Host-Elicited Germination and Mechanism of Penetration in Broomrape (Orobanche Spp.)

Orobanche is an important parasitic weed. For developing novel methods for its control, a thorough understanding of crucial stages of its development is needed. Therefore, the objectives of this project were characterization of Orobanche germination stimulants, analysis of mechanisms of haustorial penetration, and characterization and isolation of penetration enzymes. The first highly potent natural germination stimulant for Orobanche was isolated from sunflower and identified by high-field 1D (1H and 13C), 2D (1H-1H COSY, HMQC, HMBC)-NMR, GC.FT-IR, and GC.MS as costuslactone, a guaiane type sesquiterpene lactone that resembles strigol only in possessing a lactone moiety that is required for activity. The first direct in situ evidence for the enzymatic nature of the infection process of a parasitic angiosperm was established. Pectin deesterification and depletion of pectins in host cell walls were shown adjacent to haustorial cells. Pectin methyl esterase and polygalacturonase were immunocytochemically detected in intrusive cells and in adjacent host apoplast. Orobanche tissues contain inhibitors of PGase activity. PME and three PGases were isolated from Orobanche calli. PME was characterized and purified, and antibodies were prepared against it. This study presents novel findings regarding parasitism in Orobanche, which may help to open up new approaches for controlling broomrapes.