Glucose, Sorbitol and Insulin as Exogenous Agents that Monitor the Interautogamous Interval (IAI) in Paramecium primaurelia

Results from previous studies have revealed that the duration of the interautogamous interval (IAI), expressed as the number of fissions occurring between two successive autogamies, is stable and characteristic for species of the Paramecium aurelia complex (KOŚCIUSZKO & PRAJER 1988; PRAJER & KOŚCIUSZKO 1999). The duration of the IAI is genetically controlled (KOŚCIUSZKO & PRAJER 1989; MIKAMI & KOIZUMI 1983). Genomic mutations (PRAJER & KOŚCIUSZKO 1999; TAKAGI et al. 1989) as well as disturbances of morphological homeostasis of the cell, as observed in Paramecium doublets (PRAJER et al. 1999), shorten the duration of the IAI. This suggests that epigenetic factors may accelerate the induction of autogamy. The aim of this study was to search for environmental, exogenous factors which may affect the IAI duration. The first investigated factor was glucose used in such a concentration which did not change the rate of vegetative cell divisions. The second tested factor was sorbitol used as nonmetabolized sugar and applied at a similar concentration as glucose to verify a possible osmotic effect. Both these factors accelerated the induction of autogamy and shortened IAI duration in Paramecium primaurelia. An insulin hormone was also used as a candidate for a sugar dependent factor complementary to glucose. It also resulted in acceleration of autogamy induction. It was chosen to test its effect on IAI since the existence of an insulin receptor in Tetrahymena has been reported (CHRISTENSEN et al. 2003). This hormone peptide also induced an IAI shortening. The results of a search in the Ciliates genome for potential homologs of genes coding insulin receptors and insulin itself, as well as hypothetical mechanisms of action of investigated agents were discussed.