ABA enhances salinity tolerance in Chlamydomonas by
reducing ROS formation in cells
We used the fluorescent probe H2DCFDA to estimate the
cellular ROS-sensitive fluorescence in Chlamydomonas using
confocal microscopy, where the green color indicates the presence of ROS
and the red color indicates autofluorescence of chlorophyll (Fig. 4).
ROS are natural by-products of cell metabolic processes (Mallick and
Mohn, 2000), therefore non-stressed cells were also stained with
H2DCFDA to determine background levels of ROS for
quantifying salt-stressed ROS induction compared to the non-stressed
control. A very weak ROS green fluorescent signal was observed under
control growth conditions. After salt treatment, strong ROS fluorescent
signals were detected in the chloroplast and the mock sample, whereas
slight ROS signal was observed in the ABA-treated cells (Fig. 4A). These
results indicate that ABA decreased the ROS level in cells.
Intracellular ROS accumulation was measured in control and ABA-treated
cells following exposure to 125 mM NaCl by using flow cytometry. All
treatments with 125 mM NaCl significantly increased intracellular ROS
after 3 h in comparison to controls (Fig. 4B). In ABA-treated cells
there was a comparative significant reduction in ROS accumulation. Cells
treated with 50 μM ABA induced ROS to ~ 55% relative to
stressed ABA-untreated cells.