Cells of pea (Pisum sativum) that differentiate from G2 phase have extrachromosomal DNA

Velocity sedimentation in an alkaline sucrose gradient of newly replicated chromosomal DNA revealed the presence of extrachromosomal DNA that was not replicated by differentiating cells in the elongation zone. The extrachromosomal DNA had a number average molecular weight of 12 x 106 to 15 x 106 and a weight average molecular weight of 25 x 106, corresponding to about 26 x 106 and 50 x 106 daltons, respectively, of double-stranded DNA. The molecules were stable, lasting at least 72 h after being formed. Concurrent measurements by velocity sedimentation, autoradiography, and cytophotometry of isolated nuclei indicated that the extrachromosomal molecules were associated with root-tip-cells that stopped dividing and differentiated from G2 phase but not with those that stopped dividing and differentiated from G1 phase