The major cations in Lake Maryût waters

Summary The concentrations of sodium, potassium, calcium and magnesium in Lake Maryût water are determined at six stations representing the different regions of the lake during the year 1966. The sodium content varies seasonally and regionally with an annual average value of 1.0332 g/kg. The potassium content varies also seasonally and regionally following the sodium variation, with an annual average content of 0.0585 g/kg. The potassium concentration in the lake water forms about 4.5% that of sodium, compared with 3.6% in sea water and 21.6% in fresh water. The average Na/Cl ratio varies between a maximum in autumn and a minimum in summer. Contrary to the Na/Cl ratio, the K/Cl ratio is more or less correlated with salinity variations where it increases in summer and decreases in winter. The annual average Na/Cl ratio of 0.6345 for the lake water is higher than the average ratio of 0.5555 given for sea water. The K/Cl ratio has an annual average value of 0.0339 which is again higher than the average ratio of 0.0208 for sea water. The sodium and potassium chlorinity ratios decrease with the increase of chlorinity.The calcium content in the lake water reaches its maximum in summer and its minimum in autumn with an annual average content of 0.0549 g/kg. The Ca/Cl ratio for the lake water has an average value of 0.0335 which is higher than the ratio of 0.02126 for oceanic water. It increases by the increase of chlorinity and subsequently follows the salinity variation in the lake water. It also varies regionally following the distribution of carbonates in the bottom sediments.The magnesium content in the lake water has an annual average of 0.1201 g/kg. The Mg/Cl ratio increases by the increase of chlorinity, with an annual average value of 0.0733 which is higher than the average ratio of 0.06692 for sea water. Similar to calcium, the Mg/Cl ratio follows more or less the seasonal variation of salinity. The Mg/Cl ratio varies slightly from one region to another, with a slight westward increase in the lake. The average Mg/Cl ratios are the same at the six stations and the annual average ratio is 0.0733.     

含血停搏液镁离子浓度对未成熟心肌保护的影响

目的 采用幼兔离体心脏模型。模拟临床上可能出现的含血停搏液Ca^2 浓度变化,探讨适宜于未成熟心肌保护的Mg^2 浓度。方法 3-4周龄长耳白兔,依照含血停搏液不同Mg^2 浓度（0.6mmol/L,4.0mmol/L,8.0mmol/L,120mmol/L,16.0mmol/L）随机分为5组,建立Langendorff离体心脏灌注模型。采用Ca^2 浓度1.2-1.5mmol/L的含血停搏液,运用温血停搏液诱导停搏,冷血停搏液间断灌注,低温保护,终末温血停搏液控制性再灌注技术,观察以下指标：1、血流动力学指标;实验前后恢复率;心率,主动脉流量,冠脉流量,心排量,左室收缩压和左室舒张末压;2、心肌含水量;3、冠脉流出液乳酸盐含量;4、心肌肌酸激酶和乳酸脱氢酶漏出率;5、心肌细胞内Na^2 ,Ca^2 含量;6、心肌组织ATP含量;7、心肌组织SOD活性,MDA含量;8、心肌超微结构。结果 1、心率恢复率,主动脉流量恢复率及左室收缩压恢复率组间总体差异无显著性。而冠脉流量恢复率,心排量恢复率和左室舒张末压恢复率以Mg^2 浓度8.0mmol/L和12.0mmol/L为优,0.4mmol/L组最差。2、心肌含水量以Mg^2 浓度8.0mmol/L和12.0mmol/L为最低。3、冠脉流出液乳酸盐含量0.4mmol/L组,8.0mmol/L和12.0mmol/L组高于欺科2组。4、心肌乳本能部氢酶漏出率以8.0mmol/L组最低,而肌酸激酶漏出率以8.0mmol/L和12.0mmol/L组为最低。5、心肌细胞内Na^ 、Ca^2 含量;6、心肌组织ATP含量;7、心肌组织SOD活性,MDA含量;8、心肌超微结构。结果：1、心率恢复率,主动脉流量恢复率及左室收缩压恢复率组间总体差异无显著性。而冠脉流量恢复率,心排量恢复率和左室舒张末压恢复率以Mg^2 浓度8.0mmol/L和12.0mmol/L为优,0.4mmol/L组最差。2、心肌含水量以Mg^2 浓度8.0mmol/L和12.0mmol/L为最低。3、冠脉流出液乳酸盐含量0.4mmol/L组最差。2、心肌含水量以Mg^2 浓度8.0mmol/L和12.0mmol/L为最低。3、冠脉流出液乳桎卤含量0.4mmol/L组,8.0mmol/L和12.0mmol/L组高于其余2组。4、心肌乳酸脱氢酶漏出率以8.0mmol/L组最低,而肌酸激酶漏出率以8.0mmol/L和12.0mmol/L组为最低。5、心肌细胞内Na^2 含量以8.0mmol/L和12.0mmol/L组为最低,而心肌细胞内Ca^2 含量以8.0mmol/L组最低。6、心肌组织ATP含量以12.0mmol/L组为最高。7、心肌组织SOD活性以8.0mmol/L和12.0mmol/L组库最高,而MDA含量各组间总体差异无显著性。8、心肌超微结构;8.0mmol/L和12.0mmol/L组表现为基本正常未成熟心肌超微结构,而0.4mmol/L组超微结构有明显损伤表现。结论 对于未成熟心肌,当采用温血停搏液诱导停搏,冷血停搏液间断灌注,低温保护,温血停搏液终末控制性再灌注技术时,为避免含血停搏液Ca^2 浓度偏高对未成熟心肌的不利影响。应维持含血停搏液中Mg^2 浓度在8-12mmol/L。     

