Moderate Ozone Research Articles

Involvement of the thylakoidal NADH-plastoquinone-oxidoreductase complex in the early responses to ozone exposure of barley (Hordeum vulgare L.) seedlings

A possible implication of the plastid NADH-plastoquinone-oxidoreductase (Ndh) complex in the response against ozone-mediated oxidative stress in barley (Hordeum vulgare L.) leaves was investigated. After a 4 h treatment, exposure of barley seedlings to moderate ozone concentrations produced leaf-age-dependent increases in lipid peroxidation, peroxidase, and Ndh complex activities in the thylakoid membranes. A significant amount and activity of the Ndh complex were detected in mature barley leaves, but not in young barley leaves. In fact, young barley leaves behaved like ndh-deficient leaves in most of the aspects studied. When plants were exposed to photo-oxidative light after ozone fumigation, the recovery of Fv/Fm was lower in young leaves than in mature leaves. Ozone treatment significantly decreased non-photochemical quenching (qN) in young leaves, but not in mature leaves. Mature leaves showed higher levels of the energy (DeltamuH+) dependent (qE) component of qN. Treatment with antimycin A, an inhibitor of cyclic electron flow, increased the decay of qN produced by ozone in young leaves, but not in mature ones. The reduction state of plastoquinone increased after ozone treatment in mature dark-adapted leaves and was strongly quenched by far red light. It is proposed that the function of the Ndh complex helps the maintenance of qN, probably through the poising of the redox steady-state level of the intersystem carriers and then by optimizing the rate of cyclic electron flow. This should constitute an age-dependent early response in barley leaves, by contributing to minimize photoinhibition in the presence of ozone and high light.

Ozone loss and chlorine activation in the Arctic winters 1991-2003 derived with the tracer-tracer correlations

Abstract. Chemical ozone loss in the Arctic stratosphere was investigated for the twelve years between 1991 and 2003 employing the ozone-tracer correlation method. For this method, the change in the relation between ozone and a long-lived tracer is considered for all twelve years over the lifetime of the polar vortex to calculate chemical ozone loss. Both the accumulated local ozone loss in the lower stratosphere and the column ozone loss were derived consistently, mainly on the basis of HALOE satellite observations. HALOE measurements do not cover the polar region homogeneously over the course of the winter. Thus, to derive an early winter reference function for each of the twelve years, all available measurements were additionally used; for two winters climatological considerations were necessary. Moreover, a detailed quantification of uncertainties was performed. This study further demonstrates the interaction between meteorology and ozone loss. The connection between temperature conditions and chlorine activation, and in turn, the connection between chlorine activation and ozone loss, becomes obvious in the HALOE HCl measurements. Additionally, the degree of homogeneity of ozone loss within the vortex was shown to depend on the meteorological conditions. Results derived here are in general agreement with the results obtained by other methods for deducing polar ozone loss. Differences occur mainly owing to different time periods considered in deriving accumulated ozone loss. However, very strong ozone losses as deduced from SAOZ for January in winters 1993-1994 and 1995-1996 cannot be identified using available HALOE observations in the early winter. In general, strong accumulated ozone loss was found to occur in conjunction with a strong cold vortex containing a large volume of possible PSC existence (VPSC), whereas moderate ozone loss was found if the vortex was less strong and moderately warm. Hardly any ozone loss was calculated for very warm winters with small amounts of VPSC during the entire winter. This study supports the linear relationship between VPSC and the accumulated ozone loss reported by Rex et al. (2004) if VPSC was averaged over the entire winter period. Here, further meteorological factors controlling ozone loss were additionally identified if VPSC was averaged over the same time interval as that for which the accumulated ozone loss was deduced. A significant difference in ozone loss (of ≈36DU) was found due to the different duration of solar illumination of the polar vortex of at maximum 4 hours per day in the observed years. Further, the increased burden of aerosols in the atmosphere after the Pinatubo volcanic eruption in 1991 significantly increased the extent of chemical ozone loss.

