Costas SAITANIS
Professor, Director of the Laboratory of Ecology and Environmental Sciences @AUA
Journal Paper
Publication Types:
Hormesis shifts the no-observed-adverse-effect level (NOAEL)
Data from recent dose-response toxicological studies suggest that the no-observed-adverse-effect-level (NOAEL) may depend upon whether hormesis is present. A further examination of these data supports this hypothesis by showing that the NOAEL was greater for living units (organisms or cells) showing hormesis than for living units showing no hormesis. For example, some cancer tissue cells may exhibit hormetic responses to an anticancer drug while some other cancer tissue cells may not. These findings suggest that living units showing hormesis may also be less susceptible than living units not showing hormesis. However, these findings are preliminary and cannot be generalized or assumed to be a norm yet. New studies are needed to evaluate how NOAEL shifts depending on the occurrence of hormesis.
Exogenous application of melatonin to plants, algae, and harvested products to sustain agricultural productivity and enhance nutritional and nutraceutical value: A meta-analysis
Abstract
Melatonin is produced by plants, algae, and animals. Worldwide studies show diverse positive effects of exogenous melatonin on plants, edible plant products, and algae, but the potential of melatonin to enhance food and feed systems through these positive effects remains largely unexplored. Through a meta-analysis of about 25,000 observations, we show for the first time that exogenous application of melatonin significantly increases crop productivity and yields, and enhances the nutritional and nutraceutical value of edible plant products and algae by regulating diverse biological functions. We demonstrate that melatonin can improve plants, edible plant products, and algae under various current climate change scenarios, environmental pollution factors, and other stresses by about 7% to nearly 30%, on average, depending on the stressor. We also analyze various technical/methodological factors influencing the desired outcomes and identify conditions that offer optimal enhancement. We show that the positive effect of melatonin on plants and edible plant products varies among species, genera, and families, and strongly depends on the concentration of melatonin and treatment duration. The effect of melatonin is slightly lower on the monocot clade Commelinids than on the eudicot clades Asterids and Rosids. We also show that its stimulatory effect on plants depends on cultivation system, with a larger effect obtained in hydroponic systems. However, it does not depend on application stage (seed or vegetative), application route (foliage, roots, or seed), and whether the cultivation system is ex vivo or in vivo. This is the first meta-analysis examining the effects of melatonin on plants, edible plant products, and algae, and offers a scientific and technical roadmap facilitating sustainable food and feed production through the application of exogenous melatonin.
Plant susceptibility to ozone: A Tower of Babel?
Abstract
In a world with climate change and environmental pollution, modern Biology is concerned with organismic susceptibility. At the same time, policy and decision makers seek information about organismic susceptibility. Therefore, information about organismic susceptibility may have far-reaching implications to the entire biosphere that can extend to several forthcoming generations. Here, we review a sample of approximately 200 published peer-reviewed articles dealing with plant response to ground-level ozone to understand how the information about susceptibility is communicated. A fuzzy and often incorrect terminology was used to describe the responsiveness of plants to ozone. Susceptibility was classified too arbitrarily and this was reflected to the approximately 50 descriptive words that were used to characterize susceptibility. The classification of susceptibility was commonly based on calculated probability (p) value. This practice is inappropriate as p values do not provide any basis for effect or susceptibility magnitude. To bridge the gap between science and policy decision making, classification of susceptibility should be done using alternative approaches, such as effect size estimates in conjunction with multivariate ordination statistics.
Ozone biomonitoring: A versatile tool for science, education and regulation
Abstract
Ground-level ozone (O3) pollution can adversely affect human health and vegetation, thus being an important environmental issue nowadays. Ozone biological monitoring (biomonitoring) is a method of O3 monitoring by observing quantitative changes in living organisms physically present in a specific environment. Here, we provide a concise view of the field of O3 biomonitoring, along with recent advances that are expected to advance this field in the future. We also recommend that O3 biomonitoring is included in citizen science initiatives as well as in worldwide curricula of educational institutions. Policy-makers and general public may not understand biomonitoring data; hence, a major challenge is how to communicate the information to the audience in a way that permits the best comprehension.
Ozone affects plant, insect and soil microbial communities and threatens terrestrial ecosystems and biodiversity
Abstract
Elevated ground-level ozone (O3) pollution can adversely affect plants and inhibit plant growth and productivity, threatening food security and ecological health. It is therefore essential to develop measures to protect plants against O3-induced adverse effects. Here we summarize the current status of phytoprotection against O3-induced adverse effects and consider recent scientific and engineering advances, to provide a novel perspective for maximizing plant health while reducing environmental/ecological risks in an O3-polluted world. We suggest that nanoscience and nanotechnology can provide a new dimension in the protection of plants against O3-induced adverse effects, and recommend that new studies are based upon a green chemistry perspective.
Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.
On the atmospheric ozone monitoring methodologies
Abstract
Elevated ground-level ozone (O3) pollution can adversely affect plants and inhibit plant growth and productivity, threatening food security and ecological health. It is therefore essential to develop measures to protect plants against O3-induced adverse effects. Here we summarize the current status of phytoprotection against O3-induced adverse effects and consider recent scientific and engineering advances, to provide a novel perspective for maximizing plant health while reducing environmental/ecological risks in an O3-polluted world. We suggest that nanoscience and nanotechnology can provide a new dimension in the protection of plants against O3-induced adverse effects, and recommend that new studies are based upon a green chemistry perspective.
Ozone (O3) is a natural component of the atmosphere. It occurs in the stratosphere, where it protects biota against ultraviolet radiation, but also in the lower troposphere, where it can directly harm biota. Because of its (i) high toxicological potential for biota, (ii) high reactivity and molecular instability, and (iii) difficult differentiation from other reactive oxygen species, O3 challenges scientists in a continuing effort to develop methods for its monitoring. We present here the operation principles of the most used techniques, along with some new technological developments for atmospheric O3 monitoring, with emphasis upon near surface. Huge amounts of scientific data have been produced thanks to progresses in O3 monitoring technologies. However, it remains a challenge to further develop reliable methods with rapid response and high sensitivity to ambient O3, which will also be free from the disadvantages of the current technologies.
