Functional structure of the mature haustorium

Abstract

The morphology and functional anatomy of lateral and terminal haustoria are described in this chapter, with emphasis on the patterns of tissue connection with both the host and the parasite, while discussing the possible role of each tissue within the haustorium. The extent of haustorium differentiation correlates with the parasite lifestyle and phenology and with the individual interaction of each haustorium with neighbouring host tissues. While all Orobanchaceae parasites have direct xylem connections with the host, few have direct phloem connections. The pattern of vascular differentiation is regulated by hormonal interactions between parasite and host. The hyaline tissue and the graniferous tracheary elements are structures unique to the haustorium and have special roles not only in nutrient transport, metabolism and storage but also in the regulation of hydrostatic pressures and in protection against pathogens.