The biology of mycorrhiza in the Ericaceae: XVII. The role of mycorrhizal infection in the regulation of iron uptake by ericaceous plants.

The role of the ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf & Kernan in the regulation of iron uptake by ericaceous plants is investigated. Growth of the fungus is not inhibited in solution cultures containing a range (0-144 [ig ml ) of iron concentration ([Fe] ) typical of those obtained in extracts from heathland soil. Absorption of iron by the fungus occurs rapidly at low [Fe] but more slowly as [Fe] increases. Concentrations of iron in the mycelium ([Fe] ), reach 6000μg g dry weight. Mycorrhizal (M) roots of Vaccinium macrocarpon Ait. and Calluna vulgaris L. (Hull) showed a very high affinity for iron at low [Fe] , a feature not shown by non-mycorrhizal (NM) roots. The involvement of a hydroxamate siderophore in the absorption of Fe by M plants at low [Fe] is suggested. Concentrations of iron in shoots ([Fe] of NM plants of V. macrocarpon increase linearly with increasing [Fe] while those of M plants fall in the mid-range of [Fe] relative to initial and final values. Ratios of [Fe] to [Fe] are lower in M than in NM plants across the range of [Fe] examined. The extent of involvement of mycorrhizal infection in excluding the metal from shoots as [Fe] increases, is discussed, and the importance of the mechanisms of iron capture and storage in the root are assessed in terms of iron availability in natural heathlands.