Exogenous application of chemicals for protecting plants against ambient ozone pollution: What should come next?
Abstract
Elevated ground-level ozone (O3) pollution can adversely affect plants and inhibit plant growth and productivity, threatening food security and ecological health. It is therefore essential to develop measures to protect plants against O3-induced adverse effects. Here we summarize the current status of phytoprotection against O3-induced adverse effects and consider recent scientific and engineering advances, to provide a novel perspective for maximizing plant health while reducing environmental/ecological risks in an O3-polluted world. We suggest that nanoscience and nanotechnology can provide a new dimension in the protection of plants against O3-induced adverse effects, and recommend that new studies are based upon a green chemistry perspective.
Differential Ozone Responses Identified Among Key Rust Susceptible Wheat Genotypes
Abstract
Increasing ambient ozone (O3) concentrations and resurgent rust diseases are two concomitant limiting factors to wheat production worldwide. Breeding resilient wheat cultivars bearing rust resistance and O3 tolerance while maintaining high yield is critical for global food security. This study aims at identifying ozone tolerance among key rust-susceptible wheat genotypes [Rust near-universal susceptible genotypes (RnUS)], as a first step towards achieving this goal. Tested RnUS included seven bread wheat genotypes (Chinese Spring, Line E, Little Club, LMPG 6, McNair 701, Morocco and Thatcher), and one durum wheat line (Rusty). Plants were treated with five O3 concentrations (CF, 50, 70, 90, and 110 ppb), in two O3 exposure systems [continuous stirred tank reactors (CSTR) and outdoor-plant environment chambers (OPEC)], at 21–23 Zadoks decimal growth stage. Visible injury and biomass accumulation rate were used to assess O3 responses. Visible injury data showed consistent order of genotype sensitivity (Thatcher, LMPG 6 > McNair 701, Rusty > Line E, Morocco, Little Club > Chinese Spring). Additionally, leaves at different orders showed differential O3 responses. Biomass accumulation under O3 stress showed similar results for the bread wheat genotypes. However, the durum wheat line “Rusty” had the most O3-sensitive biomass production, providing a contrasting O3 response to the tolerance reported in durum wheat. Chinese Spring was the most tolerant genotype based on both parameters and could be used as a source for O3 tolerance, while sensitive genotypes could be used as sensitive parents in mapping O3 tolerance in bread wheat. The suitability of visible symptoms and biomass responses in high-throughput screening of wheat for O3 tolerance was discussed. The results presented in this research could assist in developing future approaches to accelerate breeding wheat for O3 tolerance using existing breeding materials.
Stress response and population dynamics: Is Allee effect hormesis?
Abstract
Hormesis is a fundamental notion in ecotoxicology while competition between organisms is an essential notion in population ecology and species adaptation and evolution. Both sub-disciplines of ecology deal with the response of organisms to abiotic and biotic stresses. In ecotoxicology, the Linear-non-Threshold (LNT), Threshold and Hormetic models are used to describe the dominant responses of a plethora of endpoints to abiotic stress. In population ecology, the logistic, theta-logistic and the Allee effect models are used to describe the growth of populations under different responses to (biotic) stress induced by population density. The per capita rate of population increase (r) measures species fitness. When it is used as endpoint, the responses to population density seem to perfectly correspond to LNT, Threshold and Hormetic responses to abiotic stress, respectively. Our analysis suggests the Allee effect is a hormetic-like response of r to population density, an ultimate biotic stress. This biphasic dose-response model appears across different systems and situations (from molecules to tumor growth to population dynamics), is highly supported by ecological and evolutionary theory, and has important implications in most sub-disciplines of biology as well as in environmental and earth sciences. Joined multi-disciplinary efforts would facilitate the development and application of advanced research approaches for better understanding potential planetary-scale implications.
Predicting the effect of ozone on vegetation via the linear non-threshold (LNT), threshold and hormetic dose-response models
Abstract
The nature of the dose-response relationship in the low dose zone and how this concept may be used by regulatory agencies for science-based policy guidance and risk assessment practices are addressed here by using the effects of surface ozone (O3) on plants as a key example for dynamic ecosystems sustainability. This paper evaluates the current use of the linear non-threshold (LNT) dose-response model for O3. The LNT model has been typically applied in limited field studies which measured damage from high exposures, and used to estimate responses to lower concentrations. This risk assessment strategy ignores the possibility of biological acclimation to low doses of stressor agents. The upregulation of adaptive responses by low O3 concentrations typically yields pleiotropic responses, with some induced endpoints displaying hormetic-like biphasic dose-response relationships. Such observations recognize the need for risk assessment flexibility depending upon the endpoints measured, background responses, as well as possible dose-time compensatory responses. Regulatory modeling strategies would be significantly improved by the adoption of the hormetic dose response as a formal/routine risk assessment option based on its substantial support within the literature, capacity to describe the entire dose-response continuum, documented explanatory dose-dependent mechanisms, and flexibility to default to a threshold feature when background responses preclude application of biphasic dose responses.
Effects of ozone and ammonium sulfate on cauliflower: emphasis on the interaction between plants and insect herbivores
Abstract
Ammonium sulfate [(NH4)2SO4] deposition and elevated ozone (O3) concentrations may negatively affect plants and trophic interactions. This study aimed to evaluate for the first time the interactive effects of high (NH4)2SO4 load and elevated O3 levels on cauliflower (Brassica oleracea L.) under field conditions. Cauliflower seedlings were treated with 0 (AS0) or 50 (AS50) kg ha−1 (NH4)2SO4 and exposed to ambient (AOZ, ≈20 ppb) or elevated (EOZ, ≈55 ppb) O3 for about one month, in a Free Air O3 Concentration Enrichment (FACE) system. The oligophagous diamondback moth (Plutella xylostella Linnaeus, 1758) showed a clear preference towards the seedlings treated with AS50, which intensively grazed. Plant-herbivore interactions were driven by (NH4)2SO4 availability, rather than O3, via increased nitrogen content in the leaves. Further laboratory bioassays were followed to confirm the validity of these observations using polyphagous Eri silkmoth larvae (Samia ricini) as a biological model in a standardized experimental setup. Choice assays, where larvae could select leaves among leaf samples from the different experimental conditions, and no-choice assays, where larvae could graze leaves from just one experimental condition, were conducted. In the choice assay, the larvae preferred AS50-treated leaves, in agreement with the field observations with diamondback moth. In the no-choice assay, larval body mass growth was inhibited when fed with leaves treated with EOZ and/or AS50. Larvae fed with AS50-treated leaves displayed increased mortality. These observations coincide with higher NO3 and Zn content in AS50-treated leaves. This study shows that plant-herbivore interactions can be driven by (NH4)2SO4 availability, independently of O3, and suggests that high N deposition may have severe health implications in animals consuming such plant tissues.
