Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/2/2012
Publication Date: 8/15/2012
Citation: Kaplan, F., Zhao, W., Richards, J.T., Wheeler, R.M., Guy, C.L., Levine, L.H. 2012. Transcriptional and metabolic insights into the differential physiological responses of Arabidopsis to optimal and supraoptimal atomospheric CO2. PLoS One. 7(8):1-13. Interpretive Summary: CO2, a constituent of Earth’s atmosphere, is used by the plants during photosynthesis. Elevated CO2 concentrations (e.g., up to ~1000 ppm) are beneficial with respect to enhanced photosynthesis, biomass production, and water use efficiency in plants. While there is a wealth of information on the influence of elevated CO2 on plants at two to three times current ambient concentrations (350 ppm), very little is known about the consequences of super-elevated CO2 concentrations which can occur in tightly closed systems such as space exploration. Scientists at the USDA ARS CMAVE in Gainesville Florida in co-operation with scientists at the University of Florida, NASA Biological Sciences, Dynamac Corporation, and St. Jude Research Hospital found that plant developmental stage has a major influence on how plants respond to elevated and super elevated CO2 at the molecular level (transcript and metabolite level). Additionally, there seems to be an upper limit for CO2 concentration for plants to acclimate. The complex interaction between CO2 and developmental signals for modeling gene expression requires multiple sampling points during development in response to high and super high CO2 concentrations.
Technical Abstract: Biological activity in tightly closed systems can lead to excessively high CO2 concentrations of between one and two orders of magnitude greater than current ambient levels in Earth’s atmosphere. While there is a wealth of information on the influence of elevated CO2 on plants at two to three times current ambient concentrations, very little is known about the consequences of autotrophic plant function at super-elevated CO2 concentrations. To gauge the impact of elevated and super-elevated CO2 concentrations on plants, Arabidopsis gene expression and metabolite profiles were characterized for plants grown under a near-saturating irradiance at 400 ppm, 1,200 ppm and 4,000 ppm CO2 to developmental stages (1.09) and (1.14). The findings revealed that qualitative and quantitative affects on gene expression and metabolite profile patterns were both developmental stage and CO2 concentration dependent. There were differential effects between ambient, elevated and super-elevated CO2 grown plants for photosystems, energy metabolism, starch metabolism, photorespiration, and secondary metabolism. Photosynthetic acclimation in terms of down-regulated gene expression was observed in response to 1,200 ppm CO2 at 1.09, but not at the 1.14 developmental stages. In contrast, plants exposed to super-elevated CO2 (4,000 ppm) failed to show molecular responses consistent with photosynthetic acclimation suggesting an upper limit exists beyond which plants can no longer acclimate to increasing CO2 concentration.