479:, would cause the red reaction by inclusion of iodine atoms into the spiral, and the linear sections might curl up under the influence of KOH, resulting in long helical chains which cause a blue stain upon iodine inclusion. The hypothetical spiral structure of these macromolecules seems to be related to the extensibility of the ascus wall, which is a prerequisite for the active, explosive ejection of ascospores from an ascus when its high cell turgor is released. A high cell wall extensibility is particularly required at the area of the apical pore-like opening (apical ring), through which the
230:
apical ring euamyloid, lateral wall hemiamyloid), or as an intermediate type of the same wall region. In the latter case, an overlay of blue and red can be observed in Lugol's solution without KOH pretreatment: a color change from blue to dirty reddish-brown occurs when the iodine reagent slowly diffuses into the water preparation, because the euamyloid reaction appears at lower iodine concentrations than the hemiamyloid reaction. Asci with entirely reactive walls of this type of hemiamyloidity show rainbow-like colours when low-concentrated IKI is applied.
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which was introduced in 1924 and almost completely displaced the previously used Lugol's solution. Hemiamyloidity was first reported by applying Melzer's reagent which gave a negative result without KOH, but a blue reaction when treated with KOH beforehand. Because of the frequency of hemiamyloidity in lichens,
229:
concentration in MLZ. The alternative to hemiamyloid is called euamyloid. Euamyloid and KOH-pretreated hemiamyloid structures react blue regardless of the type of iodine reagent. Hemiamyloid and euamyloid reactions may occur at a time, either at spatially separated sites of the cell wall (e.g., ascus
456:
hemiamyloid reactions are rare. Although hemiamyloidity is a very valuable taxonomic marker that permits differentiation between species or genera, this type of reaction, in particular the red reaction in IKI, is often overlooked. This neglect occurred since mycologists switched to Melzer's reagent,
420:
413:
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Hemiamyloid (red) reaction in IKI prior to KOH, in comparison with euamyloid (blue) and inamyloid (negative). Only the hemiamyloid reaction strongly depends on the applied iodine reagent (IKI, MLZ) and pretreatment with KOH, being negative in MLZ and blue when KOH-pretreated (in IKI or MLZ). Direct
157:
in the cell walls of amyloid material, however, its mechanism of action is not entirely understood. It has been observed that hemiamyloid material reacts differently when exposed to Melzer's than it does when exposed to other IKI solutions such as Lugol's, and that in some cases an amyloid reaction
165:
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
470:
The chemical background of hemiamyloidity is not clear. A hypothesis claims that short helical sections of a carbohydrate chain alternate with shorter or longer linear sections. The short helical sections, similar to
209:, but here widespread and an important taxonomic distinction criterion. If cell walls stain blue by iodine reagents without pretreatment with KOH, this is called euamyloid. The term amyloid comprises both variants.
169:
Melzer's degrades into a cloudy precipitate when combined with alkaline solutions, hence it cannot be used in combination or in direct series with such common mycological reagents such as potassium hydroxide or
461:
generally did not join this change but continued using Lugol's solution. The widespread usage of swelling herborized fungi in KOH before study further contributes to the frequent overlooking of hemiamyloidity.
225:(IKI), hemiamyloid structures react red to reddish-brown, whereas any reaction is suppressed when using Melzer's reagent (MLZ). This masking effect (false inamyloidity) is due to the high
217:
A hemiamyloid element of the cell wall does not directly stain blue with iodine reagents added to a water preparation, but only when it has been pretreated with
652:
428:
Iodine reaction of hemiamyloid ascus apical rings of
Hysteropezizella (Helotiales) in dependence of iodine reagent (IKI, MLZ) and pretreatment with KOH.
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of the iodine, which is otherwise only semi-soluble in water. Iodine is thought to be the main active staining agent in Melzer's; it is thought to
642:
Baral, H.-O. (1987): Lugol's solution / IKI versus Melzer's reagent: hemiamyloidity, a universal feature of the ascus wall. Mycotaxon 29: 399-450
472:
74:, are for structures that remain pale yellow-brown or clear. A reaction producing a deep reddish to reddish-brown staining is either termed a
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149:, bleaching and improving the transparency of various dark-colored microscopic materials. The potassium iodide is used to improve the
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solutions. When potassium hydroxide is used as a pretreatment, the alkalinity must be first neutralized before adding Melzer's.
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Melzer's reactions are typically almost immediate, though in some cases the reaction may take up to 20 minutes to develop.
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gives a similar reaction, also called an amyloid reaction. The test can be on microscopic features, such as spore walls or
672:
Kohn, L.M., and R.P. Korf. 1975. Variation in ascomycete iodine reactions: KOH pretreatment explored. Mycotaxon 3: 165-172
559:
444:
and
Ostropales, whether lichenized or not, the entire outer ascus wall layer reacts hemiamyloid. Roughly 20% of
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application of IKI to a water munt (without KOH, highlighted) is the easiest way to recognize hemiamyloidity.
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solution (KOH) or other strong bases, whereas direct application of iodine causes a red reaction when using
66:, or be a macroscopic reaction on tissue where a drop of the reagent is applied. Negative reactions, called
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is shown in material that had prior exposure to KOH, but an inamyloid reaction without such pretreatment.
