Behaviour of repetitive non-coding DNA in response to heavy metal stress in the protonemata of Funaria hygrometrica

Studies on the leafy shoots of Funaria hygrometrica have shown that the genome reacts to heavy-metal stress with the selective amplification of specific (GþC)-rich highly repetitive/non-coding DNA sequences. These studies have also shown that, when the metal-induced stress ceases, almost all the stress-induced repetitive DNA is eliminated from the genome. In this study, in order to investigate whether this reaction of genome could be associated with the developmental stage of the target organism, we analysed the behaviour of repetitive non-coding DNA in response to metal-stress in the protonemata of F. hygrometrica. That is the juvenile stage of the gametophyte phase and that precedes the leafy shoot stage. In particular, we analysed the genome of chloronemal cells in plants treated with a lead–zinc mixture similar to that found in mines in Sardinia, Italy. Our results show that, in the chloronemal cells of protonema, metal-stress induces an amplification of (GþC)-rich repetitive/non-coding DNA sequences similar to that observed in the leafy-shoot cells. However, unlike that which occurs in the leafy-shoot stage, in the protonemal stage almost all of the stress-induced repetitive DNA remains within the nucleus also after the stimulus is removed. Some hypotheses are discussed.