Correlational nutritional relationships and interactions between expansive holoparasite Orobanche laxissima and woody hosts on metal-rich soils

Abstract

Plant parasitism by other plants, combined with abiotic environmental stress, offers a unique opportunity to study correlational nutritional relationships in terms of parasite-host interactions and their functional roles in nutrient cycling in ecosystems. Our study analysed the transfer of selected mineral elements, including heavy metals, from soil to different organs in hosts (Punica granatum and Fraxinus angustifolia) and from hosts to the expansive holoparasite (Orobanche laxissima) in cinnamonic soil habitats in Georgia (Caucasus). We also identified other correlated trophic and bioactive effects in the parasite-host relationship. O. laxissima was characterized by a high accumulation tendency for micro- and macroelements, such as K and Ca, and heavy metals, such as Zn, Ni, and Cd. Parasites can reduce the concentration of heavy metals in host tissues owing to this high accumulation tendency. In total, 85 compounds were identified in the examined parasite and its hosts. Despite the distinct phytochemical content of species of the infected host, the parasite produced specific metabolites with dominant phenylethanoid glycosides (PhGs), with acteoside and crenatoside being the primary dominant compounds - ca. 98% of all polyphenols. Polyphenols in parasite specimens that are correlated with Cu and Zn are antagonistic to polyphenols correlated with Fe, Pb, Cr, and Ni. The profile of polyphenols in the host species was both qualitatively and quantitatively distinct from the profile of the compounds in the parasite and between hosts (only acteoside in group PhGs was common between the parasite and Fraxinus host), which indicates the existence of a unique compound biosynthesis pathway in the parasite. Our results demonstrated that the parasite, particularly in its flowers, exhibited higher polyphenol content, antioxidative effects (ABTS-+, DPPH, and FRAP), and inhibitory effects.

Keywords: Broomrape; Environmental stress; Host; Metal accumulation; Metal relocation; Orobanchaceae; Orobanche laxissima; Phenylethanoid glycosides; Polyphenols; Soil–host–parasite transfer.