Attachment of the parasitic weed dodder to the host.

Abstract

The parasitic weed dodder (Cuscuta pentagona L.) invades a number of potential host species, but the mechanisms responsible for ensuring tight adhesion to the wide variety of host surfaces have yet to be identified. In this study, a battery of microscopy protocols is used to examine the host-parasite interface in an effort to deduce these mechanisms. As the dodder shoot approaches the host tissue, epidermal cells in the parasite shoot elongate and differentiate into secretory type trichomes. The trichome cell walls are malleable, allowing them to elongate towards the host and bend their walls to conform to the shape of the host cell surface. The presence of osmiophilic particles (probable cell-wall-loosening complexes) at far greater numbers than found in other species presages the expansion and malleable nature of the epidermal cells. In addition to the changes in cell shape, the dodder trichome cells secrete an electron-opaque cementing substance that covers the host-parasite interface. When probed with antibodies that recognize cell wall components, the cement reacted only with antibodies that recognize chiefly de-esterified pectins but not other common wall constituents. These data indicate that dodder utilizes both a cementing layer of pectin and a radically modified epidermal cell wall to secure the parasite to the perspective host.