[Methylation of newly formed DNA in developing wheat seedlings]

The base composition (45 divided by 56 mol.% GC) and methylation level (100 . m5C/(m5C + C) = = 20% divided by 0.4%) of pulse-labelled newly formed DNA in etiolated wheat seedlings and their individual organs are markedly changed with age. The base composition of total leaf and coleoptile DNA (45 mol.% GC) remains unchanged; the changes in the methylation level are not significant (1). In the course of development of the plant organs (e. g. leaf) the level of synthesis of DNA whose composition is identical to that of nuclear DNA, is decreased and the incorporation of labelled precursors into the GC-rich (56 mol.% GC) practically unmethylated DNA is increased. In ageing coleoptiles only the synthesis of unmethylated DNA of the GC-type takes place. It is assumed that this DNA may correspond to mitochondrial DNA.