THE PRESENT INVENTION ADDRESSES THE PROBLEM OF PROVIDING A PLANT CELL DIFFERENTIATION PROMOTER WITH WHICH IT IS POSSIBLE TO PROMOTE DIFFERENTIATION FROM A CALLUS TO A NORMAL ADVENTITIOUS EMBRYO OR PROMOTE DIFFERENTIATION OF AN ADVENTITIOUS ROOT OR ADVENTITIOUS BUD FROM A PLANT CUTTING AND AS A RESULT OBTAIN A REGENERATED PLANT WITH STABILITY. THE PRESENT INVENTION PROVIDES A PLANT DIFFERENTIATION PROMOTER COMPRISING AS THE ACTIVE INGREDIENT A SPECIFIC KETOLE FATTY ACID OR DERIVATIVE THEREOF.