Effects of cadmium and lead on the growth and the activity of peroxidase and superoxide dismutase of blueberry plantlets in vitro

To study the effects of cadmium and lead on the growth of blueberry (Vaccinium ashei Reade) plantlets in vitro and on the activity of peroxidase (POD) and superoxide dismutase (SOD) of blueberry shoots, Cd2+ and Pb2+ were added separately to a cultivation medium. The results show that 0.01 mM Cd2+ significantly inhibited the growth of blueberry shoots, and the height and fresh mass of the shoots were significantly lower than those of the control; 0.05 mM Cd2+ significantly inhibited the proliferation of the shoots; the inhibitory effect on the growth and proliferation of blueberry in vitro was enhanced with the increase of Cd2+ concentration. Also Pb2+ (0.10 1.00 mM) significantly decreased the proliferation of the shoots, but it did not decrease significantly the shoot height and fresh mass. After 20 d of Cd or Pb treatments, the POD and SOD activities of the shoots increased with the increase of their concentrations, and when the concentration was 1.00 mM, the POD and SOD activities were significantly higher than in the control; the effect of Pb2+ on POD and SOD activities was generally stronger than that of Cd2+. The upregulation of activities of antioxidative enzymes played an effective role in acclimatization to these stresses, especially to Pb stress. Additional key words: antioxidants, heavy metals, Vaccinium ashei. Submitted 26 May 2020, last revision 20 September 2020, accepted 2 October 2020. Abbreviations: POD peroxidase; SOD superoxide dismutase. Acknowledgments: This work was financially supported by the National Natural Science Foundation of China (No. 20977027) and the Zhejiang Provincial Natural Science Foundation of China (No. LY16C020003). * Corresponding author; e-mail: jzchen@zjhu.edu.cn This is an open access article distributed under the terms of the Creative Commons BY-NC-ND Licence In recent years, due to the impact of human activities, a large number of heavy metals such as cadmium and lead have been released into the soil, resulting in the increasingly serious pollution in the soil (Chen et al. 2014). Cd and Pb in soil not only affect the yield and quality of plants, but also accumulate in animals and human bodies through the food chain, threatening their health (Xiao et al. 2015, Tóth et al. 2016). Therefore, the content of Cd and Pb in contaminated soil and the tolerance mechanisms of plants to Cd and Pb stress attract great attention. Blueberries (Vaccinium spp.) are perennial berry fruit trees of Ericaceae family. Blueberry fruits are popular around the world due to their nutritional value and elevated content of bioactive phenolic compounds (Kalt et al. 2007, 2020). Although many species of blueberries are native to North America, several of them especially highbush (V. corymbosum L.), lowbush (V. angustifolium Ait.), and rabbiteye (V. ashei Reade) blueberries are commercially cultivated in many countries in Europe, South America, Asia, Australia, and New Zealand (Strik 2005, Strik and Yarborough 2005). Soil is one of the main limiting factors that make it difficult to expand the cultivation scope of blueberry. Blueberry cultivation requires high soil quality; loose and acid soil rich in organic matter and with a low heavy metal content (Markus and Mcbratney 1996). However, there are few reports about the effect of heavy metal stress on the growth of blueberry. In this paper, the effects of cadmium and lead stress on the growth and antioxidant enzyme activities in blueberry (V. ashei cv. Garden blue) grown in vitro were studied, in order to provide scientific basis for promotion of blueberry growing area, as well as to give theoretical basis for revealing the tolerance mechanisms of plants to cadmium and lead. The sterile shoots of blueberry were provided by the Plant Biotechnology Laboratory at Huzhou University. The shoots were multiplied on a woody plant medium (Lloyd and McCown 1980) with zeatin (1.5 mg dm-3), agar (5 g dm-3), and sucrose (20 g dm-3), pH 5.2. Blueberry shoot cultures were kept at a temperature of 25 ± 2 °C, a 12-h photoperiod, and an irradiance at the culture level of 50 μmol m-2 s-1 provided by cool white fluorescent lamps. Stock solutions of 10 mM Cd2+ or Pb2+ were prepared using Cd(NO3)2· 4 H2O and Pb(NO3)2, respectively. For cadmium