DISTRIBUTION AND REPRODUCIBILITY OF SPIROMETRIC RESPONSE TO OZONE BY GENDER AND AGE

Hazucha MJ, Folinsbee LJ, Bromberg PA. J Appl Physiol. 2003;95:1917–1925 To determine whether the effects of moderate ozone exposure on forced expiratory volume in 1 second (FEV1) values are influenced by age and gender. Volunteers were healthy, moderately active, nonsmoking, nonallergic men ( n = 146) and women ( n = 94), of young age (18–35 years) or middle age (36–60 years). After completing baseline questionnaires and pulmonary function …

DISTRIBUTION AND REPRODUCIBILITY OF SPIROMETRIC RESPONSE TO OZONE BY GENDER AND AGE

Hazucha MJ, Folinsbee LJ, Bromberg PA. J Appl Physiol. 2003;95:1917–1925To determine whether the effects of moderate ozone exposure on forced expiratory volume in 1 second (FEV1) values are influenced by age and gender.Volunteers were healthy, moderately active, nonsmoking, nonallergic men (n = 146) and women (n = 94), of young age (18–35 years) or middle age (36–60 years).After completing baseline questionnaires and pulmonary function tests, subjects were exposed to 0.42 ppm of ozone at 22°C and 40% humidity for 1.5 hours, alternating 20 minutes of exercise with 10 minutes of rest. During exercise, ventilation was monitored for 2 minutes and electrocardiograms were recorded at 5-minute intervals. Routine spirometric evaluations were repeated after exposure. Forty-seven subjects were reexposed to ozone on 2 subsequent occasions.After the first exposure, the mean postexposure changes in FEV1 were −16.3% (range: +1% to −44%) for young men, −16.6% (range: +2% to −53%) for young women, −11.6% (range: 0% to −63%) for middle-aged men, and −6.4% (range: +2% to −28%) for middle-aged women. The levels of responsiveness of young men and women were similar, but the differences in responsiveness between all other pairs of groups were significant (P < .05). Young individuals showed greater changes on each exposure day than did middle-aged individuals (P < .05). The postexposure decreases in FEV1 tended to be smaller with increasing age for both genders, but the loss of response with aging was greater for women. The first exposure induced smaller effects, compared with subsequent exposures.The changes in FEV1 after moderate ozone exposure decreased with increasing age for both men and women, suggesting that young individuals might be at higher risk for adverse health effects after ozone exposure.Increasing attention is being paid to the effects of airborne pollutants, such as ozone, on childhood asthma. Although we must be cautious about extrapolating findings on the responsiveness of nonallergic adults to children with asthma, the results of this study suggest that the effects of ozone on pulmonary function may be greater among younger individuals.

A modeling study of an East Asian convective complex during March 2001

During March–April 2001 the University of Wisconsin Nonhydrostatic Modeling System (UWNMS) was used to provide flight planning and estimation of ozone flux into the troposphere over East Asia in support of the Transport and Chemical Evolution over the Pacific (TRACE‐P) mission. On 24 March a convective complex developed in eastern China and propagated eastward over the Pacific south of Japan. Aircraft and satellite observations, together with the UWNMS simulations, captured this convective event, which first entrained urban boundary layer air over Asia and then marine boundary layer air over the Pacific. The convective updraft split the subtropical westerly jet, deformed the tropopause upward, radiated gravity waves into the stratosphere, and induced a ring of stratospheric ozone to descend around its periphery into the middle troposphere. The DC‐8 observations and UWNMS show a vault of moderate ozone (∼65 ppbv) in the 8–12 km layer within the convection, with high stratospheric values (∼100 ppbv) subsiding around the periphery into the troposphere near 6.5 km. A new two‐scale method for diagnosing cross‐tropopause ozone flux is compared with an annular volume estimate. During this 24 hour convective event, ∼0.8 Tg ozone entered the troposphere from the stratosphere, comparable in magnitude to ozone fluxes in midlatitude cyclones.

