ANATOMY AND ULTRASTRUCTURE OF THE PRIMARY ENDOPHYTE OF ILEOSTYLUS-MICRANTHUS (LORANTHACEAE)

The primary endophyte of Ileostylus micranthus has a radial shaft that gives rise to lateral flanges in host cambia of successive years. Int erfacial contacts normally involve abutments of endophytic parenchyma eels with host secondary xylem cells. Host xylem is never penetrated, and sinker-like processes are absent. Endophytic flanges consist of ou termost contact cells, endophytic cortex, and innermost vascular core tissues. Endophytic contact cells have thickened walls, large nuclei, numerous mitochondria and plasmatubules, and densely staining cytoplas m. Contact cells appear metabolically active during endoplasmic reticu lum-mediated synthesis of osmiophilic substances. The vascular core co mprises discrete collateral bundles. Xylem is very parenchymatous; ves sels and fibers are present. Endophytic phloem includes functional sie ve elements with associated companion cells. Intrahaustorial collapsed zones develop in cortical and vascular tissues. The host-parasite int erface is a zone of dense-staining, crushed cells that originate from host and parasite tissues. Large-scale enzymatic digestion of interfac ial cells is not apparent. Suberin-like layers and ''dense-plugging'' substances develop in the walls of less than 1% of endophytic contact cells. Some host xylem vessels near the endophyte develop suberin-like layers, and vessel lumens become occluded with dense and reticulate s ubstances. These sealing phenomena are highly local and do not signifi cantly disrupt the apoplastic continuity of the host-parasite interfac e as a whole.