Cell viability
Cell number of exponential cultures was adjusted to ~ 2× 103 cells*mL-1 in fresh TAP medium containing 0 (control), 50 µM ethanol (mock) and 50 µM ABA then algal inoculates of 50 µl were spotted on TAP-1.5% Difco agar plates with and without 125 mM of NaCl (6 plates each treatment). The plates were then incubated for 6-8 days till no more colonies were developed. The survival rate of the cells incubated with NaCl was indicated as a percentage to the control colony forming units (CFUs) in which the cells were incubated without NaCl.
Monitoring of photosynthetic activity To enable measuring net photosynthetic O2 production rates, a mini photobioreactor was equipped with a multi-sensor port, AlgaeGrowth-PAM, designed in the laboratory of Prof. Zvy Dubinsky at Bar Ilan University, and manufactured by Heinz Walz (Effeltrich, Germany) (Supplementary Fig. S1), controlled by custom WinControl-3 software (Fig. S4). Cultures were collected after 24 h of different treatments with continuous optimal illumination, then were loaded in the insolated metabolic chamber, dark-adapted for 10 min at 23 °C until the maximum quantum yield (Fv/Fm) was reached, then the cultures were illuminated with a stepwise increasing actinic light of 0, 110, 150, 230, 330, 480 and 1000 μmol photons m−2 s−1 for 2 min each step for a total period of 12 min. Oxygen production was monitored by an ultra-sensitive optical oxygen sensor (Pyroscience, Ltd) that uses a fluorescence signal (synthetic dye that changes fluorescence intensity with O2 concentration) under vigorous stirring. Delta O2 was calculated and exponential fitting curves were performed to extract Pmax values.