Changes in DNA methylation in Zea mays plantlets in response to cobalt and nickel (5, 10, 20, and 40 mmol L⁻¹) evaluated by the coupled restriction enzyme digestion-random amplification technique revealed dose-related increases in hypermethylation. The effects on mitotic index and phytohormone levels were also determined. Co and Ni caused a decrease in mitotic index and an attenuation in the growth-promoting hormones gibberellic acid, zeatin, and indole acetic acid, while abscisic acid levels rose. These findings have shown that the increase in abscisic acid levels and DNA methylation depend on the concentrations of Co and Ni.

In this research we aimed to evaluate DNA damage levels, DNA methylation, and protein and pytohormone level changes in corn seedlings (Zea mays L.) exposed to 5, 10, 20, and 40 mM concentrations of lead sulfate solution (PbSO4). The results showed that all concentrations of the test material caused a decreasing mitotic index, genomic template stability (GTS), and soluble protein levels, but increased RAPDs profile changes (DNA damage) and DNA hypermethylation. Moreover, in the HPLC (high-pressure liquid chromatography) analyses, it was also observed that Pb contamination caused a decrease in the growth-promoting hormones including gibberellic acid (GA), zeatin (ZA), and indole acetic acid (IAA) levels, in contrast to increasing the absisic acid (ABA) level. The results of this experiment have clearly shown that Pb has a significant impact on the epigenetic mechanisms as well as its genotoxic effects. Some of phytohormone decreases (GA, ZA and IAA) and especially increasing ABA levels under Pb stress may be a part of the defense system against stress.