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A field study was conducted to understand the physiological responses, yield and grain quality of an old (HUW234) and a modern (HD3118) wheat cultivar exposed to elevated ozone (O 3 ). The cultivars were grown under ambient O 3 (NF) and ambient +20 ppb O 3 (NF+) conditions using open-top chambers (OTCs). The comparative study of an old and a modern cultivar showed variable physiological responses under elevated O 3 exposure. Elevated O 3 in old cultivar caused high reductions in Rubisco activity (Vc max ) and electron transport rate (J) compared to modern cultivar with simultaneous reductions in the rate of photosynthesis and chlorophyll fluorescence. In modern cultivar, high stomatal density and conductance caused higher O 3 uptake thereby triggering more damage to the adjacent stomatal cells and photosynthetic pigments coupled with reductions in photosynthetic rate and photosynthetic nitrogen use efficiency (PNUE). Modern cultivar also showed relatively high reduction in grain yield compared to old one under NF + treatment. Furthermore, grain quality traits (such as starch, protein and amino acids) of modern cultivar were better than old cultivar under ambient O 3 , but showed more deterioration under NF + treatment. Results thus indicated that modern cultivar is relatively more susceptible to O 3 and showed more negative impacts on plant performance, yield and quality of grains compared to old cultivar., Competing Interests: Declaration of competing interest Authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Two common tropical grassland species, Panicum maximum Jacq. (Guinea grass) and Cenchrus ciliaris (Buffel grass) of Indo-Gangetic plains were assessed for their responses under future level of O 3 (ambient +30 ppb) using open top chambers. Plants were assessed for foliar injuries, pigments, growth, biomass accumulation, histochemical localization of reactive oxygen species (ROS), antioxidant defense system and ROS scavenging activities at two stages. Foliar injuries were noticed at an early stage in P. maximum compared to C. ciliaris. Significant reductions were observed in total chlorophyll, growth and total biomass in both species. Significant increases in contents of melondialdehyde and ascorbic acid in P. maximum while total phenolics and thiols in C. ciliaris were found. Histochemical analysis showed more production of superoxide radicals and hydrogen peroxide in leaf tissues of P. maximum compared to C. ciliaris. It can be concluded that higher level of primary antioxidants (total phenolics and thiols) along with superoxide dismutase and ascorbate peroxidase scavenged O 3 effectively in C. ciliaris causing less reduction of biomass which is used as a feed for cattles. In P. maximum, more photosynthates were allocated for defense, leading to higher reduction in total biomass compared to C. ciliaris. The leaf area ratio was higher in P. maximum compared to C. ciliaris under elevated O 3 . The study further suggests higher susceptibility of P. maximum compared to C. ciliaris under future level of O 3 exposure.

The present field study was planned with an objective to unravel the mechanisms behind the differential responses of early and late sown wheat cultivars with respect to their defense capacity to scavenge ROS induced under elevated O 3 (EO 3 ). Experiments were performed under ambient and elevated levels of O 3 (ambient + 20 ppb) to plants inside open-top chambers (OTCs). Ozone concentrations, stomatal flux of O 3 and meteorological parameters were measured throughout the experiment. Contents of superoxide radicals (O 2 - ) and hydrogen peroxide (H 2 O 2 ) and their localization, lipid peroxidation, antioxidative enzyme activities, ascorbic acid and total phenolic contents were measured at vegetative and reproductive developmental stages. EO 3 exposure induced higher stomatal flux of O 3 in early sown cultivars. Higher contents of O 2 - , H 2 O 2 and lipid peroxidation were noticed under EO 3 in all the cultivars but the magnitude of increases was higher in late sown cultivars at the reproductive stage. Activities of glutathione reductase (GR) and ascorbate peroxidase (APX) were higher in late sown cultivars under EO 3 . Ascorbic acid and total phenolic contents were significantly higher in early sown than late sown cultivars under EO 3 treatment. The present study concludes that early sown cultivars are more efficient in their defense response due to higher induction of enzymatic and non-enzymatic antioxidants, while the induction of enzymatic antioxidants was more distinct in late sown cultivars. Non-enzymatic linked defense mechanism requires additional metabolic cost than enzymatic defense, making early sown cultivars more susceptible to EO 3 . Differential response of early and late sown cultivars with respect to antioxidative defense against O 3 stress suggests that yield responses are governed by the time of sowing and intrinsic defense responses of the cultivars. In future with rising trend of O 3 , early sown cultivars are expected to be more vulnerable to oxidative stress compared to late sown cultivars., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Ultraviolet-B radiation (UV-B) is inherent part of solar spectrum and tropospheric ozone (O 3 ) is a potent secondary air pollutant. Therefore the present study was conducted to evaluate the responses of Helianthus annuus L. cvs DRSF 108 and Sungold (sunflower) to supplemental UV-B (sUV-B; ambient + 7.2 kJ m -2  d -1 ) and elevated ozone (O 3 ; ambient + 10 ppb), given singly and in combination under field conditions using open-top chambers. The individual and interactive effects of O 3 and sUV-B induced varying changes in both the cultivars of sunflower ranging from ultrastructural variations to growth, biomass, yield and oil composition. Reduction in leaf area of Sungold acted as a protective feature which minimized the perception of sUV-B as well as uptake of O 3 thus led to lesser carbon loss compared to DRSF 108. Number- and weight of heads plant -1 decreased although more in Sungold with decline of oil content. Both the stresses when given singly and combination induced rancidification of oil and thus made the oil less suitable for human consumption.

