EFFECT OF UV-B RADIATION ON CILIATED PROTOZOA - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 228

B. japonicum possess a great amount of pigment granules, located beneath the
cell pellicle, which contain a hypericin-like pigment, called blepharismin, whereas
Ophryoglena flava is apparently colorless; the F. salina strain studied in these
experiments also contains a hypericin-like pigment, as shown by fluorescence
measurements 20-22 and the pigment granules are very similar to those found in
B. japonicum , though Blepharisma contains a much larger number of them 21 . This
explains why B. japonicum appears red-pigmented, whilst F. salina appears colorless. In
Blepharisma , the action spectrum of the step-up photophobic response indicates that
hypericin is very likely the photoreceptor pigment; in F. salina the action spectrum of
phototactic reaction 23 and immunocytochemical studies 24 indicate the presence of a
rhodopsin-like molecule. It has been suggested that the pigment responsible for
phototaxis in O .flava might be a rhodopsin-like molecule, as well. Recently, the data of
Cadetti et al. 25 have been reevaluated by Foster 26 , who concludes that a rhodopsin is
indeed the photoreceptor pigment in this ciliate.
Effect of UV-B radiation on motility
In B. japonicum , the exposure to UV radiation impairs cell motility, too 18 .
Samples were UV irradiated by means of three TL40W/12 Philips UV-B lamps, using a
cellulose acetate film to remove the UV-C component of radiation. Irradiations were
performed also with a Schott WG1 filter to remove UV-B radiation. In both
experimental conditions the total irradiance was kept about the same (a5 W/m 2 ) by
means of neutral density filters. In the presence of UV-B, the spectral distribution was
about 52% UV-B, 27% UV-A and 21% visible; UV-B irradiance was about 2.5 W/m 2 ,
comparable to that in the natural environment, whereas UV-A and visible irradiance
were about 30 and 400 times lower than the natural ones. In the irradiation condition
without UV-B, the spectral distribution was 0% UV-B, 16% UV-A and 84% visible.
UV-B irradiation for 30 and 60 minutes caused a gradual rise in the number of cells that
swim on circular trajectories and induced a significant decrease in the average speed:
from 118 Pm/s in control samples to 59 Pm/s and 7 Pm/s for 30 and 60 min irradiation,
respectively (see Fig. 3) 18 . However, recent results showed that short time UV-
irradiation (up to 10 min, at 3 W/m 2 ) causes an increase in cell speed (Lenci, personal
communication). On the contrary, cells irradiated without UV-B did not show any
movement pattern alteration, but a significant reduction of average speed was observed
after 60 min irradiation (see Fig. 3) 18 .
In F. salina low irradiance UV-B irradiation caused at a meaningful increase in
cell speed 19 , as also observed in B. japonicum . A similar experimental set-up was used:
two UV-B fluorescent tubes, TL40W/12 Philips, screened with a cellulose acetate film,
and a visible one, TLD36W/54 Philips: irradiance was about 8 W/m 2 in the visible
range and about 3 W/m 2 in the UV range (1 W/m 2 UV-A, 2 W/m 2 UV-B). The samples
were covered with: a quartz disk transparent to all wavelengths (treated samples), a
Schott WG1 filter to remove UV-B (control 1) and with a Schott GG400 filter
transparent to visible radiation only (control 2) 19 . UV-B-induced speed increase was
already detectable at short irradiation times (3 min 45 s) and reached a plateau after one
hour of exposure. Control samples, on the contrary, did not show meaningful alteration
of their swimming speed (see Fig. 4). UV-B induced motion alteration was limited to