ORIGINAL ARTICLE Aluminum inhibits root growth and induces hydrogen peroxide accumulation in Plantago algarbiensis and P. almogravensis seedlings Neusa Martins & Sandra Gonçalves & Anabela Romano Received: 7 January 2013 / Accepted: 10 May 2013 # Springer-Verlag Wien 2013 Abstract We have evaluated the impact of aluminum (Al) on germination, relative root growth, Al accumulation in roots tips, H 2 O 2 levels, plasma membrane integrity, pigment levels, protein content, and the activities of superoxide dismutase (SOD) and catalase (CAT) in seedlings of the endangered Portuguese species Plantago algarbiensis and Plantago almogravensis. We found that up to 400 μM Al had no impact on the germination percentage in either species but inhibited root growth in a concentration-dependent manner (more se- verely in P. algarbiensis). Al accumulation in the root tips of both species was concentration dependent up to 200 μM but declined thereafter despite the absence of membrane damage. We observed a concentration-dependent induction of SOD activity but no change in CAT activity resulting in the accu- mulation of H 2 O 2 (a known growth inhibitor), although its impact in P. almogravensis may be partially ameliorated by the accumulation of carotenoid pigments. Our data suggest an association between Al uptake, H 2 O 2 production, and the inhibition of root growth during early seedling development in P. algarbiensis and P. almogravensis, although the latter is more tolerant towards higher concentrations of the metal. Keywords Al uptake . Antioxidant enzymes . Hydrogen peroxide . Metal toxicity . Plasma membrane integrity . Root growth inhibition Abbreviations CAT Catalase FW Fresh weight MGT Mean germination time NBT Nitroblue tetrazolium ROS Reactive oxygen species SOD Superoxide dismutase Introduction Germination is a complex process involving the coordina- tion of physiological, biochemical, and molecular mecha- nisms that are particularly susceptible to adverse environ- mental factors (Bewley 1997). Although the impact of metal toxicity on the growth of vegetative tissues such as shoots and roots has been well documented, there have been few studies focusing on metal toxicity and germination (Kranner and Colville 2011). Physiological metal tolerance strategies in plants depend on age and the nature of the metal ions, but metal-tolerant species are thought to deploy their adaptive mechanisms throughout development, particularly during germination when the young plant is most vulnerable (Lefèvre et al. 2009). Aluminum (Al) is a major metal component in soils and is solubilized as phytotoxic ions (predominantly Al 3+ ) which inhibit plant growth under low-pH conditions (Tahara et al. 2008). Both germination and seedling growth can be inhibited if the medium surrounding the seed is contaminated with Al (Marciano et al. 2010; Gui et al. 2011). Germination and root growth tests have been used to evaluate the effect of Al in several plant species, particularly crops (Marciano et al. 2010; Zhang et al. 2010). Furthermore, Ezaki et al. (2007, 2008) used germination and relative root growth tests to measure Al tolerance in 49 wild species and in panels of Arabidopsis thaliana mutants. Plantago almogravensis Franco is an endemic species that grows along the southwest coast of Portugal in acidic, podzolic soils naturally enriched in bioavailable Al and iron (Pimentel et al. 1996; Buurman and Jongmans 2005; Serrano Handling Editor: Néstor Carrillo N. Martins : S. Gonçalves : A. Romano (*) IBB/CGB, Faculty of Sciences and Technology, University of Algarve, Campus de Gambelas, Ed. 8, 8005-139 Faro, Portugal e-mail: aromano@ualg.pt Protoplasma DOI 10.1007/s00709-013-0511-1