Assessment of Ozone Sensitivity in Three Wheat Cultivars Using Ethylenediurea

Exogenous protectants alleviate ozone stress in Trifolium repens: Impacts on plant growth and endophytic fungi

Industrialization-driven surface ozone (O3) pollution significantly impairs plant growth. This study evaluates the effectiveness of exogenous protectants [3 mg L⁻1 abscisic acid (ABA), 400 mg L⁻1 ethylenediurea (EDU), and 80 mg L⁻1 spermidine (Spd)] on Trifolium repens subjected to O3 stress in open-top chambers, focusing on plant growth and dynamics of culturable endophytic fungal communities. Results indicate that O3 exposure adversely affects photosynthesis, reducing root biomass and altering root structure, which further impacts the ability of plant to absorb essential nutrients such as potassium (K), magnesium (Mg), and zinc (Zn). Conversely, the application of ABA, EDU, and Spd significantly enhanced total biomass and chlorophyll content in T. repens. Specifically, ABA and Spd significantly improved root length, root surface area, and root volume, while EDU effectively reduced leaves' malondialdehyde levels, indicating decreased oxidative stress. Moreover, ABA and Spd treatments significantly increased leaf endophytic fungal diversity, while root fungal abundance declined. The relative abundance of Alternaria in leaves was substantially reduced by these treatments, which correlated with enhanced chlorophyll content and photosynthesis. Concurrently, EDU and Spd treatments increased the abundance of Plectosphaerella, enhance the absorption of K, Ca, and Mg. In roots, ABA treatment increased the abundance of Paecilomyces, while Spd treatment enhanced the presence of Stemphylium, linked to improved nitrogen (N), phosphorus (P), and K uptake. These findings suggest that specific symbiotic fungi mitigate O3-induced stress by enhancing nutrient absorption, promoting growth. This study highlights the potential of exogenous protectants to enhance plant resilience against O3 pollution through modulating interactions with endophytic fungal communities.

Ozone-induced oxidative stress alleviation by biogenic silver nanoparticles and ethylenediurea in mung bean (Vigna radiata L.) under high ambient ozone

Ground-level ozone (O3) is the most phytotoxic secondary air pollutant in the atmosphere, severely affecting crop yields worldwide. The role of nanoparticles (NP) in the alleviation of ozone-induced yield losses in crops is not known. Therefore, in the present study, we investigated the effects of biogenicB-AgNPs on the mitigation of ozone-induced phytotoxicity in mung bean and compared its results with ethylenediurea (EDU) for the first time. Two mung bean cultivars (Vigna radiata L., Cv. SML-668 and PDM-139) were foliar sprayed with weekly applications of B-AgNPs (0 = control, 10 and 25 ppm) and EDU (0 = control, 200 and 300 ppm) until maturation phase. Morphological, physiological, enzymatic, and non-enzymatic antioxidant data were collected 30 and 60 days after germination (DAG). The mean O3 and AOT40 values (8 h day-1) during the cultivation period were approximately 52 ppb and 4.4 ppm.h, respectively. More biomass was accumulated at the vegetative phase due to the impact of B-AgNPs and EDU, and more photosynthates were transported to the reproductive phase, increasing yield. We observed that the 10 ppm B-AgNPs treatment had a more noticeable impact on yield parameters and lower Ag accumulation in seeds for both cultivars. Specifically, SML-668 cultivar treated with 10 ppm B-AgNPs (SN1) showed greater increases in seed weight plant-1 (124.97%), hundred seed weight (33.45%), and harvest index (37.53%) in comparison to control. Our findings suggest that B-AgNPs can enhance growth, biomass, yield, and seed quality, and can improve mung bean ozone tolerance. Therefore, B-AgNPs may be a promising protectant for mung bean.

