Rate and Duration of Seed Component Accumulation in Water-Stressed Soybean

Lack of adequate soil moisture during seed filling limits seed size in soybean [Glycine max (L.) Merr.], generally by shortening the duration of seed fill. Seed growth rate typically remains largely unaffected. The smaller seeds often have increased seed protein concentration due to less detrimental effect on final protein accumulation relative to other major seed components. Such changes in seed composition despite stable rates of seed filling suggest compensation may occur among component accumulation rates or the duration of accumulation of individual seed components is affected differentially by water stress. We examined these possibilities by evaluating the rates and durations of protein, oil, and residual accumulation in two soybean lines subjected to limited soil moisture during seed filling. Results indicated that both responses (rate and duration of accumulation) to water deficit can occur. The rates of accumulation of the different seed components often compensated, resulting in a constant seed growth rate, typically favoring protein accumulation. To our knowledge, this is the first demonstration of a differential response among rates and durations of seed component accumulation when soil moisture becomes limiting. The relative stability of protein accumulation likely reflects the availability of remobilizable N late in seed filling and the dependence of oil accumulation on current photosynthesis.