Wheat biological responses to stress caused by cadmium, nickel and lead.

Several stressors like different types of heavy metals are found in the soil and can affect the growth and genomic integrity of wheat grains (Triticum aestivum L.). The aim of this study was to compare the effect of exogenous Cd (30, 60, 120 mg kg-1), Ni (50, 100 and 150 mg kg-1) or Pb (100, 200 and 300 mg kg-1) on wheat agronomic characteristics through the assessment of oxidative stress indices at protein and gene expression levels, photosynthetic pigments and genetic aberrations using RAPD analysis that were studied during two winter seasons (2015/2016 and 2016/2017). The results showed that all stressors significantly decreased the vegetative growth parameters, altered the activities of antioxidants enzymes in seedlings (after 30 days) and grains (after 5 months) and differently affected their expression levels in seedlings leaves and roots. Pb treated plants showed the poorest agronomic characteristics as it exhibited the worst affected wheat height, number of tillers, fresh and dry weight, flag leaf area as well as yield. Pb treatment caused poorest plant performance, it showed the highest proline content, least protein and chlorophyll contents, thus affects the overall plants growth followed by Cd and Ni, respectively. Furthermore, high Pb and Cd doses revealed highest degree of polymorphism and lowest degree of genome stability. Altogether, heavy metals accumulated mainly in wheat straw and induced genotoxic effect which consequently altered normal plant metabolism and pigment content which resulted in a significant reduction in wheat yield and quality. Moreover, Pb induced more genotoxic and phytotoxic effects than Cd and Ni.