Elevated tropospheric ozone and crop production: potential negative effects and plant defense mechanisms

Ozone (O3) levels on Earth are increasing because of anthropogenic activities and natural processes. Ozone enters plants through the leaves, leading to the overgeneration of reactive oxygen species (ROS) in the mesophyll and guard cell walls. ROS can damage chloroplast ultrastructure and block photosynthetic electron transport. Ozone can lead to stomatal closure and alter stomatal conductance, thereby hindering carbon dioxide (CO2) fixation. Ozone-induced leaf chlorosis is common. All of these factors lead to a reduction in photosynthesis under O3 stress. Long-term exposure to high concentrations of O3 disrupts plant physiological processes, including water and nutrient uptake, respiration, and translocation of assimilates and metabolites. As a result, plant growth and reproductive performance are negatively affected. Thus, reduction in crop yield and deterioration of crop quality are the greatest effects of O3 stress on plants. Increased rates of hydrogen peroxide accumulation, lipid peroxidation, and ion leakage are the common indicators of oxidative damage in plants exposed to O3 stress. Ozone disrupts the antioxidant defense system of plants by disturbing enzymatic activity and non-enzymatic antioxidant content. Improving photosynthetic pathways, various physiological processes, antioxidant defense, and phytohormone regulation, which can be achieved through various approaches, have been reported as vital strategies for improving O3 stress tolerance in plants. In plants, O3 stress can be mitigated in several ways. However, improvements in crop management practices, CO2 fertilization, using chemical elicitors, nutrient management, and the selection of tolerant crop varieties have been documented to mitigate O3 stress in different plant species. In this review, the responses of O3-exposed plants are summarized, and different mitigation strategies to decrease O3 stress-induced damage and crop losses are discussed. Further research should be conducted to determine methods to mitigate crop loss, enhance plant antioxidant defenses, modify physiological characteristics, and apply protectants.

Effect of ozone stress on crop productivity: A threat to food security

Tropospheric ozone (O3), the most important phytotoxic air pollutant, can deteriorate crop quality and productivity. Notably, satellite and ground-level observations-based multimodel simulations demonstrate that the present and future predicted O3 exposures could threaten food security. Hence, the present study aims at reviewing the phytotoxicity caused by O3 pollution, which threatens the food security. The present review encompasses three major aspects; wherein the past and prevailing O3 concentrations in various regions were compiled at first, followed by discussing the physiological, biochemical and yield responses of economically important crop species, and considering the potential of O3 protectants to alleviate O3-induced phytotoxicity. Finally, the empirical data reported in the literature were quantitatively analysed to show that O3 causes detrimental effect on physiological traits, photosynthetic pigments, growth and yield attributes. The review on prevailing O3 concentrations over various regions, where economically important crop are grown, and their negative impact would support policy makers to implement air pollution regulations and the scientific community to develop countermeasures against O3 phytotoxicity for maintaining food security.

Secondary metabolites responses of plants exposed to ozone: an update

Tropospheric ozone (O3) is a secondary pollutant that causes oxidative stress in plants due to the generation of excess reactive oxygen species (ROS). Phenylpropanoid metabolism is induced as a usual response to stress in plants, and induction of key enzyme activities and accumulation of secondary metabolites occur, upon O3 exposure to provide resistance or tolerance. The phenylpropanoid, isoprenoid, and alkaloid pathways are the major secondary metabolic pathways from which plant defense metabolites emerge. Chronic exposure to O3 significantly accelerates the direction of carbon flows toward secondary metabolic pathways, resulting in a resource shift in favor of the synthesis of secondary products. Furthermore, since different cellular compartments have different levels of ROS sensitivity and metabolite sets, intracellular compartmentation of secondary antioxidative metabolites may play a role in O3-induced ROS detoxification. Plants' responses to resource partitioning often result in a trade-off between growth and defense under O3 stress. These metabolic adjustments help the plants to cope with the stress as well as for achieving new homeostasis. In this review, we discuss secondary metabolic pathways in response to O3 in plant species including crops, trees, and medicinal plants; and how the presence of this stressor affects their role as ROS scavengers and structural defense. Furthermore, we discussed how O3 affects key physiological traits in plants, foliar chemistry, and volatile emission, which affects plant-plant competition (allelopathy), and plant-insect interactions, along with an emphasis on soil dynamics, which affect the composition of soil communities via changing root exudation, litter decomposition, and other related processes.