Ozone etching of a highly asymmetric triblock copolymer with a majority polydiene component

The ozone etching of thin films of a commercial polystyrene–polyisoprene–polystyrene (PS–PI–PS) triblock copolymer (Vector 4111) was studied using atomic force microscopy (AFM) and ellipsometry. The major phase of the copolymer consists of PI (82 wt.%) and the copolymer forms a cylindrical structure upon annealing. Moderate ozone doses (1.4% wt/wt) were used to etch the copolymer. This revealed two stages of the ozonation: rapid etching of the PI fragments followed by slow compacting of the remaining PS cylinders. Under certain conditions ozone treatment results in the formation of nanosized grooves in a PS matrix which is suitable for lithographic processes.

Steady state levels of free radicals in tomato fruit exposed to drought and ozone stress in a field experiment

The influence of drought and elevated ozone levels on the free radical contents of fruit from tomato has been investigated by electron paramagnetic resonance (EPR) spectroscopy. Under water deficit no differences in the signal intensity were observed between drought-stressed and control fruits, or between different harvests, from the same variety, whereas a reduction in the stomatal conductance of leaves under water deficit indicated a physiological effect of the drought stress on plants. One of the varieties investigated ( Lycopersicon esculentum cv. Kremser Perle) generally showed higher radical levels than the other two. For relatively short periods of stress (≤ 20 d), the free radical contents of fruits that had received moderate ozone exposure were significantly higher than in fruits grown in filtered chambers with charcoal filtered air. However, all fruits had similar free radical levels after ~25 d of ozone fumigation.

Calculation of chemical ozone loss in the Arctic winter 1996–1997 using ozone‐tracer correlations: Comparison of Improved Limb Atmospheric Spectrometer (ILAS) and Halogen Occultation Experiment (HALOE) results

The ozone‐tracer correlation method is used to deduce the stratospheric ozone loss in the Arctic winter 1996–1997. Improvements of the technique are applied, such as a new calculation of the vortex edge [Nash et al., 1996] and an improved early vortex reference function. Winter 1996–1997 is characterized by a late formation and an unusually long lifetime of the polar vortex. Remnants of vortex air were found until May. Chemical ozone losses deduced from two satellite data sets, namely Improved Limb Atmospheric Spectrometer (ILAS) and Halogen Occultation Experiment (HALOE), are discussed. The ILAS observations allow a detailed analysis of the temporal evolution of the ozone‐tracer correlation inside the polar vortex and, in particular, of the development of the early vortex. For November and December 1996, it is shown that horizontal mixing still influences the ozone‐tracer relation. Significant PSC related chemical ozone loss occurred beginning at mid‐February, and the averaged column ozone loss is increasing toward the middle of May. From April onwards, ozone profiles in the vortex became more uniform. The decrease of ozone in the vortex remnants in April and May occurred due to chemistry. HALOE observations are available for March to May 1997. In the period 4–16 March 1997, the calculated ozone loss deduced from HALOE and ILAS is in good agreement. The average of the result from the two instruments is 15 ± 7 Dobson units (DU) inside the vortex core, in the altitude range of 450–550 K. At the end of March, a discrepancy between HALOE and ILAS ozone loss arises due to a significant difference (0.6 ppmv) between the two data sets in the relatively low ozone minimum measured at 475 K. Nonetheless, both data sets consistently show an inhomogeneity in ozone loss inside the vortex core at the end of March. The vortex is separated in two parts, one with a large ozone loss (HALOE 40–45 DU, ILAS 30–35 DU) and one with a moderate ozone loss (HALOE 15–30 DU, ILAS 5–25 DU) for 450–550 K. The ozone loss from HALOE in 380–550 K at that time was calculated to be 90–110 DU for the large ozone loss and 20–80 DU for the moderate ozone loss. The vortex average of column ozone loss from HALOE inside the vortex core at the end of March is 61 ± 20 DU, which is an increase of about 20% compared to the earlier study by Müller et al. [1997b] brought about by the improvement of the technique.

Effects of Two Different Ozone Exposure Regimes on Chlorophyll and Sucrose Content of Leaves and Yield Parameters of Sugar Beet ( Beta Vulgaris L.) and Rape ( Brassica Napus L.)

