Melzer's reagent
Melzer's reagent is a - especially in mycology used - detection reagent . Besides water, it is the most widely used medium for studying fungi. Melzer's reagent has proven to be popular Präpariermedium in the herbarium taxonomy naturalized, because it's often annoying dead cytoplasm optically homogenized and brightens, it also suppressed due to the high viscosity of the Brownian molecular motion . It is named after its inventor Václav Melzer .
composition
Melzer's reagent is a solution of elemental iodine , potassium iodide and chloral hydrate in water. It is recommended that the reagent be freshly prepared, but it has been shown that the properties do not change noticeably over many years.
Reactions
The properties based on the iodine content of the reagent are expressed in two color reactions that are used as a feature for the classification of fungi.
Amyloid reaction
Starch (Latin = amylum) reacts with iodine, giving it a blue / purple color. As a rule, the color reaction in mushrooms is only rarely deep blue-violet, but includes all color nuances from gray, bluish-gray, light blue, gray-blue, blue to almost blue-black. This amyloidy of parts of the fungus ( spores , hyphae , asci, etc.) can be characteristic of the species in question and is therefore used for classification into genera and sections.
In the case of mushrooms , a pretreatment with potassium hydroxide solution has proven to be important for the determination of amyloidy using Melzer's reagent, since in many cases a blue reaction can only be achieved afterwards. This pretreatment is known as hemiamyloidity. Melzer's reagent has proven to be disadvantageous due to its high chloral hydrate concentration: To determine hemiamyloidity with Melzer, the iodine test must be carried out both before and after the treatment with potassium hydroxide. Lugol's solution (= Melzer's reagent without chloral hydrate), on the other hand, causes a red to red-brown reaction in hemiamyloid structures without pretreatment (not to be confused with dextrinoidicity), which is completely suppressed by Melzer's reagent.
Dextrinoid reaction (also: pseudoamyloid reaction)
Dextrin is a water-soluble breakdown product of starch. During this reaction, parts of the fungus (spores, trama , hyphae) turn deep red-brown to purple. This applies in particular to species of the genera Macrolepiota , Leucoagaricus and Leucocoprinus . Fungi that stain wine-red with Melzer's reagent or Lugol's solution are also known as dextrinoid or pseudoamyloid ; Mushrooms that do not show this color reaction are called indextrinoid . In contrast to hemiamyloidity , Melzer's reagent does not suppress dextrinoid reactions, rather the chloral hydrate it contains sometimes even increases the intensity of this red reaction (example: Lamellar trama of Mycena ). In addition, pretreatment with potassium hydroxide in dextrinoid microstructures never causes a blue reaction with iodine.
disadvantage
Disadvantages of Melzer's reagent are the suppression of a widespread type of red reaction ( hemiamyloidity ) and the fact that fungal cells usually die immediately due to the high chloral hydrate concentration.
Applied to living fungal cells, Melzer's reagent significantly reduces the visibility of the cell walls and also leads to the irreversible loss of important taxonomic features (see under Taxonomy ).
swell
- Heinrich Dörfelt , Gottfried Jetschke (Ed.): Dictionary of mycology. 2nd Edition. Spectrum Academic Publishing House, Heidelberg / Berlin 2001, ISBN 3-8274-0920-9 .
Individual evidence
- ^ MV Melzer: L'ornementation des spores de Russules . In: Bull. Soc. myc. Fr. (1924). Volume 40, pp. 78-81.