Cross walls in arbuscular trunk hyphae form after loss of metabolic activity

A time-course of Allium porrum colonized by Glomus coronaturn examined the formation of cross walls in arbuscular trunk hyphae in relation to the deve lopment and senescence of arbuscules. Mycorrhizal structures visualized using nitroblue tetrazolium as a vital st ain indicated metabolically active arbuscules and intercellular hyphae with counterstaining by acid fuchsin. The intrahyphal location and intact natur e of cross walls was examined using confocal microscopy. Their presence was correlated with the metabolic status of the mycorrhizal unit (i.e. arbuscu le branches, arbuscular trunk hypha and intercellular hypha) using an inter dependence magnified intersects technique (IMIT). Loss of metabolic activity was observed first from arbuscule branches, then from trunk hypha and lastly from intercellular hyphae. Cross walls were se en in trunk hyphae of many inactive arbuscules. The incidence of cross wall s increased with time and was associated with loss of activity. Observations suggest cross walls appeared after loss of metabolic activity in arbuscule branches in several plant-fungal combinations. The implication s of cross-wall formation for mechanisms of transfer of nutrients between f ungus and plant are discussed.