MORPHOLOGY, FINE STRUCTURE AND CHEMICAL COMPOSITION OF EXTRACELLULAR POLYMERIC SUBSTANCES IN THREE MARINE DIATOM SPECIES
- 海洋环境－已发表论文 
利用光镜和扫描电镜对厦门近海三种常见附着硅藻———爪哇曲壳藻亚缢变种(Achnanthesjavanicavar.subconstricta)、咖啡形双眉藻 (Amphoracoffeaeformis)和多枝舟形藻 (Nav icularamosissima)胞外多聚物 (Extracellularpolymericsubstances,EPSs)的形态和微细结构进行了研究 ,并初步分析了其化学组成。结果表明 ,A .javanicavar.subconstricta的胞外多聚物为透明的长柄 ,分为领、柄及垫状物三部分 ,电镜显示其微细结构为由许多纤维组成的双层实心管 ;Amphoracoffeaeformis分泌的EPS为由串连的小节组成的实心管状结构 ,许多管交织成厚的胶质块 ;Navicularamosissima的EPSs则为透明的薄膜并形成胶质膜。三种硅藻胞外多聚物的水溶性和水不溶性的主要成分均为多糖类 ,达总量的 70 %以上 ,蛋白质含量次之 ,不含脂类物质 ,但不同藻类EPS的组成差异较大。此外 ,还探讨了EPSs的功能及其分泌机理Extracellular polymeric substances (EPSs) of diatoms that exist in the form of stalks, apical pads, adhering films and fibrils, are a type of mucilaginous substance secreted in the exterior of cells. EPSs which play important roles in the life of diatoms in thier marine eco system. This paper investigated the morphology and detailed structure of EPSs in three marine diatoms, Achnanthes javanica var. subconstrict, Amphora coffeaeformis and Navicula ramosissima , isolated from the surface of seaweed collected in the Xiamen offshore. These samples were analyzed using microscope and scanning electronic microscope (SEM) methods. Their chemical compositions were also analyzed preliminary. The results showed that the morphology of EPS varied significantly among species with individual feature. EPS of A. javanica var. subconstricta has a long transparent stalk liked EPS, which usually lies on one end of cells and is composed of three parts: collar, stalk and pad. Cells of A. javanica var. subconstricta were attached to the surface of cultured vessel through the pad and many of the cells formed a cell line. The results from SEM showed that the close up of the EPS had a double layered solid tube structure made of fine fibers. Moreover, some cells have two or more stalks were observed under microscope. The EPS secreted by A. coffeaeformis was a solid tube, which is assembled by small tandemed segments with many interlaced tubes and gathered as colloid agglomeration, cell moved through the solid tubes and formed the lump. The EPS of N. ramosissima was a transparent and colloid mucous membrane, which covered on the surface of culture vessel and cells moved the membrane. There were many hollow cell hull liked membranes among of them, and spot veins were observed clearly. The preliminary results on EPS composition indicated that the compositions of both water soluble and water insoluble portions of EPS in the three diatoms were dominated by polysaccharides. Their contents exceeded 70% of total EPS, along with a small amount of protein, accounting for 3.2%—28% of total EPS. No lipid was found in the EPSs. Composition of polysaccharides and protein in EPSs varied greatly among different species, especially for the water insoluble portion: major composition of EPS in A. coffeaeformis was polysaccharides, up to 97% of total EPS content, protein content was very low, however the protein contents of EPS in A. javanica var. subconstricta and N. ramosissima were higher, 18.6% and 28% respectively. These data reflected different abilities in EPS production. The results indicate that the morphology of EPSs in different species are related to their habit, which is a result of long time adaptation, while chemical compositions of EPSs are species specific, which varies with species. The function of EPSs among species is different, which is determined by their structure and algal habit, stalks are apt to those life fixed species, tubes and membranes are apt to the motive species. Moreover, this paper also discuss the excretion mechanisms of EPSs in diatoms.