Nuclear ultrastructure: Condensed chromatin in plants is species-specific (karyotypical), but not tissue-specific (functional)

Summary In contrast to mammalian cell nuclei those of plants display nearly an identical ultrastructure in all developmental stages and tissues. This indicates that the gross organization of chromatin is species-specific, but not tissue-specific and function-dependent. The species-specific nuclear ultrastructure is determined by the basic nuclear DNA content (2 C value). The higher the DNA content, the more the euchromatin remains in the condensed state during interphase, but to a lower coiling order than the heterochromatin.Some difficulties in the interpretation of electron micrographs of cell nuclei, and the possible role of repetitive DNA sequences in the karyotypical condensation of euchromatin in plants are discussed.