Plant Science 125 (1997) 1–11 Changes in soluble carbohydrates and enzymic activities in maturing soybean seed tissues Tsung Min Kuo a, *, Cadance A. Lowell a,b , Patrick T. Smith a,c a Oil Chemical Research Unit, National Center for Agricultural Utilization Research, USDA, Agricultural Research Serice, 1815 North Uniersity Street, Peoria, IL 61 604, USA b Biology Department, Central State Uniersity, Wilberforce, OH 45 384, USA c Bldg. 10, Immunology Laboratory, NIAID, NIH, Bethesda, MD 20 892, USA Received 23 October 1996; received in revised form 11 February 1997; accepted 11 February 1997 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  -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,  -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. © 1997 Elsevier Science Ireland Ltd. Keywords: Soybean seeds; Embryo; Seed coat; Galactinol synthase; Raffinose saccharides; Invertase; Sucrose synthase 1. Introduction Mature, dry soybean seeds contain 6–17% of soluble carbohydrates [1]. The majority of these Abbreiations: FBP, fructose-1,6-bisphosphate; DAF, days after flowering; G6P, glucose-6-phosphate. * Corresponding author. Tel.: +1 309 6816275; fax: +1 309 6816686. 0168-9452/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved. PII S0168-9452(97)04619-0