Abstract
Resting cysts of the soil ciliate Colpoda cucullus Nag-1 were found to be highly resistant to UV light (254 nm); the presumed UV dose required for 99.9% inactivation was 571 mJ/cm2. On the other hand, in case of vegetative Colpoda cells, the presumed UV dose required for 99.9% inactivation was 40 mJ/cm2). We found that the nuclei of resting cysts were surrounded by autofluorescent particles (nuclei-surrounding particles; NSP). The cyst wall components (lepidosomes and ectocyst layer) were also auto-fluorescent. These auto-fluorescent structures may absorb UV light to protect cytoplasmic components.
