Photolyase activity of the embryo and the ultraviolet absorbance of embryo jelly for several Ontario amphibian species

Abstract

Organisms whose eggs develop at or near the interface between air and water may be particularly vulnerable to damage from ultraviolet radiation. The primary form of ultraviolet B (UV-B) radiation damage to biological systems is the formation of cyclobutane pyrimidine dimers (CBPDs) in DNA. The most common method of repairing this damage is photoenzymatic repair via photolyase, whose actions are specific to CBPDs. We utilized a bacterial-transformation assay to estimate the level of photolyase activity of various tissue types in seven species of amphibians collected in south-central Ontario. In this assay, the photolyase activity of a species is measured as the rate of CBPD removal from UV-B-damaged plasmid DNA by cell-free extracts created from the tissue of the species in question. The depth of oviposition and the UV-B absorbance of the embryo jelly, two variables that alter an embryo's in situ exposure to UV-B radiation, were measured to determine whether the level of photolyase activity was correlated with expected UV-B exposure. In vitro measurements of photolyase activity for the seven species were significantly different (F[6]= 10.31, p < 0.0001) and tended to be positively correlated with expected in vivo exposure to UV-B radiation.