EFFECT OF DISSOLVED OXYGEN PARTIAL PRESSURE ON THE ACCUMULATION OF ASTAXANTHIN IN CHEMOSTAT CULTURES OF HAEMATOCOCCUS LACUSTRIS (CHLOROPHYTA)

The effect of dissolved oxygen partial pressure on the accumulation of astaxanthin in the green alga Haematococcus lacustris ( Gir.) Rostaf (UTEX16) was studied in N-limited continuous chemostat cultures. The steady-state astaxanthin content measured against culture volume, cell number, and biomass dry weigh of Haematococcus cultures was proportional to the dissolved O₂ partial pressure in the culture medium, over the range of 0–50% O₂ The steady-state biomass dry weight concentrations remained at between 0.52 and 0.57 g. L^-1 over the range of dissolved O₂ partial pressure studied. Steady-state cell densities at dissolved O₂ partial pressures above the air saturation level (1.13–1.58 × 10⁵ cells.mL^-1) were about half of that measured at lower dissolved O₂ partial pressures (2.42–2.63 × 10⁵ cells.mL^-1). Both biflagellated zoospores and nonmotile aplanospores were found at steady state. The fraction of nonmotile cells was higher at dissolved O₂ partial pressures above the air saturation level (94.44–98.01%) than at dissolved O₂ partial pressure below the air level (79.64–86.12 and 91.75% ).     

Photosynthesis of two poplar clones under long‐term exposure to ozone

The photosynthetic response was studied in two clones ( Populus deltoides × maximowiczii Eridano and Populus × euramericana I‐214), known for their differential response to ozone (O₃) in terms of visible symptoms, when exposed to O₃ (60 nl l⁻¹ 5 h day⁻¹, 7 and 15 days). The photosynthetic ability was tested using gas exchange and chlorophyll fluorescence analysis. O₃ caused a decrease in the CO₂ assimilation rate at light saturation level in mature leaves of both clones. Alterations of Chl fluorescence parameters, in particular the F_v/F_m ratio and non‐photochemical quenching were also observed. The effects were similar for both clones and it could not be concluded that differential effects on electron transport capacity were responsible for the observed reduction in photosynthesis. The reduction of photosynthetic rate in Eridano was due mainly to a reduced mesophyll activity, as evidenced by the increase in intercellular CO₂ concentration and the minimal changes in stomatal conductance. In contrast, in I‐214, stomatal effects were primarily responsible, although effects on the mesophyll cannot be excluded. Data obtained indicate that the effects observed at the mesophyll level may be attributed to indirect effects caused by membrane disorders.     

Bacterially mediated precipitation in marine stromatolites

Stromatolites are laminated, lithified (CaCO₃) sedimentary deposits formed by precipitation and/or sediment accretion by cyanobacterial–bacterial mat communities. Stromatolites have been associated with these communities as far back as the Precambrian era some 2+ billion years ago. The means by which microbial communities mediate the precipitation processes have remained unclear, and are the subject of considerable debate and speculation. Two alternative explanations for microbially mediated precipitation include: (i) cyanobacterial photosynthesis increases pH in a system supersaturated in respect of CaCO₃, resulting in CaCO₃ precipitation and then laminated lithification, and (ii) decomposition of cyanobacterial extracellular organic matter (e.g. sheaths, mucilage and organic acids) by microheterotrophs leads to release of organic-bound Ca²⁺ ions and CaCO₃ precipitation. We evaluated these explanations by examining metabolically active, lithifying stromatolitic mat communities from Highborne Cay, Bahamas, using microautoradiography. Microautoradiographic detection of ¹⁴CO₂ fixation and ³H organic matter ( d -glucose and an amino acid mixture) utilization by photosynthetically active cyanobacteria and microheterotrophs, combined with community-level uptake experiments, indicate that bacteria, rather than cyanobacteria are the dominant sites of CaCO₃ deposition. In the oligotrophic waters in which stromatolites exist, microheterotrophs are reliant on the photosynthetic community as a main source of organic matter. Therefore, autotrophic production indirectly controls microbially mediated precipitation and stromatolite formation in these shallow marine environments.     

