Histological Observation Of The Spermary And Sperms Of Polymesoda Erosa And Response To Chromium Exposure

As a bivalve shellfish of corbiculaceae,Polysoda erosa is distributed in the coastal shoals of the tropics and subtropics in China,especially in the mangroves.As one of the important species in the Macrobenthos community,it has high ecological value and breeding prospects.Because of over harvesting and increasing environmental pollution,the survival and reproduction of P.erosa are seriously threatened.In this study,hematoxylin eosin staining(H.E.),tissue sectioning and transmission electron microscope(TEM)were used to observe the histological structure and sperm ultrastructure of P.erosa.At the same time,the toxic effect of hexavalent chromium(Cr(Ⅵ))on the testis of P.erosa was studied by acute toxicity test.One control group and four Cr(Ⅵ)experimental groups(4.34mg/L,8.69mg/L,17.38mg/L and 34.76 mg /L)were set up in the experiment.The sperm number,malondialdehyde(MDA)content,catalase(CAT)and glutathione S-transferase(GST)activity were measured in the spermary samples at 24 h,48h and 72 h after exposure.At the same time,real-time fluorescence quantitative PCR was used to detect the m RNA transcription level of CAT and GST genes in the spermary,and the effect of Cr(Ⅵ)on the spermary and sperm structure of P.erosa 72 hours after exposure was observed.The results shows that:(1)The spermary of male P.erosa has typical characteristics of follicular type,and the germ cells of different developmental stages are arranged in layers in the cavity.The head of spermatozoa is slender and cone-shaped,the acrosome is inverted "V",the mitochondrion is round,and the flagellum microtubule is a typical "9 + 2" structure.Acute Cr(Ⅵ)stress can cause spermary structure damage and has obvious toxic effect.Cr(Ⅵ)exposure resulted in the damage of seminal membrane,the enlargement of follicular space,the atrophy and deformation of follicular cavity,the decrease of sperm number,the destruction of sperm structure,the deformation of acrosome,the appearance of vacuoles,and the dissolution of mitochondrial crista.(2)The MDA content of spermary showed different trends under different chromium concentration.The MDA content of low concentration group(4.34 mg / L)increased first and then decreased with the extension of stress time,which indicated that the antioxidant system of P.erosa could eliminate the pressure brought by Cr(Ⅵ).When exposed to higher concentration,MDA content increased significantly(P < 0.05),indicating that high concentration of Cr(Ⅵ)stress would cause oxidative damage to the testis of P.erosa.In addition,under the same stress time,MDA content increased with the increase of chromium ion concentration.The activities of cat and GST in spermary showed differenttrends.The activity of CAT increased with the increase of stress time.At 72 h,the activity of CAT in each concentration treatment group was significantly higher than that in the control group(P < 0.01).The activity of GST enzyme increased in the early stage of the experiment,but decreased significantly in the high concentration(34.76 mg / L)for 72hours(P < 0.05).The results of fluorescence quantitative analysis showed that the changes of m RNA expression of cat and GST genes were consistent with the changes of enzyme activity.In this study,we studied the histological structure of the spermary and sperm ultrastructure of P.erosa,the toxic effect and tissue damage of P.erosa under Cr(Ⅵ)stress,and discussed the toxic mechanism of Cr(Ⅵ)on male P.erosa and its impact on the reproductive system,which provided a reference for resource protection of P.erosa.