Sugar beet (Beta vulgaris cv. Loretta) and rape (Brassica napus cv. Licolly) plants were exposed under equaldose conditions in closed fumigation chambers under twodifferent ozone (O3) pattern: Var130 (17:00–09:00 h: 40 μg O3 m-3; 09:00–17:00 h: 130μgO3 m-3) and Var220 (16:00-12:00 h: 40 μgO3 m-3; 12:00–16:00 h: 220μg O3 m-3).Control plants were exposed under carbon filtered airconditions (ozone free, CF-control). Sugar beet plants wereexposed four weeks each during 6-leaf-stage and lateralgrowth respectively. Rape plants were exposed for 14 daysduring flowering (f) or as young plants (y). In between andafter the end of exposure, plants were kept in carbonfiltered air (CF; < 10 μg O3 m-3). With respect to sucrose and chlorophyll content of leaves andseed weight, rape plants were most sensitive duringflowering. Under equal dose conditions, the most pronouncedeffects on chlorophyll and sucrose content of leaves as wellas fresh weight of taproots (CF: 100%; Var130: 97%;Var220: 83%) and of rape seeds (CF: 100%; y:Var130: 122%; Var220: 99%; f: Var130: 84%;Var220: 78%) were detected after exposure under shorttime high ozone peak conditions (Var220). Howeverglucose content in taproots (CF: 100%; Var130: 43%;Var220: 79%) and fatty acid content in rape seeds wasaffected most after exposure to moderate ozone peaks(Var130). Var130-plants seem to recover better fromozone stress than Var220-plants, but glucose content oftaproots and fatty acid content of rape seeds indicate long-lastingeffects especially in Var130-plants.Although experiments were conducted in a closed chambersystem it can be concluded, that current ozone concentrationscan induce adverse effects on these crops.

Ozone distribution in coastal central Taiwan under sea-breeze conditions

Sea-breeze circulation influences ozone concentration differently for two types of synoptic winds across the westcentral coastal plain of Taiwan. During summer months, when the synoptic flow is southerly, a strong westerly sea-breeze confined to the lower 700–800 m produces a northeastward flow. Ozone concentration is low, with a core centered at about 100 m, leading to moderate ozone concentrations in the low population density northeastern foothills. In autumn (and spring), northerly synoptic winds of about the same strength combine with less energetic westerly sea breeze to produce a southeastward flow that carries higher ozone levels into the heavily populated Taichung basin. Ozone levels are high from 80 to 400 m, with a core up to 120 ppb from about 150 to 300 m, contributing to serious ozone episodes at the southern (downwind) end of the basin. Analyzing the backward trajectories and ozone concentration showed that the weak southeastward breeze is the dominant factor affecting the occurrence of high ozone events in the region. The horizontal distribution is based on 3 yr data obtained from a network of air-pollution monitoring sites in the study area, while the vertical data comes from two 2-day tethersonde experiments, measuring wind-speed, direction, temperature and humidity, NO, NO 2, NMHC and O 3, conducted during August and November 1999.

The response of vacuolar phenolic content of common bean (Phaseolus vulgaris cv. Bergamo) to a chronic ozone exposure: questions and hypotheses.

Using open-top chamber technology, we investigated the foliar phenolic response of common bean (Phaseolus vulgaris L. cv. Bergamo) to a chronic, moderate ozone stress. Three atmospheric concentrations of ozone were tested: non-filtered air (NF) prevailing at the experimental site, and non-filtered air supplied with 40 (NF+40) and 60 nL L-1 ozone (NF+60), respectively. Both constitutive and ozone-induced non-polymerized phenolics were considered with regards to pollutant concentration, exposure time, leaf type (primary or trifoliate), and leaf growth. The biomass of primary leaves was unaffected by the tested ozone concentrations, whereas dry mass of first and second trifoliate leaves significantly decreased as atmospheric ozone increased. Characteristic symptoms were observed on the upper surface of leaves from the two ozone-supplied treatments. Their severity reflected both leaf exposure time and ozone concentration. As a whole, the total content of foliar soluble constitutive phenolics remained unchanged as the ozone increased, even for leaves almost totally covered with dark-brown discolourations. Nonetheless, among the three main detected phenolics, the accumulation of the kaempferol derivative could be significantly stimulated by ozone. Also, six ozone-induced phenolics could be synthesized by leaves exposed to the two pollutant-enriched atmospheres, and their elicitation and amount were closely connected with both exposure time and ozone concentration.

