The metabolic profiles of phenolic acids and aromatic amino acids in the Orobanche crenata parasite and its host faba bean at different infestation stages

Orobanche crenata is a root holoparasite that depends on its host for nutritional requirements. The shikimate pathway that metabolizes about 30% of the assimilated carbon in photosynthetic plants plays a role in host-parasite relationships. Aromatic amino acids (AAAs) and phenolic acids are derived from the shikimate pathway and serve as precursors of a wide number of primary and secondary metabolites. The effects of the O . crenata parasite on the phenolic acid and AAA profiles of two faba bean varieties and the differences of these compounds between the host organs and attached parasite at infestation stages were studied. Hosts and attached parasites were collected and divided, depending on the stage of parasite development, into four stages. The results revealed that phenolic acids and free AAAs tended to increase in parasitized roots compared to those of healthy roots, and the greatest increase in phenolic contents occurred at the first infestation stage. Syringic acid was observed to be unique to the parasite. Profiles of phenolic acids and AAAs were changed during the developmental stages of the parasite and differed from those of its host. Caffeic in the parasite reached more than 100 times that in Nubaria 4 host roots at the fourth infestation stage. Free phenylalanine in the parasite ranged between 2.2 and 5.5 times its level in host roots at all infestation stages. This study provides much evidence that indicates O . crenata is able to self-regulate its phenolic and AAA metabolites during its developmental stages, which differ from those of its host.