Summary The uptake of externally supplied sucrose by cotyledons of Ricinus communis is catalyzed with a K m of 30 mM, at V max 140 μmol · h −1 . g −1 FW. Sulphite affects the rate of sucrose uptake while K m is not influenced. At concentrations of SO 3 2− 1.0 mM it is inhibited. This inhibition is of the non-competitive type with K i = 5.75 mM SO 3 2− . A lowering of the transport of sucrose leads to an increase in the rate of 35 SO 2 2− uptake by cotyledons. Transport of sucrose induces an increase in the respiratory oxygen uptake, which as a result of SO 3 2− action at concentrations of 3 2− at a concentration of 0.25 mM is completely abolished by the uncoupler FCCP, while the addition of ATP to the incubation medium contributes to its additional intensification. On the other hand, FCCP has no influence on the inhibition of sucrose uptake by 10 mM of SO 3 2− in contrast to ATP which lowers the inhibitive effect of the sulphite. Disturbances caused by the action of the sulphite at various concentrations on the export of sucrose from the cotyledons to the hypocotyl of the seedlings are the result of disturbing the sucrose phloem loading mechanism and not of a direct action of this anion on the long distance transport.