Ethylenediurea protects against ozone phytotoxicity not by adding nitrogen or controlling stomata in a stomata-unresponsive hybrid poplar

Ozone (O₃) pollution is a persistent environmental issue worldwide, which causes widespread damage to vegetation, deteriorating plant health and reducing plant productivity. Ethylenediurea (EDU) is a synthetic chemical that has been widely applied in scientific studies as a protectant against O₃ phytotoxicities. Despite four decades of active research, the exact mechanisms to explain its mode of action remain unclear. Here, we aimed to reveal whether EDU's phytoprotective property is due to its control over stomatal regulation and/or its action as a nitrogen (N) fertilizer, utilizing stomatal-unresponsive plants of a hybrid poplar (Populus koreana × trichocarpa cv. Peace) grown in a free-air O₃-concenctration enrichment (FACE) facility. Plants were treated with water (WAT), EDU (400 mg L^-1), or EDU's constitutive amount of N every nine days, and exposed to ambient (AOZ) or elevated (EOZ) O₃ during a growing season (June-September). EOZ led to extensive foliar injuries (but protected against rust disease), lower photosynthetic rate (A), impaired dynamics of responses of A to changes in light intensity, and smaller total plant leaf area. EDU protected against common phytotoxicities caused by EOZ without inducing stomatal closure, since stomatal conductance (g_s) was generally unresponsive to the experimental treatments. EDU also modulated the dynamic response of A to light fluctuations under O₃ stress. N addition acted as a fertilizer but did not satisfactorily protect plants against O₃ phytotoxicities. The results suggest that EDU protects against O₃ phytotoxicity not by adding N or controlling stomata, which provides a new insight into our understanding of the mode of action of EDU as a protectant against O₃ phytotoxicity.

Sensitivity of agricultural crops to tropospheric ozone: a review of Indian researches

Tropospheric ozone (O₃) is a long-range transboundary secondary air pollutant, causing significant damage to agricultural crops worldwide. There are substantial spatial variations in O₃ concentration in different areas of India due to seasonal and geographical variations. The Indo-Gangetic Plain (IGP) region is one of the most crop productive and air-polluted regions in India. The concentration of tropospheric O₃ over the IGP is increasing by 6-7.2% per decade. The annual trend of increase is 0.4 ± 0.25% year^-1 over the Northeastern IGP. High O₃ concentrations were reported during the summer, while they were at their minimum during the monsoon months. To explore future potential impacts of O₃ on major crop plants, the responses of different crops grown under ambient and elevated O₃ concentrations were compared. The studies clearly showed that O₃ is an important stress factor, negatively affecting the yield of crops. In this review, we have discussed yield losses in agricultural crops due to rising O₃ pollution and variations in O₃ sensitivity among cultivars and species. The use of ethylene diurea (EDU) as a research tool in assessing the losses in yield under ambient and elevated O₃ levels also discussed. Besides, an overview of interactive effects of O₃ and nitrogen on crop productivity has been included. Several recommendations are made for future research and policy development on rising concentration of O₃ in India.

Elevated ozone phytotoxicity ameliorations in mung bean {Vigna radiata (L.) Wilczek} by foliar nebulization of silicic acid and ascorbic acid

The present work provides an insight into the development of biochemical adaptations in mung beans against ozone (O₃) toxicity. The study aims to explore the O₃ stress tolerance potential of mung bean genotypes under exogenous application of growth regulators. The seeds of twelve mung bean genotypes were grown in plastic pots under controlled conditions in the glasshouse. Six treatments, control (ambient ozone level 40-45 ppb), ambient O₃ with ascorbic acid, ambient ozone with silicic acid, elevated ozone (120 ppb), elevated O₃ with ascorbic acid (10 mM), and elevated ozone with silicic acid (0.1 mM) were applied. The O₃ fumigation was carried out using an O₃ generator. The results revealed that ascorbic acid and silicic acid application decreased the number of plants with foliar O₃ injury symptoms in different degrees, i.e., zero, first, second, third, and fourth degrees; whereas 0-4 degree symptoms represent, no symptoms, symptoms occupying < 1/4, 1/4-1/2, 1/2-3/4, and > 3/4 of the total foliage area, respectively. Application of ascorbic acid and silicic acid also prevented the plants from the negative effects of O₃ in terms of fresh as well as dry matter production, leaf chlorophyll, carotenoids, soluble proteins and ascorbic acid, proline, and malondialdehyde (MDA) contents. Overall, silicic acid application proved more effective in reducing the negative effects of O₃ on mung bean genotypes as compared to that of the ascorbic acid. Three mung bean genotypes (NM 20-21, NM-2006, and NM-2016) were identified to have a better adaptive mechanism for O₃ toxicity tolerance and may be good candidates for future variety development programs.

