Effects of UV-B irradiation on motility and photoresponsiveness of the coloured ciliate Blepharisma japonicum

the effects of artificial UV-B irradiation on motility, viability, photomotile responses and photoreceptor spectroscopic properties of the red ciliate Blepharisma japonicum were investigated. Both the mean velocity of the cells and the percentage of motile cells exhibiting step-up photophobic responses significantly decreased, increasing UV-B irradiation time. No marked difference with dark-kept control samples was observed in cells irradiated with visible light. Absorption and fluorescence measurements on cell suspensions indicated that no UV-B induced bleaching or spectroscopically detectable damage of the photoreceptor chromophore took place. The experimental results suggest that the UV-B target is a component of the photosensory transduction chain different from the photopigment itself and that cell vitality is damaged by a direct effect of UV-B, without any significant contribution from a pigment-sensitized photodynamic reaction.