Analysis of the relative expression level of AtPDF family genes in the roots of A. thaliana under different treatments. The seedlings were treated with 1/4 plant nutrient solution for 18 d, Nstarved for 3 d, and then treated with mM KNO 3, mM KNO 3, 10 mM KNO 3, or mM NH 4 NO 3 for 6 h before roots were harvested separately for RNA analysis.