Effects of dietary caffeine on renal handling of minerals in adult women

Thirty-seven women, aged 31-78 years, on two separate mornings consumed a decaffeinated beverage to which 6 mg caffeine/kg lean body mass or no caffeine were added. Total urine output of water, calcium, magnesium, sodium, chloride, potassium and creatinine increased in the two hours following caffeine ingestion when compared to the control beverage. Increased urinary mineral (mg)/urinary creatinine (g) ratios were seen for calcium (120 to 200), magnesium (70 to 110), sodium (3,800 to 6,200) and chloride (9,200 to 14,800), following the caffeinated beverage. Creatinine clearance did not change significantly. The percent reabsorption of calcium (98.6% to 97.5%, p less than .001) and magnesium (97.0% to 94.2%, p less than .0001) decreased significantly during the post-caffeine period. The calcium and magnesium filtered loads did not differ significantly between the caffeine and no caffeine beverages. Therefore, caffeine-induced urinary loss of calcium and magnesium is largely attributable to a reduction in calcium and magnesium renal reabsorption, although the physiological mechanism and tubular segment affected remain to be established.     

Influences of Ca and Mg ions on the egg survival of grey mullet, Mugil cephalus L.

Five kinds of artificial sea water with similar salinity, pH and osmolarity were prepared with different concentrations of calcium and magnesium ions. They were complete sea water, calcium-free sea water, half calcium-free sea water, magnesium-free sea water and half magnesium-free sea water. The fertilized eggs from induced spawnings of grey mullet Mugil cephalus , were transferred to these sea waters at two development stages, i.e. before the formation of 2-blastomere stage and at the gastrula stage. Survivals of fertilized egg in different sea waters were checked after several hours incubation, the percentage survival was used as an index of the importance of calcium and magnesium to the embryonic development. The results showed that calcium is indispensable to the embryonic development of mullet egg. Magnesium, however, is not the necessary element in the incubation medium.     

Effects of Chemical Speciation on the Mineralization of Organic Compounds by Microorganisms

