The foliar concentration of hydrogen peroxide during salt-induced C3-CAM transition in Mesembryanthemum crystallinum L.

Hydrogen peroxide (H2O2) is one of the most stable reactive oxygen species (ROS), which is produced in plants in various metabolic processes and its level can increase as a result of many stress factors. It was found that a NaCl-induced shift from C3 to CAM in Mesembryanthemum crystallinum L. leaves was accompanied with a significant increase in H2O2 concentration (as calculated on a chlorophyll basis). Moreover, the highest accumulation of H2O2 in leaves and leaf veins appeared before the maximal nocturnal malate accumulation was detected on day 6 and 9 of NaCl-treatment, indicating that salinity itself is responsible for an increase in H2O2 production. Several symptoms of functional CAM, i.e. strong increase in NADP-ME activity, and diel malate oscillations, appeared after 9–12 days of salt-treatment. The obtained results suggest that accumulation of H2O2 in leaves and leaf veins is due to salinity itself, and appears before functional CAM, but H2O2 as a trigger involved in C3-CAM transition seems to be an important factor.