Ozone risk assessment of castor (Ricinus communis L.) cultivars using open top chamber and ethylenediurea (EDU)

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.

Physiological and molecular responses of different rose (Rosa hybrida L.) cultivars to elevated ozone levels

The increasing ground-level ozone (O₃) pollution resulting from rapid global urbanization and industrialization has negative effects on many plants. Nonetheless, many gaps remain in our knowledge of how ornamental plants respond to O₃. Rose (Rosa hybrida L.) is a commercially important ornamental plant worldwide. In this study, we exposed four rose cultivars ("Schloss Mannheim," "Iceberg," "Lüye," and "Spectra") to either unfiltered ambient air (NF), unfiltered ambient air plus 40 ppb O₃ (NF40), or unfiltered ambient air plus 80 ppb O₃ (NF80). Only the cultivar "Schloss Mannheim" showed significant O₃-related effects, including foliar injury, reduced chlorophyll content, reduced net photosynthetic rate, reduced stomatal conductance, and reduced stomatal apertures. In "Schloss Mannheim," several transcription factor genes-HSF, WRKY, and MYB genes-were upregulated by O₃ exposure, and their expression was correlated with that of NCED1, PP2Cs, PYR/PYL, and UGTs, which are related to ABA biosynthesis and signaling. These results suggest that HSF, WRKY, and MYB transcription factors and ABA are important components of the plant response to O₃ stress, suggesting a possible strategy for cultivating O₃-tolerant rose varieties.

Role of Elevated Ozone on Development and Metabolite Contents of Lemongrass [Cymbopogon flexuosus (Steud.) (Wats.)]

The present study was conducted to assess the effect of elevated ozone stress on the development and metabolite contents of lemongrass, a medicinal plant. The experimental plant was exposed to two elevated ozone concentrations (ambient + 15 ppb, and ambient + 30 ppb) using open-top chambers. Samplings were carried out at 45 and 90 days after transplantation (DAT), for the analysis of different characteristics, while the metabolite contents of leaves and essential oils were analyzed at 110 DAT. Both the doses of elevated ozone had notable negative effects on the carbon fixation efficiency of plants, resulting in a significant reduction in plant biomass. Enzymatic antioxidant activity increased during the second sampling, which suggests that the scavenging of reactive oxygen species was more prominent in lemongrass during the later developmental stage. The results of the present study showed a stimulated diversion of resources towards the phenylpropanoid pathway, which is made evident by the increase in the number and contents of metabolites in foliar extract and essential oils of plants grown at elevated ozone doses, as compared to ambient ozone. Elevated ozone not only upregulated the contents of medicinally important components of lemongrass, it also induced the formation of some pharmaceutically active bio compounds. On the basis of this study, it is expected that increasing ozone concentrations in near future will enhance the medicinal value of lemongrass. However, more experiments are required to validate these findings.

Ozone control as a novel method to improve health-promoting bioactive compounds in red leaf lettuce (Lactuca sativa L.)

In this study, we determined the short-term effects of ozone exposure on the growth and accumulation of bioactive compounds in red lettuce leaves grown in a controlled environment plant factory with artificial light, also known as a vertical farm. During cultivation, twenty-day-old lettuce (Lactuca sativa L. var. Redfire) seedlings were exposed to 100 and 200 ppb of ozone concentrations for 72 h. To find out how plants react to ozone and light, complex treatments were done with light and ozone concentrations (100 ppb; 16 h and 200 ppb; 24 h). Ozone treatment with 100 ppb did not show any significant difference in shoot fresh weight compared to that of the control, but the plants exposed to the 200 ppb treatment showed a significant reduction in fresh weight by 1.3 fold compared to the control. The expression of most genes in lettuce plants exposed to 100 and 200 ppb of ozone increased rapidly after 0.5 h and showed a decreasing trend after reaching a peak. Even when exposed to a uniform ozone concentration, the pattern of accumulating bioactive compounds such as total phenolics, antioxidant capacity and total flavonoids varied based on leaf age. At a concentration of 200 ppb, a greater accumulation was found in the third (older) leaf than in the fourth leaf (younger). The anthocyanin of lettuce plants subjected to 100 and 200 ppb concentrations increased continuously for 48 h. Our results suggest that ozone control is a novel method that can effectively increase the accumulation of bioactive compounds in lettuce in a plant factory.

