Melzer's reagent
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Melzer's reagent (also known as Melzer's iodine reagent,
Composition
Melzer's reagent is an aqueous solution of chloral hydrate, potassium iodide, and iodine. Depending on the formulation, it consists of approximately 2.50-3.75% potassium iodide and 0.75–1.25% iodine, with the remainder of the solution being 50% water and 50% chloral hydrate.[2][3] Melzer's is toxic to humans if ingested due to the presence of iodine and chloral hydrate.[4] Due to the legal status of chloral hydrate, Melzer's reagent is difficult to obtain in the United States.[4]
In response to difficulties obtaining chloral hydrate, scientists at Rutgers formulated Visikol[5] (compatible with Lugol's iodine) as a replacement. In 2019, research showed that Visikol behaves differently to Melzer’s reagent in several key situations, noting it should not be recommended as a viable substitute.[6]
Melzer's reagent is part of a class of iodine/potassium iodide (IKI)-containing reagents used in biology; Lugol's iodine is another such formula.
Reactions
Melzer's is used by exposing fungal tissue or cells to the reagent, typically in a microscope slide preparation, and looking for any of three color reactions:
- Amyloid or Melzer's-positive reaction, in which the material reacts blue to black.
- Pseudoamyloid or dextrinoidreaction, in which the material reacts brown to reddish brown.
- Inamyloid or Melzer's-negative, in which the tissues do not change color, or react faintly yellow-brown.[2]
Among the amyloid reaction, two types can be distinguished:
- Euamyloid reaction, in which the material turns blue without potassium hydroxide (KOH)-pretreatment.
- Hemiamyloid reaction, in which the material turns red in hemiamyloidity).[7]
Melzer's reactions are typically almost immediate, though in some cases the reaction may take up to 20 minutes to develop.[2]
The function of the chemicals that make up Melzer's reagent are several. The chloral hydrate is a
An experiment in which spores from 35 species of basidiomycetes were tested for reactions to both Melzer's and Lugol's showed that spores in a large percentage of the species tested display very different reactions between the two reagents. These varied from being weakly or non-reactive in Lugols, to giving iodine-positive reactions in Lugol's but not in Melzer's, to even giving dextrinoid reactions in Lugol's while giving amyloid reactions in Melzer's.[4]
Melzer's degrades into a cloudy precipitate when combined with alkaline solutions,
History
The use of iodine-containing solutions as an aid to describing and identifying fungi dates back to the mid-19th century.[4]
Melzer's reagent was first described in 1924[9] and takes its name from its inventor, the mycologist Václav Melzer, who modified an older chloral hydrate-containing IKI solution developed by botanist Arthur Meyer.[7] Melzer was a specialist in Russula, a genus in which the amyloidy on the spore ornamentation or entire spore is of great taxonomic significance.[10]
References
- ^ ISSN 1882-0484.
- ^ ISBN 0-916422-09-7. p 25–26.
- ISBN 0-7627-3109-5. p 549.
- ^ a b c d Leonard, Lawrence M. (2006). "Melzer's, Lugol's or Iodine for Identification of white-spored Agaricales?" (PDF). McIlvainea. 16 (1): 43–51. Archived from the original (PDF) on 2011-07-20.
- ^ http://otc.rutgers.edu/pdf/Simon-2012-146.pdf[permanent dead link]
- ^ Leonard, Lawrence M. (Summer 2019). "Melzer's Reagent Update, 2019" (PDF). Fungi. 12 (2): 10.
- ^ a b c Baral H-O. 1987. Lugol's solution/IKI versus Melzer's reagent: Hemiamyloidity, a universal feature of the ascus wall. Mycotaxon 29:399–450.
- ^ Kohn LM, Korf RP. 1975. Variation in ascomycete iodine reactions: KOH pretreatment explored. Mycotaxon 3:165–172.
- ^ Melzer, V. (1924). "L'ornementation des spores de Russules". Bulletin Trimestriel de la Société Mycologique de France (in French). 40: 78–81.
- ^ The Russulales News Team. 2007. Introduction to the Russulales: Characteristics of the russuloid fungi Archived 2013-07-07 at the Wayback Machine, Russulales News (website).
Further reading
- Blackwell M, et al. 2001. The presence of glycine betaine and the dextinoid reaction in basidiomata. Harvard Papers in Botany 6:35–41.
- Rossman AY. 1980. The iodine reaction: Melzer's vs. IKI. MSA newsletter 31:22.