水体溶氧影响陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)对完全水淹的耐受力

溶氧是水环境中一个重要的环境因子,为了探讨水中的溶氧含量水平是否会对陆生植物的耐淹能力造成影响,研究了陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)在遭受不同溶氧含量水体完全淹没后的生长表现、存活情况和非结构碳水化合物的变化。实验结果表明:(1)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的存活。受高溶氧水体完全水淹的喜旱莲子草和牛鞭草主茎的完好程度和存活叶的数量均显著高于遭受低溶氧水体完全水淹的喜旱莲子草和牛鞭草,喜旱莲子草和牛鞭草在高溶氧水体完全水淹后的生物量比低溶氧水体完全水淹后要高;(2)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的生长,受高溶氧水体完全水淹的喜旱莲子草主茎伸长生长和不定根生长显著强于受低溶氧水体完全水淹的喜旱莲子草,在不定根的生长上牛鞭草也具有同样的表现。(3)高溶氧水环境有利于减小被完全淹没的喜旱莲子草和牛鞭草的碳水化合物消耗,两种植物在受高溶氧完全水淹后体内具有的非结构性碳水化合物含量均比受低溶氧完全水淹后高。(4)喜旱莲子草比牛鞭草能更好地耐受完全水淹,当处于低溶氧完全水淹时表现得更为明显,本研究表明入侵物种喜旱莲子草比本地物种牛鞭草具有更强的环境适应能力和水淹耐受能力。     

Evidence for alternative electron sinks to photosynthetic carbon assimilation in the high mountain plant species Ranunculus glacialis

The high mountain plant species Ranunculus glacialis has a low antioxidative scavenging capacity and a low activity of thermal dissipation of excess light energy despite its growth under conditions of frequent light and cold stress. In order to examine whether this species is protected from over-reduction by matching photosystem II (PSII) electron transport (ETR) and carbon assimilation, both were analysed simultaneously at various temperatures and light intensities using infrared gas absorption coupled with chlorophyll fluorescence. ETR exceeded electron consumption by carbon assimilation at higher light intensities and at all temperatures tested, necessitating alternative electron sinks. As photorespiration might consume the majority of excess electrons, photorespiration was inhibited by either high internal leaf CO₂ molar ratio (C_i), low oxygen partial pressure (0.5% oxygen), or both. At 0.5% oxygen ETR was significantly lower than at 21% oxygen. At 21% oxygen, however, ETR still exceeded carbon assimilation at high C_i, suggesting that excess electrons are transferred to another oxygen consuming reaction when photorespiration is blocked. Nevertheless, photorespiration does contribute to electron consumption. While the activity of the water –water cycle to electron consumption is not known in leaves of R. glacialis, indirect evidence such as the high sensitivity to oxidative stress and the low initial NADP-malate dehydrogenase (NADP-MDH) activity suggests only a minor contribution as an alternative electron sink. Alternatively, the plastid terminal oxidase (PTOX) may transfer excess electrons to oxygen. This enzyme is highly abundant in R. glacialis leaves and exceeds the PTOX content of every other plant species so far examined, including those of transgenic tomato leaves overexpressing the PTOX protein. Finally, PTOX contents strongly declined during deacclimation of R. glacialis plants, suggesting their important role in photoprotection. Ranunculus glacialis is the first reported plant species with such a high PTOX protein content.     

Rotifer occurrence in relation to water colour

Information on the distribution of 223 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to the content of humolimnic substances, measured as mg Pt/l. Most rotifers have a very wide tolerance range against this factor. The majority of the planktic species prefer a low content of humolimnic substances, and the non-planktic rotifers mainly occurring in brown-coloured water show, in addition, a preference for low pH. No connection with trophic degree could be traced.     

Ductus arteriosus responses to prostaglandin E1 at high and low oxygen concentrations

It previously has been suggested that prostaglandin E₁ (PGE₁) relaxes the ductus arteriosus in a low but not in an elevated oxygen environment. However, in the experiments reported here PGE₁ relaxed rings on fetal lamb ductus arteriosus at both low (14 to 20 torr) and high (680 to 720 torr) oxygen tensions. The threshold concentration for PGE₁ was 10⁻¹⁰ M in either PO₂ and the ED50's of PGE₁ relaxation in high and low oxygen were 8.5 ± 3.4 × 10⁻¹⁰ M and 5.5 ± 0.7 × 10⁻¹⁰ M respectively. The magnitude of the relaxation was greater for the oxygen contracted ductus arteriosus than for that exposed to low oxygen. It is suggested that earlier reports of the lack of response of the ductus arteriosus to PGE₁ in a high oxygen environment following relaxation in a low oxygen environment may be related to loss of response of the ductus arteriosus to repeated doses of PGE₁ rather than to differences in PO₂. Prostaglandin E₁ therefore may play a significant role in the regulation of ductus arteriosus tone in the elevated oxygen environment of the newborn as well as the low oxygen environment of the fetus.     