The mineralization of 1.0 to 100 ng each of four complexing compounds—oxalate, citrate, nitrilotriacetate (NTA), and EDTA—per ml was tested in media prepared in accordance with equilibrium calculations by a computer program so that the H, Ca, Mg, Fe, or Al complex (chemical species) was predominant. Sewage microorganisms mineralized calcium citrate more rapidly than iron, aluminum, or hydrogen citrate, and magnesium citrate was degraded slowest. Aluminum, hydrogen, and iron oxalates were mineralized more rapidly than calcium oxalate, and magnesium oxalate was decomposed slowest. Sewage microorganisms mineralized calcium NTA but not aluminum, magnesium, hydrogen, or iron NTA or any of the EDTA complexes. Pseudomonas sp. mineralized calcium and iron citrates but had no activity on hydrogen, aluminum, or magnesium citrate. Pseudomonas pseudoalcaligenes mineralized calcium, iron, hydrogen, and aluminum citrates but had little activity on magnesium citrate. Pseudomonas alcaligenes used calcium, iron, hydrogen, and aluminum oxalates readily, but it used magnesium oxalate at a slower rate. Listeria sp. destroyed calcium NTA but had no effect on hydrogen, iron, or magnesium NTA. Increasing the Ca concentration in the medium enhanced the breakdown of NTA by Listeria sp. The different activities of the bacterial isolates were not a result of the toxicity of the complexes or the lack of availability of a nutrient element. NTA mineralization was not enhanced by the addition of Ca to Beebe Lake water, but it was enhanced when Ca and an NTA-degrading inoculum were added to water from an oligotrophic lake. The data show that chemical speciation influences the mineralization of organic compounds by naturally occurring microbial communities and by individual bacterial populations.     

Effects of calcium and magnesium on a 41-kDa serine-dependent protease possessing collagen-cleavage activity

We report here the continued characterization of a 41-kDa protease expressed in the early stage of the sea urchin embryo. This protease was previously shown to possess both a gelatin-cleavage activity and an echinoderm-specific collagen-cleavage activity. In the experiments reported here, we have explored the biochemical nature of this proteolytic activity. Pepstatin A (an acidic protease inhibitor), 1,10-phenanthroline (a metalloprotease inhibitor), and E-64 (a thiol protease inhibitor) were without effect on the gelatin-cleavage activity of the 41-kDa species. Using a gelatin substrate gel zymographic assay, the serine protease inhibitors phenylmethylsulfonyl fluoride and benzamide appeared to partially inhibit gelatin-cleavage activity. This result was confirmed in a quantitative gelatin-cleavage assay using the water soluble, serine protease inhibitor [4-(2-aminoethyl)benzenesulfonylfluoride]. The biochemical character of this protease was further explored by examining the effects of calcium and magnesium, the major divalent cations present in sea water, on the gelatin-cleavage activity. Calcium and magnesium competed for binding to the 41-kDa collagenase/gelatinase, and prebound calcium was displaced by magnesium. Cleavage activity was inhibited by magnesium, and calcium protected the protease against this inhibition. These results identify calcium and magnesium as antagonistic agents that may regulate the proteolytic activity of the 41-kDa species.     

The role of hydrated divalent metal ions in the bridging of two anionic groups. An ab initio quantum chemical and molecular mechanics study of dimethyl phosphate and formate bridged by calcium and magnesium ions

Ab initio quantum chemical (Gaussian82) and molecular mechanics (AMBER2.0) computational techniques are employed to investigate the interaction of two anions (formate an dimethylphosphate) and a central divalent metal cation (magnesium or calcium). These systems are models for the essential GDP binding unit of the G-proteins (e.g., EF-Tu or the ras oncogene proteins) and for protein/phospholipid interactions, both of which are mediated by divalent metal cations. Various levels of hydration are utilized to examine coordination of differences between magnesium and calcium ions. Two different orientations of formate and dimethyl phosphate in direct ion contact with a magnesium ion and two waters of hydration were energy minimized with both quantum and molecular mechanics techniques. The structures and energy differences between the two orientations determined by either of the computational techniques are similar. Magnesium ion has a strong propensity to assume six coordination whereas calcium ion preferentially assumes a coordination greater than six. Likewise, water molecules attached to magnesium ion are held more rigidly than those of calcium ion, thus calcium ion is more accommodating in the exchange of water for negative ligands.     

Substrate freezing and thawing as a factor in the mineral nutrient status of mire ecosystems

The effect of freezing and thawing on the release of sodium, potassium, calcium, magnesium, iron, and aluminium directly into the sample water and into a dilute acid extractant was investigated using peat samples collected from three different mire sites. In most cases exchangeable sodium, potassium, calcium, magnesium, and iron content of the treated samples was greater than in the untreated controls. Changes in aluminium content are more probably related to drying and re-wetting of the samples than to freezing and thawing. The role of freezing and thawing in the nutrient status of mires is discussed.     

