Root growth inhibition assay

Seeds were surface-sterilized and vertically grown on MS agar plates for 5 d before transferring six seedlings to each well of a 12-well plate containing 4 mL per well of MS medium containing 2 µM RALF; 10 nM AtPep1 as control. Seedlings were transferred 3 d later to solid MS plates. Control seedlings were grown under identical conditions in a peptide-free medium. Primary root length was measured by scanning the plates and quantified using the software Fiji (https://imagej.net/Fiji; Schindelin et al., 2012). Roots from approximately six seedlings per treatment and genotype were measured. Experiments were repeated three times using independent biological replicates.