Key message: Plant-herbivore interactions are driven by high (NH4)2SO4 availability, independently of O3.
Commentary: EPA’s proposed expansion of dose-response analysis is a positive step towards improving its ecological risk assessment
Abstract
The United States Environmental Protection Agency (US EPA) has recently proposed changes to strengthen the transparency of its pivotal regulatory science policy and procedures. In this context, the US EPA aims to enhance the transparency of dose-response data and models, proposing to consider for the first time non-linear biphasic dose-response models. While the proposed changes have the potential to lead to markedly improved ecological risk assessment compared to past and current approaches, we believe there remain open issues for improving the quality of ecological risk assessment, such as the consideration of adaptive, dynamic and interactive effects. Improved risk assessment including adaptive and dynamic non-linear models (beyond classic threshold models) can enhance the quality of regulatory decisions and the protection of ecological health. We suggest that other countries consider adopting a similar scientific-regulatory posture with respect to dose-response modeling via the inclusion of non-linear biphasic models, that incorporate the dynamic potential of biological systems to adapt (i.e., enhancing positive biological endpoints) or maladapt to low levels of stressor agents.
A quantitative assessment of hormetic responses of plants to ozone
Abstract
Evaluations of ozone effects on vegetation across the globe over the last seven decades have mostly incorporated exposure levels that were multi-fold the preindustrial concentrations. As such, global risk assessments and derivation of critical levels for protecting plants and food supplies were based on extrapolation from high to low exposure levels. These were developed in an era when it was thought that stress biology is framed around a linear dose-response. However, it has recently emerged that stress biology commonly displays non-linear, hormetic processes. The current biological understanding highlights that the strategy of extrapolating from high to low exposure levels may lead to biased estimates. Here, we analyzed a diverse sample of published empirical data of approximately 500 stimulatory, hormetic-like dose-responses induced by ozone in plants. The median value of the maximum stimulatory responses induced by elevated ozone was 124%, and commonly <150%, of the background response (control), independently of species and response variable. The maximum stimulatory response to ozone was similar among types of response variables and major plant species. It was also similar among clades, between herbaceous and woody plants, between deciduous and evergreen trees, and between annual and perennial herbaceous plants. There were modest differences in the stimulatory response between genera and between families which may reflect different experimental designs and conditions among studies. The responses varied significantly upon type of exposure system, with open-top chambers (OTCs) underestimating the maximum stimulatory response compared to free-air ozone-concentration enrichment (FACE) systems. These findings suggest that plants show a generalized hormetic stimulation by ozone which is constrained within certain limits of biological plasticity, being highly generalizable, evolutionarily based, and maintained over ecological scales. They further highlight that non-linear responses should be taken into account when assessing the ozone effects on plants.
Parasitoids and predators of Physokermes hellenicus (Hemiptera: Coccomorpha: Coccidae) in Greece
Abstract
High doses of ethylenediurea (EDU) as soil drenches did not increase leaf N content or cause phytotoxicity in willow grown in fertile soil
Abstract
Ground-level ozone (O3) levels are nowadays elevated in wide regions of the Earth, causing significant effects on plants that finally lead to suppressed productivity and yield losses. Ethylenediurea (EDU) is a chemical compound which is widely used in research projects as phytoprotectant against O3 injury. The EDU mode of action remains still unclear, while there are indications that EDU may contribute to plants with nitrogen (N) when the soil is poor in N and the plants have relatively small leaf area. To reveal whether the N content of EDU acts as a fertilizer to plants when the soil is not poor in N and the plants have relatively large total plant leaf area, willow plants (Salix sachalinensis Fr. Schm) were exposed to low ambient O3 levels and treated ten times (9-day interval) with 200 mL soil drench containing 0, 800 or 1600 mg EDU L−1. Fertilizer was added to a nutrient-poor soil, and the plants had an average plant leaf area of 9.1 m2 at the beginning of EDU treatments. Indications for EDU-induced hormesis in maximum electron transport rate (Jmax) and ratio of intercellular to ambient CO2 concentration (Ci:Ca) were observed at the end of the experiment. No other EDU-induced effects on leaf greenness and N content, maximum quantum yield of photosystem II (Fv/Fm), gas exchange, growth and matter production suggest that EDU did not act as N fertilizer and did not cause toxicity under these experimental conditions.
Effects of ozone (O3) and ethylenediurea (EDU) on the ecological stoichiometry of a willow grown in a free-air exposure system.
Abstract
Ground-level ozone (O3) concentrations have been elevating in the last century. While there has been a notable progress in understanding O3 effects on vegetation, O3 effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O3 injury, however its mode of action remains unclear. To investigate O3 and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L−1, and exposed them to either low ambient O3 (AOZ) or elevated O3 (EOZ) levels during the daytime, for about one month, in a free air O3 controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O3 symptoms. We found that O3 altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O3-induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance.
