ã 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1436-8730/05/0204-255 J. Plant Nutr. Soil Sci. 2005, 168, 255±261 DOI: 10.1002/jpln.200420403 Zinc alleviates growth inhibition and oxidative stress caused by cadmium in rice Muhammad Jaffar Hassan, Guoping Zhang*, Feibo Wu, Kang Wei, and Zhonghua Chen Agronomy Department, Huajiachi Campus, Zhejiang University, Hangzhou 310029, China Accepted February 15, 2005 PNSS P04/03P Summary A hydroponic experiment with two rice cultivars differing in cadmium (Cd) tolerance was conducted to investigate the alleviating effect of zinc (Zn) on growth inhibition and oxida- tive stress caused by Cd. Treatments consisted of all combi- nations of two Zn concentrations (0.2 and 1 lM), three Cd concentrations (0, 1, and 5 lM), and two rice cultivars (Bing 97252, Cd-tolerant; Xiushui 63, Cd-sensitive). Cd toxicity caused a dramatic reduction in plant height and biomass, chlorophyll concentration and photosynthetic rate, and an increase in Cd concentration in both roots and shoots, malon- dialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in shoots. The response of all these parameters was much larger for Xiushui 63 than for Bing 97252. Addition of Zn to the medium solution alleviated Cd toxicity, which was reflected in a significant increase in plant height, biomass, chlorophyll concentration, and photosynthetic rate, and a marked decrease in MDA con- centration and activity of anti-oxidative enzymes. However, it was noted that Zn increased shoot Cd concentration at higher Cd supply, probably due to the enhancement of Cd transloca- tion from roots to shoots. Therefore, further studies are necessary to determine the effect of Zn supply on Cd translo- cation from vegetative organs to grains or grain Cd accumu- lation before Zn fertilizer is applied to Cd-contaminated soils to alleviate Cd toxicity in rice. Key words: cadmium / growth / oxidative stress / Oryza sativa L. / zinc 1 Introduction Cadmium is a highly toxic heavy metal occurring in soil natu- rally or through anthropogenic activities, such as mining, industrial waste disposal, use and disposal of batteries and sludge, application of pesticides and phosphate fertilizers (Dahmani-Muller et al., 2000). Soil Cd can be readily absorbed by plants and then poses a huge threat to human health through the food chain (Florijn and Van Beusichem, 1993). Excess Cd in the diet results in damage to the kidney tubules, rhinitis, emphysema as well as other chronic disor- ders. Extreme cases of chronic Cd toxicity can result in osteomalacia and bone fractures, as characterized by the disease called Itai-Itai in Japan in the 1950s and 1960s, where local populations were exposed to Cd-contaminated food crops, principally rice. Cadmium toxicity gives rise to damage in higher plants through interference of many molecular and physiological processes. It has been reported that Cd toxicity inhibits RNA synthesis and ribonuclease activity (Shah and Dubey , 1995), reduces nutrient uptake and transport from roots to shoots (Hernandez et al., 1996; Zhang et al., 2002), inhibits photo- synthesis by damaging the photosynthetic apparatus (Krupa, 1988; Siedlecka and Krupa, 1996) or a reduction of chloro- phyll synthesis (Larsson et al., 1998) and stomatal opening (Barcelò et al., 1986), and reduces the H + /K + exchange and the activity of the plasma membrane ATPase (Obata et al., 1996). Cadmium has also been found to cause oxidative stress (Hendry et al., 1992). Cadmium-induced enhancement of lipid peroxidation has been reported for sunflower (Gallego et al., 1996), bean (Shaw, 1995), pea (Lozano-Rodriguez et al., 1997), and barley (Wu et al., 2003). However, the studies on the response of plants to Cd-induced oxidative stress pro- vided contrasting results (Salin, 1988; Chaoui et al.,1997). The chemical similarity of Cd and Zn has been considered to be the main reason for Cd toxicity in higher plants, because Cd interferes with the normal functions of Zn in bio-metabo- lism. Therefore, great effort has been undertaken to under- stand the interaction between Cd and Zn. However, available studies have reported inconsistent results. White and Chaney (1980) reported that Cd uptake was reduced in both soybean roots and shoots through application of Zn. Eriksson (1990) found that the Zn-Cd interaction varied with the crop species. Most of the previous work suggested that the interaction between Cd and Zn is antagonistic. Wu and Zhang (2002) reported that the physiological damages caused by Cd toxi- city could be alleviated by application of Zn. Recently, Ara- vind and Prasad (2003) found that Cd uptake was sup- pressed by Zn. Simultaneously, Zn supplementation proved to be inhibitory to Cd-induced oxidative stress and beneficial for the plant's survival. The main objectives of the present experiment were to inves- tigate effects of Zn on Cd toxicity by comprehensively study- ing Cd uptake, oxidative stress, anti-oxidative enzymes, photosynthetic properties, and biomass accumulation of two rice genotypes differing in Cd tolerance. * Correspondence: Dr. G. Zhang; e-mail: zhanggp@zju.edu.cn 255