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Definition

The haustorium is a very specialized parasitic fungal structure for extracting cellular nutrients from plants.  A haustorium originates on a hyphae of a parasite and is most often associated with obligate parasites, but is also produced by some facultative parasites.  Even though it is an intracellular structure, it is not in direct contact with the host cytoplasm.  After direct penetration of the cell wall, a haustorium does not penetrate the plasma lema membrane, but invaginates the plasma lema.  Teliologically, the objective is to obtain nutrients from the host without overly disturbing the normal host cell metabolism.

 

Above: Haustoria of the lettuce downy mildew pathogen, Bremia lactucae, penetrating and invaginating cells of lettuce (Lactuca sativa) (highly magnified) .

 

Etymology. Haustorium is from the Latin word haustor = drinker.