Abstract
The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between Odontarrhena lesbiaca and broomrape parasitic species, in the light of the defense hypothesis of metal hyperaccumulation. Plant and soil samples collected from three serpentine sites in Lesbos, Greece were analyzed for Ni concentrations. Phelipanche nowackiana and Phelipanche nana were found to infect O. lesbiaca. In both species, Ni concentration decreased gradually from tubercles to shoots and flowers. Specimens of both species with shoot nickel concentrations above 1000 mg.kg−1 were found, showing that they act as nickel hyperaccumulators. Low values of parasite to O. lesbiaca leaf or soil nickel quotients were observed. Orobanche pubescens growing on a serpentine habitat but not in association with O. lesbiaca had very low Ni concentrations in its tissues analogous to excluder plants growing on serpentine soils. Infected O. lesbiaca individuals showed lower leaf nickel concentrations relative to the non-infected ones. Elevated leaf nickel concentration of O. lesbiaca individuals did not prevent parasitic plants to attack them and to hyperaccumulate metals to their tissues, contrary to predictions of the elemental defense hypothesis.
Highlights
Parasitic symbiosis describes a type of interspecific interaction in which the host organism is harmed while the parasite receives a benefit [1]
Phelipanche nana (Reut.) Soják, Phelipanche nowackiana (Markgr.) Soják and Orobanche pubescens d’Urv., were identified in serpentine soils sampled in Lesbos, but only two of them (P. nana and P. nowackiana) were found to infect O. lesbiaca
The ability of Streptanthus polygaloides to hyperaccumulate nickel did not prevent Cuscuta californica attack [43], and the same is true for the infection of Alyssum murale by Orobanche nowackiana
Summary
Parasitic symbiosis describes a type of interspecific interaction in which the host organism is harmed while the parasite receives a benefit [1]. Parasitic plants attack either roots or shoots (and rarely leaves; [2]) of their hosts using specialized structures named haustoria [3], which enable them to obtain nutrients, water, and carbohydrates through a connection with the vascular system of their host [4,5,6]. Parasitic plants present high diversity levels as about 4500 species (belonging to 20 families) have been identified, which represent about 1% of all known angiosperms worldwide [9,10]. Broomrapes are obligate non-photosynthetic holoparasitic root plants belonging to the genera Orobanche and Phelipanche (Orobanchaceae) [11,12,13], whose native distribution range mostly extends to the temperate zone of the northern hemisphere [14]. Broomrapes are estimated at around 150–200 species [15], with no direct economic importance, but with devastating consequences to infected crops (e.g., legumes, vegetables, Brassica crops) mainly through yield reductions [9]
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