Lethal genes in O5, chromosomes of Drosophila subobscura from Europe and America

In populations of D. subobscura , a species that is know for its high chromosomal polymorphism, the O₅ inversion has a rather erratic frequency distribution in the Palearctic region. An O₅ lethal chromosomal line obtained from a Balkan population near Zanjic (South Adriatic, Montenegro, Yugoslavia) was tested for lethal allelism with other O₅ lethal chromosomal lines derived from American (USA and Chile) colonizing populations, and from the French population of Taulé. No allelism was found between the Balkan lethal gene and those from America and France. Thus, the lethal genes of the O₅ inversions are not of the same origin and it is most probable that the American colonizations did not start from the Zanjic population. The general difference in the chromosomal inversion polymorphism corroborates this conclusion. The cytological analysis confirms the assumption that all O₅ chromosomes studied are identical with respect to breakage points.     

Effect of modification of storage atmosphere on phospholipids and ultrastructure of cauliflower mitochondria

Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower ( Brassica oleracea , L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O₂, 21% O₂+ 15% CO₂ or 3% O₂+ 15% CO₂. In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati-dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O₂ did not prevent phospholipid breakdown. Low O₂ prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O₂ atmosphere was lost under 3% O₂+ 15% CO₂. The high CO₂ atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO₂.     

Growth of methanotrophs in methane and oxygen counter gradients

Abstract A gel-stabilized system with counter gradients of CH₄ and O₂ was used to grow methanotrophs from wetland, agricultural and forest soils and lake sediment. Columns of semi-solid nitrate- or ammonium-minerai salts medium were continuously flushed at opposite ends with CH₄ and O₂ to create opposing concentration gradients of the two gases. Methanotrophs grew from all samples except forest soil, and were visible as thin bands after 5 to 15 days of incubation. The position of growth was CH₄ and O₂ concentration-dependent and occurred at the point of maximum possible CH₄ oxidation, where both substrates were completely consumed. Evidence was obtained for denitrification and nitrification activities concomitant with CH₄ oxidation. This approach may be useful to isolate methanotrophs with different CH₄ and O₂ requirements and to study their interactions with other groups of bacteria in nature.     

Nitrogen fixation by the unicellular cyanobacterium Gloeothece. Nitrogenase synthesis is only transiently repressed by oxygen

Abstract The extent of recovery of nitrogenase activity of Gloeothece transferred from an atmosphere of O₂ to air depended on the duration of exposure to O₂. Activity recovered at increasing rates after up to 24 h exposure to O₂ and a lag before detection of activity, present after short (1 h) exposure times, disappeared with longer exposures. Synthesis of nitrogenase de novo was implicated, since chloramphenicol, tetracycline, or repressive levels of NH⁺₄, prevented recovery of activity. Specific radioimmunoassay of the rate of synthesis of the MoFe protein of nitrogenase under O₂ correlated well with the activity measurements, and indicate that a shift from air to O₂ only transiently represses nitrogenase synthesis.     

The relationship between the in situ reduction level of the cytochrome c pool of Azorhizobium caulinodans growing in a chemostat with NH4+ or N2 as the N source and the total activity of cytochrome c oxidases

Abstract The in situ method for determination of reduction levels of cytochromes b and c pools during steady-state growth (Pronk et al., Anal. Biochem. 214, 149–155, 1993) was applied to chemostat cultures of the wild-type, a cytochrome aa₃ single mutant and a cytochrome aa₃/d double mutant of Azorhizobium caulinodans . For growth with NH₄⁺ as the N source, the results indicate that (i) the aa₃ mutant strains growing at a dissolved O₂ tension of 0.5% possess an active alternative cytochrome c oxidase, which is hardly present during fully aerobic growth, and assuming that (i) also pertains to the wild-type, (ii) the wild-type uses cytochrome aa₃ under fully aerobic conditions. For growth with N₂ as the N source, it was found that the aa₃ mutant strains growing at dissolved O₂ tensions ranging from 0.5 to 3.0% also contain an active alternative cytochrome c oxidase.     