Application and further characterization of the snap bean S156/R123 ozone biomonitoring system in relation to ambient air temperature
Abstract
Increased mixing ratios of ground-level ozone (O3) threaten individual plants, plant communities and ecosystems. In this sense, O3 biomonitoring is of great interest. The O3-sensitive S156 and the O3-tolerant R123 genotypes of snap bean (Phaseolus vulgaris L.) have been proposed as a potential tool for active biomonitoring of ambient O3. In the present study, an O3 biomonitoring was conducted, with the S156/R123 tool, along with a monitoring of O3 and other environmental conditions in an urban area in Athens, Greece, during the growing seasons of 2012 and 2013. Plant yield was evaluated to assess the effectiveness of AOT40 in interpreting O3-induced phytotoxicity. Across the two genotypes, an approximately two times lower total number of pods – and consequently lower bulk mass of seeds – was found in 2012 than in 2013, although there was no significant difference in the final AOT40 between the two years. No significant differences were observed in the stomatal density or conductance between the two genotypes, whereas it was estimated that, in both genotypes, the abaxial leaf surface contributes 2.7 fold to O3 intake in comparison to the adaxial one. By testing the role of ambient air temperature in outdoor plant environment chambers (OPECs), it was found that increased temperature limits mature pod formation and complicates interpretation of O3 impacts in terms of S156/R123 yields ratios. This is the first study providing evidence for a hormetic response of plants to ambient air temperature. This study also points out the complexity of using yield as a measure of O3 impact across different environments with the snap bean system, whereas visible foliar injury is more consistently related to O3 effects.
The first toxicological study with the antiozonant and research tool ethylenediurea (EDU): hints to its mode of action
Abstract
The antiozonant and research tool ethylene diurea (EDU) is widely studied as a phytoprotectant against the widespread pollutant ground-surface ozone. Although it has been extensively used, its potential toxicity in the absence of ozone is unknown and its mode of action is unclear. The purpose of this research was to toxicologically assess EDU and to further investigate its mode of action using Lemna minor L. as a model organism. Application of EDU concentrations greater than 593 mg L−1 (practically 600 mg L−1) resulted in adverse inhibition of colony growth. As no-observed-toxic-effects concentration (NOEL) we recommend a concentration of 296 mg L−1 (practically 300 mg L−1). A hormetic response was detected, i.e. stimulatory effects of low EDU concentrations, which may indicate overcompensation in response to disruption in homeostasis. Growth inhibition and suppressed biomass were associated with impacted chlorophyll a fluorescence (ΦPSII, qP and ETR). Furthermore, EDU increased mesophyll thickness, as indicated by frond succulence index. Applications of concentrations ≥593 mg L−1 to uncontrolled environments should be avoided due to potential toxicity to sensitive organisms and the environment.
Olive oil for dressing plant leaves so as to avoid O3 injury
Abstract
The persistence of high ground-level ozone (O3) concentration in most regions of the northern hemisphere has severe implications to crop production, wild plant conservation, and forest sustainability. Therefore, methods for plant protection against O3 and O3 biomonitoring are of high relevance; however, there is not a method that can be applied in cultivations, which are intended for human consumption. After spraying bean (Phaseolus vulgaris L. cv. Pinto) seedlings with ethylene diurea, olive oil, or myclobutanil and exposing them to O3-enriched air (90 nmol mol−1) for a week (8 h day−1), we found that commercial olive oil can be effectively used as a protectant of plants against O3. This protection is attributed to avoidance of O3 uptake into the mesophyll, via decreased stomatal conductance. Olive oil can be applied even in organic cultivations, either for biomonitoring purposes or for short-term protection of plants during O3 episodes. Further studies are needed in order to investigate potential direct reaction of O3 with olive oil. Yet, attention should be paid when myclobutanil is applied to plants which are used for O3 biomonitoring purposes due to potential confounding effects by increasing O3-caused visible injury to plant leaves.
Impacts of ethylene diurea (EDU) soil drench and foliar spray in Salix sachalinensis protection against O3-induced injury
Abstract
It is widely accepted that elevated levels of surface ozone (O3) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O3-caused phytotoxicity. Among other questions, the one still open is: which EDU application method is more appropriate for treating fast-growing tree species. The main aims of this study were: (i) to test if chronic exposure of Salix sachalinensis plants to 200–400 mg EDU L− 1, the usually applied range for protection against O3 phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O3 on S. sachalinensis; (iii) to assess the efficacy of two methods (i.e. soil drench and foliar spray) of EDU application to plants; (iv) to investigate the appropriate concentration of EDU to protect against elevated O3-induced damage in S. sachalinensis; and (v) to compare the two methods of EDU application in terms of effectiveness and EDU consumption. Current-year cuttings grown in infertile soil free from organic matter were exposed either to low ambient O3 (AOZ, 10-h ≈ 28.3 nmol mol− 1) or to elevated O3 (EOZ, 10-h ≈ 65.8 nmol mol− 1) levels during daylight hours. Over the growing season, plants were treated every nine days with 200 mL soil drench of 0, 200 or 400 mg EDU L− 1 or with foliar spray of 0, 200 or 400 mg EDU L− 1 (in two separate experiments). We found that EDU per se had no effects on plants exposed to AOZ. EOZ practically significantly injured S. sachalinensis plants, and the impact was indifferent between the experiments. EDU did not protect plants against EOZ impact when applied as soil drench but it did protect them when applied as 200–400 mg L− 1 foliar spray. We conclude that EDU may be more effective against O3 phytotoxicity to fast-growing species when applied as a spray than when applied as a drench.
Keymessage: Soil-drenched EDU was ineffective in protecting willow plants against O3-induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200 mg L− 1.
High doses of ethylene diurea (EDU) are not toxic to willow and act as nitrogen fertilizer
Abstract
Ethylene diurea (EDU) is synthetic chemical which protects plants against damage caused by ground level O3 and is used experimentally as a biomonitoring tool at doses usually ranging from 200 to 400 mg L− 1 a.i. Although several studies have investigated the protective action of EDU, this mechanism remains unclear. Important uncertainties in EDU action are whether EDU acts as a source of nitrogen (N) to plants and whether high doses are phytotoxic. In order to answer these questions, we conducted an open-field experiment where potted willow (Salix sachalinensis Fr. Schm) plants were exposed to ambient O3 conditions and treated with 0, 800 or 1600 mg L− 1 EDU as a soil drench, every nine days, for about 2.5 months. We examined approximately 50 response variables. Based on N content in different plant organs, we found that (a) all EDU was transferred to the leaves and (b) high doses of EDU increased the leaf N content. However, EDU did not affect the C content and distribution within the plant body. Still, even at the highest dose, EDU was not toxic to this fast-growing species (however such a high dose should not be applied in uncontrolled environments); and there was no EDU persistence in the soil, as indicated by soil N content. Notably, our soil was free from organic matter and N-poor.
