Mass and Composition of Developing Soybean Seeds at Five Reproductive Growth Stages1

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Abstract
Historically, days after flowering (DAF) has been the criterion for sampling developing soybean [Glycine max (L.) Merr.] seeds. Seed development rate, however, differs according to genotype and environmental conditions, leading to variable DAF values for the same seed development stage. Morphologically described growth stages (GS), in contrast, allow a rapid and convenient sampling method for seed development and composition studies. The purpose of this study was to categorize the changes in mass and composition of developing ‘Williams 79’ soybean seeds at five reproductive GS. Seed mass and composition studies demonstrated that R5 and R7 were accurate indicators of seedfill initiation and physiological maturity (PM), respectively. At R5, diy weight, protein, oil, and sugar quantity were low, while moisture content was high. Moisture content decreased slowly between R5 and R7, while seed dry weight, protein, oil, and sugar content increased. Between R5 and R7, 97% of the seed dry weight at maturity had accumulated. Monosaccharides represented 82% of the seed soluble carbohydrates at RS, but decreased to 8% by R6. Sucrose increased two‐fold between R5 and R6, then remained at a high level until R8. Raffinose and stachyose were undetectable until R7, when they represented 11 and 34% of the total soluble sugar, respectively. The largest increase in fatty acid quantity occurred between R5 and R6. Palmitic, stearic, and linolenic acid accounted for 68% of the total fatty acid at R4, but only 21% at R6. Oleic and linoleic acid accumulated most rapidly between R5 and R6, representing 79% of the fatty acid content at R6. Four acetate buffer soluble proteins were resolved by electrophoresis at R5 and eight at R6. Banding patterns remained constant between R6 and R8, while protein quantity of Bands 2 through 8 decreased. The quantity (mg seed−1) of each macro‐ and micro‐element increased at varying rates between R5 and R7. After R7, the seed moisture content decreased rapidly while the quantity and composition of stored components changed little. At harvest maturity (R8), seeds possessed 380 g protein, 230 g oil, and 160 g sugar kg−1 dry weight. These data serve as a useful characterization of changes in seed composition for future studies employing GS.