Reactive oxygen species were found in all cell types in the ovaries of D. veneta. The lowest level of those compounds was found in somatic cells, which correlates with the lowest quantity of mitochondria in these cells. The different content of ROS in particular prooocytes was interesting. The reaction level was higher in the cytoplasm than in the nucleus in some of them, while in the remaining ones it was the opposite. It is possible that these differences represent very early signs in the determination of prooocytes into oocytes or trophocytes. The low level of ROS in the central ooplasm of postvitellogenic oocytes and elevated level of these substances in subplasmalemmal positions is also characteristic. Such a result is in register with JC-1 staining which indicates more active mitochondria in the same cell regions. The reaction showing ROS distribution in the D. veneta ovary PF-2341066 corresponds well with the distribution of mitochondrial SuperOxide Dismutase. Manganese superoxide dismutase is the primary antioxidant enzyme that resides in mitochondria that can protect cells from oxidative damage by catalyzing the dismutation of superoxide to H2O2 and O2.MnSOD is important inmaintaining intracellular ROS and redox balance. Increased MnSOD protects tissues against oxidative stress. According to our results, the strongest protection MnSOD is rendered to the oocytes of the species that was studied and the weakest to the somatic cells. The occurrence of two populations of mitochondria in germ-line cells has been described in many other animal species. What is the biological reason for the Nilotinib existence of inactive mitochondria in the germ-line cells? According to Kogo et al., the separation of an inactive subset of mitochondria in amphibian oocytes is connected with their accurate transmission to the next generation. In other animal groups like mammals, fishes, nematodes, birds and insects, the existence of a fraction of inactive mitochondria in oocytes was also interpreted as being connected with the protection of this mitochondria against mtDNA mutations before they could be transmitted to the progeny. It is well established that there is a strong positive correlation between membrane potential and ROS production. At high membrane potentials, even a small increase in the membrane potential gives rise to a large stimulation of H2O2 production. Similarly, only a small decrease in membrane potential is capable of inhibiting H2O2 production. Therefore, ��mild uncoupling��, i.e. a small decrease in membrane potential, was suggested to have a natural antioxidant effect.