Key message: EDU per se does not cause toxicity to willow plants when applied as drench to a soil with no organic matter, rather, high EDU doses may act as nitrogen fertilizer in a nitrogen-poor soil.
A review study on past 40 years of research on effects of tropospheric O3 on belowground structure, functioning and processes of trees: a linkage with potential ecological implications
ABSTRACT
Wild plant species as subjects in O3 research
Abstract
Tropospheric O3, the nightmare of wild plants: A review study
Abstract
Ambient ozone (O3) poses a growing threat to the global ecosystems due to its high phytotoxicity: it may possibly reduce the productivity of wild plants as well as the species’ biodiversity. Asia hosts a remarkable number of wild plant species; thus, studies dealing with Asian species’ responses to O3 are of great importance. We have retrieved, from scientific databases, 195 papers dealing with the response of 473 wild plants species to O3. Some species we characterize as “ozonophobic” have been reported to be negatively affected by O3, even at O3 levels lower than the AOT40 threshold. This review revealed the lack of research dealing with the effects of O3 on endangered or threatened plant species, as well as on important medical plants. Such research is needed not only from an ecological point of view or in terms of biodiversity value, but also from an anthropocentric point of view. Several wild species carry unique substances that are used in medicines for healing human diseases or in agro-industry for the production of agrochemicals, thus securing human welfare.
Screening agrochemicals as potential protectants of plants against ozone phytotoxicity
Abstract
Tropospheric ozone (O3) has long been documented to cause an injury to plants, but a plants’ protectant, widely applicable in agronomical practice, does not exist. We evaluated the potential antiozonate efficacy of the antitranspirant di-1-p-menthene (Vapor Gard) compared with ethylenediurea (EDU) on Bel-W3 tobacco plants. Plants were treated either with water, or by EDU (10, 100, and 500 mg dm−3), or by vapor (1, 5, 10, and 50 ml dm−3) and were exposed either to O3-enriched (90 ppb) or O3-free air, for 12 days and 8 h day−1. EDU when applied at 10 mg dm−3 did not protect the plants against O3, but when applied at 100 and 500 mg dm−3 offered a significant protection to the plants. Vapor, when applied at 1 ml dm−3 did not protect the plants against O3, neither by terms of foliar visible injury nor by terms of aboveground biomass. In addition, when applied at 10 and 50 ml dm−3 caused phytotoxicity to all the plants, which it was expressed as necrotic spots on the leaves’ surface, misshaping of the leaves, or short plants’ height. It is obvious that vapor does not protect Bel-W3 tobacco plants against O3. The antiozonate role of di-1-p-menthene is species-specific and probably occurs only under short-term exposures.
Integrated assessment of ambient ozone phytotoxicity in Greece’s Tripolis Plateau
This is the first report of air pollution monitored in Greece’s Tripolis Plateau. We investigated ambient ozone concentrations and estimated its phytotoxicity potential based on three approaches: i) continuous instrumental monitoring at one station in the town, ii) phytodetection mapping with Bel-W3 tobacco plants in a network of 15 stations and iii) evaluation of ozone phytotoxicity by using the resistant (NC-R) and the sensitive (NC-S) white clover genotypes (the latter group was either sprayed or not sprayed with Ethylenediurea (EDU) or Azoxystrobin as ozone protectants).
The hourly ozone concentrations often exceeded 70 nmol mol-1. The average ozone concentration during the early afternoon hours (12:00-19:00) for June, July and August was 65.4 nmol mol-1. The monthly AOT40 (accumulated ozone mixing ratios over the threshold of 40 nmol mol-1) value was higher in July (9,123 nmol mol-1 h) and lower in October (2,022 nmol mol-1 h).
The Bel-W3 plants showed characteristic ozone-induced visible foliar injury symptoms at all the stations of the network, suggesting that ozone was at phytotoxic levels not only in the town, where it was measured, but also throughout the plateau.
The white clover revealed a reduction of the epigeous biomass of the NC-S by 36-57% in five harvests. The application of EDU prevented biomass reduction in the NC-S genotype, while Azoxystrobin did not offer significant protection.
These results indicate that, in rural areas of Greece, ambient ozone occurs at potentially phytotoxic levels, at least for sensitive plant species.
Ethylenediurea (EDU) as a protectant of plants against O3
Ethylenediurea (EDU) is an anti-ozonant substance that is recognized as a versatile research tool, and recently attracts increasing interest. As many wild plant species are forced into complex responses by tropospheric ozone (O3), these responses are crucial for the functioning of ecosystems and consequently for the biosphere; thus, countermeasures are required. A plethora of substances have been evaluated as to their effectiveness in protecting plants against O3. EDU is the most widely-used substance in O3 research, in order to moderate O3 effects on plant growth. We present a synoptic table with recent literature on EDU applications to plants as a protectant against O3. This table summarizes important information on these publications, and we hope to be useful to researchers intended to employ EDU in their research with wild plants, but also to researchers working with air pollution control and other scientists.
