A possible role for the thick-walled epidermal cells in the mycorrhizal hair roots of Lysinema ciliatum R Br and other Epacridaceae

Hair roots of Lysinema ciliatum R. Br. and some other Epacridaceae have thick-walled cells in the epidermis. These are preferentially colonized with mycorrhizal fungi. Individual epidermal cells containing hyphal coils separate at the middle lamella and are released into the soil. Other colonized cells remain attached to the roots, usually in groups, surrounded by bare exodermis, where epidermal cells have either collapsed or been sloughed off. It is suggested that these colonized thick walled cells can serve to prolong the mycorrhizal association and to infect new hair roots as these emerge. The thick wall has a very specialized structure and composition and could have a number of roles, either acting as a substrate or protective coat or in controlling water status and uptake. Young hair-roots are surrounded by a mucilage sheath that is similar in appearance to that in Ericaceae and apparently produced by root cap cells, not the epidermis. (C) 1996 Annals of Botany Company