Changes of DNA methylation of Isoetes sinensis under Pb and Cd stress.

To investigate the molecular response of ancient plants to heavy metal stress and to explore the feature of DNA methylation in endangered plants after exposure to heavy metals, the Isoetes sinensis, an endangered plant, was stressed with three different concentrations of two heavy metals lead (Pb) and cadmium (Cd), respectively. Then the degrees and the patterns of DNA methylation in the leaves were measured on the 14th day using Methylation Sensitive Amplified Polymorphism (MSAP) technique. The results showed that the DNA methylated profile of I. sinensis was affected by Pb and Cd stress. There was no significant difference in the amount of DNA methylation among control check (CK), Pb stress group, and Cd stress group (CK 46.96%, Pb 48.23%, and Cd 48.1%). However, full-methylation level of Pb stress group (28.34%) and Cd stress group (20.25%) was lower than control (33.91%), in contrast, hemi-methylation level Pb stress group (19.89%) and Cd stress group (27.85%) were higher than control (13.04%). The change of patterns from no methylation or hemi-methylation of internal and external cytosines into full-methylation of internal and external cytosines accounted for a large proportion in enhanced methylation aspects. The full-methylation into no methylation or hemi- or full-methylation of internal and external cytosines occupied most of demethylation. The proportion of DNA methylation (including hypermethylation) by both Pb and Cd stresses is nearly equal (39.04% and 39.71%), but the proportion of DNA demethylation by Cd is higher than that by Pb (46.86% than 33.92%).