EXPLOITATION OF THE XYLEM STREAM BY PARASITIC ORGANISMS

A taxonomically diverse group of angiosperms and certain homopteran insects derive water, inorganic and organic solutes from angiosperm xylem sap. Parasitic angiosperms are connected to their host(s) by a specialized organ (the haustorium) and form close cellular contacts with host xylem tissue, while insects tap xylem vessels by means of stylets. Adaptations to phytophagy are discussed with respect to gaining access to xylem tissue and the nutrition of sap feeders. Parasitic angiosperm-host interactions are examined in relation to recent advances in our understanding of root-to-shoot communication via the xylem (the influence of host-sourced signals on the parasite) and the functional significance of high rates of transpiration in parasitic angiosperms.