Photorecovery from the Effects of Ultraviolet Radiation in the Developing Bracon Embryo

Restoration of ultraviolet radiation-induced lesions in a biological system with light of longer wavelength than that of the damaging radiation is generally known as photoreactivation (1). It is a widespread phenomenon affecting a variety of organisms and their functions (see refs. 1 through 4 for reviews and references). Many of the functions affected are of a developmental nature-for example, rhizoid formation in the Fucus egg (5), cleavage in echinoderms (6-8), and growth and regeneration in salamander larvae (9); among insects, molt-retarding effects in the milkweed bug nymph (10) and hatching in newly laid eggs of the wasp Bracon hebetor (11) have been reported. The object of the present investigation is to study photoreactivation as it occurs over a wide range of embryonic ages in the same animal and to analyze the resulting information in terms of its morphogenetic significance. To this end, the developing Bracon embryo's response to photoreactivating light after exposure to 2537-A ultraviolet radiation has been determined and the resulting information correlated with morphologically observable developmental events. In an earlier paper, I have shown that the Bracon embryo varies considerably with respect to its sensitivity to ultraviolet radiation during development (12). This suggests that, at certain ages, ultraviolet-sensitive compounds-for example, nucleic acids-play a somewhat different or perhaps more critical role in development than at others. Since it is generally agreed that such compounds are involved in photoreactivable damage, the embryo's response to photoreactivating light might well serve as an aid in elucidating their morphogenetic role. A brief preliminary report (13) has covered part of the material contained in this paper.