a. Seedlings were transferred 5 days after germination (DAG) to medium supplemented with ammonium (grey) or nitrate (red). Root growth rates (RGR in µm/min) were monitored over a 1200 minutes period. Data represent the geometric mean (± standard error, SE) of 3 biological replicates, n=5 (ammonium) and 6 (nitrate) roots. Light and dark periods are indicated as light or dark gray background, respectively. 