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Inamyloid or Melzer's-negative, in which the tissues do not change color, or react faintly yellow-brown.
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solution (KOH). Without KOH pretreatment, the result depends much on the type of iodine reagent: with
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Melzer's, to even giving dextrinoid reactions in Lugol's while giving amyloid reactions in Melzer's.
591:
576:
Lugol's solution/IKI versus Melzer's reagent: Hemiamyloidity, a universal feature of the ascus wall.
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The function of the chemicals that make up Melzer's reagent are several. The chloral hydrate is a
134:, but shows no reaction in Melzer's reagent; when KOH-pretreated it turns blue in both reagents (
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have hemiamyloid] ascus apical rings compared to estimated 50% with euamyloid apical rings. In
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Iodine reaction in
Ascomycetes: why is Lugol’s solution superior to Melzer’s reagent?
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Melzer's is used by exposing fungal tissue or cells to the reagent, typically in a
24:
47:, producing a blue to blue-black staining. The term "amyloid" is derived from the
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Rossman, A.Y. 1980. The iodine reaction: Melzer's vs. IKI. MSA newsletter 31:22.
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609:"Melzer's, Lugol's or Iodine for Identification of white-spored Agaricales?"
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refers to a special case of cell wall amyloidity where the blue staining by
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or Melzer's-positive reaction, in which the material reacts blue to black.
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Variation in ascomycete iodine reactions: KOH pretreatment explored.
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reaction, in which the material reacts brown to reddish brown.
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Euamyloid reaction, in which the material turns blue without
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How to
Identify Mushrooms to Genus III: Microscopic Features
119:
Among the amyloid reaction, two types can be distinguished:
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preparation, and looking for any of three color reactions:
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walls, or the apical apparatus or entire ascus wall of an
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Hemiamyloid reaction, in which the material turns red in
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Adjective describing a positive test result for starches
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161:An experiment in which spores from 35 species of
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193:only occurs when the tissue was pretreated with
35:when subjected to a crude chemical test using
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54:("starch-like"). It refers to the fact that
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521:(2nd ed.). St. Paul, Minnesota:
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517:Ulloa, Miguel; Halin, Richard T. (2012).
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205:. Hemiamyloidity is so far only known in
436:Hemiamyloidity occurs in many groups of
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523:The American Phytopathological Society
155:react with starch-like polysaccharides
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483:are pressed when the ascus bursts.
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519:Illustrated Dictionary of Mycology
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554:. Arcata, CA: Mad River Press.
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607:Leonard, Lawrence M. (2006).
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201:, but no reaction when using
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39:as an ingredient of either
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622:(1): 43–51. Archived from
90:Melzer's reagent reactions
452:and different classes of
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27:or feature is said to be
590:Kohn LM, Korf RP. 1975.
550:Largent D, et al. 1977.
432:Occurrence, significance
379:MLZ (= Melzer's reagent)
374:IKI (= Lugol's solution)
651:Baral, H.-O. (2009):
440:. In most members of
31:if it has a positive
219:potassium hydroxide
195:potassium hydroxide
127:(KOH)-pretreatment.
125:potassium hydroxide
82:is a synonym) or a
172:ammonium hydroxide
574:Baral H-O. 1987.
532:978-0-89054-400-6
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108:Pseudoamyloid or
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223:Lugol's solution
203:Melzer's reagent
199:Lugol's solution
132:Lugol's solution
96:microscope slide
45:Lugol's solution
41:Melzer's reagent
33:amyloid reaction
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629:on 2011-07-20.
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525:. p. 22.
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493:Color reaction
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183:Hemiamyloidity
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178:Hemiamyloidity
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163:basidiomycetes
147:clearing agent
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136:hemiamyloidity
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581:29:399–450.
498:Iodine test
442:Lecanorales
438:ascomycetes
244:hemiamyloid
84:hemiamyloid
616:McIlvainea
597:3:165–172.
562:. p 25–26.
504:References
481:ascospores
446:Helotiales
213:Properties
207:Ascomycota
151:solubility
110:dextrinoid
86:reaction.
78:reaction (
76:dextrinoid
72:nonamyloid
52:amyloideus
595:Mycotaxon
579:Mycotaxon
466:Chemistry
249:euamyloid
239:inamyloid
68:inamyloid
689:Mycology
683:Category
487:See also
477:glycogen
187:mycology
21:mycology
103:Amyloid
29:amyloid
558:
529:
191:iodine
60:hyphal
56:starch
37:iodine
25:tissue
627:(PDF)
612:(PDF)
64:ascus
49:Latin
556:ISBN
527:ISBN
357:blue
352:blue
347:blue
342:blue
320:blue
315:blue
475:of
305:red
283:MLZ
278:IKI
273:MLZ
268:IKI
263:MLZ
258:IKI
185:in
70:or
43:or
19:In
685::
635:^
620:16
618:.
614:.
567:^
541:^
138:).
23:a
535:.
337:–
332:–
310:–
300:–
295:–
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