Tropospheric ozone (O 3 ) is a phytotoxic air pollutant causing a substantial damage to plants and agriculture worldwide. Plant productivity is affected by several environmental factors, which interact with each other. Studies related to interactions involving O 3 and different levels of nitrogen (N) are still rare and elusive. In the present study we grew two wheat cultivars (HD2967 and Sonalika) in open top chambers (OTC) under ambient (AO) and elevated O 3 (EO) (ambient + 20 ppb O 3 ) and provided two levels of N fertilization; (a) recommended nitrogen (RN), (b) 1.5 times the recommended N (HN). Growth (root/shoot ratio, leaf number and leaf area), biomass, gas-exchange (stomatal conductance (g s ), photosynthesis (A), transpiration (E), chlorophyll fluorescence (F v /F m ), physiological (chlorophyll and carotenoids), biochemical [antioxidant activity, lipid peroxidation (MDA)] parameters and leaf N content were measured at the vegetative and reproductive phases. Yield attributes (spike weight plant -1 , grain weight plant -1 , grain numbers plant -1 , husk weight plant -1 , straw weight plant -1 , 1000 grain weight, harvest index) and seed N content were analyzed at the final harvest stage. Grain yield plant -1 was decreased in Sonalika under EO irrespective of different levels of N fertilization. Seed N content decreased by 3.9% and 5.6% in HD2967 and Sonalika, respectively, under EO at RN treatment. Antioxidant defense played an important role in protecting the plants against O 3 stress which was enhanced under HN treatment. Response of antioxidants varied between the cultivar, growth phase (at the vegetative or reproductive phase) and the N levels (RN or HN). Cultivar HD2967 was characterized by higher biomass, g s and stronger antioxidant protection system, while, Sonalika showed early senescence response (decreased leaf number plant -1 , g s ) and greater resources allocation towards eco-physiological parameters (increased A and F v /F m ) at the vegetative phase, resulting in the significant decrease in the yield attributes. Further study warrants the need to screen a large number of cultivars in relation to their response to various levels of N fertilization to minimize the yield losses under highly O 3 polluted areas., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Three clover (Trifolium alexandrium L.) cultivars (Bundel, Wardan and JHB-146) were assessed for their responses to ambient ozone (O 3 ) with respect to growth, physiological and biochemical parameters at two rural sites (R1 and R2) using ethylenediurea (EDU). EDU solution (300ppm) was applied as soil drench, 10 days after germination (DAG) at an interval of 10 days up to 80 DAG. The average O 3 concentrations were 52.76 and 60.86 ppb at R1 and R2 sites, respectively during the experimental period. Ambient O 3 induced visible symptoms in all the cultivars at both the sites, with more at R2 site having high ambient O 3 levels. Visible injury was observed first in non-EDU treated plants of Wardan at R2 site. Wardan also showed maximum reduction in leaf injury under EDU treatment at both the sites with more at R2. Under EDU treatment, better adaptation to ambient O 3 at initial age of observation and higher acquisition of resources at later ages of observation at both the sites led to better physiological and biochemical adaptations in Wardan. Bundel retained more biomass in shoot as is reflected with higher shoot/root ratio and thus focused more on repair and defense. Shoot/root ratio of JHB-146 did not respond to EDU treatment and thus showed insignificant variations except at initial age of observation at R1 site. This study clearly suggests that Wardan and Bundel are sensitive to ambient O 3 and can be used as bioindicator species in areas having higher O 3 levels using EDU as a research tool., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Ozone (O 3 ) in troposphere is the most critical secondary air pollutant, and being phytotoxic causes substantial losses to agricultural productivity. Its increasing concentration in India particularly in Indo-Gangetic plains is an issue of major concern as it is posing a threat to agriculture. In view of the issue of rising surface level of O 3 in India, the aim of this compilation is to present the past and the prevailing concentrations of O 3 and its important precursor (oxides of nitrogen) over the Indian region. The resulting magnitude of reductions in crop productivity as well as alteration in the quality of the product attributable to tropospheric O 3 has also been taken up. Studies in relation to yield measurements have been conducted predominantly in open top chambers (OTCs) and also assessed by using antiozonant ethylene diurea (EDU). There is a substantial spatial difference in O 3 distribution at different places displaying variable O 3 concentrations due to seasonal and geographical variations. This review further recognizes the major information lacuna and also highlights future perspectives to get the grips with rising trend of ground level O 3 pollution and also to formulate the policies to check the emissions of O 3 precursors in India.

