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CO2, Temperature and Soil Nitrogen Effects on Soybean Seed Isoflavone Concentrations
Kim, S.-H., Jung, W.-S., Ahn, J.-K., Kim, J.-A. and Chung, I.-M. 2005. Quantitative analysis of the isoflavone content and biological growth of soybean (Glycine max L.) at elevated temperature, CO2 level and N application. Journal of the Science of Food and Agriculture 85: 2557-2566.

Important flavoniods, in the words of the authors, "are mainly found in the form of isoflavones in soybean seeds," including "phytoestrogens with various biological potentials such as antioxidative, pharmaceutical, oestrogenic and anticarcinogenic properties, with some acting as antiestrogens and being used as anticancer agents (Peterson and Barnes, 1991; Anderson et al., 1995; Anthony et al., 1996; Arjmandi et al., 1996; Holt, 1997, Chung et al., 2000)."

What was done
Well-watered plants were grown from seed to maturity in pots of sandy loam soil within the closed-environment plant growth facility of the National Horticultural Research Institute of Korea, where they were exposed to natural solar radiation and the natural daily course of ambient air temperature or elevated air temperature (= ambient + 5C) with either no added nitrogen or added nitrogen equivalent to an extra 40 kg N/ha, and where they were maintained at either ambient CO2 (360 ppm) or elevated CO2 (650 ppm). Then, at the end of the growing season, the plants were harvested and their total biomass determined, while the concentrations of 12 different isoflavones found in their seeds were quantitatively analyzed. These isoflavones included three aglycons (daidzein, genistein, glycitein), three glucosides (diadzin, genistin, glycitin), three acetyl conjugates (6"-O-acetyldaidzin, 6"-O-acetylgenistin, 6"-O-acetylglycitin), and three malonyl conjugates (6"-O-malonyldaidzin, 6"-O-malonylgenistin and 6"-O-malonylglycitin).

What was learned
The CO2-induced increase in total plant biomass at normal ambient temperatures was 96% in the case of no added nitrogen and 105% in the case of added nitrogen, while at the warmer temperatures it was 59% in the case of no added nitrogen and 68% in the case of added nitrogen. With respect to seed isoflavone concentrations, the CO2-induced increases of all twelve isoflavones were fairly similar to each other. As a group, at normal ambient temperatures the mean increase was 72% in the case of no added nitrogen and 59% in the case of added nitrogen, while at the warmer temperatures it was 72% in the case of no added nitrogen and 106% in the case of added nitrogen.

What it means
Irrespective of soil nitrogen status and air temperature, increases in the air's CO2 content produced large increases in soybean biomass, as well as soybean seed concentrations of twelve major isoflavones. Hence, it can be appreciated that as the atmosphere's CO2 concentration continues to rise in the years and decades ahead, both the amount and the potency of important health-promoting properties of soybean seeds will be significantly enhanced, providing huge benefits to humanity.

Anderson, J.W., Johnstone, B.M. and Cook-Newell, M.E. 1995. Meta-analysis of the effects of soybean protein intake on serum lipids. New England Journal of Medicine 333: 276-282.

Anthony, M.S., Clarkson, T.B., Hughes, C.L., Morgan, T.M. and Burke, G.L. 1996. Soybean isoflavones improve cardiovascular risk factors without affecting the reproductive system of peripubertal rhesus monkeys. Journal of Nutrition 126: 43-50.

Arjmandi, B.H., Lee, A., Hollis, B.W., Amin, D., Stacewicz-Saounizakis, M., Guo, P. and Kukreja, S.C. 1996. Dietary soybean protein prevents bone loss in an ovariectomized rat model of osteoporosis. Journal of Nutrition 126: 161-167.

Chung, I.M., Kim, K.H., Ahn, J.K., Chi, H.Y. and Lee, J.O. 2000. Screening for antioxidative activity in soybean local cultivars in Korea. Korean Journal of Crop Science 45: 328-334.

Holt, S. 1997. Soya: the health food of the next millennium. Korean Soybean Digest 14: 77-90.

Peterson, G. and Barnes, S. 1991. Genistein inhibition of the growth of human breast cancer cell: independence from estrogen receptors and the multi-drug resistance gene. Biochemistry and Biophysical Research Communications 179: 661-667.

Reviewed 22 March 2006