Long-Distance Electrical and Calcium Signals Evoked by Hydrogen Peroxide in Physcomitrella.

Electrical and calcium signals in plants are one of the basic carriers of information transmitted over a long distance. Together with reactive oxygen species (ROS) waves, electrical and calcium signals can participate in cell-to-cell signaling, conveying information about different stimuli, e.g. abiotic stress, pathogen infection, or mechanical injury. There is no information on the ability of ROS to evoke systemic electrical or calcium signals in the model moss Physcomitrella and on the relationships between these responses. Here, we show that external application of hydrogen peroxide evokes electrical signals in the form of long-distance changes in the membrane potential, which transmit through the plant instantly after stimulation. The responses were calcium dependent, since their generation was inhibited by lanthanum, a calcium channel inhibitor (2 mM) or EDTA, a calcium chelator (0.5 mM). The electrical signals were partially dependent on glutamate receptor ion channels (GLR), since the knockout of GLR genes only slightly reduced the amplitude of the responses. The basal part of the gametophyte, which is rich in protonema cells, was the most sensitive to hydrogen peroxide. The measurements carried out on the protonema expressing fluorescent calcium biosensor GCaMP3 proved that calcium signals propagated slowly (above 5 µm/s) and with a decrement. We also demonstrate upregulation of a stress-related gene which appears in a distant section of the moss 8 minutes after H2O2 treatment. The results help to understand the importance of both types of signals in the transmission of information about the appearance of ROS in the plant cell apoplast.