Seed Water Relations and the Regulation of the Duration of Seed Growth in Soybean

Abstract

Soybean [Glycine max (L.) Merrill] seeds and cotyledons were grown in an in vitro culture system to investigate the relationships between cell expansion (net water uptake by the seed) and dry matter accumulation. Seeds or cotyledons grown in a complete nutrient medium containing 200 mol m3 sucrose continued dry matter accumulation for up to 16 d after in planta seeds reached physiological maturity (maximum seed dry weight). Seed or cotyledon water content increased throughout the culture period and the water concentration remained above 600 g kg-1 fresh weight. These data indicate that the cessation of seed dry matter accumulation is controlled by the physiological environment of the seed and is not a pre-determined seed characteristic. Adding 600 mol m-3 mannitol to the medium caused a decrease in seed water content and concentration. Seeds in this medium stopped accumulating dry matter at a water concentration of approximately 550 g kg-1. The data suggest that dry matter accumulation by soybean seeds can continue only as long as there is a net uptake of water to drive cell expansion. In the absence of a net water uptake, continued dry matter accumulation causes desiccation which triggers maturation.