Indoor chemistry: ozone and volatile organic compounds found in tobacco smoke.

The deliberate generation of ozone in indoor settings has been promoted as a method to reduce the concentration of indoor pollutants. The present study examines the effect of ozone on a subset of volatile organic compounds (VOCs) found in tobacco smoke. The decays of these compounds were measured in a static room-sized chamber: (1) in the absence of ozone, (2) in the presence of moderate ozone concentrations (< 0.115 ppm), and (3) in the presence of high ozone concentrations (< 1.4 ppm). At moderate ozone concentrations there was little effect on the monitored VOCs. At high ozone concentrations there was a small, unanticipated reduction in the concentration of some of the saturated VOCs, apparently caused by OH radicals produced as a consequence of the ozone/alkene reactions. There was also a much larger reduction in the concentrations of those compounds with unsaturated carbon bonds. However, this reduction was largely matched by an increase in the concentration of a number of aldehydes. Some of these aldehydes are more potent irritants than their precursors. Furthermore, even a relatively small ventilation rate (approximately 0.1 h-1) would produce a greater reduction in the monitored VOCs than that produced by a moderate amount of ozone.

Effect of a chronic and moderate ozone pollution on the phenolic pattern of bean leaves (Phaseolus vulgaris L. cv Nerina): relations with visible injury and biomass production.

From sowing, bean (Phaseolus vulgaris L. cv Nerina) plants were exposed to three chronic doses of ozone for 7h.day(-1): non-filtered air (NF), non-filtered air supplied with 40nl.l(-1) ozone (NF+40) and non-filtered air supplied with 60nll(-1) ozone (NF+60). Four harvests were carried out 6, 13, 20 and 27 days after emergence. Either primary leaves, or first trifoliate leaves, or both were sampled as far as possible. For each sampled leaf, visible ozone injuries were registered, the free polyphenolic pool was analysed using HPLC and the dry matter was weighed. Visible damage on leaves was related to both exposure time and ozone concentration added. There were no adverse effects of added ozone on the biomass of primary leaves while a significant reduction of first trifoliates dry matter could be observed (NF+60 atmosphere, third and fourth harvest). Among the normally occurring phenolics, we detected a significant decrease in the accumulation of a hydroxycinnamic acid derivative as the ozone concentration increased. Nevertheless, we demonstrated that this ozone-induced modification could be sometimes distinguishable with difficulties from changes expected to be of development relevance. Beside this phenolic disbalance, we detected a de novo biosynthesis of compounds that closely depended on the level of visible ozone injury. Since their accumulation increased with leaf damage, these ozone-induced phenolics could be used to detect phytotoxic ambient levels of tropospheric ozone.

Plant responses to UV‐B: time to look beyond stratospheric ozone depletion?

Plant responses to UV‐B: time to look beyond stratospheric ozone depletion?

Respiratory Effects of Seasonal Exposures to Ozone and Particles

Whereas human respiratory effects of brief ozone exposures are well documented, much less is known about the human health effects of mid- to long-term exposures. The authors' objective in this study was to determine whether lung function or respiratory symptom changes would occur over the course of a summer season among healthy young adults working outdoors in the presence of ozone. The authors studied 72 sophomore cadets from the U.S. Military Academy at West Point, New York, 21 of whom attended special summer training in Fort Dix, New Jersey, an area characterized by elevated ozone levels; the remaining cadets attended training in areas with moderate ozone levels (i.e., Fort Benning, Georgia; Fort Leonard Wood, Missouri; and Fort Sill, Oklahoma). The authors hypothesized that adverse respiratory outcomes, if any, would be more pronounced in the group exposed to higher ozone levels. Spirometry was performed and respiratory symptoms were assessed-both before and after the summer-in a clinic at West Point. Time spent outdoors during summer training averaged 11 hr/d. Both mean and peak ozone levels were higher at Fort Dix than at the three remaining sites. Regional levels of sulfur dioxide and particulate matter less than 10 microm in aerodynamic diameter were relatively low during the study. However, all cadets reported frequent exposure to dust, exhaust, and smoke in the course of their training. Averaged across all subjects, there was a statistically significant drop in forced expiratory volume in 1 sec of 44 ml (p = .035) over the summer. There were also significant increases in reports of cough, chest tightness, and sore throat at the follow-up clinic visit. A larger mean forced expiratory volume in 1 sec decline was observed at Fort Dix, where ozone exposures were the highest. The results of this study demonstrated a seasonal decline in respiratory function among healthy young adults working outdoors in the presence of ozone and particulate matter.

