A rapid staining procedure for arbuscules of living arbuscular mycorrhizas using neutral red as acidotropic dye

Arbuscules are the most conspicuous structures of arbuscular mycorrhizas. Due to their large surface area, they are regarded as putative sites of nutrient exchange between host and symbiont. A new staining technique for arbuscules is presented in which arbuscules are selectively stained by acidotropic (i.e. based on the ion-trap mechanism) accumulation of neutral red (activity stain). Criteria to distinguish acidotropic staining from staining due to chemical affinity are presented together with approaches to minimize background staining and to check for complete penetration of the dye through the root tissues. The non-toxic staining technique allows detection of arbuscules in living roots within two to six hours. The histochemical properties of neutral red, microscopic techniques, potential pitfalls, the arbuscular life cycle, and aspects of future research are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.