Stimulation of source-applied 14C-sucrose export in Vicia faba plants by brassinosteroids, GA3 and IAA

The effect of brassinosteroids (SSHB, 24-Epi), GA3 and IAA on sucrose uptake and export from source leaf was studied in Vicia faba plants. Brassinosteroids, GA3 and IAA applied exogenously to the source leaves were found to enhance the retention of l4C-label and stimulate the uptake in discs of source leaves during 4-h treatment. The hormone-promoted sucrose uptake is probably due to modulation of the H+-ATPase activity as indicated by increasing Fmax-values for sucrose uptake. Enhanced transport of l4C-compounds to the apical sink region was observed in SSHB- and GA3-treated plants after 24 h. SSHB, GA3 and IAA applied to the sink region of Vida plants, promoted l4C-radiolabel transport to the site of hormone-treated region. On the basis of this observation, we conclude that, like GA3 and IAA, brassinosteroids affect l4C-unloading processes.