Sucrose Transport in Isolated Immature Barley Embryos

Techniques have been devised to select immature barley embryos at various stages in their development, and to study their accumulation of sucrose in vitro. Isolated embryos accumulate sucrose over a period of several hours of which some 80 per cent is conserved as a pool of free sucrose and the remainder utilized in macromolecular synthesis. The rate of sucrose uptake increases with embryo development, however the specific activity of uptake remains constant, indicating that the transport processes are fully operative early in embryogenesis. From the kinetics of sucrose uptake it is deduced that facilitated transport predominates at sucrose concentrations of 50 mM, while at higher concentrations passive diffusion makes an increasing contribution to sucrose accumulation. The substrate specificity and the sensitivity of sucrose transport to uncoupling agents, in addition to the stability of the pool of accumulated sucrose, are all indicative of active transport playing a major role in the sucrose assimilation of developing barley embryos.