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TAVERA R. and CALDERÓN E. 2013. Use of CTAB as a cost-effective solution to an old problem: the interference of the mucilage of desmids for scanning electron microscopy. Phycologia 52: 422-425. DOI: 10.2216/13-133.1
Observation of desmids in a scanning electron microscope is a problem due to abundant extracellular mucilage. The mucilage is deposited around the cells and appears as a fibrous material after drying. We compared two reagents for pretreating cells before drying. Formalin acetoalcohol, which has been used as a pretreatment, was compared with cetyltrimethylammonium bromide (CTAB), which has been used as a mucilage treatment in plants and algae. From our results, we recommend CTAB, which is readily available, inexpensive, does not require special safety handling, and is able to remove many adhering bacteria.
KEY WORDS: CTAB, Desmidiaceae, Desmids, Interference, Mucilage, SEM
The morphological investigation of desmids (Desmidiaceae, Streptophyta) presents challenges due to the polymorphism of these organisms both in the wild and in laboratory culture material. Cell wall structure is used as a distinguishing characteristic for the species and wall structures are often observed using scanning electron microscopy (SEM). How- ever, desmids secrete abundant polysaccharides that make it difficult to obtain a clean wall for observing the cell wall fine structure. Some desmids produce both capsular polysaccha- rides and extracellular polysaccharides (Smestad & Henri- quez Vieira 1994). They hinder SEM because during the dehydration of the sample some derivatives of pectin (carbohydrates and galacturonic acid) are condensed to form fibrous or amorphous layers (Pickett-Heaps 1973; Vidyavati & Dodge 1984; Baylson et al. 2001). Mucilage removal for SEM is not a new problem (Lyon 1969) and several methods have been described (Pickett-Heaps 1973; Gough et al. 1976; Vindyavati & Dodge 1984; Stastny & Kouwets 2012). Before preparing the material for SEM, the mucilage should be removed (Pickett-Heaps 1973). The most accessible and economical method uses reagents to dissolve pectin by acid hydrolysis. Specifically, a mixture of 95% ethanol, acetic acid, and formalin (formalin acetoalcohol, FAA) (Yinxin 1991) or an application of dilute hydrochloric acid (Baylson et al. 2001) has been used. Specialized reagents such as degrading enzymes have also been used. Glusulaset is a mixture of enzymes containing b-glucuronidase, sulfatase, and cellulase that digests the walls of yeast (Perkin-Elmer 2013). This enzyme mixture...