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Relationship of Cotyledon Cell Number and Seed Respiration to Soybean Seed Growth¹

Seed Growth rate in soybean [Glycine max (L.) Merr.] is known to be important in determining final yield. Factors influencing growth rate, however, are less well understood. The objectives of this study were to investigate the relationship of cotyledonary cell number and seed component (cotyledons, seed coat, and embryonic axis) respiration to seed growth rate and final seed weight for three field-grown soybean Plant Introduction (PI) lines with genetic differences in seed weight. They were PI 361.058 (light seeded, 92 mg seed^–1), PI 317.336( medium seeded, 225 mg seed^–1), and PI 416.845 (heavy seeded, 316 mg seed^–1). Seed growth rate varied from 2.6 to 10.0 mg seed^–1 day^–1, and the number of cells in the cotyledons varied from 4.6 x 10⁶ to 10.3 x 10⁶. The three PI lines examined differed in both rates and duration of cell division in the developing seeds. Seed growth rate and final seed weight were related to number of cells in the cotyledons. However, the relationship was not linear. Growth rate per cell for the heavy seeded line was approximately 67% greater than that for the light seeded line. No relationship was observed between seed growth rate or final seed weight and respiration rates. Respiration rates among PI lines for each seed component decreased similarly during seedfill. Within each PI line, respiration rates decreased faster in cotyledon tissue than in either seed coat or embryonic axis tissue. Our results indicate that seeds having a relatively high number of cells per cotyledon have greater rates of dry matter accumulation and final dry weights, and that these growth characteristics are not associated with increased seed respiration.

Key Words: Glycine max (L.) Merr. • Seed growth rate • Seed weight • Genetic differences in seed size • Seed development

² Graduate research assistant and professor, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St Paul, MN 55108.

Received for publication November 5, 1984.