Some analyses of artificially incubated eggs and hatchlings of Green and Loggerhead sea turtles

Eggs of the Green sea turtle ( Chelonia mydas ) and the Loggerhead sea turtle ( Caretta caretta ) were incubated in coral sand or silica sand moistened with distilled water. The eggs and hatchlings were analysed for calcium, magnesium and phosphorus. There was less magnesium but more calcium in the hatchlings than in the original egg contents but this was not influenced by the type of sand used during incubation. The results are interpreted as indicating that the eggshell is the major source of calcium for the developing embryos. The Logger-head sea turtle shows a greater efficiency in the incorporation of yolk magnesium and phosphorus into the embryo than does the Green sea turtle.     

The impact of diets with different magnesium contents on magnesium and calcium in serum and tissues of the rat

The impact of three different magnesium diets (70, 1,000 and 9,000 ppm) on total, ionized and bound magnesium as well as ionized calcium in serum and total calcium and magnesium in femoral bone, skeletal muscle, heart and liver of male Sprague-Dawley rats was investigated. The percentage of ionized serum magnesium was unproportionally high in rats fed a low magnesium (70 ppm) diet. Femoral magnesium was correlated with ionized and total serum magnesium. In contrast, there was generally no correlation between total serum magnesium and the magnesium fractions in skeletal muscle, heart and liver. In rats fed the magnesium deficient diet, total cardiac concentration of magnesium was even significantly increased along with total calcium content, while there were no effects on total muscle and liver magnesium. Within the single groups, ionized serum calcium was never proportional to dietary magnesium, but in all three magnesium diet groups together, it was inversely correlated with dietary magnesium. Moreover, ionized serum calcium was inversely correlated with both ionized and total serum magnesium. In all 3 groups together, the concentrations of total calcium and magnesium in heart and skeletal muscle were correlated, within the single groups correlation existed only in the 1000 ppm group. Magnesium influx via calcium channels during low magnesium intake has been seen in non cardiac tissues [35,36], but nothing similar is known about non selective channels for divalent cations in the heart [33]. Thus, magnesium uptake by cardiac cells along with calcium seems to be possible, especially at low intracellular magnesium concentrations, but is still poorly investigated. We suggest that the calcium-antagonistic effect of magnesium is related to the turnover rate of magnesium rather than to its tissue concentrations.     

Magnesium Supplementation through Seaweed Calcium Extract Rather than Synthetic Magnesium Oxide Improves Femur Bone Mineral Density and Strength in Ovariectomized Rats

Commercially available seaweed calcium extract can supply high amounts of calcium as well as significant amounts of magnesium and other microminerals. The purpose of this study was to investigate the degree to which the high levels of magnesium in seaweed calcium extract affects the calcium balance and the bone status in ovariectomized rats in comparison to rats supplemented with calcium carbonate and magnesium oxide. A total of 40 Sprague-Dawley female rats (7?weeks) were divided into four groups and bred for 12?weeks: sham-operated group (Sham), ovariectomized group (OVX), ovariectomized with inorganic calcium and magnesium supplementation group (OVX-Mg), and ovariectomized with seaweed calcium and magnesium supplementation group (OVX-SCa). All experimental diets contained 0.5% calcium. The magnesium content in the experimental diet was 0.05% of the diet in the Sham and OVX groups and 0.1% of the diet in the OVX-Mg and OVX-SCa groups. In the calcium balance study, the OVX-Mg and OVX-SCa groups were not significantly different in calcium absorption compared to the OVX group. However, the femoral bone mineral density and strength of the OVX-SCa group were higher than those of the OVX-Mg and OVX groups. Seaweed calcium with magnesium supplementation or magnesium supplementation alone did not affect the serum ALP and CTx levels in ovariectomized rats. In summary, consumption of seaweed calcium extract or inorganic calcium carbonate with magnesium oxide demonstrated the same degree of intestinal calcium absorption, but only the consumption of seaweed calcium extract resulted in increased femoral bone mineral density and strength in ovariectomized rats. Our results suggest that seaweed calcium extract is an effective calcium and magnesium source for improving bone health compared to synthetic calcium and magnesium supplementation.     

The effects of calcium and magnesium on water and ionic permeabilities in the sea water adapted eel,Anguilla anguilla L.

