Amyloid (mycology)
Hemiamyloidity in mycology refers to a special case of cell wall amyloidity where the blue staining by iodine only occurs when the tissue was pretreated with potassium hydroxide solution (KOH) or other strong bases, whereas direct application of iodine causes a red reaction when using Lugol's solution, but no reaction when using Melzer's reagent.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 potassium hydroxide solution (KOH).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.Hemiamyloid (red) reaction in IKI prior to KOH, in comparison with euamyloid (blue) and inamyloid (negative).This neglect occurred since mycologists switched to Melzer's reagent, which was introduced in 1924 and almost completely displaced the previously used Lugol's solution.