ACTION SPECTRA FOR UV INDUCTION AND PHOTOREVERSAL OF A SWITCH IN THE DEVELOPMENTAL PROGRAM OF THE EGG OF AN INSECT (SMITTIA)*

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Abstract— An action spectrum was established for the induction by ultraviolet (UV) radiation of the aberrant body segment pattern ‘double abdomen’ in the egg of the Chironomid midge Smittia. The action spectrum shows a peak at 285 nm wavelength, a shoulder at 265 nm, a slight increase from 245 to 240 nm, and a steep decline towards 300 nm. Corrections for wavelength‐dependent shielding within the egg result in transformation of the shoulder at 265 nm into a minor peak. These results are compatible with the assumption that a nucleic acid‐protein complex is involved in the initial photoreaction. This assumption is supported by the fact that the UV induction of the aberrant body segment pattern ‘double abdomen’ in the egg of Smittia is photoreversible. Wavelengths effective in this photoreversal range from 310 to 460 nm, with a peak at 440 nm. These spectral characteristics agree with action spectra for photoreactivation in other systems. Indirect photoreactivation does not occur in the egg of Smittia under the conditions of the experiments. Photoreversal with 440 nm radiation at high dose rate is temperature‐dependent. The results support the assumption that the molecular basis for photoreversal in the egg of Smittia is similar to the predominant molecular mechanism of direct photoreactivation in other systems. Targets possibly involved in the UV induction of the ‘double abdomen’ are discussed.