Flooding, gas exchange and hydraulic root conductivity of highbush blueberry

Highbush blueberry plants ( Vaccinium corymbosum L. cv. Bluecrop) growing in containers were flooded in the laboratory for various durations to determine the effect of flooding on carbon assimilation, photosynthetic response to varying CO₂ and O₂ concentrations and apparent quantum yield as measured in an open flow gas analysis system. Hydraulic conductivity of the root was also measured using a pressure chamber. Root conductivity was lower and the effect of increasing CO₂ levels on carbon assimilation less for flooded than unflooded plants after short-(i-2 days), intermediate-(10–14 days) and long-term (35–40 days) flooding. A reduction in O₂ levels surrounding the leaves from 21 to 2% for unflooded plants increased carbon assimilation by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO₂ fixed (mol CO₂)⁻¹. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O₂, averaging 0.005 mol CO₂ fixed (mol CO₂)⁻¹. Apparent quantum yield decreased from 2.2 × 10⁻¹ mol of CO₂ fixed (mol light)⁻¹ for unflooded plants to 2.0 × 10⁻³ and 9.0 × 10⁻⁴ for intermediate- and long-term flooding durations, respectively. Shortterm flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf.     

Ozone-induced ultrastructural changes in the plasma membrane of Chlorella sorokiniana

Abstract. Modifications in plasma membrane structure and permeability were observed in Chlorella sorokiniana following exposure to 0.2 gm⁻³(140 p.p.m.) O₃ for 30 min. Sixty-eight per cent of the cells were plasmolysed after 15 min O₃ exposure with disruption of organelles similar to that previously described in higher plants. Freeze-fracture exposed large areas of plasma membrane in 90% of the control cells and those exposed to O₃for short periods. After 20 min O₃ 90% of the cells cross-fracture, which indicates a change in molecular interactions in the membrane exposed to O₃ The earliest observed ultraslructural alteration is an aggregation of particles on the plasma membrane P face, statistically significant after 10 min O₃ Changes in ⁸⁶Rb influx occur during a similar time. After more extended exposure to O³ the plasma membrane P face shows regions of lipid phase transition to the crystalline state.     

Interactive effects of ozone and low UV‐B radiation on antioxidants in spruce (Picea abies) and pine (Pinus sylvestris) needles

To study the role of low UV‐B radiation in modulating the response of antioxidants to ozone, 4‐year‐old pine ( Pinus sylvestris L.) and spruce ( Picea abies L.) seedlings potted in natural soil, were exposed in phytochambers to fluctuating ozone concentrations between 9 and 113 nl 1⁻¹ according to field data recorded at Mt Wank (1175 m above sea level, Bavaria, Germany) and two‐times ambient O₃ levels. UV‐B radiation was either added at a biologically effective level of ca 1.2 kJ m⁻² day⁻¹ , which is close to that found in March at Mt Wank, or was excluded by filters (<0.08 kJ m⁻² day⁻¹). After one growth phase current‐year needles were collected and analysed for antioxidative enzyme activities (superoxide dismutase, SOD, EC 1.15.1.1; catalase, CAT, EC 1.11.1.6; guaiacol peroxidase, POD, EC 1.11.1.7) and soluble antioxidants (ascorbate, glutathione). CAT, POD, ascorbate and glutathione, but not SOD, were increased in needles of both species in response to twice ambient O₃ levels. UV‐B radiation in the presence of ambient O₃ caused an increase in total SOD activity in spruce but had no effects on antioxidants in pine. Twice ambient O₃ levels together with low UV‐B radiation counteracted the O₃‐induced increases in ascorbate and CAT in pine but not in spruce. Under these conditions spruce needles showed the highest antioxidative protection and revealed no indication of lipid peroxidation. Pine needles exposed to UV‐B and elevated O₃ levels showed elevated lipid peroxidation and a 5‐fold increase in dehydroascorbate, suggesting that this species was less protected and suffered higher oxidative stress than spruce.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Scaling of oxygen consumption of Lake Magadi tilapia, a fish living at 37°C

