Effect of Temperature, Elevated Carbon Dioxide, and Drought during Seed Development on the Isoflavone Content of Dwarf Soybean [Glycine max (L.) Merrill] Grown in Controlled Environments

The effects of elevated temperature, carbon dioxide, and water stress on the isoflavone content of seed from a dwarf soybean line [Glycine max (L.) Merrill] were determined, using controlled environment chambers. Increasing the temperature from 18 °C during seed development to 23 °C decreased total isoflavone content by about 65%. A further 5 °C increase to 28 °C decreased the total isoflavone content by about 90%. Combining treatments at elevated temperature with elevated CO₂ (700 ppm) and water stress to determine the possible consequences of global climate change on soybean seed isoflavone content indicated that elevated CO₂ at elevated temperatures could partially reverse the effects of temperature on soybean seed isoflavone content. The addition of drought stress to plants grown at 23 °C and elevated CO₂ returned the total isoflavone levels to the control values obtained at 18 °C and 400 ppm CO₂. The promotive effects of drought and elevated CO₂ at 23 °C on the 6‘ ‘-O-malonygenistin and genistin levels were additive. The individual isoflavones often had different responses to the various growth conditions during seed maturation, modifying the proportions of the principal isoflavones. Therefore, subtle changes in certain environmental factors may change the isoflavone content of commercially grown soybean, altering the nutritional values of soy products.

Keywords: Carbon dioxide; drought; global climate change; Glycine max (L.) Merrill; isoflavone; soybean