Background
Reactive oxygen species (ROS) generated during cellular metabolism or peroxidation of lipids and proteins play a causative role in the pathogenesis of cancer and coronary heart disease (CHD), as demonstrated by Slaga et al. (1987), Frenkel (1992), Marnett (2000) and Zhao et al. (2000). However, Yu et al. (2004) note "antioxidant treatments may terminate ROS attacks and reduce the risks of CHD and cancer, as well as other ROS-related diseases such as Parkinson's disease (Neff, 1997; Chung et al., 1999; Wong et al., 1999; Espin et al., 2000; Merken and Beecher, 2000)," and they therefore state that "developing functional foods rich in natural antioxidants may improve human nutrition and reduce the risks of ROS-associated health problems."

What was done
Levine et al. (2008) grew well watered and fertilized wheat plants (Triticum aestivum, cv Yocoro roho) from seed in custom-designed root modules -- "consisting of a porous tube embedded in Turface (1-2 mm particle size) substrate containing 5 g Osmocote time release fertilizer per liter" -- which were housed in Plexiglas chambers maintained at atmospheric CO2 concentrations of either 400, 1500 or 10,000 ppm for periods of 14, 21 and 28 days, while measuring a number of plant metabolic properties, among which were the leaf concentrations of several flavonoids capable of scavenging ROS.

What was learned
The thirteen researchers report that "elevated CO2 promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature." As best we can determine from the bar graphs of their results, for example, the percentage increase in total wheat leaf flavonoid concentration in going from an atmospheric CO2 concentration of 400 to 1500 ppm was 22%, 38% and 27% (the one exception to this general rule) at 14, 21 and 28 days after planting, respectively, while in going from a CO2 concentration of 400 to 10,000 ppm, the percentage increase in total flavonoid concentration was 38%, 56% and 86%, respectively, at 14, 21 and 28 days after planting. In addition, they found that "both elevated CO2 levels resulted in an overall 25% increase in biomass over the control plants."

What it means
In addition to the potential for the types of benefits described in the background material of this Journal Review, the U.S., Japanese and German scientists write that "the increased accumulation of secondary metabolites in plants grown under elevated CO2 may have implications regarding plant-herbivore interactions, decomposition rates for inedible biomass, and potential beneficial effects on plant tolerance to water stress (Idso, 1988) and cold stress (Solecka and Kacperska, 2003) due to their potentials for the scavenging of reactive oxygen species (ROS)."

References
Chung, H.S., Chang, L.C., Lee, S.K., Shamon, L.A., Breemen, R.B.V., Mehta, R.G., Farnsworth, N.R., Pezzuto, J.M. and Kinghorn, A.D. 1999. Flavonoid constituents of chorizanthe diffusa with potential cancer chemopreventive activity. Journal of Agricultural and Food Chemistry 47: 36-41.

Espin, J.C., Soler-Rivas, C. and Wichers, H.J. 2000. Characterization of the total free radical scavenger capacity of vegetable oils and oil fractions using 2,2-diphenyl-1-picryhydrazyl radical. Journal of Agricultural and Food Chemistry 48: 648-656.

Frenkel, K. 1992. Carcinogen-mediated oxidant formation and oxidative DNA damage. Pharmacology and Therapeutics 53: 127-166.

Idso, S.B. 1988. Three phases of plant response to atmospheric CO2 enrichment. Plant Physiology 87: 5-7.

Marnett, L.J. 2000. Oxyradicals and DNA damage. Carcinogenesis 21: 361-370. Merken, H.M. and Beecher, G.R. 2000. Measurement of food flavonoids by high-performance liquid chromatography: A review. Journal of Agricultural and Food Chemistry 48: 577-599.

Neff, J. 1997. Big companies take nutraceuticals to heart. Food Processing 58(10): 37-42.

Slaga, T.J., O'Connell, J., Rotstein, J., Patskan, G., Morris, R., Aldaz, M. and Conti, C. 1987. Critical genetic determinants and molecular events in multistage skin carcinogenesis. Symposium on Fundamental Cancer Research 39: 31-34.

Solecka, D. and Kacperska, A. 2003. Phenylpropanoid deficiency affects the course of plant acclimation to cold. Physiologia Plantarum 119: 253-262.

Wong, S.S., Li, R.H.Y. and Stadlin, A. 1999. Oxidative stress induced by MPTP and MPP+: Selective vulnerability of cultured mouse astocytes. Brain Research 836: 237-244.

Yu, L., Haley, S., Perret, J. and Harris, M. 2004. Comparison of wheat flours grown at different locations for their antioxidant properties. Food Chemistry 86: 11-16.

Zhao, J., Lahiri-Chatterjee, M., Sharma, Y. and Agarwal, R. 2000. Inhibitory effect of a flavonoid antioxidant silymarin on benzoyl peroxide-induced tumor promotion, oxidative stress and inflammatory responses in SENCAR mouse skin. Carcinogenesis 21: 811-816.