Surface-level ozone (O3) has been regarded as one of the most significant phytotoxic pollutants worldwide. Investigations addressing adverse impacts of elevated O3 on mung bean (Vigna radiata L.), an important leguminous crop of the Indian subcontinent, are still limited. The present study analyzed the differences on the foliar injury, reactive oxygen species (ROS) generation, antioxidative defense system, physiology, and foliar protein profile of two tropical mung bean cultivars (HUM-2 and HUM-6) exposed to elevated O3 under near-natural conditions. Both cultivars were negatively affected by the pollutant, but the response was cultivar-specific. Results revealed that elevated O3 induced higher levels of ROS (O2 (·-) and H2O2) and lipid peroxidation leading to greater foliar injury in HUM-2 compared to HUM-6. Photosynthetic pigments, photosynthetic rate, stomatal conductance, and photochemical efficiency reduced under elevated O3 exposure and the extent of reduction was higher in HUM-2. Principal component analysis revealed that photosynthetic performance and quantum yield were drastically affected in HUM-2 as compared to HUM-6. Activities of antioxidative enzymes were also stimulated, suggesting generation of oxidative stress under elevated O3. HUM-6 showed higher induction of antioxidative enzymes than HUM-2. One-dimensional gel electrophoresis analysis showed drastic reductions in the abundantly present ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large and small subunits and the decrease was higher in HUM-2. Altogether, results suggested that higher accumulation of ROS and limited induction of antioxidant defense system led to more leaf injury and impairment of photosynthesis in HUM-2 than HUM-6 depicting its higher sensitivity towards elevated O3.

The present study deals with assessment of response of a tropical soybean cultivar to O3 in relation to photosynthetic pigments, chlorophyll fluorescence kinetics, antioxidative capacity, N assimilation enzymes, metabolites, growth and yield using ethylene diurea (EDU) given as a soil drench (400) ppm at an interval of 10 days after germination up to maturity. Mean O3 concentration was 42 ppb and accumulated threshold above 40 ppb (AOT 40) was 9.07 ppm h. Lipid peroxidation and total phenolics reduced, while increases in activities of antioxidative and nitrogen assimilation enzymes, ascorbic acid, protein, photosynthetic pigments, Fv/Fm ratio, number of leaves, flowers, pods, branches and yield attributes were found in EDU treated plants. EDU alleviated the negative effects of O3 by enhancing the first line of defense against ROS and protecting N assimilation enzymes at flowering and maintaining adequate supply of photosynthates to developing pods during pod filling stage. EDU provided maximum protection between flowering to pod filling stage., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Tropospheric ozone (O3) can be deleterious to plants by decreasing crop yield and quality. Present study was conducted on six cultivars of mung bean (HUM-1, HUM-2, HUM-6, HUM-23, HUM-24 and HUM-26) grown under ambient O3 (NFC) and elevated O3 levels (ambient+10 ppb; NFC+) in open top chambers (OTCs) for two consecutive years. Ozone monitoring data showed high mean ambient concentration of O3 at the experimental site, which was above the threshold value of 40 ppb. Ozone exposure induced symptoms of foliar injury and also depicted accumulation of reactive oxygen species (ROS) which led to increased membrane damage vis-a-vis solute leakage. Root/shoot allometric coefficient (k), yield and seed quality showed negative response to O3. Differential response of mung bean cultivars against elevated O3 was assessed by comparing the levels of antioxidants, metabolites, growth, total biomass and yield. Cultivar HUM-1 showed maximum sensitivity towards O3 as compared to other cultivars. Findings of present study emphasized the possibility of selection of suitable O3 resistant cultivars for the areas experiencing high concentrations of O3., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Tropospheric ozone (O3) concentrations are rising in Indo-Gangetic plains of India, causing potential threat to agricultural productivity. Maize (Zea mays L.) is the third most important staple crop at global level after rice and wheat. Two high yielding cultivars of Indian maize (HQPM1-quality protein maize and DHM117-normal/non quality protein maize) were exposed to two levels of elevated O3 above the ambient level (NFC) viz. NFC + 15 ppb O3 (NFC + 15) and NFC + 30 ppb O3 (NFC + 30) using open top chambers under field conditions. The study was conducted to evaluate the biochemical responses of two cultivars at different developmental stages leading to change in yield responses. Initially at lower O3 dose, photosynthetic pigments showed an increase but reduction at later stage, while higher dose caused a decline at both the stages of sampling. Levels of superoxide radical (O2 (-)) and hydrogen peroxide (H2O2) significantly increased and contributed to lipid peroxidation at elevated O3. Histochemical localization assay of O2 (-) and H2O2 showed that guard cells of stomata and cells around trichomes took deeper stain at elevated O3 reflecting more formation of reactive oxygen species. Secondary metabolites like total phenol, flavonoids and anthocyanin pigments also increased in plants under O3 stress. Enzymatic antioxidants were triggered in both the cultivars due to elevated O3, while induction of non-enzymatic antioxidants was more in HQPM1. Native PAGE analysis also showed that SOD, POX, CAT, APX and GPX were stimulated at elevated O3 concentrations compared to NFC. SDS-PAGE showed reductions of major photosynthetic proteins with higher decrease in DHM117. Principal Component Analysis showed that both the cultivars showed differential response against O3 at two developmental stages. HQPM1 maintained the analogous defense strategy at both the sampling stages while DHM117 showed variable response. Overall metabolic induction of antioxidants related to defense was more in DHM117 than HQPM1. This suggests that DHM117 utilized more assimilates in maintaining the homeostasis against imposed oxidative stress, causing less translocation of assimilates to reproductive parts and thus affecting the final yield. In terms of yield it is suggested that performance of HQPM1 (quality protein maize) was better than the DHM117 (non quality protein maize).

