Environmental and Experimental Botany 78 (2012) 1–9 Contents lists available at SciVerse ScienceDirect Environmental and Experimental Botany journa l h omepa g e: www.elsevier.com/locate/envexpbot The early response of Arabidopsis thaliana to cadmium- and copper-induced stress Ana Martínez-Pe ˜ nalver, Elisa Gra ˜ na, Manuel J. Reigosa, Adela M. Sánchez-Moreiras ∗ Dept of Plant Biology and Soil Science. Faculty of Biology. University of Vigo, Campus Lagoas-Marcosende s/n, 36310 Vigo, Spain a r t i c l e i n f o Article history: Received 13 January 2011 Received in revised form 12 December 2011 Accepted 14 December 2011 Keywords: Heavy metals Abiotic stress Chlorophyll a fluorescence Photosynthesis Early symptoms Hydrogen peroxide a b s t r a c t To investigate the early (first day) effects of cadmium and copper poisoning, adult plants of thale cress (Arabidopsis thaliana L.) were treated with nutrient solution containing 50–100 M Cd 2+ or Cu 2+ . The main effect of Cu 2+ treatment was a temporary reduction in F v /F m with respect to controls, which is suggestive of transient damage to the antenna. By contrast, within 3 h of Cd 2+ treatment, leaf chlorophyll and carotenoid contents and photochemical operating efficiency (ϕ II ) fell with respect to controls, while q N and ETR rose and F v /F m remained essentially unaltered. Protein content fell initially and rose within 24 h, and a transient widespread increase in H 2 O 2 production around hour 6 evolved by hour 24 to more intense production around leaf veins when plants were watered with Cd 2+ . These alterations were not due to induced nutrient deficiency, and are interpreted as suggestive of damage to the biochemical phase of photosynthesis. The loss of pigment, and fall in ϕ II without an accompanying fall in F v /F m , might be used as early signs of cadmium poisoning. It is assumed that Cu 2+ was less harmful than Cd 2+ because of its tendency to remain in roots and because, as a fairly abundant essential micronutrient, it is subject to endogenous mechanisms of regulation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Heavy metal toxicity in soil was once a problem limited to cer- tain localities affected by mining, heavy industry, or natural mineral outcrops. Growing industrialization and the massive use of fer- tilizers and other agrochemicals in conventional agriculture have led to its now being of quite widespread concern for both natu- ral and agricultural systems (Wagner, 1993; Weisberg et al., 2003). Heavy metal toxicity not only reduces productivity but also threat- ens the food chain (Poschenrieder and Barceló, 2004). Among the most common heavy metal pollutants, and the most susceptible to accumulation through unwary agricultural practices, are cadmium and copper. Cadmium is perhaps one of the most aggressive and persistent of heavy metals. Its presence in the environment is due mainly to the application of cadmium-bearing phosphorus fertilizers to agri- cultural soils (Zawoznik et al., 2007). It is not required for life, but is readily absorbed by the roots of plants and transported to their aerial parts. It can interfere with plant physiology causing stunt- ing, root damage and chlorosis (Semane et al., 2007). It mainly affects the transport and use of water and essential elements (Ca, Fe, Mg, P and K), causing nutritional and hydric imbalance and ∗ Corresponding author. Tel.: +34 986812616; fax: +34 986812556. E-mail address: adela@uvigo.es (A.M. Sánchez-Moreiras). reducing respiration, photosynthesis, and leaf chlorophyll content (Poschenrieder et al., 1989; Rodríguez-Serrano et al., 2008; Sandalio et al., 2001; Singh and Tewari, 2003). It can cause oxidative stress by promoting the peroxidation of membrane lipids or the carbony- lation of proteins (Rodríguez-Serrano et al., 2008; Romero-Puertas et al., 2002; Sandalio et al., 2001). The levels of antioxidant enzymes – superoxide dismutases (SOD), glutathione reductase (GR), cata- lase (CAT), ascorbate peroxidase (APX) and other peroxidases (POD) – are altered by cadmium to an extent that depends on the cad- mium content of the growth medium, the duration of exposure, the growth stages of plants or organs and the species and tissue in question (Benavides et al., 2005; Rodríguez-Serrano et al., 2008; Sandalio et al., 2001). Copper is an essential micronutrient that acts as a cofactor in photosynthesis, respiration, ethylene sensing, and lignification (Jonak et al., 2004), as well as playing roles in the response to oxida- tive stress (Himelblau and Amasino, 2000). However, excess copper is toxic for most plants, reducing growth, affecting thylakoid mem- brane structure, inhibiting root elongation, altering cell transport, and modifying metabolite levels (see, for example, Schiavon et al., 2007). As a redox metal capable of catalysing reactions of Fenton or Haber–Weiss type, it takes part in the direct formation of ROS (Drazkiewicz et al., 2007; Yruela et al., 1996). Early detection of heavy metals in plants may hopefully allow the application of measures that prevent their further accumulation and their incorporation in the food chain (Ferrat et al., 2003; Van 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.12.017