SUGAR IMPORT AND METABOLISM DURING SEED DEVELOPMENT

During seed development, cell division is followed by elongation, diff erentiation and storage, In legumes, this sequence of events has been found to spread in a wave-like manner, creating a developmental gradie nt across the cotyledons. All these processes, including storage activ ities, appear to be subject to metabolic control. Sucrose is imported during seed development, and a sucrose breakdown pathway mediated by c ell wall invertase operates in the seed coat during early development. The resulting high hexose state is associated with growth and mitotic activity, The storage/maturation phase is initiated following the dev elopmentally controlled loss of invertase, and is accompanied by the f ormation of an active sucrose transport system, Invertases are therefo re regarded as a control element in the changing carbohydrate status o f seeds, and the invertase control hypothesis for seed development has emerged. Cotyledonary sucrose metabolism is controlled by a cycle of synthesis and breakdown involving sucrose-phosphate synthase and sucro se synthase, respectively; net breakdown for storage product synthesis involves sucrose synthase. The complex framework of interactions invo lved in these pathways is now being elucidated via a combination of bi ochemical, physioloscal and molecular methods.