Assessment of ozone toxicity on cotton (Gossypium hirsutum L.) cultivars: Its defensive system and intraspecific sensitivity

Anthropogenic activities help the ozone formation at the troposphere which causes toxic effects on plants and humans. Ozone is a highly reactive gas that enters in plants through stomata and initiates the overproduction of ROS which causes oxidative stress in plants that lead to the destruction of membranal lipids, proteins, impaired the production of sugars and other metabolites and ultimately damage the cell. Presented study was conducted to assess the ozone toxicity on the biomass accumulation of cotton (Gossypium hirsutum L.) cultivars and the role of antioxidative activity in intraspecific sensitivity among the tested cultivars. Results showed that the ozone exposed plants have higher accumulation of H₂O₂ and MDA correspond to the EDU supplementation which increase the membrane permeability and adversely influence the protein, starch, and biomass accumulation and allocation of the experimental cotton cultivars. On the basis of biomass reduction, cotton cultivar ADC1 is the most sensitive cultivar, while cultivars G. Cot.21 > GADC-2 and G. Cot.13 is moderately sensitive and cultivar V-797 is the least sensitive to ozone stress. Activated defense mechanism such as enhanced activity of antioxidative compounds and enzymes detoxify the ROS by scavenging H₂O₂ and protects plants against damage. However, activation of defence is variable among the cultivars and corresponded to the biomass loss. Study concluded that the ozone sensitivity among the cotton cultivars depends on the scavenging of ROS. Further, study recommended cultivar ADC-1 as an assessment tool for ozone and cultivar V-797 for cultivation at ozone prone areas to minimize the agricultural loss.

Effects of ozone phytotoxicity in reducing the yield and nutritional quality of chilli (Capsicum annuum L.)

This study was designed to assess the effects of tropospheric ozone (O₃) on the yield and nutritional quality of chilli (Capsicum annuum L. cv. Pusa Jwala) using ethylene diurea (EDU) under field conditions in Peshawar, Pakistan. Average O₃ concentration ranged between 38 and 68 ppb which is high enough to cause phytotoxic effects. Accumulated ozone exposure over a threshold of 40 ppm h (AOT40) value calculated for 3-month period was found to be substantially higher, i.e., 7.3 ppm h. Various growth and yield parameters analyzed on weekly basis showed that the plant height (6.3%), number of flowers (15%), fruits (36%), and total dry biomass (30%) and its nutritional quality parameters such as mean crude protein, fat, and fiber showed 24%, 100%, and 12% better results in EDU-treated plants as compared with control, respectively. However, mineral contents showed no significant difference (p < 0.05) for both the groups. The results of this study concluded that ambient O₃ is a threat to the selected plant species thus affecting its quality and yield and EDU remains successful in protecting the chilli (Capsicum annuum L.) against the negative effects of tropospheric ozone.

Elevated Ozone Levels Affect Metabolites and Related Biosynthetic Genes in Tartary Buckwheat

Global climate change and the industrial revolution have increased the concentration of tropospheric ozone, a photochemical air pollutant that can negatively affect plant growth and crop production. In the present study, we investigated the effects of O₃ on the metabolites and transcripts of tartary buckwheat. A total of 36 metabolites were identified by gas chromatography coupled with time-of-flight mass spectrometry, and principal component analysis was performed to verify the metabolic differences between nontreated and O₃-treated tartary buckwheat. The content of threonic acid increased after 2 days of the O₃ treatment, whereas it decreased after 4 days of exposure, after which it gradually increased until the eighth day of exposure. In addition, the levels of most metabolites decreased significantly after the O₃ treatment. On the contrary, the levels of two anthocyanins, cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside, increased more than 11.36- and 11.43-fold, respectively, after the O₃ treatment. To assess the effect of O₃ on the genomic level, we analyzed the expression of anthocyanin biosynthesis pathway genes in O₃-treated and nontreated buckwheat using quantitative real-time reverse transcription polymerase chain reaction (PCR). We found that the expression of all anthocyanin pathway genes increased significantly in the O₃-treated buckwheat compared to that in the nontreated buckwheat. Altogether, our results suggested that O₃ affected the transcripts and metabolites of tartary buckwheat, which would eventually cause phenotypic changes in plants.