Ethylene-di-urea (EDU), an effective phytoprotectant against O3 deleterious effects and a valuable research tool
Volatile compounds in Thymus sect. Teucrioides (Lamiaceae): intraspecific and interspecific diversity, chemotaxonomic significance and exploitation potential
Abstract
Thymus sect. Teucrioides comprises three species, namely, T. hartvigii, T. leucospermus, and T. teucrioides, distributed in Greece and Albania. The volatile constituents of all species of the section were obtained by hydrodistillation and investigated by GC‐FID and GC/MS analyses. Twenty populations were sampled and a total of 103 compounds were identified, representing 98.0–99.9% of the oil compositions. The oils were mainly characterized by high contents of monoterpene hydrocarbons (42.7–92.4%), with the exception of three oils for which oxygenated monoterpenes were the dominating constituents, viz., that of T. hartvigii ssp. macrocalyx, with linalool as main compound (89.2±0.5%), and those of T. hartvigii ssp. hartvigii and of one population of T. teucrioides ssp. candilicus, containing thymol as major component (46.4±3.1 and 38.2±3.9%, resp.). The most common compound in the oils of the 20 populations of the section was p‐cymene. Considerable variation was detected within and among populations, and seven chemotypes were distinguished, i.e., p‐cymene, linalool, p‐cymene/thymol, p‐cymene/γ‐terpinene, p‐cymene/borneol, p‐cymene/γ‐terpinene/borneol, and p‐cymene/linalool chemotypes. Different chemotypes may exist in the same population. Multivariate statistical analyses enabled the segregation of the oils within Thymus sect. Teucrioides into two groups, one consisting of the three subspecies of T. teucrioides and the second comprising the species T. hartvigii and T. leucospermus. A linalool‐rich chemotype, unique within the section, distinguished the oil of T. hartvigii ssp. macrocalyx from all other oils. The high oil content of p‐cymene and the preference for serpentine substrates render T. teucrioides species promising for future exploitation.
Screening of Bangladeshi winter wheat (Triticum aestivum L.) cultivars for sensitivity to ozone
Abstract
The sensitivity to ozone of ten Bangladeshi wheat cultivars was tested by exposing plants to eight ozone exposure regimes (50, 60, 80, 100, 120, 135, 150, and 200 ppb for 14, 11, 8, 6, 5, 4, 3, and 1 days, respectively, for 8 h/day) in controlled environment chambers. Visible leaf injury, dry weight, chlorophyll, carotenoid content, leaf greenness (SPAD value), quantum yield of photosynthesis, and stomatal resistance were measured to evaluate response. Shoot biomass, total chlorophyll, leaf greenness, and carotenoid content were reduced in ozone-exposed plants. Based on the results of principal component analysis (PCA)-biplot analysis, the order of sensitivity to ozone was: Akbar >> Sufi ≥ Bijoy ≥ Shatabdi > Bari-26 ≥ Gourab > Bari-25 ≥ Prodip ≥ Sourav >> Kanchan. The most important parameters to discriminate cultivars with respect to ozone sensitivity were visible injury and chlorophyll b/a ratio, whereas quantum yield of photosynthesis was less important. Differences in stomatal resistance were not a significant factor in ozone response. Regression of cultivars’ PCA scores against year of release revealed no trend, suggesting that ozone tolerance was not incorporated during cultivar breeding.
Evaluation of di-1-p-menthene as antiozonant on Bel-W3 tobacco plants, as compared with ethylenediurea
Abstract
Tropospheric ozone (O3) has long been documented to cause an injury to plants, but a plants’ protectant, widely applicable in agronomical practice, does not exist. We evaluated the potential antiozonate efficacy of the antitranspirant di-1-p-menthene (Vapor Gard) compared with ethylenediurea (EDU) on Bel-W3 tobacco plants. Plants were treated either with water, or by EDU (10, 100, and 500 mg dm−3), or by vapor (1, 5, 10, and 50 ml dm−3) and were exposed either to O3-enriched (90 ppb) or O3-free air, for 12 days and 8 h day−1. EDU when applied at 10 mg dm−3 did not protect the plants against O3, but when applied at 100 and 500 mg dm−3 offered a significant protection to the plants. Vapor, when applied at 1 ml dm−3 did not protect the plants against O3, neither by terms of foliar visible injury nor by terms of aboveground biomass. In addition, when applied at 10 and 50 ml dm−3 caused phytotoxicity to all the plants, which it was expressed as necrotic spots on the leaves’ surface, misshaping of the leaves, or short plants’ height. It is obvious that vapor does not protect Bel-W3 tobacco plants against O3. The antiozonate role of di-1-p-menthene is species-specific and probably occurs only under short-term exposures.
Spatiotemporal distribution of airborne elements monitored with the moss bags technique in the greater Thriasion plain, Attica, Greece
Abstract
The well-known moss bags technique was applied in the heavily polluted Thriasion Plain region, Attica, Greece, in order to study the spatiotemporal distribution, in the atmosphere, of the following 32 elements: Na, Al, Cl, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Zn, As, Se, Br, Sr, Mo, Sb, I, Ba, La, Ce, Sm, Tb, Dy, Yb, Hf, Ta, Hg, Th, and U. The moss bags were constituted of Sphagnum girgensohnii materials. The bags were exposed to ambient air in a network of 12 monitoring stations scattered throughout the monitoring area. In order to explore the temporal variation of the pollutants, four sets of moss bags were exposed for 3, 6, 9, and 12 months. Instrumental neutral activation analysis was used for the determinations of the elements. The data were analyzed using the Pearson correlations, the partial redundancy analysis, and the biplot statistical methods. Some pairs of elements were highly correlated indicating a probable common source of origin. The levels of the measured pollutants were unevenly distributed throughout the area and different pollutants exhibited different spatial patterns. In general, higher loads were observed in the stations close to and within the industrial zone. Most of the measured elements (e.g., Al, Ca, Ni, I, Zn, Cr, and As) exhibited a monotonic accumulation trend over time. Some elements exhibited different dynamics. The elements Mn, Mo, and Hg showed a decreasing trend, probably due to leaching and/or volatilization processes over time. Na and Br initially showed an increasing trend during the winter and early spring periods but decreased drastically during the late warm period. The results further suggest that the moss bags technique would be considered valuable for the majority of elements but should be used with caution in the cases of elements vulnerable to leaching and/or volatilization. It also suggests that the timing and the duration of the exposure of moss materials should be considered in the interpretation of the results.
