Modification of the host plasmalemma in haustorial infections of Lactuca sativa by Bremia lactucae

Abstract

The haustorial interface between Bremia lactucae and Lactuca sativa has been investigated by electron microscopy following the application of either an ATPase localization procedure or the plasma-lemma (PM) specific stain, periodic acid-chromic acid-phosphotungstic acid (PACP). Haustoria lacked any structure resembling a neckband but usually the invaginated region of the host PM around them was distinct from the uninvaginated region lining the host cell wall in lacking ATPase activity and staining only slightly with PACP. The transition in membrane characteristics occurred abruptly (as in infections by haustoria with neckbands) and was consistently at the penetration site. In the other cells containing haustoria, both the invaginated and uninvaginated regions of the plasmalemma stained abnormally with PACP. Poor staining of the uninvaginated PM was not related to the maturity of the haustorium present and also occurred in some cells in which haustorial profiles were not seen. The mechanisms by which modified domains may be formed and maintained in the plasmalemmas of the host cells and the likely physiological implications of membrane modification are discussed.