Effect of climate change relative to ozone depletion on UV exposure in subarctic lakes.

The effect of stratospheric ozone depletion on increases in ambient levels of solar ultraviolet (UV) radiation in high-latitude regions' has raised concerns about the response of northern ecosystems to environmental change. The concentration of coloured dissolved organic material, which is derived from terrestrial vegetation and acts as a screen for ultraviolet radiation, is low in high-latitude lakes. The underwater light environment in these lakes is therefore likely to be sensitive to small variations in the supply of this material, in addition to the effects of ozone depletion. Here we use fossil diatom assemblages in combination with bio-optical models to estimate the magnitude of past variations in the underwater light regime of a lake at the boreal tree line. We find large shifts in underwater UV-B, UV-A and photosynthetically available radiation associated with changes in the input of coloured dissolved organic material into subarctic lakes during the Holocene. The inferred changes in biological exposure to UV radiation were at least two orders of magnitude greater than those associated with moderate (30%) ozone depletion. Our findings indicate that freshwater ecosystems at present located across vegetation gradients will experience significant shifts in underwater spectral irradiance through the effects of climate change on catchment vegetation and the export of coloured dissolved organic material.

Analysis of the climatic mechanisms contributing to the summertime transport of lower atmospheric ozone across metropolitan Phoenix, Arizona, USA

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 15:13-31 (2000) - doi:10.3354/cr015013 Analysis of the climatic mechanisms contributing to the summertime transport of lower atmospheric ozone across metropolitan Phoenix, Arizona, USA Andrew W. Ellis1,*, Mark L. Hildebrandt2, Wendy M. Thomas1, H. J. S. Fernando3 1Department of Geography and 3Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, Arizona 85287, USA 2Department of Geography, Southern Illinois University-Edwardsville, Edwardsville, Illinois 62026, USA *E-mail: andrew.w.ellis@asu.edu ABSTRACT: High concentrations of lower atmospheric ozone can adversely affect the health of humans, plants, and animals. Over the past decade, unhealthy levels of ozone across the Phoenix, Arizona (USA) urban area have been a focus of attention for the United States Environmental Protection Agency (EPA) and local government agencies. As ozone concentrations exceeding the standard set forth by the EPA occur in a preferred location within the Phoenix metropolitan area (eastern suburb of Mesa), it has become important to gain an understanding of the mechanisms that transport ozone within Phoenix and its suburbs. The objective of the study that is presented here was to examine the climatic factors that contributed to the spatial distribution of lower atmospheric ozone across the eastern portion of the Phoenix metropolitan area in mid-to-late summer 1998. Microclimatic and synoptic-scale atmospheric contributors were linked to the mesoscale transport of ozone. Forty-three study days were stratified into 3 categories: high ozone days (exceeded the EPA standard), moderate ozone days (approached the EPA standard), and low ozone days. Eleven days of high ozone were differentiated from the days of the remaining 2 categories by an atmosphere containing less water vapor, and therefore a greater surface receipt of insolation. This is not surprising given the fact that ozone production is a photochemical process. However, the movement of the lower atmospheric ozone is also an important issue. The results of the study suggest that the drier atmosphere and resultant high insolation at the surface were associated with a proximal area of high pressure aloft. Taken together, the result was warmer ground surface and overlying air temperatures, light winds, an apparent lack of turbulent lower atmospheric mixing, and light southwesterly winds at 850 mb that advected little moisture into the area. Associated with the light synoptic flow and warm surface condition on days of high ozone was a wind regime that appears to be the product of a mesoscale thermodynamic circulation. The daytime flow on high ozone days became directed upslope toward the higher elevations of the eastern Phoenix Valley. Embedded within the flow was a plume of high ozone concentrations that extended from an urban area of high ground traffic eastward into the eastern suburb of Mesa. Conversely, moderate and low ozone days were associated with an eastward displacement of high pressure aloft, greater advection of low-level moisture from the south and southeast, smaller insolation receipt, less surface heating, and a much less organized movement of lower atmospheric ozone than on high ozone days. KEY WORDS: Ozone transport · Thermal circulation · Scale interactions · Phoenix, AZ Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 15, No. 1. Online publication date: May 15, 2000 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2000 Inter-Research.

