Abstract:  The distribution of nitric oxide synthase (NOS) during gametogenesis in Phaneroptera gracilis Burmeister was studied with NADPH-diaphorase histochemical method. The results showed that nitric oxide synthase positive reaction could be found in the cytoplasm of permatogenic cells in the different stages of the gametogenesis in P. gracilis, while NOS negative reaction appeared in matured sperms. There were NOS positive reactions in the cytoplasm of immatured oocytes in all stages. Usually, cytoplasms were stained with some heavy black while nuclear regions were not obvious. With the formation of yolk granules, the products of NOS positive reactions diminished gradually in cytoplasm until yolk granules formed completely. The follicle cells showed NOS negatively before the formation of yolk granules. After the yolk granules formed completely, the cytoplasm of follicle cells started showing NOS positively until the formation of chorion.

Key words: Phaneroptera gracilis, nitric oxide, nitric oxide synthase, NADPH-diaphorase, gametogenesis