentrations during the first days in sea water. In very cold water, survival rate was also drastically improved by giving an 8% salted diet during the 6 weeks preceding the introduction into sea water. These results show that both salty diets and exposure to brackish water during 6 days help brook charr face osmotic stress and improve their survival rate when introduced into full-strength sea water. The combined use of these preconditioning strategies might facilitate rearing this species in sea cages or silos.     

Comparison of the effects of NaCl and KCl at the roots on seedling growth,cell death and the size,frequency and secretion rate of salt glands in leaves of <Emphasis Type="Italic">Limonium sinense</Emphasis>

Twenty days’ exposure to 50 or 100 mM NaCl in the rooting medium substantially increased fresh and dry weights of seedling shoots of the recretohalophyte Limonium sinense while 200 or 300 mM were increasingly inhibitory. KCl treatment was only slightly stimulating (50 mM) or strongly inhibitory (100–300 mM). Lesser effects on leaf area were also seen. Diameter of foliar salt glands was significantly larger than that of controls in 100 and 200 mM NaCl with the effect being reversed at higher concentrations. Gland enlargement was also observed in the presence of 100 mM KCl, while larger concentrations reduced gland size. Generally, gland diameter was larger in the presence of NaCl than in KCl. NaCl and KCl also increased gland number per leaf and secretion rate per gland. At 100 and 200 mM NaCl or KCl, Na⁺ secretion per leaf from NaCl-treated plants exceeded K⁺ secretion rate from KCl-treated plants while at 200 mM, Na⁺ secretion per gland was significantly higher for Na⁺ than for K⁺. Evidence of cell death in leaves of salt-treated plants using Evans blue staining indicates that release of cell contents through loss of membrane integrity contributed to the secretion values. We conclude that the greater tolerance of L. sinenseto to NaCl compared to KCl is linked to the more effective secretion of Na⁺ than of K⁺ and, in turn, to a greater stimulation of salt gland formation and activity and larger gland diameter.     

Ultrastructural changes of rat parotid glands induced by a diet of liquid Metrecal

Summary The ultrastructure of parotid glands was studied in rats fed a diet of liquid Metrecal for two weeks and compared with that of parotid glands of control rats which received a diet of Purina lab chow. The liquid diet induced major alterations of acinar cells, but other parenchymal components were apparently unaffected.Most acinar cells of experimental rats were atrophic and some of these were undergoing necrosis. Lipid droplets and dense bodies (believed to be lysosomes) were numerous in atrophic cells. The Golgi apparatus, quantity of secretory granules, and intercellular canaliculi were smaller than in acinar cells of control rats.Such findings suggest that the secretory process was impaired and support the conclusion that parotid glands of rats maintained on a liquid diet are physiologically less active than those of chow fed rats. The decreased activity, as previously reported, may result from reduced masticatory activity.Supported by U.S.P.H.S. grant DE 02110.     

Flavonoid-induced reduction of ENaC expression in the kidney of Dahl salt-sensitive hypertensive rat

Flavonoid, a plant extract, exhibits various biological actions. Dietary flavonoid intake is reported to reduce an elevated blood pressure, however the mechanism is unknown. The epithelial Na+ channel (ENaC) in the kidney plays a key role in the regulation of blood pressure by contributing to the Na+ reabsorption in renal tubules. Thus, we investigated the effect of quercetin, a flavonoid, on ENaC mRNA expression in the kidney of hypertensive Dahl salt-sensitive rats. Dahl salt-sensitive rats of 8 weeks were acclimated for 1 week in a metabolic cage and were subsequently kept for 4 weeks under four different conditions: (1) normal salt diet (0.3% NaCl), (2) normal salt diet with quercetin (10 mg/kg/day), (3) high-salt diet (8% NaCl), and (4) high-salt diet with quercetin. Quercetin diminished the alphaENaC mRNA expression in the kidney associated with reduction of the systolic blood pressure elevated by high-salt diet, suggesting that one of the mechanisms of the flavonoid's antihypertensive effect on salt-sensitive hypertension would be mediated through downregulation of ENaC expression in the kidney.     

