To gain full understanding of salt tolerance, we also need to study responses to salinity in salt sensitive plants. Large celled Characeae are closely related to ancestors of land plants (Timme et al. 2012) and already established the basis of plant electrophysiology (Hope and Walker 1975; Beilby and Casanova 2013) and cytoplasmic streaming (Shimmen 2007). Salt sensitive Chara australis does not survive relatively mild stress of 50 mM NaCl. The membrane potential difference (PD) exhibits prompt characteristic noise (Al Khazaaly et al. 2009) and gradual depolarization to levels above -100 mV. The saline-induced noise then diminishes and the current-voltage (I/V) characteristics transform from proton pump dominated profile to an upwardly concave profile that can be modeled by H+/OH- channels (Beilby and Bisson 2012: Beilby and Al Khazaaly 2009). Zinc ion, a powerful block of animal H+ channels, reversibly abolishes both the saline-induced noise and upwardly concave I/V (Al Khazaaly and Beilby 2012), suggesting that the noise could originate from transient opening of H+/OH- channels. Eremin et al (2013) hypothesize that H+/OH- channels may be opened by rise in reactive oxygen species (ROS) concentration in the cytoplasm. Incubation of cells in 10 μM melatonin, efficient antioxidant, abolished or postponed the onset of saline-induced noise, but did not stop salinity-induced depolarization. Measurement of ROS in Chara cells upon exposure to saline medium is now in progress.