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Rates of Sucrose Release from Opened Seed Coats of Soybean as Affected by Genotypes: Relation with Rate of Seed Development¹

Six soybean [Glycine max (L.) Merr.] genotypes with small and six genotypes with large petiole diameters were selected from a broadbase population and used in a greenhouse study to establish sucrose release rates (SRR) from opened seed coats, adjusted for phloem exudate, and to relate SRR found among genotypes with their embryo dry matter accumulation rates (DMAR). Aspects of control for seedsink development were investigated. Sucrose exudate from cut pod walls was about 0.09 mg h^–1. The SRR into EDTA were maintained for 4 h and decreased about 60% when plants were moved from light to dark. The SRR were similar with sorbitol concentrations of 0.2 to 0.8 M in the collection media and decreased 39% with 1.2 M sorbitol. The SRR per seed-coat cup into 20 mM EDTA media were independent of cup area, while with 0.2 M sorbitol and 2.5 mM EDTA the rates were proportional to cup area. The 0.2 M sorbitol media was selected to measure SRR. With appropriate adjustments, SRR gave realistic DMAR. Significant differences for SRR were found among genotypes. The SRR per m² was not associated with cup area or with total seed-coat area, but was associated with petiole diameter (presumed transport capacity). Highly significant differences for DMAR were found among genotypes, but DMAR was not associated with SRR or with petiole diameter. A seed-coat component measured as SRR, though differing among genotypes, did not reflect a measure of control for seed-sink development. The DMAR differences among genotypes depended upon the integrated (source-sink) system.

Key Words: Sucrose unloading • EDTA • Source-sink relations • Glycine max (L.) Merr.

² Professor of genetics, Dep. of Genetics, Box 7614, North Carolina State Univ., Raleigh, NC 27695-7614.

Received for publication June 3, 1985.