低钾胁迫对番茄叶片活性氧及抗氧化酶系的影响

以2种不同低钾耐性大果番茄(钾敏感型番茄081018和耐低钾型番茄081034)为材料,比较低钾处理下2种番茄叶片中活性氧产生及抗氧化酶系活性和相关基因表达差异,明确植物叶片对低钾胁迫的响应机制.结果显示:(1)钾敏感型番茄在低钾胁迫时,叶片中各种保护酶(SOD及其同工酶、POD、CAT、APX)活性随处理时间延长呈下降趋势,同时活性氧(O2-、H2O2)和MDA含量急剧增加;耐低钾型番茄在低钾胁迫条件下,其各类保护酶活性均比对照水平有所升高,而且O2-、H2O2和MDA的含量增加也较少.(2)钾敏感型番茄在低钾胁迫时叶片内Cu/Zn-SOD、CAT和APX基因的相对表达量均有下降趋势,而同期耐低钾型番茄在低钾胁迫时Cu/Zn-SOD、CAT和APX的表达却明显增加,这与其对应的酶活性变化趋势同步.研究表明,低钾胁迫使耐低钾型番茄具有较高保护酶基因表达量,产生较高的保护酶活性,可降低活性氧的破坏作用,防止膜渗透性增加,使之对低钾的适应性较强,而钾敏感番茄品系则相反.     

Morphological and biochemical integrity of human liver slices in long-term culture: effects of oxygen tension

We tested the effects of low 20% O₂) and high (70% O₂) oxygen tension on the morphological and biochemical integrity of human liver slices incubated for up to 72 h in supplemented Williams' E medium in a dynamic rotating culture system. High oxygen tension was more effective than low oxygen tension for preserving morphological integrity in long-term culture 48–72 h). After 72 h of culture with 70% O₂, the lobular pattern was well preserved, and the survival of hepatocytes approximately 80%) and other cell types was good. Immunohistochemical studies showed good preservation of the region-specific expression of CYP2E1 and CYP3A4 isoenzymes for up to 72 h of incubation in 70% O₂. As compared to 20% O₂, the oxidized glutathione content and reactive oxygen species production were slightly increased in 70% O₂, suggesting that minimal oxidative stress occurred with the high oxygen tension. In conclusion, despite slight oxidative stress associated with high oxygen tension, 70% O₂ appeared more appropriate than 20% O₂ for preserving the morphological and biochemical integrity of human liver slices cultured in a dynamic organ culture system for up to 72 h. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthetic rates in relation to leaf phosphorus content in pioneer versus climax tropical rainforest trees

In Guyana dense rainforest occurs on intensely weathered acid soils, low in soil phosphorus. To investigate whether low P availability limits photosynthesis of trees growing on these soils more than N does, leaf P and N content, and their relationship with the photosynthetic capacity (A _sat, mol CO₂ m^-2 s^-1) were studied for nine pioneer and climax tree species in a range of light climates. Light environment was described using hemispherical photographs. For both pioneer and climax species, leaf P content (r ²=0.71 and 0.23, respectively) is a more important determinant of A _sat than leaf N content (r ²=0.54 and 0.12, respectively). Pioneer species have a higher leaf P and N content than climax species. At similar P or N content, pioneers have a higher A _sat than climax species. The saplings studied had a relatively high A _sat, considering their low P concentration (15–30 mol P g^-1). All species studied had a constant leaf P and N concentration and photosynthetic capacity across light climates, because specific leaf mass (g m^-2) increased similarly with light availability. This acclimation to a change in light environment makes a possible limitation of A _sat by P or N independent of light environment.     