Rapid industrialization and economic developments have increased the tropospheric ozone (O3) budget since preindustrial times, and presently, it is supposed to be a major threat to crop productivity. Maize (Zea mays L.), a C4 plant is the third most important staple crop at global level with a great deal of economic importance. The present study was conducted to evaluate the performance of two maize cultivars [HQPM1: quality protein maize (QPM)] and [DHM117: nonquality protein maize (NQPM)] to variable O3 doses. Experimental setup included filtered chambers, nonfiltered chambers (NFC), and two elevated doses of O3 viz. NFC+15 ppb O3 (NFC+15) and NFC+30 ppb O3 (NFC+30). During initial growth period, both QPM and NQPM plants showed hormetic effect that is beneficial due to exposure of low doses of a toxicant (NFC and NFC+15 ppb O3), but at later stages, growth attributes were negatively affected by O3. Growth indices showed the variable pattern of photosynthate translocation under O3 stress. Foliar injury in the form of interveinal chlorosis and reddening of leaves due to increased production of anthocyanin pigments was observed at higher concentrations of O3. One-dimensional gel electrophoresis of leaves taken from NFC+30 showed reductions of major photosynthetic proteins, and differential response was observed between the two test cultivars. Decline in the number of male flowers at elevated O3 doses suggested damaging effect of O3 on reproductive structures which might be a cause of productivity losses. Variable carbon allocation pattern particularly to husk leaves, foliar injury, and damage of photosynthetic proteins led to significant reductions in economic yield at higher O3 doses. PCA showed that both the cultivars responded more or less similarly to O3 stress in their respective groupings of growth and yield parameters, but magnitude of their response was variable. It is further supported by difference in the significance of correlations between variables of yield and AOT40. Cultivar response reflects that QPM performed better than NQPM against elevated O3.

Six Indian cultivars of Vigna radiata L. (HUM-1, HUM-2, HUM-6, HUM-23, HUM-24 and HUM-26) were exposed with ambient and elevated (ambient + 10 ppb ozone (O3) for 6 h day(-1)) level of O3 in open top chambers. Ozone sensitivity was assessed by recording the magnitude of foliar visible injury and changes in various physiological parameters. All the six cultivars showed visible foliar symptoms due to O3, ranging 7.4 to 55.7 % injured leaf area. O3 significantly depressed total chlorophyll, photosynthetic rate (Ps), quantum yield (F(v)/F(m)) and total biomass although the extent of variation was cultivar specific. Cultivar HUM-1 showed maximum reduction in Ps and stomatal conductance. The fluorescence parameters also indicated maximum damage to PSII reaction centres of HUM-1. Injury percentage, chlorophyll loss, Ps, F(v)/F(m) and total biomass reduced least in HUM-23 depicting highest O3 resistance (R%).

The individual and interactive effects of supplemental UV-B (sUV-B) (ambient + 7.2 kJ m(-2) d(-1)) and elevated O3 (ambient + 10 ppb) were evaluated under field conditions using open top chambers on two cultivars, Padmini and T-397 of linseed (Linum usitatissimum L.). Mean monthly surface level of O3 concentrations varied from 27.7 ppb to 59.0 ppb during the experimental period. Both UV-B and O03 induced the production of ROS (H2O2 and O2*-), resulting in significant damage of membranes due to lipid peroxidation and electrolyte leakage. Synthesis of secondary metabolites (flavonoids, anthocyanin, lignin and wax) was also enhanced in all the treatments, whereas biomass and yield were reduced. Alterations in frequency of stomata and wax distribution were also observed through scanning electron microscopy (SEM). Cultivar Padmini was found to be more sensitive because of higher damage of membrane vis-a-vis reduction in biomass and seed yield. However, concentrations of flavonoids, anthocyanin, lignin and wax were higher in T-397, suggesting its relative resistance against applied stress. Combined exposure of sUV-B and O3 was less harmful, as compared to their individual treatment. Among the three treatments, O3 was found to be more detrimental for overall growth and sUV-B for economic yield.