Rates of oxygen consumption were measured in the geothermal, hot spring fish, Oreochromis alcalicus grahami by stopped flow respirometry. At 37° C, routine oxygen consumption followed the allometric relationship: V o₂=0.738 M ^0.75, where V o₂ is ml O₂ h ⁻¹ and M is body mass (g). This represents a routine metabolic rate for a 10 g fish at 37° C of 0.415 ml O₂ g⁻¹ h ⁻¹ (16.4 μmol O₂ g ⁻¹ h ⁻¹). Acutely increasing the temperature from 37 to 42° C significantly elevated the rate of O₂ consumption from 0.739 to 0.970 ml O₂ g ⁻¹ h ⁻¹ ( Q ₁₀=l.72). In the field, O. a. grahami was observed to be 'gulping' air from the surface of the water especially in hot springs that exceeded 40° C. O. a. grahami may utilize aerial respiration when O₂ requirements are high.     

Oxygen-dependent stomatal opening in Zea mays leaves. Effect of Light and carbon dioxide

The oxygen requirement for stomatal opening in maize plants ( Zea mays L. hybrid INRA 508) was studied at different CO₂ concentrations and light intensities. In the absence of CO₂, stomatal opening always required O₂, but this requirement decreased with increasing light intensity. In darkness, the lowest O₂ partial pressure needed to obtain a weak stomatal movement was about 50 Pa. This value was lowered to ca 10 Pa in light (320 μmol m⁻² s⁻¹).
On the other hand. in the absence of O₂, CO₂enabled stomatal opening to occur in the light, presumably due to the evolved photosynthetic O₂. Thus, CO₂, which generally reduced stomatal aperture, could induce stomatal movement in anoxia and light. The effect of CO₂ on stomatal opening was closely dependent on O₂ concentration and light intensity. Stomatal aperture appeared CO₂-independent at an O₂ partial pressure which was dependent on light intensity and was about 25 Pa at 320 umol m⁻² s⁻¹.
The presence of a plasmalemma oxidase, in addition to mitochondrial oxidase, might explain the differences in the O² requirement at various light intensities. The possible involvement of such a system in relation to the effect of CO₂ is discussed.     

Elevated concentrations of atmospheric CO2 protect against and compensate for O3 damage to photosynthetic tissues of field-grown wheat

The effects of elevated concentrations of atmospheric carbon dioxide and ozone on diurnal patterns of photosynthesis have been investigated in field-grown spring wheat ( Triticum aestivum ). Plants cultivated under realistic agronomic conditions, in open-top chambers, were exposed from emergence to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at ambient (380 μmol mol⁻¹, seasonal mean) or elevated (692 μmol mol⁻¹) levels, [O₃] at ambient (27 nmol mol⁻¹, 7 hr seasonal mean) or elevated (61 nmol mol⁻¹) levels. After anthesis, diurnal measurements were made of flag-leaf gas-exchange and in vitro Rubisco activity and content. Elevated [CO₂] resulted in an increase in photoassimilation rate and a loss of excess Rubisco activity. Elevated [O₃] caused a loss of Rubisco and a decline in photoassimilation rate late in flag-leaf development. Elevated [CO₂] ameliorated O₃ damage. The mechanisms of amelioration included a protective stomatal restriction of O₃ flux to the mesophyll, and a compensatory effect of increased substrate on photoassimilation and photosynthetic control. However, the degree of protection and compensation appeared to be affected by the natural seasonal and diurnal variations in light, temperature and water status.     

A developmental study of Glycine max cell and protoplast isolation in relation to leaf age and photosynthetic competence

Leaf mesophyll cells were isolated from developing first trifoliate leaves of Glycine max (L.) Merr cv. Fiskeby V using a mechanical isolation procedure combined with low speed centrifugation. Cell yields of 17 ± 1.7% were routinely obtained with 55–75% intactness, as assessed by staining techniques, fluorescence transients and the ability of cells to convert to protoplasts after enzyme treatment. Rates of leaf photosynthesis were maximal in 27-day-old plants [280 μmol O₂ evolved (mg chlorophyll)^-1h^-1], from which isolated cells and protoplasts gave rates of up to 140 μmol O₂ evolved (mg chlorophyll)^-1 h^-1. Results are discussed in relation to leaf development and cell status during the attainment of photosynthetic competence.     

