Effects of Ascorbic Acid and Copper Treatments on Metallothionein Gene Expression and Antioxidant Enzyme Activities in Helianthus annuus L. Exposed to Chromium Stress

Abstract

Heavy metal pollution, which is one of the most important environmental problems, has a significant effect on plant growth and development. Plants influence all living things because of their role in the food chain. Therefore, in this study, antioxidant enzyme activities and metallothionein (MT) gene expression levels were investigated to determine the protective role of copper (Cu) and ascorbic acid (AsA) against chromium (Cr) stress. In order to determine these parameters, sunflower seeds were grown in hydroponic system after germination. Two weeks later, AsA (200 mg/L) treatment was made as foliar spray. After 24 h of the treatment, the hydroponic nutrient medium was used as the treatment solution containing different concentrations of metals (0.25 mM Cu (CuSO4·5H2O); 1 mM Cr (K2Cr2O7). The results have reduced the overall growth of plants with Cr heavy metals. Cr stress increased the amount of malondialdehyde. Furthermore, while superoxide dismutase and peroxidase activities were increased, no significant change in catalase activity was observed. Cu and AsA applied with Cr treatment significantly reduced Cr toxicity. Expression levels of MT genes (HanMT2-1 and HanMT4) were determined by qRT-PCR analysis. From the study result, it was determined that the expression levels of MT genes under Cr stress changed according to the plant tissues and were upregulated in the roots. The protective roles of Cu and AsA against Cr stress were observed. From the results of this study, it was confirmed that MT2-1 could be an effective gene resource in Cr remediation-related plant breeding programs.