Control of salt gland activity in the hatchling green sea turtle, Chelonia mydas

 We studied the control of salt gland secretion in hatchling Chelonia mydas. The threshold salt load to activate salt secretion was between 400 μmol NaCl 100 g bodymass (BM)⁻¹ and 600 μmol NaCl 100 g BM⁻¹, which caused an increase in plasma sodium concentration of 13% to 19%. Following a salt load of 2700 μmol NaCl 100 g BM⁻¹, salt gland secretion commenced in 12 ± 1.3 min and reached maximal secretory concentration within 2–7 min. Maximal secretory rate of a single gland averaged 415 μmol Na 100 g BM⁻¹ h⁻¹. Plasma sodium concentration and total osmotic concentration after salt loading were significantly higher than pretreatment values within 2 min. Adrenalin (25 μg kg BM⁻¹) and the cholinergic agonist methacholine (1 mg kg BM⁻¹) inhibited salt gland activity. Atropine (10 mg kg BM⁻¹) reversed methacholine inhibition and stimulated salt gland secretion when administered with a subthreshold salt load. Arginine vasotocin produced a transient reduction in sodium secretion by the active gland, while atrial natriuretic factor, vasoactive intestinal peptide and neuropeptide Y had no measurable effect on any aspect of salt gland secretion. Our results demonstrated that secretion of the salt gland in C. mydas can be modified by neural and hormonal chemicals in vivo and that the cholinergic and adrenergic stimulation of an exocrine gland do not appear to have the typical, antagonist actions on the chelonian salt gland. Accepted: 28 September 1999     

ANG II-induced attenuation of duck salt gland secretion does not depend upon the release of adrenal catecholamines

Pekin ducks (Anas platyrhynchos) were bilaterally adrenalectomized (ADX) using a two-stage procedure and given daily i.m. injections of 1 mg kg bw⁻¹ of dexamethasone (DEXA), a steroid lacking mineralocorticoid activity, and 0.9% saline drinking water ad libitum to counterbalance renal losses of salt and water. Mean arterial blood pressure (mmHg) fell from 161±3.7 (intact controls) to 116±6.9 (bilateral ADX+DEXA), a decrease of 27%, but heart rates (HR) were unchanged. The nasal salt glands were fully active after ADX+DEXA. Rates of fluid secretion and electrolyte and osmolal concentrations were unchanged. Secretion stopped, then rebounded several minutes later if ADX+DEXA ducks were injected i.v. with 1 μg of [Asn¹,Val⁵]-angiotensin II (ANG II) kg bw⁻¹ which showed that attenuation was not adrenal catecholamine-dependent.     

Physical and Chemical Properties of the Lipase of Thermophilic Fungus Humicola lanuginosa S-38

Some physical and chemical properties of the extracellular lipase from the thermophilic fungus, Humico la lanuginosa S–38, were investigated. The results were as follows: Sedimentation coefficient was 2.4 × 10^?13 (cm-g/sec-dyne); diffusion coefficient was 8.8 × 10^?7 (cm²/sec); and frictional coefficient was 1.22. Molecular weight was 27,500±500 and α-helix content was 18.9%. The number of amino acid residues contained in 1 mole of protein of Humicola lipase was 224. Sugar and lipid were not detected. The effect of calcium ion and denaturing reagents, such as urea, sodium dodecyl sulfate and dithiothreitol, on the thermostability of Humicola lipase was examined. It was concluded that the thermostability of Humicola lipase was not influenced by protective cofactors but was attributable to the enzyme itself. Some properties of enzyme structure which were concerned with the thermostability of Humicola lipase are also discussed.     

Glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) from Dunaliella tertiolecta. I. Purification and kinetic properties

A rapid purification procedure for glycerol-3-phosphate dehydrogenase from Dunaliella tertiolecta (strain 19-6 of the algal collection of the Univ. of Göttingen), the initial enzyme in the glycerol cycle, has been developed on the basis of affinity chromatography on Blue Sepharose and subsequent desalting by Sephadex G-50. The achieved purification was 126-fold. The pH optimum of dihydroxyacetone phosphate reduction is 7, that of glycerol-3-phosphate oxidation is about 9. The in vitro enzymatic activity obtained from cell extracts is higher than the required activity for the observed glycerol production rates under osmotic stress in vivo.