Warm Temperatures or Drought during Seed Maturation Increase Free α-Tocopherol in Seeds of Soybean (Glycine max [L.] Merr.)

Soybean seeds are an important source of dietary tocopherols, but like seeds of other dicotyledonous plants, they contain relatively little α-tocopherol, the form with the greatest vitamin E activity. To evaluate potential effects of environmental stress during seed maturation on tocopherols, soybeans were raised in greenhouses at nominal average temperatures of 23 °C or 28 °C during seed fill, with or without simultaneous drought (soil moisture at 10−25% of capacity), during normal growing seasons in 1999 (cvs. Essex and Forrest) and 2000 (cvs. Essex, Forrest, and Williams). Total free (nonesterified) tocopherols increased slightly in response to drought in Essex and Forrest. All three lines responded to elevated temperature and, to a lesser extent, drought with large (2−3-fold) increases in α-tocopherol and corresponding decreases in δ-tocopherol and γ-tocopherol. The results suggest that weather or climate can significantly affect seed tocopherols. It may be possible to breed for elevated α-tocopherols by selecting for altered plant response to temperature. Keywords: Glycine max; soybean; seeds; stress; heat; temperature; drought; soil moisture; to-copherols; vitamin E; antioxidants