Intraspecific variation in six cultivars of clover Trifolium alexandrinum L., (Bundel, Wardan, JHB-146, Saidi, Fahli, and Mescavi) has been studied with ambient and elevated O3 (ambient + 10 ppb O3) in open top chambers. Significant effect of elevated O3 was detected on different morphological, physiological, and biochemical parameters depicting differential response among the test cultivars. Results showed that the magnitude of O3 induced foliar injury symptoms varied in all the cultivars. Ozone significantly depressed photosynthetic rate, stomatal conductance, and photosynthetic efficiency, although variations were cultivar specific. Ozone treatment diminished total biomass of all the cultivars; reduction was highest in Wardan with least O3 resistance followed by Bundel, JHB-146, Saidi, Mescavi, and Fahli. According to the cumulative sensitive index, variations in the sensitivity showed that two cultivars (Wardan and Bundel) were sensitive to elevated O3, while other three cultivars (Fahli, Saidi, and Mescavi) were resistant, and JHB-146 showed intermediate sensitivity. Therefore, the present study supported the selection of sensitive cultivar of clover as a bioindicator for O3 under Indian conditions for the areas experiencing higher concentrations of O3.

Tropospheric ozone (O(3)) has become a serious threat to growth and yield of important agricultural crops over Asian regions including India. Effect of elevated O(3) (ambient+10ppb) was studied on Brassica campestris L. (cv. Sanjukta and Vardan) in open top chambers under natural field conditions. Eight hourly mean ambient O(3) concentration varied from 26.3ppb to 69.5ppb during the growth period. Plants under O(3) exposure showed reductions in photosynthetic rate, reproductive parameters, yield as well as seed and oil quality. Cultivar Sanjukta showed more reduction in photosynthetic characteristics, reproductive structures and seed and oil quality. However, total yield was more affected in Vardan. Exposure of O(3) increased the degree of unsaturation and level of PUFA, ω-6fatty acid, linolenic acid and erucic acid in oil indicating the deterioration of its quality. The study further confirmed that there is a correspondence between O(3) induced change in photosynthetic processes, reproductive development and yield and did not find any compensatory response in the final yield., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Rising O(3) concentrations in agricultural areas have been identified as a significant threat to crop production in Asia including India. The present work reports the results of a field study conducted to assess the usefulness of higher than recommended NPK dose in modifying the physiological, growth, yield, and seed quality responses of two mustard (Brassica campestris L. var. Vardan and Aashirwad) varieties under ambient ozone level at a rural site of India, using open-top chambers. Twelve hourly mean O(3) concentrations ranged between 27.7 and 59.04 ppb during the growth period. Plants in nonfiltered chambers (NFCs) showed reductions in photosynthetic rate, stomatal conductance, and growth parameters compared to the plants in filtered chambers (FCs), but reductions were of lower magnitude at 1.5 times recommended dose of NPK (1.5 RNPK) compared to recommended (RNPK). Yield and seed quality reduced significantly in plants of NFCs compared to FCs at RNPK, but no significant differences were recorded at 1.5 RNPK. There were higher N uptake and N uptake efficiency of plants in FCs compared to NFCs. Nitrogen utilization efficiency increased in Vardan, but decreased in Aashirwad in NFCs compared to FCs suggesting higher capability of N acquisition and utilization under ambient O(3), which led to a less pronounced reduction in the yield of the former than the latter variety. The differential nitrogen utilization efficiency in these varieties may be potentially used as measure of sensitivity characteristics in breeding programs for yield improvement in mustard under the present trend of increase in O(3) concentrations.

