Assessment of ethylene diurea-induced protection in plants against ozone phytotoxicity

Urbanization, industrialization and unsustainable utilization of natural resources have made tropospheric ozone (03) one of the world's most significant air pollutants. Past studies reveal that 0 3 is a phytotoxic air pollutant that causes or enhances food insecurity across the globe. Plant sensitivity, tolerance and resistance to 0 3 involve a wide array of responses that range from growth to the physiological, biochemical and molecular. Although plants have an array of defense systems to combat oxidative stress from 0 3 exposure, they still suffer sizable yield reductions. In recent years, the ground-level 0 3 concentrations to which crop plants have been exposed have caused yield loses that are economically damaging. Several types of chemicals have been applied or used to mitigate the effects produced by 0 3 on plants. These include agrochemicals (fungicides, insecticides, plant growth regulators), natural antioxidants, and others. Such treatments have been effective to one degree to another, in ameliorating Or generated stress in plants. Ethylene diurea (EDU) has been the most effective protectant used and has also served as a monitoring agent for assessing plant yield losses from 0 3 exposure. In this review, we summarize the data on how EDU has been used, the treatment methods tested, and application doses found to be both protective and toxic in plants. We have also summarized data that address the nature and modes of action (biophysical and biochemical) of EDU. In general, the literature discloses that EDU is effective in reducing ozone damage to plants, and indicates that EDU should be more widely used on 0 3 sensitive plants as a tool for biomonitoring of 0 3 concentrations. Biomonitoring studies that utilize EDU are very useful for rural and remote areas and in developing countries where 0 3 monitoring is constrained from unavailability of electricity. The mechanism(s) by which EDU prevents 0 3 toxicity in plants is still not completely known. EDU possesses great utility for screening plant sensitivity under field conditions in areas that experience high 0 3 concentrations, because EDU prevents 0 3 toxicity only in 0 3 sensitive plants. Ozone-resistant plants do not respond positively to EDU applications. However, EDU application dose and frequency must be standardized before it can be effectively and widely used for screening 0 3 sensitivity in plants. EDU acts primarily by enhancing biochemical plant defense and delaying Or induced senescence, thereby reducing chlorophyll loss, and maintaining physiological efficiency and primary metabolites; these actions enhance growth, biomass and yield of plants. We believe that future studies are needed to better address the EDU dose response relationship for many plant species, and to screen for new cultivars that can resist 0 3 stress. Although some research on the physiological and biochemical mechanisms of action of EDU have been performed, the new 'omics' tools have not been utilized to evaluate EDUs mechanism of action. Such data are needed, as is gene expression and proteome profiling studies on EDU-treated and -untreated plants.