Circadiane Rhythmik von Drosophila-Speicheldrüsen in vivo, in vitro und nach Ecdysonzugabe

Abstract

Nuclear and nucleolar volumes of Bouin-fixed salivary glands of Drosophila larvae show a bimodal circadian rhythm (12 : 12 hr light-dark régime, 20°C). The phasing of this rhythm relative to the light-dark ‘Zeitgeber’ changes in the course of ontogeny, i.e. from day 4 to day 7 during larval development. The rhythms of nuclear and nucleolar volumes seem to follow the same pattern. Living nuclei from salivary glands freshly prepared at different times of day show a bimodal rhythm very similar to the rhythm of fixed salivary glands of the same developmental age. The transverse profiles of all data under normal and inverse light-dark conditions reveal significant differences between maxima and minima. Volumes of single nuclei from salivary glands cultured up to 10 days in a chemically defined medium also oscillate in a bimodal circadian rhythm (12 : 12 hr light-dark régime, 25°C); differences between maxima and minima extend to about 10 per cent of the mean volume. The rhythm of these nuclei measured longitudinally over 36 to 48 hr coincides with the rhythm of the fixed and living nuclei in the transverse profiles. Varying relative K + and Na + concentrations of the medium have no remarkable influence on the rhythm. The rhythm persists in constant light of about 200 lx for at least 4 days; it is phase-shifted by a 6 hr ‘Zeitgeber’ shift during larval development. Pulse- or stepwise addition of ecdysone-containing medium between 13 and 18 hr caused a phase shift of the nuclear rhythm in vitro: after a small maximum at 24 hr (coinciding with the controls) phase differences of 3 to 9 hr relative to the normal and control groups can be observed later. The addition of ecdysone between 9 to 12 hr failed to shift the rhythm.