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تعداد صفحات این فایل: ۲۶ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Effects of cadmium on uptake and translocation of nutrient elements in different welsh onion (Allium fistulosum L.) cultivars~~en~~

Abstract

The concentration of nutrient elements is an important quality characteristic of vegetables, and the variation in accumulation among cultivars can provide clues about the mechanism of low accumulation of heavy metals. Pot-culture experiments were arranged under four cadmium (Cd) treatments (CK, 1.0, 2.5 and 5.0 mg/kg) to explore influences of Cd on the accumulation of nutrient elements in 25 welsh onion cultivars. There were significant positive correlations (p < 0.05) between Cd and nutrient elements in the pseudostems and leaves. There were also significant positive correlations in nutrient elements (p < 0.05) among cultivars, which might be disturbed under high Cd treatments, especially for P, Fe and Mn. Our results suggested that there is a synergistic effect on the accumulation between Cd and nutrient elements, and within nutrient elements among cultivars. In addition the uptake and translocation process of Cd was closely related to Mn in welsh onion.

۱ Introduction

Cadmium (Cd), as an important heavy metal with high bioavailability in soils, easily enters into ecosystems and accumulates through food chain, thus posing a significant threat to human and animal health. It is one of the toxic metals under scrutiny by the US Environmental Protection Agency (USEPA). In China, Cd contamination has been considered as a serious problem for food safety (Bao et al., 2013). According to the China’s Soil Pollution State Bulletin (the Ministry of Environmental Protection of PRC & Resources of PRC, 2014), the rate of Cd exceeding the standard was more than 7.0%. The primary concern with Cd is its transfer from vegetables to human bodies, because vegetables contribute more than 70% of Cd intake in human beings (Sarwar et al., 2010). At the same time, the techniques available for remediating the soil contaminated by Cd are costly and/or time consuming, which limits their application in most cases of lesser Cd contamination in the soil (Li, Zhou, Wei, & Ren, 2012). Recently, an alternative strategy to reduce the risk of soil Cd entering into food chain has been proposed, namely, the identification of Cd-excluding cultivars (Li et al., 2012). Cd-excluding cultivars are defined as cultivars that accumulate Cd at a low enough level in the edible parts of a crop to allow for safe consumption, even when grown in soils with slight or moderate Cd contamination (Li et al., 2012; Liu, Zhou, Sun, & Liu, 2009; Zhou, Kong, & Zhu, 2004). The concept of Cd-excluding cultivars is based on the theory that there is a significant difference in the uptake and distribution of toxic elements among crop species and cultivars within the same species, which has been clearly illustrated by several studies (Arivalagan et al., 2012; Chen et al., 2007; Fernandez-Ruiz, Olives, Camara, Sanchez-Mata, & Torija, 2011; Galdon, Gonzalez, Rodriguez, & Romero, 2008; Galdon et al., 2012; Singh, Sharma, & Singh, 2012). Differences in Cd accumulation levels among plant cultivars indicate variability in uptake and/or translocation of elements, including but not limited to Cd. Singh et al. (2012) found that both parentage and the breeding approach significantly affected the concentration of Fe, Zn, Cu, Mn, K and Ca in cabbage (Brassica oleracea var. capitata L.). The cultivars are considered to be one of the most important factors affecting the chemical composition of the potato (Solanum tuberosum L.) (Galdon et al., 2012). Significant differences in mineral composition among the eggplant (Solanum melongena L.) genotypes have also been observed by Arivalagan et al. (2012). Visible differences have been observed in the mineral contents among 202 rice (Oryza sativa L.) cultivars, and there was also a negative correlation between grain yield and mineral contents (Anandan, Rajiv, Eswaran, & Prakash, 2011). Similar results have also been reported in wheat (Triticum aestivum L.) (Zhang et al., 2010), Walnut (Juglans regia L.) (Cosmulescu, Baciu, Achim, Botu, & Trandafir, 2009), onion (Allium cepa L.) (Galdon et al., 2008), tomato (Lycopersicum esculentum L.) (Suarez, Rodriguez, & Romero, 2007), grape (Vitis vinifera L.) (Yang, Duan, Du, Tian, & Pan, 2010), and banana (Musa paradisiaca L.) (Sulaiman et al., 2011). The concentration of nutrient elements in plants and crops could also be influenced by other elements, especially by heavy metals. However, the response of uptake and translocation of nutrient elements to heavy metal pollution might be different, even in net direction, depending on the factor such as plant species and element types. Sikka and Nayyar (2012) found a decrease in the content of micronutrients (Mn, Fe, Cu, Zn) in Indian mustard [Brassica juncea (L.) Czern.] with the application of Cd, but a significant reduction in Fe occurred only in treatments with Cd concentrations above 50 mg/kg. Meanwhile, Liu, He, and Chen (2011) found a synergistic interaction in accumulation and translocation between Cd and Fe and a significant negative correlation between Cd and Cu or Zn concentrations in Lonicera japonica Thunb. Furthermore, the influence of heavy metals on nutrient elements vary by cultivar. Norton et al. (2010) found that Se, Cu, Mn and Ni concentrations in rice grain (Oryza sativa L.) showed significant genetic interaction with arsenic (As). Goncalves et al. (2009) also suggested that the influence of Cd on the nutrient contents in potato (Solanum tuberosum) was related to the level of Cd in the substrate, the potato cultivar, plant organ, essential element, growth medium and exposure time. The nutrient elements not only are important quality characteristics of vegetables, but also provide clues on the mechanism of low Cd accumulation. With a cultivation history of approximately 2500 years, welsh onion is one of the most important vegetables in China and other countries of Northeast Asia, Europe, and Northern America. Its cultivation area and production accounted for approximately 3% of the total vegetables in China. Our previous study showed that significant differences occurred in Cd accumulation among welsh onion cultivars (Li et al., 2012), but the nutrient elements have yet to be examined in welsh onion cultivars with different Cd accumulation characteristics. Moreover, most of the studies on how the heavy metals influence on uptake and translocation of nutrients were carried out in hydroponic experiments with very few cultivars. Hence, the present study was carried out in the pot-culture with 25 welsh onion cultivars and focused on (1) the influence of Cd on the accumulation of nutrient elements in welsh onion; (2) the uptake/translocation relationship between nutrient elements and Cd in different welsh onion cultivars; and (3) the variation in the uptake and translocation of nutrient elements with cultivars as affected by Cd.

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