Changes in soluble carbohydrates and enzymic activities in maturing soybean seed tissues

Abstract

Enzyme activities were compared with the accumulation of soluble carbohydrates in seed coats, cotyledons and embryonic axes of field-grown soybean ( Glycine max L. Merr. cv. Williams 82) seeds during seed maturation to examine the function of each seed tissue in non-structural carbohydrate metabolism. The vascularized seed coat was comparatively high in monosaccharides (glucose and fructose) which corresponded to greater acid invertase activity per gram dry weight than cotyledons and axes. The embryo (cotyledon+embryonic axis) was high in oligosaccharide content, and contained greater mean activity levels of sucrose synthase, alkaline invertase, galactinol synthase and α-galactosidase than the seed coat. There was little difference in the sucrose-phosphate synthase activity among these three tissues. The accumulation of raffinose saccharides (raffinose and stachyose) increased rapidly in the embryo during seed maturation. Activities of alkaline invertase, sucrose synthase, galactinol synthase, α-galactosidase, fructose-1,6-bisphosphate aldolase, malate dehydrogenase, and glucose-6-phosphate dehydrogenase were highest in embryonic axes. Initial maturation of soybean seeds may be distinguished developmentally by the yellowing of embryonic axes at 40–45 days after flowering. This change was found to coincide with increases in sucrose synthase and galactinol synthase activities, and with the initiation of a rapid accumulation of raffinose saccharides in the embryonic axis.