A continuous increase in the background level of tropospheric ozone (O(3)) has become a major challenge for present and future agricultural productivity at worldwide. Present study was designed to assess the impact of ambient (present) and elevated (future) concentrations of O(3) on two cultivars of Indian rice (Oryza sativa L. cvs Malviya dhan 36 and Shivani). Shoot and root lengths, number of leaves and total leaf area were severely affected by both ambient and elevated concentrations of O(3). Photosynthetic rate, stomatal conductance and photosynthetic efficiency (F(v)/F(m)) were also reduced by O(3) with more drastic effects under elevated levels of O(3). Leaf proteome showed reduction of some major proteins due to O(3). Pollen viability, viable florets plant(-1) and economic yield also showed significant negative impact under O(3)-exposure in both the test cultivars. The experimental findings depict that both the cultivars of rice demonstrate differential response against O(3), and it may help the plant breeders in selection of resistant cultivars for the area having higher concentrations of O(3)., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Ozone is now considered to be the second most important gaseous pollutant in our environment. The phytotoxic potential of O₃ was first observed on grape foliage by B.L. Richards and coworkers in 1958 (Richards et al. 1958). To date, unsustainable resource utilization has turned this secondary pollutant into a major component of global climate change and a prime threat to agricultural production. The projected levels to which O₃ will increase are critically alarming and have become a major issue of concern for agriculturalists, biologists, environmentalists and others plants are soft targets for O₃. Ozone enters plants through stomata, where it disolves in the apoplastic fluid. O₃ has several potential effects on plants: direct reaction with cell membranes; conversion into ROS and H₂O₂ (which alters cellular function by causing cell death); induction of premature senescence; and induction of and up- or down-regulation of responsive components such as genes , proteins and metabolites. In this review we attempt to present an overview picture of plant O₃ interactions. We summarize the vast number of available reports on plant responses to O₃ at the morphological, physiological, cellular, biochemical levels, and address effects on crop yield, and on genes, proteins and metabolites. it is now clear that the machinery of photosynthesis, thereby decreasing the economic yield of most plants and inducing a common morphological symptom, called the "foliar injury". The "foliar injury" symptoms can be authentically utilized for biomonitoring of O₃ under natural conditions. Elevated O₃ stress has been convincingly demonstrated to trigger an antioxidative defense system in plants. The past several years have seen the development and application of high-throughput omics technologies (transcriptomics, proteomics, and metabolomics) that are capable of identifying and prolifiling the O₃-responsive components in model and nonmodel plants. Such studies have been carried out ans have generated an inventory of O₃-Responsive components--a great resource to the scientific community. Recently, it has been shown that certain organic chemicals ans elevated CO₂ levels are effective in ameliorating O₃-generated stress. Both targeted and highthroughput approaches have advanced our knowledge concerning what O₃-triggerred signaling and metabolic pathways exist in plants. Moreover, recently generated information, and several biomarkers for O₃, may, in the future, be exploited to better screen and develop O₃-tolerant plants.

The present investigation used Linum usitatissimum L. cv. Padmini (linseed), under field conditions in open-top chambers, to evaluate the interactive effects of supplemental ultraviolet-B (sUV-B; ambient +7.2 kJ · m(-2) · d(-1)) and ozone (O(3); ambient +10 ppb). Treatment of plants with sUV-B and O(3) , individually or in combination, caused several changes in enzymatic and non-enzymatic components of the antioxidant defence system. Photo-oxidative damage caused by sUV-B and O(3) , included lipid peroxidation, changed protein profiles and caused DNA strand breakage. One-dimensional gel electrophoresis revealed that proteins of 222.24 and 50.5 kDa are specific and appear after sUV-B and O(3) exposure, and could be used as indicator proteins. Effects of sUV-B and O(3) given separately are more detrimental as compared to combined treatment. Mutational and structural alterations in linseed DNA after these stresses were also examined using RAPD with ten different primers. The study concluded that both stresses, i.e. sUV-B and O(3) , are phytotoxic, causing significant changes in metabolites, antioxidants, the leaf proteome and the genome of linseed, but their interactive effect was always less than additive., (© 2010 German Botanical Society and The Royal Botanical Society of the Netherlands.)

