The effects of LaCl 3 on membrane potential and transmembrane proton gradient for rice ( Oryza sativa ) seedling roots were studied. Highly purified plasma membranes were isolated by aqueous two phase partitioning method. Both the gradient of transmembrane proton and membrane potential were stimulated by certain low concentration of LaCl 3 and depressed by high concentration of LaCl 3. The optimal concentration of La 3+ was around 40～60 μmol·L -1 for transmembrane proton gradient and membrane potential. It is suggested that La 3+ can influence the generations and maintenances of membrane potential and transmembrane proton gradient in rice seedling roots.