How does Malus crabapple resist ozone? Transcriptomics and metabolomics analyses

Ozone (O₃), an oxidizing toxic air pollutant, is ubiquitous in industrialized and developing countries. To understand the effects of O₃ exposure on apple (Malus) and to explore its defense mechanisms, we exposed 'Hongjiu' crabapple to O₃ and monitored its responses using physiological, transcriptomics, and metabolomics analyses. Exposure to 300 nL L^-1 O₃ for 3 h caused obvious damage to the leaves of Malus crabapple, affected chlorophyll and anthocyanin contents, and activated antioxidant enzymes. The gene encoding phospholipase A was highly responsive to O₃ in Malus crabapple. McWRKY75 is a key transcription factor in the response to O₃ stress, and its transcript levels were positively correlated with those of flavonoid-related structural genes (McC4H, McDFR, and McANR). The ethylene response factors McERF019 and McERF109-like were also up-regulated by O₃. Exogenous methyl jasmonate (MeJA) decreased the damaging effects of O₃ on crabapple and was most effective at 200 μmol L ^-1. Treatments with MeJA altered the metabolic pathways of crabapple under O₃ stress. In particular, MeJA activated the flavonoid metabolic pathway in Malus, which improved its resistance to O₃ stress.

Bioindicator potential of Ricinus communis to simulated rainfall containing potassium fluoride

Background

Fluoride pollution is a global problem because of its high phytotoxicity. Fluoride is released in air, water and soil through industrial processes, where it damages various plant species. Ricinus communis is widely distributed in Brazil, India and China and has been extensively used as a phytoremediation species in heavy metal-contaminated soils. However, few studies regarding the effect of air pollutants on R. communis have been published, and no information about the exposure of this species to fluoride is available. Therefore, the aim of the present study was to investigate the effects of fluoride on R. communis morphoanatomical and physiological responses using simulated rainfall containing potassium fluoride (KF).

Methods

Young plants at approximately 10 days after emergence were treated daily with KF using simulated rainfall at 0, 1.5, 3.0 and 4.5 mg L⁻¹, for 37 consecutive days. Chlorophyll a fluorescence, gas exchange, anatomical characteristics and fluoride accumulation in the roots and leaves were evaluated after this period.

Results

No visual or anatomical symptoms were observed for the first three treatments. Necrosis and chlorosis were visually evident after the 37th day of KF application at 4.5 mg L⁻¹, followed by changes in parenchyma tissues, cell collapse and phenolic compound accumulation at the end of the experiment. No damage was observed in terms of photosynthetic photochemical and biochemical stages. Maintenance of physiological characteristics in the presence of fluoride accumulation in roots and leaves were shown to be important fluoride biomarkers. These characteristics suggest that R. communis is tolerant to 1.5 and 3.0 mg L⁻¹ KF, and is anatomically sensitive at 4.5 mg L⁻¹ KF.

Impact assessment of azulene and chromium on growth and metabolites of wheat and chilli cultivars under biosurfactant augmentation

Dye azulene and heavy metal chromium are two different types of persistent toxic compounds present in textile effluent. These compounds contaminate the soil and harm plant productivity during unchecked disposal of textile effluent to the farm soil. Environmental and safety concerns associated with crops, soil, and human health encourage the exploration of biological tools to control the issue. We hereby propose the application of biosurfactant (lipopeptide) to reduce the toxic effects of azulene and chromium in plants. Results of the study indicated that the augmentation of biosurfactant with azulene and chromium promoted seed germination, plant biomass, specific leaf weight (SLW), chlorophyll content, protein content, soluble sugar and ascorbic acid concentration in cultivars of wheat and chilli. Decreasing the level of proline under biosurfactant augmentation further confirms the reduction of oxidative stress caused by azulene and chromium amendment. The results indicated that lipopeptide biosurfactant could be an effective biological tool to reduce the toxic effect of persistent substances in soil, thus maintaining soil health and sustainable agriculture.