Three Indian black gram cultivars (Vigna mungo L. cv. Barkha, Shekhar and TU-94-2) were grown at a tropical suburban site in Varanasi, India to evaluate the varietal differences in response to ambient O(3) under field conditions using ethylenediurea (EDU). EDU (400 ppm) was given as soil drench at 10-day intervals during the growth period of the cultivars. O(3) monitoring data clearly showed high concentrations with a mean value ranging between 41.3 and 59.9 ppb. EDU treatment caused significant increases in various growth parameters and total biomass accumulation in Barkha and Shekhar. EDU caused retention of more biomass in leaves during vegetative period and translocated more photosynthates towards reproductive parts, which resulted into yield enhancement. Weight of seeds plant(-1) was higher by 36.4% and 35.6% in Barkha and Shekhar, respectively, treated with EDU compared to non-EDU-treated plants. However, TU-94-2 did not exhibit any significant difference in weight of seeds plant(-1). Starch, total sugar, amino acids and K contents increased in seeds of EDU-treated plants leading to improvement in quality response index (QRI) of seeds. EDU helped in identifying the cultivar susceptibility to O(3) stress and therefore is very useful as a monitoring tool to assess the impact of ambient O(3) on plants under natural field conditions particularly in areas experiencing moderate concentrations of O(3)., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Ozone (O3), a potent air pollutant and a significant greenhouse gas, has been recognized as a major component of global climate change. However, current increasing trends in its background level are projecting a more severe threat to natural and cultivated plants in the near future. The present study has been designed to evaluate the impact of elevated concentrations of O3 on phenotypical, physiological, and biochemical traits in two high-yielding cultivars of wheat, followed by analysis of the leaf proteome using one/two-dimensional gel electrophoresis (1-/2-DGE) coupled to immunoblotting and mass spectrometry analyses under near-natural conditions using open top chambers. Prominently, O3 exposure caused specific foliar injury in both the wheat cultivars. Results also showed that O3 stress significantly decreased photosynthetic rate, stomatal conductance, and chlorophyll fluorescence kinetics (Fv/Fm) in test cultivars. Biochemical evaluations further revealed a higher loss in photosynthetic pigments, whereas a significantly induced antioxidant system under elevated O3 concentrations pointed toward an ability of O3 to generate oxidative stress. 1-DGE analysis showed drastic reductions in the abundantly present ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large and small subunits. Western blot analysis confirmed induced accumulation of antioxidative enzymes like superoxide dismutase and ascorbate peroxidase protein(s) and common defense/stress-related thaumatin-like protein(s). 2-DGE analysis revealed a total of 38 differentially expressed protein spots, common in both the wheat cultivars. Among those, some major leaf photosynthetic proteins (including RuBisCO and RuBisCO activase) and important energy metabolism proteins (including ATP synthase, aldolase, and phosphoglycerate kinase) were drastically reduced, whereas some stress/defense-related proteins (such as harpin-binding protein and germin-like protein) were induced. In all, the present study reveals an intimate molecular network provoked by O3 affecting photosynthesis and triggering antioxidative defense and stress-related proteins culminating in accelerated foliar injury in wheat plants.

The present study showed a possibility to use phenotypic and proteomic responses in rice plants as an in vivo biomarker to detect higher concentrations of ambient ozone (O(3)). The investigation was done on two cultivars of Indian rice using open top chambers ventilated with charcoal filtered air, ambient air, ambient air with 10 ppb O(3) exposure and ambient air with 20 ppb O(3) exposure at a rural site of Varanasi, India. Results showed that the magnitude of O(3) induced specific type of foliar injury directly depends on the duration and concentration of O(3) exposure. Even the internal protein profile of injured and normal leaf demonstrated a differential expression, which directly indicates towards the molecular basis of plant's response against O(3).

Three ethylene diurea (EDU) concentrations (0, 150 and 300 mg/L) were used to evaluate the negative impact of ozone (O3) on two cultivars of Trifolium repens L. cv. Vardan and Bundel grown under natural field conditions in a suburban area of Varanasi, India. Mean O3 concentrations varied from 30.3 to 46.6 microg/L during the experimental period. Higher photosynthetic pigments and ascorbic acid concentrations were noticed in both EDU-treated cultivars over non-EDU-treated ones, but a reverse trend was found for lipid peroxidation. Growth parameters and biomass also showed increments under EDU treatment of both cultivars. The ratio of variable fluorescence to maximum fluorescence increased significantly in Vardan but not in Bundel upon EDU treatment. Results revealed that EDU concentration of 300 mg/L was more effective to combat the oxidative stress as well as protecting plants from O3 injury symptoms. The test cultivar Vardan is relatively sensitive to O3, thereby can be used as a bioindicator of O3 pollution in areas having higher O3 concentrations. Results also indicated that Bundel has more efficient antioxidant defense system than Vardan and hence was more tolerant to O3 stress.

Increase in concentrations of tropospheric ozone (O(3)) is one of the main factors affecting world agriculture production. Tropical countries including India are at greater risk due to their meteorological conditions (high solar radiation and temperature) being conducive to the formation of O(3). The most effective anti-ozonant chemical is N-[2-(2-oxo-1-imidazolidinyl) ethyl]-N-phenylurea or ethylene diurea (EDU). Due to its specific characteristics, EDU has been used in the field as a phytomonitoring agent to assess crop losses due to O(3). Field experiments were conducted on five local cultivars of wheat (Triticum aestivum L. cv HUW234, HUW468, HUW510, PBW343, and Sonalika) grown under natural field conditions in a suburban area of Varanasi, Uttar Pradesh, India during December 2006 to March 2007 to determine the impact of O(3) on their growth and yield characteristics. Mean monthly O(3) concentrations varied between 35.3 ppb and 54.2 ppb at the experimental site. EDU treatment positively affected various growth and yield parameters with difference between cultivars. EDU-treated plants showed increase in shoot and root length, leaf area, absolute growth rate, relative growth rate, and net primary productivity, indicating O(3) induced suppression in growth. EDU treatment was highly significant in different cultivars for total biomass and test weight but not for harvest index. Yield per plant was higher by 25.6%, 24%, 20.4%, 8.6%, and 1.9% in EDU-treated cultivars HUW468, Sonalika, HUW510, HUW234, and PBW343, respectively, than non-EDU-treated ones. These results clearly indicate the sensitivity of all the wheat cultivars to ambient levels of O(3) with cv HUW468 appearing to be most sensitive. The present study also supports the view that EDU has great potential in alleviating the unfavorable effects of O(3) and can be effectively used as a monitoring tool to assess growth and yield losses in areas experiencing elevated concentrations of O(3).

