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Title: Biochemical and physiological processes associated with the differential ozone response in ozone-tolerant and sensitive soybean genotypes

Author
item CHUTTEANG, CATTLEYA - Tokyo University Of Agriculture & Technology
item BOOKER, FITZGERALD - Former ARS Employee
item PRATHOMRAK, NA-NGERN - Tokyo University Of Agriculture & Technology
item BURTON, AMY - Former ARS Employee
item AOKI, MASATOSHI - Tokyo University Of Agriculture & Technology
item Burkey, Kent

Submitted to: Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2015
Publication Date: 1/4/2016
Citation: Chutteang, C., Booker, F., Prathomrak, N., Burton, A., Aoki, M., Burkey, K.O. 2016. Biochemical and physiological processes associated with the differential ozone response in ozone-tolerant and sensitive soybean genotypes. Plant Biology. 18(suppl1):28-36.

Interpretive Summary: Ground level ozone is formed by the action of sunlight on volatile hydrocarbons and nitrogen oxides produced during combustion of carbon based fuels. Although frequently considered an urban problem, ozone pollution is much broader in scope because weather systems transport the pollutants into agricultural areas. Ozone is an air pollutant that is toxic to plants, causing visible injury to foliage and a reduction in the growth and yield of sensitive crops such as soybean. Estimates suggest that current ambient ozone levels are sufficient to reduce soybean yield by 10% or more with greater yield losses anticipated if tropospheric ozone concentrations continue to rise. In the absence of successful efforts to control ozone pollution, future crop productivity may depend on the development of ozone-tolerant soybean varieties. In this study, USDA-ARS researchers and colleagues from Tokyo University of Agriculture and Technology compared biochemical and physiological traits of two soybean genotypes that differ in ozone sensitivity to determine the possible basis for the differential response. Ethylene metabolism and leaf conductance were two processes identified that contribute to the genetic differences in ozone sensitivity. The results are a first step in identifying genes that could be manipulated to develop cultivars capable of maintaining yields under elevated ozone conditions.

Technical Abstract: Biochemical and physiological traits of two soybean [Glycine max (L.) Merr.] genotypes that differ in sensitivity to ozone (O3) were investigated to determine the possible basis for the differential response. Fiskeby III (O3-tolerant) and Mandarin (Ottawa) (O3-sensitive) were grown in a greenhouse supplied with charcoal-filtered air for four weeks. Plants were then treated with O3 for 7 h d-1 in greenhouse chambers. Mandarin (Ottawa) showed significantly more visible leaf injury and hydrogen peroxide and superoxide production compared with Fiskeby III. Peroxidase activity in O3-sensitive Mandarin (Ottawa) was 31% higher in the elevated O3 treatment but it was not significantly different in O3-tolerant Fiskeby III. Ozone did not affect superoxide dismutase or glutathione reductase activities, or the leaf tissue concentrations of glutathione or ascorbic acid concentrations. Thus, variation in O3 response between the Fiskeby III and Mandarin (Ottawa) genotypes was not explained by differences in the antioxidant enzymes and metabolites tested. Ethylene emission from leaves declined in Fiskeby III following O3 exposure but was not altered in Mandarin (Ottawa). Ozone exposure reduced quantum yield of PSII, electron transport rate (ETR) and photochemical quenching (qp) in Mandarin (Ottawa) more than in Fiskeby III, indicating that the efficiency of energy conversion of PSII and photosynthetic electron transport was altered differently in the two genotypes. Net carbon exchange rates and stomatal conductance of both soybean cultivars were not significantly different following the short-term exposure to O3. In conclusion, increased sensitivity of Mandarin (Ottawa) to O3 was associated with greater hydrogen peroxide and superoxide production compared with Fiskeby III, possibly associated with genotype differences in the regulation of ethylene during the initial phases of O3 response.