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Lethal effects of far UV on pre-blastodermic embryos of Sciara ocellaris (Diptera; Sciaridae)

Virgínia Maria B. Guatimosim; André Luiz P. Perondini

Departamento de Biologia, Instituto de Biociências, Universidade de São Paulo, Caixa Postal 11461, 05422-970 São Paulo, SP, Brasil. Send correspondence to A.L.P.P.

ABSTRACT

The lethal effect of far UV was studied in Sciara embryos at four pre-blastodermic stages. In two of them the nuclei were immersed within the endoplasm (EC2 and EC3), and in the other two, the nuclei were at the periplasm (SB4.5 and SB5.5). Embryos at stages SB proved to be more sensitive to radiation. Differences in the survival curves between the two SB stages were due to an increase in the number of targets. No significant differences were observed between the survival curves for EC stages. Analysis of the fluence corrected by the absorbance of the chorion and cytoplasm, at each stage, showed that while at SB stages the nuclei were certainly being affected, at EC2 only peripheral cytoplasmic layers were damaged and, at EC3, cytoplasmic and nuclear targets were reached by UV. Irradiation at SB and EC3 resulted in immediate death, while at EC2 most of the embryos proceeded further in development (late death). Incubation at low temperatures after irradiation accentuated the effect of UV. For SB, this is probably caused by inhibition of dark repair mechanisms, while for EC, interferences in physiological factors other than repair must have occurred. Action spectra for inactivation showed peaks of efficiency at 295 nm and 265 nm respectively, for stages EC and SB. These results indicated that upon irradiation death is due at EC2 to damage imposed on cytoplasmic targets; at EC3, to nuclear and cytoplasmic lesions and at SB, to damages imposed on nuclear targets.

Keywords: UV; pre-blastodermic; embryos; Sciara ocellaris.

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