Melzer's reagent

Melzer's reagent is a - especially used in mycology - detection reagent. Besides water, it is the medium most used for the study of fungi. Melzer's reagent has become established as a popular Präpariermedium in Herbariumstaxonomie because it is the often disturbing dead cell plasma optically homogenized and brightens, it also suppressed due to the high viscosity of the Brownian motion. It is named after its inventor Václav Melzer.

Composition

Melzer's reagent is a solution of elemental iodine, potassium and chloral hydrate in water. While it is recommended to prepare the reagent fresh, it has been found that do not change the properties for many years considerably.

Reactions

The calculations based on the iodine content of the reagent properties manifest themselves in two color reactions which are brought in as a feature for classification of fungi.

Amyloid reaction

Strength (Latin = amylum ) reacts with iodine to a blue / violet staining. In general, the color reaction in fungi is deep blue violet only in rare cases, but includes all shades of gray, bluish gray, light blue, gray-blue, blue to blue, almost black. This Amyloidität of parts of the fungus ( spores, hyphae, asci, and others) may be characteristic of the species and thus contributes to the classification into genera and sections.

In ascomycetes, a pre-treatment with potassium hydroxide solution for the determination of Amyloidität Melzer's reagent has proven means to be important because in many cases only after a blue response is achieved. This pretreatment is called Hemiamyloidität. Melzer's reagent has been shown here, however, because of its high concentration of chloral hydrate as a disadvantage: To determine Hemiamyloidität with Melzer, so you have to make before the iodine test both after treatment with potassium hydroxide. Lugol's solution ( = Melzer's reagent without chloral hydrate ), however, calls for hemiamyloiden structures without pre-treatment a red to red-brown reaction produced (not to be confused with Dextrinoidität ), which is completely suppressed by Melzer's reagent.

Dextrinoidreaktion (also: pseudo- amyloid reaction)

Dextrin is a water-soluble starch degradation product. In this reaction, parts of the fungus ( spores, Trama, hyphae ) color deep red-brown to purple. This applies particularly to species of the genera Macrolepiota, Leucoagaricus or Leucocoprinus. Fungi which will anfarben with Melzer's reagent or Lugol's solution burgundy referred to as dextrinoid or pseudo- amyloid, fungi do not show this color reaction is called indextrinoid. In contrast to Hemiamyloidität chloral hydrate contained therein suppressed Melzer's reagent reactions dextrinoide not, but increasingly in some cases the intensity of these Rotreaktion (example: lamellae of Mycena ). In addition, pretreatment with potassium hydroxide never results in dextrinoiden microstructures a blue reaction with iodine.

Disadvantages

A disadvantage of Melzer's reagent is the suppression of a widespread type of Rotreaktionen ( Hemiamyloidität ) and the fact that fungal cells by the high concentration of chloral hydrate die almost immediately.

When applied to living fungal cells reduces Melzer's reagent, the visibility of the cell walls considerably and also leads to the irreversible loss of important taxonomic characteristics (see Taxonomy ).

Swell

• Heinrich Dörfelt and G. Jetschke: Dictionary of mycology. Spektrum Akademischer Verlag, Heidelberg - Berlin 2001, ISBN 3-8274-0920-9

• Detection reagent
• Mycology