Photoreactivation in Blepharisma

Abstract

1. 1. After exposure to far-ultraviolet (UV) radiation (265 nm), an equally high degree of photoreactivation (PR), about 80 to 90% of the radiation-induced division retardation, was obtained with the albino mutant of Blepharisma japonicum as with other ciliates previously tested, contrary to an earlier report. 2. 2. Maximal PR was observed only when PR light of low intensity was used and the dose was optimum. If too large a dose was applied, apparent PR was correspondingly reduced. 3. 3. Violet (405 nm) and blue (436 nm) light were most photoreactive; near-UV (366 nm) somewhat less so, and green (540 nm) and yellow light (570 nm) only slightly so. This is similar to what has been found for many other organisms. 4. 4. Under appropriate conditions similar degrees of PR were obtained for red wild-type B. japonicum as for the albino, though higher doses of PR light (longer exposures) were required. 5. 5. Under restricted conditions, which were different as to dose of PR light required, comparable PR was obtained in B. americanum, B. stoltei and B. japonicum. A high degree of PR is therefore probably characteristic of the genus, not just the albino. 6. 6. In the light of the present study, the previously reported low degree of PR of far-UV induced division delay, which had been considered exceptional among ciliates, appears to be an artifact, a result of ( a) the use of logarithmic cultures which show less PR; ( b) exposure to yellow light during handling and microscopic observation, which, though non-photoreactive to other ciliates, photoreactives far-UV damage in Blepharisma, and so reduces apparent PR measured; ( c) supraoptimal light dosages which themselves induce division delay and so reduce the measurable PR. 7. 7. Blepharisma is much more sensitive to visible light in the PR spectral range than is Colpidium colpoda, which tolerated very much larger doses without injury.