Summary The permeability characteristics to water and ions, of the seawater adapted eel, have been studied in the absence and presence of external calcium and magnesium.The absence of these divalent ions from the external medium produces an increase in the unidirectional and net water fluxes as well as a decrease in temperature coefficients. Similarly, an increase in the effluxes of sodium and chloride and a large increase in the passive loss of these ions was observed when fish were transferred to deionized water. The stimulating effect of externally added (10 mM) potassium on the sodium and chloride effluxes, when fish are transferred to fresh water is abolished in the absence of calcium and magnesium (Fig. 1). These kinetic changes are accompanied by ultrastructural changes concerned principally with the chloride cells (Figs. 2 and 3).The results are discussed in terms of the possible role of calcium and magnesium in the maintenance of the hydro-mineral equilibrium of the eel.     

The skeletal organic matrix from Mediterranean coral Balanophyllia europaea influences calcium carbonate precipitation

Scleractinian coral skeletons are made mainly of calcium carbonate in the form of aragonite. The mineral deposition occurs in a biological confined environment, but it is still a theme of discussion to what extent the calcification occurs under biological or environmental control. Hence, the shape, size and organization of skeletal crystals from the cellular level through the colony architecture, were attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth. The skeleton contains an intra-skeletal organic matrix (OM) of which only the water soluble component was chemically and physically characterized. In this work that OM from the skeleton of the Balanophyllia europaea, a solitary scleractinian coral endemic to the Mediterranean Sea, is studied in vitro with the aim of understanding its role in the mineralization of calcium carbonate. Mineralization of calcium carbonate was conducted by overgrowth experiments on coral skeleton and in calcium chloride solutions containing different ratios of water soluble and/or insoluble OM and of magnesium ions. The precipitates were characterized by diffractometric, spectroscopic and microscopic techniques. The results showed that both soluble and insoluble OM components influence calcium carbonate precipitation and that the effect is enhanced by their co-presence. The role of magnesium ions is also affected by the presence of the OM components. Thus, in vitro, OM influences calcium carbonate crystal morphology, aggregation and polymorphism as a function of its composition and of the content of magnesium ions in the precipitation media. This research, although does not resolve the controversy between environmental or biological control on the deposition of calcium carbonate in corals, sheds a light on the role of OM, which appears mediated by the presence of magnesium ions.     

湖南烟区土壤交换性钙、镁含量及对烤烟品质的影响

分析了湖南烟区主要土壤类型交换性钙、镁元素含量状况及其对烟叶品质的影响,结果表明:(1)土壤交换性钙、镁含量在不同土壤类型间存在显著性差异,交换性钙含量平均为8.87cmol/kg,以红壤含量最高;交换性镁含量平均为1.16cmol/kg,以黄棕壤含量最高;交换性钙镁比值大小依次为:红壤(11.74)>水稻土(10.25)>黄壤(6.84)>黄棕壤(6.14),在烟叶实际生产中,应重视镁肥在红壤和水稻土中的施用;(2)烟叶钙含量偏高(21.93g/kg±4.37g/kg),烟叶镁含量偏低(2.52g/kg±1.26g/kg),两者均存在广泛的变异性;(3)整体来看,烟叶钙含量随土壤中交换性钙含量的升高和镁含量的降低而显著升高;烟叶镁含量随土壤交换性镁含量的升高而升高,与土壤交换性钙含量的相关性不显著;(4)典型相关分析表明,土壤中交换性镁含量的降低可能引起烟叶钾含量的提高,从而使得烟叶钾素和镁素含量达到较好的平衡;(5)土壤交换性钙、镁含量与烟叶其它化学成分指标的相关分析表明,土壤交换性钙有利于烟株对硼和氯素的吸收,对氮、锌和锰素的吸收则有显著的抑制作用;而土壤交换性镁有利于烟叶总糖、硼素和锰素的积累,对氮、磷、铁和锌素的吸收具有显著的抑制作用。     

The Role of Hydrated Divalent Metal Ions in the Bridging of Two Anionic Groups. An ab initio Quantum Chemical and Molecular Mechanics Study of Dimethyl Phosphate and Formate Bridged by Calcium and Magnesium Ions

