A Normalized firefly luciferase luminescence (compared to renilla luciferase) as a function of external IAA concentration. Arabidopsis protoplast cells were transiently transformed with either AtPIN1 or GFP (in the case of the control) both under the control of a constitutive CaMV 35S promoter. Where indicated, 10 µM NPA was added. B Normalized firefly luciferase luminescence (compared to renilla luciferase) as a function of external NPA concentration in the presence of 100nM IAA in control GFP- (blue or red) or PIN1- (green or purple) transformed protoplasts. 