Formation of cross walls in trunk hyphae of AM fungal arbuscules and their relationship to metabolic activity

 

S. Dickson and S. E. Smith,
 Adelaide University, Australia

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 The regular occurrence of cross walls in trunk hyphae of arbuscules formed by five species of Glomus in two species of Allium was investigated. The cross wall examined using confocal microscopy showed that the structure was within the hypha and was intact with no central pore.

A time-course of A. porrum colonised by Glomus coronatum was conducted to relate presence of cross walls to the development and senescence of arbuscules. Mycorrhizal structures visualised using nitroblue tetrazolium as a vital stain indicated metabolic activity with counterstaining by acid fuchsin. Results showed cross walls were often formed at sites between metabolically active and inactive fungal regions. Cross wall presence was correlated with the metabolic status of the mycorrhizal unit (i.e. arbuscule branches, arbuscular trunk hypha and intercellular hypha) using an interdependence magnified intersects technique (IMIT) (Cavagnaro et al. 2001). IMIT analysis indicated the incidence of cross walls increased with the loss of metabolic activity.

Cross wall formation is likely to influence transfer of nutrients by allowing the delivery of P to the plant only by young metabolically active arbuscules or by preventing the possible flow of C derived from the plant out of the arbuscule. This may require a reconsideration of the previously proposed mechanisms of nutrient transfer between fungus and plant.