Title: Acclimation to Chronic O3 in Field-grown Soybean is Characterized by Increased Levels of TCA Cycle Transcripts and ROS Scavenging Compounds in Addition to Decreased Photosynthetic Capacity Authors
Submitted to: Biennial Conference on Molecular and Cellular Biology of the Soybean
Publication Type: Abstract Only
Publication Acceptance Date: June 18, 2010
Publication Date: August 8, 2010
Citation: Yendrek, C.R., Betzelberger, A.M., Nelson, R.L., Ainsworth, E.A. 2010. Acclimation to Chronic O3 in Field-grown Soybean is Characterized by Increased Levels of TCA Cycle Transcripts and ROS Scavenging Compounds in Addition to Decreased Photosynthetic Capacity. Biennial Conference on Molecular and Cellular Biology of the Soybean, August 8-11, 2010, Durham, NC. Technical Abstract: Tropospheric ozone (O3) is a pollutant that is generated by volatile organic compounds, nitrogen oxides and sunlight. When plants take in O3 through stomata, harmful reactive oxygen species (ROS) are produced that induce the production of ROS scavenging antioxidants. Climate change predictions indicate that O3 concentration will continue to rise by 25% in the next several decades. Previous research has revealed that soybean is among the most sensitive crops, with yield loss in Illinois estimated to cost growers $450 million dollars annually by 2050. To characterize the effect of elevated O3 on growth and metabolism, we have grown soybean at SoyFACE (soybean free air concentration enrichment) in ambient, 70 and 130 ppb [O3]. In order to reveal an instantaneous response to O3, plants were sampled at four times throughout the day - before and immediately following the onset of O3 fumigation as well as just before the end and immediately after fumigation. Four cultivars, IA3010, Dwight, LN97-15076 and Pana, with yield responses ranging from tolerant to sensitive, respectively, were used with the goal of identifying biochemical and molecular markers of O3 tolerance. In all cultivars, net assimilation rates were decreased in high O3, but no instantaneous drop in photosynthesis was seen after the onset of O3 fumigation, nor did net assimilation increase following the termination of fumigation. An analysis of total antioxidant capacity (ORAC) and ROS scavenging phenolic compounds demonstrated similar results, with an overall increase in abundance but no dynamic diurnal changes. Using qRT-PCR to analyze changes in gene expression of carbon metabolism related genes, widespread decrease in transcript abundance of genes related to the light reactions and Calvin cycle were observed in high O3, while an increase in TCA cycle related transcripts was seen. We conclude that in high O3, reductions in productivity are due in part to an overall decrease in photosynthetic capacity, which is exacerbated by increased respiration that is required to produce greater amounts of antioxidant compounds.