|Chang, Soo Chul|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2005
Publication Date: 1/15/2006
Citation: Kirakosyan, A., Kaufman, P., Nelson, R.L., Kasperbauer, M.J., Duke, J.A., Seymour, E., Chang, S., Warber, S., Bolling, S. 2006. Isoflavone levels in five soybean (Glycine max) genotypes are altered by phytochrome-mediated light treatments. Journal of Agricultural and Food Chemistry. 54(1):54-58. Interpretive Summary: Among edible legumes, seeds and seedlings of soybean contain relatively high levels of isoflavones, a bioactive compound that may be involved in many of the positive health effects that are associated with eating soy protein. The isoflavone levels in the seeds are much lower than in seedlings. Some recent studies have shown that phytochrome (a light sensitive pigment originally found to influence the time of flowering) is involved in the control of many plant products. This research was designed to study the role of phytochrome in the synthesis of soybean isoflavones using soybean lines with widely different isoflavone concentrations in their seeds. Seedlings were exposed to darkness and various qualities of light that affect phytochrome differently. We found that isoflavone levels were higher in dark-grown plants than light-grown plants for three of the five soybean lines which has not been previously reported in any legume species. The reverse occurred for one line which is a typical response of legumes. Changing the quality of the light at the end of the day increased isoflavone levels in the plants. These results show that phytochrome does appear to play a role in regulating isoflavone levels in developing soybean seedlings but that result of the regulation is strongly dependent on the soybean line that is studied. These results will be of interest to plant physiologists and geneticists who are interested in how genetics and the environment interact to produce plant products, especially isoflavones.
Technical Abstract: The objective of the present study was to determine whether concentrations of different isoflavones (puerarin, genistein, genistin, daidzein, and daidzin) in shoots and roots of five selected soybean genotypes would respond the same or differently to red (650 nm peak transmittance)) and far-red (750 nm peak transmittance) light treatments given under controlled environments. Levels of isoflavones (mg•g-1 dry weight biomass) present in seeds, control roots and shoots and ten days light-treated seedlings (light, dark, red and far red wavelengths) of soybean (Glycine max) were determined by HPLC analysis in comparison with known isoflavone standards. Seeds of the five soybean genotypes studied consistently stored most of their isoflavones as glucosyl conjugates (e.g., daidzin, genistin, and puerarin). For the five soybean genotypes, isoflavone levels were significantly lower in the seeds as compared with roots plus shoots of control, time zero [18 day-old] seedlings. Following 10 days of the respective light treatments, we found that (1) isoflavone levels were enhanced in dark-grown plants over light-grown plants for three of the five genotypes (a new finding) and the reverse occurred for a single genotype (a typical response of legumes) and (2) generally, far red end of day (EOD) light treatment enhanced total isoflavone levels in roots plus shoots over red EOD light treatment. Results from the present study show that phytochrome does appear to play a role in regulating isoflavone levels in developing soybean seedlings, and that this influence by red/far-red mediated phytochrome reactions is strongly dependent on the genotypes selected for study.