Protection of palak (Beta vulgaris L. var Allgreen) plants from ozone injury by ethylenediurea (EDU): Roles of biochemical and physiological variations in alleviating the adverse impacts

Ameliorative effects of ethylenediurea (N-[2-(2-oxo-1-imidazolinidyl) ethyl]-N′ phenylurea, abbreviated as EDU) against ozone stress were studied on selected growth, biochemical, physiological and yield characteristics of palak (Beta vulgaris L. var Allgreen) plants grown in field at a suburban site of Varanasi, India. Mean eight hourly ozone concentration varied from 52 to 73 ppb which was found to produce adverse impacts on plant functioning and growth characteristics. The palak plants were treated with 300 ppm EDU at 10 days after germination at 10 days interval up to the plant maturity. Lipid peroxidation in EDU treated plants declined significantly as compared to non-EDU treated ones. Significant increment in F_v/F_m ratio in EDU treated plants as compared to non-EDU treated ones was recorded. EDU treated plants showed significant increment in ascorbic acid contents and reduction in peroxidase activity as compared to non-EDU treated ones. As a result of the protection provided by EDU against ozone induced stress on biochemical and physiological characteristics of palak, the morphological parameters also responded positively. Significant increments were recorded in shoot length, number of leaves plant⁻¹, leaf area and root and shoot biomass of EDU treated plants as compared to non-EDU treated ones. Contents of Na, K, Ca, Mg and Fe were higher in EDU treated plants as compared to non-EDU treated ones. The present investigation proves the usefulness of EDU in partially ameliorating ozone injury in ambient conditions.     

Protecting the photosynthetic performance of snap bean under free air ozone exposure

Tropospheric ozone(O_3) is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O_3 damage, several agrochemicals have been assessed,including cytokinin(e.g., kinetin, KIN) and ethylenediurea(EDU) with cytokinin-like activity.In higher plant, leaves are primarily injured by O_3 and protective agrochemicals are often applied by leaf spraying. To our knowledge, the mitigating abilities of EDU and KIN have not been compared directly in a realistic setup. In the present research, impacts of elevated O3(2 × ambient O_3, 24 hr per day, for 8 days) on an O_3 sensitive line(S156) of snap bean(Phaseolus vulgaris), which is often used for biomonitoring O_3 pollution, were studied in a free air controlled exposure system. The day before starting the O_3 exposure, plants were sprayed with a solution of EDU(300 ppm), KIN(1 mmol/L) or distilled water, to compare their protective abilities. The results demonstrated that 2 × ambient O_3 inhibited net photosynthetic rate and stomatal conductance, increased the minimal fluorescence yield of the dark-adapted state, decreased the maximal quantum yield of PSII photochemistry, and led to visible injury. KIN and EDU alleviated the reduction of the photosynthetic performance, and visible injury under O_3 fumigation. The plants sprayed with EDU showed greater ability to mitigate the O_3 damage than those sprayed with KIN. Chlorophyll fluorescence imaging may have detected more precisely the differences in O_3 response across the leaf than the conventional fluorometer.     

Ethylenediurea (EDU): a research tool for assessment and verification of the effects of ground level ozone on plants under natural conditions

Ethylenediurea (EDU) has been widely used to prevent ozone (O₃) injury and crop losses in crop plants and growth reductions in forest trees. Successful use requires establishing a dose/response curve for EDU and the proposed plant in the absence of O₃ and in the presence of O₃ before initiating multiple applications to prevent O₃ injury. EDU can be used to verify foliar O₃ symptoms in the field, and to screen plants for sensitivity to O₃ under ambient conditions. Despite considerable research, the mode of action of EDU remains elusive. Additional research on the mode of action of EDU in suppressing O₃ injury in plants may also be helpful in understanding the mode of action of O₃ in causing injury in plants.     

Use of the antiozonant ethylenediurea (EDU) in Italy: verification of the effects of ambient ozone on crop plants and trees and investigation of EDU's mode of action

Twenty-four experiments where EDU was used to protect plants from ozone (O₃) in Italy are reviewed. Doses of 150 and 450 ppm EDU at 2-3 week intervals were successfully applied to alleviate O₃-caused visible injury and growth reductions in crop and forest species respectively. EDU was mainly applied as soil drench to crops and by stem injection or infusion into trees. Visible injury was delayed and reduced but not completely. In investigations on mode of action, EDU was quickly (<2 h) uptaken and translocated to the leaf apoplast where it persisted long (>8 days), as it cannot move via phloem. EDU did not enter cells, suggesting it does not directly affect cell metabolism. EDU delayed senescence, did not affect photosynthesis and foliar nitrogen content, and stimulated antioxidant responses to O₃ exposure. Preliminary results suggest developing an effective soil application method for forest trees is warranted.     

Cutleaf coneflower (Rudbeckia laciniata L.) response to ozone and ethylenediurea (EDU)

Cutleaf coneflower (Rudbeckia laciniata L.) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), non-filtered air (NF) or twice-ambient (2×) ozone (O₃). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O₃ (100%). Elevated O₃ resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDU × O₃ interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O₃ altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations.