Constancy of rDNA Content during Dedifferentiation of Carrot and Jerusalem Artichoke Explants

摘要

When carrot explants were cultured with phytohormones, DNA synthesis took place synchronously in the explants and a satellite DNA with a heavier density in CsCl than the bulk DNA replicated in the earliest phase of the first replication period. The early replicating carrot satellite consisted of a component having an identical density to carrot rDNA and another component having a density between thep-value of carrot rDNA and that of the bulk DNA. DNA-rRNA hybridization was used to explore the possibility that this early replication of the satellites leads to amplification of rDNA in the explant cells, in which massive ribosome synthesis is known to occur. The results showed that there was neither amplification nor underreplication of rRNA genes during callus formation and its growth.Experiments with explants of Jerusalem artichoke tuber, which are well known as a synchronous replication system, showed that a component slightly heavier than the bulk DNA was synthesized at the early phases of the first replication period. However, the density of this early replicating satellite differed from that of artichoke rDNA. DNA-rRNA hybridization experiments again showed no gross changes of rDNA content during dedifferentiation of this plant system.