Simultaneous analyses of chromosomes in root meristems and of the biochemical status of needle tissues of three different clones of Norway spruce trees challenged with moderate ozone levels

SummaryBiochemical effects of both low and high ozone impact in long‐term and short‐term experiments are well investigated and documented; however, short‐term treatments with moderate ozone levels have revealed divergent information concerning the biochemistry of needle tissues. Damage to the meristems of spruce trees have been found for several ozone treatments, in the form of an enhanced number of chromosomal aberrations, which appeared to be persistent for up to 2 years after the ozone challenge. One of the main aims of the present study was to determine whether a moderate ozone concentration is able to induce damage in needle biochemistry and/or only in the genetic material of root meristems. In the experiment three different clones of Norway spruce trees (Picea abies) were challenged with moderate ozone concentrations (up to 80 nl/l) for 11 weeks in greenhouses. Simultaneous investigations of root tip meristematic cells and the biochemical status of needle tissues regarding antioxidants and pigments were performed at two different sampling times: directly after the ozone treatment and 1 year later. Ozone effects in needles were absent both at the end of the fumigation and also after 1 year, but different clonal behaviour was found. Effect of ozone on chromosomal aberration rates in root tip meristems were observed and also the types of persisting chromosomal aberrations changed within the time course and within the different clones.

Accumulation of a porin‐like mRNA and a metallothionein‐like mRNA in various clones of Norway spruce upon long‐term treatment with ozone

SummaryIn a long‐term study six Norway spruce (Picea abies) clones from two different provenance regions were exposed to 150/μg/m3 and 300μg/m3 ozone in open top chambers. Differential screening of subtractive cDNA libraries made from mRNA of ozone‐treated trees identified several cDNA clones of ozone‐responsive genes, two of which were studied in more detail. One cDNA clone corresponded to a porin‐like mRNA, the other to a metallothionein‐like mRNA. Under moderate ozone exposure the accumulation of these two mRNAs was already detectable before damage symptoms became visible. The spruce clones varied in the level of accumulation for the mRNAs. This is discussed under the aspect of ozone‐induced early senescence rather than a defense reaction suppressing symptoms, because the two phenotypically most ozone‐‘tolerant’ spruce clones showed the lowest levels of accumulation for both mRNAs.

Environmental oxygen conditions during the origin and early evolution of life

The well-known sensitivity of proteins and nucleic acids to UV-radiation requires that some internally consistent protection scenario be envisioned for the origin and early evolution of life on Earth. Although a variety of ozone-surrogates has been proposed, the available biochemical, geochemical and geological evidence best supports the conclusion that free oxygen was available at levels capable of providing at least a moderate ozone screen. Levels of oxygen near 1–2% of the present atmospheric level are consistent with such a screen, and with: (1) the biochemical needs of early procaryotes considered phylogenetically more primitive than the oxygen-producing Cyanobacteria; (2) the rare-earth element data from the oxide facies of the 3.8 Byr-old Isua bandediron formations; (3) the nature and phylogenetic distribution of superoxide dismutases; (4) the need for aerobic recycling of early photosynthetic productivity dictated by the distribution of ancient sedimentary iron and organic carbon; (5) the incompatibility of dissolved reduced sulfur (to support anoxygenic photosynthesis) and ferrous iron (to support banded iron-formations) in the surface waters of the world oceans; and (6) the comparative oxygen and UV-sensitivities of modern procaryotes.