Assimilate Redistribution from Soybean Pod Walls During Seed Development1

Abstract

AbstractAccumulation of dry weight by soybean seeds occurs at a linear rate in spite of daily fluctuations in photosynthate production. This suggests a possible role for assimilate redistribution from storage in maternal fruit tissues to developing seeds. Because of their proximity to the seed, pod walls were suspected as temporary storage organs for photosynthate and nitrogenous assimilates.Populations of Norman (OO maturity) and Amsoy 71 (II maturity) soybeans [Glycine max (L.) Merr.] were field‐grown in 1977 on Cheshire fine sandy loam (Typic Dystrochrept). Weekly during reproductive growth, developing fruit were harvested and assimilates in pod walls extracted and colorimetrically determined. At midpodfilling, pods from three canopy strata were also harvested diurnally and analyzed. From the examination of dry weight and assimilate levels within these samples, evidence of storage and redistribution from pod walls was obtained.Prior to mid‐podfilling stage both cultivars accumulated maximum pod wall dry weight; Norman 290 mg pod wall‐1 on 11 August and Amsoy 71 170 mg pod wall‐1 on 25 August. Pod walls of Norman redistributed 112 mg of previously accumulated dry matter, occurring when incipient canopy senescence probably would have otherwise precluded continued linear seed growth. Assuming that these pod wall assimilates were transported to the enclosed seeds and an efficiency of conversion to seed of 41%, the redistributed materials accounted for 12.7% of the final seed yield per plant in Norman while only 1.8% in Amsoy 71.Pod walls were found to store and later redistribute starch, reducing sugars, and nitrogenous materials. The sucrose present was almost entirely in the major pod vascular bundles. Starch was a major storage product, but there was no significant diurnal variation in the amount. However, significantly more starch was accumulated by Norman pod walls in the upper third of the canopy. Glucose and fructose accumulations were depleted by redistribution in approximately the same time period as starch and nitrogenous materials.The data suggest that, in extremely short season cultivars such as Norman, assimilate storage and later redistribution by pod walls to the developing seeds may serve to effectively lengthen the period of podfilling and thus contribute significantly to final seed yield.