Soybean Reproductive Traits Evaluated in Response to Temperature Stress and Elevated Oxygen; Three Peroxidase Transgenes Reduce Seed Abortion

In a previous Arabidopsis investigation, three ovule-specific cell-wall peroxidases decreased seed abortion rates. These peroxidases were expressed in soybean plants. Because cell wall peroxidases alter extensibility, possible effects on seed size and plant yield were evaluated. Since the effects of these peroxidases in Arabidopsis were dependent on environmental stress, soybean plants were grown in controlled environment greenhouse rooms under four temperature treatments; the daily temperature averages were 26, 30, 34, and 38 °C. In this experiment in vivo oxygen levels during seed growth were 25-fold below ambient, which could affect peroxidase activities. Consequently, soybeans were grown at atmospheric (21%) and elevated (32%) O2 to evaluate peroxidase activities at higher O2. Chambers were maintained at 700 ppm CO2 in an attempt to minimize photorespiration in elevated O2. Individual seed weight decreased with increasing temperature to zero at 38 °C. In elevated O2 rooms, the oxygen concentration in developing seeds increased, but, due to leaf photorespiration, plant biomass and seed yield decreased. Seed size and shelling percentage declined equally with temperature at both O2 concentrations. Expression of all three cell-wall peroxidases reduced seed abortion; however, that did not increase yields at ambient or elevated O2. While O2 concentration is less than 1% in developing seeds, increased O2 levels in seeds were not beneficial for soybean reproduction.