Anatomy and Ultrastructure of the Haustorium of Cassytha pubescens R. Br. I. The Adhesive Disk

Haustoria in Cassytha pubescens R. Br. (Lauraceae) are initiated before the tissues of the stem are fully differentiated. The adhesive disk of the haustorium develops an "epithelium" of mostly unicellular, tightly packed trichomes that become folded at their tips upon contact with the host. The trichome initials are enveloped by microtubules prior to mitosis. The trichomes secrete adhesive polysaccharide material that contains fragments of the disintegrated cuticle. During formation of the trichomes the epicuticular wax originally covering the stem is shed. The wedge-shaped intrusive organ develops inside the hypodermis from the third cell layer of cortical chlorenchyma. The origin of the intrusive organ is independent of the position of the vascular bundles. Dissolution of cell walls in front of the intrusive organ occurs but penetration of the host seems mainly dependent on turgor pressure and extension growth. Most of the starch stored in the adhesive disk before the intrusive phase is used during penetration. The outer part of the storage tissue then forms a collapsed zone as a response to cambial activity.