OXYGEN CONSUMPTION ASSOCIATED WITH FERRIC REDUCTASE ACTIVITY AND IRON UPTAKE BY IRON-LIMITED CELLS OF CHLORELLA KESSLERI (CHLOROPHYCEAE)

Plasma membrane ferric reductase activity was enhanced 5-fold under iron limitation in the unicellular green alga Chlorella kessleri Fott et Nováková. Furthermore, ferric reductase activity in iron-limited cells was approximately 50% higher in the light than in the dark. In contrast, iron uptake rates of iron-limited cells were unaffected by light versus dark treatments. Rates of iron uptake were much lower than rates of ferric reduction, averaging approximately 2% of the dark ferric reduction rate. Ferric reduction was associated with an increased rate of O₂ consumption in both light and dark, the increase in the light being approximately 1.5 times as large as in the dark. The increased rate of O₂ consumption could be decreased by half by the addition of catalase, indicating that H₂O₂ is the product of the O₂ consumption and that the increased O₂ consumption is nonrespiratory. The stimulation of O₂ consumption was almost completely abolished by the addition of bathophenanthroline disulfonate, a strong chelator of Fe^{2 +} . Anaerobic conditions or the presence of exogenous superoxide dismutase affected neither ferric reduction nor iron uptake. We suggest that the O₂ consumption associated with ferric reductase activity resulted from superoxide formation from the aerobic oxidation of Fe^{2 +} , which is the product of ferric reductase activity. At saturating concentrations of Fe^{3 +} chelates, ferric reductase activity is much greater than the iron uptake rate, leading to rapid oxidation of Fe^{2 +} and superoxide generation. Therefore, O₂ consumption is not an integral part of the iron assimilation process.     

Effects of elevated ozone on photosynthesis and stomatal conductance of two soybean varieties: a case study to assess impacts of one component of predicted global climate change

Global climatic change scenarios predict a significant increase in future tropospheric ozone (O₃) concentrations. The present investigation was done to assess the effects of elevated O₃ (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean ( Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O₃ for 4 h·day⁻¹ from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O₃ stress. The O₃-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO₂ concentration in both O₃-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO₂ and stomatal closure. The adverse impact of O₃ stress increased at higher O₃ concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O₃-induced reductions in photosynthesis in tropical and temperate varieties are similar.     

Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O₂ increased with temperature and decreased with body weight. However, Q O₂ decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log₁₀ Q O₂ (mg O₂ g⁻¹ h⁻¹) = 0.129 log_lo salinity (%0) + 1.604 log₁₀ temperature (°C)-0.1401og₁₀(g)-2.767.     

Effects of salicylhydroxamate on respiration, seed germination and seedling growth in Avena fatua

The effects of inhibitors of alternative respiration [salicylhydroxamate (SHAM) and propyl gallate (PG)] on germination, seedling growth and O₂ uptake in Avena fatua L. (wild oats) were studied. SHAM did not inhibit germination or O₂ uptake prior to germination. SHAM-sensitive (alternative) respiration, therefore, cannot be a pre-requisite for germination. Following germination, both chemicals inhibited seedling growth with the root being more susceptible than the shoot. SHAM concentrations that inhibited root growth by 90 to 95%, inhibited O₂ uptake of 1 cm root apices by less than 15%. While sodium azide (a cytochrome-oxidase inhibitor; 1 m M ) alone inhibited O₂ uptake by only 40 to 50%, in the simultaneous presence of SHAM (or PG), O₂ uptake was inhibited by 90 to 99%. Thus: 1) respiration of wild oat seedling root apices is predominantly cytochrome-mediated and incomplete inhibition of O₂ uptake in the presence of azide alone is due to diversion of electrons to the alternative pathway and 2) even though these roots have little alternative respiration, they maintain the capacity to support a much greater flux of electrons via this path way. SHAM and PG at concentrations (0.05 to 0.4 m M ) which inhibited O₂ uptake significantly in the presence (but not in the absence) of azide had little effect on root growth suggesting that an effect(s) other than that on respiration is involved in the inhibition of root growth at higher concentrations. The effect of SHAM on wild oat root growth is not selective as it also inhibits growth of a number of crop species.     

