多子小瓜虫的形态发生及其寄生导致翘嘴鳃组织病理变化

为阐明小瓜虫的形态发生及其对鳃组织的危害过程,本文开展了多子小瓜虫的光镜观察和翘嘴鲌鳃组织病理切片方面的研究。光镜形态研究发现小瓜虫运动时呈球形,直径500-800 m;前端具有耳廓状胞口和内陷的袋状胞咽;环境温度为18℃时,滋养体经1h左右发育成包囊,体表形成一层透明胶膜,并以虫体中央的分裂沟为界进行二分裂;子代虫体从8细胞期进入16细胞期时,包囊内部形成内胞膜将子代虫体等分为两个集团。组织切片结果显示虫体呈卵圆形,挤压了周围的包裹细胞,导致组织变形;鳃小片黏连,鳃丝上皮细胞受到破坏,严重区域鳃丝结构被完全破坏。本研究解析了小瓜虫的形态发生与发育过程以及对宿主危害的组织病理结构与机制,为揭示小瓜虫的侵染、发育和成熟规律奠定了理论基础,并为小瓜虫病害的有效防控提供理论资料。     

New details from the complete life cycle of the red-tide dinoflagellate Noctiluca scintillans (Ehrenberg) McCartney

Noctilucid protozoans are among the dinoflagellates that cause red tides. Sexual reproduction may occur in this group, as they sometimes undergo gametogenesis. However, the life cycle, in particular the developmental process after gamete fusion, has not been fully elucidated. We have been able to maintain clonal cultures of Noctiluca scintillans throughout the whole life cycle and have revealed new details of various stages. In trophont populations, a small fraction of cells spontaneously transform into gametogenic cells, which undergo two successive nuclear divisions, without cellular division, probably corresponding to meiosis. The products of nuclear division migrate to the cell surface with a small amount of cytoplasm, and there further synchronously divide 6-8 times, during which the division products are connected by thin cytoplasmic bridges. Thus, numerous gametes with a semi-spindle body shape are released from the mother cell ghost. They retain two flagella that differ in length and motion, as is typical of dinoflagellates. The presence of longitudinal and transverse grooves indicates that dinoflagellate-like characteristics are conserved in the gametes, although they are not present in the specialized trophonts. Zygotes with four flagella result from the fusion of two isogametes. The zygotes change shape from spindle to spherical, with a reduction in flagellar number. The developing cell acquires a tentacle and crust, similar to large trophonts, and begins to develop a cytoplasmic network, thus completing the transformation into a miniscule trophont. These early trophonts grow to maturity as cell size increases. Our observations of the life cycle of N. scintillans may provide clues for understanding the evolutionary origin of noctilucae.     

A novel hematoxylin and eosin stain assay for detection of the parasitic dinoflagellate Amoebophrya

The parasitic dinoflagellate Amoebophrya infects broad range of marine organisms. Particularly, Amoebophrya infections in planktonic dinoflagellates can prevent or delay the formation of algal blooms, and recycle undergrazed planktonic dinoflagellates back to the microbial loop by disrupting host cells. Its ecological significance was gradually recognized along with the discovery of its enormous molecular diversity in oceanic and coastal ecosystems. Thus, we developed a reliable, easily accessible and less time-consuming assay, to detect and assess Amoebophrya infections in planktonic dinoflagellates. The modified hematoxylin and eosin staining assay provided reliable diagnosis of Amoebophrya infection by identifying the characteristic “beehive” of the multinucleate trophonts. After staining, the typical multinucleate “beehive” is evidently distinguishable from the compact nuclei of uninfected host cells. The modified hematoxylin and eosin (H & E) staining assay is easy to use, that can be routinely performed within 3 h (up to 20 samples/batch) using general laboratory equipment, supplies and chemical reagents. The produced slides with agar-embedded dinoflagellate cells can be stored for several months or even years in a dry place without noticeable loss in quality of staining. With suitable calculation, the modified H & E assay can be applied to assess the prevalence of Amoebophrya infection in planktonic dinoflagellates. This efficient and powerful assay will facilitate the investigation on the ecological roles of Amoebophryidae in coastal and oceanic ecosystem.