我国北部湾球形棕囊藻(Phaeocystis globosa)的表面形态和细胞超微结构的电镜观察

SCANNING AND TRANSMISSION ELECTRON MICROSCOPY OBSERVATION ON MORPHOLOGY AND ULTRASTRUCTURE OF PHAEOCYSTIS GLOBOSA FROM BEIBU GULF,CHINA

本文首次对分离于我国广西北部湾的一株棕囊藻(Phaeocystis)纯培养进行了形态学研究。通过对其核糖体大亚基序列(LSU rDNA)进行了系统进化分析,并运用光学显微镜、扫描电镜和透射电镜等,对该藻的游动单细胞和囊体细胞表面结构和超微结构进行了详细的观察。结果表明,通过分子序列和形态学特征确证了该纯培养为球形棕囊藻(Phaeocystis globosa)。通过分子系统进化分析,从北部湾获得的球形棕囊藻与同属的P.antarctica和P.rex的亲缘关系较近,但与P.jahnii的亲缘关系相对较远。我们发现该藻至少有两种类型的细胞:具鞭毛游动细胞和无鞭毛囊体细胞,其大小分别为2.30-3.98μm和3.69-6.49μm。具鞭毛游动细胞表面具有1-2个位置不固定但形状较为规则的圆盘状凸起,细胞表面的鳞片大小无明显差别;囊体细胞均匀地分布在囊体上,囊体细胞表面光滑,有三个较短的附属物。具鞭毛游动细胞和囊体细胞有2个或4个叶绿体,具鞭毛游动细胞的细胞核位于细胞的中下部,而囊体细胞的细胞核则位于细胞的中上部。细胞分泌物在扫描电镜样品处理过程后形成多数与细胞相连的丝状物,且丝状物形成较为规则的五角星形结构,每个角与一根丝相连,有些丝状体上有"瘤状"结构。研究结果填补了我国在球形棕囊藻形态学和超微结构研究上的空白,为深入认识其生物学特征及其成囊机理提供基础。

A strain of Phaeocystis sp was isolated from the Beibu Gulf,Guangxi,China,and its fine morphology was reported first time in the country.The flagellate and colonial cells were observed by light microscope,scanning and transmission electron microscopy,and molecular phylogeny using partial large subunit ribosomal RNA gene(LSU rDNA)sequence was also analyzed.Results show that this species is Phaeocystis globosa identified from its molecular sequence and morphological characterization.The LSU rDNA sequence and phylogenetic tree reveal that this species is more closely related to P.antarctica and P.rex,but is diverged from P.jahnii.Two cell types are observed in P.globosa:small flagellates and colonial cells,and their sizes are 2.30-3.98μm and 3.69-6.49μm,respectively.The small flagellate cell has 1-2 circular bulges,and the cell surface is covered with an external layer of scales without difference in size.Colonial cells are randomly distributed at the periphery of spherical colonies,which have smooth surface without scales and have three short appendages.Two or four chloroplasts are observed and the nucleus locates in the middle and upper parts.The filaments extruded by the cells form pentagonal star-like structures,the structure connected five filaments at their proximal ends,and a tuberculiform structure appears in some filaments.This study fills the blank in fine morphology and ultrastructure of P.globosa in China and provides a base on understanding its biological characterization and mechanisms of colony formation.