Ozone pollution threatens the production of major staple crops in East Asia

East Asia is a hotspot of surface ozone (O₃) pollution, which hinders crop growth and reduces yields. Here, we assess the relative yield loss in rice, wheat and maize due to O₃ by combining O₃ elevation experiments across Asia and air monitoring at about 3,000 locations in China, Japan and Korea. China shows the highest relative yield loss at 33%, 23% and 9% for wheat, rice and maize, respectively. The relative yield loss is much greater in hybrid than inbred rice, being close to that for wheat. Total O₃-induced annual loss of crop production is estimated at US$63 billion. The large impact of O₃ on crop production urges us to take mitigation action for O₃ emission control and adaptive agronomic measures against the rising surface O₃ levels across East Asia.

Evaluating impacts of biogenic silver nanoparticles and ethylenediurea on wheat (Triticum aestivum L.) against ozone-induced damages

Tropospheric ozone (O₃) is a phytotoxic pollutant that leads to a reduction in crop yield. Nanotechnology offers promising solutions to stem such yield losses against abiotic stresses. Silver nanoparticles are major nanomaterials used in consumer products however, their impact on crops under abiotic stress is limited. In this study, we evaluated the anti-ozonant efficacy of biogenic silver nanoparticles (B-AgNPs) and compared them with a model anti-ozonant ethylenediurea (EDU) against ozone phyto-toxicity. Growth, physiology, antioxidant defense, and yield parameters in two wheat cultivars (HD-2967 & DBW-17), treated with B-AgNPs (25 mg/L and 50 mg/L) and EDU (150 mg/L and 300 mg/L), were studied at both vegetative and reproductive stages. During the experimental period, the average ambient ozone concentration and accumulated dose of ozone over a threshold of 40 ppb (AOT40) (8 h day^-1) were found to be 60 ppb and 6 ppm h, respectively, which were sufficient to cause ozone-induced phyto-toxicity in wheat. Growth and yield for B-AgNPs as well as EDU-treated plants were significantly higher in both the tested cultivars over control ones. However, 25 mg/L B-AgNPs treatment showed a more pronounced effect in terms of yield attributes and its lower accumulation in grains for both cultivars. DBW-17 cultivar responded better with B-AgNPs and EDU treatments as compared to HD-2967. Meanwhile, foliar exposure of B-AgNPs (dose; 25 mg/L) significantly enhanced grain weight plant^-1, thousand-grain weight, and harvest index by 54.22 %, 29.46 %, and 14.21 %, respectively in DBW-17, when compared to control. B-AgNPs could enhance ozone tolerance in wheat by increasing biochemical and physiological responses. It is concluded that B-AgNPs at optimum concentrations were as effective as EDU, hence could be a promising ozone protectant for wheat.