Revitalization of urban ecosystems through vascular plants: preliminary results from the BSEC-PDF project
Tropospheric Ozone: a Menace for Crops and Natural Vegetation in Greece
ABSTRACT
Based on instrumental monitoring (AOT40s) and phytodetection (with Bel-W3 and KK6/5 tobacco cultivars) data we evaluated ambient ozone phytotoxicity in Greece. In the greater region of Mesogia-Attica, during the summer of 2000, the year before the new airport Eleftherios Venizelos (March 2001) began operating in this region, the AOT40s (ppb*h) were 16,325 over 110 days at Spata; 18,646 over 113 days at Markopoulo; 8,093 over 22 days at Artemis and 16,679 over 121 days in Athens. The Bel- W3 and KK6/5 plants were extensively injured at all places with the greatest injury occurring at Artemis. During the same summer, ozone was also monitored in three rural areas of Corinth, at the Astronomical Observatory of Krionerion, Bogdani Hill and Kiato; The highest average daily AOT40 (192 ppb*h) was observed in Krionerio, and it was almost equal to that occurred in Athens (193 ppb*h). Bel-W3 and KK6/5 plants placed at 11 rural areas in Corinth showed extended injury. The following year (2001), high injury was observed on other sets of bioindicator plants exposed in a network of 28 locations throughout the greater area of Volos and Pelion Mountain. Symptoms were more severe at Mortias, Xinovrisi, Tsagarada, Makrinitsa and Chania. The AOT40 (May-July) was 11,391 and 10,351 ppb*hours for 2001 and 2002 respectively. Severe ozone-like symptoms have also been observed on field-cultivated grape vines, onion and watermelon plants. Synoptically, our investigations suggest that ozone occurs in the Greek mainland at levels that are potentially phytotoxic for sensitive crop species and for sensitive natural vegetation species including forest trees.
Mites associated with stored products in Greece
Efficacy of repeated trickle applications of oxalic acid in syrup for varroosis control in Apis mellifera: influence of meteorological conditions and presence of brood
Effect of two azadirachtin formulations against adults of Sitophilus oryzae and Tribolium confusum on different grain commodities.
Three non-toxic insect traps useful in trapping wasps’ enemies of honey bees
Study of the weekday-weekend variation of air pollutants in a typical Mediterranean coastal town
Abstract:
A study of the air pollution in the Greek coastal town Volos was performed using the available data of the last ten years. Quantile analysis showed that ozone concentrations during weekends were higher by 5–10% in comparison to those on weekdays, while the inverse was observed for the other pollutants, indicating the occurrence of the so called |weekend effect|. Analysis of the maximum values of the high ozone period showed even higher differences. The pollutants NO, NO2, CO, and SO2 were lower during weekends compared to weekdays, by about 30%, 20%, 25% and 10% respectively.
Spatiotemporal clustering and association of Ephestia kuehniella (Pyralidae: Lepidoptera) and two of its parasitoids in bulk-stored wheat
Abstract
To assess the spatiotemporal distribution of insects in a flat storage containing wheat (Triticumn spp.), probe traps were suspended in the wheat bulk and inspected for captured insects at 15-d intervals, from June 2001 to August 2002. The grain bulk was 1 m in height, and traps were placed at the upper and the lower 0.5 m of the bulk. During the entire trapping period, 17 insect taxa were recorded. The most abundant species were Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and its larval parasitoids Harbobracon hebetor (Say) (Hymenoptera: Braconidae) and Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae). Most individuals were found in the upper bulk part. The highest E. kuehniella trap catches were found between August and November 2001 and during June and July 2002. Of the two parasitoids, H. hebetor was more abundant than V. canescens, with the exception of winter and early spring, when both species occurred at low numbers, especially H. hebetor. Spatial analysis by distance indices (SADIE) spatiotemporal analysis showed significant clustering of species, especially during summer and autumn. Early in the season and during spring 2002, at low host numbers, V. canescens occupied the locations where E. kuehniella mainly aggregated, but with the increase of E. kuehniella population, H. hebetor occupied these host groups and replaced V canescens. Although the two parasitoids competed for the same host species, both species coexisted in the storage facility during the entire trapping period.
Physico-chemical characteristics of Greek fir honeydew honey from Marchalina hellenica (Gen.) in comparison to other Mediterranean honeydew honeys
First study of anthropogenic platinum group elements in roadside top-soils in Athens, Greece
Abstract
Studio comparative su sei formulati contenenti timolo nel controllo di Varroa destructor (Anderson & Trueman) in Grecia [Comparison between six thymol based formulations in the control of Varroa destructor (Anderson & Trueman) in Greece]
Comparative Assessment of Ambient Air Quality in two typical Mediterranean Coastal Cities in Greece
Abstract
Air quality data (O3, NO2, NO, CO and SO2) of two Greek coastal cities, Patras and Volos, were analyzed and compared to evaluate: (a) the exceedances of air quality EU threshold values, (b) the diurnal patterns of air pollutants and (c) the “weekend effect” on ozone levels.
High ozone levels, close to the thresholds for human health and clearly above the threshold for the protection of plants and ecosystems, were observed in Volos. O3 levels in Volos were higher than those in Patras. NOx levels in Patras were significantly higher than the limits for human health and plants’ protection. Both, NOx and SO2 levels were higher in Patras than in Volos. The Patras’ harbor high traffic seems to drive the diurnal pattern of SO2 in that city.
The examination of the rate of ozone accumulation, during the high O3 period (Apr.–Sep.), revealed the occurrence of two phases, a fast and a slow one, with different durations in each city. We suggest that the occurrence of such two phases’ patterns should be considered in relevant ozone studies.
In both towns, the O3 levels were higher during weekends in comparison to midweek days, although NO levels were lower. Our results support the hypothesis that the weekend O3 effect is due to a combination of VOC sensitivity of the studied areas and the reduced NOx emissions during weekends. Based on the comparison of the weekend effect in the two cities, we suggest the occurrence of a feedback mechanism between peri-urban natural ecosystems (forests) and the polluting anthropogenic ones (cities).
Keywords
Morphology and life cycle of Marchalina hellenica (Gennadius) (Hemiptera: argarodidae) on pine (Parnis Mt.) and fir (Helmos Mt.) forests of Greece
Evaluation of Ozone Phytotoxicity in the Greater Area of a Typical Mediterranean Small City (Volos) and in the Nearby Forest (Pelion Mt.) - Central Greece
2004. .
