Available online at www.sciencedirect.com Environmental and Experimental Botany 63 (2008) 71–79 Effects of UV-B radiation on antioxidant parameters of iron-deficient barley plants Santina Zancan a , Irene Suglia a , Nicoletta La Rocca b , Rossella Ghisi a,∗ a Department of Biotecnologie Agrarie, University of Padova, Agripolis, viale dell’Universit` a 16, Legnaro, 35020 Padova, Italy b Department of Biology, University of Padova, via U. Bassi 58/B, 35021 Padova, Italy Received 21 December 2006; received in revised form 31 October 2007; accepted 19 November 2007 Abstract Iron deficiency is a stress frequently experienced by plants, owing to the low solubility of Fe(III) salts in neutral or alcaline soils. Iron is an essential plant nutrient as it is involved in fundamental metabolic processes. Furthermore, it is a constituent of important antioxidant enzymes, which are involved in maintaining the balance of cell redox state. UV-B radiation is an environmental problem which can alter the redox state of plants through the increased production of reactive oxygen species. In order to investigate if iron deficiency influences the antioxidant response of plants to UV-B radiation, barley seedlings, Hordeum vulgare L. cv. Express, were exposed to UV-B radiation while growing in nutrient solutions with or without iron. After eight days of growth, plants were harvested and analysed. Results show that, during the 8 days of the experimental period, in neither of the two nutritional conditions considered does UV-B exposure reduce shoot weight or induce evident alterations of thylakoid membranes in respect to controls. However, different responses to UV-B radiation between iron-deficient and iron-sufficient plants were observed at the level of parameters related to oxidative stress. In fact, in iron-sufficient plants the contents of photosynthetic pigments and ascorbate, and the enzyme activities of ascorbate peroxidase (EC 1.11.1.11) and catalase (EC 1.11.1.6) were not affected by UV-B radiation. Conversely, in iron-deficient plants the contents of ascorbate and zeaxanthin and the activity of ascorbate peroxidase increased under UV-B exposure, whereas catalase activity decreased. Furthermore, UV-B radiation induced an increase of hydrogen peroxide content which was higher in iron-deprived plants than in iron-sufficient ones. This may indicate that plants growing in an environment enriched in UV-B radiation may develop a high level of oxidative stress when iron supply is limited. © 2007 Elsevier B.V. All rights reserved. Keywords: Iron deficiency; Hordeum vulgare L.; Oxidative stress; Ultraviolet-B radiation 1. Introduction During the past two decades increased levels of solar UV- B have been measured at temperate and polar regions of the Earth’s surface as a consequence of the progressive reduction in the stratospheric ozone layer (Herman et al., 1996; Caldwell et al., 1998; Madronich et al., 1995). Owing to its high energy level, the impact of UV-B radiation on metabolic processes can be very harmful. DNA, proteins and the photosynthetic appara- tus are considered primary potential targets of UV-B radiation on plants (Jansen et al., 1998 and Holl´ osy, 2002, for recent reviews). The production of reactive oxygen species (ROS) and free rad- icals by UV-B has been also demonstrated (Hideg and Vass, 1996; Dai et al., 1997; Hideg et al., 2002; Mackerness et al., ∗ Corresponding author. Tel.: +39 049 8272910; fax: +39 049 8272929. E-mail address: rossella.ghisi@unipd.it (R. Ghisi). 2001), and the induction of antioxidative enzymes is considered to constitute a defence response to these molecules (Rao et al., 1996; Mazza et al., 1999; Costa et al., 2002; Santos et al., 2004). The accumulation of flavonoids is also considered a defence mechanism against UV-B, as they protect the mesophyll tissue through epidermal screening of this radiation. In addition, it has been shown that some of these compounds may have antioxidant properties (Rice-Evans et al., 1997). In field conditions plants commonly encounter nutrient defi- ciencies, which can even decrease their sensitivity to enhanced levels of UV-B radiation as they enhance the accumulation of UV-B absorbing compounds (Murali and Teramura, 1987; Pinto et al., 1999; Tosserams et al., 2001). Iron is an essential plant nutrient as it is involved in fundamen- tal processes such as photosynthesis, respiration, DNA synthesis and hormone formation. Furthermore, it is a constituent of important antioxidant enzymes, which are involved in maintain- ing the balance of the redox state. Iron-dependent antioxidant 0098-8472/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2007.11.013