Action spectra for UVB impacts on Blepharisma japonicum motility and photobehavior

The ciliate Blepharisma japonicum was exposed to artificial polychromatic a nd monochromatic UV radiation to evaluate the relative roles of UVB (280-31 5 nm UV radiation) and UVA (315-400 mm UV radiation) in altering its motili ty and photobehavior and to determine absolute weighting coefficients for t hese effects in the UVB range. Under polychromatic UV irradiation B. japoni cum cells showed a severe reduction of cell speed and of the capability to respond to light stimuli. At low doses, however, UV caused a significant in crease in the average velocity of a cell population. The UVB exclusion expe riments indicated that UVA does not significantly alter motility and photor esponsiveness, The increase and the subsequent decrease in cell velocity wa s observed also under monochromatic irradiation at 281, 290 and 300 nm, whe reas at 310 nm cells swim faster up to the highest photon Bur density used. The cell capability of reacting to photic stimuli, conversely, steadily de clined with increasing photon flux density at all the tested UVB wavelength s. The action spectra for the alteration of cell velocity and the impairmen t of photoresponsiveness show that the lower the irradiation wavelength, th e more remarkable are the UVB effects and suggest different targets for the increase and the decrease in cell velocity.