Nitrogen is quantitatively the most essential mineral nutrient for plants growth and development and a predominant limiting factor in crop plants productivity.Success of modern agriculture with sustainable yield performance is remarkably associated with improved nutrient use efficiency(NUE).In a previous study,we isolated an abc1(abnormal cytokinin response1) mutant,which shows severe defects in plant height,tiller number and leaf chlorophyll content.ABC1 encodes a key enzyme for nitrogen assimilation.