Lamb ductus arteriosus: Effect of prostaglandin synthesis inhibitors on the muscle tone and the response to prostaglandin E2

The prostaglandin synthesis inhibitors, indomethacin and eicosa-5,8,11, 14-tetraynoic acid (ETA), have been tested on the isolated lamb ductus arteriosus at low and high PO₂ levels. Both compounds produced a gradual contraction of the hypoxic vessel, and at equal doses the effect of indomethacin was stronger. The maximal tension output of the hypoxic tissue under indomethacin was equal to that of the oxygen-contracted control. ETA- and indomethacin-treated preparations contracted further upon transfer from a low to a high oxygen environment, and the response under indomethacin exceeded significantly control values. Control preparations were relaxed markedly by PGE₂ in low oxygen but showed little or no response in high oxygen. In contrast, preparations pretreated with the inhibitors retained their sensitivity to PGE₂ during exposure to high oxygen. The data are consistent with the idea that E-type prostaglandins play a role in the regulation of the intrinsic tone of the ductus arteriosus during foetal life. It is also suggested that the sensitivity of ductal muscle to E-type prostaglandins is controlled by the rate of endogenous prostaglandin formation.     

Oxygen binding properties,capillary densities and heart weights in high altitude camelids

Summary The oxygen binding properties of the blood of the camelid species vicuna, llama, alpaca and dromedary camel were measured and evaluated with respect to interspecific differences. The highest blood oxygen affinity, not only among camelids but of all mammals investigated so far, was found in the vicuna (P₅₀=17.6 Torr compared to 20.3–21.6 Torr in the other species). Low hematocrits (23–34%) and small red blood cells (21–30 m³) are common features of all camelids, but the lowest values are found in theLama species. Capillary densities were determined in heart and soleus muscle of vicuna and llama. Again, the vicuna shows exceptional values (3720 cap/mm² on average in the heart) for a mammal of this body size. Finally, heart weight as percent of body weight is higher in the vicuna (0.7–0.9%) than in the other camelids studied (0.5–0.7%). The possibility that these parameters, measured in New World tylopodes at sea level, are not likely to change considerably with transfer to high altitude, is discussed.In the vicuna, a unique combination of the following features seems to be responsible for an out-standing physical capability at high altitude: saturation of blood with oxygen in the lung is favored by a high blood oxygen affinity, oxygen supply being facilitated by low diffusion distances in the muscle tissue. Loading, as well as unloading, of oxygen is improved by a relatively high oxygen transfer conductance of the red blood cells, which is due to their small size and which compensates the negative effect of a low hematocrit on the oxygen conductance of blood. Blood oxygen transport is presumably favored by two factors: a relatively large heart mass and, as a result of low hematocrit, a low blood viscosity. Both are advantageous for achieving a high maximal cardiac output.     

Photosynthesis,dark respiration and light independent carbon fixation of endemic Antarctic macroalgae

Summary The light saturated photosynthesis, dark respiration and light independent carbon fixation of macroalgal species endemic to the Antarctic were measured. Five brown algae. Ascoseira mirabilis, Desmarestia anceps, D. antarctica, Phaeurus antarcticus, Himantothallus grandifolius and the red alga Palmaria decipiens were included. Rates of these three parameters at 0°C were very similar to those measured in other studies on temperate algae at higher temperature. This indicates a high degree of physiological adaptation to the Antarctic environment within these species. A comparison was made of polarographic and chemical means of measuring oxygen flux during photosynthesis and dark respiration at low temperature. There was a good correlation between measurements of oxygen evolution and carbon fixation, although apparent photosynthetic quotient values were in most cases high.Abbreviations HEPES N-(Hydroxyethyl) piperazine-N-(2 ethane-sulphonic acid) - RuBP D-ribulose 1,5-bisphosphate Contribution No. 415 from the Alfred-Wegener-Institut für Polaru. Meeresforschung     

Oxygen demand and long term changes of profundal zoobenthos

The paper attempts to combine the low oxygen content of the hypolimnion during stratification and the oxygen uptake of zoobenthos. Data of declining oxygen content in the hypolimnion and critical limits of respiration are combined for Chironomus anthracinus, Potamothrix hammoniensis and three species of Pisidium, P. casertanum, P. subtruncatum and P. henslowanum. The respiratory adaptation to low oxygen content influences both growth and population dynamics of the different species. The results have important bearing on eutrophication of the Lake Esrom ecosystem and temperate eutrophic lakes in general as well as the composition of profundal zoobenthos and its population dynamics.Publication No. 389 from Freshwater-Biological Laboratory, University of Copenhagen.     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

Plastid Alternative Oxidase (PTOX) Promotes Oxidative Stress When Overexpressed in Tobacco

