In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting 
through a methylation-dependent epigenetic mechanism. Here, the effects of Cd 
treatment on the DNA methylation patten are examined together with its effect on 
chromatin reconfiguration in Posidonia oceanica. DNA methylation level and 
pattern were analysed in actively growing organs, under short- (6 h) and long- 
(2 d or 4 d) term and low (10 μM) and high (50 μM) doses of Cd, through a 
Methylation-Sensitive Amplification Polymorphism technique and an 
immunocytological approach, respectively. The expression of one member of the 
CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by 
qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission 
electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an 
up-regulation of CMT, indicating that de novo methylation did indeed occur. 
Moreover, a high dose of Cd led to a progressive heterochromatinization of 
interphase nuclei and apoptotic figures were also observed after long-term 
treatment. The data demonstrate that Cd perturbs the DNA methylation status 
through the involvement of a specific methyltransferase. Such changes are linked 
to nuclear chromatin reconfiguration likely to establish a new balance of 
expressed/repressed chromatin. Overall, the data show an epigenetic basis to the 
mechanism underlying Cd toxicity in plants.