Fig. 1. Three drought stress treatments imposed on soybean plants at beginning seed fill (R5) in the greenhouse experiment. WW: plants were maintained at 80% field capacity (FC) after R5. GS: the soil moisture content was dropped gradually in 7 d after R5 from 80% to 20% FC; then, maintained at 20% FC for 13 d. SS: plants were maintained at 80% FC for 7 d from R5; then, soil moisture content was allowed to drop suddenly in 1 d to 20% FC and maintained for 16 d.