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

Author
item ZHANG, LU - Northeast Agricultural University
item HOSHIKA, YASUTOMO - Istituto Di Protezione Sostenibile Delle Piante
item CARRARI, ELISA - Istituto Di Protezione Sostenibile Delle Piante
item Burkey, Kent
item PAOLETTI, ELENA - Istituto Di Protezione Sostenibile Delle Piante

Submitted to: Journal of Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2017
Publication Date: 4/6/2018
Citation: Zhang, L., Hoshika, Y., Carrari, E., Burkey, K.O., Paoletti, E. 2018. Protecting the photosynthetic performance of snap bean under free-air ozone exposure. Journal of Environmental Science. 66:31-40.

Interpretive Summary: Ozone is an air pollutant that is toxic to plants, causing visible injury to foliage leading to reductions in the growth and yield of many agricultural, forestry and native species. Ground level ozone is formed from sunlight catalyzed reactions between oxygen in the air, volatile hydrocarbons and the nitrogen oxides produced during the burning of fossil fuels. Although frequently considered an urban problem, ozone is actually a regional problem because weather systems transport the pollutants into agricultural areas and forests. There are few strategies for adapting plants to ozone stress. Breeding for ozone tolerance is one option. Treating high-value plants with protective chemicals is another approach. In this study, a team of researchers from China, Italy, and USDA-ARS conducted field trials in Firenze, Italy to test the effectiveness of two chemicals in protecting ozone-sensitive snap beans from ozone stress. Treatment of plants with either ethylenediurea or kinetin prior to exposure to moderate ozone levels prevented ozone-induced foliar injury and protected photosynthesis, demonstrating that protective chemicals are an effective approach for alleviating ozone stress.

Technical Abstract: Tropospheric ozone (O3) is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O3 damage, several agrochemicals have been assessed, such as ethylenediurea (EDU) and kinetin (KIN). However, the mitigating abilities of EDU and KIN have not yet been compared directly. In the present research, impacts of elevated O3 (2× ambient O3, 24h per day, for 8 days) on an O3 sensitive line (S156) of snap bean (Phaseolus vulgaris), which is often used for biomonitoring O3 pollution, were studied in a free air exposure system. The day before starting the O3 exposure, plants were sprayed with a solution of EDU (300 ppm), KIN (1 mM) or distilled water, to compare their protective abilities. The results demonstrated that 2× ambient O3 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 O3 fumigation. The plants sprayed with EDU showed greater ability to mitigate the O3 damage than those sprayed with KIN. Chlorophyll fluorescence imaging may have detected more precisely the differences in ozone response across the leaf than the conventional fluorometer.