Mycelial growth and ochratoxin A production by Aspergillus section Nigri on simulated grape medium in modified atmospheres

Aims:  To evaluate the impact of modified atmosphere packaging on in vitro growth of Aspergillus carbonarius and Aspergillus niger , and possible effects on ochratoxin A (OTA) biosynthesis.
Methods and Results:  Ochratoxigenic isolates belonging to the species A. carbonarius and A. niger were grown on a synthetic grapejuice medium (SNM) and packaged in combinations of controlled O₂ (1% and 5%) and CO₂ levels (0% and 15%), and in air as a control. Colony diameters were recorded every 3 days up to 21 days, and OTA was analysed after 7, 14 and 21 days. The greatest reductions in mycelial growth rate were observed at 1% O₂ followed by 1% O₂/15% CO₂, whereas 5% O₂ stimulated the growth of all isolates. OTA production by A. carbonarius and A. niger isolates was minimized at 1% O₂/15% CO₂ and 1% O₂, respectively, after 7 days of incubation. Maximal OTA accumulation after 7 days was observed for all isolates in the control pack and at 5% O₂.
Conclusions:  Of the atmospheres tested, only 1% O₂ combined with 15% CO₂ consistently reduced fungal growth and OTA synthesis by A. carbonarius and A. niger .
Significance and Impact of the Study:  Storage under modified atmospheres is unlikely to be suitable as the sole method for OTA minimization and grape preservation; other inhibitory factors are necessary.     

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.     

Atmospheric nitrogenous compounds and ozone – is NOx fixation by plants a possible solution?

Air quality thresholds for O₃ for the protection of human health and vegetation set by the European Union (EU) have been exceeded in Europe regularly in the 1990s. Because target reductions for oxides of nitrogen (NO_x) set for the year 2000 are unlikely to be achieved, these O₃ exceedances are likely to continue into the next millenium. Improvements of plant tolerance towards O₃ are being investigated but very little work has been done to explore NO_x tolerance and plant acclimation to NO₂ and NO. However, it is clear that within the populations of some plant species there is wide variation, and some individuals can fix NO_x and use the nitrogen directly from the atmosphere, rather than rely upon, for example, root uptake of nitrate. It is possible that individuals capable of fixing NO_x could be selected for a range of species, and genotypes with high rates of uptake could be of value as crops or for forestation in polluted areas (e.g. landscaping in the vicinity of motorways) to reduce tropospheric concentrations of NO_x significantly and also to decrease the potential for O₃ production.     

Hydrogen Production by Rumen Holotrich Protozoa: Effects of Oxygen and Implications for Metabolic Control by In Situ Conditions

Experiments with washed suspensions of holotrich protozoa (Isotricha spp. and Dasytricha ruminantium ) showed that both organisms have an efficient 0,-scavenging capability (apparent K_m values 2.3 and 0.3 μM, respectively). Reversible inhibition of H₂, production increased almost linearly with increasing O₂ up to 1.5 μM; higher levels of O₂ gave irreversible inhibition. In situ determinations of H, CH₄, O₂, and CO₂, in ovine rumen liquor, using a membrane inlet mass spectrometer probe, indicated that O₂, was present before feeding at 1-1.5 μM and decreased to undetectable levels (<0.25 μM) within 25 min after feeding. A transient increase in O₂. concentration after feeding occurred only in defaunated animals and resulted in suppression of CH₄ and CO₂ production. The presence of washed holotrich protozoa decreases the O₂ sensitivity of CH₄ production by suspensions of a cultured methanogenic bacterium Methanosarcina barkeri . It is concluded that holotrich protozoa play a role in ruminal O₂ utilization as well as in the production of fermentation end products (especially short-chain volatile fatty acids) utilized by the ruminant and H, utilized by methanogenic bacteria. These hydrogenosome-containing protozoa thus both control patterns of fermentation by influencing O₂ levels, and are themselves regulated by the low ambient O₂ concentrations they experience in the rumen.     

