Salinity-Induced Noise in Membrane Potential of Characeae Chara australis: Effect of Exogenous Melatonin

Salt sensitive Characeae Chara australis responds to 50 mM NaCl by a prompt appearance of noise in the trans-membrane potential difference (PD). The noise diminishes with time in saline and PD depolarization, leading to altered current–voltage characteristics that could be modeled with H⁺/OH⁻ channels. Beilby and Al Khazaaly (JMB 230:21–34, 2009) suggested that the noise might arise from cooperative transient opening of H⁺/OH⁻ channels. Presoaking cells in 10 μM melatonin over 24 h abolished the noise in some cells, postponed its appearance in others or changed its characteristics. As melatonin is a very effective antioxidant, we postulated opening of H⁺/OH⁻ channels by reactive oxygen species (ROS). Measurement of ROS using dihydrodichlorofluorescein diacetate confirmed substantial reduction in ROS production in melatonin-treated cells in saline and sorbitol media. However, ROS concentration decreased as a function of time in saline medium. Possible schemes for activation of H⁺/OH⁻ channels under salinity stress are considered.