Biomonitoring of concentrations of platinum elements and their correlations to other metals
Biomonitoring of Pt, Pd, Pb, Mn, Cu, Fe and Zn was conducted using leaves (two and six months old) of laurel (Laurus nobilis L.) ornamental shrubs grown in 14 sampling sites located on the central green belts of six avenues and streets of Athens. In this biomonitoring, we determined, for the first time in Greece, the concentrations of the new urban “pollutants” Pt and Pd, and we estimated the correlations among the concentrations of all the above-mentioned metals as well as among the metal concentrations and the traffic load. Cluster analysis and principal component analysis (PCA) of the data revealed three distinct groups of metals and two groups of sites (one with high and the other with relatively low levels of pollution). Using varimax-rotated PCA for the metals, four factors were extracted explaining 92.3% of the total shared variance, which are further discussed. The importance of seasonal timing of sampling is revealed by the data and discussed in connection with the meteorological conditions.
A Field Study on the Long-Term Incidence of Acarapis woodi Rennie in Greece
The long-term incidence (% of apiaries infested) of the mite Acarapis woodi in southern Greece was monitored. Over 10 years the overall average infestation was 5.43%. Yearly maximum infestation (average 28.9%) exhibited a decreasing trend from 1986 to 1995. Infestation tended to peak in November and March and was restricted or absent during the summer. Additionally, seasonal variation of A. woodi density (% of individuals infested per colony) in three groups of colonies was followed for almost three years. At the beginning, Groups I and II had infestation rates of 10.75% and 11.25%, respectively, while Group III was not infested. Group I received no acaricide treatment while Group II was treated with 50 g menthol twice a year. There was no evidence that mites had transferred from infested Groups I and II to nearby non-infested Group III, and no difference in honey production between the groups was observed. There was a rapid decline in the infestation in all three groups, irrespective of treatment, with complete disappearance about seven months before the end of the experiment.
Photoperiodic and temperature effects on the intensity of larval diapause in Sesamia nonagrioides
Photochemical air pollutant levels and ozone phytotoxicity in the region of Mesogia–Attica, Greece
Background ozone monitoring and phytodetection in the greater rural area of Corinth – Greece
Abstract
Natural background ozone levels were monitored in three places within the greater rural area of Corinth, namely Bogdani Hill, Astronomical Observatory of Krionerion, and Kiato, and compared with ambient ozone monitored in the metropolitan area of Athens. Measurements were made sequentially, for a few weeks at each place, during the summer of 2000. In addition, ozone phytodetection, using tobacco (Nicotiana tabacum L.) plants of the Bel-W3 and Zichnomirodata varieties, was conducted in 12 places (the above included). Moreover, stomatal conductance was measured in the Bel-W3 plants, as well as in leaves of cultivated grape-vines (Vitis vinifera L.) and in needles of Aleppo pine (Pinus halepensis Mill.) trees and compared with the diurnal pattern of ozone concentrations.
The 24 and 12 (08:00–20:00) hourly averages of ozone concentrations were high in Athens (37; 51 ppb), at Bogdani Hill (53; 56 ppb) and at the Astronomical Observatory (56; 55 ppb), but relatively low in Kiato (30; 34 ppb). Furthermore, the average daily AOT40 (accumulated exposure over 40 ppb for the daylight hours) (ppb h) was 193 in Athens, 212 at Bogdani Hill, 192 at the Astronomical Observatory and 47 in Kiato. Ozone concentrations exhibited the usual diurnal pattern in Athens (altitude 50 m), where they were maximum during midday and early afternoon hours, as well as at Bogdani Hill (300 m) and in Kiato (5 m) where, however, they were maximal 1–3 h later. At the Astronomical Observatory (altitude 920 m) ozone remained constant during both daylight and night hours. The differences in diurnal patterns are consistent with those in places of different elevation, reported elsewhere.
The Bel-W3 plants were injured at all 12 places; Zichnomirodata plants exhibited lower injury and only in some of the places; probable ozone symptoms were also observed on vine plants and pine trees. The greatest injury was observed at the high altitude places of Astronomical Observatory and Mougostos. Stomatal conductance, in all three species, peaked during morning and early midday hours when ozone levels were higher in the high altitude, and lower in the low altitude, places.
Seasonal variations in the concentration of trace metals in leaves of laurel, used as bioindicator of urban traffic pollution in Athens
Effects of ozone on tobacco (Nicotiana tabacum L.) varieties
Abstract
Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.
Background benzene–toluene–xylene levels in Mesogia Plain, Attica – Greece
2002. . .
Instrumental recording and biomonitoring of ambient ozone in Greek countryside
Abstract
Among eight commercial Greek varieties of tobacco (Nicotiana tabacum L.) tested for their ozone-sensitivity levels, the Zichnomirodata (KK6/5) variety was found to be the most sensitive, although less sensitive than the well-known super-sensitive Bel-W3. Besides qualitative differences in the appearance of macroscopic symptoms these two varieties can be used simultaneously as a reliable pair of ozone bioindicators. The occurrence of ozone in the Greek countryside was surveyed by biomonitoring in 14 rural regions over the country and by a simultaneous biomonitoring and instrumental recording of ozone concentrations at a single remote side (Pournaria, Arcadia). Phytotoxic symptoms were observed mainly on the leaves of Bel-W3 and occasionally on those of Zichnomirodata varieties, suggesting that ozone levels were high enough to affect at least sensitive species. The instrumental monitoring (during a total period of 912 h) revealed maximum hourly O3 concentration 62 ppb, while the thresholds of 30, 40 and 50 ppb were exceeded for 40%, 20% and 6% of the recording period, respectively. The accumulated exposure over 40 ppb (AOT40) for the daylight hours over the 38 monitored days was 680 ppb h.
Effects of ozone on chlorophyll and quantum yield of tobacco (Nicotiana tabacum L.) varieties
Abstract
Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.