Photoinhibition and production of reactive oxygen species were studied in tobacco plants overexpressing the plastid terminal oxidase (PTOX). In high light, these plants was more susceptible to photoinhibition than wild-type plants. Also oxygen-evolving activity of isolated thylakoid membranes from the PTOX-overexpressing plants was more strongly inhibited in high light than in thylakoids from wild-type plants. In contrast in low light, in the PTOX overexpressor, the thylakoids were protected against photoinhibition while in wild type they were significantly damaged. The production of superoxide and hydroxyl radicals was shown by EPR spin-trapping techniques in the different samples. Superoxide and hydroxyl radical production was stimulated in the overexpressor. Two-thirds of the superoxide production was maintained in the presence of DNP-INT, an inhibitor of the cytochrome b₆f complex. No increase of the SOD content was observed in the overexpressor compared with the wild type. We propose that superoxide is produced by PTOX in a side reaction and that PTOX can only act as a safety valve under stress conditions when the generated superoxide is detoxified by an efficient antioxidant system.     

Observations in guanotrophic environments

Summary Examples are given of initial guanotrophy in acid oligotrophic environment and of stabilized guanotrophy of long standing, both in acid oligotrophic and eutrophic environment.Characteristic of a guanotrophic environment is the accumulation of phosphate. In hard waters phosphate is accompanied by large amounts of saline nitrogen compounds. In soft waters the saline nitrogen production seems to be inhibited through low bacteriological activity. In eutrophic guanotrophic environments oxygen production and biochemical oxygen demand are both high. In oligotrophic guanotrophic environments the oxygen content as a rule does not reach saturation and biochemical oxygen demand is fairly low. The amounts of chloride and calcium do not change significantly by the addition of excrements of birds.Diatoms, blue green algae and desmids are very scarce in guanotrophic environments. In hard waters mesosaprobic forms are present in the plankton community. In soft waters no strong saprobic tendencies could be found.During the initial stage of guanotrophy in an acid oligotrophic environment, the desmids disappear together with other sensitive species as Dinobryon pediforme and Bosmina obtusirostris. Unicellular flagellates as Chlamydomonas appear in increasing numbers. Several factors in the environment respond to the changes by increasing fluctuations of the values recorded.There was evidence of transport and introduction of microorganisms by waterfowl.     

ESR spectroscopy demonstrates that cytochrome b559 remains low potential in Ca2+-reactivated,salt-washed PSII particles

Cytochrome b₅₅₉ in various Photosystem II preparations was studled by using low temperature ESR spectroscopy. This technique was used because it is able to distinguish high from low potential forms of the cytochrome owing to the g-value differences between these species. Moreover, by using low temperature irradiation to oxidize cyt b₅₅₉ we have avoided the use of redox mediators. Previous work (Ghanotakis DF., Topper J.N. and Yocum, C.F. (1984) Biochim. Biophys. Acta 767, 524–531) demonstrated that reduction and extraction of manganese of the oxygen evolving complex, which might be expected to alter the redox properties of cyt b₅₅₉, occurs when certain PSII preparations are exposed to reductants. The ESR data presented here show that a mixture of high potential and lower potential cyt b₅₅₉ species is observed in the oxygen evolving Photosystem II complex. Treatment of PSII membranes with 0.8 M Tris converts the high potential form(s) to those of lower potential. Exposure of the membranes to 2M NaCl shifts a significant amount of high potential cyt b₅₅₉ to lower potential form(s); addition of CaCl₂ reconstituted oxygen evolution activity but did not restore cyt b₅₅₉ to its high potential form(s).Abbreviations Chl chlorophyll - cyt cytochrome - DCBQ 2,5-dichloro-benzoquinone - DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone - ESR electron spin resonance - OEC oxygen evolving complex - PS photosystem Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement     

Effects of Several Environmental Factors on Longevity and Health of the Human Population of Zhongxiang,Hubei, China

Increasing human health and longevity is of global interest. Environmental, genetic, and stochastic factors all affect longevity. Among these factors, the environment is extremely important. To investigate the relationship between the environment and longevity, we studied the environment in Zhongxiang (China), where the inhabitants commonly have long life spans. Air was analyzed for negative oxygen ions, SO₂, and inhalable particles, while drinking water and rice were analyzed for macro- and micro-elements. The air quality in this area was determined to be grade I with high negative oxygen ion content and low SO₂ and inhalable particle contents. Apart from Fe, Mn, and F, all tested elements and the pH were within national standards and World Health Organization guidelines. The percentage of long-lived people in the area was closely related to the macro- and micro-element contents of their staple food, rice. The elements in rice could be classified into three categories according to their effect on longevity: Sr, Ca, Al, Mo, and Se, which were positively correlated with longevity; Fe, Mn, Zn, Cr, P, Mg, and K, which had a weak effect on local longevity, and Cu and Ba, which had a negative effect on longevity.     