Abstract

Ab initio quantum chemical (Gaussian82) and molecular mechanics (AMBER2.0) computational techniques are employed to investigate the interaction of twoanions (formate and dimethyl phosphate) and a central divalent metal cation (magnesium or calcium). These systems are models for the essential GDP binding unit of the G-proteins (e.g., EF-Tu or the ras oncogene proteins) and for protein/phospholipid interactions, both of which are mediated by divalent metal cations. Various levels of hydration are utilized to examine coordination of differences between magnesium and calcium ions. Two different orientations of formate and dimethyl phosphate in direct ion contact with a magnesium ion and two waters of hydration were energy minimized with both quantum and molecular mechanics techniques. The structures and energy differences between the two orientations determined by either of the computational techniques are similar. Magnesium ion has a strong propensity to assume six coordination whereas calcium ion preferentially assumes a coordination greater than six. Likewise, water molecules attached to magnesium ion are held more rigidly than those to calcium ion, thus calcium ion is more accommodating in the exchange of water for negative ligands.     

Effects of calcium and magnesium on a 41‐kDa serine‐dependent protease possessing collagen‐cleavage activity

We report here the continued characterization of a 41‐kDa protease expressed in the early stage of the sea urchin embryo. This protease was previously shown to possess both a gelatin‐cleavage activity and an echinoderm‐specific collagen‐cleavage activity. In the experiments reported here, we have explored the biochemical nature of this proteolytic activity. Pepstatin A (an acidic protease inhibitor), 1,10‐phenanthroline (a metalloprotease inhibitor), and E‐64 (a thiol protease inhibitor) were without effect on the gelatin‐cleavage activity of the 41‐kDa species. Using a gelatin substrate gel zymographic assay, the serine protease inhibitors phenylmethylsulfonyl fluoride and benzamide appeared to partially inhibit gelatin‐cleavage activity. This result was confirmed in a quantitative gelatin‐cleavage assay using the water soluble, serine protease inhibitor [4‐(2‐aminoethyl)benzenesulfonylfluoride]. The biochemical character of this protease was further explored by examining the effects of calcium and magnesium, the major divalent cations present in sea water, on the gelatin‐cleavage activity. Calcium and magnesium competed for binding to the 41‐kDa collagenase/gelatinase, and prebound calcium was displaced by magnesium. Cleavage activity was inhibited by magnesium, and calcium protected the protease against this inhibition. These results identify calcium and magnesium as antagonistic agents that may regulate the proteolytic activity of the 41‐kDa species. J. Cell. Biochem. 80:139–145, 2000. © 2000 Wiley‐Liss, Inc.     

THE COMPOSITION OF FLUIDS AND SERA OF SOME MARINE ANIMALS AND OF THE SEA WATER IN WHICH THEY LIVE

1. The electrolyte composition, the pH, and freezing points of the fluids of several invertebrates and one primitive chordate are reported. 2. Fluids of the worms, echinoderms, and the clam Venus were isotonic with sea water; fluids of the Arthropoda were hypertonic to sea water. 3. The pH of all fluids was below that of sea water. In the Arthropoda and Myxine less individual variation in pH appeared than in the echinoderms and worms. 4. Ratios of ionic concentrations in the fluid to those in the sea water indicated (1) uniform distribution of ions between the internal and external media for the echinoderms and Venus, (2) differential distribution of potassium and magnesium in the worms; (3) differential distribution of sulfate, magnesium, potassium, and calcium in the Arthropoda; and (4) differential distribution of calcium, magnesium, and sulfate in Myxine. 5. The unequal distribution of ions implies the expenditure of energy against a concentration gradient across the absorbing or excreting membranes, a capacity frequently overlooked in the invertebrates. 6. The sera of the Arthropoda from diluted sea water showed higher concentrations of sodium, potassium, calcium, and chloride ions relative to the respective concentrations in the external medium than in normal sea water, and also showed different orders for those ions. 7. The increase in osmotic pressure of the sera of the animals moving into brackish water is caused by unequal accumulation of sodium, potassium, calcium, and chloride ions. Sulfate and magnesium ionic ratios do not change.     