The antiozonant EDU (ethylenediurea) was used to assess the impact of ambient O(3) under field conditions on five cultivars of tropical wheat (Triticum aestivum L.). EDU solution (0 ppm and 400 ppm) was applied as soil drench (100 ml plant(-1)) 10 days after germination (DAG) at an interval of 12 days. EDU-treated plants showed significant increments in stomatal conductance, photosynthetic rate, variable fluorescence, total chlorophyll, ascorbic acid, proline and protein contents and protective enzymes (POX, SOD and APX) activities in HUW468, HUW510 and HUW234 cultivars, while, a reverse trend was observed for lipid peroxidation. EDU application restored grain yield significantly by maintaining higher levels of antioxidants, metabolites and enzymes in cultivars HUW468 and HUW510. Sonalika and PBW343 showed least response of measured parameters under EDU treatment suggesting their greater resistance to O(3). EDU, thus proved its usefulness in screening suitable wheat cultivars for areas experiencing elevated concentrations of O(3).

A field study was conducted to evaluate the suitability of ethylene diurea (N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N'-phenylurea; EDU) in assessing the impact of O3 on mung bean plants (Vigna radiata L. var. Malviya Jyoti) grown in suburban area of Allahabad city situated in a dry tropical region of India. EDU is a synthetic chemical having anti-ozonant property. Mean monthly O3 concentration varied between 64 and 69 microg m(-3) during the experimental period. In comparison to EDU-treated plants, non-EDU-treated plants showed significant reductions in plant growth and yield under ambient conditions. Significant favourable effects of EDU-application were observed with respect to photosynthetic pigments, soluble protein, ascorbic acid and phenol contents. EDU-treated plants maintained higher levels of pigments, protein and ascorbic acid in foliage as compared to non-EDU-treated ones. The study clearly demonstrated that EDU alleviates the unfavourable effects of O3 on mung bean plants, and therefore can be used as a tool to assess the growth and yield losses in areas having higher O3 concentrations.

Enhanced anthropogenic activities affect agricultural production in many ways. An integrated study assessing the combined impact of increased tropospheric ozone and carbon dioxide on agriculture is still elusive. An investigation was carried out to study the impacts of elevated levels of CO2 (eCO2) and O3 (eO3) and their interaction on a C4 plant, maize cultivar DHM117, based on growth, physiological, and yield responses using open top chambers. Plant growth parameters remained unaffected due to eCO2 exposure. However, the toxic impact of O3 was alleviated to some extent under eCO2 concentration, as revealed by the increment in total biomass under combined exposure. CO2 fertilization increased yield by 13.8%, while a reverse trend was observed under eO3 treatment. Lowering of stomatal conductance under eCO2 partially protected the plants against O3 uptake and resulting phytotoxicity. Stimulation of total phenolic and phenylalanine ammonia lyase (PAL) activity confirmed the activation of defence mechanism to counter the oxidative stress under high O3 dose. Likewise, a significant rise in the activities of antioxidative enzymes [peroxidase (POX) and ascorbate peroxidase (APX)] involved in defence mechanisms was observed under ECO2 + EO3, leading to a reduced accumulation of H2O2 content in the test plant. This observation was further affirmed by the redundancy analysis, which revealed the significant role of enzymatic antioxidants (explained variance = 15.5%) in compensating for the damaging effect of reactive oxygen species (ROS), translating to significant changes in yield attributes under combined exposure of CO2 and O3. [ABSTRACT FROM AUTHOR]

The authors demonstrate that ozone exposure of individual multiwalled carbon nanotubes (CNTs) results in up to threefold increase in CNT conductivity and 50% decrease in carrier transport activation energy. Ozone exposure induces bond breaking in the individual shells and promotes cross-shell bridging via sp3 bond formation. Intershell bridging facilitates charge carrier hopping to inner shells, which can serve as additional charge carrier transport pathways, offsetting the effect of defect-scattering-induced conductivity decrease. The CNT etch rate systematically increases with decreasing initial outer diameter and decreases with incremental ozone exposure, which could provide means to controllably tailor the CNT conductance. The results suggest that controlled defect creation could be an attractive strategy to induce electrical conductivity increase in multiwalled CNTs for use in nanodevice wiring and related applications. [ABSTRACT FROM AUTHOR]