The effect of excess moisture on the germination of Spinacia oleracea L.

Summary The reversible inhibition of the germination of spinach (Spinacia oleracea L.) seeds in conditions which are even slightly wetter than optimal has been traced to the production, in a wet environment, of a layer of mucilage around and within the fruit coat which surrounds the true seed. Such wet seeds may however germinate readily when the temperature is lowered, or the oxygen pressure of the environment is raised, or the intact seeds are placed for a short time in hydrogen peroxide before being transferred to what normally would be an excess of water. Even in the absence of an increased oxygen supply the seeds will germinate under water provided the fruit coat, or even a small part of it where it covers the radicle, is crefully removed. No evidence has been found of a water soluble inhibitor and the findings are consistent with the hypothesis that germination is dependent on a sufficiently high rate of supply of oxygen to the sites embryonic respiration. The mucilage which is formed under wet conditions forms a barrier which prevents the transfer of oxygen to the embryo by gaseous diffusion or aqueous convection currents and restricts it to the process of aqueous diffusion, and under these conditions the rate of oxygen supply may not reach the threshold level required for germination.     

Temporal environmental change, clonal physiology and the genetic structure of a Daphnia assemblage (D. galeata–hyalina hybrid species complex)

1. In a combined field and laboratory study, seasonal relationships between water temperature and oxygen content, genetic structure (composition of MultiLocus Genotypes, MLGs) of a Daphnia assemblage (D. galeata–hyalina hybrid species complex), and the physiological properties of clones of frequent MLGs were studied. In accordance with the oxygen‐limited thermal tolerance hypothesis, essential physiological variables of oxygen transport and supply were measured within the tolerable temperature range. 2. A few MLGs (types T1–T4) were frequent during early spring and late autumn at surface temperatures below 10 °C. Clones of T1–T4 showed a low tolerance towards higher temperatures (above 20 °C) and a high phenotypic plasticity under thermal acclimation in comparison to clones derived from frequent MLGs from later seasons, and stored high–medium quantities of carbohydrates at 12 and 18 °C. 3. Another MLG (T6) succeeded the MLGs T1–T4. T6 was frequent over most of the year at temperatures above 10 °C and below 20 °C. A clone derived from T6 exhibited a high tolerance towards warm temperatures and a more restricted phenotypic plasticity. It stored high–medium quantities of carbohydrates at 12, 18 and 24 °C and showed a high capacity for acclimatory adjustments based on haemoglobin expression. 4. During the summer period at temperatures ≥20 °C, the MLG T6 was found mainly near to the thermocline, where temperature and oxygen content were distinctly lower, and to a lesser extent in surface water. At the surface, another MLG (T19) was predominant during this period. A clone of this MLG showed a very high tolerance towards warm temperatures, minimal phenotypic plasticity, low carbohydrate stores and a high capacity for circulatory adjustments to improve oxygen transport at higher temperatures. 5. This study provides evidence for connections between the spatio‐temporal genetic heterogeneity of a Daphnia assemblage and the seasonal changes of water temperature and oxygen content. The data also suggest that not only the actual temperature but also the dynamics of temperature change may influence the genetic structure of Daphnia populations and assemblages.     

Acclimation of photosynthesis to irradiance and spectral quality in British plant species: chlorophyll content, photosynthetic capacity and habitat preference

Twenty-two common British angiosperms were examined for their ability to acclimate photosynthetically to sun and shade conditions. Plants were grown under low irradiance, far-red enriched light (50 μmol m^?2 s^?1), selected to mimic as closely as possible natural canopy shade, and moderately high light of insufficient irradiance to induce photoinhibitory or photoprotective responses (300 μmol m^?2 s^?1). Light-and CO²-saturated photosynthetic rates of oxygen evolution (P_max) and chlorophyll content were measured. Large variation was found in both parameters, and two ‘strategies’ for long-term acclimation were identified: firstly a change in chlorophyll per unit leaf area which was found to correlate positively with photosynthetic capacity, and secondly changes in chlorophyll alb ratio and P_max, indicative of alterations at the chloroplast level, which were not associated with a change in chlorophyll content per unit leaf area. Combinations of these two strategies may occur, giving rise to the observed diversity in photosynthetic acclimation. The extent and nature of photosynthetic acclimation were compared with an index of shade association, calculated from the association each species has with woodland. It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in ‘sun’ species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level. A framework for explaining the variation between plant species in leaf-level photosynthetic capacity, in relation to the natural light environment, is presented. This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.