Response of rice (Oryza sativa L.) cultivars to elevated ozone stress

The plant response to elevated ozone stress reveals inter-species and intra-species disparity. Ozone-induced crop yield loss is predicted to increase in the future, posing a threat to the world economy. This study aims to evaluate the cultivar specific variation in rice exposed to elevated ozone. Fifteen short-duration rice cultivars were exposed to 50 ppb ozone for 30 days at reproductive stage. The physiological, biochemical, growth and yield traits of all test cultivars were significantly affected in response to elevated ozone. On an average, ozone stress decreased the tiller number by 22.52%, number of effective tillers by 30.43%, 1000 grain weight by 0.62% and straw weight by 23.83% over control. Spikelet sterility increased by 19.26% and linear multiregression 3D model significantly fits the spikelet sterility and photosynthetic traits with the R² of 0.74 under elevated ozone. Principal Component Analysis with total variance of 57.5% categorized 15 rice cultivars into four major groups, i.e., ozone sensitive (MDU6, TRY(R)2 and ASD16), moderately ozone sensitive (ASD18, ADT43, and MDU5), moderately ozone tolerant (ADT37, ADT(R)45, TPS5, Anna(R)4, PMK(R)3, and ADT(R)48), and ozone tolerant (CO51, CO47, and ADT36). This study indicates that the different responses of rice cultivars to elevated ozone stress through a change in plant physiology, biochemical, growth, and yield traits and the results directed to provide scientific information on plant adaptations to ozone stress and helps in efforts to search ozone tolerant gene for plant breeding.

Role of antioxidant pool in management of ozone stress through soil nitrogen amendments in two cultivars of a tropical legume

The present experiment was done on two different cultivars of a tropical legume, Cymopsis tetragonoloba L. Taub. (cluster bean) cvv. Pusa-Naubahar (PUSA-N) and Selection-151 (S-151). The experiment was conducted under ambient ozone (O3) conditions with inputs of three different doses of inorganic nitrogen (N1, recommended; N2, 1.5-times recommended and N3, 2-times recommended) as well as control plants. The objective of this study was to evaluate the effectiveness of soil nitrogen amendments in management of ambient ozone stress in the two cultivars of C. tetragonoloba. Our experiment showed that nitrogen amendments can be an efficient measure to manage O3 injury in plants. Stimulation of antioxidant enzyme activities under nitrogen amendments is an important feature of plants that help plants cope with ambient O3 stress. Nitrogen amendments strengthened the antioxidant machinery in a more effective way in the tolerant cultivar PUSA-N, while in the sensitive cultivar S-151, avoidance strategy marked by more reduction in stomatal conductance was more prominent. Enzymes of the Halliwell-Asada pathway, especially ascorbate peroxidase and glutathione reductase, were more responsive and synchronised in PUSA-N than S-151, under similar nitrogen amendment regimes and were responsible for the differential sensitivities of the two cultivars of C. tetragonoloba. The present study shows that 1.5-times recommended dose of soil nitrogen amendments was sufficient in partial mitigation of O3 injury and the higher nitrogen dose (2-times recommended, in our case), did not provide any extra advantage to the plant's metabolism compared with plants treated with the lower nitrogen dose (1.5-times recommended).

Exogenous application of chemicals for protecting plants against ambient ozone pollution: What should come next?

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.

Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings

Japanese larch (Larix kaempferi (Lamb.) Carr.) and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere. Ground-level ozone (O₃) concentrations have increased since the pre-industrial era, and research projects showed that Japanese larch is susceptible to elevated O₃ exposures. Therefore, methodologies are needed to (1) protect Japanese larch against O₃ damage and (2) conduct biomonitoring of O₃ in Japanese larch forests and, thus, monitor O₃ risks to Japanese larch. For the first time, this study evaluates whether the synthetic chemical ethylenediurea (EDU) can protect Japanese larch against O₃ damage, in two independent experiments. In the first experiment, seedling communities, simulating natural regeneration, were treated with EDU (0, 100, 200, and 400 mg L^-1) and exposed to either ambient or elevated O₃ in a growing season. In the second experiment, individually-grown saplings were treated with EDU (0, 200 and 400 mg L^-1) and exposed to ambient O₃ in two growing seasons and to elevated O₃ in the succeeding two growing seasons. The two experiments revealed that EDU concentrations of 200-400 mg L^-1 could protect Japanese larch seedling communities and individual saplings against O₃-induced inhibition of growth and productivity. However, EDU concentrations ≤ 200 mg L^-1 did offer only partial protection when seedling communities were coping with higher level of O₃-induced stress, and only 400 mg EDU L^-1 fully protected communities under higher stress. Therefore, we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O₃-induced stress is that of 400 mg EDU L^-1. The results of this study can provide a valuable resource of information for applied forestry in an O₃-polluted world.

Plant susceptibility to ozone: A tower of Babel?

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.