Alteration of N nutrition in Myrica gale induces changes in nodule growth, nodule activity and amino acid composition

Changes in nodule growth and activity and in the concentrations of soluble N compounds in nodules, leaves and xylem sap under conditions of altered N nutrition in the actinorhizal plant Myrica gale L. are reported. Altering the N nutrition of symbiotic plants may alter the internal regulation of combined N which in turn may regulate nodule growth and activity. Flushing nodules daily with 100% O₂ caused a decline in amide concentration and an increase in nodule growth although plants had recovered some nitrogenase activity within 4 h of exposure to O₂. Samples of nodules, leaves and xylem sap were derivatized and amino acids identified and quantified using either reverse phase high performance liquid chromatography or gas chromatography-mass spectrometry in single ion monitoring mode. The ratio of asparagine in the nodules to that in the xylem was much higher in plants fed N (6.7 for NH⁺₄-fed and 8.3 for NO⁻₃-fed plants) than for N₂-fixing plants (2.5). Significant amounts of ¹⁵N added as ¹⁵NH⁺₄ or ¹⁵NO⁻₃ accumulated in nodules following accumulation in the shoot which is consistent with the translocation of N to the nodules via the phloem. The uptake of ¹⁵NH⁺₄ led to the synthesis and subsequent translocation of glutamine in the xylem sap. These results are discussed in terms of the feedback mechanisms that may regulate nitrogen fixation in Myrica root nodules.     

Comparison of spectrophotometric and radioisotopic methods for the assay of Rubisco in ozone-treated plants

Radioisotopic and spectrophotometric assays for ribulose-1,5-bisphosphate carboxy-lase/oxygenase (Rubisco) initial and final activities and Rubisco content were compared in plants chronically exposed to ozone (O₃) in a greenhouse and the field. In a greenhouse experiment, Glycine max was treated in exposure chambers with either charcoal-filtered air (CF air) or 100 nl O₃ 1⁻¹ for 6 h daily during vegetative growth. Samples were collected after 7 days of exposure. In a field experiment, G. max was treated in open-top chambers with either CF air or nonfiltered air with O₃ added at 1.5 times ambient O₃ for 12 h daily. Average daily O₃ concentrations were 21 and 92 nl T1 in the CF and O₃ treatments, respectively. Samples were collected during vegetative and reproductive growth. Both assays generally yielded comparable Rubisco initial and final activities for greenhouse-grown plants regardless of the O₃ treatment. However for field-grown plants, Rubisco initial and final activities averaged 15 and 23% lower when assayed by the spectrophotometric rather than the radioisotopic method. For Rubisco content estimated by the spectrophotometric method, lower r² values for the regression of Rubisco activity vs concentratio of carboxyarabinitol-1,5-bisphos-phate were observed in O₃ than in CF-treated plants. Both assays yielded comparable Rubisco contents in the greenhouse and in the field although the variation was larger with the spectrophotometric method in field-grown plants. Growth conditions, field vs greenhouse, were more critical to the spectrophotometric assay performance than the O₃ treatments for measurement of Rubisco activity and content.     

Sensitivity of methanogenic bacteria from paddy soil to oxygen and desiccation

Abstract The effects of combinations of desiccation and exposure to O₂ were studied in pure cultures of Methanosarcina barkeri strain Fusaro and in a new Methanosarcina strain and a new Methanobacterium strain which were both isolated from dry oxic paddy soil. Incubation of bacterial suspensions under air for 200 min resulted in a decreased potential to produce CH₄, but not in a decreased viability. The inhibitory effect of O₂ slightly increased with increased salt concentration. Desiccation of bacterial suspensions under N₂ resulted in reduction of viability to 10% and of potential CH₄ production to 0.6%. Desiccation of bacterial suspensions under air resulted in a larger decrease of both viability (0.5%) and potential CH₄ production (0.03%). This decrease was smaller at rapid compared to slow desiccation. Survival and potential CH₄ production were further inhibited when the suspension was dried in the presence of sand grains or glass beads coated with FeS or FeNH₄PO₄. However, survival and potential CH₄ production increased dramatically in the presence of pyrite (FeS₂) grains. Then, as much as 10% of the initial methanogenic population survived oxic desiccation. This relatively good resistance is in agreement with observations that methanogens in rice fields survive the periods when the paddy soil is dry and oxic.     

