Staining, scoring and visualization of slides
For slide staining, 70 μ l acridine orange (20 μ g/ml)
was applied to each slide for 5 minutes and then
covered with a cover slip before observation under
a fluorescent microscope. Images of 100 randomly
selected cells were taken at 400x- magnification
using a fluorescent microscope (Nikon Eclipse 80 i)
equipped with a 450-490 nm excitation filter. Comet
tail lengths (consisting of the nuclear region and tail)
were scored visually as suggested by Collins20) into 5
comet classes (Fig. 1): a) comet class 0 (no damage,
hence no tail), b) comet class 1 (tail up to 1.5 times
the diameter of the comet nucleus), c) comet class 2
(tail 1.5−2.0 times the diameter of the comet nucleus),
d) comet class 3 (tail 2.0−2.5 times the diameter of
the comet nucleus) and e) comet class 4 (maximally
damaged with total DNA in its tail).