Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2004
Publication Date: 12/15/2004
Citation: Bennett, J.O., Yu, O., Heatherly, L.G., Krishnan, H.B. 2004. Accumulation of genistein and daidzein, soybean isoflavones implicated in promoting human health, is significantly elevated by irrigation. Journal of Agricultural and Food Chemistry. 52(25):7574-7579. Interpretive Summary: Researchers in the southern United States have developed a system of soybean production management designated as the early soybean planting system (ESPS). Soybean cultivars bred for this region and planted in May and June are often confronted with dry and hot conditions during the critical seed-fill stage. The ESPS utilizes cultivars bred for shorter growing seasons and planted in April. This system allows the plant to reach reproductive stages during more favorable growing conditions. In this study, we evaluated the storage compounds in seed produced under the ESPS system and found that the protein and oil content was equal to that of seed from a traditionally cultivated crop. Interestingly, we observed a dramatic increase in isoflavones which have been linked to various aspects of human health. Since yields and health promoting compounds are enhanced by the ESPS, this practice could lead to an increased profitability for soybean farmers.
Technical Abstract: To circumvent drought conditions persisting during seed fill in the mid-south United States soybean production region, researchers have developed the early soybean planting system (ESPS) which entails early planting of short-season varieties. Since soybean supplies a preponderance of the world's protein and oil and consumption of soy-based foods have been linked to human health, quality traits as affected by this agronomic practice should be investigated. Four cultivars of soybeans, two from each Maturity Group IV and Maturity Group V, were planted in April (ESPS) and in May (traditional) in a two-year study at Stoneville, Mississippi, USA. Near-infrared analysis of soybean seed was utilized to determine the percent accumulation of protein and oil. Dependent upon variety, the oil content of the early-planted crop was increased from 3% to 8%, while protein accumulation was not significantly changed. Visualization of protein extracts fractionated by sodium dodecyl sulfate polyacrylamide electrophoresis and 2-dimensional gel electrophoresis revealed that early planting did not affect the relative accumulation of the major seed-storage proteins, thus protein composition was equal to that of traditionally cultivated soybeans. Maturity Group IV cultivars contained a higher percentage of oil and lower protein than did the Maturity Group V cultivars regardless planting date. Gas chromatographic separation of fatty acids revealed that the percentages of saturated and unsaturated fatty acids were not significantly altered by planting date. Methanol extracts of seed harvested from different planting dates when analyzed by high-performance liquid chromatography showed striking differences in isoflavone content. Depending upon the variety, total isoflavone content was increased as much as 1.3-fold in early-planted soybeans. Irrigation enhanced the isoflavone content of both early- and late-planted soybeans as much as 2.5-fold. Accumulation of individual isoflavones glycitein, daidzein, and genistein was also elevated by irrigation. Since this cultural practice improves the quality traits of seeds, the ESPS system provides an opportunity for enhancing the quality of soybeans.