Response of net photosynthesis in bean (Phaseolus vulgaris) leaves to the elevation of the partial pressures of oxygen and carbon dioxide

Bean ( Phaseolus vulgaris L. cv. Golden Saxa) plants were grown under low artificial light or under natural daylight. The rate of net photosynthesis (P_N) was measured at: CO₂ partial pressure, p(CO₂), of 0.03, 0.09 or 0.15 kPa; O₂ partial pressure, p(O₂), of 2, 21 or 31 kPa and at light intensities of 350 or 1000 μmol m⁻² s⁻¹ (photosynthetically active radiation). In plants which had been grown under natural light, stimulation of P_N at 21 kPa p(O₂) was found only at elevated p(CO₂) and high light. It is proposed that this phenomenon is dependent on a high capacity of the photosynthetic apparatus to regenerate ribulose 1.5-bisphosphate.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products

Volatile organic compound (VOC) emissions from tobacco ( Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O₃) were investigated using proton-transfer-reaction mass-spectrometry (PTR-MS) and gas chromatography mass-spectrometry (GC-MS) to find a quantitative reference for plants' responses to O₃ stress. O₃ exposures to illuminated plants induced post-exposure VOC emission bursts. The lag time for the onset of volatile C₆ emissions produced within the octadecanoid pathway was found to be inversely proportional to O₃ uptake, or more precisely, to the O₃ flux density into the plants. In cases of short O₃ pulses of identical duration the total amount of these emitted C₆ VOC was related to the O₃ flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C₆ product was emitted per five O₃ molecules taken up by the plant. A threshold flux density of O₃ inducing emissions of C₆ products was found to be (1.6 ± 0.7) × 10⁻⁸ mol m⁻² s⁻¹.     

Vegetation Restoration and Its Effects on Carbon Balance in Guangdong Province, China

The significance of the regional carbon (C) balance of vegetation restoration to global change was studied in Guangdong Province, one of the most populated provinces in China. The percentage of the province in forestland cover increased steadily from 26.23% in 1979 to 50.11% in 1998 owing to restoration of forests. During this period, the area increase in the conifer forest was 424.83 × 10⁴ ha, whereas the area in broad-leaved, mixed, and other forests increased by 68.82 × 10⁴, 18.94 × 10⁴, and 60.46 × 10⁴ ha, respectively. C sequestration by forest soils from 1979 to 1998 was 389.36 Mt, equivalent to 1.43 Pg fixed carbon dioxide (CO₂). The total annual CO₂ sequestration by forests and the soils was 118.05 Mt, which was about half of the annual CO₂ emission in Guangdong. The role of forest management and restoration in improving the carbon balance is discussed.     

PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme , after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na ⁺ -free and Na ⁺ + Li ⁺ media but were not affected by the absence of Cl ⁻ , implying that the bicarbonate uptake was associated with Na ⁺ / HCO₃ ⁻ symport rather than Cl ⁻ /HCO₃ ⁻ exchange system.     

The relationship between cytotoxic effect and binding to mammalian cultured cells of Clostridium perfringens enterotoxin

Abstract The relationship between the cytotoxic effect and binding to different cell lines of Clostridium perfringens enterotoxin was investigated. The enterotoxin released ⁵¹Cr from Vero and MDCK cells labeled with Na₂-⁵¹CrO₄. The effect varied depending upon the dose of enterotoxin and the duration and temperature of the interaction. The enterotoxin gave no effect on FL, KB, or L-929 cells. [¹²⁵I]Enterotoxin bound specifically to Vero and MDCK cells via a binding site of distinct nature, but not to FL, KB, or L-929 cells. The number of the binding sites located on one MDCK cell (1.98 × 10⁶ sites/cell) was three times that on one Vero cell (5.64 × 10⁵ sites/cell), although the binding affinity of MDCK cell ( K _a/ 3.76 × 10⁷ M⁻¹) was 0.1 that of Vero cells ( K _a/ 3.23 × 10⁸ M⁻¹). Binding of the enterotoxin to susceptible cells was temperature-independent.     

