Ultrastructure of the host-parasite interaction in leaves of Duchesnea indica infected by the rust fungus Frommeela mexicana var. indicae as revealedby high pressure freezing

A combination of scanning and transmission electron microscopy was used to examine the host-pathogen relationship in leaves of Duchesnea indica (Andrz ) Focke infected by the rust fungus Frommeela mexicana var. indicae McCain & Hennen. Samples for transmission electron microscopy were prepared using high pressure freezing followed by freeze substitution. This protocol provi ded excellent preservation of both host cells and fungal haustoria. Each ha ustorium of F. mexicana var. indicae possessed a long slender neck with a n eck band and an expanded body that contained two nuclei positioned close to gether. The haustorial body was lobed and sometimes even branched but lacke d septa. Details of the extrahaustorial membrane that separated each hausto rium from the cytoplasm of its host cell were particularly well preserved. Extensive labyrinth cell wall ingrowths developed around haustorial necks, as well as elsewhere, in infected cells. These ingrowths appeared to be ide ntical to those present in plant transfer cells. Transfer cells are thought to be involved in intensive solute transfer over short distances. This app ears to be the first report of the development of transfer cells in respons e to infection by a plant pathogenic fungus.