Abstract/Summary:
Haustoria of Triphysaria pusilla and T. versicolor subsp. faucibarbata from a natural habitat were analysed by light and electron microscopy. The keel-shaped edge of the secondary haustorium generally splits the epidermis and cortex of the host root parallel to the root axis, and penetrates to the host vascular tissue. Anticlinally elongated epidermal cells of the haustorium constitute most of the host/parasite interface. Some of these epidermal cells are divided by oblique cell walls. Some of their oblique daughter cells as well as some undivided epidermal cells differentiate into xylem elements. Single epidermal cells occasionally intrude into the vascular tissue of the host and individual host cells can be invaded. The surface area of the plasmalemma in parasitic parenchymatous interface cells is increased by the differentiation of wall labyrinths characteristic of transfer cells and by the development of membrane-lined cytoplasmic tubules or flattened sacs which become embedded in the partly lignified interface cell-wall. Mycorrhizal fungal hyphae enter the xylem bridge in some haustoria. Implications of these observations for the function of the haustorium are discussed.



Transmissionelectron micrograph of mature haustorium in transverse section of parasite and host root at the haustorial axis. – Glutaraldehyde/osmium fixed material contrasted with uranyl acetate and lead citrate.
Thick arrows, oblique cell walls between daughter cells of one epidermal mother cell.
Thin arrows, electron-dense material lining secondary wall thickenings.
F, fungal cell.
IP, parasite interface parenchyma cell originating from epidermal cell layer.
LW, lignified secondary cell wall in xylem element.
Bar, 10 mµ
XW, xylem bridge vessel member.




Keywords: Epidermis; Haustorial interface; Hemiparasite; Orthocarpus; Transfer cells; Triphysaria; Xylem elements.








FIGUR LEGEND abs 19:
Transmissionelectron micrograph of mature haustorium in transverse section of parasite and host root at the haustorial axis. – Glutaraldehyde/osmium fixed material contrasted with uranyl acetate and lead citrate.
Thick arrows, oblique cell walls between daughter cells of one epidermal mother cell.
Thin arrows, electron-dense material lining secondary wall thickenings.
F, fungal cell.
IP, parasite interface parenchyma cell originating from epidermal cell layer.
LW, lignified secondary cell wall in xylem element.
Bar, 10 mµ
XW, xylem bridge vessel member.