Hydrogen uptake in Anabaena sp. strain CA does not protect nitrogenase from inactivation by hyperbaric oxygen

Abstract Two mutants of Anabaena sp. strain CA were used to demonstrate that oxygen-dependent hydrogen uptake was not the primary means to protect the nitrogenase enzyme complex from the deleterious effects of hyperbaric oxygen in vivo. Exposure to air caused the immediate and irreversible inactivation of nitrogenase activity in an oxygen-sensitive mutant, designated strain 22Y. Inactivation was concomitant with the destruction of the molybdo-iron (MoFe) protein of the nitrogenase complex. The mutant 22Y expressed an O₂-stable, Ni²⁺-stimulated hydrogen uptake of up to 2.7 μM H₂ per mg dry wt per h. Conversely, after exposure to 1% CO₂-99% O₂ for 3 h, both wild-type strain CA and a hydrogen uptake deficient (Hup⁻) mutant, strain N9AR, recovered 70–80% of their original acetylene reduction capacity with no apparent perturbations in the MoFe protein.     

Field estimates of oxygen consumption for the brine shrimp Parartemia zietziana Sayce (Crustacea: Anostraca) in two salt lakes in Victoria, Australia

SUMMARY. Oxygen consumption of P. zietziana was measured monthly in two saline (>60‰ salinity) lakes from November 1973 to November 1975 with short (<2 h) in situ incubations in BOD bottles. Tests in which oxygen decline was monitored continuously showed that there was no handling effect and respiratory rate was constant down to 1.8–1.9 mg O₂ 1⁻¹, about 40% of the usual initial concentration. Incubations over 24 h demonstrated no diurnal fluctuations in oxygen consumption. Multiple regression analysis indicated that 90% of the variance in respiratory rate ( R in mg O₂x10⁻⁴h⁻¹ individual⁻¹) was accounted for by changes in salinity (3%; S in ‰), temperature (7%; T in °C) and dry weight (8%; W in mg × 10⁻³): log R =−1.123+0.0025+0.021 T+ 0.756 log W. From this equation and data on population density, population respiration was calculated: 91864.5 mg O₂ m⁻² year⁻¹ in Pink Lake and 12367.5 mg O₂ m⁻²year⁻¹ in Lake Cundare.     

Physiological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strain

Abstract. The metabolic rates, as expressed by oxygen (O₂) consumption, carbon dioxide (CO₂) production, and losses in wet and dry weights, were examined for adults of three strains of the red flour beetle Tribolium castaneum (Herbst), during exposure to two modified atmospheres (MAs). Exposure of a strain selected for resistance over twenty-one generations to an atmosphere of 65% CO₂, 20% O₂ and the balance nitrogen (N₂), termed a high carbon dioxide concentration atmosphere (HCC) and exposure of an unselected strain to HCC, showed considerable levels of aerobic metabolism during exposure. For the unselected strain water loss and mobilization of energy reserves were rapid and mortality was followed by rapid desiccation. For the HCC-resistant strain water balance was maintained and energy reserves were utilized more slowly over a prolonged period. Exposure of a strain selected for resistance over twenty-one generations to a low oxygen concentration atmosphere (LOC) of 0.5% O₂ in N₂, and an unselected strain to LOC, revealed that even at 0.5% O₂, metabolism was largely aerobic in both strains. Maintenance of water balance was not a major factor causing mortality of either strain during exposure to LOC. In air, metabolic rates of both the resistant strains were lower than that of the unselected strain.     

Impacts of ozone on forests: a European perspective

In comparison with the effects of extended drought periods or severe nutrient stress, those of ozone are generally much milder, at least with respect to growth. However, there is substantial evidence from experiments, in the main using young saplings, that O₃ does impose a stress on forest trees under European conditions. Decreased chlorophyll contents and photosynthetic rates, changes in carbon allocation, increased antioxidant activity, and reductions in biomass due to O₃ have often been recorded, particularly in fast-growing species. Furthermore, ₃ appears to weaken the trees' resilience to a range of biotic and abiotic stresses. Interactions between O₃ and climatic stress, in particular drought and frost hardiness, are likely to result in potentially detrimental effects.
A link between the occurrence of O₃ and forest damage is not unequivocally established in Europe, and the problem remains of extrapolating and/or scaling up from studies on seedlings to predict responses to O₃ of mature trees and forest stands, because we know so little about acclimation to O₃. An accurate assessment is also lacking of the magnitude of the O₃ effect on European trees both in terms of the forest areas affected and its extent. In this review we suggest that C allocation is the key factor underlying the responses of trees to O₃. Stomata also play a key role, since the acquisition of C must be achieved while an effective control over water consumption is retained.