Anatomy and Ultrastructure of the Primary Endophyte of Ileostylus micranthus (Loranthaceae)

Abstract

The primary endophyte of Ileostylus micranthus has a radial shaft that gives rise to lateral flanges in host cambia of successive years. Interfacial contacts normally involve abutments of endophytic parenchyma cells with host secondary xylem cells. Host xylem is never penetrated, and sinker-like processes are absent. Endophytic flanges consist of outermost contact cells, endophytic cortex, and innermost vascular core tissues. Endophytic contact cells have thickened walls, large nuclei, numerous mitochondria and plasmatubules, and densely staining cytoplasm. Contact cells appear metabolically active during endoplasmic reticulum-mediated synthesis of osmiophilic substances. The vascular core comprises discrete collateral bundles. Xylem is very parenchymatous; vessels and fibers are present. Endophytic phloem includes functional sieve elements with associated companion cells. Intrahaustorial collapsed zones develop in cortical and vascular tissues. The host-parasite interface is a zone of dense-staining, cru...