Radiation Sensitivity of Transgenic Chlamydomonas

The unicellular green alga C. reinhardtii strain CC-125 cells (1.5 × 10⁶) were cultured in 50 mL liquid tris-acetate-phosphate (TAP) media in 250 mL flasks (Harris, 1989 ) by shaking at 25°C and 140 rpm under constant white light of 90–100 μmol photons m⁻² s⁻¹. In addition to the wild type (WT), two transgenic C. reinhardtii lines (AtTHI-OE1 and AtTHI-OE2) harboring the Arabidopsis thaliana Thionin 2.1 gene, which encodes antibacterial peptides, thionins, were used to investigate genotype-dependent radiation-sensitivity. Cells were harvested at 800 × g, dispensed, and subjected to X- or γ-irradiation as described below. The subsequent post-irradiation cultivations of the cells were performed in 10 mL fresh TAP media in 50 mL conical tubes, with an initial optical density of 0.05 at 750 nm for mock (or control) under the same culture conditions. The basal TAP medium was supplemented with 5 or 10 mM NaHCO₃ to evaluate the synergistic effect of X-rays and sodium bicarbonate on cell growth.