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. Interfacial 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 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, crushed cells that originate from host and parasite tissues. Large-scale enzymatic digestion of interfacial 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 substances. These sealing phenomena are highly local and do not significantly disrupt the apoplastic continuity of the host-parasite interface as a whole.