Water use and chemical composition of ryegrass (Lolium) cultivars

Summary Significant differences in total dry matter yields of shoots and roots were found between 11 ryegrass (Lolium) cultivars grown in a glasshouse. Although shoot yield varied significantly between individual cultivars there was no overall difference between the annual and perennial cultivars; whereas for roots, the yields of the perennial plants were much smaller than those of the annual types. Water use (g H₂O g total DM^–1) also varied significantly between cultivars. However, there was no relationship between efficient water use and dry matter production.No significant differences were found in shoot composition between the cultviars for nitrogen, phosphorus, and potassium; however, concentrations of sulphur, magnesium, calcium, and sodium varied significantly. Sodium concentrations were generally higher in the annual compared to the perennial cultivars. For roots only nitrogen, phosphorus, and sulphur differed significantly between cultivars. Of the elements only calcium in the shoots was shown to be related to water use. Thus cultivars which were low users of water also had significantly lower calcium concentrations in their shoots. Water use appeared to affect the absorption of calcium by the root to a far greater extent than the transport from roots to shoot. An apparent relationship between magnesium concentration in the shoots and water use was shown to be due to the close association of magnesium with calcium in the plant.     

A recently landlocked brackish-water lagoon of Lake Tanganyika: physical and chemical characteristics,and spatio-temporal distribution of phytoplankton

Monthly measurements of physical and chemical characteristics were made at two localities in the eastern part of a recently landlocked lagoon of Lake Tanganyika. Variables analysed were: temperature, pH, conductivity, sodium, potassium, magnesium, calcium, carbonate, bicarbonate, chloride and sulphate. Large seasonal fluctuations of salinity were recorded (1.68–8.21 g l^–1). The seasonal water input controlled algal seasonality mainly through its effect on salinity and indirectly through its influence on nutrient concentration by dissolution and dilution of the excrements of the numerous cattle and other organic matter. Phytoplankton was mainly composed of Cyanophyta and Euglenophyta. Euglenophyta dominated during the dry periods with high salinity and probably very high nutrient levels, while Cyanophyta preferred moderate salt and nutrient concentrations during the rainy periods. The phytoplanktonic community was composed of a large number of perennial and a reduced quantity of annual organisms.A spatial study of the recently landlocked lagoon revealed an ascending salinity gradient, principally due to a sodium bicarbonate/carbonate enrichment, between locations near the lake and more inland situated stations. These facts point to a lake water supply and a salt concentration by evaporation in the swamps. Proportionally lower magnesium, calcium and potassium values were recorded at high salinities, due to chemical precipitation and biotic factors.A blue-green algal bloom was observed in the eastern water-body (salinity: 4.64 g l^–1); simultaneously an important development of diatoms dominated the western water-body (salinity: 2.18 g l^–1). No significant differences in morphometry, exposure, water temperature or nutrient levels (nitrate, nitrite, ammonia, orthophosphate) were observed. The relatively low salinity and high nutrient concentration in the western water-body probably favoured diatom development during the rainy season. The relatively higher salinity in the eastern water-body during the rainy season was probably responsible for the dominance of blue-green algae through its negative influence on silica concentration and notwithstanding the high inorganic nitrogen concentration.     

Magnesium Supplementation did not Affect the Increasing Bone Zinc Concentration in Rats Given Excess Calcium as Carbonate

We investigated the effect of magnesium supplementation on zinc distribution in rats given excess calcium as carbonate. Rats were given a control diet (5 g/kg calcium and 0.5 g/kg magnesium), a high calcium diet (HC, 25 g/kg calcium and 0.5 g/kg magnesium) or the high calcium diet supplied with magnesium (HCM, 25 g/kg calcium and 2.5 g/kg magnesium) for 4 weeks. Calcium carbonate and magnesium oxide were used for increasing these mineral concentrations in diets. Although feed intake did not differ among the groups, the excess calcium suppressed feed efficiency, irrespective of dietary magnesium concentration. Femoral magnesium concentration was lower in the HC group than in the control and the HCM groups. Femoral zinc concentration was higher in the HC group and the HCM group than in the control group. The zinc concentration in the kidney was lower in the HC group and the HCM group than in the control group. The excess calcium did not affect zinc concentration in plasma and other tissues such as the liver, testis, and spleen, irrespective of dietary magnesium. These results suggest that the increasing bone zinc and the decreasing renal zinc do not result from magnesium insufficiency in rats given excess calcium as carbonate.