EFFECTS OF SIMULATED SPACE ULTRAVIOLET AND VISIBLE RADIATION UPON DRY CYSTS OF COLPODA INFLATA

Abstract— Dry cysts of Colpoda inflata were irradiated with an argon plasma arc lamp, the output of which simulates space radiation in its wavelength distribution although it is of higher intensity. Rapid evacuation reduced the rate of excystment as well as the percentage excysting; low temperature (near that of liquid nitrogen) had little effect on either measurement. All cysts were therefore irradiated at room temperature in a cell flushed with dry nitrogen. Radiation passed for 1 min through a sapphire filter, with a cutoff at 145 nm, prevented excystment. At smaller doses progressively less damaging effects were observed as judged by both the increase in time required for excystment and the percentage excysted. No dark recovery was observed in dry cysts. Exposure of cysts to radiation passed through a series of filters which progressively remove short ultraviolet wavelengths indicate that it is mainly the quartz-transmitted wavelengths (cutoff 185 nm) which damage the cysts. The presumption is that most of the vacuum-ultraviolet wavelengths are superficially absorbed; their lesser effect is also partially attributable to their lower intensity. Inasmuch as 1 min of argon lamp radiation is equivalent to 24 min in space, it is evident that Colpoda cysts would not long survive a journey in space, had they reached there in viable condition.