Synthetic rapid alkalinization factor (RALF) peptides induce reactive oxygen species (ROS) production and alkalinization in Nicotiana benthamiana and tomato leaves. The ROS burst over time after treatment with 10 μm of each synthetic RALF peptide in N. benthamiana (A) and tomato (B) leaves. (C, D) Induction of alkalinization in N. benthamiana and tomato, respectively, by RALF‐B and Sl‐RALF. For (A) and (B), line colours are as follows: dark blue, mock treatment; red, Sl‐RALF; green, RALF‐B; purple, RALF‐C; black, Sl‐RALFΔ.