EFFECT OF UV-B RADIATION ON CILIATED PROTOZOA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 236

photoreceptor pigment is strengthened. A damage to the rhodopsin-like pigment, in
addition to a damage to some steps of the sensory transduction chain, could, in fact,
explain the UV-B induced reduction of the phototactic response.

1,2

0,8

0,4

0,0

400 500 600

Wavelength [nm]

Fig. 13. Fluorescence excitation spectra (emission wavelength = 640 nm) of sonicated suspensions of
F. salina cells before (solid line) and after 120 min irradiation with UV-A and visible radiation
(dashed line) and with UV-B, UV-A and visible light (dotted line).

In the case of Ophryoglena flava an UV action spectrum of positive phototaxis
inhibition was determined under polychromatic irradiation conditions. In order not to
exclude possible repair mechanisms due to UV-A and/or visible radiation, sample were
irradiated with radiation from 280 to about 700 nm (TL40W/12 Philips and
TDL36W/54 Philips fluorescent lamps, emitting in the UV and visible, respectively),
removing increasingly larger portions of UV-B and short wavelength UV-A, by means
of coloured glass filters (see Ghetti et al., this volume). Moreover UV irradiance was
modulated by using one or three UV fluorescent lamps. UV-B irradiance was
comparable to that recorded outside by an ELDONET dosimeter (www.eldonet.org and
Häder and Lebert, this volume) in summer days.
Even these irradiance values damaged the cells and, if the exposure lasted long
enough, they were killed. However, in natural conditions the organisms might be shaded
by the organic matter usually present in lakes and ponds. Moreover, in the above-
described experimental set-up cells are continuously irradiated, whereas in the natural
environment, after being damaged by UV radiation, they can start swimming in random
direction and disperse in the water column, far from the surface.
It should be noted that the ratios between UV-B irradiance and UV-A and visible
one in the above-described experiments were much higher than those of the solar