The effect of uranyl nitrate on sucrose production and storage in corn scutellum slices

Abstract

Uranyl nitrate (1·5 × 10 −3 M) completely inhibited the storage of exogenous sucrose in slices of the corn scutellum, but had no effect on the storage of intracellularly synthesized sucrose. Sucrose production from glucose or fructose was inhibited by 15 and 35 per cent, respectively, and the inhibitions were not increased by a 10-fold greater uranyl ion concentration. Essentially the same degrees of inhibition were obtained when the slices were incubated with uranyl ion and sugar as when the slices were pretreated in uranyl ion and then washed and placed in sugar solutions. In the latter case, the inhibition was shown to be completely reversed by hydrogen ion or partially reversed by certain metal cations. Uranyl ion also strongly inhibited the exchange of sucrose between the bathing solution and the storage compartment of the cell. These results are consistent with a scheme which includes two sucrose transport membranes, one at the cell exterior for exogenous sucrose and the other at the cell interior between the sucrose synthesis and storage compartments and a membrane containing hydrophilic pores through which hexose molecules can freely diffuse from the cell exterior into the synthesis compartment.