H₂O₂-evoked calcium signals recorded in protonema cells expressing fluorescent calcium biosensor GCaMP3. For each cell, two circular regions of interest (ROIs) located in the cytoplasmic region from both sides of the nucleus were analyzed. The two panels of pictures show two different types of calcium signal propagation—at the upper panel, the signal propagates in one direction starting from the site of stimulation (basal part of the gametophyte), and at the lower panel, the signal propagation starts from one cell (marked by yellow ROIs) and propagates in two opposite directions. The changes in fluorescence intensity in different ROIs are presented in the bottom right corner of each picture panel.