The attachment organ of the parasitic angiosperms Orobanche cumana and O. aegyptiaca and its development

Abstract

Some species of Orobanche are parasitic weeds attacking the roots of various crops and causing extensive damage. The development of the young parasite was investigated using light and electron microscopy. Germinating O. aegyptiaca and O. cumana form a short root, with no root cap, which is covered by a thin cuticle. As soon as the root reaches a host, elongation stops, the apex expands, and peripheral cells become papillate. The extended apex becomes the young attachment organ. The outer papillar surface of the extended apex bears wall protuberances that are encircled with a thick cuticular belt and covered with a thin cuticle. These protuberances secrete a carbohydrate that accumulates in a subcuticular space and is released to the surface, forming a thin adhesive layer that binds the parasite to its host. Bacteria are commonly found in the secretion pool, on the papillae, and in the outer cell walls. The event of attachment of the young parasite to host surface signals a shift from the independent to parasitic phase. This change also includes a shift from the accumulation of lipids to the accumulation of starch. Key words: Orobanche, broomrape, parasitic plants, haustorium, attachment organ, root.