Seasonal patterns of viruses, bacteria and dissolved organic carbon in a riverine wetland

SUMMARY 1. Viral and bacterial abundances were studied in relation to environmental attributes over an annual period, for both planktonic and attached (sediment, aquatic macrophyte and submerged wood) habitats, in a riverine wetland.
2. Annual mean abundance of planktonic viruses ranged from 2.3 × 10⁵−3.8 × 10⁵ particles mL⁻¹ and varied according to sampling site. Significant seasonal patterns in viral abundance were evident and appeared to be linked to variations in bacterial abundance, dissolved organic carbon and inorganic nutrients.
3. Annual mean abundance of viruses associated with surfaces ranged from 1.3 × 10⁶ particles cm⁻² on aquatic macrophytes to 1.1 × 10⁷ particles cm⁻² on wood and also showed seasonal patterns. The difference in viral dynamics among the different sites emphasizes the importance of considering habitat diversity within wetlands when examining microbial communities.     

Dopaminergic Properties of Cultured Rat Carotid Body Chemoreceptors Grown in Normoxic and Hypoxic Environments

Abstract: Using dissociated carotid body (CB) cultures prepared from neonatal (postnatal days 5–7; P7) or juvenile (postnatal day 19–20; P20) rats, we compared catecholaminergic properties and mechanisms of O₂ sensing in glomus cells grown in normoxic (Nox; 20% O₂) and chronically hypoxic (CHox; 6% O₂) environments for up to 2 weeks. In Nox cultures, basal dopamine (DA) release, determined by HPLC and normalized to the number of tyrosine hydroxylase-positive glomus cells present, was similar for P7 and P20 cultures (∼0.3 pmol/1,000 cells/15 min) and was unaffected by culture duration (2 vs. 12 days). Acute hypoxia (5 and 10% O₂) caused a dose-dependent stimulation (6× and 3× basal, respectively) in DA release, that was inhibited by nifedipine (10 µ M ). DA release was also stimulated by high extracellular K⁺ (30 m M ) and iberiotoxin (200 n M ), a selective blocker of P o ₂-regulated, Ca-dependent K⁺ channel in glomus cells. The stimulatory effect of iberiotoxin was similar to 5% O₂ in P20 cultures, but substantially less (about one-half) in P7 cultures. In contrast, in CHox cultures, basal DA release was substantially elevated, ∼8× Nox levels, although this did not correlate with significant differences in stores. Further, whereas acute hypoxia (5% O₂) and high K⁺ also stimulated DA release in CHox cultures (∼2× and ∼3× basal), iberiotoxin (200 n M ) did not. Thus, after chronic hypoxia in vitro, there is an enhanced basal catecholamine release and an apparent down-regulation of functional Ca-dependent K⁺ channels in CB chemoreceptors. These cellular adaptations may relate to changes in CB chemosensitivity during chronic hypoxemia.     

The comparative effects of nitrogen and oxygen on the microflora of beef steaks in carbon dioxide-containing modified atmosphere vacuum skin-packaging (MA-VSP) systems

The effects of 80% oxygen–20% carbon dioxide (O₂–CO₂) and 80% nitrogen–20% carbon dioxide (N₂–CO₂) atmospheres were compared with respect to the microbial and sensory characteristics of vacuum skin-packaged grain-fed beef steaks stored at −1 and 4 °C. In both N₂–CO₂ and O₂–CO₂ atmospheres, lactobacilli were predominant over Brochothrix , pseudomonads, enterobacteria and yeasts and moulds. The results of the current investigation showed that the O₂–CO₂ atmospheres did not yield total viable counts in excess of 10⁵ cfu cm⁻² on beef steaks after 4 weeks of storage. However, the sensory analysis and thiobarbituric acid (TBA) values (as a measure of oxidative rancidity) of the products were unacceptable at this time. In contrast, the N₂–CO₂ atmospheres yielded maximum total viable counts of approximately 10⁷ cfu cm⁻² and the sensory analysis and TBA values of the product were judged to be acceptable after 4 weeks of storage at −1 °C. These results indicate that sensory effects of the product were influenced to a greater extent by the chemical effects of high concentration of O₂ on rancidity than by the high levels of lactobacilli.