RESUMEN
Several plant species are able to not only tolerate but also hyperaccumulate heavy metals in their aboveground tissues. Thus, in addition to secondary metabolites acting as organic defences, metal hyperaccumulators possess an elemental defence that can act as protection against antagonists. Whereas several laboratory studies have determined potential relationships or trade-offs between organic and inorganic defences, little is known about whether these traits are interconnected in the field and which factors determine the compositions of organic defences and elements of leaf tissues most. To target these questions, we collected young leaves of Arabidopsis halleri, a Brassicaceae capable of hyperaccumulating Cd and Zn, as well as soil samples in the field from 16 populations. We detected wide variation in the composition of glucosinolates-the characteristic secondary metabolites of this plant family-among plants, with two distinct chemotypes occurring. Distance-based redundancy analyses revealed that variation in glucosinolate composition was determined mainly by population affiliation and to a lesser degree by geographic distance. Likewise, elemental composition of the leaves was mainly influenced by the location at which samples were collected. Therefore, the particular abiotic and biotic conditions and potential genetic relatedness at a particular locality affect the plant tissue chemistry. A slight indication of a trade-off between glucosinolate-based organic and inorganic defences was found, but only in the less abundant chemotype. A large variation in defence composition and potential joint effects of different defences may be highly adaptive ways of protecting against a wide arsenal of biotic antagonists.
Asunto(s)
Arabidopsis/metabolismo , Glucosinolatos/análisis , Metales Pesados/metabolismo , Arabidopsis/química , Glucosinolatos/metabolismo , Compuestos Orgánicos/análisis , Hojas de la Planta/química , Hojas de la Planta/metabolismo , Suelo/químicaRESUMEN
Extraordinarily high leaf metal concentrations in metal hyperaccumulator plants may serve as an elemental defence against herbivores. However, mixed results have been reported and studies using comparative approaches are missing. We investigated the deterrent and toxic potential of metals employing the hyperaccumulator Arabidopsis halleri. Effects of zinc (Zn) and cadmium (Cd) on the preferences of three Brassicaceae specialists were tested in paired-choice experiments using differently treated plant material, including transgenic plants. In performance tests, we determined the toxicity and joint effects of both metals incorporated in an artificial diet on the survival of a generalist. Feeding by all specialists was significantly reduced by metal concentrations from above 1000 µg Zn g(-1) DW and 18 µg Cd g(-1) DW. By contrast, metals did not affect oviposition. Generalist survival decreased with increasing concentrations of individual metals, whereby the combination of Zn and Cd had an additive toxic effect even at the lowest applied concentrations of 100 µg Zn g(-1) and 2 µg Cd g(-1) . Metal hyperaccumulation protects plants from herbivory resulting from deterrence and toxicity against a wide range of herbivores. The combination of metals exacerbates toxicity through joint effects and enhances elemental defence. Thus, metal hyperaccumulation is ecologically beneficial for plants.